EETE 101 Basic Electrical Instruments PDF

POLYTECHNIC UNIVERSITY OF THE PHILIPPINES Department of Electrical and Mechanical Engineering Technology Institute of Technology NDC Campus EETE 101 Basic Electrical Instrument...

POLYTECHNIC UNIVERSITY OF THE PHILIPPINES Department of Electrical and Mechanical Engineering Technology Institute of Technology NDC Campus EETE 101 Basic Electrical Instrument Prof. Raymond L. Alfonso 0  Basic Electrical Instrument EETE 101 Prof. Raymond L. Alfonso ALL RIGHTS RESERVED. No part of this learning module may be reproduced, used in any form, or by any means graphic, electronic, or mechanical, including photocopying, recording, or information storage and retrieval system without written permission from the authors and the University. Published and distributed by: Polytechnic University of the Philippines Address: A. Mabini Campus, Anonas Street, Sta. Mesa, Manila, Philippines 1016 Website: https://www.pup.edu.ph/ Email: [email protected] Tel. No.: (+63 2) 5335-1PUP (5335-1787) or 5335-1777 1  The VMPGO VISION PUP: The National Polytechnic University MISSION Advance an Inclusive, Equitable and Globally relevant Polytechnic Education towards National Development. PHILOSOPHY As a state university, the Polytechnic University of the Philippines believes that: Education is an instrument for the development of the citizenry and for the enhancement of nation-building; and, That meaningful growth and transformation of the country are best achieved in an atmosphere of brotherhood, peace, freedom, justice and nationalist-oriented education imbued with the spirit of humanist internationalism. GOALS OF THE COLLEGE/CAMPUS Provide quality education through instruction, advance research, and extension services. Produce technology graduates for industry leaders and job providers. Develop practical-based learning facilities aligned with the emerging technology needs. Obtain National Certificate (NC) in their chosen field for further studies and other professional certifications. 2 SHARED VALUES AND PRINCIPLES 1. Integrity and Accountability 2. Nationalism 3. Sense of Service 4. Passion for Learning and Innovation 5. Inclusivity 6. Respect for Human Rights and the Environment 7. Excellence 8. Democracy PROGRAM DESCRIPTION The Diploma in Electrical Engineering Technology (DEET) program is a systematic combination of theoretical and practical courses that are delivered in conventional and digital modalities that aims to develop technologically adaptive, creatively pioneering, service-oriented, resilient, ethical, national and globally competitive Electrical Engineering Technologist with effective communication and organizational skills through a strong understanding of the fundamental theories and principles of mathematics, physical sciences, and electrical engineering technology courses. The DEET program is designed to meet the growing demand for competence and expertise in advancing the country’s Electrical Engineering Technologist profession by producing graduates that are equipped to help continue to provide major contributions, studies, and developments in the field of Technoprenueral Skills, Electrical Project Management, Design, Layout, and Estimate, Industrial Motor and Program Logic Circuit Controls, Mechatronics and Photovoltaic System Installation. COURSE DESCRIPTION Electrical instruments are the metering/measuring devices usually are in the practice of electrical engineering. Electrical parameters such as voltage, current, and resistance are the usual units being taken into considerations when in the field of the said course. The different metering devices to be discuss will able them to acquire the knowledge in what instruments is to be used and has also interpolate errors during the proceedings of the test. 3 INSTITUTIONAL LEARNING OUTCOMES (ILOs) As a polytechnic state university, PUP shall develop its students to possess: 1. Critical and Creative Thinking. Graduates use their rational and reflective thinking as well as innovative abilities to life situations in order to push boundaries, realize possibilities, and deepen their interdisciplinary, multidisciplinary, and/or transdisciplinary understanding of the world. 2. Effective Communication. Graduates apply the four macro skills in communication (reading, writing, listening, and speaking), through conventional and digital means, and are able to use these skills in solving problems, making decisions, and articulating thoughts when engaging with people in various circumstances. 3. Strong Service Orientation. Graduates exemplify strong commitment to service excellence for the people, the clientele, industry and other sectors. 4. Adept and Responsible Use or Development of Technology. Graduates demonstrate optimized and responsible use of state-of-the-art technologies of their profession. They possess digital learning abilities, including technical, numerical, and/or technopreneurial skills. 5. Passion for Lifelong Learning. Graduates perform and function in society by taking responsibility in their quest for further improvement through lifelong learning. 6. Leadership and Organizational Skills. Graduates assume leadership roles and become leading professionals in their respective disciplines by equipping them with appropriate organizational skills. 7. Personal and Professional Ethics. Graduates manifest integrity and adherence to moral and ethical principles in their personal and professional circumstances. 8. Resilience and Agility. Graduates demonstrate flexibility and the growth mindset to adapt and thrive in the volatile, uncertain, complex and ambiguous (VUCA) environment. 9. National and Global Responsiveness. Graduates exhibit a deep sense of nationalism as it complements the need to live as part of the global community where diversity is respected. They promote and fulfill various advocacies for human and social development. 4 PROGRAM LEARNING OUTCOMES (PLOs) By the time of graduation, the students of the DEET program shall have the ability to: A. Apply knowledge of mathematics and sciences to critically and creatively solve practical engineering technology problems using state-of-art technology used in the field; B. Develop and conduct appropriate experimentation, critical analysis, and interpretation of data; C. Design a system, component, or process to meet desired needs within realistic constraints such as economic, environmental, social, political, ethical, health and safety, manufacturability, and sustainability, in accordance with standards; D. Function effectively on multi-disciplinary and multi-cultural teams that establish goals, plan tasks, and meet deadlines; E. Identify, formulate, and critically and creatively solve complex problems in electrical engineering technology; F. Recognize ethical and professional responsibilities in engineering technology practice; G. Communicate effectively to a range of audiences and adapt to a multi-cultural professional environment; H. Understand the impact of engineering technology solutions in a global, economic, environmental, and societal context; I. Recognize the need for additional knowledge and engage in lifelong learning; J. Effectively articulate and discuss the latest developments in the field of electrical engineering technology; K. Apply techniques, skills, and modern engineering tools necessary for electrical engineering technology practice; and L. Demonstrate knowledge and understanding of electrical engineering technology and management principles as a member and/or leader in a team to manage projects in multidisciplinary environments. COURSE LEARNING OUTCOMES (CLOs) 1. Understand the various operating principles of metering instruments. 2. Recognize different types of errors associated with these instruments. 3. Learn about the diverse applications of various instruments. 4. Determine the appropriate device to use for specific tasks. 5. Familiarize yourself with the connections required during testing 5  Preface Electrical instruments are the metering/measuring devices usually are in the practice of electrical engineering. Electrical parameters such as voltage, current, and resistance are the usual units being taken into considerations when in the field of the said course. The different metering devices to be discuss will able them to acquire the knowledge in what instruments is to be used and has also interpolate errors during the proceedings of the test. The Learning Objectives: After successful completion of this lesson, you should be able to: Know the different types of operating principles of metering instruments. Know the different errors Know the different uses of different instruments Identify which devices is to be used Familiar with the connections when testing. 6  TABLE OF CONTENTS Title Page 1 The VMPGO 2 Preface 7 Table of Contents 8 OBE Course Syllabus 10 UNIT I Lesson 1 a. Orientation 12 b. Self-Assessment 13 Lesson 2 a. Electrical Instruments 14 b. Units, Dimensions, and Standards 19 c. Measurement Standards 22 Lesson 3 a. Insulation Tester 27 b. Kilowatt-Hour Meter 34 c. Watt Meter 41 d. Instrument Transformer 49 Lesson 4 a. AC/DC Volt Meter 56 b. Ammeter & Clam Meter 65 c. Clamp-on Meter 69 d. Tachometer 73 Lesson 5 a. Galvanometer 79 b. AC/DC Ammeter 83 c. Power Factor Meter 87 7  d. Switches 96 Examinations a. Quiz 1 113 b. Quiz 2 114 c. Quiz 3 115 d. Quiz 4 116 e. Final Examination 117 Rubrics 118 8  Lesson 1 Orientation/VGMO The Overview The Polytechnic University of the Philippines (PUP) is a government educational institution governed by Republic Act Number 8292 known as the Higher Education Modernization Act of 1997, and its Implementing Rules and Regulations contained in the Commission on Higher Education Memorandum Circular No. 4, series 1997. PUP is one of the country's highly competent educational institutions. The PUP Community is composed of the Board of Regents, University Officials, Administrative and Academic Personnel, Students, various Organizations, and the Alumni. Governance of PUP is vested upon the Board of Regents, which exercises policy- making functions to carry out the mission and programs of the University by virtue of RA 8292 granted by the Commission on Higher Education. The University is administered by an appointed President by virtue of RA 8292 and is assisted by an Executive Vice President and the Vice Presidents for Academic Affairs, Student Services, Administration, Research, Extension and Development, and Finance. The Learning Objectives: After successful completion of this topic, you should be able to: Recite the vision, mission, goals and objectives of the University. Identify the content of the syllabus, references, classroom rules and regulations, and grading system. Orientation: Please read pages 7-16 and page 18 of this course material. 9  Lesson 2 2.A. Electrical Instruments 2.B. Units, Dimensions, and Standards 2.C. Measurement Standards 2.A. Electrical Instrument The instrument by w/c quantity of anything is measured is known as measuring instrument. When such instruments remain connected in the electrical circuit to measure electrical quantity and is operated by electrical current, it is called electrical measuring instruments. There are various types of electrical instrument. These instruments are widely used for the measurement of different electrical quantities such as current, voltage, power, etc. Two Types of Electrical Instruments Absolute Instrument - Gives the value of the electrical quantity in terms of instrument constant. Such instruments do not require any comparison with standard instruments. The use of these instruments is limited to laboratory work only. Secondary Instruments - Indicates electrical quantities directly through the deflection of the pointer on the scale of the instrument. Before putting into use these instruments are calibrated with standard instruments, such instruments have the biggest application in the field of electrical measurement. 10 Classification Of Secondary Instruments Indicating Instruments - Indicates directly the instantaneous value of the electrical quantities at a particular time of observation in such an instrument, a pointer moving over a calibrated scale indicates the value of the quantity. Ammeters, voltmeter, wattmeter are the example of this type of instruments. Integrating Instruments - When the instrument measures the total quantity of electricity or electrical energy consumption over a certain period of time. Ampere – hour meters, kilowatt Hour meter come under this class of instruments. Recording Instruments - Gives a continuous record of the variations of the electrical quantity being measured over a considerable period of time. In such instruments, the moving system curries an inked pen. This pen rests on a chart wrapped over a drum which moves slowly at a uniform speed. The drum moves in a direction perpendicular to the direction of the pen. The path traced out by the pen on the chart indicates the variations in magnitude of the electrical quantity under observation over a given period. Gross Errors and Systematic Errors No electronic components or instrument is perfectly accurate; all have some error or inaccuracy. It is important to understand how these errors are specified and how they combine to create even greater errors in measurement systems. Although it is possible that in some cases errors might almost completely cancel each other out, the worst-case combination of errors must always be an assumed. A part from equipment errors, some operator or observer error is inevitable. Also, even when equipment errors are very small, the system of using the instruments can introduce a systematic error. Errors of unexplainable origin are classified as random errors. Where accuracy is extremely important, some errors can be minimized by taking many readings of each instrument and determining mean values. Gross error are essentially human errors are the result of 11 carelessness. One of the most common errors is the simple misreading of an instrument. Sometimes ammeter is read correctly but the reading is recorded incorrectly, or perhaps it is recorded in the wrong column in a table of measurements. Everyone makes these kinds of mistakes occasionally; they can be avoided only by taking care in using and reading all instruments and by thinking about whether or not each measurement make sense. Measurement errors will occur if the accuracy of an instrument has not been calibrated. Errors will also occur with analog instruments, if the pointer has not been mechanically zeroed before use. Analog ohmmeter must also be electrically zeroed for correct use; these kinds of errors can be termed gross errors, because they can be avoided with care. However, they might also be classified as systematic errors, because they are the result of the measurement system. Other systematic error occurs because the measurement system affects the measurement quantity. Errors that are result of instrument inaccuracy are also systematic errors, where more than one instrument is involved; the errors due to instrument inaccuracy tend to accumulate. The overall measurement error is then usually larger than the error in any one instrument. Digital Read Out Meter/Digital Multimeter This type of instrument has become very popular because the digital automatically with decimal point, polarity and the unit for V.A. or Ω. Digital meters are generally easier to use because they eliminate the human error that often occurs in reading different scale on an analog meter with a pointer. The basis of the DMM operation is the use of a digital converter circuit. It converts analog voltage values in the input to an equivalent binary form. These values are processed by digital circuits to be shown on the visual display with decimal values. The liquid-crystal display (LCD) is generally used. The main advantage of a digital meter is the fact that it’s easy for everybody to read and there is no chance for interpolation errors. This is ideal for utility meter, clocks and some kinds of ammeters, voltmeters and watt meters. It works well when the value of the quantity does not change often or fast. 12  There are some situations in which a digital meter is a disadvantage. One good example is the signal strength indicator in a radio receiver. This meter bounces up and down as signal fade or as you tuned the radio or sometimes even as the signal modulates. A digital meter will show nothing but a constantly changing, meaningless set of numerals. Digital meters require a certain length of time to lock in the current, voltage, power, or other quantity being measured. If this quantity never settles at any value for a long enough time, the meter can never be locking in. The main advantages of analog meters are that they allow interpolation. They give the operator a sense of the quantity relative to other possible values, and they follow along when the quantity changes. Some engineers and technicians prefer analog metering, even in situations where digital meter would work just as well. One potential hang-up with digital meters is being certain of where the decimal point goes. If you’re off by one (digital) decimal place, the error will be a factor of 10. Also, you need to be sure you know what the units are comparisons of digital and analog multi meters. Digital multi meters are superior to analog instruments in at least two important categories, accuracy and durability. The accuracy of good quality analog instruments is typically plus minus 2% of full scale, which means plus minus 4% on a half scales reading and worse farther down the scale. The least expensive digital meters can have an accuracy of better than plus minus 0.6% of the measured quantity. Many analog instruments that used taut-band suspension can survive drops to floor bench top levels, but they are likely to be damaged by greater drops. The mechanism of jeweled-bearing instruments will most certainly damage when the instrument is dropped. Digital multi meters can handle much tougher treatment and still give good service and many are designed to be water proof. Analog instruments may also suffer damaged if connected with the wrong polarity of if the measured voltage or current exceed the selected range. A digital instrument will simply indicate a negative quantity when connected in reverse and will switch automatically to an appropriate range or indicate overload when the 13 measured quantity is excessive. Monitoring a changing condition of a measured quantity is one application for which many people prefer analog instruments. The pointer of the analog instrument seems to respond more quickly than the digital display. However, digital instrument has greater solution than analog meter, so a very small change in a measured quantity will be most clearly indicated by a digital meter. Links: www.youtube.com/watch?v=ucGgo-CMYRM www.youtube.com/watch?v=p5BfMdI3cwk www.youtube.com/watch?v=gkeJzRrwe5k 14  2.B. Units, Dimensions & Standards Before standard system of measurement was invented, many approximate units were used. A long distance was often measured by the number of days, it would take to ride a horse over the distance, a horse height was measured in hands, and liquid was measured by the bucket or barrel. With the development of science and engineering more accurate units had to be device. The English-speaking people adopted the foot and mile for measuring distances, the pound for mass & gallon for liquid. Other nations followed the lead of the French in adopting a metric system, in which large and small units are very conveniently related by a factor of 10. With the increase of world trade and the exchange of scientific information between nations, it became necessary to establish a single system of units of measurement that would be acceptable internationally. After several world conferences on the matter, a metric system which uses the meter, kilogram, and second as fundamental unit has now been generally adopted around the world. This is known as the SI or International System. SI Mechanical Units FUNDAMENTAL UNITS UNIT OF LENGTH - meter (m) UNIT OF MASS - kilogram (kg) UNIT OF TIME - second (s) UNIT OF FORCE (MASS X ACCELERATION) FORCE - NEWTON (N)(M/S) UNIT OF WORK - (force x distance) WORK- joule (j) (newton -meter) UNIT OF ENERGY - joule (J) UNIT OF POWER - waH (w) SI Electrical Unit UNIT OF CHARGE - coulomb (c) UNIT OF CURRENT - ampere (A) UNIT OF ELECTROMOTIVE FORCE- volts (v) UNIT OF RESISTANCE - ohm 15 UNIT OF CONDUCTANCE - siemens UNIT OF MAGNETIC FLUX - weber (wb) UNIT OF MAGNETIC FLUX DENSITY - tesla UNIT OF INDUCTANCE - henry UNIT OF CAPACITANCE- farad (f) Scientific Notation Very large or very small numbers are conveniently written as a number, multiplied by 10 raised to a power. Note that SI systems of units, spaces are used instead of commas when writing large numbers. Four numeral numbers are an exception. One thousand is written as 1000, while ten thousand is 10,000. SCIENTIFIC VALUE PREFIX SYMBOL NOTATION 1 000 000 000 000 Tera T 10-12 1 000 000 000 Giga G 10-9 1 000 000 Mega M 10-6 1 000 Kilo K 10-3 100 Hecto h 10-2 10 10 Deka da 0.1 Deci d 10-1 0.01 Centi c 10-2 0.001 Milli m 10-3 0.000 001 Micro 10-6 0.000 000 001 Nano n 10-9 0.000 000 000 001 Pico p 10-12 SI UNITS AND SYMBOLS QUANTITY SYMBOL UNIT UNIT SYMBOL Length l Meter m 16 Mass m Kilogram kg Time t Second s Area A Square meter m2 Volume V Cubic meter m3 Velocity v Meter per second M/s Meter per second per Acceleration a M/s2 second Force f Newton N Pressure p Newton per squre meter N/m2 Work W Joule J Power P Watt W Electric Current I Ampere A Electric Charge Q Coulomb C EMF V Volt V Electric Field E Volt per meter V/m Strength Resistance R Ohm Ω 17  2.C. Measurement Standards Working Standards Electrical measurement standards are precise resistors, capacitors, inductors, voltage sources, which can be used for comparison purposes when measuring electrical quantities. The standard resistors, capacitors and inductors usually found in an electronics laboratory are classified as working standard. Working standard resistors are normally constructed of managing or a similar material which has a very low temperature coefficient. Standard Classification Measurement standards are classified in four levels international standard, primary standard, secondary standards and working standard. Thus, the working standards already discussed are the lower level of standards. International standards are defined by international agreements and are maintained at the bureau of weight and measures in France. These are as accurate as it is scientifically possible to achieve. They may be used for comparison, w/ primary standards, but are otherwise unavailable for any application. Primary standards are maintained at institutions in various countries around the world such as National Bureau of Standard. They are also constructed for the greatest possible accuracy and their main functions are checking the accuracy of secondary standards. Secondary standards are employed in industry as references for calibrating high accuracy equipment and components and for verifying the accuracy of working standard. Secondary standards are periodically checked at the institutions that maintain primary standards. In summary, working standards are used as measurement references on a day-to-day basis in virtually all electronic laboratories Secondary standards are more accurate than working standard and are used through industry for checking working standards and for calibrating high accuracy equipment Primary standards are more accurate than secondary. Then are maintained to the highest possible accuracy by National Institutions as references for calibrating secondary standards international standards are maintained by international agreement and may be used for checking primary standards. MOVING COIL INSTRUMENT Consist basically of a light weight coil of wire suspended in a field of permanent magnet. Current in the wire causes the coil to produce a magnetic field that interacts with the field from the magnet; resulting in partial rotation of coil a pointer connected to the coil deflects over a calibrated scale, indicating in the level of current flowing in the wire. The PMMC instruments is essentially a low-level DC ammeter, however, with the use of 18 parallel connected resistors, it can be employed to measure a wide range of direct current levels, the instrument may also be made to function as a DC voltmeter by connecting appropriate value of resistors in series with the coil. AC ammeters and voltmeters can be constructed by using rectifier circuits with PMMC instruments. Ohmmeters can be made from precision resistors, PMMC instruments and batteries. Multirange meters are available that combine ammeter volt meter and ohmmeter functions one instrument. The electrodynamics instruments are similar to the PMMC instrument except that it uses stationary coils instead of a permanent magnet. The most important application of the electro dynamic instrument is as a Wattmeter. Deflection Instrument Fundamentals A deflection instrument uses a pointer that moves over a calibrated scale to indicate a measured quantity for this to occur three forces are operating electromechanical mechanism or movement). Inside a deflecting force, a controlling force and a damping force. The deflecting force causes the pointer to move position when a current flows. In the permanent magnet moving coil instrument the deflecting force is magnetic. When current flows in a light weight moving coil pivoted between the poles of a permanent magnet the current sets up a magnetic field that instructs with the field of the permanent magnet a force is exerted on a current carrying conductor situated in a magnetic field. Consequently, a force is exerted on the coil turns as illustrated causing the coil to rotate on its pivot. The pointer is fixed to the coil, so it moves over the scale as the coil rotates. The controlling force in the PMMC instrument is provided by spiral springs (Fig. 1b). The springs retain the coil and pointer at their zero position when no current is 19 flowing. When current flows, the springs “wind up” as the coil rotates, and the force they exert on the coil increases. The coil and pointer stop rotating when the controlling force becomes equal to the deflecting force. The spring material must be non-magnetic to avoid any magnetic field influence on the controlling force. Since the springs are also used to make electrical connection to the coil, they must have a low resistance phosphor bronze is the material usually employed. As illustrated in figure 2 (a), the pointer and cell tend to oscillate for some time before selling down in their final position A damping force is required to minimize (or damp out) the oscillation. The damping force must be present only when the coil is in motion thus it must be generated by the rotation of the Coil. In PMMC instruments, the creeping force is normally provided by eddy currents. The coil former (or frames) is constructed of aluminum, a non-magnetic conductor. Eddy currents induced in the coil former set up a magnetic flux that opposes the cell motion thus damping the oscillations of the coil. See figure 2 (b). 20  Two methods of supporting the moving system of a deflection instrument are illustrated in Figures to the jeweled - bearing suspension to Figure 3(a), the painted ends of shafts or pivots fastened to the coil ore inserted into cone - shaped cuts in jewel (sapphire or glass) bearings. This allows the coil to rotate freely with the least possible friction. Although the coil is normally very light weight the pointed end of the pivots have extremely small areas, so the surface load per unit are can be considerable, in some cases the bearings maybe broken the shock of an instrument being slammed down heavily upon a bench. Some jewel bearings are spring supported (as illustrated) to absorb such shocks more easily. The taut band method in Figure 3(b) is much tougher than jeweled - bearing suspension. As illustrated, two flat metal ribbons (phospor bronze or platinum alloy) are held under tension by springs to support the coil. Because of the springs, the metal ribbon behave like rubber under tension, The ribbon also exert controlling force as they twist, and they can be used to electrical connections to the moving coil. Because there is less friction, taut - band instrument can be much more sensitive than the jeweled -bearing type, the most sensitive jeweled - bearing instrument give full - scale deflection (FSD) with a coil current of 25 microampere. With taut band suspension (FSD) may be achieved with as little as 2 microampere of coil current. The fact that the spring-mounted ribbon behaves as a rubber band makes the instrument extremely rugged compared to a jeweled-bearing instrument. If a jeweled – bearing is drop to a concrete floor from the 21 bench height, the bearings will almost certainly be shattered. A taut-band instrument is unlikely to be affected by a similar fall. 22  Lesson 3 3.A. Insulation Tester 3.B. KiloWatt-Hour Meter 3.C. Watt Meter 3.D. Instrument Transformer 3.A. INSULATION TESTER What is an Insulation Tester? Insulation tester used for the measurement of insulation resistance of an electrical system. An electrical system degrades its quality of insulation resistance with time and various environmental conditions including temperature, moisture, dust particles & humidity. History The Megger is just a brand, known also as the mega-ohm tester, has a long history. The device has been in regular use since 1903, but the history dates a bit further back to 1889. The device was quite popular by the 1920s. The term Megger is actually something of a nickname, since the device measures mega-ohms and it was a meter. It is a combination of the two words. Through the years, the design and purpose of the test remains the same. The only thing that has really changed is the design and the level of quality for the testers themselves. Today, it’s possible to find high quality options that are easy to use and safer than the testers from yesteryear were. 23 Uses The device enables us to measure electrical leakage in wire, results are very reliable as we shall be passing electric current through device while we are testing. The equipment basically uses for verifying the electrical insulation level of any device such as motors, cables, generators, windings, etc. This is a very popular test being carried out since very long back. Not necessary it shows us exact area of electrical puncture but shows the amount of leakage current and level of moisture within electrical equipment/winding/system. How to use? Step 1: Switch off power to the circuits you are testing. If you are not sure which breakers or fuses control the circuits, switch off the main breaker. Place a note on the breaker panel advising others not to switch on the power because you are working on the circuits. Lock the switch closed if possible. Step 2: Prepare a table in which you can record the insulation values that result from your tests. For a 110-volt circuit, leave spaces for the test results of the insulation between the black wire and the white wire and the insulation between each wire and ground. For a 220-volt circuit, leave spaces for the test results of the insulation between each of the three wires and the other two and between each of the three wires and ground. For a piece of equipment such as a circuit breaker 24 or an appliance, leave space for insulation values between each terminal and the other terminals and each terminal and ground. Step 3: Select 500 volts DC or 1000 volts DC as the test voltage on your Megger, depending on the model you are using. Check whether your model has an integrated voltage tester for live circuits. If it doesn't, check the circuits to be tested with a voltage tester to make sure they are not live. Place the positive and negative probes of the Megger on the two conductors or terminals between which you are testing the insulation resistance. If you are testing insulation resistance to ground, place the positive probe on the ground wire or the grounded metal junction box and the negative probe on the conductor or terminal. Energize the Megger for 1 minute. Read the value of the resistance at the end of the minute test and note it in your table. Continue with this testing procedure until you have values for all the spaces of your table. Step 4: Examine the resistance values you have entered in your table. According to the National Electrical Code, all values should be over 25 Megaohms. If one of the values differs substantially from all the others, check your connections and repeat the tests. If a value is below 25 Megaohms, check the circuit for the cause of the poor insulation resistance value. Operating Principle Voltage for testing produced by hand operated megger by rotation of crank in case of hand operated type; a battery is used for electronic tester. 500 Volt DC is sufficient for performing test on equipment range up to 440 Volts. 1000 V to 5000 V is used for testing for high voltage electrical systems. Deflecting coil or current coil connected in series and allows flowing the electric current taken by the circuit being tested. The control coil also known as pressure coil is connected across the circuit. Current limiting resistor (CCR and PCR) connected in series with control and deflecting coil to protect damage in case of very low resistance in external circuit. In hand operated megger electromagnetic induction effect is used to produce the test voltage i.e. armature arranges to move in permanent magnetic field or vice versa. Where as in electronic type megger battery are used to produce the testing voltage. As the voltage increases in external circuit the deflection of pointer increases and deflection of pointer decreases with an increase of current. 25  Hence, resultant torque is directly proportional to voltage and inversely proportional to current. When electrical circuit being tested is open, torque due to voltage coil will be maximum and pointer shows ‘infinity’ means no shorting throughout the circuit and has maximum resistance within the circuit under test. If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance within circuit being tested. Work philosophy based on ohm-meter or ratio-meter. The deflection torque is produced with megger tester due to the magnetic field produced by voltage and current, similarly like ‘Ohm’s Law’. The torque of the megger varies in a ration with V/I, (Ohm’s Law: V = IR or R = V/I). Electrical resistance to be measured is connected across the generator and in series with deflecting coil. Produced torque shall be in opposite direction if current supplied to the coil. 1. High Resistance = No Current: No current shall flow through deflecting coil, if resistance is very high i.e. infinity position of pointer. 2. Small Resistance = High Current: If circuit measures small resistance allows a high electric current to pass through deflecting coil, i.e. produced torque make the pointer to set at ‘ZERO’. 3. Intermediate Resistance = Varied Current: If measured resistance is intermediate, produced torque align or set the pointer between the range of ‘ZERO to INIFINITY’. 26 Types of Insulation Tester Electronic Type (Battery Operated) Important parts: a. Digital Display: A digital display to show IR value in digital form. b. Wire Leads: Two nos of wire leads for connecting megger with electrical external system to be tested. c. Selection Switches: Switches use to select electrical parameters ranges. d. Indicators: To indicates various parameters status i.e. On-Off. For example, power, hold, warning, etc. Note: Above construction is not similar for every megger, it difference appears manufacture to manufacture but basic construction and operation are same for all. 27  Manual Type (Hand Operated) Important parts: a. Analog display: Analog display provided on front face of tester for IR value recording. b. Hand Crank: Hand crank used to rotate helps to achieve desired RPM required generate voltage which runs through electrical system. c. Wire Leads: Used same as in electronic tester i.e. for connecting tester with electrical system. 28 Advantages and Disadvantages of Electronic Type Megger Advantages: Level of accuracy is very high. IR value is digital type, easy to read. One person can operate very easily. Works perfectly even at very congested space. Very handy and safe to use. Disadvantages: Require an external source of energy to energies i.e. Dry cell. Costlier in market. Advantages and Disadvantages of Manual Type Megger Advantages: Still keeps important in such high-tech world as it’s an oldest method for IR value determination. 29  No external source required to operate. Cheaper available in market. Disadvantages: At least 2 people are required to operate i.e. one for rotation of crank other to connect megger with electrical system to be tested. Accuracy is not up to the level as it’s variations with rotation of crank. Require very stable placement for operation which is a little hard to find at working sites. Unstable placement of tester may impact the result of tester. Provides an analog display result. Require very high care and safety during use of the same. Link: www.youtube.com/watch?v=gU_9-f0l3-Q 3.B. Killowatt-Hour Meter What is Kilowatt-Hour Meter? kWh meter is the electric meter that measures the amount of electrical energy in kWh that was consumed in the house. The kWh meter has a counter display that counts units of kilowatt-hour (kWh). The energy consumption is calculated by calculating the difference of the counter's reading in the specified period. 30  History Oliver B. Shallenberger Invents the A.C. Watt-Hour Meter On 14 August 1888 in Pittsburgh, Pennsylvania, Oliver B. Shallenberger received a patent for the watt-hour meter, a device that measured the amount of A.C. current and made possible the business model of the electric utility. Working on applications for A.C. power, Shallenberger stumbled onto a solution for the problem of metering. As he was tinkering with an electric arc lamp in 1888, a spring fell out and fell on a ledge inside the lamp. Shallenberger saw that the spring had rotated. Testing a hunch, he discovered that the lamp’s spinning electromagnetic fields had caused the spring to turn. Within a few weeks, Shallenberger designed a wheel that turned in relation to this rotational force, offering a means of measuring amperes per hour on an alternating current circuit. Hundreds of thousands of these meters were built in the coming decades, allowing A.C. power to take off as an everyday consumer technology. Shallenberger’s basic design remains in use today. Because these meters operated on electrical current’s induced magnetic field, they consumed virtually no power. Consumers could feel more confident that they were only being charged for the power they used, and could more accurately monitor their consumption. AC Energy Meter Working Principle Energy is the product of power and time and is measured in watt-seconds or Joule. Since the voltage and current in a DC circuit are constant values, the energy is easily computed from a measurement of power and time, W=Pt JouleW=Pt Joule 31  Where W is in watt-seconds or Joules, P in watts and t in seconds. The watt second is a too small unit and hence the larger unit kilowatt-hour (KWH) is preferred. If the current and voltage are not constant, one measures energy directly by the use of a watthour meter. Both AC and DC watt-hour meters are available, both types are summing or integrating types. The basic assembly of an AC induction watthour meter is shown in Fig. The AC induction watthour meter has voltage and current coils, but unlike the wattmeter, all the coils are stationary. The voltage coil is connected to the source lines, whereas the current coil is connected in series with the load. The combination of stationary coils is called the stator. A disk or rotor mounted on a shaft receives a torque through an electromagnetic induction whenever the two sets of coils are energized. The rotor is mechanically connected to a meter register via a gear train. A register provides a record of a number of rotor shaft revolutions and is calibrated in kilowatt-hours. A constant of proportionality, the watthour constant, Kh, is the number of watthours corresponding to one disk revolution. Thus, the energy in watt-hours is W=Kh∗disk revolutions W=Kh∗disk revolutions And in kilowatt-hours; W=Kh∗disk revolutions1000 32 Types of Kilowatt-Hour Meters Analog meters: also called electromechanical meters. They have an analog display. They do not offer any connectivity. Digital meters: also called electric meters. They have a digital display (LCD or LED display), they offer connectivity and some instant functionalities. Types of Electricity Meters: Accumulation meter 33  Interval meter Smart meter Accumulation meters, also known as single rate or flat meters, measure how much electricity has been consumed by the property. How To Read an Accumulation Meter There are three types of accumulation meter display (pictured above left to right) – Cyclometer display, dial display and digital display. The digital and cyclometer displays are easy to read – the display simply shows how much electricity has been used (kWh). Dial Accumulation Meters are slightly more confusing. They have five small dials with numbers 0 to 9. From left to right, read the numbers the dial hands fall on. If the hand falls between two numbers, then take the lowest number (unless it falls between 0 and 9, write down 9). The meter dials in the illustration on the right show a be ignored consumption of 46,925 kWh. The red dial can be ignored. 34  Accumulation Meters require a meter reader to come to the property every three months to check how much electricity has been used. This is done by calculating the difference between your current and your previous meter reads. Some energy retailers choose to offer monthly billing, in which case your bills will be estimated between meter reads. Interval Meters record electricity usage every 30 minutes. This means power retailers can charge you different rates depending on the time of the day you use electricity. Interval Meters are digital, so they’re pretty straightforward to read. If you want to estimate your next bill, then you’ll need to make a habit of jotting down the kWh figures displayed. Meter readers record interval meter data by attaching an optical probe which extracts the interval meter data and then sends it to the distributor’s systems. The distributor then processes the data up to ten times to ensure its accuracy before sending it to your retailer for billing. 35  Smart Meters, also commonly known as ‘digital meters’, are the latest in energy metering technology. Smart meters display your usage in kWh on a small digital screen. Links: www.youtube.com/watch?v=zRYESRObKqA www.youtube.com/watch?v=wp7dZH2fgUw www.youtube.com/watch?v=xtModjpxfxM www.youtube.com/watch?v=xtModjpxfxM 36  3.C. Watt Meter What is Watt Meter? The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit. Other uses are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. History 37  The Wattmeter was discovered in 1872 by Samuel Gardiner. This was a DC lamp- hour meter that was a clock with an electromagnet that started and stopped the mechanism. Construction of a Wattmeter The internal construction of a wattmeter is such that it consists of two cols. One of the coils is in series and the other is connected in parallel. The coil that is connected in series with the circuit is known as the current coil and the one that is connected in parallel with the circuit is known as the voltage coil. 38  These coils are named according to the convention because the current of the circuit passes through the current coil and the voltage is dropped across the potential coil, also named as the voltage coil. The needle that is supposed to move on the marked scale to indicate the amount of power is also attached to the potential coil. The reason for this is that the potential coil is allowed to move whereas the current coil is kept fixed. The mechanical construction of a wattmeter is shown in the figure below. Working of a Wattmeter When the current passes through the current coil, it creates an electromagnetic field around the coil. The strength of this electromagnetic field is directly proportional to the amount of current passing through it. In case of DC current, the current is also in phase with its generated electromagnetic field. The voltage is dropped across the potential coil and as a result of this complete process, the needle moves across the scale. The needle deflection is such that it is according to the product of the current passing and the voltage dropped. 39 The measurement principle of wattmeter is shown in the figure below: Applications of Wattmeter As other measuring instruments, watt meters are also used extensively in electrical circuit measurement and debugging. They are also used in industries to check the power rating and consumption of electrical appliances. Electromagnetic watt meters are used to measure utility frequencies. They are used with refrigerators, electric heaters and other equipment to measure their power ratings. This was all about watt meters. What they are used for, what is their mechanical construction and how do they work. As evident, they are of extreme importance and extensive use in electrical related industries and like other measuring devices, are quite easy to use and accurate. How to use a Watt Meter? You can use a watt meter to determine how much power appliances and other electronic devices are using around your home. This article will show you how, but with the caveat that some appliances, like refrigerators and Window Air Conditioners cycle through phases. The watt meter only provides a snapshot of electricity use at the exact moment it’s plugged in. However, these devices are exceptionally effective at measuring electricity used when a device is on, and when it’s powered off but still plugged in (referred to as vampire power). 40 Things you’ll need: A Watt Meter Any electronic device or appliance on a standard 120-volt line (with a standard plug) 3 prong to 2 prong adapter (if the outlets in the home are 2 prong) Before proceeding, check out this quick video to see just how easy it is to use a watt meter to test vampire energy losses, plug loads, etc.: 1. Unplug your electronic device from your wall or power strip. You’ll need to have the watt meter plugged into your wall or power strip in order for it to work, so either find an empty plug or unplug the device you’d like to test. 2. Plug your watt meter into your wall outlet or power strip. Now that you’ve found or made an empty spot for your watt meter go ahead and plug it into either the wall outlet or power strip. Once you’ve done that you should start to see your watt meter turn on. 3. Plug your electronic device into your watt meter. Now that your watt meter is plugged in, you’re ready to start testing your electronics. Go ahead and plug in your first electronic and watch your watt meter. Is it registering anything? If so (and your electronic device is turned off) than you’ve discovered what is known as vampire power. Now, go ahead and turn your device on. What does your watt meter read? Depending on the type of watt meter you have there are several different ways you can view your findings. One is by simply seeing the actual wattage being consumed by your electronics. However, some watt meters will allow you to view your findings by both monthly and yearly cost (assuming the electronic device is running 24/7). At this 41 point we’d recommend that you go from room to room in your home and check all your electronics to discover where you can be saving money. 0.0 to 0.5 Many times, a watt meter will read something odd, like one very common model that simply reads 0.0 to 0.5 watts when measuring some devices. This does not mean energy is being used at that moment–it simply means that the level of energy flowing through the device is small enough not to be measured accurately by the device. It may well be 0.5, or it may well be 0. Types of Watt Meters Electrodynamic The traditional analog wattmeter is an electrodynamic instrument. The device consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. The current coils are connected in series with the circuit, while the potential coil is connected in parallel. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. A current flowing through the current coil generates an electromagnetic field around the coil. 42 Electronic Watt Meter Electronic wattmeters are used for direct, small power measurements or for power measurements at frequencies beyond the range of electrodynamometer-type instruments Prodigit Model 2000MU (UK version), shown in use and displaying a reading of 10 watts being consumed by the appliance. Digital A modern digital wattmeter samples the voltage and current thousands of times a second. For each sample, the voltage is multiplied by the current at the same instant; the average over at least one cycle is the real power. The real power divided by the apparent volt-amperes (VA) is the power factor. Advantages of Digital Multimeters 43  They are more accurate than analog multimeters. They reduce reading and interpolation errors. The 'auto-polarity' function can prevent problems from connecting the meter to a test circuit with the wrong polarity. Parallax errors are eliminated. If the pointer of an analog multimeter is viewed from a different angle, you will see a different value. This is parallax error. A digital multimeter's numerical display solves this problem Digital multimeter displays have no moving parts. This makes them free from wear and shock failures. The reading speed is increased as it is easier to read. Unlike analog multimeters, zero adjustment is not required. Accuracy is increased due to digital readout. You can make mistake in reading the scale in analog multimeter, but digital multimeters have a LCD display to show accurate reading. DMMs can be used in testing continuity, capacitors, diodes and transistors. More advanced digital multimeters can also measure frequency. The 'auto-ranging' feature of a digital multimeter helps in selecting different measurement ranges, which can prevent damage to the meter if the wrong range is selected. Portable size makes it easy to carry anywhere. Some advanced digital multimeters have microprocessors and can store the readings for further processing. Disadvantages of Digital Multimeters The LCD display depends on a battery or external power source. When the battery is low, the display will be dim, making it difficult to read. In case of fluctuations or transients, it can record an error. Warming of the meter during its use can change its properties leading to errors in measured value. The A/D converter has a limitation on word length which can cause quantization noise giving rise to error in measured value. There is a voltage limitation. If it is increased beyond the limit, the meter will be damaged. 44  The digital nature makes it unsuitable for adjusting tuning circuits or peaking tunable responses. They are expensive due to high manufacturing cost. Links: www.youtube.com/watch?v=Nyn2S7eLdB4 www.youtube.com/watch?v=_Q4l1lQeKPs www.youtube.com/watch?v=tVMsBMTVqp0 45  3.D. Instrument Transformer History 1830 - Michael Faraday work with electromagnets and discover the property of induction. 1836 - Rev. Nicholas Callan invents the induction coil. 1876 - Pavel Yablochkov uses induction coils in his lighting system. 1878 – 1883 - The Ganz Company uses induction coils in their lighting systems with AC incandescent systems. 1881 - Charles F. Brush develops his own design of transformer. 1880 – 1882 - Sebastian Ziani de Ferranti creates an early transformer. 1882 - Lucien Gaulard and John Dixon Gibbs first built a “secondary generator” which they designed with open iron core. The invention was not very efficient to produce. It was first used in a public exhibition in Italy in 1884. Later, they designed a step-up transformer. They sold to Westinghouse. Later, they lost rights to the patent when Ferranti took them to court. Uses Used to bring voltage or current up or down in an AC electrical circuit. Used in AC system for measurement of electrical quantities. [i.e. voltage, current, power, energy, power factor, frequency] Used to transfer electrical power while isolating powered device from power source for safety reasons; assures the safety of operators as well. 46  Used in power transmission. How to use? Current Transformer Connect the primary winding to the source Use a fuse(s) for safety purposes Connect the Secondary Winding to an Ammeter. Configure the ammeter. Wait for the reading, the supposed accuracy is high. Voltage Transformer Connect the primary winding to the source. Use a fuse(s) for safety purposes Connect the Secondary Winding to a Voltmeter. Configure the Voltmeter. Wait for the reading, the supposed accuracy is high. AMMETER ANALOG DIGITAL VOLTMETER 47  ANALOG DIGITAL Using Current and Potential Transformer Operating Principle Current Transformer Is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter Consists of only one or very few turns as its primary winding. are a series connected type of instrument transformer Uses Step-up Transformer to reduce current to secondary coil. Primary winding is the coil that draws power from the source. The secondary winding is the coil that delivers the energy at the transformed or changed voltage 48  to the load. Usually, these two coils are subdivided into several coils in order to reduce the creation of flux. Ratios Most current transformers have the standard secondary rating of 5 amps with the primary and secondary currents being expressed as a ratio such as 100/5. This means that the primary current is 20 times greater than the secondary current so when 100 amps is flowing in the primary conductor it will result in 5 amps flowing in the secondary winding. A current transformer of say 500/5, will produce 5 amps in the secondary for 500 amps in the primary conductor, 100 times greater. Phases of CT’s CT’s Representation Voltage Transformer The primary winding consists of a large number of turns which is connected across the high voltage side while the secondary winding has lesser number of turns which is connected to the voltmeters. A voltage step-down transformer which reduces the voltage of a high voltage circuit to a lower level for the purpose of measurement. These are connected across or parallel to the line which is to be monitored. These can be single phase or three phase potential transformers. 49  Irrespective of the primary voltage rating, these are designed to have the secondary output voltage of 110 V. Ratio The PT is typically described by its voltage ratio from primary to secondary. A 600:120 PT will provide an output voltage of 120 volts when 600 volts are impressed across its primary winding. Standard secondary voltage ratings are 120 volts and 70 volts, compatible with standard measuring instruments. 4 PT’s Representation Current Transformer Potential Transformer Types of Instrument Transformer 1. Current transformer 2. Potential transformer 50 Current Transformer A type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter. Three Basic Types of Current Transformers Wound Current Transformer Have a primary winding that is directly connected to the conductor in a series. The conductor is the device that measures the actual input current. The resulting “stepped down” current is completely dependent on the turn ratio available between the primary and secondary windings in the transformer chosen. Toroidal Current Transformer Slightly different in that they don’t have a primary winding at all. Rather the conductor is threaded directly into the transformer via a hole or window. This is a configuration that is commonly seen in split core transformers because it allows them to be opened and closed without disrupting the circuit they are attached to. Bar Type Current Transformers Doesn’t have a primary winding of its own. It uses the actual cable or bus bar of the existing circuit as its primary winding, giving it a single turn type configuration. These are often used in high voltage circuit situations because of their ability to be 100% insulated from high operating voltage environments and ability to handle larger currents. Potential Transformers 51  A voltage step-down transformer which reduces the voltage of a high voltage circuit to a lower level for the purpose of measurement. The primary winding consists of a large number of turns which is connected across the high voltage side or the line in which measurements have to be taken or to be protected. The secondary winding has lesser number of turns which is connected to the voltmeters. Types of Voltage or Potential Transformers Conventional Wound Type Transformer Very expensive because of the requirement of the insulations. A wire-round type of transformer. Capacitor Potential Transformer A combination of capacitor potential divider and a magnetic potential transformer of relatively small ratio. Utilized for higher voltages Optical Potential Transformers Used in optical equipment applications to measure resistance and reactance. Link: www.youtube.com/watch?v=YSMGYf4hozo 52  Lesson 4 4.A. AC/DC Volt Meter 4.B. Ammeter and Clamp Meter 4.C. Clamp-On Meter 4.D. Tachometer 4.A. AC/DC Volt Meter History of Voltmeter 53  Hans Christian Oersted (1820) The original principals behind voltmeters were established by a Danish physicist named Hans Christian Oersted (1777-1851) in 1820, when he discovered that an electric current in a wire produced a magnetic field around it. André-Marie Ampère (1820) The first ammeter, which is actually just an extremely sensitive and nonresistant voltmeter, was used by physicist Andre Ampere as early as 1820 to measure current. Pliotron (as he called it). The triode became a key component of vacuum tube voltmeters as well as amplifiers used in radio and television. Schenectady, New York. VOLTMETER Voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog Voltmeter 54  Note: Voltmeter is constructed in such a way that it has a very high value of resistance. Working Principle of Voltmeter The main principle of voltmeter is that it must be connected in parallel in which we want to measure the voltage. Parallel connection is used because a voltmeter is constructed in such a way that it has a very high value of resistance. If that high resistance is connected in series than the current flow will be almost zero which means the circuit has become open. Actual picture of voltmeter used in series. Diagram of voltmeter in series. If it is connected in parallel, the load impedance comes parallel with the high resistance of the voltmeter and hence the combination will give almost the same the impedance that the load had. Also, in parallel circuit we know that the voltage is same so the voltage between the voltmeter and the load is almost same and hence voltmeter measures the voltage. Actual picture of voltmeter used in parallel. Diagram of voltmeter used in parallel. 55 DC VOLTMETER Circuit diagram of DC Voltmeter DC voltmeter is a measuring instrument, which is used to measure the DC voltage across any two points of electric circuit. AC VOLTMETER Circuit diagram of AC Voltmeter The instrument, which is used to measure the AC voltage across any two points of electric circuit. The main difference of AC voltmeter to DC voltmeter is that AC voltmeter use rectifier while DC voltmeter does not. 56  Circuit diagram of AC Voltmeter Circuit diagram of DC Voltmeter Note: Rectifier is an electrical device which converts an AC into DC by allowing a current to flow through it in one direction only. Types of Voltmeter 1. Permanent Magnet Moving Coil (PMMC) Voltmeter It is an instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field: and is only used for measuring DC currents. 57  2. Moving Iron Voltmeter Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. The force of this attraction depends upon the strength of the said magnetic field. If the magnet is electro magnet, then the magnetic field can be easily calibrated by the current through the coil. 3. Electrodynamometer There are two types of coil present in the electrodynamometer. They are the moving coil that moves the pointer with the help of spring control, and the fixed coil that is divided into two equal parts and are connected in series with the load, therefore the load current will flow through these coils. 4. Rectifier Voltmeter 58  They are used for AC or DC measurements. For DC measurement we have to connect a PMMC meter which measures pulsating DC voltage which measures rectified voltage which is connected across the bridge rectifier. 5. Induction Type Voltmeter The operation of induction type instruments depends on the production of torque due to reaction between two magnetic fluxes having some phase difference OR reaction between flux of an AC magnet and the eddy current induced by this flux. These types of instruments are used only foe AC measurements. 6. Electrostatic Type Voltmeter 59  Electrostatic Voltmeters operating on the electrostatic principle use the mutual repulsion between two charged plates to deflect a pointer attached to a spring. These types of instruments are used for high voltage AC measurements as well as DC. These are of electrostatic disc type capacitor connected across the circuit which is to be measured. The electrostatic voltmeters can be categorized into three types based on the mechanical configuration. Those are repulsion, attraction, and symmetrical. Deflecting system consists of deflector which is suspended from a torsion filament or it can be pivoted by the bearings. 7. Digital Voltmeter (DVM) The Digital Voltmeter is an instrument which can give the output voltage not by deflection but directly indicating the value. It is a very good instrument to measure the voltage as it eliminates completely the error due to parallax, approximation in measurement, high-speed reading can be done and it can also be stored in memory for further analysis. The main principle is that the value is measured by the same circuit arrangement but that value is not used to deflect the pointer, but it is fed to the analog to digital converter and displayed as the digital value. Advantages of Analog Voltmeters Analog needle movement gives a better idea of order of magnitude and trend than a digital readout. 60  Does not require a power supply beyond the test current source. Disadvantages of Analog Voltmeters Multiple scales can cause confusion Lacks auto-polarity technology, incorrectly connected test leads can result in needle deflection and damage to the device. Parallax error, which occurs to improper reading of analog measurements. Analog Voltmeter Advantages of Digital Voltmeter It can be programmed, so controlling by computer can be achieved. It has automatic range selection. Gives good stability. It provides better resolution, for example it can be read on 1 volt input range. The internal calibration does not depend on the measuring circuit. It has high speed reading. Disadvantages of Digital Voltmeter It gives some extra feature and it’s much more expensive. 61  Speed of operation is limited due to the digitizing circuit. It is usually very hard to spot transient voltage spikes. Digital Voltmeter Link: www.youtube.com/watch?v=gbxxlvw2HZc 62  4.B. Ammeter and Clamp Meter What is Ammeter? It is an instrument for measuring electric current in amperes (A). Instrument used to measure smaller currents such as milliampere and microampere. History: The moving-iron meter was invented by Austrian engineer Friedrich Dexler in 1884. Types of Ammeter: 1. Permanent Moving Coil Ammeter Instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field. 63  2. Moving Iron Ammeter This type of meter responds to both direct and alternating currents (as opposed to the moving- coil ammeter, which works on direct current only). The iron element consists of a moving vane attached to a pointer, and a fixed vane, surrounded by a coil. 3. Electro-Dynamometer Ammeter An electro-dynamometer is an instrument used for measuring the electric power. The basic principle was laid out in an 1848 paper by Wilhelm Weber (1804-1891): when the same current passes through two concentric coils placed at right angles to each other, the resulting torque depends on the square of the current. 64  4. Rectifier Type Ammeter The rectifier ammeter uses the moving coil along with the rectifier for measuring the current. The main use of the rectifier is to convert the alternating current into the direct current. Uses of Ammeter: It is used to measure electrical current in units of amperes. The use of ammeter is vast, ranging from school laboratories to construction industries. It is also used to measure the flow of current through the wiring of newly constructed buildings to ensure that the current is not too high or too low and has the ability to power electrical devices within a safe range. How to use an Ammeter: 1. Set the ammeter current type and range. 2. Test the infernal fuse of your ammeter. 3. Break the circuit. 4. Connect the ammeter leads to the circuit. 5. Restore power to the circuit and take the reading. 6. Cut power and return the circuit to normal. Advantages: 65  It able to provide accurate reading that can be easily be noted. They can be battery powered. They are portable and can be taken outdoors to circuit that do not have any power source near them. Disadvantages: The disadvantage of using ammeter is that you can easily burn them out. It doesn’t take much. It has low resistance and any mistake will let a current surge through. It will happen so fast you wouldn’t have a chance to do anything. 66  4.C. Clamp Meter What is a Clamp Meter? It is an electrical test tool that combines a basic digital multimeter with a current sensor. History: Amprobe invented the first clamp meter in 1948 and has continued to innovate and evolve. Types of Clamp Meter: 1. Current Transformer Clamp Ammeter 67 It is equipped with rigid jaws made of ferrite iron. The jaws are individually wrapped by coil of copper wire. Also, it only measures alternating current. 2. Hall Effect Clamp Ammeter It can measure both AC and DC current up to the kilohertz (1000 Hz) range. Like current transformer clamp, it uses iron jaws to concentrate the magnetic field but unlike current transformer clamp meter, the jaws are not wrapped by copper wire. Instead, the magnetic field generated by the conductor is focused across one or more gaps in the core after the jaws are clamped around the conductor. 3. Flexible Clamp Ammeter 68  Also known as Rogowski coils. Unlike current transformer and Hall Effect clamp meters, they have no iron core. Instead, they use wound, helix-shaped coil which responds to the rate of change of a conductor’s magnetic field around which they are place. It only measure AC current and it is more efficient to use in tight places. Uses: Used to measure the current flowing through a conductor. An AC Clamp meter basically consists of a current transformer in its jaws, bar CT usually. A DC Clamp meter is quite different. It uses a Hall Effect sensor for measuring the current. A clamp meter measures the vector sum of the currents flowing in all the conductors passing through the probe. How to use a Clamp Meter: 1. Switch ON the meter and remove the probes (if attached). 2. Select the AC current or DC current function using the dial. 3. Open the jaw-like structure using the side lever and insert the conductor through which the current is to be measured. 4. Then close the jaw-like structure and level the conductor between the alignment marks inscribed on the jaws. 5. The display will show the appropriate reading. Users can change the resolution as per requirements, but most meter models do this automatically. 69 Note: It is recommended that all measurements should be taken for conductors that are insulated properly. DO NOT measure around live wires. Advantages: They are used for a wide range of measurements and are best suited for use in noisy electrical environments. It provides hassle free measurement and increases efficiency and productivity as it is not necessary to shut down the circuit supply. Disadvantages: The only disadvantage of this test equipment (Clamp meter or Tong tester) is that the accuracy of the tong-tester is considerably low. Importance: Today’s clamp meters include most of the basic functions of a digital multimeter (DMM), such as the ability to measure voltage, continuity and resistance. Link: www.youtube.com/watch?v=z-KfZvbjyBY 70  4.D. Tachometer History of Tachometer The first Tachometer is widely considered to have been developed by the German engineer, Dietrich Uhlhorn in 1817. Uhlhorn needed a gauge to measure the speed of machines. Little did he know that within 200 years this simple device was going to be a standard feature on vehicles driving in every continent on the Earth. 71  The Tachometer was first used to measure speed on a vehicle (a locomotive) in 1840. Even though the first petrol or gasoline powered automobile was developed in 1886 (by Karl Benz), it is unclear when the first car featured a Tachometer. Types of Tachometer Analog Tachometers Comprise a needle and dial-type of interface. They do not have provision for storage of readings and cannot compute details such as average and deviation. Here, speed is converted to voltage via use of an external frequency to voltage converter. This voltage is then displayed by an analog voltmeter. Digital Tachometers 72  Comprise LCD or LED readout and a memory for storage. These can perform statistical operations, and are very suitable for precision measurement and monitoring of any kind of time-based quantities. Digital tachometers are more common these days and they provide numerical readings instead of using dials and needles. Contact and Non-Contact Tachometers The contact type is in contact with the rotating shaft. The non-contact type is ideal for applications that are mobile, and uses a laser or optical disk. In the contact type, an optical encoder or magnetic sensor is used. Both these types are data acquisition methods. Time and Frequency Measuring Tachometers Both these are based on measurement methods. The time measurement device calculates speed by measuring the time interval between the incoming pulses; whereas, the frequency measurement device calculates speed by measuring the frequency of the 73 incoming pulses. Time measuring tachometers are ideal for low-speed measurements and frequency measuring tachometers are ideal for high-speed measurements. Working Principle: Pulses are fed to the tachometer at the frequency to be measured. A scale factor is applied to produce readings of desired types (linear speed, flow rates, etc.) Two Basic Principles: 1. Principle of fixed time-based tachometer 2. Principle of reciprocal tachometer The ignition system triggers a voltage pulse at the output of tachometer electrochemical part whenever the spark plug fires. The electrochemical part responds to the average voltage of the series of pulses. It shows that the average voltage of the pulse train is proportional to the engine speed. The signal from the perception head is transmitted by standard twin screened cable to the indicator. The tachometers are temperature compensated to be able to handle operations over a range of -20 to +70 degrees. Advantages and Disadvantages Tachometers have brushes, which wear, and need to be maintained. Tachometers have magnets, which can weaken over time, or if overheated, and cause erroneous measurements. Tachometers output an analog voltage, which is proportional only to speed, so rotor angle cannot be determined like with an encoder. Due to the analog voltage, they are also suceptible to loading effect, depending on the input impedance of the measurement device or other factors in the circuit, especially at low speed. Not as accurate as an encoder, especially at low speed. Analog tachometers generally cost more than encoders because they are more material- intensive, and also due to being phased out in favor of encoders; hard to find and expensive when you find them. 74 Phase Sequence Indicator The sequence in which three phase voltages attain their positive maximum values is defined as the phase sequence. It refers to the relation between the voltages or currents in three phase system. Consider the three phases as red-R, yellow-Y and blue-B phases. Types of Phase Sequence Indicator 1. Rotating Type 2. Static Type Rotating Type Phase Sequence Indicators 75  The rotating type phase sequence indicators show the direction of the phase sequence by rotating the disc placed at the center of the instrument. It has three terminals which are connected to the terminals of the measured devices. The eddy EMF causes the eddy current in the disc. The interaction of the eddy current and the rotating magnetic field produces the torque because of which the disc starts rotating. The direction of the disc shows the phase sequence of the supply system. If the disc rotates in the clockwise direction, the phase sequence is RYB. The anticlockwise direction of the aluminum disc is because of the reverse phase sequence. Static Type Phase Sequence Indicators The static phase sequence indicators consist two lamps and an inductor. The device whose phase sequence is used to be known is connected to the static phase sequence indicators. If the lamp 1 is dim and the lamp 2 glows brightly, then the phase sequence of supply is RYB. If the lamp 1 glows brightly and the lamp 2 is dim, the device has reverse phase sequence. The brightness of the lamp depends on the voltage drops occurs across it. The working of the static phase sequence supply can more easily be understood with the help of the following analysis. Let the phase sequence of the supply is RYB, and the relationship of the phase concerning the voltage is VRY, VBY and VRB as shown in the figure below. Working Principle It works on the principle of induction motors. The principle of rotating type phase sequence indicator is similar to that of a three-phase motor. Consider the working of a motor for a better understanding of these indicators. For three phase motors, we require three phase power supply, whereas this three-phase power must be supplied in a particular sequence. Let us assume that the three phase supply given to the motor has a phase sequence of RYB, then the motor will rotate in clockwise direction – and, if the phase sequence of supply is reversed, then the motor will rotate in counter clockwise direction. This may cause severe problems to the load and entire system. 76 Link: www.youtube.com/watch?v=QVSQLfnKytk Lesson 5: 5.A. Galvanometer 5.B. AC/DC Ammeter 5.C. Power Factor Meter 5.D. Switches 5.A. Galvanometer 77 What is Galvanometer? The device used for detecting the presence of small current and voltage or for measuring their magnitude. History: 1820 - The earliest galvanometer was reported by Johann Schweigger at the University of Halle on 16 September 1820. 1826 - William Thomson (Lord Kelvin) from the early design invented in 1826. 1882 - Jacques-Arsène d'Arsonval and Marcel Deprez. By 1888, Edward Weston Working Principle It works on the principle of conversion of electrical energy into mechanical energy. When a current flows in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional to the current flowing through it. Types of Galvanometer 1. Tangent Galvanometer 78  2. Astatic Galvanometer 3. Mirror Galvanometer 4. Ballistic Galvanometer Tangent Galvanometer It works by using a compass needle to compare the magnetic field generated by an unknown current to the magnetic field of the Earth. It contains an insulated copper wire coil on a non-magnetic circular frame. Astatic Galvanometer It contains two magnetized needles that run parallel to each other, suspended by a silk thread, with their magnetic poles reversed. The lower needle gets deflected by the 79 passing current’s magnetic field. The second needle cancels out the dipole movement of the first one to cancel out the effects of Earth’s magnetic field. Mirror Galvanometer It is used to achieve higher sensitivity for detecting extremely small currents. It contains horizontal magnets which are suspended from a fine fiber inside of the vertical coil, with an attached mirror to its magnets. A beam of light reflects from the mirror acts as a long mass-less pointer by falling on a graduated scale across the room. Ballistic Galvanometer It is sensitive in mature and used to measure the quantity of charge that is discharged through it. The moving part of the galvanometer has a large moment of inertia, 80 giving it a long oscillation period. It may be of the moving coil type or of the moving magnet type. Advantages A moving coil galvanometer can be made highly sensitive increasing number of turns in coils, magnetic field, area of the coil, and decreasing torsion constant of the spring. As the coil is wound over a metallic frame, the eddy currents produced in the frame bring coil to rest quickly. Disadvantages Its sensitiveness cannot be changed at will. All types of galvanometers are easily damaged by overloading. Link: www.youtube.com/watch?v=eZmkgs97tCo 5.B. AC/DC Ammeter History of Ammeter 1870 — 1890 - Philip Lange. This Westinghouse engineer developed galvanometers including circuit controllers, voltmeters and ammeters. 1870 - Edward Weston he was an early innovator in the electrical industry developing DC systems in the 1870s. 1880 - Elihu Thomson developed many types of magnetic coil driven ammeters for use with his complete DC electrical systems in the 1880s. 81 1888 — 1910 - William Stanley this great inventor of western Massachusetts was not only a pioneer of early AC power but developer of both magnetic coil-driven ammeters and static plate volt/ammeters. Uses of Ammeter Used to measure the electric current in a circuit. Ammeters were used in order to be able to take readings of the current flowing through a circuit. Working Principle The main principle of ammeter is that it must have a very low resistance and also inductive reactance. It has very low impedance because it must have very low amount of voltage drop across it and must be connected in series connection because current is same in the series circuit. Types Of Ammeter 1. Moving-coil Ammeter 2. Electrodynamics Ammeter 3. Moving-Iron Ammeter 4. Hot Wire Ammeter 5. Integrating Ammeter 6. Pico Ammeter Moving Coil Ammeter 82  It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The modern form of this instrument was developed by Edward Weston. Electrodynamic Ammeter An electrodynamics movement uses an electromagnet instead of the permanent magnet of the d’Arsonval movement. This instrument can respond to both alternating and direct current. Moving-Iron Ammeter 83  Moving iron ammeters use a piece of iron which moves when acted upon by the electromagnetic force of a fixed coil of wire. This type of meter responds to both direct and alternating currents. Hot Wire Ammeter In a hot-wire ammeter, a current passes through a wire which expands as it heats. Although these instruments have slow response time and low accuracy, they were sometimes used in measuring radiofrequency current. Integrating Ammeter There is also a range of devices referred to as integrating ammeters. In these ammeters the current is summed over time, giving as a result the product of current and time; which is proportional to the energy transferred with that current. These can be used for energy meters or for estimating the charge pf battery or capacitor. Pico Ammeter 84  It measures very low electrical current usually form the Pico ampere range at the lower end to the mill ampere range at the upper end. Pico ammeters are used for sensitive measurements where the current being measured is below the theoretical limits of sensitivity of other devices, such as multi-meters. Advantages As there is direct or alternating current in electricity, ammeters can be configured to take readings of either of both of these types of currents. Ammeters usually have very low resistance against current in order to be able to provide accurate readings. Disadvantages As ammeters are unable to resist current, if they are connected to an incompatible device, it could damage the ammeters and even cause a short circuit, along with permanent damage to the ammeter. Not only that, the improper use of ammeters may even pose as a danger to the user. Links: www.youtube.com/watch?v=OsjrES1Ow-Q (DC Ammeter and Voltmeter) www.youtube.com/watch?v=rn2LnxCs6zw (AC/DC Ammeter and Voltmeters) 5.C. Power Factor Meter What is Power Factor Meter? The power factor meter measures the power factor of a transmission system. The power factor is the cosine of the angle between the voltage and current. The power factor meter determines the types of loads using on the line, and it also calculates the losses occur on it. The power factor meter is used for measuring the power factor of the balanced load. 85 2 Types of Power Factor Meter 1. Single Phase Electrodynamometer 2. Three Phases Electrodynamometer Single Phase Electrodynamometer Power Factor Meter The meter has fixed coil which acts as a current coil. This coil is split into two parts and carries the current under test. The magnetic field of the coil is directly proportional to the current flow through the coil. Three Phase Electrodynamometer Power Factor Meter The electrodynamometer is only useful for the balanced load. The moving coil is placed at an angle of 120º. They are connected across different phases of the supply circuit. Both the coil has a series resistance. 86  Analog Digital Power factor is a measure of the ratio of the 'total power' kVA (also known as apparent power) that is demanded by your site and the 'real power' kW that is used on your site. 87  The total power demand on the network is usually greater than the real power. The ratio of the real power to the total power is your power factor, a number between 0 and 1. The higher the power factor the more efficient your site is at utilizing the supplied power. A business with a low power factor may result in higher capital expenditures and operating costs for the electricity network, compared to a similar business with a high- power factor. These higher costs usually have to be passed on to all customers in the form of higher tariff rates. A simple analogy to explain power factor is that of a cappuccino. Here the mug must have sufficient capacity to contain both the coffee and the froth, corresponding to the total power. The froth represents the reactive power and the liquid represents the real power. We only gain real value from the liquid. 88 89 90 How to Measure Your Power Factor There are a variety of ways to measure your power factor: Logging devices on equipment. More complicated measurement and logging equipment installed on individual circuits. 91  Electricity metering may also have the ability to record power factor (typically ½ hour interval data) for the entire site and this information may be available from your electricity retailer. If you don't have the skills in-house, you may engage an external specialist to help you to assess your power factor and identify any causes and solutions to improving your power factor. There are a variety of reasons that a site may have poor power factor but the main causes are: Inductive loads such as transformers AC motors Welding equipment Arc furnaces and fluorescent lighting Benefits of Improving Your Power Factor There are a number of benefits to increasing your power factor: 1. Reduced demand charges. To reduce your demand on the electricity network which may lower your electricity costs if you are one of the small number of customers currently being charged under a kVA demand tariff 2. Contractual compliance. To help you meet your connection requirements outlined under your connection agreement 3. Increased capacity. Reducing demand on the network may allow you to connect additional machinery or equipment without the need to upgrade the network 4. Equipment life. To lower voltage being supplied to equipment which can damage or otherwise shorten the life of some equipment 5. Reduced carbon footprint. To reduce the supply of electricity to your site and so reducing your carbon footprint Ways to Improve Power Factor A poor power factor can be addressed in a number of ways. The most common approach is to install power factor correction equipment (PFC). PFC equipment is essentially a capacitor bank – which stores and provides reactive power when required. PFC equipment can be applied to separate pieces of equipment or installed in bulk to the site’s main switchboard. 92 Steps to Identify and Implement Power Factor Correction Identify if your site has opportunity to improve power factor. There are a variety of ways to measure power factor, including: Logging devices on individual equipment. More complicated measurement and logging equipment installed on individual circuits. Electricity metering may also have the ability to record power factor for the entire