Podcast
Questions and Answers
What happens to the polarity of the coils when the current reverses direction?
What happens to the polarity of the coils when the current reverses direction?
How are the phase windings A, B, and C arranged in relation to each other?
How are the phase windings A, B, and C arranged in relation to each other?
What determines the number of poles in the stator?
What determines the number of poles in the stator?
What is characteristic of the most popular type of rotor used in AC motors?
What is characteristic of the most popular type of rotor used in AC motors?
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What is the main purpose of skewing the rotor slots?
What is the main purpose of skewing the rotor slots?
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What kind of current flow results in north poles in the phase windings?
What kind of current flow results in north poles in the phase windings?
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What components make up the induction motor?
What components make up the induction motor?
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What material is usually used for the bars in the rotor's construction?
What material is usually used for the bars in the rotor's construction?
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What is the primary function of the stator in an induction motor?
What is the primary function of the stator in an induction motor?
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What describes the layout of a two-pole stator?
What describes the layout of a two-pole stator?
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How is the rotor designed in an induction motor?
How is the rotor designed in an induction motor?
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What effect does the magnetic field in the stator have on the rotor?
What effect does the magnetic field in the stator have on the rotor?
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What separates the rotor from the stator in an induction motor?
What separates the rotor from the stator in an induction motor?
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What happens as the magnetic field in the stator rotates?
What happens as the magnetic field in the stator rotates?
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What is the role of the shorting ring in the rotor?
What is the role of the shorting ring in the rotor?
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What characteristic of the stator windings contributes to the rotation of the magnetic field?
What characteristic of the stator windings contributes to the rotation of the magnetic field?
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What happens to the top electromagnet when the bottom electromagnet is moved?
What happens to the top electromagnet when the bottom electromagnet is moved?
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What characterizes an asynchronous AC induction motor?
What characterizes an asynchronous AC induction motor?
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Which statement is true regarding the advantages of AC induction motors?
Which statement is true regarding the advantages of AC induction motors?
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What induces an electromagnetic force in the rotor of an AC induction motor?
What induces an electromagnetic force in the rotor of an AC induction motor?
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What is the outcome of the interaction between the magnetic fields in an AC induction motor?
What is the outcome of the interaction between the magnetic fields in an AC induction motor?
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Which property defines the phenomenon of 'slip' in AC induction motors?
Which property defines the phenomenon of 'slip' in AC induction motors?
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Why are induction motors often considered the workhorses of industry?
Why are induction motors often considered the workhorses of industry?
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What initiates the formation of a set of electromagnets in the stator of an AC induction motor?
What initiates the formation of a set of electromagnets in the stator of an AC induction motor?
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What is the primary application for integral horsepower motors?
What is the primary application for integral horsepower motors?
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What material are most explosion proof motor enclosures typically made from?
What material are most explosion proof motor enclosures typically made from?
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Which regulatory agencies set standards for explosion proof motors in the United States?
Which regulatory agencies set standards for explosion proof motors in the United States?
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What is a key responsibility for users regarding hazardous locations?
What is a key responsibility for users regarding hazardous locations?
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What is a characteristic of TENV motors compared to integral horsepower motors?
What is a characteristic of TENV motors compared to integral horsepower motors?
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What happens to the magnetic field phasors at 90 degrees?
What happens to the magnetic field phasors at 90 degrees?
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How is a permanent-split capacitor motor configured?
How is a permanent-split capacitor motor configured?
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What is the impact of the capacitor size in a permanent-split capacitor motor?
What is the impact of the capacitor size in a permanent-split capacitor motor?
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What defines a single phase induction motor?
What defines a single phase induction motor?
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How can the direction of the permanent-split capacitor motor be changed?
How can the direction of the permanent-split capacitor motor be changed?
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What is a major drawback of the permanent-split capacitor motor?
What is a major drawback of the permanent-split capacitor motor?
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What is the maximum horsepower typically applied for permanent-split capacitor motors?
What is the maximum horsepower typically applied for permanent-split capacitor motors?
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What is the effect of dual phasors on a single phase motor?
What is the effect of dual phasors on a single phase motor?
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What is the primary purpose of a totally enclosed non-ventilated (TENV) motor enclosure?
What is the primary purpose of a totally enclosed non-ventilated (TENV) motor enclosure?
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How does a totally enclosed non-ventilated (TENV) motor dissipate heat?
How does a totally enclosed non-ventilated (TENV) motor dissipate heat?
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What type of environments are totally enclosed fan cooled (TEFC) motors suitable for?
What type of environments are totally enclosed fan cooled (TEFC) motors suitable for?
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What feature distinguishes totally enclosed fan cooled (TEFC) motors?
What feature distinguishes totally enclosed fan cooled (TEFC) motors?
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What is the key disadvantage of a totally enclosed non-ventilated (TENV) motor?
What is the key disadvantage of a totally enclosed non-ventilated (TENV) motor?
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What common feature is found in larger horsepower TENV motors?
What common feature is found in larger horsepower TENV motors?
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What mechanism prevents injury in totally enclosed fan cooled (TEFC) motors?
What mechanism prevents injury in totally enclosed fan cooled (TEFC) motors?
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For which type of applications are TENV motors generally used?
For which type of applications are TENV motors generally used?
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Study Notes
Jadeer Learning Manual - Electrical Area 5
- Classification: General Business Use
- This manual covers electrical aspects, specifically for the plant electrical maintenance at an intermediate level within Area 5.
- The document revision is 2024.01.
- Date of issue: 05 Nov 2024
- Next review date: 01 Oct 2027
- Developed by: Marwan Owaidhah (12943) Electrical Trainer and others (Subject Matter Experts)
- Reviewed by: Ali Fallatah (12610), Bandar Al-Mesawi (13107), Ahmed Haresi (33423) Electrical Specialists
- Approved by: Area Owners/Leaders
Electrical Motors
- Rotating electrical machines are divided into two parts: motors (converting electrical energy to mechanical) and generators (vice versa).
- Both types function via the interaction of a magnetic field and a set of windings.
- Different motor types exist (AC and DC).
- Types of AC motors (asynchronous and synchronous) are discussed.
- AC motors are further classified by, single-phase and three-phase.
- AC motors are broadly categorized into single-phase motors and three-phase motors.
- Single-phase motors are often used in home appliances, while three-phase motors find use in industrial settings.
Learning Objectives
- Working principle, construction, and types of AC motors
- AC motors' maintenance and protections
- DC motors' basic, construction, and protections
- Basic principle of motor operated valve (MOV)
- Troubleshooting of AC/DC motors
Table of Contents
- Introduction
- Working principle, construction, and types of AC motors
- Motor name plate description (ANSI, IEEE, IP protection, area/zone classification)
- AC motor protection basics
- Maintenance of AC motors
- Troubleshooting of AC motors
- DC motor basics, construction and operation
- Troubleshooting of DC motors
- Maintenance of DC motors
Motor Introduction
- Rotating electrical machines are typically divided into two parts: Motors and generators.
- Motors convert electrical energy into mechanical energy and generators vice versa.
- Essentially, both mechanisms operate through the interaction of a magnetic field and a set of windings in a mechanism
- Various types of Motors exist, each with inherent characteristics.
Types of Motors
- Synchronous motors
- Induction motors
- Single phase and three phase motors are further types of AC motors.
AC Motors
- Motors are devices that use electrical energy to produce motion.
- AC motors are commonly used in many residential, commercial and industrial applications, such as in pumps, fans, winders, conveyors and mixers.
NEMA/IEC
- The National Electrical Manufacturers Association (NEMA) establishes standards for electrical products, primarily in North America.
- The International Electrotechnical Commission (IEC) develops recommended electrical practices used in various countries.
- IEC and NEMA standards cover motors, and products meeting or exceeding these standards are considered IEC motors.
Force
- Force is a push or pull, often due to electromagnetism, gravity or a combination thereof.
- The net force is the vector sum of all forces acting on an object.
- Forces in the same direction additive.
Torque
- Torque is a rotational force that causes an object to rotate.
- Torque is the product of force and radius (or lever distance).
Inertia
- Mechanical systems follow the law of Inertia.
- Objects at rest tend to stay at rest, whilst moving objects want to stay at the same speed and heading until another force acts upon them.
Power
- Work is accomplished when force creates motion.
- Work is calculated by multiplying force and distance.
- Power is the rate of doing work, often calculated by dividing work by the time taken.
- Horsepower is a unit for power and equals 550 foot-pounds per second.
Electrical Energy
- Voltage across a conductor causes electrons to flow, and this flow of electrons is a movement, leading to work.
- Power measures the work done in a circuit per unit time (1 Amp moving at 1 Volt).
Power Consumed
- Power consumed in a resistor is directly proportional to both the voltage and the current flowing through it.
- The formula to calculate power consumed (Watts) is power equals voltage times current.
Power in AC Circuit
- True power is measured in watts (W) describing how much energy is consumed in an AC circuit.
- Reactive power is calculated by multiplication of voltage and current, measured in VARs.
- Apparent power represents the overall power. Power factor is the ratio of true to apparent power.
Horsepower & Kilowatts
- AC motors in the US are usually rated in horsepower units, while those in Europe are rated in kilowatt units.
- KW = 0.746 x HP (kilowatts = 0.746 x horsepower)
- HP = 1.341 x KW (horsepower = 1.341 x kilowatts)
Three-Phase Power
- Single-phase power uses one voltage source; three-phase power uses three phases—waves off by 120 electric degrees.
- Three-phase is typically used in large-scale industrial operations and less so in domestic settings.
Magnetism
- All magnets exhibit two characteristics: they attract/hold metal objects like iron, and they orient to approximately a north-south direction when free to move.
- Magnetic flux lines emanate from North poles and conclude at South poles.
Electromagnetism
- A flow of current through a conductor creates a magnetic field (surrounding it).
- The field is proportional to the magnitude of the current.
Electromagnets
- Electromagnets are created with coils of conductors through which a current is passed.
- Applying a DC voltage helps create a larger/stronger magnetic field centered within the coil. This is the core.
Changing Polarity
- The polarity of an electromagnet's magnetic field changes in accordance with the direction of current flowing through it.
- In an AC system, the polarity of the magnetic field changes at the same frequency as the AC source.
Induced Voltage
- Applying a magnetic field and moving it near a conductor results in a voltage being induced in the conductor (the induced voltage is proportional to the rate at which magnetic field changes)
Electromagnetic Attraction
- Similar poles oppose each other, whereas dissimilar poles attract each other.
- The movement of the magnetic field induces a voltage and correspondingly, a current is produced.
Asynchronous AC Induction Motors
- AC induction motors are suitable for constant speed operation in various industrial settings.
- The rotor speed (of the motor) differs from the rotating magnetic field speed.
- Induction motors are economical and are easy to maintain, are the most popular types of AC motors used in industry.
Description
- The stator comprises windings which are fixed to the casing.
- The rotor is composed of cylindrical, laminated, and conductive metal bars.
AC Motor Basic Construction and Working Principle
- Rotor (consisting of aluminum or copper bars) is mechanically and electrically connected to the rings.
- The most common rotor design is 'squirrel cage'.
Start
- The most direct method of visualizing this rotation, is to choose a start time when no current is flowing in one part (phase) of the stator.
- If the motor starts, the next event will follow based on the previous state of the phases.
- The field generated in the phases determines the direction of the magnetic field created, which rotates in accordance to frequency of the AC and the number of poles.
Time 1 & Time 2
- The magnetic field has rotated 60 or 120 degrees from the previous state.
- Current flow, as well as the pole orientations (north-south) of the stator and the rotor, change accordingly.
360 Degree Rotation
- The magnetic field has rotated a complete 360 degrees, or 1 revolution in conformity with the specified frequency.
- This process of completing a rotation is repeated 60 times per second in a 60HZ system.
Stator of Induction Motor
- The stator is composed of several thin aluminum or cast iron laminations that comprise a hollow cylinder.
- These slots embed insulation-coated wires, creating electromagnets when current is supplied
Stator Continue
- Three stator coils (2 coils per phase) create a magnetic field with successive opposing poles.
- These windings alternate polarity in accordance with the frequency of the AC supply.
- The coils are wound so that when the current reverses, so too does the polarity of the poles.
Stator Continue (Applied AC)
- The phases A, B, and C are spaced 120 degrees apart.
- The number of poles is determined by how many times each winding coils appears as either a North pole or a South pole in the motor.
- When AC voltage is applied to the stator the windings currents result in north and south poles along the motor axes.
AC Motor Basic Construction and Working Principle
- The rotor is composed of several thin laminations of steel with evenly spaced bars of aluminum or copper.
- The rotor's bars are mechanically/electrically connected by rings, creating a structure much like a "squirrel cage".
Design
- The rotor's slots (where the bars are embedded) are skewed to reduce magnetic humming, noise levels, and harmonics.
- The rotor slots are also not identical in size and shape to one another to prevent rotor locking.
How a rotor works
- The rotor's magnetic field, formed by interactions of the stator's magnetic field, causes the rotor to rotate.
Induction Motor Characteristics
- Starting torque, locked rotor torque, and locked rotor current measurements reflect the nature of motor's interactions under starting condition.
- Induction Motors usually draw greater than 100% of their full load current during start.
Starting Characteristics
- Starting Motor and Locked Rotor Current (LRC) values are functions of the motor's voltage and design.
- Torque increases with increasing rotor speed under load, then generally drops to zero when full synchronous speed is attained.
- Motor torque will vary according to the amount of load applied.
Speed-Torque Curve of an Induction Motor
- Starting torque is also referred to as locked rotor torque.
- Accelerating torque is the point at which torque increases to its maximum.
- Breakdown torque represents the maximum pull out torque available at zero speed.
Full-load torque
- Torque declines as rotational speed increases beyond the breakdown.
- Full load torque is attained slightly below 100% of the synchronous speed.
Horsepower & Kilowatts
- Units of power that are frequently used are kilowatts or horsepower.
- A typical formula to convert horse power to kilowatts and vice versa exists.
Electrical Energy
- Voltage applied to a conductor creates a flow of electrons, resulting in work being performed.
- The rate of this work is power, measured in watts.
Motor Protection
- In industrial electrical systems motors are subject to faults, which lead to potential damage and reduced efficiency.
- Motor failures are principally classified as electrical, mechanical or environmental, safety and other issues.
- Costs associated with motor failure include repair/replacement costs, removal and installation costs.
- Possible causes of motor failure include: Persistent Overload, Normal Deterioration, High Vibration, Poor Lubrication, and High Ambient temperature.
Thermal Stress
- Overheating is a significant contributor to motor failure.
- Thermal stress can lead to failures in major components.
Risks for an Overheated Motor
- Winding insulation degradation and thermal failures directly related to winding operating temperatures.
- Excessive temperatures can lower the remaining life of the insulation, a function that can be described with a curve.
Thermal Protection / Overload Protection
- Motor protection devices include thermal relays and components that monitor the motor temperature and respond to excessive temperatures.
Thermal Limit Curves
- A diagrammatical analysis of motor's operating temperature changes when subjected to different conditions and corresponding time periods, including:
- Hot Running, Cold Running. Cold Locked Rotor, and Hot Locked Rotor overload curves.
- Motor acceleration curves @100 % voltage, and acceleration curves @80 % rated voltage.
Over Voltage Protection
- Overvoltage condition can affect load current and power factor, often leading to higher internal temperatures.
- The overvoltage element should ideally be set 10% above the rated voltage of a motor.
Under Voltage Protection
- Insufficient voltage leads to increased motor current, potential heating and a resulting decrease in performance.
- The under-voltage trip should typically be set to 80-90% of the rated voltage of the motor to effectively prevent potential problems in its performance.
Unbalance Protection
- Unbalanced voltage conditions (in a three-phase system) lead to unequal line voltages.
- These imbalances can produce excessive heating in the motor's stator and rotor.
Ground Fault Protection
- Ground fault is when a current bypasses the load and flows to ground through an external path.
- This can happen due to damaged insulation or a fault current.
Summation Method with Six CTS
- When six CTs are used, the values for each phase might not be equal during start conditions.
- This can sometimes be problematic with a differential protection system and might necessitate setting a slower or more sensitive differential system pick-up to accommodate start-up circumstances.
Biased Differential Protection - Six CTs
- This method allows use of different ratios for system/line and neutral CTs.
- It includes a dual slope characteristic to accommodate faults associated with external or internal faults.
Short Circuit Protection
- Short circuits are a critical operational hazard affecting motor performance resulting in excessive overcurrent faults potentially damaging the motor's internal structure.
- Overcurrent protection systems include protective devices such as fuses, and circuit breakers.
- An overload or starting circumstance may result in extremely high starting currents.
Stator RTD Protection
- Use of RTDs (Resistance Temperature Detectors) allows temperature monitoring of the stator windings.
- Setting RTD parameters at a level that is not higher than the maximum allowed temperature ratings by the insulation standards will increase operational life of the motor.
Additional Protection
- Limit Start Condition to accommodate situations where the motor is already hot.
- Time limit between starts is also possible in accordance to limit the risk of repeated running events.
- Sensor usage and protection to detect failures in bearings
Scheduled Routine Care
- Regular maintenance of a motor is important for operational efficiency and prolonged lifespan.
- Routine inspection and preventative maintenance are ideal for minimizing operational problems.
Cleaning Dirt and Corrosion
- Removing dirt, dust, and corrosion from motor components is critical for heat transfer, and insulation integrity.
Heat, Noise and Vibration
- Noise and/or vibration, often indicate system failures or faults in the motor.
- Motor problems can include misalignment, worn bearings and/or loose parts.
- Excessive heat is a primary indicator that the motor or surrounding system may need maintenance and/or repair.
DC Motor Overview
- DC motors consist of a coil of current carrying wire, and these have a magnetic field with a commutator and brushes.
- Applying power produces a magnetic field causing rotational motion.
- There are four basic types of motors
Advantages
- Simple design, easy to control speed and torque.
Disadvantages
- High maintenance
- Spark in flammable environments.
DC Series Motor
- Primarily designed for high-torque, low-speed operations e.g., cranes, lifts etc.
- Series motors can tolerate high starting currents to generate significant torque, but have poor speed regulation.
DC Shunt Motor
- DC shunt motors deliver relatively constant speed, across a load range, when compared to other motor types.
DC Compound Motor
- A compound motor design is comprised of both the series and shunt windings, offering a favourable trade off in terms of speed and torque response.
Permanent Magnet Motor
- Considered cost-effective, particularly for low horsepower applications.
- They have high starting torque and good speed control characteristics.
- However they are usually limited to 150% of their rated torque due to potential demagnetization concerns.
General Construction
- The different parts, including the frame, stator, commutator, brush assembly, armature, and bearings, of a DC motor are shown.
Principle of Operation
- A visual representation of the mechanisms underlying the function of a DC motor that include voltage across windings and current interactions with the motor's magnetic fields to produce rotational motion
- The roles of commutator and brushes and related processes and interactions are detailed in this section of the manual.
Troubleshooting Electrical Faults in DC Motors
- A systematic procedure for identifying and rectifying electrical issues in DC motors is suggested.
- The procedure prioritizes checking easily detectable faults like broken wires, or loose connections first, and followed by more in-depth diagnosis as necessary.
Short Circuit Protection
- Explores when a motor experiences short circuits due to excessive current surge and its implications in relation to potential motor malfunction, or damage.
- Details the important criteria and conditions to be checked.
Stator RTD Protection
- Uses RTDs for stator winding temperature monitoring.
- Provides an operational limit for the thermal behaviour of the stator and protects it from exceeding its maximum permitted temperature rating.
Additional Protection
- Describes various supplementary protection methods for motors to prevent premature operational failure, including time limit between repetitions of the on/off action
- Includes different methods of motor protection against bearing and winding failures.
Maintenance Factors
- Describes the considerations that might affect the frequency of motor maintenance, such as ambient temperature, starting/stopping frequency, and parts that are problematic.
- Routine inspections and maintenance involving the components of the motor are detailed, and are generally undertaken without disconnecting from the load.
Cleaning Dirt and Corrosion
- Cleaning motor parts is a good preventative maintenance practice for preserving the functionality of a motor.
- Various actions to remove dirt from the casing, internal sections and other parts will help improve the operational and longevity of the motor.
Lubrication
- Lubrication of the bearings and other moving parts is essential to maintain smooth operation, and prevent premature wear on components.
- The type of lubricant used is often dependent on the motor type and the operational environment.
Re-Greasing
- Re-greasing is a procedure, suitable to be carried out while the motor is operating to allow new grease to be evenly distributed throughout the motor's grease ports.
Workplace Safety
- Highlighting safety precautions during maintenance procedures on motor components is emphasized.
- Includes the important need for isolated motors before any physical inspections.
Motor Trouble Shooting Chart
- Summarizes fault causes, symptoms, and recommended remedies for various operational issues in a clearly presented table format.
Motor Problems
Describes potential problems (including motor stall, problems related to low or high voltage, and more) in terms of their root causes and operational symptoms, together with a methodical approach for a solution.
Additional Protection
- Detail supplementary protective measures for motors in various fault conditions. Specific considerations that are usually considered are: start inhibit, start/hour limit, bearing RTD protection and the acceleration trip mechanisms.
Power & Control Cables
- The roles and general information about power and control cables are detailed, including their construction characteristics.
- The various cable types include single-core cables and multi-core cables, alongside their respective characteristics including their insulation types and material properties.
Learning Objectives
- Understanding basic power and control cables.
Basic Knowledge of Electrical Power Cables
- Details the essential features of electrical power cables.
- The core components that comprise the structure of the cable, alongside the various materials often used in constructions, are presented in this section, such as conductors, insulations and the different types of insulation material available.
Basic Electrical Power Cables Safety Tips
- Safety procedures during the handling and inspection of live electrical cables are detailed to avoid electrocution and other injuries.
Secondary Selective System
- Details the steps, and actions required to switch on a secondary power source to the primary source of electrical power, when the normal or primary source is disconnected, or if there is an abnormal fault condition.
PLC (Programmable Logic Controller)
- A computer-like industrial control system is comprehensively explained.
- The various components, and their functions, in the construction/physical structure of a PLC, including input/output, memory and processor components are explained.
Ladder Logic Programming
- A visual programming language useful in instructing PLCs is elaborated.
- Details the use and importance of ladder logic to perform simple and complex operations.
PLC Scan
- A description of how a PLC executes its programming in a repetitive scanning procedure.
- The time required to perform the scan depends on various relevant factors
Input and Output Devices, Sensors, and Actuators
- Clarifies how input and output devices are classified in a PLC system, and the function of each.
- Provides examples to show how they are helpful in an industrial setting to control and monitor input operations.
###Analog Inputs and Outputs
- Expands on the discrete devices to include how continuous input/output devices (analog) operate in conjunction with PLCs.
- Expounds how analog devices convert physical conditions into electrical signals.
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