Electricity Theory PDF

ELECTRICITY THEORY History of Electricity Electrical Theory Units of Electricity Electrical Circuits...

ELECTRICITY THEORY History of Electricity Electrical Theory Units of Electricity Electrical Circuits Magnetism and Electrical Current Direct and Alternating Current Transformers, Inductors, Capacitors, and Power Factor Cost of Electrical Power and Energy  ELECTROCUTION The lowest level at which people can perceive electrical current is about 0.001 A (1 milliamp). At currents higher than 0.05 A (50 milliamps), heat produced by electrical current is enough to burn human skin and tissue. At levels of current flow exceeding 0.1 A (100 milliamps), the heart stops. A person may survive an electrocution if his or her heart can be started again. ELECTRICAL THEORY Classical Theory: Modern Theory: Flow Of Electrons Flow of Charged Particles  Conductors, insulators, and semiconductors carries electrical current without CONDUCTORS providing too much resistance to current flow materials that resist the flow of INSULATORS electricity materials that are neither good SEMI-CONDUCTORS conductors nor good insulators good conductors at high temperature and insulators at low temperature PRODUCING CURRENT FLOW PIEZO ELECTRICICTY THERMO ELECTRICITY STATIC PRODUCING CURRENT FLOW MAGNETO ELECTRICITY PHOTO ELECTRICITY ELECTRO CHEMISTRY  UNITS OF ELECTRICITY VOLTAGE AMPERAGE RESISTANCE Electromotive The rate of A measure of force that current flow in the opposition drives the a closed to current current flow electrical flow in an Expressed in system. electrical Volt (V). Expressed in circuit. Ampere (A). Expressed in Ohm (Ω). UNITS OF ELECTRICITY OHM’S LAW POWER ENERGY Electric current The rate at The rate at is proportional which work is which power is to voltage and accomplished. being inversely 𝑷 = 𝑬𝑰, Watts consumed proportional to over a resistance. specified 𝑬 = 𝑰𝑹, Volts period of time. 𝑸 = 𝑷𝒕, Wh BASIC ELECTRICAL CIRCUITS A continuous path along which an electric current can flow. Open Circuit Closed Circuit Short Circuit CIRCUIT CONFIGURATIONS SERIES CIRCUIT the current passes through each component in the circuit without branching out 𝒏 𝑰𝑻𝒐𝒕𝒂𝒍 = ෍ 𝑰𝒊 𝒊=𝟏 𝒏 𝑬𝑻𝒐𝒕𝒂𝒍 = ෍ 𝑬𝒊 𝒊=𝟏 𝒏 𝑹𝑻𝒐𝒕𝒂𝒍 = ෍ 𝑹𝒊 𝒊=𝟏 CIRCUIT CONFIGURATIONS PARALLEL CIRCUIT the current branches off to individual components in the circuit. 𝒏 𝑰𝑻𝒐𝒕𝒂𝒍 = ෍ 𝑰𝒊 𝒊=𝟏 𝑬𝑻𝒐𝒕𝒂𝒍 = 𝑬𝟏 = 𝑬𝟐 = ⋯ 𝑬𝑵 𝟏 𝑹𝑻𝒐𝒕𝒂𝒍 = 𝒏 𝟏 σ𝒊=𝟏 𝑹𝒊 MAGNETISM AND ELECTRICAL CURRENT DIRECT AND ALTERNATING CURRENTS DIRECT CURRENT ALTERNATING CURRENT (DC) (AC) Current flow in one Current flow is in direction (negative to constantly changing positive) in an electrical directions. circuit.  Alternating current power SINGLE-PHASE THREE-PHASE (1ɸ) (3ɸ) Peaks in voltage at 90⁰ and 270⁰, By the time a complete cycle of 360⁰ has with a complete cycle at 360⁰ completed, three phases of power have each peaked in voltage twice. Power is not delivered at a constant A steady stream of power is delivered at a rate. constant rate, making it possible to carry There is one neutral wire and one more load. power wire with current flowing There are three power wires, each 120⁰ out of phase with each other. between them. All three phases of power have entered the Change flow in current and voltage cycle by 120⁰. about 60 times per second  TRANSFORMING VOLTAGE AND CURRENT TRANSFORMERS An electrical device that transfers an AC and voltage from one circuit to another using induction phenomenon Used in a circuit to change voltage, current, phase, and other electrical characteristics. IMPEDANCES INDUCTOR CAPACITORS Coil of wires that creates Composed of metal plates EMF separated by air or dielectric Created as current flows material such as paper, through coils or windings ceramic, or mica found in motors, Store electrical energy in an transformers, and light electrostatic field and release fixture ballasts. it later 3 COMPONENTS OF AC POWER APPARENT REAL POWER REACTIVE POWER POWER the “working generates the the “power power” that magnetic field available to use performs useful required for the “total” effort in a circuit inductive power required (e.g., creating devices to by an inductive heat, light, and operate device motion) it is expressed in expressed in expressed in units called volt- volt-amperes watts (W) or amps-reactive (VA) or kilovolt- kilowatts (kW) (VAR) or ampere (kVA) kilovolt-amperes reactive (kVAR) POWER FACTOR The power factor (PF or cosϕ) The power factor measures how effectively the total delivered power is being used. 𝑹𝒆𝒂𝒍 𝑷𝒐𝒘𝒆𝒓 𝑷𝑭 = ( ) 𝑨𝒑𝒑𝒂𝒓𝒆𝒏𝒕 𝑷𝒐𝒘𝒆𝒓 PF = watts/(volt. amps) = W/VA The power factor is a number between 0 and 1 (frequently expressed as a percentage). POWER FACTOR A PF is less than 1.0 means the circuit’s wiring has to carry more current than would be necessary to deliver the same amount of real power. A higher PF at the motor means more of the supplied energy will be transferred into useable work by the electrical system. A low PF means the current flowing through electrical system components is higher than necessary to do the required work—an inefficient use of power. A low PF is caused by an electrical circuit having a greater amount of inductive load than capacitive load. Pf correction The main advantages of the PF correction are as follows: A high PF reduces the load currents, resulting in a Power companies typically considerable saving in hardware impose low power factor costs (i.e., conductors, penalties, so by correcting the switchgear, substation PF, this penalty can be avoided. transformers, and so on). The electrical load on the power company is reduced, which allows the power company to supply the surplus power to other consumers without increasing its generation capacity.