| AC |
Alternating current. Current that reverses direction at regularly recurring intervals of time. In the U.S., AC alternates 60 times per second, or 60 hertz. |
| alternating current |
AC. Current that reverses direction at regularly recurring intervals of time. In the U.S., AC alternates 60 times per second, or 60 hertz. |
| armature |
A device found in generators that has many separate coils wound around it. When the armature rotates in the generator, it creates a magnetic field and produces current. |
| bridge rectifier |
A type of full-wave rectifier with four diodes. A bridge rectifier converts both the positive and negative cycles of AC voltage to DC. |
| brushes |
Devices that conduct electricity between non-moving wires and moving parts that are moving. Brushes are used in generators to pass current from wires to rotors. |
| brushless exciter |
An AC generator design that mounts a small DC generator on its shaft. When rotated, brushless exciters provide the direct current to excite the magnetic field. |
| center tap |
The point where all three windings in a wye connection connect to one another. Center taps divide secondary windings and alter a transformer's turn ratio. |
| circuit breakers |
A safety device that detects excess current in a circuit to prevent overheating. Circuit breakers often contain a bimetallic strip that bends and trips a switch that opens a circuit. |
| closed loop |
An electrical cycle in which the amount of output is directly proportional to the amount of input. A closed loop is formed in delta connections by connecting the starting coil of one phase to the end of the next. |
| coil |
Loops of conducting wire around a magnetic core. Coils are used to create magnetic fields when current passes through them. |
| conductor |
A material or element that allows free movement of electrons and, therefore, allows the easy flow of electricity. Most conductors are metals. |
| constant |
A value, number, or variable that does not change. In frequency, the number of poles is a constant. |
| copper loss |
A power loss due to current flowing through wire. Copper loss is proportional to the resistance of the wire and the square of the current. |
| copper loss |
A power loss due to current flowing through wire. Excessive copper loss can lead wires to overheat and burn through the insulator. |
| core |
A component of a transformer. A core that is iron or steel provides a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings in the transformer. |
| current |
The flow of electricity. Current is measured in amperes (A). |
| cycles |
The course of travel of a sine wave. During one cycle, a sine wave travels from its peak positive voltage to 180°, then to its peak negative voltage and back to 0. |
| DC |
Direct current. Current that flows in one direction. DC is expensive and inefficient, making AC the better choice for power. |
| delta |
A connection of three components where a triangular series circuit is formed. Delta connections are used in three-phase power systems. |
| delta/delta |
A transformer with both the primary and the secondary connected as a delta. The delta/delta is a type of three-phase transformer. |
| delta/wye |
A transformer with the primary connected as a delta and the secondary connected as a wye. The delta/wye is a type of three-phase transformer. |
| diodes |
A two-terminal semiconductor device that allows current to flow through it in only one direction. Diodes have low resistance in one direction and a high resistance in the other direction. |
| direct current |
DC. Current that flows in one direction. DC is expensive and inefficient, making AC the better choice for power. |
| distribution substation |
A bank of step down transformers near the end users. The distribution substation converts voltage closer to the required usable levels. |
| distribution system |
A circuit of users linked to a generating station and substations. Distribution systems are typically arranged as either radial or interconnected systems. |
| efficient |
Having an energy output that is close to the total energy supplied. An efficient system has very little resistance loss. |
| electric shock |
The flow of electricity through the body. Electric shock can be fatal. |
| electrical energy |
A form of power created by the movement of electrons. Mechanical energy is converted into electrical energy by generators. |
| electromagnets |
A magnet that gains an attractive force only when current passes through it. Electromagnets are extremely powerful. |
| electrons |
A negatively charged particle that orbits the nucleus of an atom. Electrons flowing between albums causes electricity. |
| enclosure |
A physical barrier used as protection. An enclosure provides mechanical or electrical protection to components used in a system. |
| excitation current |
The DC required to magnetize a piece of metal. Excitation current creates the magnetic field in a revolving field generator. |
| exciter |
An AC generator that is used with another generator or motor to generate a magnetic field. Exciters provide additional current through electromagnets to create more lines of flux. |
| filtered |
The state caused by a rectifier in which the ripple effect has been removed. Filtered AC is kept as close to its peak value as possible. |
| filters |
A device that diminishes the ripple present in rectified AC. Filters keep rectified AC current (DC) as close to peak value as possible. |
| flux leakage |
Flux lines that are lost to the surrounding air. Flux leakage occurs with flux lines that do not follow the core. |
| frequency |
A measurement of the number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz). |
| full capacity |
The maximum amount of electricity that can flow without damaging equipment. Generators are run at full capacity. |
| full-wave rectifier |
A rectifier that flattens both positive and negative halves of the incoming AC to pulsating DC. The full-wave rectifier is used more often than other designs because it is more efficient than a half-wave rectifier. |
| fuses |
A safety device that detects excess current in a circuit to prevent overheating. Fuses often have a component that melts and opens the circuit. |
| generating station |
A building where a utility company houses large linked AC generators. Generating stations can create large amounts of power for widespread use. |
| generators |
A device that converts mechanical energy into electrical energy. Generators use the process of electromagnetic induction to convert energy. |
| generators |
Devices that convert mechanical energy into electrical energy. Generators that convert energy using magnetic induction. |
| half-wave rectifier |
A rectifier that flattens only the positive or negative half of the incoming AC to pulsating DC. The half-wave rectifier is less efficient and needs more filtering than a full-wave rectifier. |
| hertz |
Hz. A unit of frequency equal to one cycle per second. Hertz are used to express AC cycles. |
| hollow core |
A square-shaped laminated iron transformer core with an open center. In hollow core transformers, the windings surround the sides of the core. |
| H-type core |
A type of transformer core that surrounds the windings on four sides. The construction of the H-type core helps to lessen flux leakage. |
| in-phase |
The condition in which generators rotate so they have corresponding points that cross the same places at the same time. When generators are in-phase, they may be considered synchronized. |
| insulator |
A material that does not readily conduct electricity. Insulators can be constructed from rubber and glass. |
| interconnected systems |
A distribution system with multiple available power sources that can loop throughout the network. In interconnected systems, if one source goes down, a different source can be activated to maintain service. |
| iron |
A silver-white, metallic element that is highly magnetic. Pole pieces are often constructed of iron. |
| kilovolt-amps |
kVA. Units used to rate transformer and generator strength. A kilovolt amp is one thousand volts. |
| kilovolts |
kV. A unit of measurement of potential energy in a circuit at a specific point. A kilovolt is equal to one thousand volts. |
| kVA |
Kilovolt-amps. Units used to rate transformer and generator strength. One kVA is one thousand volts. |
| laminated |
Sealed together in multiple layers of thin sheets to construct the core of a transformer. Laminating helps to reduce resistance losses. |
| lines of flux |
Imaginary lines of force that surround a magnet. Lines of flux form a magnetic field. |
| load |
A component in a circuit that converts electrical energy into light, heat, or mechanical motion. Examples of loads are motors, appliances, and light bulbs. |
| load |
A component in a circuit that converts electricity into light, heat, or mechanical motion. Examples of loads include light bulbs, appliances, or machines. |
| lockout/tagout |
A method of protecting employees from accidental machine startup through proper locking and labeling of machines. Lockout/tagout is an essential practice for safe repair of machines. |
| magnetic field |
The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion. |
| magnetic flux |
A measure of the strength of the field formed around a magnet. Magnetic flux is expressed in webers (Wb). |
| magnetic induction |
The process in which a material becomes magnetized in a magnetic field. Magnetic induction commonly takes place within metals. |
| mechanical energy |
A combination of kintetic and potential energy resulting from the force of gravity or movement of a machine component. Mechanical energy is created by generators using magnetic flux. |
| mutual induction |
The ability of one coil to induce a voltage into another coil. Mutual induction is used in transformers to step up or step down voltage. |
| network system |
A distribution system where multiple power sources are connected to each user to guarantee uninterrupted power. Network systems are expensive, so they are only used when constant power is vital. |
| north pole |
The negative side of a magnet. The differences between the north pole and south pole of a magnet create lines of flux. |
| open delta |
A transformer connection that does not complete the triangle, using only two of the three sides. An open delta is used when full power is not needed. |
| output |
The generation of a result from a particular process. Electrical output is the voltage or current produced. |
| output voltage |
The amount of electrical pressure or potential that is generated from a process or machine. In a generator, output voltage is generated in proportion to the turns that exist in the armature conducting wire. |
| parallel circuits |
An electrical system that has multiple paths for the flow of electricity. Parallel circuits can be formed by linking generators together. |
| peak negative voltage |
The lowest negative point on a wave. The peak negative voltage indicates the maximum negative voltage of the wave. |
| peak positive voltage |
The highest positive point on a wave. Peak positive voltage indicates the maximum positive voltage of the wave. |
| personal protective equipment |
PPE. Any of the various articles of clothing or safeguarding devices that workers wear to ensure their safety. Common personal protective equipment worn during electrical work includes safety glasses, rubber-soled footwear, and gloves. |
| phase |
A measurement of the number of voltages in one cycle. Most AC generators are three-phase. |
| polarity |
Having a positive or negative charge. Polarity determines the direction in which current flows. |
| pole pieces |
Magnetic devices mounted on the inside of a generator armature. Pole pieces form electromagnets that create lines of flux when connected to windings. |
| poles |
Opposite ends of an axis. Poles also refer to the opposite ends of a magnet. |
| poles |
Two oppositely charged ends of a magnet. The relationship between the poles causes magnetic flux. |
| power distribution |
The circuit that travels from generating stations to end users to provide electrical power. Power distribution is expressed in hertz. |
| power supply |
A device that converts AC to DC. A power supply contains a rectifier to convert current. |
| primary winding |
The first winding that current passes through in a transformer. The primary winding contains multiple thin wires that are wrapped into a coil. |
| prime mover |
A device that supplies the turning force necessary to turn the shaft of a generator or alternator. Examples of prime movers include steam turbines and diesel engines for AC generators. |
| radial system |
A distribution system with only one power source. In a radial system, if the power source goes out, power is lost to the entire circuit. |
| rectifiers |
A device used in an electrical circuit to convert AC to DC. Rectifiers use diodes to prevent current from flowing in more than one direction. |
| rectify |
When a diode changes AC. When AC is rectified, it is converted to DC. |
| regulation |
A system of control. Voltage requires regulation to stay at a constant level. |
| reserve generator |
A generator that is used when the primary generator or generators cannot generate enough voltage to meet demand. Reserve generators are activated when more power is needed. |
| ripple |
Current that is not stable and characterized by a varying value. AC output constantly ripples, unlike the constant values of DC. |
| rotating armature generators |
A device that generates alternating current by rotating an armature through a stationary magnetic field. Rotating armature generators use slip rings and brushes to conduct current from the armature to the load being powered. |
| rotating field coil |
An electromagnet that rotates to produce a magnetic field. In a rotating field generator, rotating field coils turn instead of the armature. |
| rotating field generators |
A device that generates alternating current through a rotating magnetic field and a stationary armature. Rotating field generators are the most commonly used type of AC generator. |
| rotor |
A device found in alternators that contains many windings. When a rotor rotates inside an alternator, it creates a magnetic field, which produces alternating current. |
| rotor |
A device found in generators that rotates and creates a magnetic field that produces AC. Rotors contain wire windings. |
| secondary winding |
The second winding that current passes through in a transformer. The secondary winding contains fewer, but thicker wires that are wrapped into a coil. |
| shell core |
A type of core that surrounds the windings to create a strong magnetic coupling. Shell cores are shaped like the letter E. |
| short circuit |
A circuit where current takes a shorter, unintended path between two conductors. Short circuits can cause fires, but fuses and circuit breakers prevent them. |
| sine wave |
The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines. |
| single-phase |
AC voltage that has only one sine wave. Single-phase is a continuous, single, alternating current cycle. |
| slip rings |
A conductive device attached to the end of a generator rotor. Slip rings conduct current to brushes in generators. |
| south pole |
The positive side of a magnet. The differences between the south pole and north pole of a magnet create lines of flux. |
| spike |
A sharp, sudden increase in voltage in a circuit that can damage equipment. Spikes are caused by malfunctions or changing load conditions. |
| stator |
The stationary windings of a motor. Stators are usually found inside of an AC motor. |
| step down |
In electricity, a phrase used to describe voltage adjustment. To step down voltage means to decrease voltage. |
| step up |
In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage. |
| synchronized |
Meeting the necessary conditions to operate in exact unison. Generators are considered synchronized if they have identical voltage, frequency, and phase rotation. |
| terminals |
A connecting point in a circuit to which a wire can be attached. Terminals help to connect electrical components to one another. |
| three-phase |
A continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large scale distribution systems. |
| toroid core |
A ring-shaped electromagnetic transformer core. The toroid core is very efficient because it minimizes flux leakage. |
| transformer |
A device that uses electromagnetic induction to transfer electrical energy from one circuit to another without changing its frequency. A transformer is most often used to change line voltage. |
| transformer substation |
A bank of step up transformers near the generating station. Transformer substations increase voltage as high as 800kV for widespread distribution. |
| transformers |
A device that transfers electrical energy from one circuit to another, without changing the frequency, using electromagnetic induction. A transformer is most often used to change the line voltage. |
| turbine |
A machine that uses the motion or energy of moving water or wind to produce movement in paddles, buckets, or other devices arranged in a circle. Turbines convert this mechanical motion to electricity. |
| turns ratio |
A comparison of the number of turns in the primary versus the number of turns in the secondary windings. Based on the turns ratio, transformers step voltage up or down. |
| voltage |
A measure of electrical pressure or potential. Voltage is measured in volts (V). |
| windings |
The conducting coils that are wound around the armature in which voltage is induced if moved within a magnetic field. Windings are also used to transfer voltage in transformers. |
| wire resistance |
The opposition to current flow in a conductor. Constant wire resistance is a benefit of the usage of alternating current. |
| wye |
A connection of three components where one end of each component is connected at a common point. Wye connections are used in three-phase power systems. |
| wye/delta |
A transformer with the primary connected as a wye and the secondary connected as a delta. The wye/delta is a type of three-phase transformer. |
| wye/wye |
A transformer with both the primary and the secondary connected as a wye. The wye/wye is a type of three-phase transformer. |