Glossary of Power Generation and Delivery Terms

ALTERNATING CURRENT. A Current which alternates regularly in direction. Refers to a periodic current with successive half waves of the same shape and area.

ARMATURE. A cylindrical, laminated iron structure mounted on a drive shaft. It contains the armature winding.

ARMATURE WINDING. Wiring embedded in slots on the surface of the armature, Voltage is induced in this winding on a generator.

AUTOTRANSFORMER. A transformer in which a part of the winding is common to both the primary and secondary circuits.

BRUSH POLARITY. Used to distinguish between the electrical polarity of the brushes and the magnetic polarity of the field poles.

BUCK OR BOOST TRANSFORMERS. Tranfomers used to boost (increase) a voltage or to buck (lower) it. These are small amounts of change.

BUS WAY. A system of enclosed power transmission that's current and voltage rated.

CIRCUIT BREAKER. A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself when properly applied within its rating.

COMMUTATING POLES. Interpoles, energized by windings placed in series with the load circuit of a DC motor or generator.

COMMUTATOR. Consists of a series of copper segments which are insulated from one another and the mounting shaft; used on dc motors and generators.

COMPOUND-WOUND GENERATOR. A dc generator with a shunt and series, double field winding.

CONDUIT PLAN. A diagram of all external wiring between isolated panels and electrical equipment.

CONSTANT-CURRENT TRANSFORMERS. Used for series street lighting where the cur rent must be held constant with a varying voltage.

CORE-TYPE TRANSFORMER. The primary is wound on one leg of the transformer iron and the secondary is wound on the other leg.

COUNTER EMF. An induced voltage developed in a dc motor while rotating. The direction of the induced voltage is opposite to that of the applied voltage.

CUMULATIVE COMPOUND-WOUND GENERATOR OR MOTOR. A series winding is connected to aid the shunt winding.

CURRENT. The rate of flow of electrons which is measured in amperes. CURRENT FLOW. The flow of electrons.

DELTA CONNECTION. A circuit formed by connecting three electrical devices in series to form a closed loop. Used in three-phase connections.

DIFFERENTIAL COMPOUND-WOUND GENERATOR. A series winding is connected to oppose the shunt winding.

DIODE. A two-element device that permits current to flow through it in only one direction.

DIRECT CURRENT (dc). Current that does not reverse its direction of flow. It is a continuous nonvarying current in one direction.

DISCONNECTING SWITCH. A switch which is intended to open a circuit only after the load has been thrown off by some other means, not intended to be opened under load.

DISTRIBUTION TRANSFORMER. Usually oil filled and mounted on poles, in vaults, or in manholes.

DOUBLE-WOUND TRANSFORMER. Has a primary and a secondary winding. These two windings are independently isolated and insulated from each other.

EDDY CURRENT. Current induced into the core of a magnetic device. Causes part of the iron core losses, in the form of heat.

EFFICIENCY. The efficiency of all machinery is the ratio of the output to the input. output

= efficiency input

FEEDER. The circuit conductor between the service equipment or the switchboard of an isolated plant and the branch circuit overcurrent device.

FLUX. Magnetic field; lines of force around a magnet.

FUSE. An overcurrent protective device with a circuit opening fusible part that's heated and severed by the passage of overcurrent through it.

GENERATOR. Machine that changes mechanical energy into electrical energy. It furnishes electrical energy only when driven at a definite speed by some form of prime mover.

GROUNDED. Connected to earth or to some conducting body that serves in place of earth.

HERTZ. The measurement of the number of cycles of an alternating current or voltage completed in one second.

HYSTERESIS. Part of iron core losses.

IDENTIFIED CONDUCTOR (NEUTRAL). A grounded conductor in an electrical system, identified with the code color white.

INDUCED CURRENT. Current produced in a conductor by the cutting action of a magnetic field.

INDUCED VOLTAGE. Voltage created in a conductor when the conductor interacts with a magnetic field.

INDUCTION. Induced voltage is always in such a direction as to oppose the force producing it. INSTRUMENT TRANSFORMERS. Used for metering and control of electrical energy, such

as potential and current transformers.

INSULATOR. Material with a very high resistance which is used to electrically isolate two conductive surfaces.

ISOLATING TRANSFORMER. A transformer in which the secondary winding is electrically isolated from the primary winding.

LENZ’S LAW. A voltage is induced in a coil whenever the coil circuit's opened or closed.

MOTORIZING. A generator armature rotates as a motor.

NEC. National Electrical Code.

OPEN DELTA. Two transformers connected in a “V” supplying a three-phase system.

PARALLEL CIRCUIT. A circuit that has more than one path for current flow.

PERMEABILITY. The ease with which a material will conduct magnetic lines of force.

POLARITY. Characteristic (negative or positive) of a charge. The characteristic of a device that exhibits opposite quantities, such as positive and negative, within itself.

POLE. The north or south magnetic end of a magnet; a terminal of a switch; one set of contacts for one circuit of main power.

POLYPHASE. An electrical system with the proper combination of two or more single-phase systems.

POLYPHASE ALTERNATOR. A polyphase synchronous alternating current generator, as distinguished from a single-phase alternator.

POWER FACTOR. The ratio of true power to apparent power. A power factor of 100%, is the best electrical system.

RATING. The rating of a switch or circuit breaker includes (1) the maximum current and volt age of the circuit on which it's intended to operate, (2) the normal frequency of the current; and (3) the interrupting tolerance of the device.

RECTIFIER. A device that converts alternating current (ac) into direct current (dc).

REGULATION. Voltage at the terminals of a generator or transformer, for different values of the load current; usually expressed as a percentage.

REMOTE CONTROL. Controls the function initiation or change of an electrical device from some remote place or location.

RESIDUAL FLUX. A small amount of magnetic field.

RHEOSTAT. A resistor that can be adjusted to vary its resistance without opening the circuit in which it may be connected.

SEMICONDUCTOR. Materials which are neither good conductors nor good insulators. Certain combinations of these materials allow current to flow in one direction but not in the opposite direction.

SEPARATELY-EXCITED FIELD. The electrical power required by the field circuit of a dc generator may be supplied from a separate or outside dc supply.

SERIES FIELD. In a dc motor, has comparatively few turns of wire of a size that will permit it to carry the full load current of the motor.

SERIES WINDING. Generator winding connected in series with the armature and load, carries full load.

SHELL-TYPE TRANSFORMER (Double Window). The primary and secondary coils are wound on the center iron core leg.

SHIELDED-WINDING TRANSFORMER. Designed with a metallic shield between the primary and secondary windings; provides a safety factor by grounding.

SHORT AND GROUND. A flexible cable with clamps on both ends. It is used to ground and short high lines to prevent electrical shock to workmen.

SHUNT. To connect in parallel; to divert or be diverted by a shunt.

SHUNT GENERATOR. Dc generator with its field connected in parallel with the armature and load.

SILICON-CONTROLLED RECTIFIER (SCR). A four-layer semiconductor device that's a rectifier. It must be triggered by a pulse applied to the gate before it will conduct electricity.

SINGLE-PHASE. A term characterizing a circuit energized by a single alternating emf. Such a circuit's usually supplied through two wires.

SOLID STATE. As used in electrical-electronic circuits, refers to the use of solid materials as opposed to gases, as in an electron tube. It usually refers to equipment using semiconductors.

SPEED REGULATION. Refers to the changes in speed produced by changes within the motor due to a load applied to the shaft.

STEP-DOWN TRANSFORMER. With reference to the primary winding the secondary volt age is lower.

STEP-UP TRANSFORMER. The secondary voltage is higher than the primary voltage.

THREE PHASE. A term applied to three alternating currents or voltages of the same frequency, type of wave, and amplitude. The currents and /or voltages are one-third of a cycle (120 electrical time degrees) apart.

THREE-PHASE SYSTEM. Electrical energy originates from an alternator which has three main windings placed 120 degrees apart. Three wires are used to transmit the energy.

TORQUE. The rotating force of a motor shaft produced by the interaction of the magnetic fields of the armature and the field poles.

TRANSFORMER. An electromagnetic device that converts voltages for use in power trans mission and operation of control devices.

TRANSFORMER BANK. When two or three transformers are used to step down or step up voltage on a three-phase system.

TRANSFORMER PRIMARY TAPS. Alternative terminals which can be connected to more closely match the supply, primary voltage.

TRANSFORMER PRIMARY WINDING. The coil that receives the energy. TRANSFORMER SECONDARY WINDING. The coil that discharges the energy at a trans formed or changed voltage, up or down.

UNDERCOMPOUNDING. A small number of series turns on a compound dc generator that produces a reduced voltage at full load.

VOLTAGE CONTROL. Intentional changes in the terminal voltage made by manual or automatic regulating equipment, such as a field rheostat.

WELDING TRANSFORMERS. Provide very low voltages and high current to arc welding electrodes.

WIRING DIAGRAM. Locates the wiring on a control panel in relationship to the actual location of the equipment and terminals, specific lines and symbols represent components and wiring.

WYE CONNECTION (Star). A connection of three components made in such a manner that one end of each component is connected. This connection generally connects devices to a three-phase power system.