Elecrical Transformer Vocabulary

branch circuit

The part of a distribution system consisting of circuit conductors, between the final overcurrent protection and the outlet or load attached.

busbar

Thick, rigid strips or bars of copper that serve as a common connection between several circuits. Busbars are usually used near the switchboard and can be enclosed in busways.

busway

The part of a distribution system consisting of metal enclosed busbars. Busways come in premade sections that can be fitted to any shape needed.

center tap

The point where all three windings are connected to each other in a wye connection. For delta connections, one of the lines must be tapped to produce a neutral.

core

A component of a transformer. The iron or steel core provides a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings.

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.

delta/wye

A transformer with the primary connected as a delta and the secondary connected as a wye.

enclosure

A physical barrier designed to provide mechanical or electrical protection for components used in a system.

feeder

A circuit conductor between the power supply source and a final branch circuit overcurrent device.

grounding conductor

A conductor used to connect equipment in a wiring system to ground.

interconnected system

A distribution system with multiple available power sources that can loop throughout the network. If one source goes down, a different source can be activated to maintain service.

kilovolt-amp

A unit used to rate transformer and generator strength. A kilovolt is a thousand volts.

laminated

Sealed together in multiple layers of thin sheets to construct the core for a transformer. Lamination helps reduce resistance losses.

line voltage

The voltage present between any two of the conductors in a three-phase system. It is 1.732 times higher than phase voltage in a wye connection.

local power distribution system

The part of a distribution system located within a building. Local distribution systems are the responsibility of shop electricians and maintenance workers and fall under NEC rules.

main disconnect switch

A heavy, spring-loaded switch on a factory switchboard that can cut off power to the entire building. Switchboards with more than six switches or breakers are required by the NEC to have a main disconnect.

motor control center

A modular assembly specifically designed to plug in motor control units. Motor control centers are supplied by a common bus, usually straight from the switchboard.

mutual induction

The ability of one coil to induce a voltage into another coil. This principle is used in transformers to step up or step down voltage.

NEC

The standard for minimum safe electrical installations. The National Electrical Code is adopted in some form as law in all 50 states.

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.

overcurrent

Excess current that may result from overload, short circuit, or ground fault. Devices like fuses and circuit breakers protect against overcurrent.

panelboard

A single panel distribution cabinet or wall cutout box that holds automatic overcurrent protection devices for lighting, heat, or power circuits.

phase symbol

(Φ) The Greek letter Phi, used to represent phases, such as in a 3Φ4W system.

phase voltage

The voltage between any one conductor and ground.

plug-in busway

A type of feeder busway with electrical control that allows loads to be added along the bus structure.

primary winding

Turns of wire on a transformer core, used to transfer voltage from the input to the core.

radial system

A distribution system with only one power source. If that source goes out, power is lost to the entire circuit.

secondary winding

Turns of wire on a transformer core, used to transfer voltage from the core to the outside load.

single-phase

A continuous single alternating current cycle.

step up

In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.

substation

Any grouping of switchgear and transformers located near a source or user. Substations are used to alter voltage levels and provide a service point of electrical control.

switchboard

A freestanding assembly of panels with metering equipment, overcurrent and other protection devices. Switchboards take a large block of power from a substation and break it down into smaller blocks for use within a building.

switchgear

A combination of disconnect switches and breakers used to isolate equipment in substations.

tap

A wire connected to the midpoint of a transformer secondary winding. This allows the transformer to use different turns ratios.

terminal

A connecting point in a circuit where a wire is attached to create an electrical connection.

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.

three-phase power

The most common form of AC power for distribution. Three-phase power has three overlapping AC cycles offset by 120 degrees.

transformer

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.

turns ratio

A comparison of the number of turns in the primary versus the number of turns in the secondary of a transformer.

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.

wye/wye

A transformer with both the primary and the secondary connected as a wye.