POWER AND DISTRIBUTION TRANSFORMER TERMS DEFINITION 1

POWER AND DISTRIBUTION TRANSFORMER TERMS DEFINITION 1

accessories:Devices that perform a secondary or minor duty as an adjunct or refinement to the primary or major duty of a unit of equipment.

alternating current:A periodic current the average value of which over a period is zero.

ambient temperature:The temperature of the medium such as air, water, or earth into which the heat of the equipment is dissipated.

ampacity:Current-carrying capacity expressed in amperes, of a wire or cable under stated thermal conditions.

autotransformer:A transformer in which at least two windings have a common section.

bushing:An insulating structure including a central conductor, or providing a central passage for a conductor, with provision for mounting on a barrier, conducting or otherwise, for the purpose of insulating the Conductor from the barrier and conducting current from one side of the barrier to the other.

conservator: An oil preservation system in which the oil in the main tank is isolated from the atmosphere, over the temperature range specified, by means of an auxiliary tank partly filled with oil and connected to the completely filled main tank.

core: An element made of magnetic material, serving as part of a path for magnetic flux.

core form transformer: A transformer in which those parts of the magnetic circuit surrounded by the windings have the form of legs with two common yokes. See also: shell form transformer.

core loss: The power dissipated in a magnetic core subjected to a time-varying magnetizing force. Core loss includes hysteresis and eddy-current losses of the core.

corona: Obsolete term. See: partial discharge (PD).

current transformer: An instrument transformer intended to have its primary winding connected in series with the conductor carrying the current to be measured or controlled.

delta connection: So connected that the windings of a three-phase transformer (or the windings for the same rated voltage of single-phase transformers associated in a three-phase bank) are connected in series to form a closed circuit.

distribution transformer: A transformer for transferring electrical energy from a primary distribution circuit to a secondary distribution circuit or consumer's service circuit. See also: power transformer.

eddy-current loss: The energy loss in conductors resulting from the flow of eddy currents and circulating currents (if any) in parallel windings or in parallel winding strands. There is no test method to determine individual winding eddy loss or to separate transformer stray loss from eddy loss. The total stray and  eddy loss is determined by measuring the total load loss during the impedance test. The total stray and eddy loss is determined by subtracting the I2R loss from the load loss as follows:

PEC + PSL = PLL – I ²R

where

PEC is the eddy current loss, watts,

PSL is the stray loss, watts,

PLL is the load loss, watts,

I²R is the loss due to current and resistance, watts.

eddy currents: The currents that are induced in the body of a conducting mass by the time variation of magnetic flux.

excitation current: The current that flows in any winding used to excite the transformer when all other windings are open-circuited. It is usually expressed in percent of the rated current of the winding in which it is measured.

ferroresonance: A phenomenon usually characterized by overvoltages and very irregular wave shapes and associated with the excitation of one or more saturable inductors through capacitance in series with the inductor.

gas-filled transformer: A sealed transformer, except that the windings are immersed in a dry gas that is other than air or nitrogen.

grounding transformer: A transformer intended primarily to provide a neutral point for grounding purposes. Syn: three phase earthing transformer (IEC). See also: rated kVA of a grounding transformer; voltage rating of a grounding transformer.

hysteresis loss: The energy loss in magnetic material that results from an alternating magnetic field as the elementary magnets within the material seek to align themselves with the reversing magnetic field.

instrument transformer: A transformer that is intended to reproduce in its secondary circuit, in a definite and known proportion, the current or voltage of its primary circuit, with the phase relations and waveform substantially reserved.

I²R loss: The loss that is due to the currents in, and the direct-current resistance of, the windings. The I²R loss is determined by measuring the direct-current resistances using a direct current and voltage and then a calculation is performed using the winding currents.

Reference: : IEEE Std C57.12.80™-2002 IEEE Standard Terminology for Power and Distribution    

                    Transformers