Accuracy - The degree of uncertainty with which a measured value agrees with the ideal values. Accuracy class of instrument transformers are defined by the requirements of:

• ANSI C57.13 Standard metering accuracy classes are 0.3, 0.6 and 1.2.
• IEC 60044-1 Standard metering accuracy classes are 0.2, 0.5 and 1.0.

Active Power - The RMS voltage multiplied by the RMS current of the fundamental multiplied by cosine (where is the phase angle between the current and voltage).

Ambient Temperature - Temperature of the surrounding air.

Apparent Power - The product of the applied voltage and current in AC circuit. Apparent power, or volt-amps, is not the true power of the circuit since power factor is not considered in the calculation.

Auto Transformer - A transformer used to step voltage up or down. The primary and secondary share a single winding, therefore the primary and secondary are not isolated.

Auxiliary Power - A power source, other than that producing the measured input quantity, which supplies the power necessary for the correct operation of the transducer.

Average Responding - The measurement of an AC voltage or current obtained using a DC instrument with a rectifying input circuit that converts AC energy to DC. The meter scale or readout is usually calibrated in terms of the corresponding RMS values, but is accurate only for pure sine wave inputs.

BIL - Basic Insulation Level

Bimetallic - See Temperature Measurement Device, Bimetallic

BLOG - A BLOG (weB LOG) is a WEB based diary which covers any subject the author(s) desires to cover. A BLOG can have one to many authors, each contributing entries. Subjects range from war zone correspondence, to arts & crafts topics, to family correspondence.

Burden - In current or potential transformers burden in VA is the maximum load the transformer can support while operating within its accuracy rating.

Calibration - Adjustment of a instrument so the output is always within a specified range for particular values of the input.

Current Transformer - An instrument transformer used to accurately scale ac currents up or down and/or to provide isolation. Generally used to scale large primary or bus currents to usable values for measuring (or control) purposes. The current measurement range is expressed as the ratio of full scale primary current to full scale secondary current. The primary winding is connected in series with the conductor carrying the current to be measured or controlled. There are two classifications of current transformers. Single Loop Primary type and Wound Primary type. In Single Loop type current transformers the primary winding is provided by the line conductor and is not an integral part of the transformer. In Wound Primary type the primary winding is an integral part of the transformers and usually consist of more that one turn. Wound Primary transformers are used in applications that require very high accuracies, as the position of the primary winding relative to the core magnetic field is fixed.

Current Ratio - Commonly used when specifying a current transformer. It is the relationship between the primary input value and by the secondary output value. For example: a current transformer that has a primary input value of 250 Amperes and a secondary output value of 35 ma will have a Current Ratio of 250:0.035.

Delay on Energization - A term describing a mode of operation relative to timing devices. Delay begins when the initiate switch is closed, or upon application of power to the input. Same as Delay on Make.

Delay on Make - Same as delay on energization.

Dielectric Strength - The continuous voltage a dielectric can withstand without deteriorating.

Duty Cycle - The amount of time that a particular device is operating or on ... expressed as time or percentage.