Measurement & Instrumentation

9% of exam

Instrument transformers & metering, insulation & ground testing.

4 concepts

Exam areas

A. Instrument transformers and metering

Instrument Transformers: CTs, VTs, Burden, and Accuracy Classes

How CTs and VTs scale primary quantities for meters and relays: ratio math, polarity marks, burden, accuracy classes, saturation, and the open-CT hazard.

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Three-Phase Power Measurement and the Two-Wattmeter Method

Blondel's theorem, the 1-, 2-, and 3-wattmeter methods, two-wattmeter math and sign rules below 0.5 PF, and kWh/demand metering with CT/VT multipliers.

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B. Insulation testing

Insulation Resistance Testing: Megger, PI, DAR, and Dielectric Tests

Pick DC test voltages, correct IR for temperature, judge PI against IEEE 43 limits and DAR against common field guidelines, and know when DC/AC hipot and tan-delta testing apply.

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C. Ground resistance testing

Soil Resistivity and Ground Resistance Testing

Measure soil resistivity with the Wenner four-pin method and electrode resistance with fall-of-potential (61.8% rule), three-point and clamp-on tests.

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