When testing instrument transformers, you are trying to verify which two parameters?

• A. Polarity and burden
• B. Voltage and current
• C. Resistance and impedance
• D. Insulation and temperature

Answer: (A)

Instrument transformers must preserve the correct phase relationship and be able to drive the load on their secondary accurately. The two things you’re verifying when testing them are polarity and burden.

Polarity matters because the secondary voltage or current must move in the correct direction relative to the primary. If polarity is wrong, a percentage meter or protective relay can respond incorrectly—readings can be off, and relays may trip or fail to trip when needed. Ensuring the correct polarity guarantees that increases on the primary produce the expected, correctly oriented response on the secondary.

Burden is the impedance connected to the secondary. The transformer’s accuracy, including its ratio and phase angle, depends on this burden staying within its rated limits. If the secondary burden is too heavy or not appropriate for the transformer’s rating, the ratio can shift and the phase angle can become erroneous, degrading measurement accuracy and protection performance.

Voltage and current are the quantities being reduced by the transformer, not the specific verification targets in this test. Resistance/impedance and insulation/temperature relate to other characteristics or safety concerns, not to the immediate polarity and burden verification focused on proper metering and protection operation.