NETA Transformer Testing Procedures 5

Question 1

A transformer nameplate shows a BIL of 150 kV. During an applied voltage test, the correct test voltage per NETA MTS would be applied for:

Accepted Answer

1 minute

Answer

NETA MTS specifies that applied (hi-pot) voltage tests on transformers are held for 1 minute at the rated test voltage.

Question 2

When interpreting DGA results using the Rogers Ratio method, a ratio of CH4/H2 < 0.1 combined with C2H2/C2H4 < 0.1 is most consistent with:

Accepted Answer

Partial discharge (corona)

Answer

The Rogers Ratio pattern with low CH4/H2 and very low C2H2/C2H4 is characteristic of partial discharge or corona activity.

Question 3

During a transformer load tap changer (LTC) resistance test, erratic resistance readings across tap positions most likely indicate:

Accepted Answer

Worn or pitted contacts within the LTC

Answer

Erratic or inconsistent resistance across LTC tap positions is a classic sign of worn, pitted, or dirty tap changer contacts.

Question 4

The Karl Fischer titration method is used in transformer testing to determine:

Accepted Answer

Water content in transformer oil (ppm)

Answer

The Karl Fischer titration is the standard chemical method for precisely measuring water (moisture) content in transformer insulating oil in parts per million.

Question 5

A three-winding transformer is tested for short-circuit impedance. Which winding combination provides the impedance between the primary and tertiary windings?

Accepted Answer

Short the tertiary, energize the primary, measure impedance

Answer

To measure primary-to-tertiary impedance, the tertiary is short-circuited, voltage is applied to the primary, and impedance is calculated from the measured values.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Transformer Testing Procedures 5