NETA Transformer Testing Procedures 4

Question 1

When performing a turns ratio test on a three-phase transformer, the acceptable deviation from the nameplate ratio is typically:

Accepted Answer

±0.5%

Answer

NETA acceptance criteria require the measured turns ratio to be within ±0.5% of the nameplate ratio.

Question 2

A transformer's insulation resistance reading is taken at 40°C. To correct this value to 20°C, you should:

Accepted Answer

Multiply by a correction factor greater than 1

Answer

Insulation resistance decreases with increasing temperature, so readings at elevated temperatures must be multiplied by a correction factor to normalize to 20°C.

Question 3

During a sweep frequency response analysis (SFRA) test, a significant deviation in the mid-frequency range (1 kHz–100 kHz) most likely indicates:

Accepted Answer

Loss of clamping pressure or winding deformation

Answer

Mid-frequency deviations in SFRA are associated with loss of clamping pressure or mechanical winding deformation.

Question 4

What is the primary purpose of performing a dissolved gas analysis (DGA) on transformer oil?

Accepted Answer

To detect incipient faults through gas generation patterns

Answer

DGA identifies fault types such as thermal overheating, partial discharge, and arcing by analyzing gases dissolved in the insulating oil.

Question 5

A power factor tip-up test on a transformer bushing compares power factor at two voltages. An increasing power factor with increasing voltage indicates:

Accepted Answer

Partial discharge activity within the bushing

Answer

An increase in power factor with voltage (tip-up) suggests ionization or partial discharge activity inside the bushing.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA Transformer Testing Procedures 4