NETA System Commissioning and Analysis 3

Question 1

During commissioning of a UPS system, what test verifies the battery's ability to support full load for the rated backup time?

Accepted Answer

Capacity discharge test

Answer

A capacity discharge test draws rated load from the battery and measures the time until the battery voltage drops to the end-of-discharge voltage, confirming rated backup time.

Question 2

A newly commissioned protective relay system exhibits a race condition where two relays trip simultaneously on a fault. What commissioning step should have prevented this?

Accepted Answer

Time-current coordination review and testing

Answer

Time-current coordination review ensures relay pickup values and time delays are properly staggered to achieve selectivity, preventing simultaneous operation.

Question 3

What is the primary reason for performing a power frequency overvoltage (AC hipot) test on newly installed cable rather than using only a DC hipot test?

Accepted Answer

AC testing better replicates operating stress and is more sensitive to certain defects in extruded insulation

Answer

AC hipot testing applies voltage stress that more closely mirrors in-service conditions, and it is more effective at detecting voids and treeing defects in XLPE and EPR insulation.

Question 4

During commissioning of a large motor control center (MCC), feeder tap units are found to have contact resistance values 50% above the manufacturer's limit. What is the correct action?

Accepted Answer

Remove the units, clean or replace contacts, and retest before energizing

Answer

Units with contact resistance exceeding manufacturer limits must be corrected before energization to prevent overheating, arcing, and equipment damage.

Question 5

What does the term 'vector group' describe on a transformer nameplate, and why is it critical during commissioning?

Accepted Answer

The phase displacement and winding connection between primary and secondary

Answer

The vector group denotes the winding configuration (delta or wye) and the phase angle displacement between primary and secondary, which must match when paralleling transformers.

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test

NETA System Commissioning and Analysis 3