NETA Power Systems Analysis & Troubleshooting 3

Question 1

A symmetrical three-phase fault calculation requires knowledge of the system's:

Accepted Answer

Positive-sequence impedance only

Answer

Zero-sequence impedance only

Answer

Negative-sequence impedance only

Answer

Both positive- and zero-sequence impedances

Question 2

When testing a motor for insulation condition using a Polarization Index (PI) test, a PI value below 2.0 for a Class B motor indicates:

Accepted Answer

Questionable insulation requiring further evaluation

Answer

Excellent insulation in new condition

Answer

Normal operating temperature exceedance

Answer

Correct grounding of the motor frame

Question 3

In a power system short circuit study, the X/R ratio is important because it determines:

Accepted Answer

The DC offset component of fault current and equipment duty

Answer

The rated continuous current of the bus

Answer

The nominal system operating voltage

Answer

The transformer magnetizing inrush magnitude

Question 4

A grounded wye-delta transformer connection is commonly used as a grounding transformer primarily to:

Accepted Answer

Provide a zero-sequence current path on an otherwise ungrounded system

Answer

Step up voltage for transmission

Answer

Reduce transformer magnetizing losses

Answer

Limit transformer inrush current

Question 5

During a frequency sweep (sweep frequency response analysis) test on a transformer, a change in the high-frequency signature compared to the baseline most likely indicates:

Accepted Answer

Winding deformation or displacement

Answer

Tap changer in the wrong position

Answer

Insufficient cooling oil level

Answer

Core lamination shorting

Question 6

The primary purpose of a transfer trip scheme in transmission line protection is to:

Accepted Answer

Communicate a trip command to a remote breaker for high-speed clearing

Answer

Automatically reclose the breaker after a fault

Answer

Reduce fault current magnitude through impedance insertion

Answer

Switch to a backup transformer on loss of the primary

Question 7

When measuring zero-sequence impedance of a transformer, the test is performed by:

Accepted Answer

Connecting all three LV phases together and driving current with the neutral

Answer

Applying rated voltage to all three phases simultaneously

Answer

Short-circuiting the HV terminals and applying voltage to the LV terminals

Answer

Testing each phase individually at power frequency