NABCEP Inverter Systems 4

Question 1

A grid-tied inverter displays a 'Ground Fault' error and shuts down. What is the most likely cause?

Accepted Answer

An unintended current path exists between a current-carrying conductor and ground

Answer

A ground fault error indicates that current is flowing through an unintended path to ground, typically caused by insulation failure or wiring errors in the DC array.

Question 2

What is 'frequency-watt' (Freq-Watt) control mode in a grid-tied inverter?

Accepted Answer

A grid support function that reduces inverter output power when grid frequency rises above threshold

Answer

Frequency-Watt (or Freq-Watt) control reduces inverter active power output as grid frequency increases above a set threshold, helping stabilize grids with excess generation.

Question 3

For a transformerless grid-tied inverter, NEC requires which of the following to reduce leakage current risk?

Accepted Answer

Ground fault protection device (GFPD) integrated into or paired with the inverter

Answer

NEC 690.5 requires ground fault protection for ungrounded PV systems (common with transformerless inverters) to detect and interrupt ground fault currents that could cause fires or shock hazards.

Question 4

A string inverter has two independent MPPT inputs. How does this benefit the system designer?

Accepted Answer

It permits strings with different orientations or shading conditions to be optimized independently

Answer

Dual independent MPPT inputs allow strings facing different directions (e.g., east and west) or with different shading profiles to each operate at their individual maximum power points rather than compromising to a single point.

Question 5

What is 'volt-VAR' (Volt-VAR) control in advanced grid-interactive inverters?

Accepted Answer

Reactive power (VAR) output adjusted in response to local grid voltage to help regulate voltage

Answer

Volt-VAR control allows inverters to absorb or inject reactive power (VARs) in response to grid voltage deviations, helping utilities maintain voltage within acceptable limits on distribution feeders.

(NABCEP) North American Board of Certified Energy Practitioners Solar Practice Test

(NABCEP) North American Board of Certified Energy Practitioners Solar Practice Test

NABCEP Inverter Systems 4