Inverter Systems Flashcards
7 cards from real NABCEP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Inverter Systems flashcards as text
What is the primary function of an anti-islanding protection feature in a grid-tied inverter?
Answer: Disconnect the inverter from the grid when utility power is lost
Anti-islanding protection automatically disconnects the inverter from the utility grid when grid power is lost, preventing the PV system from energizing downed lines and endangering utility workers.
A string inverter is rated for a maximum DC input voltage of 600V. On a cold winter morning, the open-circuit voltage of the array measures 620V. What is the most likely result?
Answer: The inverter may be damaged or its warranty voided
Exceeding the inverter's maximum DC input voltage can permanently damage internal components and typically voids the manufacturer's warranty.
Which inverter topology uses a high-frequency transformer to provide galvanic isolation between the DC array and the AC output?
Answer: High-frequency transformer-based inverter
High-frequency transformer-based inverters use a transformer operating at high frequency (kHz range) to provide galvanic isolation while remaining more compact than line-frequency transformer designs.
When multiple string inverters are installed in a commercial system, each inverter must have:
Answer: Its own AC disconnect accessible to utility personnel
NEC 690.15 requires each inverter to have its own AC disconnect means that is accessible to utility workers for safe de-energization.
What does the term 'MPPT range' refer to in inverter specifications?
Answer: The range of DC input voltages over which the inverter can perform maximum power point tracking
The MPPT range specifies the DC voltage window (minimum to maximum) within which the inverter's maximum power point tracking algorithm can operate to extract maximum power from the array.
A single-phase string inverter with CEC efficiency of 96% is producing 5,000W of AC output. Approximately how much power is being dissipated as heat?
Answer: 208W
At 96% efficiency, 4% of DC input power is lost as heat; DC input ≈ 5000/0.96 = 5,208W, so heat dissipated ≈ 208W.
Which of the following is a key advantage of a transformerless inverter compared to a transformer-based inverter?
Answer: Higher efficiency and lower cost due to elimination of transformer losses
Transformerless inverters eliminate transformer copper and core losses, resulting in higher peak efficiencies (often >97%) and reduced weight and cost compared to transformer-based designs.