Single-Phase Loss/Drop in Commercial (C&I) and Utility Inverters

Ginlong Technologies Single- Phase Loss in C&I and Utility Inverters  

1. Scope

This document describes the behavior and evaluation of inverter performance during   Single-Phase Loss testing as conducted during utility interconnection verification.

 The purpose of this test is to confirm that the inverter can properly detect abnormal voltage and frequency conditions associated with the loss of one phase and disconnect from the grid in accordance with applicable interconnection requirements.

2. Single-Phase Loss

When a Single-Phase Loss Test is conducted on the inverter side of the transformer (transformer secondary), the inverter and/or multiple Solis inverters connected in parallel forming a single Distributed Generator are expected to detect the resulting voltage and frequency imbalance and disconnect from the grid within the required time limits. Detection is typically based on protection functions such as:

• Voltage unbalance
• Phase loss detection
• Frequency deviation
• Vector shift or phase angle monitoring

Under these conditions, the inverter and/or multiple Solis inverters connected in parallel forming a single Distributed Generator are directly exposed to the electrical disturbance, and test results generally represent the inverter’s protection performance.

When the Single-Phase Loss Test is performed on the utility side of the transformer (transformer primary), the measured response at the inverter terminals may differ due to the electrical characteristics of the transformer and system configuration. Factors that may influence the test results include:

• Transformer vector group (e.g., Delta-Wye, Wye-Wye)
• Transformer core construction (three-leg vs five-leg core)
• Grounding configuration
• Transformer impedance
• Load conditions

Because the transformer can partially mask or redistribute voltage unbalance, the inverter may not experience the same disturbance levels as when the test is conducted on the secondary side. As a result, additional engineering evaluation may be required to interpret the results.

The utility or system transformer is therefore a critical component in Single-Phase Loss testing, particularly when the test is performed on the transformer primary. Proper assessment must consider transformer characteristics and system conditions to ensure that inverter protection requirements are met.