Tripping of circuit breakers in PV installations due to zero sequence field impedance

On the roof of a wool processing company a 385 kWp PV installation is installed. When production of the installation is more than 60% of the rated power the circuit breaker trips. Measurements show high THD(U) of phase voltages and variable waveform of both voltage and current. Analysis of the installation showed that a Yy₀ transformer is installed introducing a high zero sequence field impedance. Unbalance in the injected current combined with a zero sequence impedance leads to high voltage drops and distorted phase voltages. Measurements also show high RMS values of the current in the neutral conductor. Analyses show that the tripping of the circuit breaker is caused by the measurement method of the device itself. Higher current values are calculated due to multiple zero crossings of both voltage and current. This paper gives the practical measurement results, causes of errors and the solution to the stated problems.