SMA STP 33-US-41 - Page 62

6 Troubleshooting
SMA Solar Technology AG
User ManualSTP33-62-US-41-BA-en-1162
WARNING
Danger to life due to electric shock from destruction of the measuring device
due to overvoltage
Overvoltage can damage a measuring device and result in voltage being present in the
enclosure of the measuring device. Touching the live enclosure of the measuring device results in
death or lethal injuries due to electric shock.
• Only use measuring devices with a DC input voltage range of 1000V or higher.
Procedure:
In order to check the PV system for ground faults, perform the following actions in the prescribed
order. The exact procedure is described in the following sections.
• Check the PV system for ground faults by measuring the voltage.
• If the voltage measurement was not successful, check the PV system via insulation resistance
measurement for ground faults.
Test by Measuring the Voltage
Proceed as follows to check each string in the PV system for ground faults.
If PV module switches are installed that comply with the SunSpec communication signal for Rapid
Shutdown systems, the voltage measurement can be taken as described. After the inverter is
disconnected, the PV module switches no longer receive the "Permission-to-Operate" signal and
output a standby voltage instead of the module voltage as per their specification. The respective
string voltage can be determined via the standby voltage. When calculating the ground fault
location, the module voltage must be replaced with the standby voltage as specified by the PV
module switch.
Procedure:
1.
DANGER
Danger to life due to high voltages
• Disconnect the inverter from any voltage sources (see the inverter installation manual).
2. Measure the voltages:
• Measure the voltage between the positive terminal and the ground potential (PE).
• Measure the voltage between the negative terminal and the ground potential (PE).
• Measure the voltage between the positive and negative terminals.
If the following results are present at the same time, there is a ground fault in the PV
system:
☑ All measured voltages are stable.
☑ The sum of the two voltages to ground potential is approximately equal to the
voltage between the positive and negative terminals.
3. If a ground fault is present, determine the location of the ground fault via the ratio of the two
measured voltages and eliminate the ground fault.