Calculating the insulation resistance
The expected total resistance of the PV system or of an individual string can be calculated
using the following formula:
total
The exact insulation resistance of a PV module can be obtained from the module manufacturer
or the datasheet.
For the resistance of a PV module an average value can be assumed: for thin-film PV modules
approximately 40 MOhm and for polycrystalline and monocrystalline PV modules
approximately 50 MOhm per PV module (for further information on calculating the insulation
resistance see the Technical Information "Insulation Resistance (Riso) of Non-Galvanically
Isolated PV Systems" at www.SMA-Solar.com).
Required devices:
☐ Suitable device for safe disconnection and short-circuiting
☐ Measuring device for insulation resistance
Device required for safe disconnection and short-circuiting of the PV array
The insulation resistance can only be measured with a suitable device for safe disconnection
and short-circuiting of the PV array. If no suitable device is available, the insulation
measurement must not be carried out.
Procedure:
1. Calculate the expected insulation resistance per string.
2.
Danger to life due to high voltages
• Disconnect the inverter from all voltage sources (see Section 2.2, page 7).
3. Install the short circuit device.
4. Connect the measuring device for insulation resistance.
5. Short-circuit the first string.
6. Set the test voltage. The test voltage should be as close as possible to the maximum system
voltage of the PV modules but must not exceed it (see datasheet of the PV modules).
7. Measure the insulation resistance.
8. Eliminate the short circuit.
9. Measure the remaining strings in the same manner.
☑ If the insulation resistance of a string deviates considerably from the theoretically
calculated value, there is a ground fault present in that string.
10. Reconnect to the inverter only those strings from which the ground fault has been eliminated.
11. Reconnect all other strings to the inverter.
12. Recommission the inverter (see Section 8, page 25).
13. If the inverter still displays an insulation error, contact Service (see Section 11, page 30). The
PV modules might not be suitable for the inverter in the present quantity.
5 Checking the PV System for Ground Faults
SMA Solar Technology AG
Service Manual
21
SB30-60TL-21-SG-en-11
Summary of Contents for SUNNY BOY 3000TL Single Tracker
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