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INSULATION TEST
Poor insulation can cause solar modules to undergo dielectric breakdown. Weak module concepts (for instance, cells that are positioned too close to the module frame) as well as material weaknesses (for instance, low-quality adhesive laminates), are just a few of the possible causes of insufficient insulation.
An insulation test shows whether a solar module provides adequate insulation between its electricity-conducting components and the module frame, or surrounding environment. The measurements essentially amount to an electrical safety test.
The measurement process
To measure the insulation resistance, a solar module’s short-circuited outputs are connected to the positive pole of a DC insulation tester with current limitations, while the module’s exposed metal section is connected to the negative pole. With the help of an insulation tester, a voltage of 1,000 V plus twice the maximum system voltage is applied to the module. As a rule, this means: 1,000 V + 2 × 1,500 V = 4,000 V. The rate at which the voltage is increased is limited to a maximum of 500 V per second. Once the target voltage is reached, it is maintained for 1 minute before measurements are completed. Within this minute, the module cannot suffer dielectric breakdown or show signs of any leakage. After the measurement, the voltage is dropped to zero and the module is discharged by short-circuiting the dielectrimeter’s clamps.
In the next step, voltage is applied, either 500 V, or, if higher, the maximum system voltage. After the voltage has been increased to the predefined value at a maximum speed of 500 V per second, it is maintained for 2 minutes. The insulation resistance is measured. After the conclusion of the measurement process, the voltage is reduced to zero, and the module is discharged again by short-circuiting the dielectricmeter’s clamps.
Rating
- During the minute-long test at 1,000 V plus twice the maximum system voltage, there should be no breakdowns or development of leakage paths.
- Modules with a surface area of less than 0.1 m2 should have an insulation resistance no lower than 400 Megaohms.
- In the case of modules with a surface area of more than 0.1 m2, the insulation resistance multiplied by the module surface area should not be lower than 40 Megaohms.
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