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Electrical Safety Testing for Photovoltaic Cells and Panels

There are several standards that cover various aspects of photovoltaic module testing, including the following:

• UL 1703, Flat-Plate Photovoltaic Modules and Panels
• IEC 61730, Photovoltaic (PV) module safety qualification
• IEC 61215, Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval
• IEC 61646, Thin-film terrestrial photovoltaic (PV) modules – Design

UL 1703 and IEC 61730 are the basic standards, covering requirements for safety and construction of photovoltaic modules to address prevention of electrical shock and fire hazards. These two base standards are to be used in conjunction with IEC 61215 and IEC 61646. IEC 61215 is specific to crystalline silicon modules, and IEC 61646 to thin-film modules. UL 1730 will soon be superseded by UL IEC 61730.

IEC 61730-1 -2 1st Ed. – 2004, and UL 1703 3rd Ed. – 2002
Electrical safety tests called out in IEC 61730 and UL 1703 include Dielectric Withstand, Bonding Path Resistance, and Insulation Resistance. Manufacturing and production tests require Dielectric Withstand and Ground Continuity testing be performed on every module.

Bonding Path Resistance testing outlined in the standard requires the resistance between the ground terminal or lead and any accessible conductive part be less than 0.1 ohms. The resistance is to be measured with a test current of 2 times the fuse rating.

Ground Continuity production testing requires only that there is an electrical connection between the ground terminal and all accessible conductive parts. Note that, if CSA certification is required, CSA 22.2 No. 0.4 – 2004, Bonding of Electrical Equipment should be reviewed. When a production continuity test is required by the standard to verify electrical connection, this requires a 10A Ground Continuity test.

Hipot (Dielectric Withstand) testing is performed with test conditions of (1000V + 2 x max voltage) DC. The voltage shall be ramped up from 0V to required value within five seconds and held for one minute, with leakage current not exceeding 50uA. The reason for ramping up the voltage is to prevent false failures due to capacitive in-rush current. For modules that have a system voltage of less than 30VDC, the test voltage is 500VDC. The voltage is to be applied between all current-carrying parts and all accessible parts. The tests are to be performed on samples after humidity, temperature, water spray and corrosive atmosphere tests have been performed.

Production testing for Dielectric Withstand is required under the same conditions as above; test time can be reduced to one second if voltage is increased by 120%. A module or panel with a system voltage rating of 30V or less is not required to be tested.

Wet Insulation Resistance testing is carried out by immersing the panel into a solution for two minutes. The insulation resistance is then measured between the shorted output terminals of the module and the solution. This test is intended to verify that the solar panel or the solar cell array has insulation high enough to reduce the possibility of fire and electrocution hazards, even when the module is wet.

Insulation Resistance testing is performed using a test voltage of 500 VDC. The minimum resistance is 400 Mohms for a module having an area of 0.1m2 or less. Larger modules are required to have the measured resistance times the area of the module greater than 40 Mohms*m2.

IEC 61215 2nd Ed. – 2005
The specific standard for crystalline silicon modules is IEC 61215. This standard requires the safety tests similar to the base standards.

Insulation Resistance Test or Withstand Voltage Test
Withstand Voltage testing is carried out by shorting a positive terminal and a negative terminal of the solar panel or a solar panel array, and then applying a predetermined voltage between the live electrical section and the outer housing (which refers to the bottom surface reinforcement member, the frame, and ground terminals). This test is intended to verify that the product (the solar panel and the solar panel array) is free from any dielectric breakdown attributed to aging of insulation. As for a test method and test apparatus for Withstand Voltage testing, it is important to apply a direct current across test terminals of an object to be tested.

Withstand Voltage testing is performed with test conditions of (1000V + 2 x max voltage) DC. The voltage shall be increased from 0V to the required value within five seconds and held for one minute with leakage current not exceeding 50uA. Production testing for Dielectric Withstand is required under the same conditions as above, or test time can be reduced to one second if voltage is increased by 120%.

Wet Leakage Current Test or Insulation Resistance Test
Insulation Resistance testing is carried out by shorting a positive terminal and a negative terminal of a solar panel or a solar panel array, and then by applying a predetermined voltage between the live electrical section and the outer housing (which refers to the bottom surface reinforcement member, the frame, and ground terminals). This test verifies that the solar panel or the solar cell array has insulation high enough to reduce the possibility of fire and electrocution hazards.

There are no other particular requirements on the test method and test apparatus. Preferably, the test apparatus includes the function of discharging a charge accumulated during the resistance test of the insulation resistance having a capacitive component. The insulation resistance test is performed using test conditions of an application voltage of 500 V for an application time of one minute, with a minimum limit typically 400 Mohms or (40 Mohms*m2)/Area(m2). Test apparatus can be purchased at professional companies such as HARREXCO AG. 

IEC 61646 2nd Ed. – 2008
The specific standard for thin-film terrestrial photovoltaic modules is IEC 61646. This standard requires the same safety tests to the base standards of IEC 61730 and UL 1703.

Inverters
Devices such as inverters, converters, charge controllers and interconnection equipment that convert DC to AC also have to have Hipot and Ground Impedance testing. UL 1741 and IEEE 1547 cover inverters and other equipment.

For products that employ power connectors, those connectors are normally investigated using UL 498, Attachment Plugs and Receptacles, and/or UL 1977, Component Connectors Used for Data, Signal and Power Equipment Applications. Note that electrical connectors must be certified for outdoor use in wet locations with exposure to sunlight (i.e., UV exposure resistant). If a customer should choose to create a listed power connector for use with photovoltaic modules and panels, also note that these devices must be designed robustly enough to withstand use as a DC circuit interrupt device under overload conditions, as outlined in UL 498 and UL 1977.

UL 1741, Inverters, Converters, Controllers and Interconnection System Equipment for use with Distributed Energy System, covers a variety of devices used in conversion of electricity from a variety of sources, including fuel cells, photovoltaic, and wind energy systems, to another form of electricity for both grid and non-grid connected systems. This standard is to be used in conjunction with and to supplement IEEE 1547, Interconnecting Distributed Energy Systems with a Power System. IEEE 1547 covers general requirements, such as voltage regulation, synchronization, integration of grounding, monitoring and isolation, to manufacturing and commissioning tests.

UL 1741 1st Ed. – 1999 Testing
Dielectric Withstand testing is required both for compliance and production testing. The dielectric withstand is applied between input and output wiring to accessible dead metal, and between input and output wiring to accessible low voltage and limited energy parts including terminals.

Test voltages for Dielectric Withstand testing are based upon rating voltage. Products with a 250V or less rating are tested at 1000VAC for 60 seconds or 1200VAC for one second. The equivalent DC can be used if the product can be damaged by AC potential. Products rated over 250V are tested at 1000VAC + 2 x rated voltage for 60 seconds, 1000VAC + 2.8 x rated voltage for one second, 1400VDC + 2.8 x rated voltage for 60 seconds, or 1700VDC + 3.4 x rated voltage for one second.

The equipment for Dielectric Withstand testing shall have a visual indication that high voltage is being applied, visual and/or audible indication of failure, and manual reset switch in the event of failure. If the tester has a transformer less than 500VA, there must be a voltmeter in the output. Testers with a transformer of 500VA or greater shall have a voltmeter, indicating voltage selector or visible marking indicating output voltage.

Ground Impedance testing is required in compliance testing. The equipment ground to any other metal part that is required to be grounded shall not exceed 0.1ohms. The impedance is measured at 25A and a frequency of 60Hz. The open circuit compliance voltage shall not exceed 6V. n

References: www.conformity.com