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Pickering Relay
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Reed Relays for Monitoring Photovoltaic Efficiency & Fault Detection

The largescale harvesting of electricity through photovoltaic (PV/solar) cells is extremely popular in the renewable energy sector and continues to reduce our dependence on fossil fuels. However, a 2022 report by the International Energy Agency (IEA) states the cost of new renewable installations (PV and wind farms) has increased, reversing, in the organization’s words, “…a decade-long cost reduction trend.”

Solar farm efficiency must be high to produce a good ROI, and the most common threat to that efficiency is electrical current leaking to ground. Leaks can be the result of poor installation but, more commonly, they develop over time in the PV panels and in the cables carrying the DC voltage to the inverters for conversion into AC for connection to the grid.

The leak is essentially some of the power generated by the PV cells finding a path to ground when the isolation resistance (RISO) between equipment and earth has reduced to less than 40MΩ. Between 20 and 40MΩ, the RISO can still be considered healthy. Less than 20MΩ and there’s cause for concern, as the insulation is degrading. A RISO of less than 1MΩ will almost certainly result in power loss and possibly permanent damage, and even fire.

Also, some faults are intermittent. For example, the build-up of moisture/condensation in a panel overnight can cause the RISO to be low during the first few hours of operation in sunlight.

Current leaks to ground can be detected by temporarily placing a current sensing circuitry between the terminals of the PV cells and ground, as per diagram 1.


Diagram 1 The current sensing circuit includes a resistor of a known value (typically a high impedance). When the circuit is switched in, the known resistance will effectively be placed in parallel with the RISO. The current that flows through the sensing circuit can be used to calculate the RISO.

To engage the current sensing circuit, it is necessary to connect to a high voltage. Relative to ground, the negative and positive outputs of the solar panel will typically be about 600V in direct sunlight.

Finding this guide interesting?

Download the full guide now to learn more about monitoring photovoltaic solar farm efficiency and how to detect faults in order to prevent power loss, permanent damage, or even fire.

The guide explains the current sensing circuit and which high-voltage switching technologies should be considered.

Full contents of the guide includes:

  • PV System Monitoring
  • Switching Technologies
  • Reed Relay Terminology
  • Recommended Products
  • Why Pickering for Reed Relays?
application guide_small

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Series 219 High Voltage SMD 3kV

All contact configurations are offered with three coil voltages, 3V, 5V, or 12V. Switching is up to 0.7A and 10W, while the operating temperature range spans from -40°C to +105°C.

Series 104 Mini SIL up to 5kV

Small high voltage reed relays in Form A and Form B. Up to 5000 V stand-off, 1000 V switching. 5, 12 or 24 V coils. Suitable for transformer testing.

Series 119 Mini SIL up to 3 kV

Very small isolation reed relays in Form A and Form B configurations. Up to 3000 V stand-off, 1000 V switching. 3, 5 or 12 V coils. Suitable for cable testers.

Series 131 Mini SIL up to 1.5 kV

The smallest high voltage relays available. 1 Form A. Up to 1500 V stand-off, 1000 V switching. 3, 5, or 12 V coils. Suitable for mixed signal semiconductor testers.

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