Power-grid test equipment — insulation analyzers, transformer-ratio testers, cable-fault locators and grid-simulation rigs — switches measurement and protection circuits at voltages far above board-level electronics. The relays inside these instruments have to stand off kilovolt-level signals, add negligible leakage to a high-impedance measurement, and keep doing it across a long service life. This note maps those requirements to the HVR high-voltage reed relay series.
What grid testing asks of a switch
Grid test circuits span roughly 1 kV to 100 kV depending on the class of equipment, and a relay in the signal path is judged on four points:
- Low, stable contact resistance, so the switch does not add error to a ratio or resistance measurement.
- High open-contact and coil-to-contact isolation, with stand-off into the tens of kilovolts, so one channel cannot leak into another at full test voltage.
- Fast, repeatable actuation for dynamic and scanned measurements.
- Long life, on the order of 108 operations, in instruments that run through long automated test sequences.
A sealed reed contact addresses these together: the contacts are closed inside a glass capsule, so they neither oxidize nor collect the contamination that slowly raises the contact resistance of an open armature, and the small blade mass gives fast, repeatable timing.
HVR series for power-system test
The HVR high-voltage reed relay family is offered in 4 / 5 / 6 / 10 / 15 / 20 kV withstand versions, with contact switching voltage to 10 kVDC, insulation resistance of 10 TΩ and above, epoxy encapsulation and creepage distance greater than 32 mm. Selecting a version is driven by the maximum test voltage the channel carries, with the withstand rating chosen for headroom above it rather than at it; a channel that routinely switches 10 kV is better served by a 15 or 20 kV part than by one rated to its exact operating point.
Where the relays are used
Insulation resistance testing
Before energizing power infrastructure, insulation resistance is measured against the threshold set down by the applicable standard or site procedure. The relay switches the measurement circuit at test voltage, and its own open-contact leakage has to be many orders below the insulation current being measured — otherwise the instrument reads its switch instead of the DUT. Teraohm-class insulation is what keeps that error negligible.
Transformer-ratio testing
A ratio tester switches cleanly between a reference winding and the winding under test. Low and stable contact resistance on both paths keeps the ratio calculation free of a per-channel offset, while high contact-to-contact isolation lets the reference and test sides sit at different potentials during the measurement.
Cable-fault location
Cable-fault locators route high-voltage pulses down a cable to localize a fault along kilometers of conductor. The relay matrix that directs these pulses needs fast actuation and high pulse-current tolerance without edge distortion, since pulse shape is part of how the fault distance is derived. HVR versions cover the pulse switching, with the 5 / 10 / 20 A pulse-current options available where a locator drives harder pulses.
Selection notes
Two practical points recur. First, separate continuous switching voltage from breakdown/withstand when reading the data sheet — a 20 kV withstand part is not operated at 20 kV continuously, and designing to a margin improves both accuracy confidence and life. Second, treat creepage and board layout as part of the isolation budget: the relay’s 32 mm internal creepage only delivers its rating if the PCB around it maintains the corresponding clearances for the working voltage. With those two points observed, the HVR family gives grid-test designers a single sealed-contact platform across the full 4–20 kV span.
About SHR AUTOSENSOR
SHR AUTOSENSOR TECH LIMITED (SHR AUTOSENSOR) manufactures high-voltage reed relays, mercury wetted relays and high-voltage DC contactors. Contact: [email protected] | +86 13761571029 | www.reed-relay.com