Precharging contactor for electric motor test bench

An automobile manufacturer needed a precharging contactor for their electric motor test benches that could withstand arcing during switch-on. They previously used a high-voltage relay, but its contacts frequently welded.

Schaltbau investigated the clearances and creepage distances in the high-voltage relay, then compared these parameters with its own DC contactors. The double pole C294 DC contactor was selected. The C294 has better insulation parameters than the high-voltage relay; but most importantly it has solid contacts that withstand arcing better than a high-voltage relay.

What does the C294 precharging relay do?

Before the system is switched on, the capacitors have to be charged. This is done via a separate precharging path – with a resistor that limits the current flow. The C294 precharging contactor closes the precharging path. Once the capacitors are two-thirds charged, the main contactor is activated. Then the C294 opens the precharging path again.

Why was the C294 chosen?

• Better clearances and creepage distances than the high-voltage relay
• Rated impulse withstand voltage U_imp up to 12 kV
• Contact pills prevent contact welding

Note

Schaltbau also provides the CT power contactor as the main contactor in many test bench applications.