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 Uimp 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.