For capacitor switching, the challenge are that the peak current often rises up to 100 times of nominal current. For reliability of system, contactors have to meet the specific requirement in capacitor switching. According to these rigorous standards, ABB has researched, developed and produced the specific UA…RA contactor capacitor switching.
UA...RA 3-pole contactors for capacitor switching, can be used in installations in which the peak current far exceeds 100 times nominal current. The contactors are manufactured completely with their damping resistors and can be used without additional inductances. The capacitors must be discharged (maximum residual voltage at terminals ≤ 50 V) before being re-energized when the contactors are making.
The UA…RA contactors are fitted with a special front mounted block, which ensures the serial insertion of 3 damping resistors into the circuit to limit the current peak on energization of the capacitor banks. Their connection also ensures capacitor precharging in order to limit the second current peak occurring upon making of the main poles. The insertion of resistors allows to damp the highest current peak of the capacitor when switching on, whatever its level. Electrical durability of UA...RA is more than 300,000 cycles with switching frequency 240 cycles/hour. It ensures that the system can secure uptime during operation.
The UA…RA series 3-pole contactors are designed with the block type. Main poles: 3 main poles, 1 tangential point inside, AC control system with many levels and a wide range of accessories.
With designed and developed specification, UA...RA contactors are the reliable and simple solution to improve stability in capacitor switching.