UPS Frequently Experiences Power FailuresBecause the AC InputCircuitBreaker on the Input Side Bears Only a Small Current

Publication Date:  2013-02-17 Views:  134 Downloads:  0
Issue Description

A site of project S in country EG is configured with two 6 kVA Kelong UPSs. The circuit breaker on the PS48600 that connects to the UPS often trips, and manual reset sometimes cannot solve the problem. The UPS liquid crystal display (LCD) often displays an AC power failure alarm.

Handling Process

The mains is actually normal when an AC power failure alarm is generated and the UPS can work properly after the load is disconnected. The UPS input and output are normal. After the load is connected, the circuit breaker on the power system that connects to the UPS trips. Therefore, it can be concluded that the fault cause is from the circuit breaker. Identify the fault by performing the following steps:

   Step 1      Check the UPS input circuit breaker.

The circuit breaker is normal.

   Step 2      Check the UPS circuit breaker in the AC power distribution of the power system.

The circuit breaker is normal.

   Step 3      Set the UPS circuit breaker in the AC power distribution of the power system to ON.

   Step 4      Set the UPS input circuit breaker to ON.

The UPS works properly.

   Step 5      Check the bearing current of the UPS circuit breaker in the AC power distribution of the power system.

The bearing current is 10 A. If a 6 kVA UPS is fully loaded, the maximum load current is around 25 A. Therefore, a 32 A circuit breaker is required.

Root Cause

The maximum load current is 25 A, but the circuit breaker on the input side bears only a maximum of 10 A current.

Solution

Replace the 10 A circuit breaker with a 32 A circuit breaker.

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