Breaker Trip

Symptom

Circuit breaker trips as the power supply is started or as power is brought up.

Fault

• Short in the station
• Shorted converter SCR
• Shorted inverter SCR
• Shorted diode
• Shorted capacitor

Solution

Isolating the short:

1. Disconnect the output wires to the high voltage transformer. This isolates the power supply from the station. Start the power supply. If the breaker does not trip, the problem is in the station.

2. Separate the converter section from the inverter section
   1. Breaker does not trip and dc bus is generated across 27 to 29, the problem is in the inverter section
   2. The breaker trips with the converter separated
      1. Check for a shorted converter SCR
      2. Bad dc bus cap - this can be checked by checking the ac ripple across 27 to 29. Set the scope for 5ms/div, 5v/div, and ac coupling. If the ripple is extremely high, over 10v, a dc bus cap is open.
3. Inverter section isolation (no breaker trip in converter section isolation). The inverters can be run separate from each other (rating higher than 5kw).
   1. First run SCRs 1 and 2 separate from SCRs 3 and 4.
      1. Disconnect the white gate lead from SCRs 3 and 4
      2. Disconnect wire 73 from L3
      3. Pull the start button and note if the breaker trips, then re-connect everything.
   2. Now run SCRs 3 and 4 separate from SCRs 1 and 2
      1. Disconnect the white gate leads from SCRs 1 and 2 .
      2. Disconnect wire 31 from L2

      Pull the start button and note if the breaker trips
      
      If the breaker trips with each inverter run separate, ohm check for a faulty capacitor in the inverter, output, or series capacitors (C14 - C25). If the breaker tripped with one inverter running, but did not trip when the other inverter was run, look for a bad SCR or diode in the inverter that tripped the breaker.

   NOTE: For higher powered power supplies with 6 SCRs, disconnect 1 pair at a time (i.e. S1&S2, S3&S4, S5&S6). Each pair can hold a maximum of about 7.5 KW.