Equipment in CB testing station

A laboratory (direct) type testing station tests circuit breakers for short-circuit making and breaking capacity using its own short-circuit generator, so tests can be done under controlled conditions.

Main parts of the equipment

1. Short-circuit generator: a special alternator designed to withstand repeated short circuits; driven by an induction motor. Its excitation is controlled to set the test current and voltage.
2. Flywheel: coupled to the generator shaft; it stores kinetic energy so that speed stays almost constant during the short circuit.
3. Driving motor: brings the generator and flywheel up to speed; it is disconnected before the test.
4. Exciter: supplies controlled DC field current to the generator.
5. Master (back-up) breaker: connected between generator and test circuit; it protects the generator and clears the circuit if the test breaker fails.
6. Make switch: closes the circuit at a chosen instant on the voltage wave, so a symmetrical or asymmetrical current can be produced.
7. Short-circuit transformer: steps the generator voltage up to the test voltage; it is built to withstand short-circuit forces.
8. Reactors and resistors: adjust the magnitude and power factor of the test current.
9. Capacitors: adjust the rate of rise of restriking voltage (RRRV).
10. Test cell: a strong enclosure where the breaker under test is installed, for safety.
11. Measuring and recording equipment: potential dividers, shunts/CTs and oscillographs (now digital recorders) to record current, voltage and timing.
12. Control room: for sequence control of all switches and observation.

 Motor ─ Flywheel ─ SC Generator ─ Master CB ─ Make
                         │                   switch
                      Exciter                  │
          Reactor ─ SC Transformer ─ Test CB ─ Load
          (control of I and pf)     (test cell)