--- title: "Equipment in CB testing station" subject: "Switchgear and Protection" chapter: 6 key: "semester_6/switchgear_and_protection:cb-testing-station" source: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/cb-testing-station site: BCT Engineering --- # Equipment in CB testing station Switchgear and Protection · Chapter 6: Circuit Breakers - Asked in: 2076 Bhadra, 4 marks - Video: [Switchgear –Testing Facilities](https://www.youtube.com/watch?v=rZeY5kX-dEw) — Electrical Research and Development Association - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/cb-testing-station - Whole chapter: https://www.bctengineer.com/md/semester_6/switchgear_and_protection/chapter-6 ## Question What are the main parts of equipment which are used for the testing of a circuit breaker in a laboratory type testing station? ## Short answer Main parts include a short-circuit generator with flywheel and exciter, master breaker, make switch, and short-circuit transformer. Reactors/resistors control current and power factor, capacitors adjust RRRV, plus test cell, measuring equipment, and control room. ## Answer 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. ```text Motor ─ Flywheel ─ SC Generator ─ Master CB ─ Make │ switch Exciter │ Reactor ─ SC Transformer ─ Test CB ─ Load (control of I and pf) (test cell) ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the role of the flywheel in a laboratory testing station? A. It keeps the generator speed almost constant during the short circuit B. It steps up the voltage C. It protects the generator D. It adjusts the power factor Answer: A. The flywheel stores kinetic energy so the speed does not drop while the generator supplies the short-circuit current. (Key point: Short-circuit generator and flywheel) 2. What is the purpose of the master (back-up) breaker? A. To set the test voltage B. To protect the generator and clear the circuit if the test breaker fails C. To record current D. To start the driving motor Answer: B. It is placed between the generator and the test circuit as a safeguard. (Key point: Master breaker) 3. Why is a make switch used? A. To adjust RRRV B. To step up voltage C. To record current waveforms D. To close the circuit at a chosen instant on the voltage wave, giving symmetrical or asymmetrical current Answer: D. Closing at a selected point on the wave controls the degree of asymmetry of the test current. (Key point: Make switch) 4. Which components adjust the rate of rise of restriking voltage? A. Reactors B. Resistors C. Capacitors D. Exciter Answer: C. Reactors and resistors adjust current magnitude and power factor; capacitors set RRRV. 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