Circuit breaker survey

[Audio] Circuit breaker survey, GE change over operation (BOE 4/1times, Last 22/13)(Q 14/48) How would you prepare main circuit breaker survey for visual examination, generator change-over operation and reverse power trip test? (16M) (A) Preparation of Main Circuit Breakers for Survey First, isolate the circuit breaker and make it safe for inspection. Visually inspect the main circuit breakers in the main board, emergency board and section boards. Open the circuit breaker panel and check all internal wiring and terminal connections for damage and tightness. Inspect the main contacts, arcing contacts and auxiliary contacts for wear, overheating and correct alignment. Check the fixed and moving contacts of the isolator for damage and proper contact condition. Inspect the mechanical linkages for wear, looseness or stress damage. Remove and clean the arc chutes, then check that they are properly aligned and free from dust. Check the overload and short-circuit protection settings according to the specified values. Test the circuit breaker closing and tripping operations in isolated condition. Test the emergency hand charging arrangement for the closing spring. Check that the mechanical indicators for OPEN, CLOSED and ISOLATED positions operate correctly. Generator Change-Over Operation 1. To achieve smooth manual synchronizing, the incomer's speed must be adjusted to obtain approximately the same frequency as shown on the bus-bar frequency meter e.g. 60 Hz. 2. The incoming generator voltage can be set by its AVR or manual trimmer (if available) to be equal to the bus-bar voltage. 3. Fine tuning of the speed can now be observed on the synchroscope or synchronizing lamps. 4. The incomer is adjusted so that the synchroscope indicator rotates slowly clockwise (fast direction) at about 4 seconds per indicator revolution. 5. The circuit-breaker should be closed as the indicator approaches the 12 o'clock (inphase) position. 6. Breaker closing between 5-to and 5-past the 12 o'clock synchroscope position is satisfactory as long as the pointer rotation is fairly slow. 7. The pointer of incoming generator's ammeter will show very little kick when correctly synchronized. Reverse Power Trip Test Reverse power occurs when a generator loses prime mover power while running in parallel. The faulty generator acts as a motor and overloads the other generators. The reverse power relay senses the fault and trips the ACB..

[Audio] The relay contains a lightweight aluminium disc placed between two electromagnets. The upper electromagnet has a voltage coil and the lower electromagnet has a current coil. Magnetic fields induce eddy currents in the disc and create torque. During normal power flow, the trip contacts remain open. When power reverses, the disc rotates in the opposite direction and closes the trip contacts. This energizes the breaker trip circuit and trips the ACB. A 5-second time delay prevents unnecessary tripping during synchronization surges.