Judgment and analysis of rotor inter-turn short circuit of hydroelectric turbine generator:
Rotor inter-turn short circuit is one of the common faults of hydroelectric turbine generator, which is very detrimental to the safe operation of the generator. There are two situations of inter-turn short circuit: one is that it occurs shortly after the generator is switched on. When the generator is not loaded or the load is very light, an inter-turn short circuit occurs. The phenomenon is smoke. coming out of the pit and the insulation. The smell of burning. The other is an inter-turn short circuit that occurs after long-term operation of the generator. There are many reasons, such as poor manufacturing process, improper operation and maintenance, metal shavings or dust falling on the stator winding, etc. -short circuit if not cleaned for one lFor a long time, it is also possible for small animals like rats to crawl into the stator chamber and cause a short circuit between the turns.
For the first case, when an inter-turn short circuit occurs, due to very light or no load, the stator voltage and current changes are not obvious (the voltage power supply is normal), but there is smoke in the pit, and there is a smell of burnt insulation. Service personnel should measure and inspect the generator with voltage transformers, current transformers and instruments according to the load of the generator, whether there is smoke or odor in the pit and whether the noise of the generator is abnormal, etc. Differential protection to eliminate faults. Where conditions permit, two-in-one protection (overcurrent, undervoltage and overvoltage) should also be used to clear faults. When the conditionsare not met, the generator's emergency protection can clear the fault.
For the second case, when a short circuit between turns occurs, this is due to a large load or full load. The stator voltage and current will change significantly. The stator current increases and the voltage decreases. At this point, the generator load should be reduced immediately and the duty manager and electrical branch manager should be reported promptly. After seeking permission from the chief engineer, officials of the biotechnology department and the dispatch station, disconnect the excitation switch and derail the generator to stop it. When conditions permit, external inspection and measurements should be carried out as much as possible to accurately locate the fault point. For example, the current value and voltage variation of the short circuit between spires can be measured, and the unbalanced magnetic pull force can be measured. When you are sure that the generator can continue to operate. Generators must be operated in parallel with the consent of the reporting manager. When the conditions are not met. The fault must be resolved by generator backup protection.
Currently, hydroelectric generators use self-excitation and the minimum terminal voltage of a hydroelectric generator is 6.3 KV. An excitation transformer is therefore necessary. Currently, only the three-machine excitation system using an auxiliary exciter does not require an excitation transformer.
The function of the generator excitation transformer is to provide excitation power to the generator excitation device. The specific performances are as follows:
(1) Before the generator voltageis established, the terminal voltage is 0 and the circuit breaker disconnects the stator coil of the generator from the primary coil of the step-transformer and the generator The coil does not have a closed loop. The excitation transformer is installed at the front end of the universal circuit breaker. After the turbine generator reaches a certain speed, close the excitation switch, generator and excitation transformer. form a closed loop. Press the start button and the generator will use the remaining power. The magnet immediately creates a voltage (200 V ~ 300 V). Increasing the turbine speed and adjusting the excitation voltage can make the generator output meet the grid connection requirements.
(2), encourageAfter the output of the magnetic transformer is rectified, it forms a DC power supply for the excitation power of the SCR generator.
The excitation transformer ist a device specially designed to provide three-phase AC excitation power to the generator excitation system. The excitation system converts the three-phase power into DC power of the generator rotor through the thyristor, thus forming the excitation transformer. Generator excitation magnetic field. , adjusting the firing angle of the thyristor through the excitation system to achieve the purpose of adjusting the motor terminal voltage and reactive power. It is usually connected to the generator output. Since the output voltage of the generator is high and the rated voltage of the excitation system is low, a step-down transformer is required.