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Generator reverse power protection principle

          Generator reverse power protection is one of the important generator protection, I produced 988 generator backup protection device, with generator reverse power protection, users are welcome to consult! 

Generator Reverse Power Protection.jpg

988 generator backup protection device

Generator reverse power protection introduced

          Turbine generator and grid parallel operation, for some reason the main steam turbine door closed, the generator from the output power into the grid power to maintain the synchronous generator speed and loss, this state is called reverse power operation, At this moment, the generator will be a motor running, that is, drawing active power from the system and dragging the turbine to rotate. This operating condition has no effect on the generator, but for steam turbines, prolonged steam-free operation will result in higher exhaust temperature and overheating of the tail blades. As the cylinder is full of non-flowing steam, it will generate friction with the steam turbine blades heat, the turbine blades overheating and low-pressure cylinder exhaust temperature rises, the low-pressure cylinder as a whole upward expansion, the rotor center up, the same position in the bearing Case caused by the unit vibration.

Generator reverse power protection 

          Reverse power protection for the input terminal PT secondary three-phase voltage and generator CT secondary three-phase current. When the generator to absorb active power action. Therefore, the reverse power protection can accurately respond to the power of the opposite direction of the abnormal conditions, the timely issue of signals in the allowable time automatically shut down.

Reverse power protection action time problem.

          Electrical protection, when the turbine reverse power operation, the first signal, the delay after a certain time to protect the action of the motor output de-solute generator, the delay time is based on steam turbine to allow steam-free operating conditions to set the time, usually 1 ~ 3 minutes. If we change the way of de-soldering the generator to solve the generator by adopting the program trip reverse power protection action, the number of times of reverse power operation is more than that of delaying the generator by the closed signal of the automatic main steam valve. Therefore, from the angle of protecting the steam turbine, Time can be shortened, as long as the steam turbine control system can escape the grid and due to the instantaneous reverse power operation caused by jumping generator can be. Shorten the protection trip time in some cases will bring benefits, for example, when the turbine is shut down due to blade failure, the automatic main steam valve is closed, start the program to trip reverse power protection solution generator, if the delay is too long, the Will exacerbate the damage of the turbo-generator set.

Reverse power protection action results

          For the generator outlet switch is non-three-phase mechanism linkage switch, reverse power protection action outlet should only jump the motor outlet switch, and should not jump off the magnetic switch. 

When the generator is in non-full-phase operation, that is, the generator outlet switch is not all-phase open or all-phase closed, three-phase generator stator current imbalance occurs negative-sequence current and vibration, induction in the rotor surface twice Frequency of current, causing the rotor fever, severe burned rotor. When the generator is in the no-load condition, the negative sequence current generated or generated by the generator with non-full-phase operation is very small. The generator outlet switch is not all-phase disconnected, the de-excitation switch is simultaneously disconnected and the prime mover's energy supply When cut off, the negative sequence current generated by the generator is the largest, affecting the system and the generator to the maximum. Therefore, the related power supply must be cut off immediately, thus expanding the accident range. 

          Therefore, when the reverse power protection is tripped to open the motor outlet switch, the de-excitation switch is not tripped. If the generator outlet switch is not all-phase open, the excitation current can be immediately reduced to keep the generator running at no load. deal with.

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