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Maintenance and repair of generator
Time: 2017/5/24 10:21:44
Generator reverse power protection
Reverse power protection of generator, also called power directional protection. In general, the direction of power generator should by the generator to the bus, but when the magnetic or some other causes of generator loss is likely to become a generator, motor running, which absorb active power from the system. This is the reverse power. When the reverse power reaches a certain value, the generator protects the action, or acts on the signal, or acts on the trip.
Steam generator, steam turbine after the main valve closed, as synchronous motor running: absorb active power while towing a turbine can be issued to the system reactive power, long running blades of steam turbine generator reverse power protection, the main protection of steam turbine from damage.
The setting calculation of the inverse power protection of the steam turbine is to determine the operation power Pdz and the operation delay t of the protection.
1, the action of power Pdz tuning turbo generator reverse power protection power can be calculated as follows: Pdz = (Krel*P1) / Krel power coefficient Pdz reliability of reverse power protection, 0.8 P1 main steam valve is closed, the steam turbine to maintain synchronous speed rotation of the power consumption rate, in addition to the size of the structure and the outside of the steam turbine capacity and power structure, also the main steam system and turbine generator (the pipeline structure and has no bypass pipe etc.) the general rated power of 1.5~2% turbo generator generator ETA drag when rotating efficiency, so 0.98~0.99: Pdz = (1.2~1.6%) PN PN rated power generator. In practice, Pdz= is preferable to 1~1.5%PN.
2, action delay generator reverse power protection action delay, should be in accordance with the main steam turbine valve closed after allowing the operation time to set, the allowable time is generally 10~15min. Calculation and operation practice show that when the steam turbine system has bypass pipe, the operation time is longer. Therefore, according to the time after the steam turbine main valve is closed to allow the setting time to be adjusted, the action delay of the protection is desirable. 5~10min. After action, the line is applied to eliminate the magnetic field. In addition, most of the large turbo generators recently put in use the reverse power protection to start the tripping circuit of the program. At this point, the operation time is usually 1~2s. For program controlled reverse power protection,
Since the operation time is short, the actual reverse power may be very small due to the inertia of the turbine and generator in a short period of time after the main valve is closed. Therefore, the value of the inverse power should not be greater than 1%PN.
The following protection shall be installed according to the capacity of the generator for the possible faults and abnormal working conditions of the generator.
(1) longitudinal differential protection: for the stator winding and its lead line of interphase short-circuit protection.
(2) transverse differential protection: one phase to turn short circuit protection for stator winding. Only when the stator winding has two or more parallel branches to form the two or three neutral point leads is provided with this kind of protection.
(3) single phase grounding protection: single-phase earthing protection for generator stator winding.
(4) excitation circuit grounding protection: for the excitation circuit of ground fault protection.
(5) loss of excitation protection, to prevent large generator excitation (low excitation current excitation current is lower than the static stability limit of the corresponding excitation (or lose) the excitation current is zero), from the system to absorb a large amount of reactive power and negative impact on the system, 100MW and above capacity generators are installed this protection.
(6) overload protection: the generator acts on the protection of the signal when it exceeds the rated load for a long time. The small and medium sized generator is only equipped with sub overload protection, and large generator shall be installed with overload of stator and overload of excitation winding respectively.
(7) the stator winding current protection: when the longitudinal differential protection of generator outside short circuit, short circuit protection components or circuit breakers refused to move, such as the protection of external short-circuit backup, the backup protection also doubles as a longitudinal differential protection.
(8) the stator windings of overvoltage protection: to prevent sudden rejection to the full load caused by stator winding overvoltage, hydro generator and turbine generator are installed over voltage protection, small and medium sized turbo generator is usually not installed over voltage protection.
(9) negative sequence current protection: asymmetric short-circuit or three-phase load asymmetry in power system (such as electric locomotive, arc furnace and other single-phase).