Mar. 02, 2022
Low frequency accumulation protection
Low frequency cumulative protection reflects the cumulative effect of system frequency reduction on the turbine. The protection is composed of sensitive frequency relay and counter, locked by the auxiliary contact of the outlet circuit breaker (that is, when the generator stops running, the low-frequency accumulative protection also stops running). When the accumulative system frequency is lower than the frequency setting value of 47.5Hz, when the accumulative time reaches the setting value of 3000 seconds, the action will send a delay signal of 30 seconds. The device can be monitored in real time during operation: constant value, frequency F and accumulated time are displayed. Differential protection of generator transformer, differential protection of transformer and differential protection of high voltage transformer are the main protection against interphase short circuit fault of protected components. In case of out-of-zone fault, the current imbalance caused by inconsistent CT characteristics of each side can be reliably avoided, and the in-zone fault protection has sensitive action. In order to avoid protection misoperation under transformer inrush current, the protection adopts second harmonic locking. The protection has the function of disconnecting the differential current without locking the second harmonic. When the differential current reaches the set value, the fault is removed instantly. The protection has CT line break locking function (not actually used). CT line break discrimination is the same as generator differential protection.
Excitation circuit overload protection
Excitation loop overload protection is used for rotor excitation return passing current or overload protection, which is divided into three phases, consisting of fixed time and inverse time.
The action current of the fixed time part is set according to the condition that it can reliably return under the rated current of normal operation. It acts on the signal and reduces the excitation current after the time limit T1 (5s) (the effect of reducing the excitation current is useless); The action characteristic of inverse time limit is determined according to the overload capacity of generator excitation windings, and the protection action is to power off the train. The maximum counter time limit is 10 seconds.
Generator rotor point grounding protection
One-point grounding protection of generator rotor is used to reflect the one-point grounding fault of generator rotor circuit. The protection adopts ping-pong switching principle. The positive and negative voltage of the rotor circuit to the ground is sampled successively, and the rotor grounding resistance and grounding position are calculated in real time by solving two different grounding circuit equations. After a delay of 2 seconds, the guard applies to the signal.
Symmetric overload protection for generator
The protection device consists of fixed time limit and inverse time limit. Fixed time segment 5 seconds after the signal is applied. The inverse time action characteristic is determined according to the capacity of the generator to withstand overload current, and the action is to solve the problem. The protective device can reflect the heat storage process of the generator stator.
Generator negative sequence overload protection
The protection device consists of fixed time limit and inverse time limit. The fixed time action current is set according to the negative sequence current value that the generator allows for a long time and the current value to avoid the imbalance of the negative sequence current filter under maximum load, and is applied to the signal after the 3-second time limit. The inverse time action characteristic is determined according to the ability of the generator to withstand negative sequence current, and the action is to solve the demagnetization. The protective device can reflect the heat storage process of the generator rotor.
Guangxi Dingbo Power Equipment Manufacturing Co., Ltd. established in 2006, is an manufacturer of diesel generator in China, which integrates design, supply, commissioning and maintenance of diesel generator set. Product covers Cummins, Perkins, Volvo, Yuchai, Shangchai, Deutz, Ricardo, MTU, Weichai etc. with power range 20kw-3000kw, and become their OEM factory and technology center.
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