3.4　Requirements on the Operation Capability of the Units under Abnormal Conditions

3.4.1　In the case of abnormal operating conditions,the units shall comply with the following requirements:

1　The standard frequency of the electric power system is 50Hz,and in special cases where the system frequency rises to 51Hz or drops to 48Hz within a short time,the units shall comply with the following requirements:

1）The units shall be able to operate continuously when the system frequency is in the range of 48.5Hz to 50.5Hz；

2）The units shall be capable of operating continuously for no less than 300s each time when the system frequency is in the range of 48Hz to 48.5Hz；

3）The units shall be capable of operating continuously for no less than 180s each time when the system frequency is in the range of 50.5Hz to 51Hz.

2　When the system voltage varies within a certain range,the units shall be capable of operating and supplying power normally.

3.4.2　The low frequency protection of 300MW and above turbine generator units shall be capable of recording and indicating the accumulated operating time when the frequency is abnormal,and capable of accumulating operating time at each abnormal frequency respectively.

3.4.3　The generators shall comply with the following requirements for asynchronous operation:

1　When oscillation occurs in the electric power system and the oscillation center is located outside the generator-transformer unit,the generator shall be able to withstand 5-20 oscillation cycles；if the oscillation center is located inside the generator-transformer unit,the out-of-step protection shall be initiated immediately.

2　The generators involved in loss-of-excitation asynchronous operation for a short time shall comply with the following requirements:

1）The power grid has sufficient reactive power capacity to maintain a reasonable voltage level.

2）The generator current is smaller than 60%to 70%of the three-phase short-circuit current at the outlet.

3）The units can automatically reduce the load to the permissible level rapidly.

4）The auxiliary power supply system served by the generators can be automatically switched over to another power supply.

3　If the excitation cannot be restored in a short time specified,the units shall be disconnected from the power grid.

3.4.4　Each generator shall be able to serve the specified steady-state negative sequence loads for a long time,and can withstand the specified negative sequence current surge in the event of sudden asymmetric short-circuit faults.

3.4.5　The generating units shall be able to withstand 180°faulty synchronization for at least five times within the permissible service life.The operation of the generators shall not be affected by the single-phase reclosing of high voltage lines.