3.3　Voltage Measurement and Insulation Monitoring

3.3.1　The AC voltage shall be measured for the following circuits:

1　Stator circuits of synchronous generators and generators/motors.

2　Main AC busbars at various voltage levels

3　Tie lines of the electric power system（at line side）

4　Other circuits that are equipped with VTs.

3.3.2　The AC voltage shall be measured and recorded for the voltage quality monitoring points in the electric power system and the voltage busbars of steam turbine-generators with a capacity of 50MW and above.

3.3.3　For 110kV and above main busbar and transformer circuits with neutral being solidly grounded，three phase-to-phase voltages shall be measured.In contrast，for 66kV and below main busbar and transformer circuits，only one phase-to-phase voltage shall be measured.In case of the main busbar and transformer circuits where a single voltage transformer is wired，only single-phase voltage or one phase-tophase voltage may be measured for the transformer circuit.

3.3.4　The insulation shall be monitored for the following AC systems:

1　Stator circuits of synchronous generators and generator/motors.

2　Busbars and circuits without neutral being effectively grounded.

3.3.5　For main busbar whose neutral is not effectively grounded，one phase-to-phase voltage of the busbar should be measured and three phase voltages should be monitored for the insulation.

3.3.6　The insulation of the stator circuits of generators may be monitored through measuring the zerosequence voltage of the auxiliary secondary winding of the generator voltage transformers or through measuring the three phase voltages of the generators.

3.3.7　The DC voltage shall be measured for the following circuits:

1　Excitation circuits of synchronous generators and generator/motors and output circuits of the associated automatic and manual excitation adjustment system.

2　Excitation circuits of synchronous generators.

3　DC generator circuits

4　Main busbars of DC system，and DC output circuits of battery packs and charging and float charging rectifying devices.

5　Output circuits of major power rectifying devices.

3.3.8　The insulation shall be monitored for the following DC system circuit:

1　Excitation circuits of synchronous generators and generators/motors.

2　Excitation circuits of synchronous motors.

3　Main busbars of DC system and major DC circuits.

4　Output circuits of major power rectifying devices.

3.3.9　The DC system shall be equipped with insulation monitoring devices which directly measure insulation resistance values with an accuracy class of not lower than class 1.5.