1. PROPER OPERATION OF GENERATOR
1.The generator should be continuously running for long time to the specification on the
nameplate.
2.Regarding the voltage fluctuation of the voltage of the generator during proper operation, it
should be ±5% of the rated value, given that the generator output is stable. The maximum value
should be lower than 110% of the rated value, and the field current should be under rated value.
3.When the frequency fluctuation is within±5HZ, the generator can work under rated condition.
When the frequency is under 49.5HZ, the rotor current should be under rated value. The unit is
not allowed to run at a very slow speed
4. The generator is not allowed to be in phase-deficient operation. The three phase currents
should be balanced. When the generator is running with rated load, the difference of three phase
current should be under 20% of the rated current, and the current of each phase should be under
rated value.
5. The power factor for the generator in operation should be ensured as 0.8., generally less than
0.95. When the power factor is under 0.8, the rotor current should be under the allowable value.
At the same time, the stator current should also be under the allowable value.
2. MONITORING AND MAINTENANCE OF GENERATOR IN OPERATION
Generally patrol inspection for the generator should be carried out every one hour. When
monitoring the generator, the operators should be focused and careful to detect the problems
timely to ensure the safety.
(1)Temperature: the temperature change of the winding, core and bearing should be monitored all
the time. If there is sudden increased in temperature, the unit should be stopped immediately to
figure out the reasons behind that.
(2) Oil level of bearing: The oil level of the bearings should be regularly checked. If the oil level
is higher than normal level, it might be caused by oil leakage of the oil cooler; if the oil level is
lower that normal level, it might be caused by leakage of oil tank or unlocked valve on the
pipeline.
4)Vibration and noise: the vibration and noise should be monitored strictly. If there is
obvious change of vibration and noise, the unit should be stopped for inspection.
(5) Collector ring: regularly check the sparks of the brush and working condition of the
brush. If excessive sparks are detected, proper treatment should be applied.
(6) Cooler: if the cooler is found to be blocked, or in small flow, the cooling effect is not good
as before. Proper treatment should be applied.
(7)Auxiliary equipment: check all the time the operation status of the generator and its
auxiliary equipment.
3. MAINTENANCE OF THE TURBINE-GENERATOR SET
(1)Routine maintenance
Clean regularly the surface of the cooling water pipeline of the upper bracket, casing and
bearing to remove the oil dirt and dust. Remove the ashes of the carbon brush on the
bracket and plate to avoid the failure of excitation loop being grounded.
(2)Maintenance of slip ring and brush
The brushes should be replace when it gets too short, and the replacement of the brush
should be done by experienced staff when the unit is shut down. For each time, one brush
should be replaced, or half of the brushed under special circumstance. The new brushes
should be well grinded and balanced.
DRYING METHOD OF THE GENERATOR
short circuit drying method
Make the three phases of the stator winding short circuited, and when the unit reaches
rated speed, apply field current, thus heating the generator by the heating effect of the
current.
Points to be noticed:
a. monitor the stator current closely. At the beginning, the current should not be much,
because if big current is applied, only the winding surface will be hearted, not the inside. At
the beginning, the current is better to be control within 50% of the rated current. After 1-2
hours’ heating, increase the short circuit current to 75% of the rated current, and then to
rated current until the generator is dried.
b. The temperature should not be increased too fast. Keep a close eye on the temperature of
stator and core, if the temperature increases too fast, reduce the short circuit current.
c. Regularly check if there is overheating or smoking phenomenon.
Natural air drying method
Start up the turbine, and when the generator reaches rated speed, the natural air will get
rid of the moisture out of the generator. In this way, it takes short time to dry up the
generator. To shorten the time for drying, heating device can be installed at the air intake to
increase the air temperature.
DC current drying method
To dry the rotor windings, a DC welding machine can be used as drying source to transfer
the DC current into the winding to the heat the generator. As for the amount of current, the
maximum should be under the AC value specified on the nameplate and generally, it is
appropriate to be 50% of rated AC current