802613 Mercury DAMPER

The high voltage that is produced by an operating generator set can cause severe injury or death. Before performing any maintenance or repairs, ensure that the generator will not start.Place the engine control switch in the "OFF" position. Attach "DO NOT OPERATE" tags to all starting controls. Disconnect the batteries or disable the starting system. Lock out all switchgear and automatic transfer switches that are associated with the generator.
Table 1
Required Tools
300-8648 Insulation Testing Gp
349-4206 Insulation Testing Gp Periodically, use an insulation tester to check the insulation resistance of the generators main stator winding. The frequency of this test is determined by the generators environment. Previous insulation tester readings will also determine the frequency of this test.Test the main stator windings with an insulation tester in the following situations:
The generator set is started for the first time.
The generator set is removed from storage.
The generator set is operating in a humid environment. Test every 3 months.
The generator set is not protected from the elements in an enclosed area. Test every 3 months.
The generator set is installed in an enclosed area. This area needs to be low in humidity and this area needs to have steady temperatures. Test every 12 months (minimum).
The generator set has not been run under load for 3 months. Test the generator set weekly. Use space heaters around the generator set if the generator is exposed to a sea water environment or if the humidity is above 75 percent. Also use space heaters if a test result was below 3 megohms.Space heaters must be used whenever the generator set is not under load. Space heaters must also be used whenever salt is present or whenever high humidity is present. Using a space heater in this fashion is the only way to maintain insulation tester readings above 1 megohm. Use space heaters only when the generator is not running.For additional information, refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".Recommended Procedure for A Periodic Insulation Test
Personal injury or death can result from electrocution.The megohmmeter is applying a high voltage to the circuit.To avoid electrocution, do not touch the instrument leads without first discharging them. When finished testing also discharge the generator windings.
Take the generator out of service.
Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first. Refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".
Inspect the installation. Determine the equipment that will be tested by the insulation tester.
Discharge the capacitance of the windings.
Isolate the stator windings of the generator by disconnecting all other leads and cables from the generator terminals. Isolate the connections to the voltage regulator, the control panel, the switch gear, or other devices.
Connect the insulation testers RED lead to ground.
Connect the insulation testers BLACK lead to the Wye point or star point of the generators windings.
For units that are 600 V or less, set the voltage to 500 V. For units that are more than 600 V, set the voltage to 1000 V.
Use the 30/60 Time Resistance Method:
Apply voltage.
Observe the readings at 30 seconds. Observe the readings at 60 seconds.
Record the 60 second reading. This reading must be corrected for temperature.
Record temperature.
Record humidity.
Remove voltage.
Evaluate the readings. The actual value of the resistance may vary greatly between generators. For this reason, the insulations condition must be evaluated. Base this evaluation on the comparison between the 60 second resistance readings and the readings that were taken on previous dates. These two readings must be taken under similar conditions. If a 60 second resistance reading has a 50 percent reduction from the previous reading, the insulation may have absorbed too much moisture. Switch the insulation tester to the "OFF" position. Switch the insulation tester to the "OFF" position will discharge the insulation testers leads. Disconnect the insulation testers leads.Note: The results from the insulation resistance checks indicate when cleaning and/or repairing is becoming critical. Generally, insulation resistance will vary greatly with temperature. Therefore, always test at the same temperature and humidity. Refer to Illustration 1.Serial Number (Engine)____________________Serial Number (Generator)____________________
Illustration 1 g00633226