DRYING WINDINGS
Generators in service may inadvertently have their windings exposed to splashing or sprayed water. Units that have been in transit or storage for long periods of time may be subjected to extreme temperature and moisture changes causing excessive condensation. Regardless of the source of moisture, wet windings should be thoroughly dried out before operating the unit. If this precaution is not taken, serious damage to the generator can result. The following procedures may be utilized in drying the generator’s windings. Winding wetness and situation limitations will influence the method selected.
Space Heaters
An electric heater may have been supplied with the generator. When energized from a power source other than the generator, the heater will gradually dry the generator. Enclosing the unit with covering and inserting additional heating units can accelerate this process. A hole should be left at the top of the covering to permit the escape of moisture. Care should be taken not to overheat various accessory equipment mounted with the generator.
Forced Air
Another method to dry the generator is to run the set with no excitation (see startup procedure item #2). The natural flow of ambient air through the generator will tend to dry the windings. This method can be accelerated by adding a source of heat at the air intake to the generator. Heat at point of entry should not exceed 80 C (180° F).
TESTING
Visual Inspection
Remove covers and look for any obvious problems: burnt windings, loose connections, broken wires, frayed insulation, cracked brackets, missing hardware, etc. Check for foreign objects that may have been drawn into the generator. Verify that the generator’s air gaps (main rotor and exciter) are free from obstructions. If possible, rotate the generator manually to ensure free rotation. Never “bar over” the engine generator set using the generator fan.
13
WARNING
QUALIFIED ELECTRICAL PERSONNEL MUST CONDUCT THE FOLLOWING TEST. LETHAL VOLTAGE MAY BE PRESENT AT BOTH THE GENERATOR AND VOLTAGE REGULATOR TERMINALS DURING THIS PROCEDURE. CAUTION MUST BE EXERCISED NOT TO COME INTO PERSONAL CONTACT WITH LIVE TERMINALS, LINKS, OR STUDS. SERIOUS INJURY OR DEATH COULD RESULT.
Constant Excitation Test
(12V BATTERY TEST)
The generator “no load” voltage is dependent on exciter input voltage and generator speed. With the generator operating at rated speed and 12 volts dc applied to the exciter field, the generators terminal voltage will be near rated value.
1.Shutdown the generator set and connect a voltmeter on the generator terminals.
2.Disconnect the regulator’s F+ (F1) and F- (F2) leads and connect them to a 12V battery. Caution should be taken to ensure that the battery is not exposed to any potential arcing.
3.With no load on the generator (main breaker open) run the generator at rated speed. Measure the generator’s terminal voltage and compare this value with values recorded during installation.
If voltage readings are normal, the main generator and excitation are operating properly. Troubleshooting should continue with the regulator. If readings are not normal the problem is in the generator. Continue testing diodes, surge suppressor, and windings.
Continuity / Resistance Test
The generator has four components that can be checked using an ohmmeter: exciter stator, exciter rotor, main stator and main rotor. Each of these components is comprised of various windings that form a complete electrical path of relatively low resistance. Using an ohm meter measure the loop resistance of each component. Compare these measured values with the values listed in the specification section of this manual. Note that very small resistance values require precision equipment to make accurate measurements; however, a standard ohmmeter will provide a good indication of winding continuity.