FLANGE 4N1799 - Caterpillar

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.
Use the following procedure in order to test the rotating rectifier.
Stop the generator set. Disconnect the wires for the AVR and isolate the wires for the AVR.
Make an assembly for separate excitation. The assembly can use a 12 V battery or a variable DC power supply as a power source. Refer to Step 3 for an assembly that uses a 12 V battery. Refer to Step 4 for an assembly that uses a variable DC power supply.
Illustration 1 g01015807
(A) Exciter Field
(B) Diode (one Amp)
(C) Rheostat (50 Ohms 300 W)
Connect a 12 V battery in series with a rheostat (C) of "50 Ohms 300 Watts" and a diode (B) on both wires for the exciter field (5+ and 6-). Go to step 5.
Illustration 2 g01015808
(D) AC supply
(E) Variable power supply
(F) Exciter field
(G) Diode bridge
Connect a variable power supply and a diode bridge to both of the wires for the exciter field (5+) and (6-).
The assembly should have characteristics that are compatible with the power for the field excitation of the generator.
Operate the generator set at rated speed.
Gradually increase the current of the exciter field by adjusting the rheostat or the variable power supply. Measure the output voltage and the current at no load. Measure the output voltage and measure the current at no load.
The generator is operating properly when the output voltage is at the rated value and the output voltage is balanced within 1 percent for the rated level of excitation.