CAMSHAFT GP 2609308 - Caterpillar

SR 4 Generators With VR3 Voltage RegulatorsThe VR3 Voltage Regulator contains parts which have the ability to "sense" voltage. The "sensing" is performed at the input of the VR3 Voltage Regulator. Under certain conditions, these parts may fail and cause a loss of voltage "sensing" ability. If this happens, the generator output voltage will go to maximum.
This potential problem exists with most voltage regulator manufacturers. Once the sensing voltage is lost, the voltage regulator "sees" this as a low voltage condition. The voltage regulator forces the generator to try and overcome the low voltage condition in an attempt to bring the voltage back to normal. This causes the generator to switch to a full output condition and a possible overvoltage condition is created.
If the sensing is lost at the input of the voltage regulator, then the load connected to the generator output may be unable to tolerate the overvoltage condition. Suitable overvoltage protection must be provided to disconnect the load from the generator.
The following demonstrates a typical condition and response to overvoltage conditions for the VR3 Voltage Regulator.
Self-Excited Regulators (SE) (see Illustration 1)
Mode 1: Failure of any component such that the regulator "sees" a loss of sensing at lead 20 or 24.
Result: Output of the regulator will be shut off and the generator output voltage will be at minimum.
Mode 2: Failure of any component such that the regulator "sees" a loss of sensing at lead 22.
Result: The regulator will go to "full field" resulting in the generator output voltage going to maximum. This will normally result in a fuse failure (opening), turning off the regulator. If the fuse(s) should fail to open, the overvoltage condition will continue for approximately 12 seconds. At this time, the over-excitation limit built into the regulator will turn the regulator off.
If sensing leads 20 or 24 are lost, generator output will be at minimum for the VR4 Voltage Regulator ONLY.
Illustration 1. Self-Excited Regulator (SE). Droop transformer (CT1) and droop rheostat (R1) may or may not be supplied. The exciter field is L1.Permanent Magnet Excited Regulators (PM) (see Illustration 2)
Mode 1: Failure of any component such that the regulator "sees" a loss of sensing at lead 20, 22, or 24.
Result: The regulator will go to "full field" resulting in the generator output voltage going to maximum. This condition will continue for approximately 12 seconds. At this time, the over-excitation limit built into the regulator will turn the regulator off.
Mode 2: Failure of any component such that the regulator "sees" a loss of input from the PM exciter on leads 11, 12, or 13.
Result: If one lead is lost, generator output capability will be reduced. Generator output voltage will drop if capability is exceeded. If two or more leads are lost, generator output voltage will be at minimum.
Illustration 2. Permanent Magnet Excited Regulator (PM). Droop transformer (CT1) and droop rheostat (R1) may or may not be supplied. The exciter field is L1, the stator is L5.