PLATE 4343868 - Caterpillar

Illustration 1. Large frame SR4 generator.
Illustration 2. Small frame SR4 generator. Earlier AVR's
Several types of AVR's are used on large frame SR4 generators. Originally, all large frame SR4 generators used either the large self excited AVR, shown in Illustration 3, or the large permanent magnet excited AVR, shown in Illustration 4. Detailed service information for these ARV's is available in SR4 Generator Service Manual, Form SENR2180-01.
Illustration 3. Large self-excited AVR used on large frame SR4 generators
Illustration 4. Large permanent magnet excited AVR used on large frame SR4 generators.The large AVR's are designed to cutoff excitation if an abnormally high excitation current continues for 10 seconds. This causes the generator to stop generating voltage. A problem with earlier self-excited AVR's is that the AVR would reset itself when the voltage fell to zero. This would cause the generator to start generating voltage again until high excitation current would stop the generation again ten seconds later. This cycling would continue until the fault or overload condition was corrected. The large permanent magnet excited AVR did not have this problem. An improved large self-excited AVR was developed to prevent the voltage cycling during a fault or overload.
Improved Large Self-Excited AVR
The improved large self-excited AVR has a new M3 circuit board and K1 circuit breaker. When an overload or fault causes high excitation current for ten seconds, the K1 circuit breaker is tripped and the generator stops generating. The K1 circuit breaker must be manually reset before the generator can be brought back onto the line. Detailed service information for this AVR is available SR4 Generator Service Manual, Form SENR2180-01.
New voltage sensing transformers, T1 and T2, are also used in the improved large self exciting AVR. The new transformers are more reliable because of improved transformer construction methods.
Illustration 5. Improved large self-excited AVR. Small Self-Excited AVR
The small self-excited AVR is now used on all 580 frame and 680 frame self-excited SR4 generators. See Illustration 5. It has single phase half wave regulation. Detailed service information for this AVR is available in SR4 Generator Service Manual, Form SENR7968-03.
Illustration 6. Small self-excited AVR used on 580 and 680 frame size large frame SR4 generators. Remote Mounted Voltage Level Adjustment Rheostat
The large SR4 regulators require a 1000 ohm remote mounted voltage level adjustment rheostat. If a lower resistance value rheostats is used, the generator voltage will be too high. For example, if a 500 ohm rheostat is used, a typical 480 volt generator will regulate at 485 volts minimum.
The small SR4 regulators require a 500 ohm remote mounted voltage level adjustment rheostat.