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TECHNICAL INFORMATION BULLETIN	May 08, 2002
Generators	SR4B (2DN1-1562, 2ED1-1770, 2FN1-1584, 2HN1-610, 2SN1- 701, 3FN1-1122, 5SN1-745, 5VA1-820, 5YA1-1201, 5ZA1- 775, 6DW1-1269, 6LA1-874, 6SA1-2391, 8FD1-749, 8NN1- 1034, 8XS1-522, 8ZD1-890, 9CN1-590, AAD1-502
	Component Code: 1404

SUBJECT: 5kV Class Droop Current Transformer (CT) that Is Installed on Certain SR4B Generators May Not Operate as Designed

PROBLEM:

The factory-installed droop CT's on certain 2400 volt through 4160 volt (medium voltage) SR4B generators may be marginal in VA size. SR4B generators that are marginal in VA size may begin to saturate at full generator load or may begin to saturate at near-full generator load. Caterpillar voltage regulator (VR) droop circuits that are used on SR4B generators utilize a 5 ampere secondary CT output that is converted to 5 volts across the 1 ohm droop resistor. This may result in the following:

An inaccurate reactive VAR when paralleling multiple generators
An imprecise PF (or VAR) stability when paralled to a utility source

SOLUTION:

Caterpillar has redesigned the droop circuit and removed the 123-6046 Resistor. In the medium-voltage SR4B generators, the 123-6046 Resistor has been replaced with a 204-3544 Current Transformer. The 5 kV CT's remain the same. The 204-3544 Current Transformer is mounted on the existing generator terminal DIN rail and is wired as follows:

Output wire 5 from the droop CT connects to the 204-3544 Current Transformer input terminal H1
Output wire 6 from the droop CT connects to the 204-3544 Current Transformer input terminal H2
Transformer output terminal X1 is wired to the existing generator terminal 5
Transformer output terminal X2 is wired to the existing generator terminal 6

From this point, the VR droop circuit wiring remains unchanged. The VR3 utilizes a 197-3531 Rheostat. The DVR and the VR6B are connected direct. See Illustration 1 for wiring details.

A parts kit (218-4827) will be available for the field retrofit for the 3500 product. The parts kit will include all of the components necessary to make the change-over as described above.

Utilization and set-up for reactive droop paralleling between generators is not affected by this change. Observe standard recommended proactices for proper cross-current compensation (CCC) wiring between the CT's. This change also does not affect the CCC operation.

Illustration 1. Wiring Diagram