AVR Question

Probably for cross current compensation. If two generators are paralleled, if the voltages are not set equal, reactive current flows between them. The current sense compensates for this.

http://www.pecplc.com/index.php/articles/control-of-synchronous-generators-with-droop-and-cross-current-compensation

Most likely for just a plain voltage regulator to allow the user to model the voltage at a remote point, without having to sense the voltage at that remote point. (Line Drop Compensation). The user adjusts based on line X & R estimates, or actually measures the voltage at the remote point while at some part or full load, and enters the impedance that gives them the desired voltage at the remote site.

Also, during fault conditions, it is desirable for a generator to produce enough current to trip overcurrent relays. If the generator has SCTs, saturable current transformers typical of a static excitation system (per above), these provide excitation during large current flows in the generator stator circuit (stator current transformed into large field currents), but probably not the CT circuits the OP is referring to.

It is possible on a machine with perhaps a rotating exciter, the field excitation could be boosted quickly (see field forcing) during times of large current and low voltage, to ensure you supply enough current to trip protective relays outside of the generator zone, in a timely manner. The generator overcurrent relays with voltage restraint (51V) work to allow this large current to be maintained longer if the low voltage associated with a fault is sensed. The faster the external fault is cleared, the less stress on your rotating machine

These items should be explained in the AVR manual, along with the methods to set up the appropriate adjustments that go along with the sensing circuits. It's quite possible that the need for the current compensation does not apply to your particular installation.

A block diagram of the regulator will show what those values are used for, perhaps in the technical manual you must ask for separately, often.

Are you talking about automobile DC generators (also known as dynamos)?

You haven't been back. Is it an automotive DC generator (dynamo) or something like a standby diesel AC generator?