Direct Acting Trip Test on ACB

Can you supply a little more information please? Direct acting trip, do you mean manually-initiated remote electrical trip test of the ACB?

Not sure what PI test is either (its not Proportional Integral control), it sounds like a pulse tester but why do you want to pulse test the ACB in the first place? Are you trying to confirm the trip curve characteristics for yourself?

Io, Ir & Im settings, are these on the piece of test equipment you are trying to use? What exactly is the piece of test equipment and what is its purpose (this isn't a standard test maintenance that I am aware).

Direct acting trip is the thermal and magnetic element incorporated in the circuit breaker to trip the breaker in the event of an overcurrent fault.

The Io, Ir, Im settings are part of the Air Circuit Breaker. PI is Primary Current Injection test set used to inject a large current to simulate a fault current. Ir is the thermal trip and Im is the magnetic trip current.

Yes, you are right. Direct Acting trip test is not a standard test. Direct Acting Trip test is usually carried out on an Air Circuit Breaker which uses a shunt trip coil and external protection relay to check that it is functioning.

If you are trying to test the Air Circuit Breaker's trip characteristic curves (by injecting a set current and seeing if it trips in the required time) you are going to need copies of them for a start. If you don't already have them, get them from either the Air Circuit Breaker manufacturer's website or off the web. If you don't know what curves your Air Circuit Breaker has, check the manufactures documentation (it should be in there).

How is the Io, Ir & Im setting on the ACB related to each other and the In (nominal rating of the ACB)

As I said above they all add together to create a specific characteristic "trip curve" response (Time VS Current).

Try a google search of "trip curve."