Impedance of Circuit

How can I measure the impedance of the circuit which is supplied by either generator 1 or generator 2 under full load condition?

www.keysight.com/used/us/en/knowledge/gu...to-measure-impedance

I need to ask you as to "why" you need to accomplish this?

I have never seen this done in a flight line environment. 

Do you have problems with an aircraft?

I don't know if Boeing has any special testers for this purpose. 

I believe some failure modes of constant speed drive maybe attributed to unacceptable impedance of the supplied circuit

Let's reevaluate this one.

I still like to know what's happening with the aircraft????

By impedance, we're just talking resistance in a A/C circuit. CSD's (or generators) output 3 Φ alternating current at 115VAC and 400Hz. This output is monitored by both the GCU (Generator Control Unit) and the BPCU (Bus Power Control Unit). Voltage and frequency are two aspects, but current load plays a huge role as to "if" the generator is allowed on the the A/C distribution bus. CT's (Current Transformers) monitor both the output load and user load on all three phases.

If either the Volts/Freq's falls out of tolerance or a differential load is sensed..... the CSD is disconnected from the bus. Usually when this happens, the GCU will kill the field input to the generator. All output from the generator is stopped.

The BPCU should record the actual fault in BITE Memory (Built In Test). When fault history is reviewed, the actual propblem should be known.

Impedance load would be sensed as a load imbalance. This could be caused by a short to ground or open phase (high resistance). Either one will trip the generator off.

Is the generator falling off line? Does it fail internally requiring replacement? Are you sure voltage/freq sensing is good. Is one of the CT's failing?