How does one determine the direction of AC power flow?

I understand how you can measure voltage and current with simple
instrumentation, but this is AC and the average value of those
parameters is zero. How can you tell in which direction the power is
going?

Let's put this in the form of a puzzle: There are three adjacent soundproof rooms A, B, and C. You are told that only one of the following conditions is true:

1. There is an AC generator in A feeding power through open buss bars in room B to a resistive load in room C.

or

2. There is an AC generator in room C feeding power through open bus bars in room B to a resistive load in room A.

You are shut inside room B and are to determine whether condition 1 or 2 described above is true. Remember, the rooms are soundproof so you can't tell from sound leakage whether room A or C has the generator. Also since the load is 100% resistive, assume that the power factor is 1.

Questions 1. Can you determine the direction of power flow just from measurements to the AC buss bars in room B ?

2. What sort of instrumentation would you need?

3. Do you need to break the circuit to make the measurements?

Any takers?

Beachcomber

I understand how you can measure voltage and current with simple

Let's put this in the form of a puzzle: There are three adjacent soundproof rooms A, B, and C. You are told that only one of the following conditions is true:

1. There is an AC generator in A feeding power through open buss bars in room B to a resistive load in room C.

or

2. There is an AC generator in room C feeding power through open bus bars in room B to a resistive load in room A.

You are shut inside room B and are to determine whether condition 1 or 2 described above is true. Remember, the rooms are soundproof so you can't tell from sound leakage whether room A or C has the generator. Also since the load is 100% resistive, assume that the power factor is 1.

Questions 1. Can you determine the direction of power flow just from measurements to the AC buss bars in room B ?

2. What sort of instrumentation would you need?

3. Do you need to break the circuit to make the measurements?

Any takers?

Beachcomber