A couple of general questions about Power Monitoring the AC input on a DC Drive.

[bdn2004]

A power monitor was installed at the locations shown on the attached schematic.

1) Would it have made any significant difference had the CT's for the power monitor be installed on the line side of of the line reactors that feed into this drive ?

2) The power monitor voltage recording gives the voltage in Volts to Neutral on each phase. This is a three-phase load with a three-phase 3 wire service. There is no neutral connection. Why do we get that result ?

 

[Compositepro]

What result?

 

[waross]

The first question is why are you looking at the power quality.
The answer to that will determine where in the system to connect the meter.
Connected as shown will show the power quality of the bare drive.
Comparing that with a connection at the other side of the reactor will show the effectiveness of the reactor.
You may be concerned with the plant power quality for the sake of compliance with utility power quality limits.
In that case, the meter should be connected at the point of common coupling. That is often the main incoming service.
If you have primary metering the connection becomes more challenging.
The transformer will act as a filter. However if the power quality is acceptable on the secondary of the power transformer, it should be acceptable on the primary side.

The missing neutral.
Many plants are fed from a grounded wye transformer.
If that is the case you may use ground as a neutral connection.
WARNING. THE NEUTRAL MUST BE CONNECTED FIRST AND DISCONNECTED LAST.
AN OPEN NEUTRAL MAY RESULT IN LETHAL VOLTAGES.

If your main transformer uses a delta secondary or an impedance ground, we can give you a method of developing an artificial neutral.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

The CT location will make no difference in the current readings.

The voltage readings are possibly a setting issue. Do you mean you didn't connect the neutral on the logger or that the logger doesn't have a neutral terminal?

 

[bdn2004]

We are measuring the power usage of this dc drive over a week's time. It's not energized when it's installed or when it's removed. And it's inside of an enclosure.
And that's right, the neutral terminal on the logger is not connected. Should it have been connected to the cabinet ground?

It makes sense the current is the same either of the series connection. I'm aware there will be a voltage drop.

The incoming voltage is 480V, 3-phase, fed from a bus duct bus plug that is ultimately fed from a 480V, 3-phase, Delta-Wye solidly grounded transformer in a unit substation.

 

[LionelHutz]

I would ground the neutral terminal of the logger.