Incorrect CT Phase Angles leading to wrong power readings 3

[rockman7892]

We are bringing a new plant power distribution system online which is the reason for alot of my posts lately. I am a fairly new engineer who is trying to learn a lot of this stuff as it happens. I appreciate all of the help from this forumn.

On our main breaker we have a Multilin 750 protective relay, and a Multilin PQMII power quality meter. When looking at the currents on the Multilin, they are showing up strange for they are blinking between some current value and zero. I'm not sure if this is because I have a bad relay, or because of what I am seeing on my PQM meter which is as follows:

When looking at the PQMII meter I notice that I am getting negative kW power readings. I find this strange, so when I look at the current phasors they look strange as well. I know this negative kW reading is incorrect because I have another PQMII meter downstream measuring the exacty same load giving the exact same readings except the numbers are positive. This is why I am thinking that I may have a CT or a PT out of phase on the PQMII and ML 750 on the main breaker, which are both looking at the same CT's. Here are the readings I took off of the PQMII.

Voltge Phasors:

Vab = 4137 @ 0 deg LAG
Vbc = 4181 @ 120 deg LAG
Vca = 4172 @ 300 deg LAG

Current Phasors:

Ia = 27A @ 255 deg LAG
Ib = 27A @ 18 deg LAG
Ic = 27A @ 130 deg LAG

Three phase real power = -152 kW
Three phase Reactive Power = -130 kVAR
Three phase Apparant Power = 195 kVA
Three phase power factor = .74 LAG

I'm guessing that the CT's are out of phase with the PT's. Does this make sense?

 

[kanjanathep]

Hi rockman

How is going,have you already find out that wrong with multilin 750?
Have you already check CT,VT input of 750 and also from VT and CT to the relay input must be same phase(not wrong wiring).

jack

 

[kanjanathep]

One again,
For the correct operation of many relay features, the instrument transformer polarities
shown above in the Typical Wiring Diagram on page 3–8 must be followed. Note the solid
square markings shown with all instrument transformer connections. When the
connections adhere to this drawing, the arrow shows the direction of power flow for
positive watts and the positive direction of lagging vars. The phase sequence is user
programmable to be either ABC or ACB rotation.

good luck
jack

 

[rockman7892]

It turns out I discovered that the reason the Vca phasor was reading 300deg instead of 240deg was because there is an error in the PQMII meter that calculates this phasor wrong.

There was a firmware revision to correct this issue that was no implemented on my meters. So it turned out that it wasn't a wiring problem but rather an issue with the meter itself.

Just thought I'd share this with everyone who helped.

Thanks Again!