Phase to Phase votages in Metering 4

[jhonsom]

Do customers generally what to see phase- phase voltages (VAB,VBC,VCA) or Phase -Neutral voltages (VAN,VBN,VCN) in the Feeder Protection Relay Metering despite of delta or wye connected PT inputs ?

 

[davidbeach]

With wye connected VT inputs you can see either. With delta connected VT inputs there is no way of knowing the phase-neutral voltages.

 

[rbulsara]

Usually both are readable in digital meters. But phase to phase voltage indication is the norm (from the days of analog meters)

Rafiq Bulsara

http://www.srengineersct.com

 

[jhonsom]

Ya but what I want to know is it ok to show phase to phase voltage only despite of wye connected PT input to the relay. Is there customers who want to see phase to neutral voltages?
Sorry about wrongly wording the previous post.
We do over/under protection on both PP, PN like 27P,59P, 27PP, 59PP . I would like to know what is the significance of 27P, 59P or metering P-N voltages?

 

[davidbeach]

There are all sorts of voltage balance problems that can't be seen if only phase-phase voltages are available. Why try to limit what is displayed when the device is capable of more?

 

[jhonsom]

Could you please explain this in detail as I didn't think from that angle " There are all sorts of voltage balance problems that can't be seen if only phase-phase voltages are available"

 

[PHovnanian]

Think of a set of three phase voltages such that all of the phase to phase voltages are equal and offset by the requisite 120 degrees. But the neutral voltage is offset such that the phase to neutral voltages are not balanced.

The ability to observe this P-N voltage unbalance may provide the customer a way to spot an impending problem before it reaches the over/under voltage protection trip points.

 

[LionelHutz]

The customer also would not have bothered to install line to neutral metering transformers if they did not want to see those voltage. This requires 3 single phase PT's while an open-delta metering connection can meter phase to phase with 2 single phase PT's.

 

[waross]

The normal display is Phase to phase.
For protection and problem analysis phase to neutral voltages are often helpful.
In the old, old, ungrounded delta systems, voltmeters were sometimes used instead of lamps, or along with lamps for ground detection.
Bottom line, if the customer wants to check the incoming voltage, display phase to phase.
For protection and metering wye connected PTs and line to neutral voltages are often used.
Many display devices are capable of displaying more than one parameter. If you are using such a device, consider wye connected PTs and displaying line to neutral as well as line to line voltages.

Bill
--------------------
"Why not the best?"
Jimmy Carter