METERING CHANGE OVER.

[apprenteng]

We do have a client metered on 11kV. The facility is fed via two 11kV lines, initially supplied via a single feeder,A. Feeder B was on stand by but could be connected to the bus via an airbreak switch when A had a permanent fault. A changeover using voltage as the actuator was used. Both lines are now energized upto the respective breakers on request by the client,and a manual change over is carried out to the other feeder when onegoes off. The facility has one meter and the utility is not ready to instal another meter. I am trying to come out with a new autochangeover for the VTs; I have parralled the currents from CTs on both feeders to the meter but I need to have an autochange-over for the VTs.

The tie breaker is ever on and using loss of voltage as a change over mode is not possible anymore since both lines are usually energized upto the respective breaker. I thought of using the breaker contacts but the utility may not allow this for the purpose of integrity,lest they steal power... The diagrams are attached. Any suggetions?!

Note: The incoming cable confuration was ahd to be modified as shown in the diagram for the purpose of phasing out with the clients loads.

 

[PUNGLU]

I agree with Scottty that no work is more important than human life....
But why not try this:-

Change the supply to the feeder on breaker A. Go the source of B and shift the cable terminations as below:

Y to R
R to B
B to Y

In doing this you shift the voltages +120 degrees according to your diagram.

You will not need to swap the CT secondaries now. You will now change the seondary connections of the PTs to match those of PTs on breaker A.U can then use one contactor with changeover contacts.

I believe the above can be done with the bus energized from feeder B since you will not open the CT secondaries

 

[waross]

My bad. I see that the CTs appear to be correctly connected.
Is there any common point to which the PTs can be connected?
I realize that you probably don't get to say, but I would use an electronic meter from ABB or GE. They are capable of being programed to store almost any value that they measure and/or calculate. I have received from the utility, a computer disk with six weeks of kilowatt and individual phase voltage and current values at 15 minute intervals.
The customer issue in this case was voltage trends. Could the transformer taps be safely dropped to a lower utilization voltage?
In your instance, in the event that a contact failed on one phase of your changeover contactor, the billing information may be closely estimated by the current trends and the voltages on the healthy phases.
If I was forced to "go outside the box" and introduce a contactor to a revenue metering installation, I would try to use this feature as a recovery back up.

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