Why does SR469 Show 4000% Current Unbalance
Why does SR469 Show 4000% Current Unbalance
(OP)
I have three SR469's each feeding identical motors (250 HP, 575V). The current readings appear correct and visual inspection of the CT's appear correct (polarity & wiring - although wiring has not been confirmed by electrically tracing).
All three show current unbalance readings in the 2500%-4000% range. Any ideas what is wrong?
Voltages are approx. 612,608,610.
Thanks for any help.
All three show current unbalance readings in the 2500%-4000% range. Any ideas what is wrong?
Voltages are approx. 612,608,610.
Thanks for any help.





RE: Why does SR469 Show 4000% Current Unbalance
Seems strange to have such high unbalance readings since using the NEMA method of calculating you can only have a maximum of 100% unbalance (loss of a leg). Although, I never used these particular relays.
RE: Why does SR469 Show 4000% Current Unbalance
"Venditori de oleum-vipera non vigere excordis populi"
RE: Why does SR469 Show 4000% Current Unbalance
Must be a CT wiring problem?
RE: Why does SR469 Show 4000% Current Unbalance
You can also check the SR469 power and var readings.
RE: Why does SR469 Show 4000% Current Unbalance
One of 4 possibilities:
1. Fault in the primary circuit
2. Fault at CTs
3. Fault in wiring (between CTs and relay)
4. Fault at Relay
Number 1 is not a possibility, because it happens on three different places. Thus your fault can be either at the CTs, the wiring, or the relay. Because this fault occurs on three different places, it has to be a common problem on all the places.
What kind of scheme do you use on this relay? (residual connection, core balance method, etc.) And are there not a metering feature on this relay that shows the different line currents and the unbalance current? Many times, by just looking to these currents, you can almost guest where your problem is or what kind of problem you have.
The most common problems I have encountered on this kind of fault is wrong connections at the back of the relay:
Connected on the wrong place/location.
Connected on the wrong element (1A instead of 5A and vice versa.)
Also, if you have a connection/test block, makes sure it is bridged out at the correct places.
RE: Why does SR469 Show 4000% Current Unbalance
RE: Why does SR469 Show 4000% Current Unbalance
I believe the currents were relatively balanced (less than 1%). I will check some more settings and try changing the system phase sequence to ACB from ABC to see the effect.
Thanks for all the responses thus far.
RE: Why does SR469 Show 4000% Current Unbalance
RE: Why does SR469 Show 4000% Current Unbalance
RE: Why does SR469 Show 4000% Current Unbalance