Transformer blown primary fuse detection using secondary 1

[JTG]

We have a problem detecting blown primary fuses on a main substation transformer. The primary has fuses only. The secondary side of the transformer has a circuit breaker with a GE Multilin 760 relay. We want an inexpensive method to look for unbalanced phase or phase loss due to blown fuses on the primary by utilizing the CT's and PT's on the secondary. At this point, we want to alarm as soon as fuses are blown. This would allow us to switch to another transformer and replace the blown fuses on the first unit. We want something inexpensive and to use existing equipment if possible.

 

[rcw retired EE]

Blown primary fuses should generate negative sequence voltages on the transformer secondary. The 760 relay has negative sequence current and voltage elements that could be set to detect and trip.

 

[alehman]

Open phase detection can be difficult depending on the loads. Motors induce voltae back on to open phases. Some types of transformers will produce phantom voltages on the secondary corresponding to the open primary leg.

Negative phase sequence voltage is good, but not 100% reliable. If there is load on the system, it is probably best to use negative phase sequence overcurrent (ANSI 46), incombination with under/over voltage (27/59).

Also see thread238-101093
and

http://www.basler.com/php/download.php?file=practical.pdf&id=204&type=res