Open phase detection on distribution
Open phase detection on distribution
(OP)
Our system has an issue with detecting an open phase or an open phase with a jumper that swings down into the phase below it in our distribution system. The arrangement is a step down delta-wye grounded transformer in the substation that feeds a bunch of wye-ground-wye-ground distribution transformers in the field. There is a programmable relay in the substation, the distribution transformers are fused, and there is a mix mash of automated and comm. controlled reclosers in the field.
When I first was told this problem, my first response was to use negative sequence or a I2/I1 ratio to detect an open phase. The problem I am seeing with this is that if your jumper fails near the end of the feeder, you will have a hard time detecting an open phase with I2 or an I2/I1 ratio without making them overly sensitive. All the other transformers further up the feeder drawing I1 will make it difficult to see the open phase from the substation. Someone brought up to have the relay alarm on large step changes of negative sequence current. I don't know how well that works. Nor do I like the idea of having to investigate each arrangement to determine what a "large" step change is.
How do you guys go about tackling this problem?
When I first was told this problem, my first response was to use negative sequence or a I2/I1 ratio to detect an open phase. The problem I am seeing with this is that if your jumper fails near the end of the feeder, you will have a hard time detecting an open phase with I2 or an I2/I1 ratio without making them overly sensitive. All the other transformers further up the feeder drawing I1 will make it difficult to see the open phase from the substation. Someone brought up to have the relay alarm on large step changes of negative sequence current. I don't know how well that works. Nor do I like the idea of having to investigate each arrangement to determine what a "large" step change is.
How do you guys go about tackling this problem?






RE: Open phase detection on distribution
RE: Open phase detection on distribution
In our case the line has only a handful of transformers along it's length, and very little load.
In your case, a transmitter at the far end, and one, two or three recievers at the substation.
May not be your best option, but it is an option.
RE: Open phase detection on distribution
RE: Open phase detection on distribution
RE: Open phase detection on distribution
RE: Open phase detection on distribution
In the past, the plain old telephone system was the way to detect open circuits. In the future smart meters will fix it. In the present, we have not been able to widely apply negative sequence relaying on our distribution feeders due to a few factors:
-It is tough to keep feeders tightly balanced.
-Single phase switching between feeders or during cold load pickup appears as high negative sequence currents.
-Line to ground faults beyond delta-wye transformers look like negative sequence current.
RE: Open phase detection on distribution
The sequence network for an open phase is all three networks in parallel. I don't know what the network is for a jumper falling into another phase but I suspect it is similar. SLG would change some with adding an impedance to the ground. If the networks are in parallel for a jumper falling into a phase just like with the open phase network, the amount of zero sequence current flowing during this condition would be dependent on how Z0 compares to Z1 and Z2.
Where can I find the network for this condition? The Clarke transformation I thought could do this double contingency but I can't find the paper.