Self-Powered Relay Limitations
Self-Powered Relay Limitations
(OP)
What are the limitations of self-powered relays?
We are pushing a vendor of our 34.5kV switchgears to provide 3A pick-up on ground faults with a self-powered relay. The vendor says that he doesn't believe one exists. If that is true, what is the reason?
I'm new to the company and I'm not directly involved (at least not yet) with the issue but I want to understand it better. I have some basic knowledge of relays but obviously not to this degree (at least not yet).
We are pushing a vendor of our 34.5kV switchgears to provide 3A pick-up on ground faults with a self-powered relay. The vendor says that he doesn't believe one exists. If that is true, what is the reason?
I'm new to the company and I'm not directly involved (at least not yet) with the issue but I want to understand it better. I have some basic knowledge of relays but obviously not to this degree (at least not yet).






RE: Self-Powered Relay Limitations
The limits are you don't have flexable curves.
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
Alan
RE: Self-Powered Relay Limitations
However, if this delay could skuew your curve enough to cause a coordination concern, look at the electromechinical relays.
Another concern is the elecrromechinical and solid-state relays operate a little different on the IOC units. And to think or it there maybe a difference in how the relays respond to harmonics.
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
But the questions is how do you intend to trip your breaker?
The capacitor trip is hard to find, other than the Basler unit. But the breaker needs to be sized for it (and the relay contacts).
Or is this a replacment application?
RE: Self-Powered Relay Limitations
Basically it was realized that the relay protection did not fully meet our desired pickup amp specification. We need a self-powered (or dual-powered) unit for safety reasons relating to our setup.
I understand the data collection advantages or maybe even a slight time advantage, what I'm having trouble understanding is why there is a difference in the pick-up amps between a self-powered relay or one with an external power supply. Is it an issue with CT powering of the relay at lower amps?
RE: Self-Powered Relay Limitations
RE: Self-Powered Relay Limitations
This may be a dumb question, but isn't it possible to power the relay using a CT or PT on one of the phase lines?
RE: Self-Powered Relay Limitations
However a PT powered relay can have a pickup setting much lower than a CT powered relay.
So a dual powered relay is one option. But if you are using a battery to trip your breaker, then consiter a DC powered relay. If you don't have a battery, then a CT or dual powered relay is required.
If you are using a capacitive trip device, then higher rated contacts may be required.
RE: Self-Powered Relay Limitations
Alan
RE: Self-Powered Relay Limitations
Our spec. requires a pickup between 3 & 10 amps for a ground fault. Where we were even getting ground overcurrent protection I believe it was like 50 amp pickup which is greater than the rated current let alone anywhere near the 20% mark.
RE: Self-Powered Relay Limitations
How do you manually trip it....electrically or with the manual spring release button?
Alan
RE: Self-Powered Relay Limitations
Is there no DC system? Is there no AC station service? Is there lighting in this building? If so, there's got to be a better way of powering that relay. I would not trust a charged cap to supply enough trip current for a breaker on intuition.
RE: Self-Powered Relay Limitations
Are you sure you don't have a standard cap trip device that is powered by AC to keep the unit charged and trip the breaker?
Alan
RE: Self-Powered Relay Limitations
Some relays (not of american design) can charge an internal capacitor from a CT alone. But given a large fault will charge the capacitor very quickly, and a smaller fault will charge the capacitor slowly, which I supose fits in with some relay curves.
RE: Self-Powered Relay Limitations
Guess there is always another way.
Alan