Protective Relays

Thread Starter


Joined May 7, 2005
Hello, I am an Engineering Analyst working in the Power Generation industry. I work with various utilities in helping them improve the reliability of their plant. Recently I've been working on a project relating to Protective Relays. My question is, what has been your experience in Preventive Maintenance on Protective Relays? EPRI recommends testing/inspection of relays on a 4 to 8 year frequency depending on criticality and service. What do you find from your experience that the industry should be doing as far as maintaining Protective Relays?

David Bridgen

Joined Feb 10, 2005
While not having experience of protective relays I have recently retired from a working life in electronics.
It has always been said that the most unreliable of all components is the electro-mechanical relay. This makes a 4 to 8 year inspection/testing regime seem, to me at least, an inordinately long time. Neverthless, it is reasonable to make the assumption that the people who arrived at that figure were professionals in their field and took m.t.b.f. figures into account.


Joined Jan 22, 2004
hi dave,

me too, never haved any experience on protective relays, but i do deal a lot on relays. i have never come across that idea of a 4 - 8 year period and i totally agree that term is quite long for a heavily used relay or it's too short for a not so often used relay.

it has been my experieced that relays that has to handle 1A and by using a 2A relay does not stay long. so in practice if the current to be handle is 1A, i use 5A and as a results it stays reliable for quite a long period. :p

Erin G.

Joined Mar 3, 2005
The reason the time period is so long in a power plant is because most power plant equipment that's being protected runs for 15 to 22 months at a time. If you think about it, you can not shut down a boiler feed water pump to test it's protective relay without shutting down the boiler the pump is feeding water to. That in turn would shut down the turbine that the boiler is providing steam to. And that would shut down the generating unit that the turbine is spinning.

Protective relay testing is usually last on a planned outage list, because the protective relays only actuate once every year or two in this environment.

When I was in manufacturing, the protective relays were tested at least every two years. These relays were likely to see more use, (trips or deliberate cycles were likely 2 to 3 times or more per year) due to the different operating environment.

I think that the varous industries test on a schedule desinged to meet the demands of the equipment application.