Metering functions in the Digital relay Vs dedicated multifunction meter in the Incoming Mains 1

[NickParker]

My colleague and I are discussing the need for a dedicated multifunction meter that displays parameters like voltage, current, kW, kWh, kVA, kVAR, etc., on the incoming mains of the switchgear. He argues that since it's not tariff metering, operators can simply refer to the digital relays installed in the switchgear. I believe that having a dedicated multifunction meter would allow even non-electrical trained operators to easily monitor these parameters.

I’d appreciate input from the forum on this matter.

 

[cranky108]

We have had the same discussion. And what came from that is some non-electricals don't feel comfortable pushing buttons on the relays, but during switching they need to see current go to zero to indicate an open breaker.

 

[davidbeach]

Relay displays can be set to show the metering values, rotating from one set of values to another all without any button pushing. It's also, ultimately, irrelevant what values the multifunction meter shows, what's important is what the meter is seeing. Usually they're the same thing, but sometimes one is wrong for some reason. If the MFM is wrong, people can panic needlessly, but if the relay is wrong there's a problem that needs to addressed immediately.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[catserveng]

I have done quite a few retrofits last several years where having ability to read metering off the protective relay is desired.

To Cranky's comment, yes, most folks not familiar with the relays don't want to touch them, a pretty simple solution since just about all newer protective relays have communication options, is to just mount a remote small HMI panel in a local safe location that displays the desired parameters. A remote panel is a pretty cost-effective solution for most applications, and pretty easy to implement.

At a number of facilities I have worked at we have taken the relay data to a plant monitoring system, again using the relays standard comms protocols in most cases. I have a personal like about this since as a service guy I don't know how many times I have come across relays that the plant thought was fine because the breaker was still closed (and it's been a lot over the last 10 years), but the relay was disabled. Using the relay for metering data and getting some basic operating parameters from it help assure you know the relay is actually working.

I don't like dedicated multifunction meters for a couple reasons, David's comment is spot on, a lot of trouble calls done when the meter reads different than something else, most times it is a very small amount off but to some folks any variation can be alarming. My main beef with adding another meter is most times it isn't wired thru a test switch, so if it fails or needs to be worked on, you have to take down critical voltage and current sensing circuits to fix it. Also a lot of switchgear these days has a lot going on at the back of the door, do you really need another device and associated wiring there?

My big selling point for this issue was safety, a lot of folks in a plant aren't technically "qualified persons" and shouldn't be too close to live switchgear in operation, especially in the current 70E environment.

So, I think being able to read metering data safely from the protective relays is a real benefit to most operations, my 2.5 cents worth.

MikeL.

 

[cranky108]

We also still use a syncroscope meter, where it is difficult to display on the relay the moving angle.

 

[bacon4life]

Although many relays can be set to scroll through metering values, the font size and screen brightness often require standing within arms length of the relay in order to be able to read the screen. Separate multifunction are often readable from the far side of the control room and well outside the arc flash boundary.