GEC CDG16 Puzzle
GEC CDG16 Puzzle
(OP)
I have a problem trying to test the operation of a CDG 16 and similar relays on an teaching rack in our university. I do not register any current when I inject at pins 9 and 10. Before injection, I measure 0.8 ohm at these inputs which I thought would have been the relay impedance. On the drawing I see shorting contacts. How do they operate? Where are they? Is it possible that they have a connection with this problem. Or the relay coils are burnt? We have over 10 similar relays and they behave the same way. I have used similar relays elsewhere without problems. On the manual I also see a connection which looks like a thermocouple junction. If this part breaks, certainly no current will register. Please assist with all this.






RE: GEC CDG16 Puzzle
Do your relays have the setting plug on the front panel? If the setting plug is missing then you won't pass current through the relay.
Pull the relay from its case and measure directly on the rear terminals of the relay. You should be able to measure the coil impedance from there. Don't touch the disc!
RE: GEC CDG16 Puzzle
RE: GEC CDG16 Puzzle
There is a special test plug used. Often I dont have that. In order to isolate
the CT shorting mechanism, a Zip Tie (Tie wrap, cable tie), whatever it is referred as
can be used to open up the CT shorting, if the test plug is not available.
Stick that in it (opening up the automatic shorting link), may help, without disturbing the wiring.
RE: GEC CDG16 Puzzle
RE: GEC CDG16 Puzzle
Now the CDG 16 is totally outdated. Teaching how to test CDG 16 would not add good value to the students. The academic community should update themselves to match with the current trend.
Now the industry trend is to use microprocessor based digital relays. These are not that expensive for the institutes to buy on sample basis. May be the institutes get a special discount or free on promotional basis.
Hope I am not offending your institution!!!
RE: GEC CDG16 Puzzle
I disagree - the old electro-mechanical relays are a great teaching aid. The modern relays give absolutely nothing away about how they operate because modern relays replicate the functions through mathematics. I'm not arguing that an electro-mechanical relay is a better relay than a modern numerical type, only that they are a lot easier for a student to get to grips with the concepts because they can see it in front of them.
RE: GEC CDG16 Puzzle
Depending on the plug selected and the relay's burden, some test sets will fail to produce the current.
And I agree with ScottyUK. We train new staff with a CDG at first so they can visualise what a modern relay does.
RE: GEC CDG16 Puzzle
While I have no interest in ever installing another electromechanical protection relay, I have great admiration for the gurus that figured them out. The numeric relay requires a computational infrastructure, but once you have that any calculation can be performed. But to figure out how to make an impedance element, supervise it with a directional element, and then put three phases (or three zones) worth of that in a single case took some really outstanding engineering.
RE: GEC CDG16 Puzzle
I have a book written by a guy named Kaufmann who was employed by Metropolitan-Vickers, which became GEC many years later. It might be an interesting read for you if you are interested in the history of our industry and the old ways of doing things. http://www.amazon.co.uk/The-Protective-Gear-Handbo...
RE: GEC CDG16 Puzzle
RE: GEC CDG16 Puzzle