# OLd fashoined electrical principles question

#### efiste2

Joined Mar 22, 2009
3
New to the forum and i apologise if this post is in the wrong topic, I am studying a circuit from a Summation Transformer that is used in an aged HV protection relay system called SOLKOR, the summation transformer in my basic understanding compares a 3 phase output current/voltage of 3 bar primary current transformers fitted into HV switchgear, and induces a single phase voltage for the relay to act upon and to transmit down a pilot wire. Its probably a basic circuit for you chaps, but could anyone explain to me the role or any possible roles of the capacitor that the arrow points too. The circuit is fully AC and the capacitor is across the two terminals that outputs the single phase voltage to a pilot wire that is connected to a similar transformer and the other end of a high voltage feeder,

#### bertus

Joined Apr 5, 2008
21,674
Hello,

I do not know if it is a capacitor.
It could also be a spark gap. A device that draws sparks as the voltage gets to high.

Greetings,
bertus

#### efiste2

Joined Mar 22, 2009
3
Thats a very good theory mate,

#### thatoneguy

Joined Feb 19, 2009
6,359
It could be an RFI reducing X2 cap, does the single phase enter at this point, as in a motor starter, or is it tapped from this point, for monitoring? If it is the latter, the cap would be for interference supression.

#### efiste2

Joined Mar 22, 2009
3
The remote end voltage enters at this point, or the output leaves at this point, the system is a balanced voltage system and uses a circulating current in the pilot cables to trip circuit breakers at each end of the cable. so in theory the circuit the capacitor is in can have upto 5A AC flowing in it for a second. Im not sure on the RFI theory as its a very course protection and dates back to the early fifties and id be suprised if it had that much detail designed into it, but im not discounting it.......

#### thatoneguy

Joined Feb 19, 2009
6,359
I guess without knowing the value it's a bit harder. It is an LC tank circuit of sorts, something for a 3 phase motor starter?