Medium Voltage Breaker Operation

[kingtutley]

I am a relatively recent grad and am still trying to learn what I assume are basics of the power protection systems in fossil power plants.

I am working to gain an understanding of the operation of LV and MV switchgear/breakers etc. I have manual from Schneider that I downloaded from their web site, but I just don't get it.

Attached is a page that shows what they say represents the typical control circuit scheme. This makes no sense to me. If I read this right, then the breaker won't stay closed.

Looking only at the Trip Circuit in the middle, the 2 52a contacts should close when the breaker is closed, right? Well, this charges the 52/TC (Trip Coil). Won't this trip the breaker? What did I miss?

Aside from this, according to the manual, the 52Y coil (Anti-Pump Relay) is supposed to keep the breaker from pumping open and closed if there should be a trip signal when the close circuit is energized. What? Again, if I read this right, the close coil will be energized, and close the breaker, only if it is open (52b contact in series), and the springs must be charged (52LS) and latched -- which means that it is ready to operate (52LC). But if the breaker has ever been closed, then the 52Y coil will ALWAYS bee charged (aside from loss of control power) and hence wil ALWAYS prevent the closing coil from being energized. What am I missing? Am I just that far off?

 

[davidbeach]

What you are missing is all the external control circuitry. What you have is just what is in the breaker, there will be a fair amount of additional control circuitry that determines when the trip and close circuits become energized. Most of the time neither the trip nor close circuits are energized.

 

[burnt2x]

kingtutley,
Consider it this way;
52Y is an auxiliary relay of the breaker 52. When an "ON" command is sent via terminal #3, and all the closing interlocks satisfied (normally closed (NC) contacts 52Y, 52b, 52LS, 52LC are close), closing coil 52CC energizes and pulls the linkages of the main breaker to "ON" position. When the main breaker closes, "normally open" NO auxiliary contacts of the breaker 52a closes and activates 52Y. Auxiliary NO contact of 52Y relay holds the 52Y relay from dropping out (together with parallel contact 52a). At this moment, NC contact of 52Y parts breaking the closing circuit, almost at the same moment as the NC contact of the breaker 52b opens.
This setup prevents energization of the closing coil when the breaker is already "ON". Otherwise you'll burn the closing coil by turning the control knobs for a very long time.
Hope this comes crystal clear now.