Dedicated Bay Control Intelligent Electronic Device 3

[Mbrooke]

Why do some utilities, primarily those outside North America, choose to use a independent bay control relay separate from the protection relay?

Why not just combine the bay control and protection functions into a single 421 or 411L? Seems a bit redundant to utilize a 451 just for bay control while not enabling its protection functions.

 

[beyond86]

For example, we have a bypass breaker with the possibility to transfer any of HV lines through this breaker. When we take a main breaker of HV line in maintenance, we transfer HV line to bypass breaker and leave this HV line in service. All relay protection IEDs of this HV line change to trip bypass breaker by secondary switches.
So if we had combined BU and protection in one relay, we wouldn't able to leave the HV line in service.

 

[davidbeach]

One set of line (or transformer) relays that can trip the normal breaker or the substitution breaker is easily done. The SEL-4xx relays make that possible with just a couple of inputs to tell the relay which breaker (or both) is in service.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

@Beyond86: Do your relays allow for the control of two breakers? I ask because I think with modern relays a single protection relay can be made to control two breakers as David indicated.

FWIW I still see bay controls on systems with no substitution breaker scheme. Maybe its historic, maybe there is a reason.

 

[beyond86]

Do your relays allow for the control of two breakers?

Protection relays can trip two breakers (main and bypass), it depends on position of secondary switches, but each breaker has its own bay control unit.
Bypass bay has only one IED, which implements only control functions, not protection. But protection IED of each feeder can switch to trip bypass breaker instead of main.

 

[beyond86]

I ask because I think with modern relays a single protection relay can be made to control two breakers

Yes, but we have one bypass breaker and 15 main breakers for each HV line. Each HV line can be transferred to the bypass breaker.

maybe there is a reason.

The reason is that you can take each main breaker in maintenance and leave primary equipment in service. Or when a control IED of a main breaker is brake down, downtime of primary equipment is a minimum.

 

[Mbrooke]

So why not merge control and protection into one relay at each bay? Position switches tell the relay to either ignore or accept the bypass breaker.

 

[beyond86]

So why not merge control and protection into one relay at each bay? Position switches tell the relay to either ignore or accept the bypass breaker.

In this case, we have to mount secondary conductors from a bypass breaker to all protection devices of HV lines. Circuits of coil control, disconnectors control, SF6 control, etc. It demands additional cost.
And I have a question, for what purpose? It's the easiest to install one bay control device to a bypass breaker and mount a couple of conductors from a bypass breaker to protection devices of HV lines (trip coil 1, trip coil 2, 50BF start).

 

[Mbrooke]

Any schematics?

I think it would not be that much more difficult to run an extra CT circuit and a sync circuit through each rack. I can't picture needing to run the discos, that can stay on the coupler's relay.

 

[beyond86]

Any schematics?

It's local schematics, I added eng comment. It's a schematic of a main protection of HV line 220 kV.
CT circuits:

Trip circuits:

And these all connections with a bypass control unit.

 

[Mbrooke]

Thanks. But being honest an SEL-411L/421 would be much the same making things simpler over all.

 

[Mbrooke]

@Beyond86: Forgot to upload these yesterday, but they worth their weight in gold. They have absolutely revolutionized how I view M&T and the paradox which used to accompany it:

https://files.engineering.com/getfi...c343d243a616&file=Main_and_transfer_1_pap.pdf

https://files.engineering.com/getfi...c3785181125&file=Main_and__transfer_2_ppt.pdf

Great respect to the engineer and who discovered this and his contributions.

 

[davidbeach]

Seems vaguely familiar somehow...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

David, if you feel comfortable giving the author credit, I'd seize on the opportunity. Honor is granted even where the recipient feels humble.