low voltage main-tie-main

[jaime.A]

Existing system:
Low-voltage 480V/277 Switchgear with kirk-keys on the Main-tie-main. This system does not have an automatic transfer scheme.

New Design:
480/277 switchgear with main-tie-main and use magnum DS 3000A CB. I would like to implement an automatic transfer scheme, so which control system do you guys recommend I was thinking of using two SEL-751 relays.

I am under the impression that kirk-keys are used to reduce operator error and, in this case prevent paralleling the two feeders. Some circuit breakers have a lever to open/ close the breaker if a kirk-key is used in conjunction with automatic transfer scheme how would the system work if an operator needs to be present to physically unlock/ lock the kirk-key?

 

[waross]

The disconnects now safetied by the Kirk Keys would be replaced or left in series with mechanically interlocked contactors or breakers that are part of the Auromatic transfer switch.
You probably need two transfer switches, one on each feeder and both in parallel on the tie.
With that in place you may remove the Kirk Interlocks.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

I am not familiar with magnum DS 3000A CB. Some CB on the market have specially designed by the CB manufacturer flexible wire linkage with some simple interlocking mechanism mounted on the side of the CB chassis, between incoming 1-tie-incoming 2., where the CBs are placed side-by-side panels.
BTW: Any electrical interlock shall be implemented on the under-voltage release circuit, not on the shunt release.
Che Kuan Yau (Singapore)

 

[b_gibb]

Are you already planning to have the SEL-751s for protection purposes? If so, then they could do the ATS logic with no problem. If not, an SEL-751 for just logic purposes is an expensive solution.

Typically those low-voltage DS breakers come with integrated LSIG protection, no? Just confused about where the SEL-751 came from.

From the DS manual (page 31/68): "Mechanical interlock—A family of mechanical interlocks are available to interlock the closing of two or three Magnum circuit breakers The mechanical interlock holds one or more circuit breakers tripped (prevents closure) when others are closed A lever assembly is mounted on each breaker, which interfaces with the pole shaft and the tripper bar The lever assemblies are interconnected with either cables or rods, depending upon the relative orientation of the breakers Rods can be used only when the circuit breakers to be interlocked are vertically stacked Cables can be used for any orientation of the breakers Mechanical interlocks are available for both fixed and drawout circuit breakers, and in both two-way and three-way versions An illustration of a two-way cable interlock mounted on two drawout circuit breakers is shown in Figure 60"



ben
bengibb.ca
powerdesignerpro.com

 

[wcaseyharman]

I think there are almost an infinite number of control systems to use. The older gear I’ve encountered did it with breaker aux contact wiring and a timed delayed undervoltage relay.
This could be easily incorporated into a plant DCS system, a PLC, microprocessor relay or almost any modern intelligent device.

If it were me, and there wasn’t an associated PLC or microprocessor relay, I’d be tempted to just use a timed delayed undervoltage relay and some wiring.

 

[waross]

Over the years, I have learned by sad experience, that when there is a possibility of a line to line short due to mis-operation, you should have both mechanical and electrical interlocks. Some applications should have more than one electrical interloack.
I have seen almost every mode of failure, both mechanical and electrical.
I have more than once seen damage done that would have been avoided with a second electrical interlock.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jaime.A]

wcaseyharman and b_gibb you guys are correct about using a PLC I was overcomplicating things. Apparently, Eaton offers A PLC just for this scenario that integrates into their switchgear. To prevent user error, The DS LVPCB has push buttons, so maybe we can cover the on and off buttons and add a Kirk-key system for the covers.

 

[wcaseyharman]

We have some Eaton MV gear with their PLC performing an auto transfer function. Works fine as far as I know.

 

[waross]

Mechanical interlocks are available
for both fixed and drawout breakers, and in both two-way and
three-way versions

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

ASCO manufactures an LV main-tie-main transfer switchgear incorporating a manual bypass feature that enables maintenance of the ATS mechanism itself without interrupting the supplied load.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]