Transfer Switch Application Design Question

[adamscb]

Forum,

I've been tasked to coming up with a transfer switch design that will feed an entire switchgear lineup in our plant. I wanted to take advantage of the expertise on this forum, and see what everyone's opinions are. See attached for a crude picture.

The load is below 400A, so that is what the transfer switch was spec'd out to be. I know that transfer switches are meant to be put in series with the circuit, so that when it senses that normal line power is lost, it will transfer to the generator. However, the transformer/switchgear combo is all one unit; copper busbar directly connects the switchgear main and the secondary side of the transformer. Obviously this poses some problems. So, a solution that I've been brainstorming is attached.

The transfer to generator would go something like this:

1. Throw down the 4160v switch on the primary of the transformer
2. Throw down the 400A fused disconnect and lock out
3. Attach generator leads to transfer switch
4. Start up generator (transfer switch should automatically transfer to generator)

The transfer to normal line power will go something like this:

1. Turn off generator
2. Unlock 400A disconnect and engage
3. Throw 4160v switch back into service (the transfer switch will switch back to line "normal" mode)

The 400A fused disconnect prevents the transfer switch from thinking that "normal" line power has been restored, thus preventing the transfer switch from switching back to "normal".

This is still in the early planning stages. We attach a generator to this switchgear during our annual shutdown, but we literally have to wire it in to the back of the gear itself. We want a transfer switch to make the lockouts safer and easier.

Has anyone used a transfer switch like this before? Thoughts? P.s. I'm aware that the transfer switch likely won't read the correct amperage - that's not a concern.

 

[adamscb]

Sorry guys the picture is pretty small. On the top left there's a step-down 4160v to 480v transformer (reading left to right), with a disconnect on the 4160 side. The yellow bar represents the copper busbar in the switchgear. The box is the transfer switch, with the line connection on the top (with a 400A fused disconnect in series). The generator connection is on the left side of the transfer switch, and the load connection is on the right side.

 

[Ingenieur]

I'd cut the bus bar to eliminate the parallel path
then it becomes a std automatic sequence/configuration

 

[ron]

Since the ATS could be manually transferred, you could end up in a situation where the utility and generator are inadvertently feeding the load bus. You would have to interlock in some way. But you have ruined the concept of an ATS, which you really just made a MTS (manual transfer switch).

Why not intercept the 4160V incoming and add the ATS there? Granted you would need a 4160V Generator or a 480V generator with a step up transformer, but then it is completely automatic.

 

[adamscb]

Since the ATS could be manually transferred, you could end up in a situation where the utility and generator are inadvertently feeding the load bus. You would have to interlock in some way. But you have ruined the concept of an ATS, which you really just made a MTS (manual transfer switch).

Why not intercept the 4160V incoming and add the ATS there? Granted you would need a 4160V Generator or a 480V generator with a step up transformer, but then it is completely automatic.

I would rather keep the transfer switch rated for 480v, and not spend the big bucks on a 5kV transfer switch.

 

[Ingenieur]

Cut the bus bar
you have to get in their to tap/drill it for connections anyways
simple, best method, cheap
depending on geometry you could mount the xfer sw on the backside outside wall between the genset and sg
stub in/out thru the wall and you are done