Safe Bus motor transfer scheme

[jhonsom]

Please help me with your experience of which is the safest schemes for safe bus transfer among for critical load power plant:

residual voltage transfer, slow transfer, in- phase transfer, parallel transfer , fast transfer, etc...

Also tell me the didadvantage of fast transfer, our relay has the capability talk to each other over communication protocol.

 

[electricpete]

Fast bus transfer shifts among supplies quick enough that there is not time for the motor to drift out of phase.

Slow bus transfer calculates time for voltage to decay to 33% before reclosing (or some other means to prevent exceeding 133% voltage difference with incoming line)

Parallel transfer I assume means you parallel energized supplies (which are known in-phase). That seems ideal.

Residaul voltage transfer?
In-phase transfer?
What do those terms mean?

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[ScottyUK]

You could try Googling 'fast bus transfer' and doing some research first. There are a number of companies making fast bus transfer relays and in amongst them are a few cautionary documents and the occasional tale of 'when it all went wrong'. You really need to define what you mean by 'safest' too: most likely to successfully transfer; shortest transfer time; least likely to take out the alternate source feeding into a fault; etc.

Here's one to start with:

https://w3.energy.siemens.com/cms/u...plicationNotes/Documents/TechTopics11Rev0.pdf

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If we learn from our mistakes I'm getting a great education!

 

[dpc]

The "safest" method is probably to shut down all the motors, de-energize the bus, do the transfer, re-energize and re-start all the motors.

Residual voltage method is generally safe, but it means all the motors basically shutdown and have to be re-started.

Fast bus transfer is a complex subject and will depend on the application, motor sizes involved, nature of the process, and many other variables.

In addition to the link Scotty posted, you may want to look here:

http://www.beckwithelectric.com/main/products/syncromaster/motorbustransfer/mbt.php