Fast Bus transfer in the power plants

[elecpl123]

Hi Guys,

Can any body give the details of fast bus transfer in the power plants(Unit Incomer &station Tie).my questions are
1.What should be the time duration of tie bkr closing when the unit incomer going to trip.
2.Undervoltage trip for the motor fedders in the Unit board

 

[dpc]

That would take a lot of explaining. I'm sure there are some good resources on the Web. Basically the goal is to transfer sources so quickly that motor residual voltage keeps the bus voltage up and motor starters, relays, etc do no drop out.

Generally the close and trip commands are initiated at the same time, or very nearly so. Or the trip signal is sent via an early opening or closing breaker aux contact on the closing breaker.

As for undervoltage tripping of motor feeders- this is not much used in the US.




"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[davidbeach]

Beckwith makes a relay to control that whole process; perhaps a read through of the manual would provide many answers, including answers to questions you don't know you have yet.

 

[ELEP]

We provided ABB's HSTS(High speed transfer system)'SUE 3000' system which makes it possible to obtain transfer times equal to 100 ms with the use of all conventional circuit-breakers.

With HSTS system for three circuitbreakers(Unit, Station & Bus-tie): when the loss of voltage in one of the two power supply units is detected, the closing command of the bus-tie and the opening command for the switchgear unit without voltage are launched simultaneously.

 

[ScottyUK]

Simultaneously? No wait for confirmed open of the dead source before initiating closure of the bus tie? Sounds like a good way to drag your good source down by feeding into a fault if the breaker fails to open. Of course ABB make perfect breakers so it's not really a problem, all perfect except the ones they supplied to our plant.


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

 

[ELEP]

ofcourse there are many conditions to be verified to close tie-CB; loss of incomer voltage, incomer current, incomer CB aux. contacts etc.., even protective relays which blocks HSTS operation.

 

[rcw retired EE]

Beckwith engeineers and others wrote an IEEE paper "Make Automatic Power Source Transfers a Success for your Plant" (Industrial Applications Transactions March/April 2001) that covers this in detail.

It explains the pitfalls of undervoltage transfer initiation, closed versus open tranfer, and other issues.

There may be a copy on the Beckwith website. (I can't post my copy.)

 

[slavag]

Hi.
We was used also ABB HBT on the REC316*4 base.
Yep, possible option of very fast transfer, that means simultaneously command to open and close, but we cancelled this option, close command only after verification of open position of "faulty" CB.

In the old power plants, we was used a simple logic, NC contact of UAT CB via LOR NO contact is directly connected to the close coil of RAT CB ( ot bus-tie), normal time for full cycle about 120ms.

Best Regards.
Slava

BTW, undervoltage trip for the motor feeders is about 5-7sec with 0.8-0.85Un voltages

 

[ScottyUK]

Slava,

Waiting for a confirmed breaker open signal makes sense. Simultaneous open and close commands is a risky solution.


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

 

[ELEP]

ScottyUK;

Simultaneous, closing command for bus-tie and the opening command for incomer under detection of loss of voltage, under fault condition need to confirm CB open.

There is facility in HSTS, we can programme logic upon loss of voltage & under fault condition.
Under fault condition transfer time is of the order of 250ms.

 

[elecpl123]

hi Guys,
Thanks for all response,

My Questions are,

1.actually in my closing ckt of tie bkr in logic they have included the Sync Check Conditions( of UAT I/C synchronism check between Station line PT and Unit Bus PT Should be OK,what may be the reasons for this
2.what should be the time duration of this transfer

 

[slavag]

Hi Elecp123
Sorry, but you must firstly read manual of one of the type of HBT relay.
Please take in account, your "standard" SC function is "static" function:dU, df, dPhi.
HBT is dynamic function, it's "learn" residual voltage on the bus.

Time duration:...we had also about 500ms
Best Regards.
Slava

 

[rbulsara]

If it helps, most in-phase transfers like automatic closed transition switches (only sync check, not active synchronizing) are designed to complete the transfers in 100ms. This accounts for up to 50ms of opening one source and up to 50ms for closing the another. This are unintended time delays needed for normal operation.

Most utility co. requires a backup protection to separate the two sources if the paralleling time exceeds 500ms but that is a long time. I set my back up protection to 300ms.