Protection Setting of Incomers with Bus Tie Breaker

I'd rather talk about bustiers instead.

This is naughty...er.... knotty subject. You really need to get hold of bustiers to understand the the hidden issues and get into intelligent discussion

You are so right! But I am so unrepentant.

By your own admission "you don't know how it works" so the best advice is hire someone that does know what they are doing.

Best you hire a professional to do this for you, if you don't know then it is likely you shouldn't be performing this sort of work. Is it even your responsibility or the responsibility of, say the senior plant Engineer/local electrical board?

Safety first, don't be afraid to say "I am not qualified and comfortable to perform this work we need to hire someone qualified to perform this particular work!

In some countries, house insurance is not paid out for amateur mistakes.....as you said, a professional and evidence of that are a requirement, such evidence could be a paid bill, paid by a bank transfer, not cash in hand to the professional.....

Just a thought, you said it right....

A question, what was he saying about ladies underwear????? Got me interested!! No wonder he posted Anon!!

<...don't know how does it work...>

One could always:

• Ask a colleague
• Read the manual for the equipment
• Phone the equipment supplier

Why was the relay set to 50% if each feeder is sized for 100%?

What are the actual settings now? Is this a 'song and dance' over nothing?

<...Gentlemen...>

Are other categories of person prohibited from replying? |:-(

"...how to change the relay setting?...", you don't. Why do you believe it should be?

"...there must be some sort of logic...", there is, but it is not yours. The logic is that the relay is set to protect the components that deliver the power (conductors, transformers, switchgear, etc.), not the equipment that utilizes the power (motors, loads, and other power consuming equipment).

"...i don't know how does it work...", correct, and under those circumstances you shouldn't be messing with it, instead leave it to those who do know. Walk away before you cause some real problems.

Dear ram,

The reason why I'm asking because I wanted to know the concept behind and my curiousity, of course the competent person would do the setting and coordinatin of protection system

1. "...how to change the relay setting?...", you don't. Why do you believe it should be? - If the setting were based on 50% load for both feeders, the unfaulted feeder would be tripped if it has to carry 100% load, or otherwise the setting usually is based on 100% load, is that correct?, but if the setting is based on 100%, the incomer wouldn't trip if overload occur (suppose one of the feeder breakers 51 unable to trip & unavailbility of 50BF function, bus-tie breaker open), what do you think in this case.

"...wouldn't trip if overload occur...", certainly you'll agree that if there's no overload at 100% load then how could the current carrying equipment be overloaded at 50% load since nothing has physically changed.

If you're still confusing equipment safety with overload protection I suggest that you read ramvinod's post again, then get a good book on breaker coordination studies for further information.

LOL!!

Also a great answer....lets hope he understands it!!

General concept of protective relay settings to protect the equipment. Let us say there is a feeder connects Main switch board and sub switch board through a cable. The relay setting has to be set based on the cable rating not on the load connected. In your case both the incomers A and B to be set for Busbar capacity or Incomer capacity. Even the relay at the tie breaker has to be set for the same rating but it can be set to trip faster than incomer at A and B. May be under normal circumstance the breaker A and Breaker B can carry 50 % of the load but the relay has to be set for 100% of the capacity.

I have seen relays with different group settings. Set up the incomer protection relays to monitor the bus tie and when it is closed it will use the 100% settings. When it is open, the relay will use the 50% settings.

What relays are you using?What are your voltage and current settings?What is type of Switchgear are you using.etc etc.
You're asking how to change the relay setting. Don't you have a manual at hand?
I suggest you either provide the missing details or well ask your immediate senior.
Regards,
MOQ

What a enthusiastic replies!

The basic concept, you many refer to the answer from #ramvinod. I think it is quite good and simple.

I wanna talk how to change over of A-T-B system in practical.

When normal bus (Inc. A or Inc. B) takes open due to fault/maintenance, Bus-T will be closed to supply power to dead bus.

Automatic operation, we call it ATS (Auto transfer switching).

Manual operation, we call it MTS (Manual transfer switching).

And the condition to activate the transfer is 27 (U.V.) normally but it depends on the decision from Owner/PMC (Engineers).

After clear all action (fault clear, done maintenance), you feel them back.

Let me talk one case as below;

Inc. A opened, Bus-T closed, Inc. B closed.

In this condition, you need to make them normal like below;

Inc. A closed, Bus-T opened, Inc. B closed.

For this, you may choose two action.

a. MBB (make before break)

To go to Inc. A and make it closed. Then after checking Sync with Inc. B, Inc.A becomes closed. After some ms, Bus-T will be opened.

b. BBM (break before make)

To go to Bus-T and make it opened. And go to Inc. A and make close it.

In 'a' case, Bus A is not be dead but need to see Synchronization.

This operation concept have to be discussed with Owner/PMC/Vendor. And there are various conditions and limitations.

I hope you consider it is one of the cases for your doubts.

Hope it help you.