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Join Date: Aug 2014
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Coorporation Between MV And LV System, Both Have ATS Function

08/05/2014 12:22 AM

Hi all,

I have been testing and commissioning an substation have following features:

- 6kV system: have two incomings and one buscoupler, auto transfer between 2 Incoming when one loses power

- 0.4kV system: have two incomings (from 02 Transformer fed by above 6kV) and one bustie, auto transfer too.

My question is how much time I should set for ATS relays in MV and LV system sothat they work reliably and predictability. Have you got any example for this system ?

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#1

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 1:04 AM

No I don't, and if you don't, you are in the wrong line of work.

How can you test and commission a substation if you don't know what you are doing?

Are you aware of any local and national codes that may regulate this?

Have you asked the local authorities?

Have you asked the insurance company who will have to pay for the deaths caused by your incompetence?

Have you ask the customer?

Have you asked your boss?

Have you asked the project engineer?

Have you asked your wife?

Have you no shame?

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#4
In reply to #1

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 1:58 AM

You don't? thats ok, thanks anyway

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#2

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 1:23 AM

I want the system with the bustier.

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#3
In reply to #2

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 1:28 AM

Many do.

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#5

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 2:03 AM

Now, time transferring between two incomings is same for both MV and LV

I still wonder when one MV Incoming lost, will ATS at LV system work or only ATS at MV work?

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#6
In reply to #5

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 2:52 AM

Ask for the Commissioning Plan/Record document.

Ask for training.

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#8
In reply to #5

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 9:16 AM

You really shouldn't have them the same, because if one source loses power, it will be a race to determine which one switches. You have to determine which is your priority - which one you would rather switch, MV or LV. You really don't need both.

1. If one transformer can both LV breakers' loads continuously, then just use the ATS on the LV side. Turn off the ATS function on the MV.

2. If you need both transformers each to carry their share the LV loads longer term (but one can handle the combined load short-term), then use the MV ATS function.

The time delay for switching when power is lost depends on how long you can stand to be without power, and how the loads handle the power. For example, large motors aren't going to like the power dropping out and restarting within a few seconds. You may want to switch after seconds, or after minutes. Depends on what your loads require.

If it's more complex, you need to hire a consultant to analyze what will happen on a loss of power (and restoration of power), and recommend appropriate settings to work for you.

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#7

Re: Coorporation between MV and LV system, both have ATS function

08/05/2014 3:20 AM

Could you test this?

In what case would both systems have to switch at the same time? Is it not more that they are separately secured with the ATS?

What could possibly go wrong even when they switch at the same time?

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#9

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/05/2014 10:09 AM

If you want a "bumpless" transfer on loss of power so that the downstream equipment does not shutdown/trip, the ATS settings should be the same timing on both 6KV and .4KV systems protection.

For instance:

The auto transfer at/on the 6KV system is looking at the incoming power, not the load side.

Therefore, if one of the primary feeds "incomings" to the 6KV trips/opens and the auto transfer operates correctly, the .4KV system should not ever see any loss of power and therefore the ATS on the .4KV system would not have cause to operate.

If one of the 6KV feeders to the .4KV system should trip/open, the .4KV ATS should operate so that the downstream equipment on the load side of the .4KV system does not ever see any loss of power.

Reason: The ATS for each system must operate independently so that because it is possible to have a loss of incoming power to the .4 KV system primary being fed from 6KV system without having a loss of incoming power to the 6KV system.

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#10
In reply to #9

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/05/2014 12:55 PM

It's probably not going to work that way. A lot depends on how stable the OP's MV supplies are - is he seeing regular voltage dips or drop-outs, or is it very infrequent?

The ATS needs to see some level of voltage drop to decide when to switch. Usually there is also some delay, to make sure it's not just a brief sag, but a real power loss.

If the ATS is configured to switch on a sag (voltage below ~90% nominal, for example), and this happens frequently (even once every few weeks), the MV breakers start racking up lots of operations quickly. They are designed for a finite number of operating cycles, and they could thus count up hundreds or thousands of operations a year. This puts a lot of wear & tear on the mechs.

If the ATS is set to require essentially a total loss of voltage (say below 50%) to cause it to switch, then the LV side will see a blink no matter what the ATS on the MV side does. You can't avoid it. The only way to get a no-blink transition is to switch immediately on a sag (assuming you can do it before voltage gets too low!) which gets back to the previous concern I brought up. The breakers would be switching back and forth all the time for any little disturbance.

What han't been defined by the OP is how sensitive his loads are, and what switching time requirements are necessary. Can he deal with a blink, or even a 30-second delay? How stable is his power source? How fast can his ATSs switch anyway? If they can switch fast enough, how often can they switch reliably before the wear on the ATS gives him problems? I could think of more questions, but you get the idea.

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#11
In reply to #10

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/05/2014 1:10 PM

Good points.

Hopefully the OP is still reading all of this and it triggers a nerve so that he (they) will entertain some advice from a competent system protection coordination service.

I keep wondering where the system operations philosophy documentation (if any exists) plays into these types of issues and questions.

Surely some competent person or group designed the installation and recorded the "directions" somewhere. Maybe not.

I just cannot make myself accept and embrace "winging it" or "Wagging" it when dealing with electrical or mechanical protection is so dangerous.

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#12

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/05/2014 11:54 PM

Just an idea to run past you all.

To give the priority to the MV, have the MV ATS block the LV ATS.

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#13

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/06/2014 8:03 AM

Thanks all,

I should set ATS in MV system is priority, time transferring in MV is shorter than that in LV and have signal blocks ATS in LV.

There are some MV motor fed by MV busbar, if I set time is 0.5s, is that ok?

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#14
In reply to #13

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/06/2014 1:14 PM

Typically, the motor undervoltage protection at MV level is set at 2sec delay. So, it is important to delay the MV transfer by atleast 2sec.

Further, if 0.4kV ATS delay can be set more than 2sec. it ensures that the ATS at 6kV and 0.4kV are coordinated well.

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#15

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/11/2014 4:51 AM

Somebody confused you. Any incomer failure in 6kV system, ATS ( or bus coupler) in the 6KV system will be ON depending on the Time setting, time required for operating the breaker motor. Similarly, any incomer failure in 400V system, Buscoupler will ON. I believe you have interlock between the 3 breakers( 2 incomers and Bus coupler). You can set the same time- no coorporation ( correct term is " coordination") required between MV and LV

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#16
In reply to #15

Re: Coorporation Between MV And LV System, Both Have ATS Function

08/11/2014 5:07 AM

Thank friend, my big mistake, it should be "coordination".

As your comment, yes we have interlock between 3 breakers, only 2 allowed to close in one time. And ATS function is only to close Bustie or Buscoupler once failure incoming been trip. Delay time is very transferring time I considered.

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