Transformer secondary Settings

[victa1288]

I am dealing with a ulitity company. I am doing a coordination settings for a pump station. Utility company is doing their own settings. They insist on using instantanneous settings for SEL587(Secondary of transformer). But their settings would make trip the whole pump station, which is not coordinated with downstream. Their argumanet is, they have to trip the transformer at a lower fault level as soon as possible to protect the personel because of arc flash. But nomally nobody is there. What can we do with this?

Thank you.

 

[davidbeach]

Are they tripping instantaneously on overcurrent or are they tripping instantaneously on transformer differential? The differential is inherently selective and can trip instantaneously without any loss of coordination.

 

[dpc]

Normally the transformer primary overcurrent element can utilize instantaneous protection that is set slightly above the maximum secondary fault current. This does not cause any coordination problems. But use of instantaneous on the secondary overcurrent protection generally doesn't coordinate.

I'd probably double check to make sure they are talking about instantaneous on the secondary overcurrent element.

 

[stevenal]

The 587 is a transformer relay that includes differential and over current elements. As Davidbeach said, there is no coordination issue with differential. If they want instantaneous over current, I would suggest using a switch to enable the element whenever live maintenance is performed.

 

[victa1288]

they are tripping instantaneously on overcurrent.

 

[dpc]

Primary current or secondary current? Your OP said secondary but just wanted to confirm since primary would not be a problem if set correctly. High-speed tripping on the secondary would be a possible problem, as you surmise.

 

[l3city]

victa1288: "But their settings would make trip the whole pump station, which is not coordinated with downstream"

How far is the Utility Co involved?? Are they involved up to or after the secondary design? Usually Util Co. is responsible up to the primary and the transformer. After the XFMR, secondary side, it's up to the contractor. I don't know your specific details, but set-up your limits with the Util. Co., and don't let them tell you what you do with your design (of course, just to mention, and as you might know, you will be responsible for all electrical after the XFMR sec. side)
regards

 

[victa1288]

It is secondary current.

Utility transformer is only 50m away from Switchgear. I am involved only in seconday design so I am responsible for the secondary of transformer.

 

[l3city]

victa1288: "I am involved only in seconday design so I am responsible for the secondary of transformer"

Ok, Is the Util. Co putting its hands on your design side?? Who is deciding to install this "tripping" device, you or the Util company?? Are this requirements suposed to be met according to the Util. Co manual/code?

If any problems in the future who's gonna fix/pay it, you or the Util. Co.?

victa1288, you wrote: "Utility company is doing their own settings." who is the designer here?? I'm confused now, but as I previously posted, make sure who is going to take responsibility/liability, and proceed.

 

[stevenal]

The '07 National Electrical Safety Code is now shipping. Included now for the 1st time are arc flash exposure rated PPE for utility workers. This may be their attempt to conform to the new requirements. The simplest method to coordinate most of the time while minimizing exposure is to install a maintenance toggle switch as I suggested above. Another possibility is to extend the differential protection zone to the switchgear.

 

[victa1288]

I3city, You' got the point. Util. Co does the settings so if there are any problem, they are going to fix it.

Stevenal, I will suggest them to install a maintenance toggle switch in order to coordinate most of the time while minimize the arc flash exposure to Utility workers.