Bus bar differential protection for the 11kV power plant main switchboard using sensor type CTs

[krisys]

One of the reputed European vendor is proposing sensor type CTs for the bus bar differential protection in their new switchboard. This is the main switchboard in the power plant. However my end user has some reservations on using sensor type CTs, as these are not proven. Since this is the heart of power generation system at site, the end user does not want to take any chance.

In this context, I would like to hear the experience and views from my fellow panelist. Looking forward for your valuable feedback.

 

[dpc]

No experience, but GE (now ABB) in US has offered something similar in their low voltage switchgear for several years. Personally, I'd be inclined to stick with conventional CTs and relays unless there is an significant cost advantage to the "fly by wire" system.

 

[krisys]

Thanks DPC.

The Switchboard in question here will be from ABB, Czech Republic.

Few more experiences would be appreciated.

 

[FreddyNurk]

I can't claim much in the way of operational experience with them, but they have been around for a while now. One of the MV switchboards on a project I was involved with came with them and associated protection relays, all from one OEM, although that was over 10 years ago. That site was only really operational for a couple of years so no long term perspective on them. I am, of course, presuming that you're referring to the Rogowski coil style of sensor.

They have a number of advantages and a few disadvantages when used as portable test equipment, to be honest I'd be happy to use them for a new installation, provided I can get the associated relays and equipment suitable to use them.

EDMS Australia

 

[krisys]

FreddyNurk (Electrical),

Thanks for your valuable feedback (positive). Yes, it is Rogowski coil.

I don't know whether any one has any negative feedback on the Rogowski coil based bus bar differential protection.

 

[davidbeach]

So, if real CTs are known to work, why experiment? Are they paying you to participate in an experiment? Are they willing to provide one system with real CTs and one with their sensors and compare the two over some extended period of time? No doubt there's something out there better than the conventional wound CT with its known issues, but are you saving enough money to gain a payback if you experiment with their next generation approach and don't have a backup? For the typical Protection Engineer there's a huge difference between doing the same again, and trying something new. We're much more likely to get pushed into doing something new than to get pulled there by attractive new features. Good, bad, or indifferent, nobody wants serial number 1, nobody wants a new gizmo. Sure, put the gizmo in, in parallel, at the manufacturer's expense, to see how it would perform vs. the normal approach. But nobody pays a Protection Engineer enough to make a radical change. Work slightly better comes well after the requirement to catch everything the present approach catches.

 

[stevenal]

What do you mean by sensor? Rowgowski coil? If so, I’d say they were proven. Also might avoid saturation problems of low ratio CTs.