Pringle swiches

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laidman

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We have a 3000A Pringle switch that is about 40 yrs old. We are getting what appears to be nuisance trips. I believe the switch needs rebuilding as the indicator shows fault even when the switch is closed. I'm wondering if there is a fault on the system tha is not large enough to trip the switch or if the switch is bad. Also can someone tell me the minimum fault curent needed to trip the switch.
Thanx
 
Re: Pringle swiches

I had a problem with a Pringle switch and I am going to pass on to you the solution.
When we had a very damp day with a lot of moisture in the air, sometimes a fuse would blow on one phase. This was a 600 volt, 3-phase 600-amp. switch.
I had the men check the load side wiring with a 1000 volt megger, but they could not find any bad readings to ground, or shorted across phases.

The first-line supervisor wanted to use a hypot tester to find the problem, but I would not allow him to use the hypot, my feeling is that the hypot can be a destructive test.

Well one day, when I was not available and a fuse blew, the first-line supervisor used the hypot tester on the Pringer switch load side wiring, and he found the problem. The switch was mounted on a slate material. When he applied a high voltage,(and I do not recall what voltage level that he applied) he found on the slate a track of current going to ground. And this was our problem. They dug out the burnt track in the slate, and sealed it with an insulating glyptal. They were able to put the switch back in service and then he ordered a new slate for the switch. Moral of this story, we would never have found the problem with using the megger. I am thinking now, if we had used the 5000 volt megger, would we have found the problem initially.
 
Re: Pringle swiches

The problem did occur on bad weather days but the switch is located in dry room with no sign of moisture. But this could be a down stream fault due to moisture. On one 400A feeder we do show 3.3A on the ground but this shouldn't trip the switch. thats why I was asking what the minimum fault was to trip the switch.
 
Re: Pringle swiches

the pringle switch is just that--a big knife switch! it has a trip coil that will open it up when it recieves a voltage from the control section of your switchgear. general electric--ite--square d, etc.. if you have ground fault protection, this can trip it. if you blow a fuse it will trip. there can be other trips incorporated depending on the specifications. the manual trip is mechanical and pushed a bar to release the switch.

i have replaced six of these switches in my career. the biggest problem is they are not "maintained"! the manufacturer recommends it to be serviced every seven years. at this time it is de-energized --- cleaned---lubricated---operated--and the trip setpoints are checked and operated! the last one we replaced was actually stuck in the "closed" position! the original lubrication had hardened around the blades to where they were stuck! it had never been operated since it fed the emergency distribution panel. for liability reasons pringle will not sell just the operator without the blade portion of the switch. one building engineer had no knowledge of how they operate -- how it requires ratcheting the handle to close -- and was panic stricken when it didn't close and kept turning the handle past the stop until he snapped the handle off in his hand! the machined bolt isn't very big. the instructions are posted on the front--but he never was exposed to actually operating a main prinkle breaker. for this reason, when working in on switchgear where we need to close a main-- i always try to get the building engineer to close it.

we also had a 4000 amp unit come apart when we attempted to close it after replacing a blown up bus duct. for alienment reasons the knife switch is driven by a rotating ball assemble. this sheared off. we had to call the power company to shut down the vault--then we closed the switch by hand -- then re-energized the vault. we tied a rope around the switch with a 2X4 ten feet away so it could be opened in an emergency. this was our disconnect means until the switch could be replaced.
 
Re: Pringle swiches

You are so right the most important thing to do is have the pringle switches maintained serviced. Most of the time when something happens it's to late and the switch needs to be replaced.
Think about it how often does the switch operate.Then when something trips it and you can't reset it. I had the problem and had to replaced two 3000amp switches in the building. The owner took my advice and started having the switchgear serviced every year.
 
Re: Pringle swiches

I have also changed out many pringle type switches based on inadequate maintenance performed. Contact resistance problems, lubricant seized not allowing switch to open. But the ques. with the ground fault most of them have a zero sequence type sensor. verify the setting on the relay and use the manufacturer's testing recommendations and inject current through this sensor to verify that it is within specs. Depending on loading this could be set too low or not tripping in the correct time setting. Be careful on the trip delay because of the arc flash hazards But this would rule out nuisance trips based on problems with the ground fault system. Also dealing with pringle switches recommend DLRO testing and infrared once a year at least.
 
Re: Pringle swiches

Thanks guys we have arranged for maintenance. But it may too late. We have been in the building for two years and have no records of any service on the switch. for all we know it has'nt been checked for forty years.
 
Re: Pringle swiches

consider maintainance also insures that the switch blades fully engage on a "close" operation.
as we have found with infrared scanning, a switch that only closed about 60 per cent of the blade contact surface causing exessive temperatures on the contacts! this can also happen on disconnect switches that do not get operated.
 
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