Tagged: Cts. 85c. Stock Items.
This topic contains 4 replies, has 3 voices, and was last updated by Todd Lommen 1 month, 3 weeks ago.
What are utilities stocking for bushing and bar type cts. with a 85c temp. rating.
Is there something specific you’re looking for? We don’t do much in the way of bushing or slip over bushing type CTs but we do have some window and some bar type CTs in stock for both indoor and outdoor ranging from 7 up to 25 kv.
We are looking to standardize on just enough ct sizes in stock to suite our needs.
We go as large as 2500 kva three phase padmount transformers on our system.
Most of our installations are padmount and we use the slide on or bushing mount cts.
We fasten the socket most times to the secondary cabinet of the given transformer.
We size the ct for the full load output secondary amps of the transformer using the largest rating factor we can get at the 85c temperature rating.
If anything we may give up some accuracy on the light load end of things, at least that is our thinking.
Does everyone using bushing mounted cts in a padmount transformer have 85c rated cts? or staying at the 55c rating, or 30c rating.
BSE has a High Accuracy Extended Range CTs, I am asking, Is there any benefit to looking into this type of ct? and/or is anyone using them?
And would this help to eliminate how many different ct sizes we would have to stock yet be accurate in our energy measurement at each setting.
Is there a way to insert a picture here on this forum??
I would highly suggest moving to high accuracy extended range CTs. Then you can size to the transformer and not worry about loosing registration on the low end. A .15S class CT will keep its .15% accuracy rating usually down to 1-3% of name plate depending on manufacturer specs. At MP we have switched to the extend range high accuracy and we have gone with 3 sizes. 600:5 bar type CTs for the smaller wall mount CT cabinets up to 1200 amps. Then for larger services we don’t do metering in the transformer but rather we make them install a service connection cabinet on the same pad as the transformer and meter from there. For this we use a 1000:5 window CT for service up to 2000 amps and then 2000:5 CTs for any services 2000 to 4000 amps. Anything above 4000 we consider a custom engineered job.
If you are metering in the transformer it probably wouldn’t be a bad idea to stick to the 85C CTs but I don’t know if it would exactly be necessary. How often would a customer actually get to that full range of the 85C vs the 55C rated RF? You could always do the 55C and just oversize them some to account for the higher possible temps in side the transformer and with the better CTs not worry about registration issues.
All of our installations we make electrician install a CT cabinet or Transition cabinet. We stopped installing CT’s inside a transformer about 15 years ago. It leads to many issues including gopher/mice, but also makes testing these services much easier for personnel. Not to mention the customer can add load easy in a CT cab or Transition cab. Safety is also increased with this in my opinion.
We use GE JCR-OW (Encompass – Extended Range) 250/5 Bar type with RF of 4 which pushes our low end of 4% to 400% of nameplate which covers almost anything inside a CT cabinet with bar type CT’s.
Our Bushing Mount CT’s we have been using the GE Encompass 500/5 CT’s with a RF of 4 which again covers 4% to 400% of nameplate (20 amps to 2000 amps) metering very accurate which we have been happy with.
Above that we will use the GE Encompass JAD-OW – Extended range – 1000/5 CT’s with a RF of 4 also. Covering 4% to 400% nameplate.
With these 3 CT’s – We cover nearly every service we would ever put in –
We are adding some of the Astra line of the padmount of Extended Range CT’s now also – We really like these too –
The 500/5 is a High Accuracy – High Temp CT with a rated burden of .5 – These also have a 4% to 400% accuracy range (20 amps to 2000 amps)
They also carry the 1000/5 CT which we have been using also with same accuracy and RF
You must be logged in to reply to this topic.
The Upper Midwest Metering Association serves the upper midwest states of Minnesota, Iowa, Wisconsin, South Dakota, and North Dakota. We provide connections for members, utilities, meter schools, and vendors in our bi-annual meetings and continuous dialog throughout the year.