Transformer Hot spot CTs - How and when to use?
Transformer Hot spot CTs - How and when to use?
(OP)
I have a Virginia Transformer 42MVA 69/13KV. There are two CTs- one on the B phase of High side winding and one on the B-phase Low side winding. These CTs are wired to the Transformer Monitor relay and I am guessing that these are meant for Hot Spot calculations. So, any confirmation on what these CT are for (other than Hot Spot)? How to use them for that purpose? Should both be used or just one is fine?
Thanks.
Thanks.






RE: Transformer Hot spot CTs - How and when to use?
You mention a transformer monitoring relay, something intelligent. Not knowing what you have, the temperature monitor device may take 2 CT inputs. If you choose not to use the second (X2 - LV B Phase CT), be sure to short it out!
If this is a new transformer, pay close attention when commissioning the CT's. The Hot Spot CT's will typically have a similar ratio to any protection CT's, but will have a much lower kneepoint voltage. You do not want to have a Hot spot CT feeding a protection circuit!
The transformer monitor relay can control fans, send alarms, trips, metering info. Please indicate what device you have if you have further questions.
RE: Transformer Hot spot CTs - How and when to use?
RE: Transformer Hot spot CTs - How and when to use?
RE: Transformer Hot spot CTs - How and when to use?
RE: Transformer Hot spot CTs - How and when to use?
The SEL device may also have provisions for a 2nd CT for the LV winding temp - depends on what cards were ordered with it.
RE: Transformer Hot spot CTs - How and when to use?
Our transformers use a CT on LV A phase for temperature monitoring and CT on LV B phase for LTC control. If one of these CTs feeds a heated well to simulate winding temperature, the CT will have quite a bit of burden on it. If the transformer may be used in paralleling applications with a Beckwith controller, having a dedicated CT for the circulating current paralleling method is desirable.
Per SEL application note AN2011-04 the 2414 can be used as an LTC controller in addition to a temperature monitor/fan controller.
http://www.selinc.com/WorkArea/DownloadAsset.aspx?...
Our three winding transformers are the only ones with high side hot spot CT's.
Smallgeek, in this transformer would the no load losses be accounted for by the top oil temperature measurement?
Depending on the transformer and LTC design, the theoretical hot spot may be in either winding or may shift from one winding to the other as the LTC operates. Our temperature monitors are programmed with the parameters for the higher rise for the worst case combination of DETC and LTC positions. Perhaps the original specifier cared about a few theoretical degrees?
RE: Transformer Hot spot CTs - How and when to use?
In some other models the CT current will heat a bellow in the instrument so that the gradient will add up to the bourdon tube movement to show hot spot over top oil which will be picked up by a top oil sensor.
When only one WTI is used the maximum hot spot from tests will be used for calibration.