Multi-Ratio CTs
Multi-Ratio CTs
(OP)
A simple question with many different opinions. What is the proper method of terminating the unused terminals / taps of a multi-ratio CT? It's obvious that the taps which are internal to the selected ratio series should be isolated and insulated from ground. But what about the extended windings, possibly on both sides of the selected ratio? It seems right to short these to the closest used tap. I would expect high voltages to be developed on the these terminals if they remained open. Any info would be appreciated. Thanks in advance for your feedback.






RE: Multi-Ratio CTs
RE: Multi-Ratio CTs
One secondary 'loop' will keep the CT core out of saturation.
RE: Multi-Ratio CTs
RE: Multi-Ratio CTs
The secondary multiwinding CTs have unused individual secondary windings shorted.
RE: Multi-Ratio CTs
But to be clear, when using multi-ratio CTs, you connect the burden to the 2 terminals needed for the ratio desired. The other terminals are to be left open and not shorted!
RE: Multi-Ratio CTs
The multi-winding secondary CT are accomplished on multicore CTs.
Visit
https://www.kuhlman.com/clientdata/ReplacementGeneratorCurrentTransformer.pdf
for a multi core current transformer, HW-945
RE: Multi-Ratio CTs
A typical single-winding tapped-CT style is Table 8 Current Transformer Ratings, Multi-Ratio Type in IEEE Std C57.13-1993 …Instrument Transformers
RE: Multi-Ratio CTs
RE: Multi-Ratio CTs
Thank for the link to the GE manual. I have to admit, I disagree with their comments on high-voltages developing on MR CT where the full winding is not used. They give quite a bit of justification, but I believe some of their assumptions are incorrect. Particularly, when they say that a completed saturated core will not have any voltage across its secondary. This is incorrect...just look at a typical excitation curve...the CT will maintain a voltage close to its knee-point voltage.
In fact, in some applications, intentional saturated CTs are used for power sources of electronics/lights, etc... at HV, when the power requirements are low. This way a power source of relatively constant voltage can be used without having to provide isolation to the HV level.
RE: Multi-Ratio CTs