Differential CT grounding
Differential CT grounding
(OP)
Hi everybody!
It is recommended that for a differential relay connection, the CT’s should be grounded at one end only and not at both ends. I will really appreciate if someone explains me in detail what problem is encountered if the CT’s are grounded at both ends. Is the relay going to trip due to an external fault (short circuit as well as ground fault)?
Thanks in advance.
It is recommended that for a differential relay connection, the CT’s should be grounded at one end only and not at both ends. I will really appreciate if someone explains me in detail what problem is encountered if the CT’s are grounded at both ends. Is the relay going to trip due to an external fault (short circuit as well as ground fault)?
Thanks in advance.






RE: Differential CT grounding
RE: Differential CT grounding
See recommendations in ANSI/IEEE Std C57.13.3-1983 …Guide for the Grounding of Instrument Transformer Secondary Circuits and Cases Figures 11-15 pertain to differential relaying applications.
RE: Differential CT grounding
See PTB #87
RE: Differential CT grounding
RE: Differential CT grounding
http://www.geindustrial.com/pm/notes/artsci/art12.pdf
for theoretical background and references:
"Grounding the Secondaries of Differentially Connected CT's"
RE: Differential CT grounding
The CT's on either side of the generator do not have a common connection point when using the DGP relay, so they are treated as separate circuits, and earthed separately.
Generator Differential schemes for older protection relays had the CT star points connected together and could be treated as one set of CT secondaries, so only one earthing connection is used.