Delta connected CT¦s for overcurrent protection
Delta connected CT¦s for overcurrent protection
(OP)
I need to understand when and why should i use delta connected CT´s for ocrecurrent protection. I saw this kind of connection to protect grounding transformers, and one to protect a bus bar with tap relay adjusted to pickup 1.2 times 3 transformer rating capacity
thanks
thanks






RE: Delta connected CT¦s for overcurrent protection
RE: Delta connected CT¦s for overcurrent protection
From your description, it appears the delta connection of CT secondaries is done to exclude zero sequence currents from coming to the overcurrent relay.
This is a sure way of making the overcurrent protection exclusive to phase faults (as earth faults produce zero sequence currents).
I am not sure if there is any specific advantage in doing so except, may be, making the relay coordination more straight forward.
RE: Delta connected CT¦s for overcurrent protection
Connecting the CTs in delta means that this current circulates and no current is measured by the relay.
The only time the relay measures current is for a fault on the grounding transformer, hence a faster operation is possible.