Current Transformers for 400 kV System

The one and & half breaker arrangement uses 3 breakers for every 2 circuits. Now every breaker needs a CT so you get 3 CT for every 2 circuits. 4 CTs are needed in the 1.33 breaker/circuit system which uses 4 switching units for every 3 circuits. Eventually the 1.5 Breaker system has 3 CTs.

Check how 3 cts will help.. I understand 4 cts are very much required.

Dear Raggul,

Please note that in general, according to your applications the number of CTs is decided. However, nothing is stated that 3 CTs instead of 4 CTs in one and half breaker scheme is the acceptable system. Maybe it is the minimum acceptable scheme but not the optimum one.

The control, metering and protection schemes of the one and half bus configuration is the most complicated one with regard to CT coordination and wiring.

Each CB in the one and half configuration has CTs on both sides. The middle CB is the one which has the largest number of CTs on both sides. Because, it has to coordinate with the outer busbars breakers.

Therefore, as previously mentioned according to your scheme of metering and up to which level of reliable and redundant protection scheme is required, you can decide the required number of CTs.

Best regards,

3 ct will only work if the third ct has the capability to replace the 4th ct. This is given by the number of the secondaries needed, rated power.