Difference Between Bus CT and Line CT

1. Bus CT senses current in a bus; Line CT senses in a line. No difference in function, maybe in construction, as to whether you use donut-type CTs on a power circuit breaker or free-standing CTs by themselves.

2. SIL is Switching Surge Impulse Level, which is used in evaluating surge protective devices such as arresters, vs. BIL (Basic Impulse/Insulation Level) which is a rating of individual items of electrical apparatus. BIL is often chosen to be 25-30% higher than the protection provided by the arresters. It's not specific to 400kV, just an engineering decision as to where to start in insulation coordination.

BIL is the level of a lightning strike equipment can withstand, and is not calculated. Equipment is built to certain standards and rated with a BIL in kilovolt value based on historical statistics and construction methods that have exhibited the capability to withstand a particular impulse of high voltage.BIL rating will be dependent on the dielectric strength of the insulation materials used a design

BIL is basic insulation level as per you or in other words it would be "basic impulse level" which implies the limit up to which an insulator could withstand impulse due to lightning strikes. Please be noted that BIL is the term connected mainly to insulators.

hey...tanuja....what r u doing in UAE?electrical engineer?pls reply thru mailbox.....

@tanuja

thanks for your reply.can you please send any write up regarding equipment selection guide for substation (like CT, CVT, CC, ISO) etc

my email id :- saraswatapalit@yahoo.com

once again thanks for your reply

regards

saraswata

regards

Bus CT & Line CT selection depends what type of protective relay you are going to connect. If the bus CT covers the LBB protection the primary current of CT will be the bus rating. Where as if Line CT is used for O/C, E/F protection the class will be accordingly 5P20 etc current ration will be according to the current flow in the feeder. For Measuring current Power, Cl-1 etc. You can refer to IEC 60044 for better understanding.