current injetion

These two terms are related to the testing of the protection system which involves the CT and protection relays.

Primary current injection is the injection of current in the primary circuit of the CT, while secondary current injection is the injection of current directly to the protection relay. In the case of primary current injection, the bad thing is you need high current value to inject (generally the phantom set is used to generate the high current value), but the good thing is the protection system is tested including the CT. On the other hand, for the case of the secondary current injection, you can inject a current up to 5A (generally a secondary current injection set is used) but only the protection relay is tested.

-MS

I would like add it also makes sure the polarities of ct and pt .

The primary current injection comes before the secondary current injection.

i.e. the first recent inject occurs prior to the prior previous injection.

Got it?

MSAMAD respone is correct. In addition, it would be best to carry out both primary and secondary injection test to ensure protection circuits are operational.

In the primary injection, you could check 1) polarity of the CT 2) accuracy of installed wiring 3) protection relays and meters in the circuit could be verified if they are all fully functional, most important, the circuit breaker is tripping.

In the secondary current injection, 1 A or 5 A is injected, wiring from protection relay to breaker is verified, but not wiring from CT to protection relay.

Best regards,

rudy_fernando5r