CT Stability Testing

[zaza123]

I have few doubts about CT Stability testing for Differentials relay. The differential relay is protecting the Cables.
1) How much current shall be injected in Cables from Test kit while testing Stability & Unstability
2) What is the acceptable differential current flowing during the testing of Stability.
3) The differential relay has two sides ( Side 1 & Side2)
The two sides are designated based on UPstrean & Downstrean CT.What is acceptable difference between the Current for two sides

thanks in advance.

 

[rcw retired EE]

Differential protection on a cable or bus or a generator is easy because there are no phase angle and ratio shifts due to transformer windings and no energization inrush currents.
Amps in = amps out.

Test currents for primary or secondary injection tests depend on your relay settings adn CT characterisitcs and maximum through fault currents.

Check the relay instruction book for suggested values.