Harmonic Currents in a Capacitor Bank

[Sphaler]

Hi all,

Just a general protection question. I am tasked with sizing CTs for a 275kV C-filter H-configuration capacitor bank. And since we are on a pretty tight budget, I am wondering if it is necessary to take into account the harmonic currents when sizing my LV CTs? I am unsure if most relays out there would even pick them up (Siemens/ABB/etc).

Greatly appreciate your input. Thanks!

 

[LionelHutz]

Generally speaking, the total continuous current shouldn't be greater then the primary rating of the CT.

 

[warickwrx]

Some other things to perhaps consider

I would also check on the filtering capabilities of the protection relays. This should not be really be a concern with modern numerical relays but can pose a problem with older static type relays that may be using basic filtering techniques. Secondly I not sure what protection functions you are opting for but then again if you are buying a specific capacitor protection relay it should incorporate a comprehensive suite of generic functions. I would agree with LionelHutz in terms of the ratio and nominal current but bare in mind there are also effects like inrush current (rich in harmonics)and ct saturation. These can be overcome by point on wave switching devices and proper ct core type selection. Furthermore one could introduce a damping reactor in the bank to limit the inrush current.