False Operation of Protective Relays

Maybe. Do you know what the guide means by "inrush current"? Please explain.

In your last thread you were told that you should do your own research work. The whole idea of it is for you to learn.

Problem comes when you switch capacitor bank back to back at non-zero voltages.

See this document and look for peak transient currents and transient frequencies involved due to capacitors and effective series inductance forming impedance and L-C resonance tank circuit.

Ref. of prof. SJ Kulas

www.icrepq.com/ICREPQ'09/480-kulas.pdf

Ref. M.F. Iizarry-Silvestrini, PREPA T. E. Vélez-Sepúlveda, PREPA

www.ece.uprm.edu/~lorama/TomasMiguel.pdf‎

Very old rules from school:

1) The voltage across a capacitor cannot change instantaneously.

2) The current through an inductor cannot change instantaneously.

You can see this from the definitions of capacitance and inductance.

Practically what does this mean?

1) When a cap initially gets switched into a circuit, the ESR (Equlivelent Series Restance) dominates.

2) When an inductor gets switched into a circuit, the resistance of the winding dominates.

The high magnitude of electrical current required to charge the capacitor plates (inrush current) exceeds the maximum threshold current limit programmed in the protective relay(s).

The protective relay(s) see this as an electrical fault and initiate a "trip" thereby isolating (opening) the source power and protecting the equipment.

This phenomonon can be avoided by the use of inductors which oppose the sudden change in current being added in series with the capacitors initially then removed once the circuit has reached stability.

This is a "way too simplistic" explanation and you would be best served to review the science of power conditioning and the affect of such on system power factor and protective relaying schemes.

Once you get familar with the idealogy, in-depth discussion(s) of particular subjects and/or questions are much easier to facilitate and understand.