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Wye Grounded Capacitor Bank: Single Point Grounding Neutral Cable Specification

Wye Grounded Capacitor Bank: Single Point Grounding Neutral Cable Specification

Wye Grounded Capacitor Bank: Single Point Grounding Neutral Cable Specification

(OP)
Hi after all these years I have finally decided to register in this great forum.

I am currently working on a project that involves the installation of two 45MVAR 69KV Wye-Grounded fuseless capacitor banks. We have a 69KV Breaker and a half scheme where we are going to install one cap bank per 69KV bus. Due to the fact that both banks are in the same station and same voltage we will experience back to back switching transients and IEEE C37.99 recommends that one either approaches the neutral groudning as "Single Point Grounding" or "Peninsula Grounding". We are looking to implement the single point grounding option however the standard states that and Insulated cable.
My question is how you go about selecting the voltage rating of the cable? Anyone familiar on how to specify this cable or can point me out to some good references or guidelines that I could follow? What type of cable is reccomended and could potentially be the most economical solution? I have been told to use a 15kV Concentric neutral URD cable but I want to justify my selection with references and calculations.

Thanks for your input in advance!

RE: Wye Grounded Capacitor Bank: Single Point Grounding Neutral Cable Specification

Hi

The larger capacitor bank installations on our network use normally use a 22kV 185mm INSULATED CABLE ( unarmored, unscreened) connecting the neutral point of all three phases to earth i.e., Single point grounding. On the larger banks the phase racks are interconnected using 11kV cable. Our utility standard calls for a minimum of 11kV. The insulated cable joining remote parallel neutral starpoints should have a current carrying capacity that is at least equal to the full load current of the bank. Similarly the earthing conductor current capacity shall be approximately the same as the capacitor phase-connection current capacity.

RE: Wye Grounded Capacitor Bank: Single Point Grounding Neutral Cable Specification

(OP)
warickwrx,

Thanks for your input. I have been told to use a 15kV cable but I am curious how to actually come up with that specification. I am reluctant to specify something without fully understanding how the determination to use "X" cable was made. Do you have any insight on how your utlity standard came to the conclusion that the minimum cable in your system should be 11kV? Any references or such that may lead me to a justification on what cable to use? On another hand wouldn't you want to size the neutral current carrying capacity to be in line with the available fault current duty and fault clearing times?

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