We are using zig-zag transformer for system earthing in 33 kV, 6.6 kV system in an Oil and Gas Industry. Zig-zag transformer is earthed via a resistor to limit the fault current to 200 A. Now, we want to increase fault current to 400 A. Proposal is to connect another zig-zag transformer. This will serve dual purpose of increasing fault current as well as redundancy in system earthing in case of failure of one zig-zag.
My question is - instead of connecting another, cannot we reduce the resistance to increase the fault current to 400 A (zig-zag is rated for 400 A)? If we remove resistance will there be difficulty in segregating faulter feeder from un-faulted one (due to smaller angle difference between faultd and un-faulted one)? If both zig-zag are in service, will there be any change of angle of faulted current from earlier case of one zig-zag due to paralleling of earth fault current?
Another question - can we use directional negative sequence over current protection along with directional earth fault protection to increase reliability in detecting faulted feeder in case of earth fault?
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
