Unbalance: neutral current vs. blown element fuses

Exact solution of this double-wye bank at the live bus voltage (IEEE C37.99 method): neutral current (blue) and the overvoltage on the remaining elements of the faulted group (orange, right axis). Alarm at the first blown fuse, trip before 110 %. Purple dot: estimate from the neutral CT; ring: independent estimate from the phase-current spread.

Neutral current (A)Element overvoltage (%)Live estimates

Harmonics: amplification by the bank / network resonance

Parallel resonance at h_r = √(Ssc / Q). Curves: design network (700 MVA) and weak network (410 MVA, dashed). Bars: measured 5th and 7th bank current (% of fundamental, right axis). Dotted line: live resonance order.

Amplification, 700 MVA410 MVAMeasured 5th / 7th

Capacitor bay

33 kV bus, isolator, breaker, series reactors and the double-wye bank with the neutral CT, with live sensor values. Red = beyond the twin's alarm limit.

Condition sensors

Bars against the alarm limits in the twin file (red line).

Twin health: expected vs. actual

Measured vs. expected