Line Capacitor Bank Voltage Rise

Switching a capacitor bank onto a feeder raises the voltage, and the rise is what decides whether the bank helps the end of the line or pushes the head of it over limit. A capacitor injects leading reactive current; that current flowing back through the reactance between the bank and the source raises the voltage at the point of connection. The rise depends on the reactance BETWEEN the bank and the source, so the further out the bank sits the bigger its voltage effect and the smaller its loss-reduction effect per kVAR -- the two goals pull in opposite directions, and this one line of arithmetic is where the trade shows. The number that gets people is the light-load case, and it is the reason this reports the result at two conditions rather than one. A fixed bank sized for peak-load power factor is still connected at three in the morning, when the load is a fifth of peak, the drop it was cancelling is gone, and the rise it produces is the whole story. A feeder head sitting comfortably at peak can be over the ANSI C84.1 Range A upper limit at light load with the same bank, the same reactance, and nothing having changed but the hour. That is why banks get switched rather than fixed, and the largest bank that still fits under the limit at light load is reported so the size question is answered rather than argued. Steady state, one bank, one location, radial feeder. It does not model switching transients, which is where capacitor problems actually live: inrush on back-to-back switching, restrike across the switch contacts, and the voltage magnification that damages customer equipment and trips adjustable-speed drives. It does not check harmonic resonance, which is a separate screen and the other reason a bank sizing fails. It does not produce a voltage profile along the feeder or coordinate the bank against a regulator's bandwidth, and a bank inside a regulator's zone will interact with it. ANSI C84.1, IEEE 1036, the utility's capacitor application guide, and a distribution power-flow study govern.

percent rise = bank kVAR x reactance from the source to the bank / (10 x line-to-line kV squared); rise in volts on a 120 V base = percent rise x 1.2; leading current = kVAR / (sqrt(3) x kV); the largest fixed bank is the relation worked backwards against the headroom at light load.

The distribution capacitor voltage-rise relation as standard practice, by name, with ANSI C84.1 Range A named for the limit the result is tested against. The limit and both pre-switching voltages are entered because the adopted range and the feeder's profile are local. ANSI C84.1, IEEE 1036, the utility's capacitor application guide, and a distribution power-flow study govern.

One multiplication and one division; no ANSI voltage table is reproduced, the limit is entered.

Estimate. AHJ and licensed professional govern.

Field names used by the API: bank_kvar, line_voltage_kv, reactance_to_source_ohm, peak_load_voltage_v, light_load_voltage_v, upper_limit_v, rise_pct, rise_volts_120_base, leading_current_a, light_load_result_v, peak_load_result_v, max_bank_kvar

• Steady state, one bank, radial feeder no switching transient, inrush, or restrikeIEEE 1036
• The voltage limit is entered the adopted ANSI C84.1 range is localANSI C84.1
• No harmonic resonance check that is a separate screen and the other way a bank sizing failsIEEE 1036