##### Capacitor Bank Protections

The current of the protection fuses should be selected as If≅2In.

51 relay should be set with a delay for 0.1 seconds between 4-6In (short circuit protection)

50 relay should be set with a delay for 4 seconds for 1.3In (overload protection)

50N relay is recommended to be set with a delay for 4 seconds at the setting of 0.05In (overload protection)

The value of resistor R (kΩ) required to be connected across the capacitor to drop the voltage of the capacitor battery with a capacitance of C (μF) to under 75 V after 10 minutes (600 seconds), can be calculated as below:

For Delta connection

For Star connection

U:System voltage (V)

In: Capacitor nominal current (A)

##### Inrush Current (I_C) Calculation When a Single Battery is Connected to the Circuit

- - U: Phase-Neutral voltage (V)
- - Xc: Phase-Neutral capacitive reactance (Ω)
- - XL: Total inductive reactance between batteries (Ω)
- - Q; Q_1; Q_2: Battery powers (kVAr)
- - S_SC: Short circuit power (kVA) at the point where the capacitors are connected
- - I_N : Nominal current (A_rms) of the battery.
- - I_SC : Short circuit current (A_rms) at the point where the capacitor bank is connected.

The value of the inductor to be connected in series with the capacitor to limit the inrush current down to I_C ≤100I_N:

##### Inrush Current (I_C) Calculation When (n) Number of Capacitor Batteries are Connected in Parallel:

Inrush current (IC) when a capacitor battery is connected in parallel with an energized capacitor battery

##### Calculations Related to Capacitor Banks:

In capacitors I_max=1.3 I_n

- V_max=1.1 V_n - 12 hours / day
- V_max=1.2 V_n - 5 min
- V_max=1.3 V_n - 1 min

When a capacitor bank with a power of Q (kVAr) is connected to a system with a short circuit power of S_sc (kVA), the resonance frequency is:

- S: Power (kVA) of the transformer supplying the capacitor
- S_SC: Short circuit power (kVA) of the transformer supplying the capacitor
- Z_SC: Short circuit impedance of the transformer supplying the capacitor (%)

Determining the Q_N of the capacitor required in order to provide a capacitive power of Q_s to a system with a voltage of (U_s):