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Capacitor Bank Maintenance Protocol

Table of Contents

In this article, we will explain the recommended steps for the maintenance of your capacitor bank.

Maintenance With Capacitor Bank Disconnected

Basic Monthly Maintenance Protocol

  • Visually inspect the capacitors.
  • Check the protection fuse.
  • Control the ambient temperature (average of 35 °C In accordance with IEC 60831).
  • Control the service voltage (especially during moments of low load, it must not exceed the nominal +10%)

Basic Bi-Annual Maintenance Protocol

  • Keep the capacitor terminals clean.
  • Verify the state of the contacts of operating elements.
  • Check that the capacitor current is not lower than 25% nor greater than 120% of the nominal value by phase and that there is no phase unbalance greater than 15%.

Basic Annual Maintenance Protocol

  • Carry out a dielectric rigidity test by applying 2.5 kV for 1 second between the terminals of the capacitor and earth.
  • Check the capacity of the capacitors at the different steps.
  • One indirect check may be to check that the consumption is manual.
  • Check the tightness of all terminal connections.
  • Inspect the fuses:
    • Power Circuit: NH fuses. Check continuity and temperature.
    • Power Circuit: Check the continuity and temperature of the three-pole or four-pole circuit breaker
    • Control Circuit: Check the continuity and temperature of the two-pole circuit breaker.

Tightening Torque Of Electrical Connection

  • The connections must be tight.
  • The tightening torques for the fuse bases, circuit breakers and contactors are indicated here:
Tightening torques of the cables to the fuse base
Fuse baseTorque (Nm)
Torques of power cables to two-pole and three-pole circuit breakers
Circuit breakerTorque (Nm)
In ≤ 3 x 63 A2
In ≤ 2 x 6 A2
Torques of cables to connector terminals
ModelAuxiliary (Nm)Power (Nm)

Key Points For Inspecting Contactors

  • Check that the plastic parts are not blackened and do not show signs of burning or hardening.
  • Check that the head is properly inserted.
  • Check the tightness of cables and terminals, as shown in the table above.
  • The terminals must be clean.
  • If the capacitor bank includes RD discharge resistors, check they are in good condition (that they are not open or show signs of burning).
  • Cleaning the contactors: In dirty environments (dust, sawdust, rust particles, etc.) vacuum the contactor periodically. There is no estimated time frame for cleaning, it depends on the amount of dirt that is inside the capacitor bank.
Connection of discharge resistor

Key Points For Inspecting Capacitors

  • Inspect the cables and terminals.
  • They should not be overheated or blackened.
  • The terminals must be clean.
  • The slow discharge resistors must be in good condition.
  • They must not be open or show signs of burning.
  • Check the tightness of the capacitor terminals, as shown in table below.
Torques of the cables to the capacitor terminals.
Cylindrical CapacitorPower Terminal Torque (Nm)
30 kvar @ 480 V2
15 kvar @ 480 V2
25 kvar @ 415 V2
12.5 kvar @ 415 V2

Key Points For Inspecting Regulators

  • Check that the regulator does not show signs of deterioration and the display is lit as normal.
  • Inspect the cables and terminals. They should be clean and should not be hardened or overheated.
  • Inspect the connections and the insertion of removable power strips:
    • The power strips must be well fastened on removable regulators.
    • Check that the terminals are tightened properly.
    • The recommended torque is 0.6 Nm.

Cleaning The Cabinet

  • Remove possible metallic and non-metallic particles.
  • Clean the inside of the cabinet.
  • Clean ventilation grilles.

Maintenance With Capacitor Bank Connected

Cleaning The Cabinet

  • Check that the main switch turns on and off without having to force the mechanism.
  • If there is an individual earth leakage protection for the capacitor bank, check its proper operation by pressing the test button.
  • Check that the auxiliary control voltage is within the tolerance limits.
  • If the capacitor bank has an autotransformer, check that it is in good condition and shows no signs of deterioration.
  • Force the connection and disconnection of the capacitors in manual mode. (refer to the regulator’s manual before carrying out these actions) and perform the following checks:
    • Check that the contactors connect and disconnect properly.
    • Check that the contactor, once connected, does not rattle or vibrate.
    • Check the consumption of the capacitors in each of the phases.

Note: If consumption is ±25% less than that indicated in table below and the voltage is within the tolerance limits, this is usually a sign of degradation of the capacitors. If this is detected in any capacitor, it should be replaced with another capacitor.

Nominal consumption of capacitor paths, by power and voltage.

PowerIn, Current: 3 x 230 V ~In, Current: 3 x 400 V ~
2.5 kvar6.28 A3.6 A
5 kvar12.56 A7.2 A
7.5 kvar18.85 A10.8 A
10 kvar25.12 A14.4 A
12.5 kvar31.41 A18 A
15 kvar37.7 A21.6 A
20 kvar50.24 A28.8 A
25 kvar62.82 A36 A
30 kvar75.4 A43.2 A
40 kvar100.48 A57.6 A
50 kvar-72 A
60 kvar-86.4 A
80 kvar-115 A

Regulator Check

  • Refer to the manual of the specific regulator used in the capacitor bank. This manual is always supplied with the capacitor bank.
  • Check that there are no faulty segments on the display.
  • Check that the keyboard is operating properly.
  • Enter Setup and check the adjusted values.
  • Force the manual connection and disconnection of a step.

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