Capacitor Bank Testing: Importance and Procedures Explained

Capacitor Bank Testing: Importance and Procedures Explained

A collection of capacitors of comparable ratings is known as a capacitor bank. These capacitors are arranged in parallel or series sequence to gather electrical energy. A capacitor bank is usually applied to an AC source of power. This helps to rectify or compensate for power factor lag or phase shift. These banks can also be connected to a DC power supply. This helps increase the comprehensive quantity of the power supply’s ripple current capacity or the stored energy. The primary use of a capacitor bank is to collect and store electrical energy to meet the operational requirements while ensuring the required power factor levels for the electrical equipment. 

Now the question arises: what is the need for testing these banks, and how to test a capacitor bank. If you are curious to know the answers to the same, continue reading. This blog will list all the different types of tests conducted on capacitor banks, their importance, and their procedures.

What is the Role of Capacitor Bank Testing?

The significance of capacitor banks in a power system can never be neglected as they play a crucial role in controlling the power factor correction. The power factor correction units perform various functions based on their location in the system. The power factor correction of capacitor banks changes due to moisture, temperature, time, and harmonics. To perform their best, the installed capacitor banks must be tested regularly and maintained to the highest quality. 

Although capacitor banks of the finest qualities function quite well, their operation can weaken with time. This results in a decrease in the power factor of your system. Eventually, this leads to power factor loss. Therefore, it is essential to regularly test the capacitor bank and ensure its reliability and performance. 

A capacitor bank is static equipment. It must be examined at regular intervals to ensure proper maintenance. If they are not tested or maintained regularly, they can pose serious hazards to the industry.

What are the Different Types of Capacitor Bank Tests?

Testing capacitor banks is not a brief process. It involves several types of tests. A professional technician tests a bank based on its type and requirements. Below are the different types of capacitor bank tests.

  1. Design Tests or Type Tests of Capacitor Bank
  2. The type tests performed on capacitor banks are–

    • High Voltage Impulse Withstand Test.
    • Bushing Test.
    • Thermal Stability Test.
    • Radio Influence Voltage (RIV) Test.
    • Voltage Decay Test.
    • Short Circuit Discharge Test.
  3. Routine Test of Capacitor Bank
  4. Short Time Over Voltage Test
  5. Terminal to Case Voltage Test
  6. Capacitance Test
  7. Leakage Test of Capacitor Units
  8. Discharge Resistor Test
  9. Loss Determination Test
  10. Fuse Capability Test of Internal Fused Capacitor Unit
  11. Pre-commissioning or Installation Test of Capacitor Bank
  12. Capacitance Measurement
  13. High Voltage Insulation Test

How to Perform the Capacitor Bank Testing?

How to test the capacitor bank? It's a thorough process requiring several different steps. You need to have expert knowledge and practice to carry out the capacitor bank testing. Therefore, it is always suggested that you leave this to a professional. Below is the step-by-step procedure for capacitor bank testing.

  • Carry Out an On-Site Risk Assessment
  • All tests must be done with Capacitor Bank De-energized
  1. Contact with high voltage at capacitor bank primary connections
  2. Extreme fault current
  3. Stored energy in charged capacitors
  • Carry Out Secondary Isolation
  • Record Plant Details

Record details of each capacitor unit

  1. Manufacturer’s name
  2. Manufacturer’s type description
  3. Manufacturer’s serial number
  4. Year of Manufacture
  5. Measured Capacitance 
  6. Rated Capacitance as marked on the nameplate
  7. The serial number of each capacitor can
  8. Rated Output Qn
  9. Rated Voltage Un
  10. Rated Current In
  11. Temperature Category
    • Visual Inspection of Capacitor Bank Condition
    • Measure Insulation Resistance
    • Measure Capacitance
    • Measure Reactance
    • Carry Out High Voltage Test
    • Check the Balancing of Each Bank
    • Carry Out Primary Injection
    • Complete Pre-commissioning Checklist
  12. Check if sheet metal work is free from transport damage 
  13. Check if sheet metal work is assembled correctly
  14. Check that all fixed panels are bolted in their position
  15. Check if all door fittings are tight
  16. Check if door locks operate optimally
  17. Check if the overall appearance and clean paintwork 
  18. Check if all correctness and tightness of control cable terminations
  19. Check if capacitors are neat and free from breaks or leaks
  20. Check if busbar connections are correctly torqued
  21. Check if capacitor bushing connections are correctly torqued correctly
  22. Check the operation of the earth switch
  23. Check the operation of the isolator
  24. Check the operation of discharge timers and electrical interlocking
  25. Check the operation of point-on wave relays
    • Energize and Carry Out on Load Tests

Benefits of Capacitor Bank Testing

As you are now aware of the basic steps on how to check 3 phase capacitor banks, you must know about the benefits of this testing. 

  • Decreases system’s line current 
  • Enhances load’s voltage level 
  • Minimises system losses
  • Enhances source current’s power factor 
  • Reduces alternator’s load
  • Reduces load’s capital investment per megawatt
  • Decreases electricity bill


Summing Up

Using electrical systems is crucial and quite helpful in industrial units. One such component is the capacitor bank. However, to maintain its efficiency, it is essential to get them tested regularly. Reading above must have introduced you to the detailed process of how to test capacitor banks. But do not do it yourself unless you are trained for it. Always rely on experts for this. Also, if you are looking for the highest quality capacitor banks, shop from the e-shop of Schneider Electric to relish the convenience and high-quality products at the same time. 

Frequently Asked Questions

Q1. What is a capacitor bank?

Ans: A capacitor bank is a collection of different capacitors arranged in series or parallel to collect and store electrical energy for an electrical system. 

Q2. What is capacitor bank testing?

Ans: Testing the efficiency and functioning of capacitor banks is known as capacitor bank testing. It involves various types of tests to identify faults in the banks’ functioning.