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Capacitor Bank

Comprehensive Electrical Maintenance: Tailored for the UAE's Dynamic Needs

At Core Systems, we specialize in Electrical Maintenance Contract in Dubai and across the UAE. Our team of certified professionals is dedicated to ensuring the longevity and efficiency of your electrical systems. With our Electrical Maintenance Service, we provide comprehensive checks and repairs to prevent downtimes and ensure compliance with UAE’s stringent electrical standards.
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The proportionality rate between real power and apparent power is defined as the power factor, which is measured in kilowatts (kW). Apparent power, measured in kilovolt-amperes (kVA), is a fundamental measure that reflects the electric efficiency of distributing voltage and current, regardless of whether it is actually performing work. Power factor correction is achieved by adding capacitors to the power distribution system. An automatic controller, which switches capacitors and reactors at intervals, is the most effective method. The most basic application involves employing a fixed capacitor bank. When the power factor drops below specified values, power factor correction capacitors can reduce energy charges by bypassing the standard electric utility charges. These capacitors are installed to address power factor issues caused by inductive loads affecting the electric utility.
Premature failures in power factor correction capacitors and related circuitry can be caused by several factors, including:
  • Harmonic currents
  • Poor ventilation
It is crucial to routinely inspect power factor correction capacitors to ensure they are functioning properly. 

Safety First

Although most capacitors are equipped with a discharge circuit, there is still a risk of electric shock if the circuit is damaged. Extreme caution is necessary when testing capacitors with voltage applied. Maintenance of capacitor banks requires careful attention to individual equipment and its application. Additional hazards are associated with working with current transformer (CT) circuits, including wiring and shorting blocks. Even if the capacitor bank is de-energized, there is still a risk of electrical shock from the CT wiring due to the potential for lethal voltages across the CT terminals.

Visual Inspection and Cleaning

Conduct a thorough visual inspection of the system, including:
  • Checking for damaged components and leaking capacitors
  • Looking for signs of heat or moisture damage
  • Replacing filters in cooling fans
  • Avoiding the use of compressed air for cleaning; instead, use a vacuum to clean the units
Before re-energizing the capacitors, perform an insulation integrity test between the bus phase-to-phase and phase-to-ground points.

Capacitor Bank Infrared Inspection

A thermal imager is an invaluable tool for evaluating electrical capacitor banks. Before testing, ensure the system has been energized for at least one hour. Begin by checking the controller display to confirm that all stages are connected and verify that the cooling fans are operating correctly.

Perform an infrared examination of the enclosure before opening the doors. Based on your arc flash assessment, wear the appropriate PPE when working near energized equipment. Use the thermal imager to inspect power and control wiring, looking for loose connections. A thermal analysis can identify poor connections by showing increased temperatures due to extra resistance at connection points. Ideally, a good connection should show no more than a 20°F increase above the ambient temperature. There should be minimal temperature variation phase-to-phase or bank-to-bank at connection points.

An infrared inspection can also detect a blown fuse by highlighting temperature differences between blown and intact fuses. A blown fuse in a capacitor bank stage reduces the available correction. Some units have blown fuse indicators, while others do not. If a blown fuse is detected, shut down the entire bank and investigate the cause. Common causes include faulty capacitors, reactor issues, and poor connections at line-fuse, load-fuse, or fuse clip points.

Additionally, check for temperature variations among individual capacitors. A capacitor not involved or connected during the inspection should be cooler. Keep in mind that temperature may be higher in the upper sections due to convection. However, if the controller indicates that all stages are connected, significant temperature variations typically point to an issue. For example, high temperatures could cause the capacitor’s internal pressure device to activate before the external fuse, causing the capacitor to be removed from the circuit unexpectedly.

Capacitor Bank Current Measurements

Use a multimeter to measure the current input to the controller from the capacitor bank by employing a current clamp around the CT secondary conductor. Measure the current through the breaker feeding the capacitor bank for phase imbalance with all stages connected. Log all readings to establish a future benchmark.

Capacitor Bank Power Factor Measurements

Use a meter that measures voltage, current, power, and demand simultaneously for power factor measurement. A DMM isn’t sufficient, but a power quality analyzer with a current clamp can provide accurate data. A power logger can also perform a 30-day load study for a comprehensive analysis.

Capacitor Bank Capacitance Measurements

Before measuring capacitance, de-energize the capacitor bank and wait for the duration specified in the manufacturer’s service bulletin. While wearing the appropriate PPE, verify with a properly rated meter that no AC voltage is present. Follow your facility’s lockout/tag-out procedures. Use a DC meter rated for the voltage being tested, and measure capacitance for each stage—phase-to-phase and phase-to-ground. There should be no voltage present. The presence of voltage indicates the capacitor may not be fully discharged. If no voltage is detected, measure the capacitance with the meter and compare the reading to the manufacturer’s specifications for each stage.

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