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Frequently Asked Questions About Capacitor Compensation Cabinets
2025-09-28
What exactly does a capacitor compensation cabinet do? Can it really save electricity?
Simply put, the core function of a capacitor compensation cabinet is to "compensate reactive power and improve efficiency". The inductive loads in our factories, such as motors and transformers, not only consume active electrical energy (electricity that actually does work) during operation but also reactive electrical energy (electricity that maintains the magnetic field). Although reactive electricity does not do work directly, it occupies the grid capacity, leading to a decrease in the power factor. After installing a capacitor compensation cabinet, it can generate capacitive reactive power to offset the reactive power consumption of inductive loads, increasing the power factor to above 0.9. This brings two benefits: first,saving electricity bills—power grid companies will impose fines on users with low power factors, and reaching the standard power factor can avoid fines and even get rewards; second, stabilizing voltage—with less reactive current, the line voltage drop is reduced, motors start more smoothly, and frequent tripping is avoided. A machinery factory I served before had a power factor of 0.75 before installing the cabinet, with thousands of yuan in fines monthly. After installation, the power factor increased to 0.93, not only eliminating fines but also saving about 8% on electricity bills monthly.
Do all factories need to install it? What power of equipment requires it?
Not all scenarios need it; it mainly depends on the load type and power:
Workshops dominated by clothing factories and lighting have few inductive loads, and the power factor is already high (above 0.85), so installation is optional;
However, places with many inductive loads such as machinery factories, cement factories, and injection molding factories—for example, with multiple motors above 10kW or a total power consumption exceeding 100kW—must install it. Otherwise, the power factor will definitely not meet the standard, electricity bill fines are inevitable, and production may be affected due to unstable voltage. I encountered a small hardware factory with a total power of 80kW and three 5kW motors. Without a compensation cabinet, the voltage always dropped during the summer peak electricity consumption period, and the punch press often jammed. After installing a 15kvar compensation cabinet, the voltage stabilized and production efficiency improved.
How to choose the capacity of the capacitor compensation cabinet? What problems will occur if it's too small or too large?
Capacity selection cannot be arbitrary; it must be calculated based on the actual reactive power demand. The formula is: compensation capacity Q = P × (tanφ1 - tanφ2), where P is the active power, φ1 is the power factor before compensation, and φ2 is the target power factor. For example: A factory has an active power of 200kW, a power factor of 0.7 before compensation (tanφ1≈1.02), and a target of 0.95 (tanφ2≈0.33). Then Q = 200 × (1.02 - 0.33) = 138kvar, so a 150kvar cabinet can be selected (leaving a 10% margin). If it's too small—the power factor cannot be increased to the standard, and fines will still be imposed; if it's too large—over-compensation will occur, leading to leading power factor, which in turn causes grid harmonics, burning capacitors or electricity meters. I saw a textile factory that chose a too-large cabinet, and as a result, 2 capacitors were burned in 3 months, causing losses of thousands of yuan.
What should be paid attention to during installation? Can it be placed anywhere casually?
The installation location and wiring are crucial, and 3 details must not be wrong:
- Close to the load concentration area: It is best to install it near the transformer outlet cabinet or the distribution box of the motor group, so that reactive power compensation is more direct and line loss is small. Do not install it in a corner far from the load, otherwise the compensation effect will be reduced.
- Dry and ventilated environment: Capacitors are afraid of moisture and high temperature. They cannot be installed in humid places such as basements and bathrooms, nor near heat sources such as boilers and ovens. When I installed a cabinet for a food factory before, it was first placed next to the boiler room, and the capacitors frequently bulged in summer. After moving it to a well-ventilated and dry power distribution room, everything was fine.
- Reliable grounding: The cabinet must be grounded separately, with a grounding resistance ≤4Ω. Otherwise, there will be safety hazards in case of leakage. When wiring, distinguish between phase lines and neutral lines. The Rated current of the circuit breaker of the capacitor cabinet should be more than 1.5 times the current of the compensation circuit to avoid overload tripping.
During daily maintenance, how to judge whether the capacitor compensation cabinet is working normally?
Just look at 3 places without complex instruments:
- Power factor meter: During normal operation, the pointer should be stable between 0.9-0.95 with little fluctuation. If the pointer swings back and forth, it may be that a group of capacitors is broken or the load changes too much; if the pointer is below 0.85, it means the compensation capacity is insufficient or the cabinet is faulty.
- Sound: During normal operation, there is only a slight "buzzing" sound in the cabinet; if there is a "sizzling" discharge sound or a "pop" sound, it may be that the capacitor is broken down or the wiring is loose, and you must cut off the power immediately for inspection.
- Temperature: Touch the capacitor shell with your hand; the temperature should not exceed 40℃. If a group of capacitors is particularly hot, it means it is about to break and needs to be replaced in time. I touch them every week during patrols, and finding problems in advance can avoid sudden tripping and production suspension.
The capacitor cabinet often trips or the capacitor bulges. What's the matter?
These are the two most common problems, and the reasons are basically among the 3 types:
- Excessive grid harmonics: Equipment such as frequency converters and electric welders in the factory will generate harmonics, which will break down the capacitors, leading to bulging or tripping. The solution is to add reactors in the capacitor cabinet to suppress harmonics. A car parts factory I served before always had capacitor failures after installing frequency converters, and the problem was solved after adding reactors.
- Capacitor aging: Capacitors have a service life, generally 3-5 years. They are prone to bulging beyond the service life. It is recommended to check them regularly (annually) and replace aging capacitors in time. Do not use them reluctantly, otherwise, fires may occur.
- Overload operation: The compensation cabinet works for a long time beyond the rated capacity. For example, the actual reactive power demand is 200kvar, but a 150kvar cabinet is used. The capacitors will be overloaded and heated, leading to tripping. In this case, a cabinet with a larger capacity must be replaced.