Nonlinear load equipment such as frequency converters, servo drives, and electric heating/melting furnaces are widely adopted in the industrial field. Although these devices have enhanced efficiency and intelligence levels, they have quietly imposed "hidden burdens" on the power grid - a sharp increase in reactive power, voltage fluctuations, and a decline in power quality. Especially after the large-scale integration of new energy such as wind power and photovoltaic power, due to their fluctuating and nonlinear characteristics, the inductive load characteristics of the power grid have been further intensified. Therefore, an increasing numbers of compensation capacitor cabinets to be equiped in power transmission and distribution systems to maintain system power quality, improve power factor and reduce reactive power loss. So, what exactly does a compensation capacitor cabinet compensate for? Is it an electric current? Or voltage? Or perhaps reactive power?
1. Compensate reactive power
The essence of a compensation capacitor cabinet is to compensate for the Reactive Power which generated by inductive loads in the power system. In other words, the compensation capacitor cabinet achieves power factor correction by changing the phase Angle between the current and the voltage, but in essence, it is to regulate the flow direction of reactive current. Although reactive power is not directly converted into useful energy (such as mechanical energy or thermal energy), it is the "magnetic field energy" necessary for the normal operation of the power system and is mainly used to maintain the electromagnetic fields of equipment such as motors and transformers.
In an alternating current circuit, the relationship among active power (P), reactive power (Q), and apparent power (S) satisfies:
The function of the capacitor compensation cabinet is to provide "capacitive reactive power" to the system to offset the "inductive reactive power" consumed by the load (especially motors, transformers, etc.), thereby reducing the total reactive load of the system, improving the power factor, reducing line losses, and stabilizing the voltage level.
2. Working principle of Capacitor Compensation cabinet: Inductive load "borrows power", capacitor "returns power"
We can explain the compensation principle with a simple metaphor: Inductive loads (such as motors) are like users who like to "borrow on credit", "borrowing reactive power" from the power grid to establish a magnetic field. Capacitors are like good neighbors who "pay in advance", "sending out reactive power in advance" at the right time to help the power grid relieve the pressure on power supply. The current of a capacitor leads the voltage by 90°, while the current of an inductive load lags behind the voltage by 90°. When the two are connected in parallel, they can offset each other, thus making the power system current and voltage stay in-phase, improving the power factor, and reducing the apparent power and line loss.
3. Does the capacitor compensation cabinet serve as voltage compensation or current compensation?
To the point, the capacitor compensation cabinet is not compensate voltage or current directly. It doesn't aim for increasing or stablizing voltage, not reducing the amplitude of the current. Actually Its target of action is the phase difference of the circuit, and the core objective is to improve the power factor.
However, in practical, capacitor compensation can indeed enhance voltage stability (as the line reactance voltage drop is reduced); The current decreases (because the apparent power drops); System capacity release (transformers and lines no longer take the blame for reactive power); In addition, it can also save energy and reduce consumption (reduce line loss and equipment heat generation).
Fig1 Linear load
4. The thoughts of compensation under conditions of inductive, resistive and capacitive loads
- Inductive loads (Generally, loads with inductive parameters, that is, loads that conform to the characteristic of voltage leading current, are called inductive loads.) : such as motors, transformers, and rectifier will absorb a large amount of reactive power. Capacitors are required to compensate for inductive reactive power, and a conventional capacitor compensation cabinet can meet the requirements.
- Resistive loads: such as incandescent lamps, resistance furnaces, heaters, etc., whose current and voltage are in phase and do not require reactive power, thus no need compensation. The characteristic of resistive loads is that the current and voltage change synchronously, zero phase difference, and heat is generated during operation.
- Capacitive loads: such as some UPS power supplies, filter capacitors, long-distance power transmission line, and no-load cables, etc., may cause the "overcompensation" phenomenon of capacitive reactive power. In thiscase, reactors are necessary to be introduced to absorb the excess reactive power to prevent the power factor from "leading" and causing voltage oscillation.
5. The capacitor compensation drives the "big project" of energy efficiency optimization
The capacitor compensation cabinet is not designed for "directly compensating current" or "increasing voltage", but it precisely regulates the direction and form of electrical energy. Its function as helping the power grid reduce "useless work" and enhance "effective energy". Essentially, it is about "optimizing the power structure and improving power quality". In fact, it can avoid being charged additional power factor adjustment fees by the power grid due to a low power factor. Reduce the line current and release the power supply capacity to improve the power supply efficiency; Furthermore, it can alleviate the problem of voltage drop in long-distance power supply to maintain voltage stability and protect equipment.
From the direct effect, it reduces the total current, lowers the overall loss, releases the capacity of transformers and lines, enables the connection of more loads, and optimizes the efficiency of the power grid! For enterprises to reduce electricity expenses and avoid fines due to non-compliance with power factor standards at the same time! In addition, it can suppress voltage fluctuations, reduce the impact of harmonics, thereby improving power quality and enhancing the stability and reliability of the system!
Under the background of smart grids, the integration of new energy and energy conservation and emission reduction, capacitor compensation cabinets play a significant role and are an indispensable part of every modern power distribution system.