Performance of Reactor Operation
Reactive Power Compensation: Forms and Common Devices in Power Systems
Reactive Power Compensation: Forms and Common Devices in Power Systems
Reactive power compensation plays a critical role in modern power systems by improving power factor, reducing line losses, and stabilizing system voltage. Depending on installation location, compensation characteristics, and equipment type, different reactive power compensation solutions are applied to meet various operating requirements.
1. Reactive Power Compensation by Installation Location
1.1 Local Compensation
Local compensation is typically applied to large motors or high-power electrical equipment. Capacitors are directly connected to the load, usually protected by series fuses, and are switched on and off together with the equipment. When disconnected, the load winding serves as the capacitor discharge path.
This method is simple, cost-effective, and provides direct compensation at the load point. However, when equipment operates intermittently, capacitor utilization is low, limiting overall compensation efficiency. It is most suitable for continuously operating large motors and stable loads.
1.2 Distributed Compensation
Distributed compensation is installed at load terminals that are far from the main transformer, often combined with low-voltage compensation on the user side. This approach significantly reduces line losses and helps improve voltage levels at the end of distribution feeders.
Capacitor banks can be switched according to load variations, providing flexible compensation. While performance is good, the overall investment cost is higher due to multiple installation points. It is suitable for long-distance power supply systems with voltage drop issues.
1.3 Centralized Compensation
Centralized compensation is typically installed in substations to compensate for the reactive power demand of main transformers and the supplied voltage area. The required capacity is determined by considering transformer rating, reactive power flow, and existing compensation on distribution lines and user loads.
In practice, 35 kV substations usually allocate 10%–15% of transformer capacity for reactive power compensation, while 110 kV substations may allocate 15%–20%. This solution is easy to install and reliable in operation but provides less targeted compensation for individual loads.
2. Reactive Power Compensation by Operating Characteristics
2.1 Static Reactive Power Compensation
Static compensation uses passive components such as capacitors and reactors connected in series or parallel to adjust reactive power flow. Typical applications include fixed capacitor banks, switched capacitor banks, and reactor banks.
These systems feature simple structure, low cost, and high reliability, making them suitable for industrial and commercial systems with relatively stable loads. However, their response speed is limited and they are less effective under rapidly changing load conditions.
2.2 Dynamic Reactive Power Compensation
Dynamic compensation employs power electronic devices and control systems to adjust reactive power output in real time. Typical solutions include SVC, SVG, and DSTATCOM.
Dynamic systems offer fast response, high accuracy, and effective voltage regulation, making them suitable for applications with strict dynamic performance requirements. Their main drawbacks are higher cost, increased system complexity, and more demanding maintenance.
2.3 Hybrid Reactive Power Compensation
Hybrid compensation combines static and dynamic solutions. Static devices such as capacitors and reactors provide base compensation, while dynamic devices like SVC or STATCOM perform fine adjustment.
This approach balances performance and cost, offering improved flexibility and control. It is widely used in systems with complex reactive power demands and frequent load fluctuations.
3. Common Reactive Power Compensation Devices
3.1 Shunt Capacitors
Shunt capacitors supply capacitive reactive power to offset inductive reactive power from loads, thereby improving power factor. Their current leads voltage by 90°, compensating for inductive current lag.
They are widely used in distribution networks and industrial facilities due to low investment cost and simple installation. However, they are sensitive to harmonics and frequency variations.
3.2 Static Var Compensator (SVC)
An SVC consists of thyristor-controlled reactors and capacitor banks. By adjusting reactive power output, it stabilizes system voltage and optimizes power factor.
SVCs are commonly used in high-voltage transmission systems and large industrial applications. They provide fast response and wide compensation range but generate harmonics and require relatively large installation space.
3.3 Static Synchronous Compensator (STATCOM)
STATCOM is based on voltage-source converter (VSC) technology. By controlling output voltage magnitude and phase angle, it delivers precise and fast reactive power compensation.
STATCOMs are widely applied in wind farms, photovoltaic plants, transmission networks, and systems requiring rapid dynamic compensation. They offer superior performance and low harmonic impact, though initial investment and technical complexity are higher.
3.4 Automatic Capacitor Banks
Automatic capacitor banks integrate multiple capacitor stages controlled by a controller that monitors voltage, current, and power factor in real time. Capacitors are automatically switched to maintain optimal power factor and avoid overcompensation.
They are widely used in low- and medium-voltage distribution systems and commercial buildings. While cost-effective and easy to operate, their compensation capacity is limited for large or highly dynamic loads.
3.5 Synchronous Condenser
A synchronous condenser is a synchronous machine capable of absorbing or supplying reactive power by adjusting excitation current. It also provides rotational inertia, improving system stability.
These devices are mainly used in large power plants and substations but are gradually being replaced due to large size, high losses, and high maintenance requirements.
3.6 Filter Reactors
Filter reactors are used together with capacitors to form passive harmonic filters. In addition to reactive power compensation, they suppress harmonic currents and improve power quality.
They are suitable for systems with significant nonlinear loads such as rectifiers and variable frequency drives. However, filtering effectiveness may be limited in systems with complex harmonic spectra.
3.7 Thyristor Switched Capacitors (TSC)
TSC systems use thyristor switches to rapidly connect or disconnect capacitor banks, enabling fast reactive power adjustment.
They are suitable for industries with frequent load fluctuations, such as steel, mining, and rolling mills. While response speed is excellent, equipment cost is higher and additional harmonics may be introduced.
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