The Promotional Value of Delta's Third Generation Var Compensation Device SVG

1. Background and Current Status of Traditional Reactive Power Compensation Devices

With China's rapid economic development over the past thirty years, power electronic equipment has become widely used in various industries. Typical nonlinear loads such as frequency converters, rectifiers, inverters, switching power supplies, and energy-saving lamps are increasingly prevalent in power distribution systems. However, traditional reactive power compensation devices, instead of effectively improving the power factor and reducing line losses in modern power distribution systems, have become major sources of failure—severe capacitor oil leaks, frequent series reactor burnouts, and fuse explosions. In severe cases, this can lead to serious accidents such as system fires and power outages. Below are typical photos showing harmonic-induced problems in compensation cabinets and systems.

Figure 1. Contactor burnt out

Figure 2 Severe oil leak damage

Figure 3 Short circuit to ground

Figure 4 System Fire

By testing the data before and after the implementation of traditional reactive power compensation in the power distribution room of a large shipbuilding company in Zhejiang, it can be clearly seen that traditional reactive power compensation severely amplifies harmonics.

Figure 5 Power Distribution System Architecture Diagram

The test location is the 380V low-voltage main incoming switch side of transformer #1:

Table 1 Comparison before and after the implementation of traditional reactive power compensation devices.

The data above clearly shows that before and after the implementation of traditional reactive power compensation devices: the voltage distortion rate of the power distribution system increased from 4.8% to 6.5%, exceeding the national standard 14549-93; the current distortion rate of the power distribution system increased from 9.5% to 18.9%, and the total harmonic current increased from 112A to 202A; the current waveform of the power distribution system changed from an irregular single peak to a double peak, with the 5th and 11th harmonics being the most significantly amplified.

The power distribution system frequently experiences capacitor damage and severe oil leaks, as well as unexplained breakdowns and damage to the air compressor inverter module.

Figure 6 Local system fault

It is understood that the power distribution system includes a large number of nonlinear power sources such as welding machines and frequency converter-controlled air compressors, which have high harmonic content. The introduction of traditional reactive power compensation devices into the power distribution system will lead to the following risks:

Traditional reactive power compensation devices severely amplify the harmonic content of the system, causing the harmonic content at the point of common coupling to exceed the standard and pollute the power grid, which attracts the attention of the power supply department. In severe cases, the power supply department will issue a power outage rectification notice to the enterprise.

Traditional reactive power compensation devices cannot track load fluctuation speed, which may cause system resonance, leading to overvoltage and overcurrent of electrical equipment, resulting in protection power failure, production interruption, and serious consequences.

Because traditional reactive power compensation devices cannot operate normally, the power factor of the power distribution system is low, and a large amount of reactive current flows through transformers, busbars, and various power distribution components, causing the capacity of transformers, busbars, and various power distribution components to decrease and generate serious heat, which may lead to overload and burn out the equipment.

Amplified harmonics produce a skin effect, which can cause electrical components such as transformer coils, busbars, circuit breakers, and cables to overheat. Overheating of these components can lead to fires, short circuits, and other problems, posing a significant risk to system safety.

Excessive voltage harmonics can severely interfere with the low-voltage system of the entire production line and damage the control modules of equipment such as frequency converters and switching power supplies, causing the production line to malfunction and affecting the company's profits.

The amplified harmonic voltage superimposed on the fundamental voltage fluctuates rapidly with the load, resulting in large voltage fluctuation amplitude and high frequency, which has a significant impact on product quality and lifespan.

Harmonics can easily cause protection malfunctions, impacting the protection limits of circuit breakers and causing them to trip or even burn out unexpectedly. Once this happens, it can cause significant losses to the production line.

The above situations will ultimately result in the power distribution system not being able to operate continuously and safely, users not being able to get an effective return on their investment, users' product costs and operating costs increasing, users' production efficiency or production capacity decreasing, and users consuming huge amounts of energy.

Traditional reactive power compensation devices cause a significant amplification of harmonic content in the power distribution system, and the components of the compensation devices frequently burn out. The reasons are analyzed as follows:

Capacitive reactance exhibits low impedance to higher harmonics. Capacitive reactance is related to the following parameter: XL = 1/(2 × 3.14 × f × C). The higher the harmonic content of the power distribution system, i.e., the higher the frequency, the lower the capacitive reactance. Under the same voltage, this will cause abnormal amplification of the capacitor current. This leads to an abnormal increase in harmonic current in the power distribution system, resulting in overcurrent in capacitors, contactors, fuses, and wires, causing severe overcurrent and overheating, and consequently, frequent damage to the electrical components of the compensation device.

Harmful effects of harmonic voltage on capacitors. Traditional reactive power compensation devices amplify harmonic currents in the power distribution system. These harmonic currents, coupled with the transformer inductive reactance and system impedance, cause voltage distortion in the power distribution system. Excessive harmonic voltage, superimposed on the system's fundamental voltage, leads to a rise in system voltage, causing the capacitor terminal voltage to exceed its rated voltage. According to relevant data, a 10% increase in capacitor terminal voltage can halve the capacitor's lifespan. When the background harmonic voltage on the grid side exceeds the standard, it also shortens the lifespan of capacitors in traditional reactive power compensation devices.

Resonance: Traditional reactive power compensation devices are capacitive loads, exhibiting a fixed resonant frequency with the inductive reactance of the distribution system transformer. Frequent load fluctuations cause these devices to switch on and off frequently. Furthermore, capacitors gradually lose capacitance over time, contributing to the high risk of resonance in traditional reactive power compensation systems. When resonance occurs in the distribution system, it can lead to abnormal increases in voltage and current, severely damaging the electrical load and distribution equipment.

Traditional reactive power compensation devices cannot track rapid load fluctuations. When the power distribution load fluctuates rapidly, traditional reactive power compensation cannot track it. When frequent switching occurs, the surge voltage and current during capacitor switching can also cause rapid damage to the capacitor bank. In severe cases, it can lead to explosions and fires of traditional reactive power compensation devices, causing system power outages and other accidents.

The above problems are risks that traditional reactive power compensation devices cannot avoid!

4.2 Countermeasures and Suggestions

To address the problems of harmonic amplification, ineffective power factor improvement, and inability to track rapid load changes caused by traditional reactive power compensation devices, the third-generation reactive power compensation device—the Static Var Generator (SVG)—effectively solves these problems.

4.2.1 Static Var Generator (SVG) Principle

SVG is based on a high-power voltage-source inverter. By adjusting the inverter's output voltage, it forms an adjustable fundamental voltage difference or harmonic voltage difference with the system voltage, thereby controlling the reactive current or harmonic current injected into the system to achieve the purpose of compensating for reactive power and suppressing harmonics.

Figure 7 SVG Working Principle Diagram

Bidirectional reactive power compensation: It can compensate for both capacitive and inductive loads, and can guarantee a power factor of 0.99 without fluctuation under rated capacity;

Harmonic filtering: The main harmonic content of the power distribution system, such as the 5th, 7th, 11th and 13th harmonics, is filtered out to ensure that the harmonic content of the system complies with the national standard 14549-93.

Fast tracking response: The full response time for SVG tracking load with filtering compensation is less than 20ms;

Precise compensation to eliminate resonance: SVG filter compensation is precisely based on the needs of the power distribution load, and there is no overcompensation problem, thus eliminating the possibility of resonance caused by capacitive factors in the power distribution system.

Table 2 Performance Comparison of SVG and Traditional Reactive Power Compensation Devices

4.2.3 Economic Analysis of SVG and Traditional Reactive Power Compensation Devices

Traditional reactive power compensation devices mainly consist of capacitors or capacitor-reactor arrays, whose costs have risen relatively steadily with economic development. In contrast, SVG's core components are power electronic devices such as IGBTs and DSPs, whose costs are trending downwards as material applications mature. The faster the adoption and application of these components, the faster their prices will decrease, leading to a rapid convergence between the two.

In summary, SVG products are adapted to the characteristics of modern power grid distribution and are the most advanced third-generation reactive power compensation devices that completely replace traditional reactive power compensation devices.

5 SVG Product Application Cases

5.1 Project Background

The copper SCR rolling production line of a non-ferrous metallurgical enterprise suffers from severe low-voltage interference, causing frequent damage to the frequency converter module, and the power quality urgently needs to be improved.

Figure 8. On-site environment of SCR copper rolling production line

5.2 Project Significance

Harmonic mitigation can effectively improve the reliability of power supply systems and eliminate harmonic hazards. It can also significantly improve the power factor of power distribution systems and drastically reduce high-frequency oscillations caused by harmonics, thus lowering noise levels during the operation of rolling mill equipment. Therefore, this harmonic mitigation method for the rolling mill not only ensures the safe operation of its power distribution system and improves production efficiency, but also saves energy and reduces consumption, resulting in significant economic benefits.

5.3 Test Results

Actual measurements during the operation of the roughing and finishing rolling mills revealed characteristic harmonics of the 5th, 7th, 11th, and 13th orders, indicating a high harmonic content. The load changes at several cycles during rolling line operation, placing extremely high demands on the response speed of harmonic mitigation equipment.

A Delta 300KVAR static var generator is installed on the low-voltage main incoming side of the 1250KVA copper-rolled transformer.

The waveform on the network side was restored from severe distortion to a sine wave.

Table 3 Comparison before and after the Static Var Generator is put into operation

5.6 Installation Images

Figure 9 Installation site photo

5.7 Project Review

A non-ferrous metallurgical enterprise successfully solved the harmonic and reactive power compensation problems in the roughing and finishing rolling mills by using Delta static var generators on its copper rolling line. This improved the power quality of the rolling line's power distribution system, ensured the reliability of the power distribution system, and achieved extremely significant harmonic control and energy-saving effects. The entire project was fully installed and commissioned in July 2011 and has been in operation ever since.

6. Summary

Traditional reactive power compensation devices, due to their inherent electrical characteristics, cannot meet the load demands of modern power distribution systems. The third-generation SVG (Static Var Compensator) overcomes these problems, not only resolving harmonic and reactive power issues in power distribution systems but also inherently mitigating resonance risks as a current source. It ensures the safe, reliable, and low-power operation of power distribution systems, making the widespread adoption of SVG products in power distribution systems a growing trend.

About the author:

Zhou Wei, male, born in October 1972, graduated from the National University of Defense Technology of China with a major in Computer Information Management. He is currently the manager of the Energy-Saving Application Products Department at Delta Electronics Co., Ltd., where he is engaged in the development, planning, and marketing of power quality products and has many years of industry experience in the field.