Distinctive functions and advantages of SVG solution

SVG is one of the core devices and core technologies of the flexible AC transmission system (FACTS). It is used to perform reactive and harmonic compensation in the power system. SVG is connected in parallel to the power grid, which is equivalent to a variable reactive current source. Its reactive current can quickly change with load reactive power and harmonic current, and automatically compensate the reactive and harmonic currents required by the system. The main functions of INPSVG are as follows:

l  Improve line transmission stability 

l  Maintain the receiving end voltage, enhance system voltage stability

l  Compensate reactive power of the system, improve power factor

l  Harmonic dynamic compensation, improve power quality

l  Suppress voltage flicker and fluctuation

l  Suppress three-phase imbalance

Instead of using large-capacity capacitors and inductors, INPSVG uses high-frequency switch of high-power electronic devices to achieve conversion of reactive power. Compared with conventional compensation solutions, it has the following advantages:

l  Faster response time

l  More effective suppression of voltage flicker

l  Wide operating range, large compensation capacity

l  Flexible compensation methods, including reactive power compensation, voltage compensation, negative sequence compensation, harmonic compensation and comprehensive compensation

l  No harmonics occur when providing reactive power

l  Output harmonics lower than 13th harmonic when compensating harmonics

Typical usage occasion of SVG

Regional power grid

There is a large amount of reactive load in the regional power grid, such as power lines, power transformers and users’ electrical equipment. A large amount of reactive load will reduce the transmission of active power and system power factor, increase line loss, and is not conducive to economic operation of the entire regional power grid. INP SVG can perform comprehensive reactive power compensation for regional power grids, stabilize grid voltage, reduce line losses and improve power quality.

Electric arc furnace (EAF)

EAF is a kind of impact nonlinear load. It generates a large amount of harmonics and negative sequence currents during operation, which may cause great voltage fluctuations and flicker of the power grid, and the power factor is extremely low. INP SVG can quickly detect the reactive and negative sequence current of the EAF and compensate within 5ms to suppress voltage flicker and stabilize busbar voltage. High-voltage filtering device manufactured by IN-POWER can effectively eliminate higher harmonics of the system and provide fundamental reactive power, and improve the power factor.

Subway

The power factor of subway in the daytime is about 0.9, while only about 0.3 at night. The daily average power factor is about 0.78, and reactive power fluctuates greatly. Due to charging effect of the cable, the subway system is in a reactive power releasing state at night, which causes the busbar voltage to rise and jeopardizes the stability of electrical equipment and system. INP SVG can quickly and accurately perform reactive compensation on power system of the subway, which stabilizes the busbar voltage and improves the power factor, thus solving the reactive power releasing problem.

Electrified railway

Electrified railway belongs to single-phase load with frequent fluctuations, which causes severe imbalance and also reactive power compensation and harmonic problems to the traction substation. The deterioration of power quality also jeopardizes safe operation of the locomotive. INP SVG can dynamically adjust the reactive power of the power supply system, improve the power factor and solve the imbalance problem. Besides, the filtering device can effectively filter out the higher harmonics and solve the reactive and harmonic problems.

Wind power station and solar power station

With the widespread use of wind power technology, the proportion of installed wind power generating capacity in the power grid increases, and its effect on the power grid also increases. Due to randomness of wind power generation, the active and reactive power of the power system will all be impacted and lead to voltage fluctuations. In addition, low voltage fault of the power system will affect gird connection of the wind power station and affect safe operation of the wind turbine. Therefore, the national standard clearly stipulates that wind power stations must be equipped with reactive voltage regulation system. In case of low voltage fault, INP SVG can dynamically adjust the reactive power level, stabilize the busbar voltage, reduce the reactive output of the fan, thus improving stability of the regional power grid.

Port

The load of port features great change, rapid speed change and short-time heavy load, and belongs to reactive power impact load. The commonly used thyristor AC and DC drive devices may generate a large amount of harmonics. Port enterprises are important loads and the quality of power supply for the port must be guaranteed. INP SVG can quickly track load changes of the port, respond to load reactive changes in time, and ensure power factor of the power supply system. At the same time, high-voltage filtering device manufactured by IN-POWER can effectively eliminate higher harmonics of the system and provide fundamental reactive power, and improve the power factor.

Problems caused by reactive power and harmonics

Reactive power problem

The existence of resistive and inductive loads in power systems, such as asynchronous motors, transformers, fluorescent lamps, etc., consumes a large amount of reactive power, while large-capacity impact reactive load can cause rapid fluctuations in system voltage. Power electronic converter devices, especially popularization of various phase-controlled rectifiers, also consume a large amount of reactive power. This leads to various problems such as deterioration of power quality, increase in transmission loss, three-phase imbalance, and reduction of effective utilization of power transmission and transformation equipment.

Conventional reactive power compensation device generally adopts contactor or thyristor switching control, which features slow response speed, fixed switching compensation capacity, large floor space and complex maintenance. The new dynamic var generator can overcome these shortcomings, effectively stabilize the voltage of the power grid, improve the power quality and reduce the reactive power loss.

Harmonic problem

The widespread application of non-linear loads such as rectifiers and converters in the system will generate a large amount of harmonic currents into the grid, causing grid voltage distortion. Harmonics will not only cause eddy current losses in power equipment and lines and increase line losses, but also will induce system resonance, resulting in harmonic overvoltage and equipment damage. Large amount of harmonics can also cause failure of relay protection and automatic control systems, affecting normal production activities.

Conventional filters mostly use capacitor and series reactors to form low impedance characteristic at characteristic frequency, to absorb harmonic currents. Due to the passive absorption method, the equipment is susceptible to system impedance, which may cause system resonance, overload and other hazards; the floor space is large, and the electromagnetic components have interference to the environment. On the contrary, SVG adopts active output mode, which is not affected by system impedance, has no danger of overload, and has small floor space. It can effectively offset harmonic currents in the power grid, improve power quality and reduce harmonic losses.

Operating principle of SVG

The principle of INPSVG (Static Var Generator) is to connect the VSC (Voltage Sourced Converter) to the grid in parallel via reactor or transformer, and adjust the output voltage magnitude of the AC side of the inverter, so as to change the reactive current magnitude of the input system, quickly absorb or emit reactive power, thus realizing rapid regulation of reactive power.

Technical features of SVG

Angular topology

Star topology

Product features

l  Full digital control system, fast response speed. The step response speed is less than 5ms;

l  Intelligent fuzzy control strategy, optimized control algorithm, improved compensation accuracy, and power factor can be controlled to 1;

l  Low power design, equipment loss is less than 3% at full load;

l  Modular design, convenient maintenance of equipment, power module replacement time is less than 5 minutes on average;

l  Flexible compensation method, equipped with multiple compensation functions and automatic optimization function;

l  The complete machine is fully loaded and aging for 24 hours before delivery.