Static Var Generator (SVG) / Static Synchronous Compensators STATCOM

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With high levels of performance, efficiency and reliability, Static Var Generators (SVGs) represent the next generation of Flexible AC Transmission Systems.

Compared to traditional SVC technology, the SVG / STATCOM offers faster response, stronger flicker restrain capability, lower harmonic content and a wider range of operation. SVGs / STATCOMs also have a more balanced ratio between capacitance and conductance than SVCs, which enhances their constancy.

Features include:

  • Improve power transmission stability
  • Maintain receiving end voltage level
  • Reactive power compensation leading to high power factor and low line losses
  • Restrain voltage fluctuation and flicker
  • Mitigate 3 phase unbalance

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The Static Var Generator Provides the Ultimate in Power Grid Stability

Keeping electric power running within very specific limits requires special technology, and the best technology you can use for this purpose is the Static Var Generator (also known as a Static Synchronous Compensator) from CSE Uniserve. For simplicity, these long names are usually abbreviated to SVG and STATCOM.

Operations that are smaller in scale may be able to get by with only standard static var compensators, but for high demand applications, you’ll definitely feel greater assurance with the SVG.

Key Differences Between SVG/STATCOM and SVC

Below is a quick summary of the main differences between SVG and SVC, so you can see easily determine which technology is most suitable for your intended application and your project budget:

  • SVG costs considerably more than SVC.
  • SVG is considerably faster than SVC.
  • SVG is considerably smaller in size than SVC.
  • SVG holds constant current better than SVC.
  • SVG can experience higher voltage losses than SVC.
  • SVG interfaces directly to the power source, where SVC does not.
  • SVG has controllable voltage source, where SVC uses dynamic reactance.
  • Overall, the characteristics of SVG are better than those of SVC.

Based on these comparisons, it is possible to conclude the situations where each technology is best suited. For example:

  • If you have a low budget: SVC is cheaper.
  • If you have very limited space for installation: SVG is more compact.
  • If protection against voltage losses is most important: SVC experiences fewer losses.
  • If protection against over-voltage is most important: SVG is more suitable.
  • If you need constant current with minimal variation: SVG is more stable.
  • If you need a very fast response: SVG will respond fastest.
  • If you need to interface directly to the power source: Only SVG can do this.

Of course, no single factor should be the deciding factor; instead you should look at the whole picture before making a decision. For example, if you have a low budget but limited space, SVG could still be the better option.

An Example of SVG in Operation

SVG is used for correcting situations where the grid system has an unacceptable power factor, unacceptable voltage regulation, or current stability.  In some cases, an SVG os STATCOM is required by a Utility to protect he general Grid from issues created by large motor starting or other high draw events.

Where SVC systems use a thyristor controlled reactor (TCR), the SVG uses an insulated gate bipolar transistor (IGBT) to perform switching operations. In order from slowest to fastest, this is how the common switching technologies rank:

  • Mechanical switching is slowest.
  • TCR switching is faster than mechanical switching.
  • IGBT is faster than TCR and mechanical switching.

The IGBT switching is controlled by a metal-oxide-semiconductor (MOS). This allows it to operate at really high speeds, so it is a technology used in systems where fast response times are critical. The IGBT also has numerous protective mechanisms that kick in when the component fails. The IGBTs used in SVGs are modular, allowing them to be quickly disconnected and replaced in case of component failure.

The power source is usually interfaced with directly, and this power source is usually a bank of large DC batteries, providing capacitor charge. The SVG will either generate current or absorb it, depending on the amplitude of voltage arriving through the voltage source converter. This damps harmonics very effectively – even more effectively than SVC, which is already very good – and gives a consistent output, resulting in better safety and continuity of transmission.

Available Now from CSE Uniserve

If you have questions about Static Var Generator operation, we have the answers. Our engineering consultants will even be delighted to offer you a free consultation, so you can get a very thorough assessment of your intended application and the right advice to make sure you get the best result. You can also call us directly on 1800 987 616.

CSE Uniserve is Australia’s leading supplier of electrical equipment & engineering services. We design our technology to assist industries in delivering successful project outcomes, such as our slip energy recovery system & variable speed drives. Visit our website or contact us for more information.

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Description


The SVG / STATCOM is a voltage source converter (VSC) using insulated gate bipolar transistors (IGBTs) or insulated gate commutated thyristors (IGCTs) to achieve reactive power compensation.

 

STATCOM Main Components

STATCOM Converter

The key element of this technology is the standard basic Power Module (see Figure 2.1). These Power Modules are connected in series to obtain a high AC voltage with extremely low harmonic distortion, and very low dv/dt. This also allows use of a low switching frequency that reduces power losses.

The Power Module is also designed to guarantee high maintainability due to its special electrical plugs so it is very easy to install or remove.

The converters are designed to be installed within a specially designed container.

The converters are cooled by forced air cooling. The basic semiconductor devices are IGBT.

STATCOM Starting System

The STATCOM starting device is composed of an arrester, connecting reactor, charging resistance and bypass switch (circuit breaker). The main role of the connecting reactor is to limit the instantaneous current when STATCOM is first energised.

The charging resistance is used to restrict the inrush current. Once the DC capacitors are fully charged, the charging resistor by-pass switch is closed and STATCOM can start normal operation.

Disconnectors and Earthing Switches

The switches are adequately sized to carry the maximum steady-stage and overload currents including fault, inrush, harmonic currents and over-voltage.

The Earthing switch shall be closed during device maintenance and repair for safety reasons.

The disconnectors and earthing switches are positioned to enable maintenance work to be carried out in complete safety throughout the entire unit.

 

STATCOM Control Strategy Design

STATCOM control strategy is categorized into primary control strategy and secondary control strategy.  Primary control strategy offers device reactive power control, constant system reactive power control, power factor control, and constant system voltage control.  The secondary control strategy offers low voltage ride through control, conditioned restarting control, pulse locking control etc.

Constant System Reactive Power Control

This control strategy means STATCOM can compensate all system reactive power dynamically to make system reactive power to be effectively 0, or compensate part of system reactive power dynamically to keep the system reactive power to a constant value.

According to the system current detected by STATCOM and STATCOM output current, Load current can be calculated. The reactive component can be calculated through PARK transformation of load current.

Power Factor Control

Power factor control can make system power factor reach to the reference value which is usually supplied by customers. STATCOM completes the task of controlling system power factor by outputting corresponding reactive power detected by using the calculation method of power factor control.

Iq_ref is the reference value of reactive power, Cos_ref is the reference value of power factor, Ip_load is load active power, Iq_load is load reactive power, Coff_cos is a reference value coefficient which can be calculated by the equation as below.

Constant System Voltage Control

STATCOM generates reactive power fast with the slope in transient process to maintain stability of the power grid.

STATCOM receives the output from a closed-loop regulator as the reactive current (or reactive power) reference that the compensator should generate.  A PI controller is used to ensure voltage regulation in both steady state and transient state.

When the voltage drops and the compensator U-I characteristics decreases, STATCOM can adjust the amplitude and phase of the AC voltage of its convertor to provide the required reactive current.  This is limited by the rated current of STATCOM. When the voltage reference changes, the U-I characteristics will move upwards or downwards accordingly.

The Voltage Regulator compares the measured control variable with the reference value, and then puts it in the transfer function of the controller. The controller then calculates the reactive current according to STATCOM U-I characteristics and generates (absorbs) the same amount of current for compensation through the STATCOM closed-loop controller.

The slope of the U-I characteristics curve known as difference adjustment rate, is defined as the ratio of voltage amplitude increment to current amplitude increment in the linear control area of the compensator.

The slope can also be defined as the ratio of voltage change to voltage rating when STATCOM generates maximum reactive power. The slope is usually kept in between 0% to 10%  and is typically between 3% to 5%.  In practice, current feedback is used to calculate the slope in order to get control diagram of the voltage regulator:

 

Device Reactive Power Control

STATCOM can be operated in open-loop control mode, which means operators can control STATCOM to output any required reactive power value in the range of rated capacity.  In this way, we can detect the device’s control precision or test the device’s basic characteristic.

Device reactive power control only outputs fixed reactive power without considering the system reactive power situation. Under special working conditions, device reactive power control is very useful and can be operated by receiving a reference value from the user’s SCADA/PLC system or will also accept manual input.

 

 

    • The compact footprint of our SVG / STATCOM means it can be containerised for ease of deployment and relocation. This brings significant advantages in utility and industrial scenarios where geographical requirements for reactive power compensation can shift over time.

 

Specifications:

 

      • PCC voltage – 500kV plus

 

      • SVC voltage – 6kV / 10kV / 27.5kV / 33kV

 

      • Capacity – 2Mvar to 20Mvar plus

 

 

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