Power Quality Solution: SVG (Static VAR Generator)
Introduction:
Power Quality(PQ) solution SVG is a Flexible AC Transmission Systems (FACT) device which provides fast acting reactive power in high voltage (HV) network, balance unity power factor, and sustain voltage(when voltage low it’s act as a capacitive SVG and when voltage high it’s act as a inductive). It is also called as instantaneous step less reactive power compensators.
In most of the Industries for power factor correction, Automatic Power Factor Correction Units (APFCU) is used. The disadvantage of APFCU is that it has slow reacting time to load change hence system is in constant over/under compensation. Now a day due to harmonics capacitors gets overloaded and contactor get continuously fails. Whereas SVG has different approach for power factor correction which utilizes high speed three level inverter for reactive power correction. In ¾ of the cycle full real time power factor correction is done.
There are two types of SVG are as follows:
- Transmission SVG: Connected on power system to correct transmission line voltage
- Industrial SVG: Connected nearby load to improve PQ
Working Principle:
The SVG has a wide range of applications, where ever the load demands dynamic reactive power, Harmonics, and three phase unbalance currents. The SVG are of rack mounted, wall mounted type, and cabinet type. It consists of High Frequency Inductor, IGBTs (insulated-gate bipolar transistor), IGBT driving modules and Controller.
SVG is connected in between power grid and load. At load side external CT is used to detect load current. Controller divides the load current into active and reactive power by using advanced logic control arithmetic’s then is PWM signal is send to IGBT driving module. The on & off control of IGBT is done at average 20 kHz frequency. At last the inductive/capacitive power compensation is produced on inverter induction, whereas CT continuously detects the output current and sends negative feedback to controller and next logical operations are done to achieve more accurate and stable system.
The waveforms are of voltage and current for load and supply voltage (Power grid) and current waveform is of SVG. Load current waveform is of lagging type, for that SVG is producing leading current to compensate the lag and make system stable.
Difference between old solution and new solution on the basis of parameters:
| Parameters | Capacitor or Reactor Bank | Static VAR Generators |
| Response time | Contactor-based solutions take at least 30s to 40s to mitigate the problem where as thyristor-based solutions 20ms to 30ms | Real-time mitigation of power quality problems as the overall response time is less than 100µs |
| Output | Depends on step sizes, cannot match load demand in real time, Depends on grid voltage as capacitor units & reactors are used | Instantaneous, continuous, step less and seamless, Grid voltage fluctuation has no influence on the output |
| Power factor correction | Capacitor banks needed for inductive loads and reactor banks for capacitive loads. Problems in systems with mixed loads, Not possible to guarantee unity power factor as they have steps, system will be having continuous over and under compensation | Corrects simultaneously from -1 to +1 power factor of lagging (inductive) and leading (capacitive) loads, Guaranteed unity power factor at all times without any over or under compensation (step less output) |
| Unbalance | Do not correct load unbalance | Can correct by selecting the amount of load balancing |
| Design & sizing | Reactive power studies needed to size the proper solution, Usually oversized to better adjust to changing load demands, Need to be designed taking into account system harmonics, Custom-built for specific load and network conditions | Not required extensive studies as it is adjustable, Mitigation capacity can be exactly what load demands, Unaffected by harmonic distortion in the system, Can adapt to load and network conditions & changes |
| Resonance | Parallel or series resonance can amplify currents in the system | No risk of harmonic resonance with the network |
| Transients | Caused by the switching of capacitor units or shunt reactors | Not created (no switching of passive components) |
| Overloading | Possible due to slow response and/or variation of loads | Not possible as current limited to max. RMS current |
| Footprint & installation | Medium to large footprint, especially if several harmonic orders, Not simple installation, especially if loads upgraded frequently | Small footprint and simple installation as modules are, Compact in size. Existing switchgear can be used |
| Expansion | Limited and depends on load conditions and network topology | Simple (and not dependant) by adding modules |
| Maintenance & lifetime | Using components that need extensive maintenance like fuses, circuit breakers, contactors, reactors and capacitor units, Switching, transients and resonance reduce lifetime | Simple maintenance and service life up to 15 years as there is no electro-mechanical switching and no risk of transients or resonance |
Followings are the industries where is suggested to use SVG:
- Automotive and Welding plant
- Steel plants and Rolling mills Textile Industries
- Process industries
- Crane and Compressor loads
- Pulp and Paper industries
- Rubber industries
- Chemical and Cement factories
- Water treatment plants
Advantages of SVG are as follows:
- Step-less dynamic reactive power compensation
- Very fast real-time response
- Complete solution for providing PF correction, Harmonics Mitigation and load balancing
- Programmable and Customizable
- Improving voltage stability for weaker networks or generator fed power supply
- Do not require detail system study and no amplification of load harmonics
SVG Technical Specifications:
- TYPE: 220V/ 400V / 500V/ 690V
- Max neutral wire current: 30KVAR/50KVAR/ 75KVAR/100KVAR
- Nominal voltage: +/-20%
- Rated frequency: 5OHz±5%
- Reactive power compensation rate: >95%
- Network: 3-wire/4-wire
- Machine efficiency: >97%
- Switching frequency: 16 kHz
- Installation: Rack/wall hanging
- Into the way of line: Back entry (rack type), top entry (wall-mounted)
Conclusion:
SVG is small size IGBT based device which deliver instantaneous capacitive and inductive power to maintain reactive power and power factor. It optimized for highly dynamic applications where conventional capacitor or reactor banks unable to track the loads.
Keywords: #manufacturing #electricalindustry #powerindustry #powerquality
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