The proliferation of wind farms can have an adverse impact on grid performance and stability. India is still developing its Grid Code which will set limits on future wind farms, and STATCOMs will play an increasingly important role in helping wind farms to comply with the Code.
India´s electrical power system is evolving with increasing energy production from renewable energy sources, ie. wind, solar, biomass. Wind power in particular is expanding faster than the other sources with realisation of larger capacity generators of more than 2 MW each, and projects with wind power generation in hundreds of mega-watts. India has an estimated gross wind power potential of 100,000 MW mainly in the states of Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Maharashtra, Rajasthan and Tamil Nadu, and 30,000MW of additional wind power capacity is envisaged to be installed in the 12th plan (2012-17) (1).
Grid Integration Challenges
Wind power integration and transmission infrastructure has to be planned based on com¡bined rated power of the wind farm. However due to variability of power generation, depen¡ding on wind speed, there is always a low Capacity Utilisation Factor of the transmission infrastructure. Fluctuations in the wind speed are transmitted as fluctuations in mechanical torque, leading to voltage fluctuation, voltage sag, swells, flicker, harmonics etc. Hence large wind farms pose stability and control issues when integrated to the power system. In case of wind farms located in remote areas away from load centres, the long transmission line capacitance and reactance start to play a crucial part during no-load and severe load chan¡ging conditions.
This necessitates additional control and compensating equipment to enable recovery from severe system disturbances. Without reactive power compensation, such situations can stress the entire network, and in weaker grids may even cause a grid collapse.
Basically wind power integration substation needs additional equipment which has the ability to dynamically absorb or inject reactive power (VAr) into the power grid. Hence dynamic reactive power compensation for grid connected wind energy generation has following objectives.
Dynamic Reactive Power Compensation
Static Synchronous Compensator (STATCOM) offers a fast and step-less Var compensation on high-voltage electricity networks offering better performance and response to electrical system transients. STATCOM is based on Voltage Source Converter (VSC) technology, which uses low-voltage cells in series to realise a high voltage output. This is the same technology being used for state-of-the-art VSC-HVDC systems By controlling the output voltage to be either higher or lower, STATCOM will draw a capacitive or inductive current from the system. Even without control action STATCOM has a natural tendency to compensate for changes in system voltage, but its low stored energy means it can do this much more rapidly than a synchronous condenser. Also unlike a constant impedance device like a capacitor or inductor whose output current will decrease with voltage, STATCOM can continue to generate its maximum output current even at low system voltages as it is not dependent on passive reactive components.
The main features and advantages of STATCOM may be summarised as follows:
It has fast response time & stronger mitigation ability for voltage fluctuation
STATCOM can be realised in containerised solution for deploying at remote sites of wind power integration substations. Moreover it can be easily re-located and rapidly deployed in areas needing immediate VAR correction.
STATCOM solution is modular, future system expansions are possible with minimum engineering costs
It can self-start and voltage-balance without the need for any external power source or equipment.
Sustainable power sources, like wind energy, are becoming more essential considering India´s population growth, and industrialisation. However the proliferation of wind farms can have an adverse impact on grid performance and stability. Hence countries with large established wind energy generation, have already defined an Electrical Grid Code to ensure minimum disturbances due to wind variability. India is still developing its Grid Code which will set limits on future wind farms here. Considering these developments, STATCOMs will play an increasingly important role in helping wind farms to comply with the Grid Code.
1) ´Transmission Plan for Envisaged Renewable Capacity´, Power Grid Corporation of India Ltd., July, 2012 (www.powergridindia.com)
2) National Level Consultation on National Wind Energy Mission, January, 2014 (www.mnre.gov.in)
3) Indian Electricity Grid Code (IEGC), Mini¡stry of Power (http://powermin.nic.in/)
4) ´Wind Farm Power Evacuation & Grid Integration´, IEEE ISGT Asia 2013 by NSM Raoetal
The author is Lalit Tejwani, Country Manager, India, Rongxin Power Electronic Co Ltd. He can be reached at firstname.lastname@example.org
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