An Introduction to FACTS Presented by T.S.L.V.Ayyarao Assistant Pofessor GMRIT
Why do we need Transmission Interconnections? Delivery of Electrical Power To minimize the total power generation capacity and Fuel cost. To supply electricity to the loads at minimum cost with a required reliability. Transmission is an alternative to a new generation resource. Economic energy or reserve sharing is constrained by transmission capacity
Why do we need Transmission Interconnections?Can we use the full potential of Transmission interconnections? As power transfers grow, the system becomes more complex to operate. The power systems of today are mechanically controlledIf so what? Switching devices are mechanical and there is little high speed Mechanical devices cannot be initiated frequently.
Why do we need Transmission Interconnections? Mechanical devices wear out quickly. In view point of both dynamic and steady state operation, the system is really uncontrolled. In recent years, power demand increases day by day. Increased demand and absence of long term planning leads to less security and reduced quality of supply.
Opportunities for FACTSFACTS technology opens up opportunities to control power and enhance the usage capability of lineFACTS controller uses Control the current through the line at reasonable cost. Enables the power to flow under normal and contingency conditions To control the interrelated parameters (series impedance, shunt impedance, current, voltage, phase angle)
Opportunities for FACTS To damp oscillations at various frequencies below rated frequency. Enable a line to carry power closer to its thermal rating. Mechanical switching replaced with power electronics
Power Flow in an AC System In ac system, the electrical generation and load must balance at all times. The electrical system is self-regulating. If generation is less than load, voltage and frequency drop. Active power flows from surplus generation areas to deficit areas.
Power Flow in a Meshed System A adjustable series capacitor controls the power flow Mechanically switched series capacitor is limited by wear and tear. A series capacitor in a line may lead to subsynchronous resonance. This occurs when mechanical resonance frequencies of the shaft of a multiple turbine generator unit coincides with 50hz minus the electrical frequency of the line.
Power Flow in a Meshed SystemIf series capacitor is thyristor controlled It can be varied as often as required Rapidly damp any sub-synchronous resonance conditions Damp low frequency oscillations in the power flow Avoid risk of damage to generator shaft and system collapse Greatly enhance stability of the network.
Limitations of loading capability For best use of transmission asset and to maximize the loading capability, what are the limitations?There are three kinds of limitations Thermal Dielectric Stability
Limitations of loading capability ThermalFor overhead line, thermal capability is a function of ambient temperature, wind conditions, conditions of conductor, and ground clearance. The FACTS technology can help in making an effective used of newfound line capability. DielectricBeing designed very conservatively, most lines can increase operation voltage by 10% or even higher. FACTS technology could be used to ensure acceptable over- voltage and power flow conditions.
Limitations of loading capability StabilityThe stability issues that limit the transmission capability include: 1. Transient stability, dynamic stability, steady-state stability, frequency collapse. Voltage collapse, and sub-synchronous resonance. 2. The FACTS technology can certainly be used to overcome any of the stability limits.