PART IV - Power Capacitors and Reactive Power Controls
Chapter 24. System voltage regulation and improving power quality
• Capacitors for improving system regulation
• Series capacitors
• Rating of series capacitors
• Advantages of series compensation
• Analysis of a system for series compensation
• Reactive power management
• Influence of line length (Ferranti effect)
• To optimize the power transfer through reactive control
• Transient stability
• Auto-reclosure scheme for transient stability
• Switching of large reactive banks
• Automation of power network for dynamic stability through SCADA
• Serial data transmission and communication interfaces
• Introduction to communication protocols
• Security of SCADA system
Capacitors for improving system voltage regulation
Another important application of capacitors is to improve the voltage regulation of a power supply system. The regulation of a power system at the receiving end is defined by % Regulation
Higher regulation will mean a higher voltage fluctuation at the receiving end, resulting in poor stability of the system. Regulation up to 3–5% may be considered satisfactory. To improve the regulation of a system, power capacitors can be used in series at the receiving end of the system.
The basic purpose of series capacitance is to offset the content of excessive line inductance, reduce the line voltage drop, improve its voltage regulation and enhance the power transfer capability and hence the stability level of the system. It can accordingly find application at all high-current and high-impedance loads such as
• An electric arc furnace, where heating is caused by arc plasma between the two electrodes. The arcing makes the circuit highly inductive, besides generating unbalanced currents (third harmonics), due to different touchdown arc distances in the three electrodes which make it a non-linear impedance load.
• An induction furnace, where the heating is due to eddy current losses induced by the magnetic field.
• Electric arc and resistance welding transformers as for spot, seam and butt welding.
• Large scale electrolysis of aluminium, copper or zinc.
• A long transmission line, say, 400 km and more, for a radial line and 800 km and more for a symmetrical line, as discussed later.
• It can also be applied to an HV distribution network that has a high series inductive reactance to improve its receiving-end voltage.
Automation of power network through Supervisory Control and Data Acquisition (SCADA) system
In this age of mechanization, SCADA has become an inevitable tool for automation. With the availability of microprocessors and digital signal processing intelligent technologies that are prompt, accurate and more importantly reliable, human involvement in monitoring and control of complex activities in industries and power management can be kept to the minimum. Automation enhances the integrity, reliability and dynamic stability level of a system. Such supervisory systems are becoming the state-of-the-art, around the world to monitor and control complex activities in power management and industries like steel, cement, chemical, fertilizers, petrochemical, refineries etc. achieving,