SVC – Static compensators intended for electric energy improvement within industrial networks. Static Var Compensator is designed to decrease disturbances caused by changes in reactive power and voltage fluctuations and at the same time to stabilize the parameters of electric energy. In general, these are the systems containing reactors and/or thiristor controlled capacitors switched onto the electroenergetic network. They can be treated as parallel regulated susceptance. Thiristors are the connection element in the circuit.

Consumers using non linear items have great influence on the quality of energy.
In the feeding networks they cause:

• higher harmonics
• voltage fluctuation as a result of varying loads
• light flickering
• reactive power demand

Above problems can be eliminated from the network by using SVC equipment. SVC is individually designed on the basis of typical components to meet specific client’s needs. These problems can appear simultaneously. Optimum solutions can be found after technical and economic analysis.

For example:

1. Harmonics can be absorbed by filters. The filter circuit of the SVC system reduces the total harmonic distortion below specified levels.
2. Unbalanced voltage can be stabilized by using thiristor controlled reactors and capacitors
3. Rapidly varying reactive power causes flickering lights which can be avoided by thiristor controlled reactors
4. Unbalanced reactive power load can be reduced by using thiristor controlled reactors and capacitors

 

A typical source presented by Nokian for these kind of disturbances is electric arc furnance. Number of benefits can be seen within a steel plant:

• voltage fluctuations reduced by 80%
• increased voltage on the load bus which decreases the steel processing time and thus increases productivity
• improved power factor
• the arc furnance stabilized by the SVC has a positive effect on the consumption of graphite electrodes
• the harmonic distortion is limited below specified levels by the filter circuit of the SVC

 

DATA REQUIRED FOR THE DESIGN OF COMPENSATOR
Static compensators are designed individually, taking into consideration the special characteristics of each plant.
Data required for the design of SVC:

• schematic diagram of the system to which the compensator is to be connected
• maximum and minimum short circuit power in the point of common coupling
• information about reactive power distortions and load
• harmonics details (network parameters analysis)
• design limitations, for example acceptable voltage fluctuation and harmonics level, reactive power requirements and the control speed
• any additional or special compensator requirements
• environmental characteristics

Compensator systems can contain:

• Thyristor Controlled Reactors (TCR)
• Fixed Capacitors (FC)
• Thyristor Switched Capacitors

In practice there are different compensator solutions, each with its own characteristics.
The most popular systems are:

• compensator with fixed capacitor and controlled reactor current type FC/TCR
• compensators with travel switched capacitor bank steps type TSC