Series capacitors

Series capacitor - connected in series at the far end of a long transmission or FTP distribution line to offset the reactive component of the line impedance, contain the voltage drop and enhance the receiving-end voltage. It can support a transmission or distribution system in the following ways ... 

Rating of series capacitors 24/779 Advantages of series conrpensation 24/780 Analysis of a. systenr for series compensation 24/782... 

Series and shunt capacitors both provide the same degree of compensation. But it is the correct reactive support that provides a more stable system less prone to load and voltage lluctuations. Thus i Judicious choice between the shunt and the series capacitors is required. In the following our main thrust is to arrive at the most appropriate type and extent of reactive support to achieve a higher level of utilization of a power transmission or distribution system, on the one hand, and more stability, on the other. 

This rating will be much less than the nominal voltage of the system. But since the series capacitors operate at... 

Figure 24.4 Dampening circuit across the series capacitors to limit the fault level...

If a large induction motor is switched on such a system it is possible that its rotor may lock up at the sub-synchronous speed and keep running at higher slips. This situation is also undesirable, as it would cause higher slip losses in addition to higher stator current and overvoltage across the series capacitors. 

Since the line impedance, R + J (Xl - Xc), will reduce with a series compensation, the fault level of the system will rise. It should not matter if the fault level of the system is determined by the impedance of the source of supply, ignoring any other impedance of the circuit (Section 13.4.1 (5)). Moreover, such a situation is automatically averted through the protection of the series capacitors, as discussed below, by which the capacitors are bypassed during a line fault, the line restoring its original impedance, hence the original fault level. Nevertheless, when it is required to limit the system fault level, inductive coupling circuits may be provided to reduce the fault to the desired level. This is also discussed below ... 

We will notice subsequently that series and shunt compensation are complementary. What a shunt capacitor cannot do, a series capacitor does and vice versa. On a secondary transmission system, say up to 66 kV, a shunt compensation may always be necessary to improve the power factor, as the load would mainly be indtictive. A series compensation may become essential, to improve the stability of the system, to cope with load fluctuations, switching of non-linear loads and voltage fluctuations occurring on the other power system or the grid to which this system may be connected. 

Series capacitors have also proved to be an easy way of relieving an already overstressed distribution netw ork to meet ever-growing load demands, particularly when it is not practicable to add another line for reasons of cost or space. 

Through careful management of the reactive pow er. making use of shunt and series capacitors and reactors, we can provide support to an overstressed LT or FIT stipply system, and achieve optimum utilization and a higher level of stability. 

Figure 24.13 Receiving-end voltage is flattened with the use of series capacitors...

Compensation required = 0.61 X o per unit length. Series capacitors making up 0.61 Xlq introduced... 

This value can be reduced by decreasing the value of X , which is possible by providing series capacitors in the line. If X(2c is the series compensation, then the modified impedance... 

Inductive reactance of overhead lines of section B-B. (7) Capacitive reactance of series capacitors. 

The series capacitors tire connected in series with the power lines to provide reactive control to an individual load or to a power distribution or transmission system. They are therefore switched with the pow er lines and are thus permanently connected devices. 

Standard for series capacitors in power systems Shunt capacitors, both LT and HT... 

Research Station. M.P Electricity Board. Central Board of Irrigation and Power. India, Series Capacitor Application to Sub-transmission Sxsiems Case Studies. I cehnical Report No. 66, Nov. (1988). 

The following are a few common methods for the protection of series capacitors. 

There may be a number of ways by which the series capacitors can be protected against line faults. Commonly used methods are briefly discussed below. 

---