Reactive power injection is required to maintain the voltage at various points in the transmission line, so in order to maintain the voltage with in specified limits at various points in the transmission line going for the reactive power injection or reactive power compensation. the reactive power compensation may be shunt compensation or series compensation or it can be afford by various devices.
series compensation : In series compensation it can be afford by the reactors and capacitors, so basically the series reactors are air cored reactor, iron cored reactor from the constructional point of view or it can also say tap saturable reactor and the operational point of view it can be fixed reactor and variable reactor and they can also be on the type of housing indoor reactor and outdoor reactor.
Is Reactive Power injection Useful ?
The series reactor are nothing but current limiting reactors, this series reactors are placed in series of the line and they are also called as neutral earth reactors when we are placed between the neutral and earth in star connected load. These reactors are employed in industrial arc furnance when the occurrence of the fault is very high, the occurrence of high faults like short circuit fault, 3-phase fault, Asymmetrical and symmetrical fault there will be a high current flowing, so in order to limit the high current and protect the devices from high current, we are going for series reactors or current limiting reactors.
Series capacitors are providing the line such that the effective reactance of the line can be neutralized, Reactive power injection. so we are having the inductive reactance and capacitive reactance then the inductive reactance will be neutralized by capacitive reactance.
power without compensation will be given by,
Pw= VsVrsinδ / Xl
power with series compensation given by,
Pse= VsVrsinδ / (Xl – X)
Pse / Pw = Xl / (Xl – Xc)
then, Pse / Pw = 1/ [1 – (Xl / Xc)Kse]
Kse = series compensation offered
when series compensation offered is 50% then,
Kse = 0.5
when series compensation is 75% then, Kse = 0.75
i,e., the series compensation increases the efficiency of power transfer capability.
shunt compensation : The shunt compensation is offered by shunt reactor and shunt capacitor, shunt reactor purpose is to observe the lagging VAR at light loads. In light load condition or no load condition there is increase in voltage at receiving end voltage for long transmission and medium transmission this effect is ferrenty effect, then this ferrenty effect is not deserved so we are going for the lagging VARs. thermal power plant
The shunt reactors are Air core, iron core and saturable reactors, in reactors there will be high magnetizing current, if we are using a iron core reactors this magnetizing current cause the high hysteresis loss. As there is high hysteresis losses in iron core reactors is used for small ratings and small transmission voltages.
As in the Air cored reactors there is no effect of hysteresis losses because the Air cored reactor is without iron core and magnetizing effect is nullified and then the Air cored reactors are used for higher ratings and higher transmission voltage. The mass observed by the iron core and Air cored reactors will be proportional to the square of the terminal voltage. tap saturable reactor it is possible to use when saturated at some selected voltage between the range of ±10% of the rated voltage.
when saturated and the saturation can be done by the phase controlled thyristers. when saturated the VARs observed by this tap saturable reactor will be changing rapidly with small increasing the voltage. That is the small increase in the voltage at the recieving end side which is leading to a ferrenty effect. there is a possibility of using tap saturable reactor in paralel with the capacitor. If there is high voltage transmission line and there is step down
transformer the figure shows the parallel connection of a capacitor with the tap saturable reactor, so initially this combination behaves like a capacitor this capacitor deliver the lagging VAR and observe the leading VAR. The characteristics at low voltage will be a capacitor and at high voltage it will be a tap saturable reactor. The slope correction capacitor is used in series with the tap saturable reactor in order to match the characteristics of the tap saturable reactor with the requirements of the systems.
Thyristor controlled reactor with fixed capacitor : There is high voltage transmission line with step-down transformer and inductor is in series with the similar anti parallel thyristers and fixed capacitor parallel with this combination. Here this will provide the leading VARs and lagging VARs as we are having the inductors and capacitors. The thyristers are used control the current in the reactor and the fixed capacitor are used to provide the lagging VAR and inductor will observe the lagging VAR, the firirng angle of the thyrister can be controlled by PA controller.
Thyrister controlled reactor with thyrister switch capacitor : The capacitors are series with the similar anti-parallel thyristers and this thyristers is series with the inductors. The similar anti parallel thyristers will switch the capacitor, now the capacitor bank is requirement will be based on the practical consideration from the operating voltages, maximum compensation required and current rating rating of the thyristers based on this three factors number of capacitor banks used can be determined. The fixed capacitor is series with the reactor so the this combination will act as a tune filter to filter out the 5th and 7th harmonics .
Click Here – hindime