Installation of series Capacitor Bank in Transmission Lines. 2

[Matola]

Hello,
Am Baxter from Malawi working with ESCOM. I do load flow studies for the utility. We usually have low voltage profile in the Northern part since all generating plants are in the Southern region. Is installing series capacitors in the transmission lines a better solution to voltage problems? If Yes would you please help me with the specification for the capacitor on 132kV transmission line. Thanks in advance.

 

[Desrod2]

Not much to work with but it all depend on the cause of your voltage drop. Do you have problem all the time or just at peak load? Poor power factor could be solved by using shunt capacitor banks at receiving end improving voltage profile. Did you investigate that? Shunt capacitor are easier to maintain and could be installed at substations. Do you have stability problems? Did you investigate the impact of adding series capacitors?

 

[krisys]

As I understand, the series capacitors will be generally used to improve the stability margin and thus to transfer more power through the transmission line. The voltage drops shall be dealt with either connecting shunt capacitors at load ends or by installing SVC (or now a days STATCOM is more fashionable!!!).

Probably, for the subject you have in your hand, you may certainly need to perform additional studies, other than simple load flow study.

 

[Matola]

Thank you, the voltage drops in the system are usually experienced during peak hours. we have installed shunt capacitors,and have a bit improvement. We were trying to explore on series capacitor banks,, I use DigSilent Powerfactory software to perform the loadflows, but the impact was negligible. I thought it was because of the parameters i used, that is why i needed someone with practical experience to advise. I appreciate your enlightment. I still need to know the specifications of series capacitor banks available, say susceptibility/capacitance if you know anywhere i can find this information.

 

[krisys]

Matola,
Approach any reputed supplier/manufacturer of the series capacitors. They would provide you some basic information, from where you should be able to move forward.

 

[marks1080]

The series cap is used to increase capacity on the line. You'll have to spec it out based on your particular system. Protections typically involve having a breaker that closes during a fault to short the cap to ground.

 

[davidbeach]

Not short the cap to ground, that would be big problem. The breaker simply closes around the cap, shorting it out, removing the current from the cap, and returning the line impedance to its non-compensated value.

 

[marks1080]

Sorry. Yes David is correct. Short the cap out, not to ground. That would be bad.

 

[juleselec]

As others have pointed out, series caps are used primarily to expand a line's real power transfer capability (i.e. increase surge impedance loading) and can also improve transient stability. In principle, series compensation could improve voltages at the receiving end since the line itself consumes less reactive power, but it would require a fair amount of compensation.

Moreover, if you install the series caps near turbine generators, you run the risk of having sub-synchronous resonance or torsional oscillation problems. You're probably better off using standard shunt compensation at the far end / northern part of the line. Or if you have cash, then an SVC would give you better voltage control across different operating points.

 

[FPelec]

Hello Batola,
which are the characteristics of the 132 kV line (length, conductor cross section, positive sequence impedance and capacitance)?
132 kV lines are often equipped with small conductors, so that the resistive voltage drop is not neglibile if compared to inductive voltage drop. If the voltage drops is mainly resistive series and shunt capacitors will not give you much benefits.


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