Analysis of Capacitor Banks' Role in Enhancing Transient Stability

This report delves into the crucial role of capacitor banks in improving the transient stability of power systems. It begins by defining transient stability and its significance in maintaining the synchronism of power systems following disturbances. The report then explains the functionality of capacitor banks, including their use for energy collection, power factor correction, and reactive power compensation. It differentiates between shunt and series capacitor banks, detailing their respective applications and benefits. Shunt capacitor banks are highlighted for their role in voltage regulation and power factor improvement, while series capacitor banks are discussed for their ability to compensate for abnormal current variations. The report concludes by acknowledging the limitations and challenges associated with capacitor banks, such as potential failures and transient disturbances during switching, while emphasizing their overall importance in enhancing power system reliability. The report also provides references to further reading on the topic.

Running head: ROLE OF CAPACITOR BANKS IN TRANSIENT STABILITY 1
Role of Capacitor Banks in Transient Stability
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ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 2
Role of Capacitor Banks in Transient Stability
Transient stability in a power system can be defined as the ability of the synchronous
power system to quickly regain its synchronism after it has been subjected to a severe
disturbance. It is usually linked to parallel operation of electrical machines such as the
synchronous generators (Eremia & Shahidehpour, 2013). The disturbances in the power system
occur when the system losses one or all of the critical elements of the system such generating
units or major loads. Disturbance can also be as a result of switching activities performed on the
various elements of the system and fault clearing processes. Power systems are frequently
subjected to disturbances which cause transient instabilities that can have adverse effects on the
system (Grigsby, 2017). Therefore, appropriate components must be applied to maintain or
improve power system stability. This paper focuses on how capacitor banks are used in the
power system to improve the stability of a power system.
A capacitor bank is a group of capacitors having the same rating connected in series or in
parallel with each other and they are usually utilized in power system for energy collection
purposes (Gitizadeh, Ghavidel, & Aghaei, 2014). Besides energy collection and storage,
capacitor banks are also used to maintain the stability of a power system through power factor
correction and reactive power compensation. Moreover, they are used in direct current power
supply systems for stepping up of the ripple current capacity and the stored energy (Miah, 2018).
A typical capacitor bank is illustrated in the figure below.

ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 3
Figure 1: Capacitor Bank
The demand of alternating electrical energy can either be in an active form or a reactive
form. The active power is delivered by the generating units while the reactive power is as a result
of the inductive electrical elements connected within the system. The inductive loads usually
comprise of devices with electromagnetic circuits such as motors, fluorescent bulbs, and other
inductive loads. The reactive power can also be as a result of the transmission line and
distribution network inductance (Shankar, Thottungal, & Priya, 2015). The reactive power
should be compensated appropriately so that the power factor can be maintained within the
required limits. The required limits of power factor are usually between 0.9 and unit power
factor. Unit power factor is not achievable in a typical power system due to the presence of
inductive loads. However, the value should be as close as possible to unity. In circumstances
where the value of power factor falls below the specified limits, an amperage burden is imposed
in the system and the related equipment’s for the available active power causing a situation of
instability within the system. Reactive power compensation is necessary to curb the instability
caused by the scenario discussed above and is done through the use of static capacitor banks
(Suguna, Jalaja, & Sugavanam, 2016). A schematic diagram of the capacitor bank is shown
below:

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Figure 2: Schematic Diagram of a Capacitor Bank
Capacitor banks can either be connected in series or in parallel to form series banks and
shunt capacitor banks respectively. Capacitor banks in which the capacitors are connected in
parallel as are usually used in the regulation of power factor and is known as a shunt capacitor
bank. They are installed throughout the system to perform various functions that improve the
stability of the system (Nasri, Ghandhari, & Eriksson). A typical shunt capacitor bank is
illustrated in the figure below.
Figure 3: Shunt Capacitor Bank

ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 5
Shunt capacitors installed near the load promote the stability of the power system through
maintaining the power factor within the required limit. They do so by reducing the total current
that flows in the distribution feeder line thereby improving the voltage profile of the feeder line
while minimizing the losses. Substations with installed shunt capacitors experience lower
loadings and therefore have improved contingency switching options which reduces the impact
of switching activities on the stability of the power system (Pavella, Ernst, & Ruiz, 2012).
The shunt capacitors installed along the transmission and sub transmission line up to
67kv promote the stability of the power system through performing voltage control functions.
They boost the power transfer capabilities of the lines thereby minimizing the possibility of
failure in any of the transmission lines which may consequently cause instability in the entire
system (Micah, 2018).
High voltage shunt capacitors are used in high voltage transmission line systems to
support the voltages used in the transmission. This application of shunt capacitor usually limits
the possibility of transient instabilities in situations where the transmission grids are overloaded
(Grigsby, 2017). Moreover, the shunt capacitor banks slightly increase the operating voltages of
the transmission buses there by reducing the current required to drive a load, this reduces the
losses and possibilities of instabilities in the system.
Series capacitors banks are also used in transient stability improvement. They form part
of the impedance of the transmission line and since the capacitive reactance is always active any
abnormal variation below or above the recommended current of the transmission line is
automatically compensated. The use of series capacitors banks along transmission for transient
stability improvement does not necessarily require continuous adjustment in and out of the load

ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 6
as it is the case with shunt capacitors. Also, series capacitors are not affected by sudden loss or
addition of load into the system (Eremia & Shahidehpour, 2013).
In conclusion, capacitor banks play vital roles in transient stability. They are installed at
any point if the power system so that they can perform power factor correction, voltage
regulation, reactive power compensation and loss reduction duties. However, the effectiveness
and the efficiency of the capacitor banks is limited by the challenges that are related to their
continued use within the power system. For example, the capacitor banks may fail during
operation and cause failure of the entire system or destruction of the system’s components.
Moreover, the switching of the capacitor banks may cause transient disturbances into the system
which may lead to the damaging of critical elements in the power system network (Shankar,
Thottungal, & Priya, 2015). The use of capacitor banks in transient stability is also influenced by
the high costs required setting up and running the bank infrastructures.

ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 7
References
Eremia, M., & Shahidehpour, M. (2013). Handbook of electrical power system dynamics:
Modeling, stability, and control. Hoboken, NJ: John Wiley & Sons.
Gitizadeh, M., Ghavidel, S., & Aghaei, J. (2014). Using SVC to economically improve transient
stability in long transmission lines. IETE journal of research, 60(4), 319-327.
doi:10.1080/03772063.2014.961571
Grigsby, L. L. (2017). Power system stability and control. Boca Raton, FL: CRC Press.
Miah, A. M. (2018). Real-time localized control of transient stability by the localized transient
stability (LTS) method with static VAR compensator (SVC). 2018 International
conference on smart grid and clean energy technologies (ICSGCE).
doi:10.1109/icsgce.2018.8556778
Nasri, A., Ghandhari, M., & Eriksson, R. (2012). Appropriate placement of series compensators
to improve transient stability of power system. IEEE PES Innovative smart grid
technologies. doi:10.1109/isgt-asia.2012.6303243
Pavella, M., Ernst, D., & Ruiz, D. (2012). Transient stability of power systems: A unified
approach to assessment and control. Berlin, Germany: Springer Science & Business
Media.
Shankar, C. U., Thottungal, R., & Priya, C. S. (2015). Enhancement of transient stability and
dynamic power flow control using thyristor-controlled series capacitor. 2015 IEEE 9th
International conference on intelligent systems and control (ISCO).
doi:10.1109/isco.2015.7282298

ROLE OF CAPACITOR BANK IN TRANSIENT STABILITY 8
Suguna, R., Jalaja, S., S., & Sugavanam, K. R. (2016). Transient stability improvement using
shunt and series compensators. Indian journal of science and technology, 9(11).
doi:10.17485/ijst/2016/v9i11/89402