The present day electric power system, is a complex and highly networked entity. The large interconnected electric power network is vulnerable to several disturbances that pose a major threat to power system security, sometimes leading to major blackouts. The objective of this paper is to describe the problem of power system security and briefly discuss the various security assessment methods, and examine their individual advantages and disadvantages. Some preventive and corrective counter-measures to enhance the system security are also discussed briefly.
Power system security is the ability of the system to operate and remain stable following any
reasonably credible contingency (outages of lines, transformers, generators etc.) or adverse
system change, without violating any operational constraints (such as, short circuits, change
in c due to faults, loss of system components, sharp increase in load,
bus voltage violations etc.) in the post contingency steady state. The objective of power
system operation and control is to supply uninterrupted power to the consumers within an
acceptable limit of voltage and frequency. During operation, power systems are routinely
affected by unpredictable faults and failures. Therefore, power systems should be operated in
such a way that they are able to withstand any disturbance [1]. Conventional security
assessment methods assess the security of the system by checking whether the system is able
to remain in its normal operating state following a single contingency, i.e., tripping of a
transmission line/transformer, or a generator. Typically, power systems operate with N-1
security criterion (N-1 means that the system will remain in a normal operating state if any
single component out of N components fails). N-1 security criterion is considered because
probability of simultaneous tripping of two or more elements is very small.
In recent years restructuring of the power industry has broken the monopoly of vertically
integrated utilities in the energy market and discouraged inefficient production practices
among utilities due to competitive environment. In deregulated market generation, transmission and distribution are unbundled, and are controlled by different utilities.
Restructuring has resulted in more effective usage of the existing resources (generators,
transmission lines, etc.), which is why under the new operating paradigm, power systems are
often operated with equipments operating very near to their capacity. This reduces the reserve
margins. Therefore, N-1 security criterion may not be secure enough in the present context
and we need to re-look the security aspects of power systems. |
