*Reliability Evaluation of Power Systems DOI: http://dx.doi.org/10.5772/intechopen.85571*

The third index is the expected energy not supplied (*ϵENS*), which is defined as the expected size of energy not being supplied by the generating unit(s) residing in the system during the period considered due to capacity deficit or unexpected

The implementations of these indices are now increasing since they are significant in physical and economic terms. Compared with generation reliability evaluation, there are also reliability indices related and pertinent to network (transmission

There are two basic concepts usually considered in network reliability, namely,

The first criterion considers violation of voltage limits and violation of line rating

The transmission and distribution networks can be analyzed in a similar manner

A bulk generation model must consider the size of generation reserve and the severe outage(s) occurrences. An outage in a generating unit results in the unit being removed from service in order to be repaired or replaced. Such outages can compromise the ability of the system to supply the load and, hence, affect system reliability. An outage may or may not cause an interruption of service depending on the margins of generation provided. Outages also occur when the unit undergoes maintenance or other planned works necessary to keep it operating in good condi-

• A planned outage that results when a component is deliberately taken out of service, usually for purposes of preventive repair or planned maintenance

• A forced outage that results from sudden and emergency conditions, forcing

or carrying capacity, and the second criterion assumes that lines are of infinite

to that used in generation reliability evaluation, that is, the probability of not satisfying power continuity. This would give frequency and duration in network evaluation a simplification that is necessary. Provided the appropriate component reliability indices are known, it is relatively simple to calculate the expected failure rate (*λ*) of the system, the average duration of the outage (*r*), and the unavailability (*U*). To do this, the values of *λ*, *r* and *U* are required for each component of the

severe power outages [7, 8].

capacity.

system [9–11].

**Figure 1.**

**144**

*Generating unit probable states.*

and distribution) reliability evaluation.

violation of quality and violation of continuity.

*Reliability and Maintenance - An Overview of Cases*

**2. Types of system outages and deficits**

tion. The outages can be classified into two categories:

the generating unit to be taken out of service

The status of a generating unit is described as morphing into one of the several possible states, as shown in **Figure 1**.

To investigate the effect of a unit on system generation reliability, it is imperative to know its probability of residing in each state as in **Figure 1**. Hence, the following section introduces some basic probability concepts.
