**6.2 Method of implementation**

shown by **Figure 8**, in which system cost (*SC*) increases as the reliability level increases. At the same time, the outage cost (*OC*) decreases because of reliability improvement and adequate generating capacity additions. The most optimal reliability levels vary between 0.07 and 0.13 days/year (see **Figure 8**). However, in some cases adding new capacity may not signify the ideal solution to meet increasing future loads and maintain enhanced reliability levels. Therefore, it is better to improve an operating unit's performance through regular preventive maintenance. Likewise, establishing a good cooperation between the supply side (electric company) and the demand side (the customers) through well-coordinated load management strategies may further improve financial performance (1£ = 4.5 SR).

**6. Applications of reliability indices in power system interconnection**

• When connecting isolated electrical systems, each system needs a lower generation reserve than the reserve when it is isolated and at a better level of

• When interconnecting isolated electrical systems, it is possible to share the available reserve so that each system maintains a lower level of reserve before being interconnected. This will result in both lower installation costs (fixed

• The electrical connection reduces the fixed and operating costs of the total

• In emergency and forced outage conditions, such as breakdowns, multiple interruptions, and the simultaneous discharge of several generators, which may cause a capacity deficit that is incapable of coping with current loads and possibly a total breakdown of the electrical system as a whole, electrical interconnection helps to restore the state of stability and reliability of electrical

• The interconnection of power systems enables the exchange of electrical energy in a more economical manner, as well as the exchange of temporal energy and the utilization of the temporal variation in energy demand.

• The electrical connection through the construction of larger power plants with higher economic return and reliability increases the degree of cooperation and the sharing of potential opportunities and possibilities that are available

• By nature, the various loads do not have peak values at the same time. As a result of this variation in peak loads (maximum demands), the load of the interconnected systems is less than the total load of each system separately,

thus reducing and saving the total power reserve for systems.

costs) and decreased operation costs (variable costs).

A review of the main advantages of electrical interconnection between electrical

**6.1 Introduction**

reliability.

installed capacity.

between the electrical systems.

systems.

**154**

power systems is summarized as follows:

*Reliability and Maintenance - An Overview of Cases*

The above brief review of the main advantages and merits of electrical interconnection from an economic and technical point of view highlights the usefulness and importance of conducting electrical interconnection studies between the systems as they relate to the cost of capital and operational costs on the one hand and the improvement of their levels and performance on the other. Such studies are especially significant after the completion of the infrastructure of electrical systems. Indeed, the next step is to seriously consider linking electrical systems through unified national networks throughout the widespread Kingdom.

Most power systems have interconnections with neighboring systems. The interconnection reduces the amount of generating capacity required to be installed as compared with that which would be required without the interconnection. The amount of such reduction depends on the amount of assistance that a system can get, the transfer capability of the tie-line, and the availability of excess capacity reserve in the assisting systems.

One objective to be mentioned in this context is to evaluate the reliability benefits associated with the interconnection of electric power systems. Therefore, this study is focused on the reliability evaluation of two systems that may be viewed upon as both isolated systems and as interconnected systems. The analysis of this type explores the benefits that may accrue from interconnecting systems rather than being isolated as well as deciding viable generation expansion plans.

A 5-year expansion plan for systems A and B assuming a reliability criterion of 0.1 days/year (0.1–0.6 frequently quoted as appropriate values in most industrial countries) was determined. The analysis represents the expansion plans for both systems as being isolated and interconnected. An outcome of these expansion plans is shown in **Figure 9**.

If the two systems (A and B) are reinforced whenever the reliability index (risk level) falls below the prescribed level (i.e., ) at any year of the planning horizon, the results shown in the following table exhibits that the number

**Figure 9.** *LOLE levels before and after systems interconnection.*

of added units and their cost are reduced if the two system are interconnected rather than being isolated.

The expansion of the electricity sector during the last three decades has resulted in the many electricity companies throughout the Kingdom being integrated into what was known, for a short time, as "the Saudi Consolidated Electric Companies (SCECOs)." These companies later merged into a single more reliable, efficient, and less expensive company known as the "Saudi Electricity Company (SEC)." Moreover, some areas (Eastern and Central) have been linked via a tie-line in order to prepare for the integration of the entire Kingdom under a unified national network. Experts and planners of electrical power systems find it economically and technically unfeasible to increase the electrical capabilities of electric power plants that are often isolated, dispersed, and distant. However, after the completion of the structures of these systems, the next and natural step, to achieve advantages and benefits, is to connect these electric power systems to each other through unified transmission networks. Undoubtedly, linking these power systems will both reduce the cost of construction and provide reserve and fuel, all while increasing the strength of the electrical system and maximizing its capability to meet current and

One practical example demonstrating the evolving of industry of electric sector in the Kingdom of Saudi Arabia will be shown in this section. The availability of network can be analyzed in a similar manner to that used in generating capacity evaluation (Section 3.1). Therefore, the probability of failing to satisfy the criterion of service adequacy and continuity can be evaluated. Provided the appropriate component reliability indices are known, it is relatively simple to evaluate the expected failure rate (*λ*) of the system, the average duration of the outage I, and the unavailability or annual outage time (*U*). To do this, the values of *λ*, *r*, and *U* are

The state-space transition diagram for a two-component system is shown in

*λ*þ*μ*.

(10)

*μ*<sup>1</sup> þ *λ*<sup>1</sup>

*μ*<sup>1</sup> þ *λ*<sup>1</sup>

*μ*<sup>1</sup> þ *λ*<sup>1</sup>

*μ*<sup>1</sup> þ *λ*<sup>1</sup>

� *<sup>μ</sup>*<sup>2</sup> *μ*<sup>2</sup> þ *λ*<sup>2</sup>

� *<sup>μ</sup>*<sup>2</sup> *μ*<sup>2</sup> þ *λ*<sup>2</sup>

� *<sup>λ</sup>*<sup>2</sup> *μ*<sup>2</sup> þ *λ*<sup>2</sup>

� *<sup>λ</sup>*<sup>2</sup> *μ*<sup>2</sup> þ *λ*<sup>2</sup>

The probability of a component being in the up state is . Also, the probability of a component being in the down state is *<sup>λ</sup>*

Probability of being in state 1 <sup>¼</sup> *<sup>μ</sup>*<sup>1</sup>

Probability of being in state 2 <sup>¼</sup> *<sup>λ</sup>*<sup>1</sup>

Probability of being in state 3 <sup>¼</sup> *<sup>μ</sup>*<sup>1</sup>

Probability of being in state 4 <sup>¼</sup> *<sup>λ</sup>*<sup>1</sup>

The most accurate method for analyzing networks including weather states is to use the Markov modeling. However, this becomes impractical for all except the simplest system. Instead, therefore, an approximate method is used based upon

future electric loads.

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

**7.3 Practical example**

*7.3.1 State probabilities*

simple rules of probability.

**157**

**Figure 10**.

required for each component of the system.


System costs as isolated and interconnected:

Therefore, it can be concluded from the above analysis that both systems will benefit from the interconnection. The reliability of both systems can be improved, and consequently the cost of service will be reduced through interconnection and reserve sharing. However, this is not the overall saving because the systems must be linked together in order to create an integrated system. The next stage must, therefore, assess the economic worth that may result from either interconnection or increasing generating capacity individually and independently.
