Why var compensation is usually required

Reactive power is an essential component of an electric power systems: without it, rotating machines could not rotate, and transmission lines could not transmit active power. The ability to control or compensate reactive power has many benefits. MVAr ratings of equipment are typically specified following the necessary power system studies that can be carried out by our engineers or by third party engineers.

For example, in rotating load as induction motor, which is the main industry motor, the reactive power is essential for producing the revolving magnetic field required for successful operation. In the transmission and distribution networks of electric power, the reactive power is required to fulfill the requirement of proper operation.

The value and the direction of the reactive power in such networks vary according to load level and power factor [1] [2] [3]. These lines are essentially reactive networks of distributed parameters characterized by their series inductance and shunt capacitance [4] [5] [6] [7]. Reactive power flow, however, has a number of undesirable consequences.

It increases the drawn current for the same load level, which in turn increases the losses, maintenance and cost of the power system operation.

Moreover, it reduces the power stability margin. It under heavy level of reactive power probably results in voltage instability [8] [9] [10] [11]. Different reactive power compensating strategies are reported in the literature.

The compensating techniques either conventional or recent suffer from limitations. For example, the reactive output of SVC topologies is proportional to the square of the voltage magnitude. Therefore, the SVC provided reactive power decrease rapidly as voltage decreases, which reduces its stability. Moreover, STATCOM operates under balanced operating conditions; thus its performance is deteriorated under abnormal operating conditions.

In this article, comprehensive analysis for the phenomenon of reactive power is provided. The different indices for the reactive power are highlighted. Then, examples of reactive power compensating scheme are addressed regarding operational constraints and performance characteristics. Simple and clear analytical expressions are advised to expose explicitly the relation between the STATCOM and different aspects of power system operation. Finally, the conclusion highlights the main points in the dilemma of reactive power.

As mentioned before that reactive power is elementary for some load to function; therefore the majority of loads are functioning at lag power factor which is less unity. Figure 1 shows the variation of the power factor of a load with the drawn reactive power either inductive or capacitive. The active load power is assumed 1. Figure 1 shows that a load power factor is heavily dependent on the drawn reactive power and vice versa.

Moreover, for inadequate design the load results in flowing large reactive power and hence degrading the power factor. Reactive power flow, as mentioned, could result in uneconomic operation of the power system, as it increases the current magnitude and hence copper and reactive losses in the transmission and distribution networks. This is shown Figure 2.

The power system in Figure 2 is assumed to operate at rated voltage and 1. This hypothetical value for line resistance is assumed to depict the worst design case.

Figure 1. Power factor versus reactive power. Figure 2. Load current star and line losses dotted versus reactive power. Figure 2 shows that current magnitude and losses increases for non-zero reactive power despite inductive or capacitive. This definitely impacts the economic operation of a power system, which eventually affects the end-line customers. To visualize the full dilemma of reactive power, Figure 3 shows the efficiency of 0.

In producing Figure 3 , only ohmic losses in the tranmission line are considered. Figure 3 shows how could the flow of the reactive power impacts the efficiency. The figure shows that the efficiency is reduced under the flow of the reactive power despite its sign.

This is attributed to the fact that Figure 3 is generated for uncompensated operation. Different techniques are emerged to remedy the problem of reactive power circulation. Successfully reported this slideshow. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads.

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Synchronous condensers. In general, the problem of reactive power compensation is related to load and voltage support. In load support the objectives are to increase the value of the system power factor, to balance the real power drawn from the ac supply, to enhance voltage regulation, and to eliminate current harmonic components produced by large and fluctuating nonlinear industrial loads. Voltage support is generally required to reduce voltage fluctuation at a given terminal of a transmission line.

Reactive power compensation in transmission systems also improves the stability of the ac system by increasing the maximum active power that can be transmitted. See also: Voltage stability.