May 2014

In general, shunt compensators are classified depending on the technology used in their implementation. Rotating and static equipments were commonly used to compensate reactive power and to stabilize power systems. In the last decades, a large number of different static FACTS controllers, using power electronic technologies and digital control schemes have been proposed and developed. […]

Figure 25.1 shows the principles and theoretical effects of shunt reactive power compensation in a basic ac system, which comprises a source V1, a transmission line, and a typical inductive load. Figure 25.1 a shows the system without compensation, and its associated phasor diagram. In the phasor diagram, the phase angle of the current has been

Shunt compensation is used basically to control the amount of reactive power that flows through the power system. In a linear circuit, the reactive power is defined as the ac component of the instantaneous power, with a frequency equal to 100/120 Hz in a 50 or 60 Hz system. The reactive power generated by the

Figures 24.6, 24.7, and 24.8 show three types of hybrid active/passive filters, the main purpose of which is to reduce initial costs and to improve efficiency. The shunt passive filter consists of one or more tuned LC filters and/ or a high-pass filter. Table 24.2 shows comparisons among the three hybrid filters in which the

Nonlinear loads drawing non-sinusoidal currents from utilities are classified into identified and unidentified loads. High-power diode/thyristor rectifiers, cycloconverters, and arc furnaces are typically characterized as identified harmonic-producing loads because utilities identify the individual nonlinear loads installed by high-power consumers on power distribution systems in many cases. The utilities determine the point of common coupling with

Power transformers connected directly to generators can experience excitation and short-circuit conditions beyond the requirements defined by ANSI/ IEEE standards. Special design considerations may be necessary to ensure that a power transformer is capable of withstanding the abnormal thermal and mechanical aspects that such conditions can create. FIGURE 2.21 Typical simplified one-line diagram for the

There are many different accessories used to monitor and protect power transformers, some of which are considered standard features, and others of which are used based on miscellaneous requirements. A few of the basic accessories are briefly discussed here. LIQUID-LEVEL INDICATOR A liquid-level indicator is a standard feature on liquid-filled transformer tanks, since the liquid

When a transformer is taken off-line, a certain amount of residual flux remains in the core due to the properties of the magnetic core material. The residual flux can be as much as 50 to 90% of the maximum operating flux, depending the type of core steel. When voltage is reapplied to the transformer, the

The ability to adjust the turns ratio of a transformer is often desirable to compensate for variations in voltage that occur due to the regulation of the transformer and loading cycles. This task can be accomplished by several means. There is a significant difference between a transformer that is capable of changing the ratio while

THERMAL CONSIDERATIONS The losses in the windings and the core cause temperature rises in the materials. This is another important area in which the temperatures must be limited to the long-term capability of the insulating materials. Refined paper is still used as the primary solid insulation in power transformers. Highly refined mineral oil is still