Power System Transients Theory and Applications by Akihiro Ametani
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Power System Transients Theory and Applications by Akihiro Ametani

When lightning strikes a building or a transmission tower, an electric current flows into its structures, which are made of electrically conductive materials such as steel and copper. The electric current produces a high voltage called “overvoltage” (or abnormal voltage), which can damage or break electrical equipment installed in the building or in the power transmission system. The breakdown may shut down the electrical room of the building, resulting in a blackout of the whole building.

If the breakdown occurs in a substation in a high-voltage power transmission system, a city where electricity is supplied by the substation can experience a blackout. An overvoltage can also be generated by switching operations of a circuit breaker or a load switch, which is electrically the same as a breaker in a house. A phenomenon during the time period in which an overvoltage occurs due to lightning or switching operation is called transient, while electricity being supplied under normal circumstances is called steady state.

In general, a transient dies out and reaches a steady state within approximately 10 μs (10−6 s) in the lightning transient case and within approximately 10 ms (10−3 s) in the switching transient case. Occasionally, a transient sustains for a few seconds if it involves resonant oscillation of circuit parameters (mostly inductance and capacitance) or mechanical oscillation of the steel shaft of a generator (called subsynchronous resonance).

In order to design the electrical strength of electrical equipment and to ensure human safety during a transient, it is crucial to perform a transient analysis, especially in the field of electric power engineering. Chapter 1 of this book describes a transient on a single-phase line from the physical viewpoint and how this is solved analytically by an electric circuit theory. The impedance and the admittance formulas of an overhead line are described. Simple formulas that can be calculated using a pocket calculator are also explained so that a transient can be analytically evaluated.

Since a real power line is three-phase, theory that deals with multiphase lines is presented. Finally, the book describes how to tackle a real transient in a power system. Chapter 1 also presents the well-known simulation tool electromagnetic transients program (EMTP), originally developed by the US Department of Energy, Bonneville Power Administration, which is useful in dealing with a real transient in a power system. Chapter 2 describes wave propagation characteristics and transients in an overhead transmission line.

The distributed-parameter circuit theory is applied to solve the transients analytically. The EMTP is then applied to calculate transients in a power system composed of an overhead line and a substation. Various simulation examples are demonstrated, together with comparison with field test results.  Chapter 3 discusses transients in a cable system. A cable system is, in general, more complicated than an overhead line system, because one phase of the cable is composed of two conductors called the metallic core and metallic sheath.

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