D. P. Sen Gupta

Electrical machine dynamics

In this chapter, we shall look at the dynamic performance of some typical machines using approximate methods of solution. The analytical technique developed in the previous chapter leads to more exact solutions and will be used later, in the form of generalised machine theory. There is, however, the danger that by formulating equations in a ‘mechanical manner’ and solving them by using a digital computer, one may lose sight of the physical processes that are involved. The approximate methods often help us to obtain a physical insight into the behaviour of the systems.

Low frequency oscillations in power systems: A physical account and adaptive stabilizers

This paper presents a physical explanation of the phenomenon of low frequency oscillations experienced in power systems. A brief account of the present practice of providing fixed gain power system stabilizers (PSS) is followed by a summary of some of the recent design proposals for adaptive PSS. A novel PSS based on the effort of cancelling the negative damping torque produced by the automatic voltage regulator (AVR) is presented along with some recent studies on a multimachine system using a frequency identification technique.

Rural electrification in India: the achievements and the shortcomings

A summary is presented of the achievements and highlights as well as some of the shortcomings of Indias rural electrification program. The socio-economic problem as well as technical problems associated with this program are touched on. The emphasis is on the technical problems which are also pertinent to other developing countries. >A summary is presented of the achievements and highlights as well as some of the shortcomings of Indias rural electrification program. The socio-economic problem as well as technical problems associated with this program are touched on. The emphasis is on the technical problems which are also pertinent to other developing countries.<<ETX>>

The legacy of Nikola Tesla: 2. AC power system and its growth in India

Electrical power supply has grown enormously during this century. In 1950 the total capacity of generators producing electricity in India was less than 3000 MW. Today, the power generating capacity is around 120,000 MW. The polyphase AC system, which is to a large extent the legacy of Nikola Tesla, is central to all power generation. Power systems these days are complex interconnected networks spread across the country. How are they structured? How have we been doing in India?

The legacy of Nikola Tesla

Alternating Current (AC) is used all over the world today. In India we use AC at 50 Hz (cycles per second) and in USA and Canada at 60 Hz. During the latter part of the 19th century, even during the early part of the 20th century, Direct Current or DC was widely used. Had we continued with DC, electricity would not have been as widely available as it is today and its use would have been cumbersome, costly and severely restricted. We owe it mainly to the Serbian genius Nikola Tesla that electricity has reached almost every nook and corner of most continents.

Synchronous machine oscillations

We have seen that the dynamical stability of an electromechanical system is determined by the damping and synchronising torque coefficients and the inertia constants. In a mechanical system damping and spring constants can be easily visualised—damping, for instance arises due to friction. In an electrical system, mechanical friction constitutes a small part of the total damping, the main damping torque being of electrical origin. In trying to understand the electrically generated damping, we can tell intuitively that this is caused by power dissipation due to copper loss. In a machine, during steady-state operation, copper loss takes place continually and largely accounts for the power difference between input and output. If, however, the rotor begins to oscillate about its steady-state angular velocity, oscillating currents induced as a result, generate additional copper loss. For instance, if an oscillating current ∆I sin (ωot + α) in a winding is superimposed upon a 50 Hz steady-state current 1 sin ωt, where ω0 = hω, then the additional average copper loss is (8.1) where the integration period is the common repetition time for the two oscillatory currents. This additional copper loss appears to be the only dissipation (neglecting mechanical damping) which may suppress the rotor oscillation and bring it back to its normal uniform angular velocity. This argument, however, cannot explain why the rotor oscillations may sometimes build up, indicating the presence of negative damping—apparently produced by copper loss which is always positive. We shall see presently that the physical nature of damping is more complicated than that.

A review of basic machine theory

There are many types of rotating electromechanical energy converter. When these transform mechanical energy to electrical energy, they are called generators. When they convert electrical to mechanical energy, they are operating as motors. Most energy converters can operate either as generators or motors. We shall, however, refer to these rotating electromechanical energy converters simply as electrical machines.

Electrical machine dynamics continued

In Chapter 4 we have seen that the general dynamical analysis of a machine involves the determination of the initial steady state conditions of operation, the magnitude, nature, and duration of the disturbing forces, and the calculation of the dynamical response. It is thus necessary to have detailed information about the parameters of the machine and the nature of nonlinear functions and saturation effects associated with them.

Electrodynamical equations and their solution

In Chapter 2, we dealt with mutually coupled stationary coils (Section 2.7). This was followed by a review of the performance characteristics of a.c. and d.c. generators and motors.

Improvement of Dynamic Stability of a Synchronous Generator Using pI f and p 2 I f as Feedback Signals in the voltage Regulator Loop

Abstract Signals proportional to pI f and p 2 I f are suitably mixed and fed as stabilizing signals into an automatic voltage regulator of a synchronous generator. Digital computer studies and laboratory tests indicate that these signals help to damp out oscillations of a synchronous generator connected through an impedance into an infinite busbar.