O. P. Malik

Fast generator protection against internal asymmetrical faults

An on-line digital computer technique for the protection of a generator against internal asymmetrical faults is described in this paper. The proposed technique relies on the detection of a second harmonic component in the field current at the onset of a fault in the armature winding. Discrimination against external faults is achieved by monitoring the direction of the negative sequence power flow at the machine terminals. Tests have been conducted on a laboratory synchronous generator for various types of internal and external faults. Results show that the total time for internal fault detection and tripping is well within half a cycle of the 60 Hz signal. A simple extension to negative sequence relaying and loss of excitation relaying is proposed.

Digital Control Scheme for a Generating Unit

Computer applications in power systems have tended to evolve at the supervisory levels in system operation. Controls at the generation levels remain primarily an analog domain. To make the entire system operation flexible it is essential that the control devices be compatible. This points towards the application of computers as dedicated direct digital controllers at the primary control levels. This paper describes the development of an integrated and compatible scheme for complete digital control of a generating unit. The overall concept and details of a physical model being built to test the proposed control scheme are given.

Digital differential protection of a generating unit scheme and real-time test results

This paper presents an on-line digital computer technique used for differential protection of a synchronous generator. It provides fault detection and tripping well within half a cycle and is also capable of discriminating between internal and external faults. In the latter case, sufficient restraint signals are generated to overcome maloperation. Further, the scheme is highly reliable even with CT saturation due to heavy through faults on the generating unit. On-line tests using a laboratory synchronous generator show the results for different types of internal and external faults with varying fault incidence inception.

A Digital Device to Measure Angular Speed and Torque Angle

A device to measure the angular speed and torque angle of a synchronous machine is described. Measurements of very high accuracy are made in a very short time. The output signals are available in a digital format suitable for direct use in an on-line digital control device.

Transient stability and optimal control of parallel A.C.-D.C. power systems

For a parallel ac-dc power system, the effect of a controlled dc link on system stability and damping depends on the system operating conditions.Thus a controller which improves stability at one operating condition may have a detrimental effect at other system operating conditions. Further, when the machine power angle to the ac line angle is high, improvement in stability is difficult to obtain solely by the control of a d.c. link. The variation with operating conditions of the influence of a dc link control on system performance indicates that a predictive or adaptive control mode would be needed to improve system stability over a wide range of system performance. The paper, therefore, examines both the conventionaI and optimal control of the link for large disturbance performance of a parallel ac-dc power system and digital simulation results show interesting features of optimal control. From a practical implementation point of view, full state optimal feedback law is suitably modified to be a linear combination of reduced state variables by an eigenvalue grouping technique and the performance of the actual nonlinear system with the suboptimal controller is quite encouraging.

Studies on an SCR Controlled Variable Speed DC Shunt Motor

This paper describes the analytical and experimental studies on a variable speed dc shunt motor driven by a single phase full-wave rectified power supply using SCRs. The studies comprise torque-speed characteristics and system stability. The expressions derived in the paper can be gainfully employed in designing such speed control circuits.

Design and test results of a software based digital AVR

The design and test results of a digital automatic voltage regulator are described in the paper. The basic control unit is a mini-computer supported by a digital hardware interface, signal transducers and a teletype. The flexibility of the digital AVR software has been exhibited in both open-circuit and synchronized tests. Digital AVR operation has been categorized into two modes, i.e., normal and special. Observations made from various tests allow guidelines to be laid as to the best possible manner in which to operate the digital AVR. A large number of features and control options have been incorporated into the design and have proven very useful in determining the best approach to be taken in digital control of a generating unit.

Closed Loop Optimization of Power Systems with Two-Axis Excitation Control

This paper describes the results of studies made to improve the dynamic response and damping torques of power systems incorporating synchronous machines with 2-axis excitation control. Dynamic optimization techniques have been used to determine the optimum controls subject to a quadratic integral performance index. The system has been simulated as a seventh order, closed loop, non-linear model incorporating speed governor and voltage and angle regulators. Modified quasilinearization and first order gradient methods have been utilized for solving the optimization problems for this non-linear system. The investigations indicate that optimal control of doubly excited synchronous machines is possible and that it yield, s improved transient performance. Incidentally, some possible limitations of the quasilinearization technique have also been brought out.

Digital Controller for a Turbine and Alternator

A control scheme utilizing an on-line minicomputer which assumes complete control of a generating unit is described in this paper. The basic design incorporates a minicomputer and interface signal transducers, and a teletype unit to perform in real-time the tasks of voltage regulation and speed control. The proposed scheme has been tested on a laboratory scale model of a generating unit. Results from tests of voltage, load and speed control are described in the paper.

Theoretical Analysis of a Single-Phase Induction Watthour Meter

The paper describes a theoretical method of determining the response of an induction watthour meter for steady- state inputs rich in harmonic content. Mathematical derivations obtained are rather complex and are amenable to solution by iterative techniques. Significant practical results can only be obtained by the use of a digital computer.