Static Circuits Research Articles

Automatic load control for turbine generators

This paper describes a load-control apparatus recently installed on two 20,000-kw turbines at the power plant of the Tennessee Coal Iron and Railroad Company at Fairfield, Ala., to reduce the magnitude of load swings imposed on a tie line by a hot-strip mill in the Tennessee Coal Iron Company plant. The power plant contains three 20,000-kw turbine-driven generators and is tied in with the Alabama Power Company to furnish the steel-mill load. Previous to the installation of the equipment herein described, the three 20,000-kw turbine generators have carried load under control of their speed governors and the variations in strip-mill load which are about 20,000 kw were imposed upon the Alabama Power Company tie line causing objectionable disturbances on the connecting power system. It was desired to develop a means of imposing all or part of the strip-mill load on the Tennessee Coal Iron and Railroad Company turbine generators to reduce these disturbances. Several methods were considered, and the one selected was based upon a static watt-measuring circuit, the output of which is an Amplidyne generator. The Amplidyne in turn operates the pilot motor of an hydraulic (oil) relay at the turbine to control the steam admission valves.

Dampins and synchronizing torques of power selsyns

SELSYN systems are used very widely as power drives and as indicators when it is necessary to have the position of an element correspond synchronously with that of a controlling element which is remotely located. The receiver Selsyn is used either directly as the output driving motor or as an input to a following power-amplifying stage of a control system. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> In the study of such Selsyn systems and of the control systems of which Selsyn systems form one of the links, it becomes necessary to determine the hunting-torque characteristics of these machines (that is, the damping and synchronizing torques for small oscillations) as affected by speed, load, oscillation frequency, and, of course, the various design factors. The direct calculation of these hunting-torque characteristics is difficult, but within the past few years methods have been developed whereby the machine performance may be represented by equivalent static electric circuits. The purposes of this paper are: 1. To show how these hunting-torque characteristics can be simply determined by measurements on equivalent electric circuits set up on an a-c network analyzer. 2. To present some of the results of studies made of specific Selsyn systems.

Damping and Synchronizing Torques of Power Selsyns

SELSYN systems are used very widely as power drives and as indicators when it is necessary to have the position of an element correspond synchronously with that of a controlling element which is remotely located. The receiver Selsyn is used either directly as the output driving motor or as an input to a following power-amplifying stage of a control system.∗ In the study of such Selsyn systems and of the control systems of which Selsyn systems form one of the links, it becomes necessary to determine the hunting-torque characteristics of these machines (that is, the damping and synchronizing torques for small oscillations) as affected by speed, load, oscillation frequency, and, of course, the various design factors. The direct calculation of these hunting-torque characteristics is difficult, but within the past few years methods have been developed whereby the machine performance may be represented by equivalent static electric circuits. The purposes of this paper are: 1. To show how these hunting-torque characteristics can be simply determined by measurements on equivalent electric circuits set up on an a-c network analyzer. 2. To present some of the results of studies made of specific Selsyn systems.

Ignitor excitation circuits and misfire indication circuits

Several circuits are available for excitation of ignitron rectifiers. Static magnetic-impulse circuits are used for most applications. Several such circuits are discussed in some detail. Ignitor requirements are given, and circuit requirements affecting the choice of excitation circuits are indicated. While ignitor failures are rare, they should be detected promptly to utilize all apparatus to the best advantage. Two conditions may arise 1. When two anodes operate in parallel from a single transformer winding. 2. When a single anode is connected to each transformer winding. Means for detecting ignitor misfiring are described for both conditions.

Ignitor Excitation Circuits ana Misfire Indication Circuits

Several circuits are available for excitation of ignitron rectifiers. Static magnetic-impulse circuits are used for most applications. Several such circuits are discussed in some detail. Ignitor requirements are given, and circuit requirements affecting the choice of excitation circuits are indicated. While ignitor failures are rare, they should be detected promptly to utilize all apparatus to the best advantage. Two conditions may arise 1. When two anodes operate in parallel from a single transformer winding. 2. When a single anode is connected to each transformer winding. Means for detecting ignitor misfiring are described for both conditions.

An Extension of the Method of Symmetrical Components Using Ledder Networks

IN his now classical paper on symmetrical components Fortescue analyzed the behavior of synchronous and induction machinesoperating under unbalanced conditions. In this analysis Fortescue assumed that the stator and rotor windings themselves were symmetrical, that the rotor windings were either short-circuited or connected to balanced static circuits, and that the stator windings were connected to unbalanced circuits. Under these conditions there are unbalanced currents of a single frequency in the stator, and balanced currents of two different frequencies in the rotor. It has since been shown how the method of symmetrical components is applied when the rotor windings are connected to unbalanced circuits and the stator windings are connected to balanced circuits. Under these conditions there are unbalanced currents of a single frequency in the rotor, and balanced currents of two different frequencies in the stator.

An extension of the method of symmetrical components using ladder networks

IN his now classical paper on symmetrical components Fortescue analyzed the behavior of synchronous and induction machinesoperating under unbalanced conditions. In this analysis Fortescue assumed that the stator and rotor windings themselves were symmetrical, that the rotor windings were either short-circuited or connected to balanced static circuits, and that the stator windings were connected to unbalanced circuits. Under these conditions there are unbalanced currents of a single frequency in the stator, and balanced currents of two different frequencies in the rotor. It has since been shown how the method of symmetrical components is applied when the rotor windings are connected to unbalanced circuits and the stator windings are connected to balanced circuits. Under these conditions there are unbalanced currents of a single frequency in the rotor, and balanced currents of two different frequencies in the stator.

A Static Constant-Current Circuit

Static constant-current circuits have been constructed by connecting an iron-core reactor, with predetermined characteristics, in parallel with a capacitor of a specified size such that the resultant input current is independent of line voltage. This parallel circuit is connected in series with the element through which the current is to be regulated. The current will remain essentially constant for large variations in line voltage; large variations in load impedance; or a variation in both quantities simultaneously as long as the variation in voltage across the parallel circuit does not exceed certain limits. This type of circuit is useful for applications where a constant heating independent of line voltage is desired; for series lighting circuits; and vacuum-tube filament circuits.

A static constant-current circuit

A static constant-current circuit