Showing papers in "Transactions of The American Institute of Electrical Engineers. Part Iii: Power Apparatus and Systems in 1959"

Stray-Load Losses in Polyphase Induction Maclines

Abstract: The total stray-load loss of a polyphase induction machine of the squirrel-cage type is given by the formula: WL = WC + WE + WSL1 + WSL2 + WZ + WB + WK (13) where the several items, except Wc, are given by equations 1, 7, 6, 9, 10, and 12. The sum of WE and Wc can be determined separately from the other losses by measuring the input to the stator when balanced polyphase currents are flowing, with the rotor removed, and subtracting from this the I2R losses calculated on the basis of the d-c resistance of the winding at the test temperature, as required in the Morgan method of load-loss measurement. However, the end loss will differ somewhat from that under load, because the rotor end winding currents are not present. The total loss can be measured by the dynamometer method, either as a motor alone, or by the differential dynamometer method as the average of a motor and a generator, or by the pump-back method or the Morgan method, as outlined in a companion paper. 1 From a theoretical point of veiw, all these methods should give equivalent results, except that the Morgan method would be expected to give a stray loss slightly lower than the true value when the rotor has closed slots.

Determination of Lightning Response of Transmission Lines by Means or Geometrical Models

Abstract: The voltages produced across the tower insulators of transmission lines struck by lightning can be determined both by measurements on geometrical models and by calculations. Measurements which have been made on geometrical models of the Ohio Valley Electric Corporation's (OVEC) 345-kv transmission towers agree well with the calculations of Lundholm, Finn, and Price.1 A simplified theory has been developed, using electromagnetic field concepts and the distributed constants of transmission lines, which explains the relationships between insulator voltages and lightning voltages and lightning stroke currents. This theory includes the effects of the magnetic field produced by the return stroke and the changing electric fields produced by neutralization of the charged column of the leader.

The Relation of Capacitance Increase with High Voltages to Internal Electric Discharges and Discharging Void Volume

Abstract: A practical means of estimating the fractional volume of gas space in insulation from high-voltage capacitance and dissipation factor measurements has been suggested in this paper. This method has been evaluated by tests on models and various high-voltage insulation specimens. An analysis has been derived relating the observed a-c capacitance and dissipation factor increase with high voltages to the individual electric discharges between the surfaces of gas spaces in insulation.

Ferroresonance of Grounded Potential Transformers on Ungrounded Power Systems

Abstract: Potential transformers that have their primary windings connected in Y and grounded, on an otherwise ungrounded circuit, may oscillate with the distributed capacitance to ground of the circuit following a voltage disturbance. This oscillation, termed here as ferroresonance, may be of several frequencies and will persist if energy losses are not sufficiently high. The amount of losses required to damp out these oscillations is influenced to some extent by the ratio of the applied voltage to that at which the transformer saturates. One method to increase the energy losses and thus protect the transformer and circuit against the results of sustained oscillations is to load resistively the secondaries of the potential transformers either individually or by connecting the secondaries in delta with the loading resistor in one corner of the delta. The required broken-corner delta resistance for the more critical (one-half fundamental) frequency may be estimated from the empirical equation RB = 100La/N2 where RB = broken-corner delta resistance, ohms La = potential transformer primary inductance during saturation, millihenrys (inductance of primary viewed as separate coil in air) Another method using Fig. 14 has been given. Both methodsare predicated on the transformer being fluxed for line-to-line voltage. Maximum transformer primary currents during ferroresonance in the one-half fundamental frequency mode have been estimated with the use of Figs. 9 and 14 Comparison of required loading and maximum primary currents with the results of laboratory tests on two types of potential transformers has shown good agreement.

A Utility's Functional Evaluation Tests for High-Voltage Stator Insulation

Abstract: This is a progress report on research projects conducted in co-operation with the AIEE Rotating Machinery Insulation Subcommittee, the Canadian Electrical Association's Apparatus Section, and individual manufacturers and utilities For the functional evaluation required by a utility, a voltage-endurance test was chosen as most indicative of the ionization resistance which is considered critical in short-bore water-wheel generators, and a test of endurance of the mechanical effects of thermal cycling was chosen as most applicable to the critical qualities of insulation for steamturbine generators and other long-bore machines Test equipments of moderate size and cost have been developed for voltage and mechanical endurance Emphasis has been laid on close control of aging influences; variation of voltage test "lives" of similar samples has been reduced to within a ratio of three to one The voltage-endurance equipment is finding further use in studies of effects upon insulation life of various dry-out, overvoltage testing, and operating practices The mechanical-endurance tester is being used in a study of the optimum clearances between coil side and slot for various insulations

Correlation of Forced and Free Oscillations of Coils and Windings

Abstract: This paper shows that there exists a simple relationship between the forced and free oscillations of coils and windings which are generally treated in the literature as two separate phenomena. As a consequence, a correlation also exists between certain natural frequencies of a coil or winding under different terminal conditions. Experimental measurements on air coils, iron-core coils, and transformer windings prove the correctness of the theory. The frequencies are determined analytically by energy methods.

Bundled Conductor Voltage Gradient Calculations

Abstract: Radio interference and corona loss studies on high-voltage transmission lines require a knowledge of voltage gradients which exist at the surface of conductors. This paper covers such calculations for extra-high-voltage (ehv) lines using 2-, 3-, and 4-conductor bundles. The results are presented in graphical form so that bundled conductor designs, for a specified voltage gradient at line voltages up to 500 kv, can easily be obtained.

Mathematical Models for Use in the Simulation of Power Generation Outages II-Power System Forced-Outage Distributions

Abstract: The numerical results presented in this paper, in Tables I through VI, apply only to the PSEG system. First presented is a summary of the forced-outage data collected; see Table I. Table II compares the actual distribution of up-period duration with an exponential distribution. Then, Tables III and IV give estimates of average up-period duration and the probabilities of an outage being a halfoutage for the four classes of units. Table V shows the component failure rates for mature units. Table VI gives the details of the durations and postponements of down periods. Comments on the numerical results are given in the section "Results" at the beginning of the paper.