Donald G. Kasten

The Effects of Distribution Voltage Reduction on Power and Energy Consumption

Voltage reduction is a practice which has long been used by electric power companies during emergencies to reduce peak demand. Since 1973, some have suggested that it can also be an effective energy conservation method. Others disagree. The purposes of this paper are to: 1) present what is known about the effects of voltage reductions on real power, reactive power, and energy, for individual and composite loads; 2) discuss the problems associated with conservation voltage reduction proposals; and 3) suggest promising approaches for further study. Tests were conducted to determine the real and reactive power dependencies on voltage of a three-phase 5 hp induction motor. The following conclusions are derived from the information presented in this paper. 1) Appliances, motors, and feeders generally show initial reductions of power consumption at reduced voltage, but little reliable information concerning energy exists. 2) Because of the lack of hard evidence and the problems associated with conservation voltage reduction programs, it would be premature for any regulatory agency to mandate such programs at the present time.

Power transformer resonance-measurements and prediction

The authors describe and summarize the results of impedance measurements of 12 converter transformers and 12 nonconverter transformers in the 50 Hz to 1 MHz frequency range. Impedance characteristics associated with various parameters are discussed. Studies of transformer winding first resonant frequencies and prediction equations are presented. Many conditions are represented: single and three-phase transformers, different core and winding designs, high voltage and low voltage windings, and various terminations. From measured driving point impedance, it can be clearly seen that the profile of impedance changes both in terms of magnitude and phase angle as a function of frequency. The first resonant frequency is found at the first zero crossing of the phase angle. The highest value found was 80 kHz. >

HDVC converter station tests in the 0.1 to 5 MHz frequency

Radiofrequency (RF) quantities in and around an HVDC converter station were measured in the 0.1 to 5 MHz frequency range to provide baseline data for the formulation of a means to predict the RF performance of such stations. Special records were taken at selected points and traverses in the station. The RF voltages of buses were measured and ground-level electric field strength and magnetic flux density measurements were conducted. To obtain the maximum amount of information about a converter pole when it is considered as an RF source, swept frequency (broadband) measurements were selected as the prime records for the analysis of pole performance. The principal source of the RF noise is the firing valve. Additional impedance versus frequency measurements of station components were also performed for undertaking RF modeling of the converter station. >

Modeling of converter transformers using frequency domain terminal impedance measurements

Frequency-dependent node-to-node impedance function (NIF) models of power system equipment based on systematic broad frequency range (50 Hz to 1 MHz) external driving point impedance measurements are described. Such models are needed to calculate and predict the radio frequency electromagnetic (EM) noise produced by the valve ignition of a converter station. The application of the transformer frequency-domain NIF model related to HVDC converter station EM noise calculations is demonstrated. Calculated performance data are compared with field measurements. >

Measurement of the frequency dependent impedance of major station equipment

High-voltage direct-current (HVDC) converter stations generate radio frequency (RF) electromagnetic (EM) noise due to valve firing. The noise propagates into the AC and DC switchyards and along their corresponding transmission lines. This noise can affect the performance of adjacent communication, control, and computer equipment, and it can interfere with carrier system operation. Therefore, it is important to measure, predict, and mitigate the EM noise and interference. Measurements on equipment are necessary for the purpose of determining these impedance characteristics. A description is given of the instrumentation, improved measurement procedures, a systematic measurement program, and equipment representation concepts. All these have been developed and applied successfully in practice in the course of a project sponsored by the Electric Power Research Institute (EPRI). Transformer-related examples are used to illustrate the more relevant features of the study. >

Scale Model Studies of Station Grounding Grids

The design and use of scale models for evaluating the performance of grounding grids is described. Construction details of two electrolytic tanks of different sizes and of a number of scale- model grids are discussed, together with the associated instrumentation. Results are presented showing the potential profiles for a number of grids and the effects of the number of meshes, the use of ground rods, and non-uniform soil resistivity.

Partial discharge measurements in air and argon at low pressures with and without a dielectric barrier

Partial discharge (PD) characteristics in air and argon under low pressures down to 13.3 Pa (0,1 Torr) and 60 Hz AC energization are studied in an energized needle-plane electrode arrangement. The electrode configuration, vacuum chamber, facilities, and electrical connections for the experimental setup are described. Two cases are studied for each of two gases, air and argon, with 20 mm spacing between the two electrodes: (1) with and (2) without a Teflon/spl reg/ cap (dielectric barrier). Results for the four series of experiments and analysis of the discharge current pulse waveforms are presented. Topics discussed are the typical waveforms of the discharge current pulses at different pressures, and discharge current pulse rise time vs. pressure relationships.

Modeling of ground grid and metallic structure currents in high voltage a.c. substations for the computation of electromagnetic fields

Abstract A mathematical model for accurately computing the ground grid and metallic structure currents in high voltage a.c. substations is presented in this paper. The developed model considers not only the current leakage to the soil but also resistive and inductive effects. The model is then implemented in a computer program to calculate current distribution of any configuration of ground grid and metallic structures. The accuracy of the model is demonstrated by comparison with the field measurements.

Calculation of single phase AC and monopolar DC hybrid corona effects

Operating a hybrid HVAC and HVDC power transmission line is an option for increasing the efficiency of power transmission and overcoming the difficulties in obtaining a new right-of-way. This paper proposes a new calculation method for the study of hybrid power line corona. The proposed method can be used to calculate DC corona losses and corona currents in DC or AC conductors for single phase AC and monopolar DC hybrid lines. Profiles of electric field strength and ion current density at ground level can be estimated. The effects of the presence of an energized AC conductor on DC conductor corona and DC voltage on AC conductor corona are included in the method. Full-scale and reduced-scale experiments were utilized to investigate the hybrid line corona effects. Verification of the proposed calculation method is given.

Development of procedures for partial discharge measurements at low pressures in air, argon and helium

Partial discharge (PD) characteristics in air, argon and helium at pressures between 101 kPa (760 Torr) to about 0.27 kPa (2 Torr) under 60 Hz AC energization were studied with various electrode arrangements. Measurements are presented for two representative electrode configurations, (1) needle-plane, with 20 mm spacing and a dielectric barrier, and (2) a twisted pair of insulated conductors. Typical PD current pulse waveforms are presented. Difficulties in adhering to measurement guidelines defined by the IEC 60270 standard are described, and suggested modifications of the standard procedures are presented for measurement and calibration for low-pressure PD.