Ross Caldecott

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.

Scale Model Studies of AC Substation Electric Fields

Energized scale models of EHV/UHV substations can be used as design tools to detennine the electric field distribution. To prove the method, an energized scale model of an existing 345-kV substation has been designed and built. The paper reviews modeling and instrumentation problems and their solutions, calibration and verification tests, and discusses the accuracy of model measurements. Comparison of corresponding test points shows that the agreement between substation and model measurements is good: the mean of absolute values of errors is about 4.6%. In the course of the study, the electric field strength of the model was mapped, and the effects of a wide range of modifications were examined. The feasibility of short circuit (charging) current measurements on model vehicles was also proven.

A computer program for HVDC converter station RF noise calculations

HVDC converter station operations generate radio frequency (RF) electromagnetic (EM) noise which could interfere with adjacent communication and computer equipment, and carrier system operations. A generic Radio Frequency Computer Analysis Program (RAFCAP) for calculating the EM noise generated by valve ignition of a converter station has been developed as part of a larger project. The program calculates RF voltages, currents, complex power, ground level electric field strength and magnetic flux density in and around an HVDC converter station. The program requires the converter station network to be represented by frequency dependent impedance functions. Comparisons of calculated and measured values are given for an actual HVDC station to illustrate the validity of the program. RAFCAP is designed to be used by engineers for the purpose of calculating the RP noise produced by the igniting of HVDC converter valves. >

Design and RF Operation of Scale Model of Dickinson ??400 kV HVDC Converter Station

HVDC converter stations inherently create electromagnetic interference. If a converter station is located in a sensitive electromagnetic enviromnent with a concentration of communication, computer and broadcasting systems (e.g., in urban areas), the interference. could prove troublesome and, therefore, would be a concern to utilities.

Radio frequency performance analysis of high voltage DC converter stations

High voltage DC converter station operation generates radio frequency electromagnetic noise which could interfere with adjacent communication, computer, and carrier system operations. This paper discusses the parametric studies of RF noise characteristics of a typical HVDC converter station. The studies were performed by using a generic computer program for calculating the RF noise from a converter station. The program was developed as part of a series of studies sponsored by the Electric Power Research Institute (EPRI, USA). The calculations provide insight into the EM performance of converter stations and show the effects of individual components within the station.

Model Study of VDC ELlectric Field Effect

Energized scale models of HVDC transmission lines and converter stations can be used as design tools to determine the electric field distribution in their vicinity. To prove the method, energized scale models of a ±400-kV HVDC test line and of the Arrowhead ±250-kV converter station have been designed and built in order to compare the electric field distribution of the full-scale facilities with that of the models. Linear scale factors were 1/50 for the line and 1/33.33 for the station. The paper reviews instrumentation, modeling and scaling problems and their solutions: calibration and verification test; and discusses the accuracy of the model measurements. Comparison of corresponding ground level electric field strength test ranges shows that the agreement between full-scale and model measurements is good. Techniques were developed for full- scale and model conductor tests in laboratories, and for field and model experiments. An experimental method (the method of images) of determining the corona onset voltage of actual bipolar HVDC transmission lines with single conductors was developed. Additional experiments were conducted in various areas of the model converter station. Features studied were: electric field and ion current profiles under energized and partially deenergized conditions, effects of ground wires, and effects of shielding. The feasibility of worst case open-circuit voltage and short-circuit current measurements on model objects and vehicles was demonstrated.