High Power Test Laboratory Research Articles

An Innovative Solution for Type Testing of Power Transformers

Abstract Type tests are essential to assess the short circuit withstand capabilities of transformer windings. The mechanical durability of power equipment are checked against the mechanical forces developed during making/breaking short circuit operations. These type tests are generally carried out in indoor transformer test laboratories. Testing of Power Transformer for size more than 200 MVA in 765/400 kV voltage class in an indoor laboratory is not economically feasible. Now a days, power transformer manufacturers are fabricating single phase auto- power transformers of size up to 630 megawatt volt ampere (MVA) rating. Type testing of these transformers in indoor laboratories is not feasible. In view of this, strong short circuit fault feeding capabilities of the national grids can be utilized for type testing of these power transformers in an online manner. However, this may affect the grid operation/control during weak grid operating conditions. Recently, National High Power Testing Laboratory is established for testing of power transformer upto of 630 MVA. This is a unique online transformer test facility for testing of 765/400/220/132 kV class power transformers. An offline simulation has been carried out in this article, to assess the impact of online type testing on the Indian National grid. In this article, an online testing scheme has been presented which enables the national grid operator to analysis the prevailing grid condition & subsequently to decide the safe rating of the power transformer for online testing. The simulated results are cross checked with field results and it is found that simulated results are close to actual field results. The concurrence of simulated and field results helped in successfully commissioning of the testing laboratory.

New Static “AirArc” EMTP Model of Long Arc in Free Air

In this paper, long arcs in free air are investigated. A long arc was induced in the high-power test laboratory at FGH-Mannheim, Germany. From the recorded arc data, the features of the arc were derived and analyzed, including elongation effects associated with these arcs. Based on this analysis of a real arc, a new “AirArc” static arc model, including the length variations, was derived and incorporated into the Alternate Transients Program-Electromagnetic Transients Program software package in which it was simulated. The arc is modeled as a current-dependent voltage source with a characteristic-distorted rectangular voltage that elongates nonlinearly over time. Fault arcs are a significant source of harmonics that distort other voltages and currents in the network. The time-domain and spectral-domain features of the simulated arc are compared with those of the real arc. The assessment of transient processes during arcing faults was carried out using the discrete wavelet transform.

Nonlinear compensation to enhance the input dynamic range in analog optical fiber links for the high current short circuit test

Due to their galvanic insulation and EMI immunity properties, optical fiber links have been used in the transmitter–receiver system of an analog voltage measuring system at a high-power mid-voltage testing laboratory with a highly aggressive EMI environment. This paper introduces the application of a nonlinear compensation to limit the voltage range at the input of a voltage-controlled oscillator, which is used to produce the pulsed frequency modulation needed to transmit the analog signals over the optical fiber links. The proposed dynamic range compensation system is based on nonlinear circuits to accommodate the input range of the voltage-controlled oscillator. This approach increases the transient signal handling capabilities of the measuring system. This work demonstrates that the nonlinear compensated optical fiber approach yields a unique, electrically isolated, lightning-proof analog data transmission system, for remote measuring systems in the highly aggressive EMI environment of high-power test laboratories.

New testing method for the classification of contact materials for vacuum circuit breakers

A new testing method to classify contact materials for high-current interruption with vacuum circuit breakers (VCB) is described. The testing effort is reduced by diminishing the contact gap and the contact area as well as by an adequate testing circuit. Consequently, the number of experiments can be increased for the benefit of a high statistical certainty in the classification of contact materials. The test results are in good agreement with the results of full-size short-circuit current interruption tests carried out in a high-power testing laboratory with VCB equipped with contact materials classified in the new testing circuit.

Two-dimensional modelling of internal arc effects in an enclosed MV cell provided with a protection porous filter

Medium voltage (MV) cells have to respect standards (for example IEC ones (IEC TC 17C 2003 IEC 62271-200 High Voltage Switchgear and Controlgear—Part 200 1st edn)) that define security levels against internal arc faults such as an accidental electrical arc occurring in the apparatus. New protection filters based on porous materials are developed to provide better energy absorption properties and a higher protection level for people. To study the filter behaviour during a major electrical accident, a two-dimensional model is proposed. The main point is the use of a dedicated numerical scheme for a non-conservative hyperbolic problem. We present a numerical simulation of the process during the first 0.2 s when the safety valve bursts and we compare the numerical results with tests carried out in a high power test laboratory on real electrical apparatus.

Reproduction of FRP Blade Failure for Wind Power Generators by Lightning and its Mechanism

In Japan, lightning damage to FRP blades for wind power generators is increasing, together with the increase in wind power generator installation in recent years. Lightning damage is a big issue in Japan since lightning in Japan seems to be severer than in Europe and the US. In Kochi, Shikoku, Japan, six 600-750kW grade generators have been installed, and some of them have been damaged by lightning several times. In order to solve this issue, the Kochi University of Technology received a research request of lightning protection, sponsored by the Kochi prefecture in 2002. After surveying the literature and questioning related organizations such as NREL (National Renewable Energy Laboratories) and Toray USA, experiments to reproduce lightning damage to FRP specimens were planned. The specimens prepared for this research are 1/2 size models and a 2/4 part of the full size blade. In the previous experiment, flat plate specimens of 450mm width × 2.5m length × 4mm thickness were used, and the experiments produced the damage by lightning. However, the damages were not exactly the same as the ones in the actual field. Therefore, this experiment aims to reproduce the blade failure in the actual field and to clarify the failure mechanism, using the 1/2 size blade model and full size blade specimens. The experiments were conducted mainly in the Toshiba Hamakawasaki High Voltage High Power Testing Laboratory as was made in the previous experiments. This Testing Laboratory is one of the biggest test laboratory for experiments involving high electric voltage and large current. The results showed the reproduction of the failed blades in fields, and clarified the failure mechanism.

On the Modeling of Long Arc in Still Air and Arc Resistance Calculation

An important macroscopic arc parameter, describing its complex nature is the arc resistance. It can be easily calculated by using the well-known Warrington formula. Authors investigated the results of Warrington's tests. By taking into account the conditions under which they are obtained (e.g., inaccurate measurement devices), it is unquestionable that these results are today highly empirical and not accurate and general enough. Laboratory testing provided in the high-power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the basis for the research results presented in the paper. Based on the analysis of laboratory-recorded arc voltage and current waveforms, the new arc model is derived. An example of arc computer simulation using the new model is given. Based on the new arc model, a new approach to arc resistance calculation is presented. The new formula for arc resistance is compared with the old Warrington formula.

The transformer short-circuit test and the high power laboratory in China the past, present, and future

Over the last half-century, the transformer industry in China has experienced substantial development due to the study of the short-circuit performance of power transformers by using short-circuit tests. This is because power transformers operating in power systems are exposed to short circuits, which cause high short-circuit currents of more than 10 times the rated current and are dangerous to the transformer. In this paper, the author reviews short-circuit testing of distribution transformer, including power transformers. The Hushita I High Power Test Laboratory is also described in this paper along with its main equipment and test capabilities. Potential for future development is also discussed.

Long arc in free air elongation effects modeling and simulation

AbstractIn the paper the elongation effects on the long arc in still air are investigated and modelled. Arc is initiated under laboratory conditions in the high power test laboratory FGH‐Mannheim (Germany). Based on the analysis of laboratory arc voltage and current wave forms, the new dynamic arc model, taking into account the arc length variation, is derived. An example of arc computer simulation using the new model is given. The main features of the simulated arc are presented. The main features of both the real and the simulated arc are given in the time and the spectral domains.

Long arc in free air: laboratory testing, modelling, simulation and model-parameters estimation

The results of an investigation into the long arc in free air is presented. The long arc in free air is initiated under laboratory conditions in the FGH-Mannheim high-power test laboratory (Germany). Based on the arc voltage and the arc current data records obtained in the laboratory, the main features of the arc are derived. In the second stage of the research, a new arc model is developed. The arc is modelled as a current dependent voltage source with the characteristic distorted rectangular waveform. Examples of computer simulations of the arc using new models are given. The main features of the simulated arc are also described. Features of the real and modelled arc are given in the time and the spectral domains. The interaction between the arc and the network is analysed. Through computer simulation, a typical example of an arcing fault on an overhead transmission line is given. Finally, the least squares error estimation method for arc model parameter estimation is presented. The unknown model parameters are successfully estimated from the computer-simulated and laboratory-obtained data.

New dynamic model, laboratory testing and features of long arc in free air

In this paper the long arc in free air is investigated. First, arc is initiated under laboratory conditions in the high power test laboratory FGH-Mannheim (Germany). Based on the laboratory obtained data records, the main features of arc are derived. By this arc, voltage and current are processed. An important feature of arc, the variation of arc length, is analyzed. Based on the analysis of arc voltage and current wave forms, the new dynamic arc model, taking into account the arc length variation, is derived. Arc is modeled as a current dependent voltage source with the characteristic distorted rectangular waveform and arc length dependent amplitude. Arc is considered as a source of higher harmonics distorting by this other signals in the network. An example of arc computer simulation using the new model is given. The main features of simulated arc are presented, too. Features of both the real and the simulated arc are given in the time and the spectral domains.

A new approach to arc resistance calculation

An important macroscopic arc parameter, describing its complex nature is arc resistance. As known, the fault arc resistance can be calculated by the Warrington formula. The authors investigated the results of Warrington's tests. Warrington derived a relation for the arc voltage by using the measured arc voltage gradient and arc current as input data. By analyzing these measurements and by taking into account the conditions under which they are obtained (inaccurate measurement devices), it is unquestionable that the results are highly empirical and not accurate and general enough. Laboratory testing, provided in the high power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the base for the research results presented. In this paper a new approach to arc resistance calculation is given. Two independent approaches delivered the same equation. Both approaches are based on a suitable and a simple arc model assuming the rectangular wave form of the arc voltage, which is in phase with the arc current wave form. The new formula for arc resistance is compared with the Warrington formula. The influences of arc elongation are also investigated.

A computerized high-power testing laboratory

An integrated hardware and software system for testing electrical equipment is presented. The system integrates various functions that traditionally have been carried out by independent systems in high-power testing laboratories. It provides an easy way to prepare, execute, and analyze tests in a high-power/medium-voltage laboratory with a high degree of security and less time for test preparation. The general characteristics of the laboratory, and the hardware and software designs are presented. >

Digital Acquisition and Numerical Processing of Measuring Signals, in a High Voltage Circuit Breaker Testing Laboratory

This paper presents the data acquisition system used at the High Power Test Laboratory at les Renardieres (EDF - France) since the beginning of 1984. The hardware configuration is first described. The main problems are underlined in order to justify the choice of the adopted system. Then the major outlines of the developed softwares (and the encountered difficulties) are presented. An example, relative to a 245 kV circuit breaker terminal fault shows the results given by the digital system. The acquired experience proves that automatic analysis of signals permits to satisfy speed and accuracy criteria.

Switckgear and Control Features of Enlarged High-Power Testing Laboratory

Higher capacity testing facilities are being put into service at the Westinghouse Electric Corporation high-power testing laboratories at East Pittsburgh. This paper deals primarily with some of the switchgear and control features of the increased capacity facility.

Apparatus used for high-power switchgear testing

The paper deals with the equipment and construction of modern high-power testing laboratory capable of testing circuit breakers of ratings up to 1 500 MVA at voltages up to 132 kV.General details of the power circuit are given, including the generator, super-excitation system, load and power factor control, step-up and step-down transformers, and switchgear.The metering and instrument equipment is also described, particulars being given of both low- and high-frequency oscillographs and their associated components.