Gas Insulated Substation Research Articles

Transient impedance of GIS grounding grid

The transient impedance of a grounding grid for a commercial 550 kV gas-insulated substation (GIS) was measured on site using steep front currents with rise time from 100 ns to 2 /spl mu/s. From the measured results, it was found that the transient impedance of the measured grid for those currents is simulated by a series circuit with an inductance 1 /spl mu/H and a resistance 3 /spl Omega/. Applying the obtained impedance to the lightning surge analysis, it is pointed out that the grounding condition at an arrester tank end has a remarkable influence on the protecting performance of a surge arrester. >

Radio interference and transient field from gas-insulated substations

Gas-insulated substations (GIS), owing to their compact nature, offer an attractive alternative to conventional substations in areas where space is limited such as in urban areas. Consequently, it is important to address the issue of environmental conditions within the substation and in the surrounding areas. This paper reports the results of radio interference (RI) and transient field measurements at two GIS in Ontario, Canada. For comparison with RI levels taken at the GIS, RI levels outside two hospitals in the Toronto area were also measured. The transient field study covers electromagnetic interference (EMI) levels generated during switching operations, and includes measurements inside and outside the GIS. Measurements show that RI levels from the GIS were either below background levels, or contributed little to the background. RI levels outside the GIS and the hospitals were similar. Peak transient field values up to 580 V/m were measured inside the station building, and dropped to background values of 10 V/m at about 120 m from the station. The transient field (E) dropped off at a rate of 3/2 power with distance (d) from the air-insulated 115 kV bus, i.e. E/spl prop/d/sup -1.5/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Partial discharge diagnostics for gas insulated substations

A defect such as a free metallic particle or stress-raising edge on an electrode could lead to breakdown in a gas insulated substation (GIS), but may be detected by the partial discharges it generates. Of the various detection means available, most success has been achieved with either acoustic transducers to detect sound waves from the discharge, or electrical couplers to pick up the ultra-high-frequency (UHF) signals generated inside the GIS chambers. All new GIS in the UK are fitted with internal couplers for UHF monitoring, and two examples of continuous monitoring schemes on 400 kV GIS at nuclear power stations are described. Further developments, which are already well advanced, include specifying and measuring the coupler characteristics, making use of expert systems to interpret the UHF discharge data, and extending the monitoring system to include the performance of circuit breakers and other equipment. >

Calibrating the UHF technique of partial discharge detection using a PD simulator

The paper describes a technique for simulating the presence of partial discharges in gas-insulated substation (GIS) equipment. The technique employs a pulse generator to inject current pulses through a suitable protrusion. The current pulses have similar temporal characteristics to those produced by an actual discharge event, with the added advantage that their magnitudes can be controlled accurately. Because the pulses are highly reproducible, they are ideally suited for investigating the UHF technique of partial discharge detection. The paper discusses the relationship between the magnitude of the UHF signal received by a coupler and the discharge magnitude. It also shows that the coupler signal is dependent on the protrusion length and on the spatial relationship between the protrusion and the coupler. The implications for practical discharge measurements in GIS also are discussed. >

UHF detection of leader discharges in SF/sub 6/

The ultra-high frequency (UHF) technique of partial discharge detection has been used to study the partial discharges produced by electrode protrusions and surface contamination in a gas insulated substation (GIS). The paper describes the stages of discharge development from inception to breakdown. The work has shown that the UHF technique may be used to identify distinct phases of discharge activity corresponding to discharge inception and a prebreakdown condition. The prebreakdown activity is detected as an increase in the UHF signal magnitude which has been attributed to the formation of leader-type discharges. These discharges form an essential part of the breakdown process, and their detection can be used to identify when the system is close to breakdown. The paper describes a filtering technique that may be employed to optimize the sensitivity of UHF leader detection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of gas pressure sensor for fault location system in gas insulated substation

This paper reports on increasing the sensitivity of a gas-insulated substation (GIS) fault location system using gas pressure sensors. It describes the results of studies on engineering problems arising where methods and sensors for this purpose are actually applied, while presenting the results of performance proof tests carried out with actual equipment, together with some results of their analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigation of overvoltages in a gas insulated substation (G.I.S.) caused by a lightning stroke

A back flashover for a shielding failure can be caused by a lightning stroke, which will damage equipment and devices in a gas insulated substation if the devices' maximum voltages are exceeded. In this study, the branch timetable method, which is implemented from the lattice diagram method, is used in a computer program for the calculation of overvoltages in the gas insulated substation, as a result of a shielding failure, so that the gas insulated substation performance under lightning stroke can be determined. The study of the lightning performance of a gas insulated substation is very important for the purpose of designing lightning overvoltage protection systems.

Power frequency electric and magnetic fields from a 230 kV gas-insulated substation

Gas-insulated substations (GIS), owing to their compact nature, offer an attractive alternative to conventional substations where space is limited, such as in urban areas. Consequently, it is important to address the issue of environmental conditions in and around the GIS. This paper presents the results of a survey of power-frequency electric and magnetic fields in and around a 230 kV/28 kV GIS. The survey was designed to cover the electric and magnetic fields from the substation equipment and from the power lines and cables surrounding the substation. It also includes a determination of the shielding effect of the GIS bus sheath. The information provided should allow the prediction of electric and magnetic field levels from other GIS of similar design. >

Development of detection and diagnostic techniques for partial discharges in GIS

This paper describes detection and diagnostic techniques for partial discharges in gas insulated substations (GIS). Partial-discharge current waveforms of SF/sub 6/ gas and external noise characteristics of actual substations were investigated, and a measuring system having sensors in GIS and employing frequency range of VHF band was developed. By this system, detecting very small partial discharges of several 10 pC level has become possible. Also, a neural network system, focusing attention as a method for recognizing patterns, was applied for determining causes for partial discharge in GIS, and its applicability has been proved. >

Assessing the risk of failure due to particle contamination of GIS using the UHF technique

The ultra high frequency (UHF) technique has been used to study the partial discharges produced by free conducting particles in gas insulated substations (GIS) with a view to predicting the probability of particle-triggered breakdown. Statistical techniques have been developed to describe the motion of a single particle. It is possible to identify whether the particle is capable of crossing to the busbar, which is a necessary condition for particle-triggered breakdown. In addition, the technique can be used to assess the size of the particle, which is useful for making a qualitative assessment of the breakdown risk. The implications for the continuous discharge monitoring of GIS are discussed. >

Computational study of very fast transients in GIS with special reference is effects of trapped charge and risetime on overvoltage amplitude

Very fast transient phenomena in gas insulated substations (GIS) have been studied by computer simulation. The influence an overvoltage amplitude of trapped charge, risetime and section length of GIS is described. Under identical conditions, the amplitudes of overvoltages caused by very fast transients at the same point in a circuit, but having different trapped charges, are connected by a simple relation due to the linear nature of the circuit. In the case of high predicted overvoltages, the assumption of 1 pu trapped charge causes a large overestimation of the overvoltage which can be in excess of 20%, in comparison with the overvoltage due to 0.4 pu trapped charge, a value which, in practice, is rarely exceeded. For an open ended circuit, the assumption of zero risetime can cause an overestimation of more than 30% in the overvoltage in comparison with the case of 5 ns or more risetime. Variation of the trunk section length has a greater effect on the overvoltages than that of a branch section. The difference in the overvoltages at an open end for various section lengths can be in excess of 50%. In some cases even a small variation of section length causes a very large change in overvoltages.

Induced transients in substation cables: measurements and models

An extensive set of switching transient EMI response measurements on several types of substation cables and internal cable wires is described in this paper. Measured and predicted cable/wire current and voltage transients at both air-insulated substations (AIS) and gas-insulated substations (GIS) are presented, for system voltages ranging from 115 kV to 500 kV. The maximum peak-to-peak amplitudes of measured wire transients are found to vary from around 1 A to almost 20 A (current in amperes), and from 0.3 kV to almost 7 kV (voltage in kilovolts). Predictive models for field-driven coupling, as well as for direct-driven coupling via current transformers or capacitively-coupled voltage transformers (CTs/CCVTs), are presented. Model predictions are compared to and validated against measured wire transients. >

The 345-kV underground/underwater Long Island Sound cable project

A high-voltage underground/underwater cable system was installed to increase the transmission capacity from the mainland of New York to Long Island. The use of high-pressure fluid-filled (HPFF) pipe-type cable on the land portion represents the largest application of paper-propylene-paper (PPP) insulated cable in the United States. State-of-the-art technologies were implemented in the use of fiber optic cables for relay protection, temperature monitoring and leak detection systems, SF/sub 6/ gas-insulated substations, and underwater cable laying and embedment techniques. The design and installation of a 750 MVA, 43 km (26.6 miles), 345 kV underground/underwater electric transmission system are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Acoustic monitoring of partial discharges in gas insulated substations using optical sensors

A study has been made of the feasibility of applying optical fibre sensing technology to acoustic monitoring of partial discharges within gas insulated substations (GIS). A test rig has been constructed to simulate a section of GIS in which acoustic sources could be placed. This has been used to test the optical systems which showed greatest promise of having the capability of monitoring these partial discharges. Experimental results are presented which show that acousto-optical sensing, using fibredyne interferometry, of partial discharges within GIS is feasible in principle. However, further work is needed to extend the sensitivity range to acoustical amplitudes of about 10−14 m which correspond to signals from the weakest discharges requiring detection.

Investigations of multiple reignition phenomena and protection scheme of shunt reactor current interruption in GIS substations

Field measurement and computer analysis concerning 150 MVA shunt reactor current interruptions at a 275 kV gas insulated substation (GIS) were carried out to verify that high-frequency current interruptions can be caused by certain system structures on the circuit breaker power supply side. A shunt reactor current-interrupting test was conducted with phase angle control, which is considered to be the best method for preventing multiple reignitions, using short-circuit test facilities. The possibility of stable reignition-free interruption was confirmed, even when the longest arcing time is preset. >

An in progress experience on seismic qualification of gas insulated substations

An approach to the seismic qualification of standardized gas-insulated substations (GISs) is presented. Starting from experimental and analytical activities performed on standardized metal-enclosed primary distribution substations (170 kV), a methodology suitable for lower (MV) and higher (EHV and UHV) voltage ranges is defined, taking into account the site characteristics in terms of seismic severity and soil properties.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Addendum II to bibliography of gas-insulated substations

Addendum II to bibliography of gas-insulated substations

Detection of parallel discharges in gas insulated substations

Four methods for partial discharge (PD) detection in gas-insulated substations were considered. Laboratory tests were carried out to determine the efficiency of these methods to detect defects and to discriminate among different defect types. The sensitivity of the methods is compared and the applicability of the methods in the field is discussed. In the laboratory the standard PD measuring method showed a good sensitivity to defects. In the field condition the standard PD measuring method can have a sensitivity much lower than in laboratory, due to the rather high noise level expected. In the laboratory two of the alternative PD detection methods (namely the acoustic method and electrical method including a field probe inside the GIS) have shown a sensitivity to fixed-type defect discharges, while showing less efficiency relative to the mobile particles considered in the study. >

Accurate modeling of capacitively graded bushings for calculation of fast transient overvoltages in GIS

Two simulation models (distributed and lumped parameter models) to analyze the behavior and adequacy of design of capacitor-type bushings for GISs (gas-insulated substations) during very fast transients are proposed. The first model is formed by a cascade of multiphase transmission lines that reproduces the inductive and capacitive behaviour of the bushing well. The second model is formed by a cascade of lumped parameters, in which the shunt branches are realized by means of series RC elements. Both models are suited for the EMTP program by the Bonneville Power Administration, Portland, Oregon. They have been validated by comparing calculation results to laboratory measurements performed on an actual bushing. Either of the models can be chosen according to the user's needs. They differ in the accuracy level, computation burden etc. In any case, both models can be set up by only using the geometric and electrical design characteristics of the actual bushing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

More accurate modeling of gas insulated substation components in digital simulations of very fast electromagnetic transients

It is pointed out that very fast electromagnetic transients caused by switching operations in gas insulated substations (GIS) cannot be calculated if conventional techniques of modeling and simulation are used. The selection and adjustment of the most suitable models as well as determinations of their limitations in digital simulations of very fast transients in GIS are investigated. Results obtained from very extensive field tests and from digital simulations for different types of GIS have been used for the development of more accurate models for GIS components and GIS as a whole. A comparison between field test and calculation results permits the development of a model which takes into account the most decisive physical phenomena inherent in the very fast transients in the GIS. This is a prerequisite for designing and manufacturing power system components as well as for control and protection of the system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>