HV Substations Research Articles

Determining the actual reduction factor of distribution cable lines with applied cross-bonding

The considered problem appears as the consequence of the fact that many metal installations surrounding power lines in urban areas are situated under the surface of the ground and cannot be visually determined or verified. This paper presents the methodological version that enables solving the problem in the case of cable lines with cross-bonding, but it can also be applied with higher accuracy to cable lines with no applied cross-bonding than the existing one. It is based on the test measurement of currents appearing in two cable line phase conductors during a simulated ground fault in the supplied HV substation. By using the here-presented methodology it is possible to put the grounding problem of high-voltage distribution substations into realistic frameworks. Its application in practice shows that the actual conditions for solving this problem are much more favorable than was considered before.

Modular Multilevel Matrix Converter as Solid State Transformer for Medium and High Voltage AC Substations

The use of power converters as solid state transformers is an attractive solution to modernize the power network, but this solution has not been fully addressed for MV and HV substations. This paper presents a customized and simple control for the Modular Multilevel Matrix Converter (M3C), specially conceived for its operation on synchronous ports, which is the case of AC substations. The control allows bidirectional power transfer, generation/absorption of reactive power and provisions of ancillary services. The converter is compared to the back-to-back Modular Multilevel Converter (B2B-MMC) where the key performance indicators to carry out the comparison are power efficiency, number of semiconductor devices, passive components required, footprint, voltage cell balance, fault blocking capability and stress of components. The simulation results show the features, performance and attractiveness of the M3C topology in a 33/11 kV, 16 MW substation under different operating conditions, including grid faults and dynamic operation. The M3C presents similar efficiency and performance than the B2B-MMC, but it uses fewer semiconductor devices, passive components and total cell capacitor energy than the B2B-MMC, reducing cost and footprint. The experimental results show the performance of the M3C under less ideal conditions including a substation transformer saturation and power step response.

A Comprehensive Study Approach for Evaluation of Resonance and Ferro-Resonance in HV Substations A Case Study: Khuzestan Regional Electric Company

Resonance and ferroresonance in power systems are categorized as two destructive phenomena especially in HV networks which their occurrence are being initiated in consequence of a power system event. Also, Ferroresonance phenomenon may be initiated by non-power system event such as lightning strike. Hence, the study of resonance and ferroresonance requires an exhaustive evaluation of possible network events in different network configurations. In each event, the analysis of network voltages is conducted based on identified allowable limits by IEEE 519 standard as an evaluation critera. In this paper, a novel comprehensive study approach is proposed for study of ferroresonance phenomena in power networks. The proposed approach comprises different steps including substation equipment modeling, EMT simulation of the probable switching events, evaluation of correspondence results, and finally detecting the probable ferroresonance occurrence. Furthermore, a novel approach for resonance study is also presented. Voltage and current limits are implemented to define an impedance criteria for performing resonance evaluation of network buses. Findings – The proposed method is implemented for study of resonance and ferroresonance in all HV substations of the Khuzestan regional electricity network. By performing the proposed evaluations, the probable condition which may lead to resonance and ferroresonance occurrence are identified. The results are highly valuable for network operators in prevention of unintended overvoltages occurrence.

Thermal Impact of Lightning Current Injection into A Floor Housing High-Voltage Substations

In this paper the ionization problem of the ground, during the injection of lightning current through the earth of electrical installations is presented; this soil degradation has negative consequences on the performance of the earth electrodes through its transient impedance. To resolve this problem, we analyzed the measured samples of the earth resistance of the Lingwala / Kinshasa HV substation, where the soil is sandy-clay; the model of the dynamics of soil heating for a temperature variation simulated in Matlab gave us satisfactory results characterized by a decreasing exponential of the resistivity of the soil which gives the image of the pre-ionization which means an impedance low-value earth electrode transient which reflects its good performance. These encouraging results are safety indicators for electrical installations; they are aimed particularly at designers of industrial installations, operators of HV substations in electrical networks, and managers of buildings open to the public such as banks, hospitals, and large spaces. Keywords-- Thermal impact; injection; Lightning current; Ground; Job; High tension

Power network-planning optimization considering average power not supplied reliability index: Modified by chance-constrained programming

In this paper, a mixed-integer linear formulation for optimization multi-stage power system is represented. In order to achieve the best results, all facilities should be considered simultaneously due to the interconnection between power network equipment. In this paper, power plant, HV and MV substations and Distributed Generation (DG) are regarded concurrently to create an integrated power system planning. Furthermore, a reliability index called Average Power Not Supplied (APNS) in load point is modelled. Stochastic programming in the Chance-Constrained approach is also utilized to overcome uncertain parameters containing demand in load points, nominal voltages and facility failure rates. The mathematical model is tested on a real life case study in four schemes containing with or without considering DG and in certain or uncertain environment. Using both DG and MV substation in schemes planning leads to the establishment of a parallel system to improve network reliability. Since each scheme has specific requirements, it’s mathematical formulation is discussed in detail. The proposed formulation determines the optimum system configuration, including feeder routing, siting and sizing for power plant, HV/MV substation and DG. The numerical results show that planning in uncertain environment has a higher cost in comparison with certain model, but the results are more close to real world operations. Based on the obtained results a planner can estimate the cost components in different environments. Also in uncertain schemes, the growth in confidence levels increases the grid total cost. Therefore, planners must create an appropriate balance between confidence level and system total cost. Numerical results suggest that using DGs leads to a decrease in the required substations, their power to service load points and APNS cost. Thus using DGs can be an economic alternative to decrease system total cost. The achieved results indicate that the proposed planning for designing a power network has a desirable performance in practice.

A study on resilient and cost-based design in power distribution network against severe hurricane

Vulnerability mitigation is the solution for creating resilient distribution networks aims to prevent the uncontrollable outage propagation. This paper presents a new resilience index as a powerful tool to enhance the resilience of distribution systems against extreme hurricane events. The suggested framework provides a comparative study for optimal feeder routing problem and HV substation placement from the cost and resilience viewpoints. Once, the network is planned based on cost minimization, and then the proposed resilience index is calculated for the planned network. Finally, the network is planned based on resilience enhancement and afterward the planned network's cost is calculated. In case of resilient-based planning, the studied area is divided into small sites with different wind speed to evaluate the geospatial characteristics of hurricane and a fragility index is calculated for each distribution network component located at each sites. Both cost- and resilient- based networks are planned using deterministic and probabilistic approaches. In deterministic approach, network planning is done according to the worst prediction, the highest wind speed. But in probabilistic one, some scenarios with specified probability are defined for wind speed. Results show that, fragility index is high when considering worst prediction, so this less probable scenario needs higher investments. In this regards, scenario based planning, can lead to the best compromised solution considering cost and resilience which the obtained results validate the accuracy of the modellings and efficiency of the proposed method.

Preliminary testing and assessment of safety conditions of HV substations located in urban areas

This paper presents a method enabling the elimination of the inductive influence of metal installations surrounding a test circuit on the estimated value of grounding system impedance in a tested HV substation. By disregarding this influence, the preliminarily estimated values of the ground potential rise and potential differences (touch and step voltages) within and in the vicinity of an HV substation can be significantly smaller in comparison to their actual values. Due to this, the definite assessment concerning the safety conditions in some HV substations can be considered as satisfied although it is not the case. The analytical part of the presented test method is developed on the basis of the analysis of a complex electrical circuit formed by many, known and unknown, inductively and conductively coupled elements during a simulated ground fault in the tested substation. The developed analytical expressions are based on the measured values of two currents obtained by simulated ground-fault in the tested substation. One of them is a simulated ground-fault current, while the other current is the one induced in one of the phase conductors included in the test circuit only for obtaining this induced current.

Smart Protection Scheme For Radial Distribution System

In this paper,the study of optimal coordination of directional overcurrent relays along with relay communication in HV substations is proposed. The relay coordination problem is non linear.It typically consist of two groups of control variables(Time Dial Settings:TDS and Plug Settings:PS). The purpose of relay coordination is to propose the suitable settings for all releases and ensure the coordination. The differential evolution is employed to solve for solutions of optimal relay coordination. The relay coordination is mainly done to improve selectivity of the relay to particular fault. ETAP is so popular for its capability for modelling of power system networks and analyzing various studies and Real Time simulations.

Investigation on Dielectric Failure of High Voltage Equipment in Substation Caused by Capacitor Bank Switching

This paper investigates transient phenomenon of electrical stresses caused by capacitor bank switching, damaging HV equipment in substation. The system of aged air-insulated 115 kV substation is modeled by using Alternative Transients Program-Electromagnetic Transients Program. The failed current transformer (CT) was comprehensively modeled and investigated. The comprehensive model for electrical transient simulation has been developed by using actual data and derived data from real physical dimension of equipment. The simulated results are challenged by comparison of the results from theoretical calculation according to international standard and the results from simulation including on-site measurement. The comparison results to verify the accuracy of the developed model are satisfactory. The results show that electrical stresses affecting CT by voltage stress exceeds CT’s 123 kV rating together with the frequent switching operations as hundreds of times per year. These lead to degradation of CT insulation, especially at the top insulation portion close to HV terminal due to non-linear voltage distribution. Consequently, CT explosion finally occurred. This developed model is used as an effective tool for switching transient investigation to determine electrical stresses caused by various switching operations. With the known electrical stresses, the proper rating of equipment in HV substation can be selected.

Reduction of the fault current passing through the grounding system of an HV substation supplied by cable line

The paper presents an original analytical procedure developed for the determination of the part of ground fault current dissipated through the substation grounding system (electrode) into the surrounding earth in the cases when a specific measure has been taken to reduce it. The practical realization of this measure is simple and consists of burying one bare copper wire of a sufficient length together with the feeding cable line. The presented method enables a quick, and, for practical purposes reasonably accurate determination of the copper wire length providing the required safety conditions in the considered HV distribution substation and its vicinity. The developed analytical procedure is simplified by introducing an equivalent neutral conductor substituting all three cable line metal sheaths as well as all surrounding metal installations. The presented quantitative analysis shows that the effects achieved by this measure are significant.

Cyber Defense Budget Assessment in Smart Grid Based on Reliability Evaluation Considering Practical Data of HV Substation

Cyber Defense Budget Assessment in Smart Grid Based on Reliability Evaluation Considering Practical Data of HV Substation

Experimental Investigation of the Cooling Efficiency Impact Factors of Oil-immersed Transformer Split Cooling Systems

Split cooling system is widely adopted for transformer cooling in underground HV and EHV substations in China. The cooling efficiency of oil-immersed transformer split cooling system is influenced by many factors, such as the cooling mode, the separated distance between transformer and the cooling installation, and the hoisting height of the cooling installation, etc. In this paper, typical cooling mode and split cooling installations in underground HV and EHV substations in Shanghai are investigated. For the investigation of the impacts of these factors on the cooling efficiency, cooling experiments are carried out with different layouts of split cooling installations on an 110kV/80MVA oil-immersed transformer and its split cooling system. The investigation and experimental results show that the cooling efficiency of the ODWF, OF/OF/AN and ONAN cooling modes decreases in turn. The horizontal distance between the transformer and the split cooling installation has little influence on the cooling efficiency, whilst the hoisting height of the cooling installation will significantly affect the cooling efficiency. Lifting the radiator will slow down the oil flow between the transformer and the radiator in the cooling system and thus reduce the cooling efficiency.

Analysis and Optimization of Electric Field Distribution in 1200kV SF6 Insulated Power Frequency Test Transformer

With the fast development of HV and EHV underground substations in large cities, the demand and technical challenge of field insulation test for HV and EHV power transmission equipment is increasing fast also. As the traditional field insulation test equipment, oil-immersed cascaded power frequency test transformer is very difficult to face the challenges because of its large size and weight. SF6 insulated test transformer, as the new site test equipment, also needs to be designed smaller in size. As a result of the size reduction, it will increase the risk of breakdown and partial discharge. This paper introduces the electric field analysis and design optimization of a newly designed 1200kV SF6 insulated test transformer. The finite element analysis software INFOLYTICA is adopted for the electric field simulation. The simulation results demonstrated its main design of size and insulation. In some particular regions where the electric field is significantly uneven distributed, optimization design is provided.

Reliability assessment of HV substations equipped with fault current limiter considering changes of failure rate of components

Owing to the increasing electricity load demand on one hand and in order to have a reliable electric network on the other hand, constructions of new transmission lines and generation sources are extremely essential. Such expansions, however, raise the fault current level which can even exceed the maximum short-circuit level rating of the circuit breakers (CBs). High fault current, in addition to the adverse effect on the CB function, can damage other substation equipment suddenly or over the time. To this end, severity of the fault current is a key factor in the substation reliability assessment. In this context, fault current limiters (FCLs) which are employed to decline the fault current level need to be precisely modelled and their impact should be extensively studied. In this study, the effect of FCL on the failure rate of substation equipment is first investigated. A computational technique for assessing the substation reliability is accordingly devised. As the location of FCL installation in a given substation or in substations with different arrangements would not be the same, various credible configurations are incorporated here. The results show that from the perspective of reliability indices, double-bus double-breaker and one breaker and a half configurations are more suitable for FCL installation.

A ride-through power structure for CFETR

The China fusion engineering test reactor (CFETR) is an ITER-like tokamak system for fusion energy development. It could output 50-200 MW fusion power in phase I for demonstrating power generation with complete structure of fusion power plant, and 1 GW output power can be expected in phase II. Its ITER-like HV substation receives power from the 500 kV transmission grid for powering its pulsed power electric network (PPEN) and steady-state electric power network (SSEN). This paper describes the concept design of the electric power system, with emphasis on its turbine generator implemented with flexible doubly fed induction generator (DFIG). DFIG has ride through ability during the plasma-off period. Its capability diagram is configured to analyze its operation range. Similar to ITER, the CFETR also requires about 1 GVar reactive power to be compensated. Based on this requirement, the generator is expected to generate part of reactive power to compensate and stabilize the local power network.

Progress in CFETR Power Stations Concept Study

While EAST experiment was running in 2012, the project of the China fusion engineering test reactor (CFETR) concept design was started. This ITER-like tokamak system will be the second full superconducting tokamak in China based on EAST technology. In phase I, it has 50–200 MW heat output for demonstrating power generation. The fusion power stations contain complete structure of fusion power plant (FPP) which do not appear in the ITER and huge HV substation which receives power from the 500 kV transmission grid for powering its pulsed power electric network (PPEN) and steady-state electric power network. Furthermore, its structure of turbine generator of FPP is similar to that of a nuclear power station of the pressurized-water reactor. This paper describes the typical CFETR loads and put forward the requirements of short circuit capacity of HV grid. It analyzes different strategies of putting the generator power to the grid, i.e. on the 500 kV grid for future DEMO power structure or 66 kV medium-voltage local grid for self-use. In period between twice burning plasma, conceptual solutions are presented to maintain thermal circuit operation.

50 years in icing performance of outdoor insulators

During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.

On optimal multistage electric power distribution networks expansion planning

The optimal expansion planning of electric power distribution network to meet system load growth and overcome to pseudo dynamic behavior of network parameters considering a large number of constraints is a hard satisfactory multiobjective optimization problem. This paper implements new developed Imperialist Competitive Algorithm (ICA) for the optimal expansion planning of distribution network. The topology of medium voltage (MV) distribution network as backbone of electric power distribution systems is designed by optimal sizing, siting and timing of medium voltage network components such as HV substation and MV feeders’ routes. A multistage expansion planning is proposed to consider dynamic behavior of the system parameters asset management and geographical constraints. In order to reach the global solution an efficient coding is developed for ICA parameters. The Greedy algorithm is used to solve the minimum spanning tree problem to construct a radial configuration of the mesh network. At each stage of the problem the results are fully illustrated either by figures or by tables. A sensitivity analysis is used to show the robustness of the results with respect to ICA parameters variation. The obtained results are compared with GA as well known heuristic optimization tool. The efficiency and capability of the methodology has been tested on an under developed relatively large-scale distribution network.

Implementation of Full Adaptive Technique to Optimal Coordination of Overcurrent Relays

This paper proposes a full adaptive technique for setting all overcurrent (OC) relays in HV substations. This technique can be used online and there is no need to employ a telecommunication infrastructure. It is based on an appropriate equivalent circuit of the power grid in the substation, online estimation of the equivalent circuit parameters, and application of the equivalent circuit to estimate the required short-circuit currents. This full adaptive technique is used in setting the OC relays of a typical 230/20-kV substation connected to a sample 9-bus grid. Significant advantages of the proposed technique over the usual setting method are shown by comparing the corresponding results. Furthermore, the technique is improved to resolve problems due to penetration of distributed generation. Developing this adaptive setting technique is a step toward introducing self-adjustment OC relays.

Reliability Study of HV Substations Equipped With the Fault Current Limiter

Of particular interest to restrict the short-circuit level of interconnected power systems is to exploit fault current limiter (FCL) technologies. FCLs let the system planners devise new reliable and rather economical substation configurations and provide the possibility of proposing a promising cost-effective and prompt solution to the fault current over duty problem in the existing substations. This paper attempts to assess reliability of substation architectures accommodating the FCL operation and, besides, numerically investigates the FCL's impacts on the substation reliability indices. In order to clarify the proposed approach, two case studies with and without FCL are analyzed and compared. Although the discussions raised here are applicable for reliability modeling of all structures, five common substation configurations, namely: (1) single-bus single-breaker; (2) double-bus single-breaker; (3) ring bus; (4) one breaker and a half; and (5) double-bus double-breaker are considered in this paper. Numerical studies reveal that FCL deployment, while keeping the maximal flexibility of substation, may deteriorate the reliability indices of the substation due to the possible failures of FCLs.