Band 21, Heft 4

In this paper, the existence of arc in an electrical contact gap is investigated. A 14 and 42 V DC electrical circuit for an automotive vehicle is considered and the factors which causes arc are identified. A plate–plate, cylinder–cylinder and cone–cone electrical contact are considered for which the closed-state resistance and open-state capacitance are acquired for Al, Cu, Fe, Ni, Au and Pt materials. The voltage, current and power characteristics curves of the electrical contact are obtained for the equivalent automotive DC system. The temperature and electric field of the electrical contact is also reported. The breakdown voltage and electric field for the micro-gaps of 0.5–10 µm are presented and the boundary for arcless operation of the electrical contact is identified. Arc existence is analyzed for four circuit conditions with various voltage and current levels. Simulations are executed using COMSOL Multiphysics Finite Element software tool and the results were related with calculated values. The results show that power has more influence on the arc existence in electrical contact. Electrical contact does not produce an arc due to voltage and electric field. The plate–plate electrical contact with Pt material performs better in terms of arcless switching. These electrical contacts would have an influential role in the design of an arcless, less weight, low cost, reliable electrical contact for next-generation automotive DC power system.

Based on the background of Huainan–Wannan UHV AC double circuit transmission line, the mechanism of the transient recovery voltage (TRV) is analyzed in the case of a wire of split conductor failure. The simulation model is established to simulate the TRV of the circuit breaker when the multiple split conductors are in different positions, and the influence of the induced voltage on the TRV is also considered. The simulation results show that the more the number of fault split conductors is, the more serious the TRV is, and the peak and rate of rise of TRV are increased due to the induced voltage. Therefore, it is very important to consider the coupling effect on the transient characteristics of circuit breakers in practical engineering.

The power system oscillations in the grid are an issue of concern to the system operator. They may transform a stable system into an unstable system when the system is operating on the edge and contingency occurs. The oscillations developed in the system may grow and spread across the power grid if no timely, corrective action is taken to mitigate them. The paper presents the ultra-mega power plant generation complex related blackout analysis. The case study presented in this paper demonstrates the utilization of synchrophasor data to have a better realization about the grid disturbance. It covers some of the important dynamic simulation studies considered representative of various scenarios during this. The paper illustrates utilization of Prony analysis using multiple signals and Fast Fourier Transform methods in conjunction with frequency data obtained in real-time from PMUs installed in the western regional grid of India to determine the frequency of oscillations, its magnitude, and related damping during this disturbance. The focus of this study involves the application of these techniques to gain insight into the oscillatory behavior of the system during this disturbance associated with ultra-mega power plant having generation capacity greater than or equal to 4000 MW from the western part of Indian grid. Based on this, distinct categorization of oscillations into “local mode” and “inter-area mode” of oscillations was done for enhanced understanding about the type of oscillations getting excited during this disturbance.

The growing demand for quality in the Energy Distribution Service, both by consumers and by regulatory agencies, obliges most distribution utilities to apply technologies that can be easily implemented and produce results in a short term horizon. The telecontrol technology is an essential tool every time it is necessary to fast restore the energy supply. This technology, which is completely supervised and controlled by the system operation center, allows the fast detection of a fault at a distance and switch an equipment without the aid of the operating crew, thus reducing the time that the power supply is unavailable. The present paper describes a Telecontrol Project, incorporated in an electric energy distribution utility in Brazil and compares the results in quality improvement with others usual investment actions, such as operating and maintenance procedures, laterals protection and network reinforcement. This paper shows, analyzing the results, that to improve the reliability indexes in a short time, when the company’s economic recovery is more important, the application of remotely controlled switch is more effective.

The foremost problem facing by the photovoltaic (PV) system is to identify the faults and partial shade conditions. Further, the power loss can be avoided by knowing the number of faulty modules and strings. Hence, to attend these problems, a new method is proposed to differentiate the faults and partially shaded conditions along with the number of mismatch modules and strings for a dynamic change in irradiation. The proposed method has developed in two main steps based on a simple observation from the Current versus Voltage (I-V) characteristic curve of PV array at Line-Line (LL) fault. First, the type of fault is detected using defined variables, which are continuously updated from PV array voltage, current, and irradiation. Second, it gives the number of mismatch modules (or short-circuited bypass diodes) and mismatch strings (or open-circuited blocking diodes) by comparing with the theoretical predictions from the I-V characteristic curve of PV array. The proposed algorithm has been validated both on experimentation using small scale grid-connected PV array developed in the laboratory as well as MATLAB/Simulink simulations. Further, the comparative assessment with existing methods is presented with various performance indices to show the effectiveness of the proposed algorithm.

The electrical transformer is one of the most used equipment in electrical power systems. The non-linear electrical loads are increasing, mainly in the electrical distribution system, and the electrical power transformer is inserted in this scenario, supplying these loads. Consequently, the increasing non-linear loads affect the electrical transformers and their factors directly, like in the dependency between temperature and harmonic increase. Therefore, to study the influence of harmonics in the transformer’s temperature, one should understand how it will behave with these changes in the electrical power system. For this reason, in this article, numeric simulations and tests were performed to predict the transformer temperature behavior. The proposal is a numeric technique for coupling two equations, thermal and electromagnetic, of an electrical transformer, considering heat sources regarding joule, eddy current, and hysteresis effect. To evaluate the numeric simulation and understanding the electrical transformer behavior in real-life, tests with specific harmonic orders (3rd, 5th, and 7th) and their combinations and a test with less than 10% total harmonic distortion, according to IEEE 519 standard were performed. It is verified that the electrical transformer temperature rises with the increase in harmonic amplitude and its orders. Results show that the industry must be aware of the effects of the increasing non-linear loads when designing the next generation of transformers concerning their durability and lifetime.

A new principle of UHVDC Line pilot protection based on internal parameters of the trigger angle of converter is proposed, in order to improve the ability of the protection to withstand transition resistance. Through the analysis of UHVDC control system, it is found that, due to the regulation of control system, in terms of trigger delay angle of rectifier side and trigger leading angle of inverter side, the change tendency in internal fault and external fault is different. Thus, the protection criterion is constructed. Compared with the traditional protection principle using voltage and current to establish protection criteria, this principle uses internal parameters as protection quantity. The simulation based on PSCAD/EMTDC verifies the effectiveness of the protection principle.

This paper presents a phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines. Detection and classification of faulty phase(s) have been carried out by deriving indices from the change in phasor values of current with a distance of one cycle. The derived indices have zero values during normal operating conditions whereas the index corresponding to the faulty phase exceeds the pre-defined threshold in case of occurrence of a fault. A separate ground detection algorithm has been utilized for the identification of involvement of ground in a faulty situation. The performance of the proposed technique has been evaluated for intra-circuit, inter-circuit and simultaneous faults with wide variations in system and fault conditions. The suggested technique has been evaluated for over 23,000 diversified simulated fault cases as well as 14 recorded real fault events. The performance of the proposed technique remains consistent under Current Transformer (CT) saturation as well as different amount and direction of power flow. Moreover, suitability to different power system network has also been studied. Also, faults having fault current less than pre-fault conditions have been detected accurately. The results obtained suggest that it is able to detect faulty phases as well as classify faults within quarter-cycle from the inception of fault with impeccable accuracy. Besides, as modern digital relays have been already equipped with phasor computation facility, phasor-based technique can be easily incorporated with relative ease. At last, a comparative evaluation suggests its superiority in terms of fault classification accuracy, fault detection time, diversify fault scenarios and computational requirement among other existing techniques.

SF 6 gas is a kind of gas medium widely used in the insulation of power equipment. However, due to the greenhouse effect of SF 6 , new environmentally friendly gas that can instead of SF 6 has been the goal for researchers. CF 3 I gas is one of the most promising alternative gases for SF 6 . In this paper, two-term Boltzmann equations of CF 3 I/N 2 /CO 2 ternary gas mixture at 0.1 MPa and 300 K are calculated to obtain an electron energy distribution function (EEDF), an electron drift velocity V e , a critical fold breakdown field strength ( E / N ) cr of the ternary mixed gas, and the synergy effect coefficient is used to analyze the synergy effect between the mixed gases. The calculation results show that the CF 3 I/N 2 /CO 2 ternary mixture has a synergistic effect, and the 50% CF 3 I/40% N 2 /10% CO 2 ratio scheme makes the mixed gas most likely to replace SF 6 from the physicochemical properties. Comparing the calculated data of this paper with the data of other works of literature, the validity of the calculation method and calculation data in this paper is verified, which provides theoretical support for the research of SF 6 alternative gas.

Core temperature ( T c ) estimation plays an important in role in establishing an effective thermal management system of a battery. In the present work, T c of a lead acid (Pb) battery was estimated using a Kalman filter, based on a thermal model of the battery using convection resistances and capacitances. The governing equations based on measured surface temperature ( T s ) and ambient temperature ( T amb ) were derived. Since T c cannot be measured directly, estimation technique was used to predict the same using measured T s and T amb . Five test cases for which the profiles of T c versus time were available were analyzed. It was found that the errors in the predictions varied from 0.25 °C to 3.5 °C., depending on the nature of T c profiles, with minimum errors when T c has slow variations with time.

In an electrical system, power quality (PQ) is becoming significant to all types of consumers. With the increase of power demand from end users, maintaining the quality of power within the limitations is a major problem. This paper describes power quality issues like voltage sag, voltage variations, voltage fluctuations, individual harmonics, inter-harmonics and power frequency variations in a grid connected system with a three-phase induction motor connected as a load. This system is tested in according to International Electro technical Commission (IEC) Std. 61000-4-11/4-13/4-14/4-28 which are allowed to the load through a regenerative grid simulator. Test procedures of the system equipment and the detailed analysis of the monitored and measured results are also described in this paper.

The motor losses are directly affecting the efficiency of the high voltage induction motor (HVIM). It is an important parameter of the motor design. In order to analyze the influencing factors of the HVIM losses, a 10 kV, 1000 kW HVIM is taken as an example to establish a 2D finite element model. The correctness of the model has been verified by the comparison of experimental data and calculated data. The finite element calculation method is adopted to numerically solve the electromagnetic parameters of the prototype. Based on electromagnetic parameters, the influence of the rotational speed of the HVIM on the core loss is analyzed, and the variation of the rotational speed on the core loss is obtained. Secondly, the influence degree of load rate on the core loss of HVIM is determined. Finally, the variations of different material characteristics on losses are studied. In addition, the effects of different speed and load rate on the copper loss of the HVIM are also studied. The analysis of this paper provides reference and engineering practical value for the optimization design of HVIM.