kV Side Research Articles

Study on phase selection control characteristics of fast vacuum circuit breakers suitable for new power systems

Abstract With a high proportion of new energy access to the power system, the user side of the randomness and volatility of distributed photovoltaic large-capacity access to the 10 kV medium-voltage distribution grid operation results in more frequent fluctuations in the system voltage and more frequent switching of reactive compensation of the shunt capacitor bank on the 10 kV side of the conventional substation. Conventional reactive compensation switching circuit breakers adopt a spring mechanism whose mechanical stability is insufficient and the selection of the relevant fit capacitor bank accuracy is not enough. The 12 kV fast vacuum circuit breaker of small mechanical dispersion for selection related to the combination was proposed. First of all, based on the neutral grounded and ungrounded system of the capacitor bank, the strategy of capacitor bank phase selection closing was developed. For the action characteristics of the phase selection of the 12 kV fast vacuum circuit breaker, the variation laws of mechanical dispersion and the influence factors such as ambient temperature, capacitance voltage, capacitance degradation, mechanical wear, and conductive rod deformation were obtained by simulation and experiment. The results showed that the ambient temperature and capacitance voltage had a great influence on the switching time of the fast circuit breaker, while other factors had a small influence. Again, the pre-breakdown characteristics of the 12 kV fast vacuum circuit breaker were obtained by experiments. The results showed that the influence of contact opening distance and pre-breakdown voltage was a linear relationship, and the pre-breakdown slope was 30 kV/mm. According to the pre-breakdown closing characteristic curve, the pre-breakdown time of the fast circuit breaker was 0.45 ms at most. The feedforward compensation mechanism based on a neural network was proposed to compensate for the action characteristics of the fast circuit breaker and aimed to improve the phase selection accuracy. Finally, two rounds of capacitive current switching tests of 12 kV fast vacuum circuit breakers with C2 level were carried out in a third-party test station. The accuracy of phase closing is within the ±0.5 ms closing window, effectively preventing the occurrence of closing inrush current.

EMERGENCY MODES MODELING IN A COMPLEX LOAD NODE: HIGH-FREQUENCY COMPONENTS OF SIGNALS

The purpose of the study is to show the features of the occurrence of high–frequency components in current and voltage signals in various elements of the electrical complex by the example of modeling emergency modes in power lines and a complex load node and to analyze their mutual influence.
 
 Materials and methods. The signals of currents and voltages during transients in a power line and the load node with a three-winding transformer were modeled using the author’s software. The calculations are based on the method of synthetic circuits (Dommel’s algorithm). The main attention is paid to the occurrence of high-frequency components of current and voltage during short circuits and switching.
 
 Results. Modeling of the three-phase short circuit in a 110 kV transmission line when it is divided into P-sections demonstrates how significantly the level of high-frequency components differs in each of the three phases. This is manifested primarily in voltage signals. In a complex load node with a 110/35/10 kV transformer, short circuits and switching on the 35 kV side significantly affect the currents and voltages on the 10 kV side. It is shown that a higher level of high-frequency components of current signals corresponds to energy recovery modes in case of imbalance and run-out of the powerful asynchronous motor on the 10 kV side. The possibility of using the obtained results for the classification of faults in electrical systems is discussed.
 
 Conclusions. The level and spectral composition of the currents and voltages high-frequency components in transient modes depends on the initial phase and is of interest for the faults analysis and classification. The nature of these oscillations is determined by the resonant frequencies of the electrical circuits that occur during switching and short circuits.

ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ НАКОПИТЕЛЕЙ ЭЛЕКТРОЭНЕРГИИ В ЭНЕРГЕТИЧЕСКИХ СИСТЕМАХ

This paper explores the possibility of using different types of electric power storage devices in energy systems. A comparative analysis of such types of storage devices as: electrochemical, electrical, electromagnetic, mechanical. The properties of lead-acid, nickel-cadmium, sodium-sulfur, lithium-ion batteries, supercapacitors, superconducting magnets, kinetic storage devices are analyzed with the identification of advantages and disadvantages of their use; the fields of their application are considered. The possibility of integrating storage devices with renewable energy sources is being considered. The analysis of the averaged load schedules for the winter and summer periods is performed; the feasibility of using the drive to smooth out the peaks of the consumption load schedules is justified. A schematic solution for connecting an electric power storage device with a control system for a medium-voltage power supply network is proposed. The connection of the drive in such a system is provided on the 0.4 kV side using converter devices. The using of an AC-DC converter with a control system in such a system regulates the flows of active power in order to perform a two-way energy conversion in the case of energy accumulation by the storage device and energy return to the network.

Providing a combined solution to reduce very fast transient overvoltages in gas insulated substations

The use of gas-insulated substations in high voltage levels of power systems is expanding due to its many advantages, such as the need for less space, resistance to environmental pollution, high reliability, and no need for continuous maintenance. One of the phenomena that threatens the insulation distances inside the closed enclosure in these substations is very fast transient voltages. These overvoltages are dangerous for the equipment inside the substation and connected to it as a result of the switching operation of gas-insulated substations, and if repeated, it can damage the internal insulation of the equipment. Also, these transient overvoltages in special cases such as extremely high voltages may cause serious damage to expensive substation equipment. Therefore, in this article, while examining the existing methods to limit very fast transient overvoltages in different and sensitive points of GIS substations, a new combined method based on the simultaneous use of nanocrystalline rings in the busbar and two XLPE cable paths, The direction of connecting the power transformer to the substation is provided. The results of the simulation on the 230 kV side of the GIS substation of Arak city show that the method proposed in this article has the lowest range of overvoltages compared to other methods. By using the proposed combined method, the range of very fast transient overvoltages in the power transformer terminal of the network under study is reduced by 60 % and this reduction can be seen in other points of the substation as well.

Overcurrent and ground fault relay protection settings at tranformator-1 150kV/20kV Braga substation

The occurrence of a malfunction at the substation results in power outages and losses in the electrical energy distribution system to consumers. Many tests are carried out to see the performance of the protection system, including the parameters of the over current relay (OCR) and ground fault relay (GFR) in the electrical energy distribution system. This research aims to analyze OCR and GFR values, analyze OCR setting, drop-off, and pick-up values, and analyze OCR time characteristics using DigSilent Power Factory 15.1 software based on existing equipment specification data at the Braga substation. The results show an OCR accuracy level of around 94% on the 20 kV and 150 kV sides. Meanwhile, 92.39% on the 20 kV GFR side and 94.87% on the 150 kV side. The setting value for the pick-up current is 0.92 A on the 20 kV side of the GFR and the drop-off current is 0.85 A on the 150 kV side with a pick-up current of 0.39 A and a drop-up current of 0.37 A. Setting a value on the 20kV side is greater than on the 150 kV side due to the difference in current transformer ratio values. The simulation results show that the OCR and GFR characteristic curves on both sides meet the criteria for a protection system with good performance.

Research on Step-down Resonance Suppression and Filtering Device

In recent years, offshore wind farms have developed rapidly, and their installed capacity is getting bigger and bigger, and the offshore distance is getting farther and farther. In order to meet the needs of large-capacity and long-distance offshore wind power transmission, the AC submarine cable has the characteristics of long distance, high voltage and large cross-section. Along with the significantly improved transmission capacity, its equivalent capacitance is also increasing, which further reduces the resonance frequency of the offshore wind power AC transmission system. If the parallel resonance frequency of the offshore wind power transmission system is close to the main harmonic current frequency band of wind turbines, it will cause harmful system resonance and harmonic amplification, significantly increasing the harmonic current of grid-connected lines and the voltage distortion rate of nodes in nearby power grids, and seriously affect the safety of equipment and the safe and stable operation of offshore wind power transmission system. A step-down resonance suppression filtering device applied to the offshore wind power transmission system is proposed. The AC cable is connected to the low-voltage 35 kV side of the compensation winding of the centralized control center to eliminate the resonance risk of the 220 kV system and filter out the harmonic current. Compared with the existing technical scheme, the device has the advantages of simple control, reliable operation, stable resonance suppression effect, low operation loss and the like, and has great engineering popularization value.

Effect of geomagnetic storms on a power network at mid latitudes

Solar activities may disturb the geomagnetic field and impact the power grid via geomagnetically induced currents. We study active and reactive powers as well as the power factor of Iran’s power grid transformers (230 kV and 400 kV) and their correlations with geomagnetic disturbances indices (SYM-H < −30 nT and sizable horizontal geomagnetic field fluctuation) from 19 March 2018 to 20 March 2020. Out of 128,627 cases with a transformer power factor of less than 0.7, we observe that 12,112 samples correlated with SYM-H. Our investigation shows that about 4 percent of two years, the SYM-H has values less than −30 nT. Analysis of high-performance transformers (a power factor greater than 0.7 at 95 percent of working time) shows at least a 55 percent correlation of power factor less than 0.7 and SYM-H less than −30 nT. We observe that the transformers’ power factor of Rafsanjan-Kerman and Sarcheshmeh-Kerman (wye connection on 230 kV side) substations decreased to less than 0.7 and correlated with SYM-H. We show that the reactive power of the Sefidrood-Guilan and Shahid Beheshti-Guilan transformers (wye configurations) increased considerably on 9 January 2020 and positively correlated with SYM-H may produce large GICs at this part of the grid. We observe that the increase in reactive power at the Shahid Beheshti-Guilan substation correlated with the sizable changes in the horizontal field was recorded by the Jaipur station. However, more details (temperature and current of transformers) need records to estimate the impact of geomagnetic induction current on the power grid.

ON THE ISSUE OF COMPENSATION OF THE REACTIVE POWER LOADING UNIT OF THE INDUSTRIAL ENTERPRISE

This paper solves the practical problem of reactive power (RP) compensation of the load unit of the chemical plant. The peculiarity of this node is the presence of powerful asynchronous motors in the absence of synchronous machines.&#x0D; The load node is powered by a node substation located on the territory of the enterprise, on a 150 kV transmission line. Two step-down transformers TDNS–1600–150 / 6 kV, power supply load 0,4 kV from two transformers TM-2500–6 / 0.4 kV are installed at the settlement substation.&#x0D; The total active load of the unit is 12,540 kV, reactive — 7,210 kVAr. Currently, the main source of RP for the node is the power supply system (SPS) and partially generators of its own thermal power plant (TPP) with a capacity of 2–112 MW.&#x0D; As you know, factory TPP are sources of thermal energy for the technological needs of enterprises with low electricity production, so the possible task of choosing the best source of reactive power.&#x0D; The situation in the supply of electricity to industrial enterprises of Ukraine is complicated, it is determined by the ever-increasing tariffs for electricity, and is also regulated by the instructions on compensation of RP.&#x0D; Here it is necessary to note the latest instructions of the Ministry of Energy of Ukraine dated 06.02.2018 № 87 and the NERC supplement dated 28.01.2018, which regulate the procedure for settlements for the generation (consumption) of reactive power by industrial enterprises. A feature of the new methodology is the determination of the economic equivalent of reactive power (EERP), taking into account the cost of active energy. &#x0D; Based on the standard power factor (according to the new method tg–0.25), the reactive power from the SPS for the load unit can be obtained in the amount of 3140 kVAr. Uncompensated RP in the amount of 4070 kVAr, and taking into account the increase in load by 5% — 4480 kVAr, it is advisable to compensate at the expense of the own needs RP.&#x0D; Given the above, the best option to compensate for the RP of the load node are the capacitor banks (BSC) to the lack of synchronous motors to drive the technological mechanisms of the enterprise.&#x0D; The classical method of technical and economic calculations for reactive power compensation, set out in the works of F.F. Karpova and L.V. Litvak, provides for the definition of such a parameter as the cost of active power losses, which includes the following components: a — specific costs due to the expansion of SPS to cover losses of main power (UAH / kW) and b — specific costs of electricity generation (approximately equal to the cost of electricity on power plant tires (UAH / kWh)). Determining the values of these components is significantly difficult to the lack of systematic data on the cost of electricity, especially in the requirements of the Ministry of Energy for the purchase of energy from renewable sources, which may affect the accuracy of some data, but not essential.&#x0D; According to the calculations: indicator a = 4110 UAH / kW, b = 0,573 UAH / kW and the specific cost of active power losses С0 = 6075 UAH / kW. Then the amount of costs for the transfer of reactive power from the power center to the voltage node will be 109.9 thousand UAH.&#x0D; Of the two options for installing BSC on the 6 kV or 0.4 kV side, you should choose the option of transmission of RP through step-down transformers TM-2500–6 / 0.4 kV, which is confirmed by the calculations performed (certainly take into account the significant difference in BSC cost of 0.4 kV).&#x0D; Estimated costs for the installation of BSC on the 6 kV side are: 4´20995 = 83980 UAH, taking into account the cost of the input device and the battery of capacitors with a capacity of 1125 kVAr. For each section of 6 kV busbars, two sections of over-regulated BSC are installed, as with a stable reactive load, if necessary, one section of capacitors can be completely disconnected.&#x0D; As you can see, a more economical option is to install BSC at the enterprise in the load node, taking into account the SPS requirement for consumption of RP in the hours of minimum active load. In the long run, this technical solution gives a significant economic effect.

Configuration of suppression schemes against high-frequency transient reignition overvoltages caused by shunt reactor switching-off in offshore wind farms

It is crucial to protect offshore wind farms from overvoltages because of bad accessibility and high maintenance costs. During the process of switching-off a shunt reactor with a 40.5 kV vacuum circuit breaker, high-steepness reignition overvoltages may occur. In order to reproduce this reignition overvoltage accurately and further determine a suitable mitigation scheme, this paper proposes a new quantitative evaluation framework, which comprehensively considers its magnitude and steepness. Firstly, main component models of a typical offshore wind farm are developed in PSCAD/EMTDC, which consider their high-frequency transient characteristics. Subsequently, the transient characteristics of reignition overvoltages at the 35 kV side of shunt reactors are analyzed. Then, for the sake of investigating the mitigation performance of different overvoltage protective schemes, a quantitative evaluation is conducted. Simulation results show that switching-off shunt reactors in offshore wind farms can cause high-frequency transient reignition overvoltages characterized by a high amplitude and a high steepness at its terminals. It is found that a resistor-capacitor filter or a new scheme combining a surge arrester with a smart choke can be installed on the terminals of shunt reactors to decrease both the magnitude and the steepness of reignition overvoltages.

ANALISA PROTEKSI OVER CURRENT RELAY (OCR) DAN GROUND FAULT RELAY (GFR) PADA TRANSFORMATOR DAYA GARDU INDUK

ABSTRACT&#x0D; In the electric power distribution system, the power transformer is an equipment plays an important role in a substation. In a distribution system, a fault cannot be predicted. This fault can be in the form of a 3-phase, 2-phase, or 1-phase short-circuit fault to ground. In order to prevent this, a good and reliable protective equipment is needed, one of which is the Over Current Relay (OCR) and Ground Fault Relay (GFR) which are used as backup protection for power transformers. The work principle of the OCR is to detect the presence of a short-circuit current between phases and the work principle of the GFR is to detect a short-circuit current from the phase to ground, the results of the analysis carried out describe when the fault current exceeds the predetermined setting value then Over Current relay and Ground fault Relay takes instantaneous decisions or by slowing down the opening of the PMT in the event of a disturbance. After doing the calculations, for the setting current (OCR) on the 150 kV side, 277.2 A was obtained with the TMS (OCR) time setting of 0.31 and for the setting current (GFR) on the 150 kV side, 35.22 A was obtained with the TMS time setting ( GFR) is 0.44. For the setting current (OCR) on the 20 kV side, 2,078.4 A is obtained with the TMS time setting (OCR) of 0.23 and for the setting current (GFR) on the 20 kV side, 96.07 A is obtained with the TMS time setting (GFR) namely 0.3.&#x0D; Keywords: Transformer, Over Current Relay, Ground Fault Relay, OCR, GFR

On-line data splicing power flow analysis method based on sensitivity

This paper proposes an online data splicing power flow analysis method based on sensitivity analysis. Since the step-down transformer in the whole network data is usually equivalent to the 220 kV side, the equipment below 220 kV is not modeled in detail, and the provincial network data is modeled to 110kV and 35 kV voltage level equipment in detail. Different levels of modeling have a greater impact on the accuracy of stability analysis and calculation. Therefore, the purpose of improving data accuracy is achieved by splicing the entire network data (external network) and provincial network data (internal network). This paper is based on the sensitivity analysis method to stabilize the tie-line power by adjusting the output of the external network units, and form the whole network data that can accurately analyze the stability characteristics of the provincial network. The problem of power flow deviation caused by the voltage and angle deviation of the nodes at both ends of the regional tie line during the data splicing process is solved. Through the actual application of splicing the entire network and Hunan Provincial Network data, the effectiveness and necessity of the proposed method have been verified.

Redesign Gas Insulated Switchgear to Semi Air Insulated Switchgear 500 kV side and 150 kV side in EHVS Kembangan

The main role of 500 kV extra high voltage Gas Insulated Substation in transmission system is serves connection between the electrical generation and transmission system. To improve equipment performance and the quality and reliability of electricity distribution need time to maintain gas insulated line compartment but preparation to maintenance requires a long time, limited maintenance duration and long implementation of gas evacuation. This paper is object to redesign Gas Insulated Switchgear (GIS) to Semi Air Insulated Switchgear (AIS) on 500 kV side and 150 kV side with new design of Gas Insulated Line compartment in order to accelerate maintenance and gas evacuation job. with surveys, observations, analyses and Root Cause Problem Solving (RCPS), it can be seen the initiation of improvement to accelerate the maintenance of IBT and accelerate the repair of anomalies in the gas insulated line. After redesign Gas Insulated Switchgear to Semi Air Insulated Switchgear, this results show maintenance IBT after redesign is 25 hours faster and duration anomaly on GIL after redesign 24 hours faster.

Design Of Interlock High Voltage Bay Transformer 150/20 kV System Simulator

Simulator is a tool or means that is needed in learning to replace the role of a real system or equipment. The simulator providing a solution for repetitive operation of equipment. This is not possible on the actual equipment such as in a high voltage transformer of electrical distribution system. The purpose of this study was to design a simulator of a 150/20 kV transformer bay interlock system using a PLC as a control device and computer monitor as a display (human machine interface). In this simulator there are 15 states to describe the interlock system between the circuit breaker and the disconnecting switch both on the 150 kV side and on the 20 kV side. Interlock system design using state diagram method. PLC Ladder diagrams are written with CX-programmer software and HMI programming using CX-Supervisor software. The validity test of the simulator is done by using event validity techniques. The design results show that the overall interlock system runs as a whole with the percentage of validity is 100 percent or with a validity index 1, so it can be concluded that the simulator of the 150/20 kV transformer bay interlock system can be used as a learning tool to replace the real system.

Field analysis of switching transient process on the 35 kV side of a substation connecting to PV plant

To reveal the real causes of two explosion faults of potential transformer (PT) on a substation connecting to PV plant, an on-line monitoring equipment with a sampling rate of 40 MS/s for the transient voltage was installed on the secondary side of the PT. By switching the 35kV bus bar onto the main transformer, the switching transient processes on the PT were obtained. The field measured transient process indicated that the switching transient voltage caused by switch operation induced the resonance between the charging circuit and the PT and the resonance may be the direct cause of the PT explosion. The effective measures to suppress resonance in this substation are proposed.

CLASSICAL METHODS TO PREDICT THE PERFORMANCE OF BUCHHOLZ RELAY BY GIVING THE PHENOMENA OF INCIPIENT FAULT INTO THE OIL IMMERSED TRANSFORMER

This work explains the classical methods for predicting the performance of the Buchholz relay. The traditional methods use the simulation by giving a phenomenon of incipient fault into the oil-immersed transformer. The Buchholz relay is a type of mechanical relay whose operating mechanism is influenced by oil and gas in the transformer tank tend to move into the expansion tank through the interconnecting piping. This device is a critical component that is integrated into the oil-immersed transformer protection philosophy. An electronic circuit-based simulator that is integrated with a circuit breaker operation control panel was chosen as a means for creating conditions during alarm or trip. The performance measurement provides simulated fault conditions for setting on alarm and trip. The provision of faults simulation in the form of pressing a push-button one time to simulate the existence of an alarm condition. In that condition, the CBs control panel does not operate, but the appointment of an alarm signal. Based on that, the Buzzer sounds and the status check trip is still normal or "no lock-out". Giving full pressure as a form of simulation for trip conditions on the Buchholz relay, the control panel designates the condition of the two CBs (side of 150 kV and 20 kV side) open, and the alarm signal designation also occurs with Buzzer sounding. Hence, the check trip status becomes "lock-out". The Buchholz relay serves to detect the presence of gas caused by local heating or pressure surges in the transformer oil. After giving all of the conditions, the Buccholz relay performance is known.

Modeling of balancing transformers to determine the effectiveness of their application

One of the urgent problems is providing consumers of distribution electric networks with high-quality electricity. The most important indicators of the quality of electricity are the level and asymmetry of voltage, the deviation of which from the normative indicators leads to disruption of operation and a decrease in the service life of electrical equipment. If the standard indicators of electricity are not met, the consumer has the right to demand compensation from the electricity supply companies. For balance the voltage on the 0.4 kV side of the step-down substations, it is promising to use transformers with a balancing winding both in new construction and in their reconstruction. The problem of determining the effect of the use of transformers with a balancing winding is that the manufacturer does not provide the necessary parameters for them to ensure the calculation of the phase voltage level when connecting an asymmetric load. Also in existing software products, such as, for example, Matlab/Simulink, there are no ready-made mathematical models of the transformers under consideration. As a result, it is impossible to reliably assess the benefits of replacing conventional transformers with a balancing winding, when the task of a feasibility study for the reconstruction of a substation arises in order to ensure standard indicators of the quality of electricity and reduce electricity losses.

Hierarchical Evaluation of Distribution Network Access Capacity Taking Into Various Prosumer Group Load Forecasts

Now the measurement means of access capacity at all levels of distribution network are insufficient and it is difficult to calculate effectively based on limited data. This paper proposes a hierarchical evaluation method of access capacity of distribution network with multiple prosumer group load forecasting. Firstly, a load dynamic prediction model is constructed. According to the typical load model of historical data mining, a unit prediction model of typical users is established by using the conjugate gradient RBF neural network learning algorithm. Then, according to the charge-discharge dynamic model of the energy storage power station and the load dynamic prediction results, an assessment model of access capacity at the 10kV side was constructed. By analyzing the known load type, load type ratio and transformer capacity on the low-voltage side, the conversion coefficient of 10kV side load to 0.4kV side transformer capacity is obtained by weighting different types of loads proportionally. Then, access distribution capacity of different prosumer group can be obtained based on conversion coefficient. It can ensure the effective measurement of access capacity at all levels of distribution network under the premise of meeting N-1 safety criteria. Finally, an example is given to demonstrate the effectiveness of the proposed method.

The impact of the larger number of non-linear consumers on the quality of electricity

Theoretically this paper will explain the formation of higher harmonic components in the electricity network, their causes, consequences on consumers and the ways of their elimination. Transformer role in the Dyg connection will be explained on the concrete example. For a specific example the waveform of primary (R) phase at 10 kV voltage level, the current of the secondary (r) phase and the neutral conductor at the 0.4 kV voltage level will be determined as shown in the concrete example in the work. Harmonic content will be determined up to 15 harmonics and the effective value of all these currents (phases R and r). THD for current of primary (R) phase and secondary (r) fase will be calculated. In this paper, the dimensional three-phase filter is set to eliminate the maximum harmonic component of current of the primary (R) phase on the 10 kV side of the transformer. The waveform, the corresponding harmonic content for the current and THD of primary (R) phase will be determined. Additional measures have been proposed to reduce the THD. Another parallel filter has been realized to eliminate the second by size harmonic components of primary (R) phase current. It will also compare THD for primary (R) phase as in the previous cases. For the total duration of the simulation, the used time is Tstop = 0.1 sec. All of the above simulations will be realized in the MATLAB/PSB program package and simulation models will be displayed.

RETRACTED: Research and application of safety assessment for flexible joints of lightning arresters

A design method of aeroelastic model wind tunnel for substation frame lightning rod structure was presented in this paper in order to improve the effectiveness of wind tunnel design of aeroelastic model. The wind-induced vibration of frame lightning rod was studied aiming at the breakage of lightning rod of 220 kV side frame in a 500 kV substation, and the wind tunnel test of three air-elastic models of lightning rod was conducted. The dynamic strain at the bottom of the lightning rod is obtained by the fiber grating strain measurement technique. The wind-induced dynamic response of the structure is studied, the dynamic effect of wind on the structure is analyzed, and the reference is provided for further study on fracture.

Research on 0.4kV Mobile Cable Branch Box Containing Cable Fast Conversion Device

Clients of 0.4kV side of substation are supplied by single power source in existing electrical connections. If superior substations go wrong, their users may suffer a loss of power, which has a significant influence of safety and reliability of distribution network. A 0.4kV mobile cable branch box containing cable fast conversion device is proposed in this paper, it could effectively improve the quality of power supply and performing varies way of emergency repairs combined with generator car.