281 results about "Harmonic elimination" patented technology

Three-level inverter and rectifier power conversion systems and space vector modulation (SVM) controls having even-order harmonic elimination for neutral voltage balancing with a predefined vector switching sequences for half-wave symmetry in open loop system operation. The vector sequence listings for each SVM diagram segment includes switching state entries individually indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of the power conversion system, with listings for each pair of first and second diametrically opposite diagram segments include symmetrically opposite switching states, with positive levels in the entries of the listing for the first segment corresponding to negative levels in the entries of the listing for the second segment and vice versa.

A light-emitting diode (LED) tube is applied to a lamp holder with a ballast, and has a lighting module, a first control module and a second control module connected to two ends of the lighting module, and a harmonic elimination module connected to the first and second control modules and parallelly connected to the lighting module. Each of the first control module and the second control module has a simulation circuit unit and a rectification unit. Each of the simulation circuit units and the harmonic elimination module has a switching element. The first and second control modules adjust electrical signals from the ballast, and the harmonic elimination module eliminates harmonic waves generated by the ballast so that the lighting module is compatible with the ballast and is lit. Accordingly, the LED tube can be directly mounted on a fluorescent lamp holder with the lamp holder intact.

Three-level inverter and rectifier power conversion systems and space vector modulation (SVM) controls having even-order harmonic elimination for neutral voltage balancing with a predefined vector switching sequences for half-wave symmetry in open loop system operation. The vector sequence listings for each SVM diagram segment includes switching state entries individually indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of the power conversion system, with listings for each pair of first and second diametrically opposite diagram segments include symmetrically opposite switching states, with positive levels in the entries of the listing for the first segment corresponding to negative levels in the entries of the listing for the second segment and vice versa.

A method of designing a random pulse width modulation (RPWM) inverter with unwanted harmonic elimination, which first uses a Fourier analysis and a numerical analysis to eliminate the unwanted harmonic components, next uses the equal area approach to produce switching angles to be used as start values for solving non-linear equations, next selects low-order harmonics to be eliminated and randomly sampled harmonics to solve the equations and obtain pluralities of switching angles for eliminating different harmonics, next applies pluralities of harmonics to a random probability function to thereby obtain a harmonic distribution, and finally uses a random sampling to evenly disperse the higher side-band harmonic components and effectively suppress the low-order harmonic components.

The invention provides an optimization control method based on selective harmonic elimination pulse width modulation (SHEPWM). The optimization control method based on the SHEPWM comprises the following steps: writing amplitude expressions of fundamental waves and controlled harmonic waves of all times in an arraying mode, confirming amplitude of the fundamental waves and the controlled harmonic waves of all times, and obtaining a switch angle. The optimization control method is combined with characteristics of amplitude frequency of a filter, obtains the most advantageous size value of the amplitude of the controlled harmonic waves by optimizing an objective function, improves the harmonic wave distribution condition of an SHEPWM wave form, reduces amplitude of surplus harmonic wave, enables a total harmonic content to reduce, and even removes the big surplus harmonic waves. Small amplitude changes of a controlled harmonic wave component can cause great influence on harmonic wave distribution of output voltage, and suitable changes can reduce amplitude of surplus harmonic wave components of a traditional SHEPWM method.

The present invention discloses a long and thin bore diameter and cylindricity measurement method based on dual-sensor error separation. A standard ring gauge is taken as a calibrating device to sleeve a dual-sensor measuring head, a first harmonic elimination approach method is employed to calibrate the dual-sensor measuring head, the dual-sensor measuring head is sleeved with the bore of a measured workpiece, the complete cycle scanning measurement is performed section by section along the axial direction and the circumferential direction of the bore, the distance measurement data of each section of the two sensors are employed to obtain average values and perform difference to realize calculation and separation of line feed errors of each section and the eccentricity error of each section is separated to convert the finally processed measurement data to a rectangular coordinate system and add the eccentricity error of the corresponding section in the data points of each section so as to restore the contour of the measured bore, the least square method is employed to obtain the diameter of the bore contour, and the cylindricity evaluation method is employed to perform cylindricity calculation. The long and thin bore diameter and cylindricity measurement method based on the dual-sensor error separation can realize calibration of an unidirectional electronic measurement head so as to effectively separate the line feed errors of a guide rail and the eccentricity error of each section of the bore of the workpiece so as to greatly improve the detection precision of the long and thin bore diameter and the cylindricity.

Three-level inverter and rectifier power conversion systems and space vector modulation (SVM) controls having even-order harmonic elimination for neutral voltage balancing with a predefined vector switching sequences for half-wave symmetry in open loop system operation. The vector sequence listings for each SVM diagram segment includes switching state entries individually indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of the power conversion system, with listings for each pair of first and second diametrically opposite diagram segments include symmetrically opposite switching states, with positive levels in the entries of the listing for the first segment corresponding to negative levels in the entries of the listing for the second segment and vice versa.

In the transformer, line side windings connected in star type continuous form is adopted in inner side. Structure of outer side is three groups divided, N groups phase shifted cake typed line side windings. The invented transformer solves issues of harmonic polluting on power grid and harmonic wastage, possessing advantages: reliable operation, simple maintenance, small harmonic current at power grid side, low noise, low heat generated, high power factor. When being applied to high voltage frequency control, the invention solves issues: heating of motor, torque ripple, influence of dv / dr and common mode voltage on insulation of motor. The invention can reaches ideal effect of harmonic elimination even if out of balanced currents occurred, providing advantages of approximate to sinusoidal waveform output, high conversion efficiency etc.

The invention discloses a micro-grid voltage disturbance control method with voltage harmonic compensation, and belongs to the field of electrical technology. According to the invention, droop control, proportional resonance control and harmonic compensation control are mainly employed for a plurality of inverters in parallel connection. When a micro-grid voltage fluctuates, reactive power is uniformly divided through droop control, and a disturbance voltage is adjusted. Also, the high-order harmonic wave of the micro-grid voltage can be extracted through detection, the first-order elimination is carried out through proportional resonance control, and then the second-order elimination is carried out through the harmonic compensation control. Finally, the above results are outputted in a voltage mode through a PWM control inverter. The method can effectively improve the operation characteristics of an intermittent and unstable power supply in real time, also can adjust the voltage disturbance and the harmonic voltage, achieves the effects of voltage stabilization and voltage harmonic elimination, improves the capability of micro-grid regulation and control, improves the stability and reliability of the micro-grid operation, and improves the grid-connected capability of a micro-grid.

The invention relates to a five-level ANPC (Active Neutral-Point-Clamped) converter, particularly to a suspended capacitor voltage control method of the five-level ANPC converter. The suspended capacitor voltage control method comprises the following steps of applying SHEPWM (Selective Harmonic Elimination Pulse Width Modulation) pulse waves to the five-level ANPC converter; performing real-time detection on a suspended capacitor voltage value of the five-level ANPC converter, performing comparison on the suspended capacitor voltage value and a reference value of the suspended capacitor voltage and determining whether a suspended capacitor needs to be charged or discharged; detecting whether the load current of the five-level ANPC converter is positive or negative and selecting the redundancy switch state which is suitable for the ANPC converter according to the positive or negative load current of the five-level ANPC converter and the determined charging and discharging state required by the suspended capacitor; performing charging and discharging on the suspended capacitor of the five-level ANPC converter through the selected switch state until that the variable quantity of the suspended capacitor voltage is zero within a sampling period and performing repeated detection on the suspended capacitor voltage value. According to the suspended capacitor voltage control method of the five-level ANPC converter, the appropriate redundancy switch state is selected according to the direction of the load current and the size of the suspended capacitor voltage so as to enable the suspended capacitor voltage to be fluctuated within a small range.

The invention relates to a single-phase earth fault line selection method of a 10kV power distribution network earthing system. When the ratio between the inductance impedance value of an arc suppression coil and the impedance value of a harmonic elimination resistor is within some ratio range, and a single-phase earth fault occurs in the 10kV power distribution network earthing system, the difference between the zero-sequence voltage and the zero-sequence current of a fault outgoing line will be smaller than a preset value, and a protection device outputs a fault indication signal and an outgoing line switch actuating signal when the conditions are satisfied. The single-phase earth fault line selection method of the 10kV power distribution network earthing system has the advantages that parameter characteristic values on an arc suppression coil loop of the10kV power distribution network earthing system are adopted to be combined with the zero-sequence voltage and the zero-sequence current of the 10kV power distribution network earthing system, the changes of a phase angle cannot be easily influenced by factors such as operation conditions of the10kV power distribution network earthing system, criterion output is stable, and accuracy of judgment is high. The single-phase earth fault line selection method of the 10kV power distribution network earthing system can rapidly achieve fault location, can greatly improve the degree of automation of a power distribution network, can greatly reduce the time of a blackout of a user, reduces loss caused by the blackout, overcomes the defects existing in a small-current earthing operation mode, and has good social benefit and economic benefit.

The invention discloses a specific harmonic eliminating optimum method of three-level single-phase bridge inverter, which is characterized by the following: calculating the harmonic eliminating angle of single-phase bridge left and right bridge arms; eliminating more high order harmonic wave; reaching less harmonic wave distortion rate of inverter output voltage; improving harmonic wave property of output voltage effectively.

The invention discloses an SHEPWM (selective harmonic elimination pulse width modulation) control circuit, a double-T-type three-level SHEPWM inverter parallel system and method therefor. The double-T-type three-level SHEPWM inverter parallel system comprises two T-type three-level inverters, wherein the direct current sides of the three-level inverters are connected to a same direct current voltage source in parallel; each IGBT of the T-type three-level inverters is driven by the SHEPWM control circuit; and the alternating current sides of the T-type three-level inverters are filtered by a filter and then are connected in parallel to realize a grid connection function.

The invention discloses a digital automatic harmonic elimination device which comprises a residual voltage input unit, a harmonic elimination unit, a singlechip and a display setting unit. Data collected by the residual voltage input unit collects is converted by an A / D and sent to the singlechip which calculates and obtains data larger than a fixed value given by the display setting unit and triggers a bidirectional thyristor to switch on by controlling an optocoupler; the harmonic elimination unit is switched in a PT open triangle, a voltage collecting unit for collecting the three-phase voltages of a bus is also switched in the A / D connected with a data interface of the singlechip which calculates the data collected by the voltage collecting unit, obtains a residual voltage by and compares the residual voltage with a residual voltage obtained by the open triangle; single-phase grounding occurs if a difference value is smaller than the setting value, and power frequency resonance occurs if the difference value is larger than or equal to the setting value. The invention can accurately distinguish the defaults, such as the power frequency resonance, the single-phase grounding, and the like, accurately eliminates the system resonance in time and has the functions of over-voltage protection, low-voltage protection and PT break judgment.

The invention discloses an active power filter (APF) and thyristor switched filter (TSF) hybrid compensation device for an electric rig, which comprises a passive part, an active part, an electric quantity data acquisition module of a well site and the compensation device, a control module of a TST, and a control module of an APF. The filtering characteristics of the TSF are improved by utilizing the APF, so that when the TSF works in a combined manner, 2 to 10 times of harmonic currents injected into a power supply system of the well site are controlled within a given value, and the harmonic currents of the well site are prevented from being amplified when different filtering branches of the TSF are switched in a combined manner; and by adopting the structure that the APF is connected in parallel with a fundamental resonance module of a fifth filtering branch of the TSF through a coupling transformer, the capacity of the APF is very small, so that the APF is beneficially controlled, the cost of the whole set of device is reduced, the problem of overlarge harmonic currents occurring when the TSF is switched in a combined manner is effectively solved, and then the tasks of reactive compensation and harmonic elimination of the well site can be completed more safely and more effectively.

The invention relates to a method for realizing selective harmonic elimination modulation by adopting a fixed control cycle. The method is technically characterized by comprising the following steps of adopting the fixed control cycle to control the vector decoupling of a PWM (pulse width modulation) rectifier, so as to obtain the amplitude and the angle of the given voltage, and deriving the angle of the given voltage to obtain the frequency of the given voltage; using the angle of the given voltage as an initial value, and carrying out number integration on the frequency, to obtain a relatively continuous angle; carrying out monotone processing on the relatively continuous angle; according to the monotone-processed continuous angle and the received amplitude, searching a table to output the SHEPWM (selective harmonic elimination pulse width modulation) pulse. The method has the advantages that the vector closed loop control method of the fixed cycle is combined with the selective harmonic elimination modulation, so the complicated variable cycle control is avoided, a power converter system has the quick and accurate dynamic response capability and good current harmonic property in the steady state, the low-order harmonics in the output voltage of a converter can be obviously inhibited, and the method is especially suitable for high-power application occasions.

The invention provides an intelligent PT harmonic elimination and phase selection method and device. A three-phase five-pole voltage transformer PT is adopted to acquire voltage data in a power grid, and sampling of three-phase bus voltage and zero-sequence voltage is performed by a voltage sampling module when zero-sequence voltage occurs; sampling of zero-sequence current of all feeder lines is performed by a current sampling module, all sampling values are inputted to a single-chip microcomputer, the amplitude and the phase of all phases of voltage and zero-sequence voltage are calculated and judged by the single-chip microcomputer, fault phases and fault lines are selected, faults are classified into instantaneous faults or permanent faults according to duration of single-phase earth faults, and only alarming is actuated for protection as for the instantaneous single-phase earth faults so that reliability of power supply can be guaranteed; and tripping is actuated for protection apart from alarming as for the permanent single-phase earth faults so that safety of power supply can be guaranteed.

The invention provides a one-phase open-circuit fault-tolerant control method for a six-phase permanent magnet synchronous motor, and relates to the technical field of multi-phase motor control. The method comprises: aiming at fault tolerance research after one-phase open circuit of the six-phase permanent magnet synchronous motor with the phase displacement of 30 degrees, using a neutral point isolation mode, considering the influence of fifth harmonic waves, providing a six-phase static coordinate transformation matrix corrected after a fault is established, and establishing a voltage and torque mathematical model under fundamental waves according to the matrix and a rotating coordinate transformation matrix; under the condition that a no-load air-gap magnetic field is not sinusoidal, deriving a mathematical model of a quintuple harmonic space, analyzing the coupling relation of d-q subspaces in a voltage equation transformed by a rotation transformation array, and providing a secondary rotation coordinate transformation array and a voltage compensation formula for eliminating d-q axis voltage coupling after decoupling. In consideration of the influence of the quintuple harmonicflux linkage and inductance on the voltage and torque of the six-phase permanent magnet synchronous motor in a fault-tolerant mode, torque pulsation containing four times of angular frequency and sixtimes of angular frequency is eliminated by injecting quintuple harmonic.

The invention discloses a harmonic optimization and modulation method suitable for a multi-level converter. The technical means of selective harmonic elimination pulse width modulation and the technical means of phase shifting are combined in the method. For low-order harmonics, the low-order harmonics are eliminated by solving a two-level selective harmonic elimination equation set; for high-order harmonics, optimization is carried out on the total number of several orders of harmonics with the phase shifting angle as a variable, phase shifting superposition is carried out on two-level waveforms through the phase shifting angle obtained through optimization to obtain multi-level waveforms, and finally a control signal of each switching tube is determined according to the multi-level waveforms. By means of the method, several orders of low-order harmonics can be eliminated, the suppression effect on the high-order harmonics is obvious, and the calculation amount is hardly increased.

The invention discloses a selective harmonic elimination pulse width modulation control method of eliminating dead zone effect and a device thereof, which are used for a neutral point clamped NPC multi-level converter. The selective harmonic elimination pulse width modulation control method comprises steps that the current voltage closed-loop control of the NPC multi-level converter is carried out, and a voltage modulation ratio and a real-time phase are calculated in a real-time manner; a preset switching angle storage table is queried according to the voltage modulation ratio, and a standard switching angle corresponding to the voltage modulation ratio is acquired; the standard switching angle is modified according to the output current direction, the delayed- conduction arc value, and the early-shut off arc value of the NPC multi-level converter, and the dead zone effect of the standard switching angle is eliminated, and then the modified standard switching angle is acquired; based on the modified standard switching angle, an angle interval, in which is disposed the real-time phase, is determined, and a driving pulse having a dead zone corresponding to a real-time angle is acquired according to the angle interval and a preset corresponding relation table, and then the NPC multi-level converter is driven. The influences of the dead zone effect on the driving pulse of the converter are eliminated, and the harmonic level of the converter is optimized.

A reactive power compensation system for compensating reactive power requirements in an electrical power system. The reactive power compensation system includes a static synchronous compensation unit, a current harmonics elimination unit, and a compensation control unit. The static synchronous compensation unit includes a plurality of static synchronous compensation modules for compensating reactive power in the electrical power system. The current harmonics elimination unit includes a plurality of active filter modules for eliminating current harmonics generated in the electrical power system. The compensation control unit implements a sequential control mechanism for regulating the operation of the static synchronous compensation modules and the active filter modules.

The invention provides a switched capacitor N-level inverter and a modulation method thereof. The inverter comprises a single DC input power supply, a switched capacitor unit and a full bridge unit. The switched capacitor unit is connected in parallel with the single DC input power supply and used for performing series-parallel conversion between the single DC input power supply and the capacitorsof the switched capacitor unit and outputting a multi-step voltage. The full bridge unit is connected in parallel with the switched capacitor unit, and is used for outputting the multi-step voltage output by the switched capacitor unit after positive-negative polarity conversion. The modulation strategy adopted is a step wave specific harmonic elimination modulation mode based on the combinationof specific harmonic elimination and step wave modulation. The inverter of the invention can output any level by expanding the modular structure of the switched capacitor sub-modules, and the number of power devices of the inverter is greatly reduced through a simpler modular structure.

The invention relates to a fast switching arc and harmonic elimination-based single-phase grounding fault line selection and location method and belongs to the circuit protection technical field. According to the fast switching arc and harmonic elimination-based single-phase grounding fault line selection and location method, when grounding occurs, zero sequence voltage triggers a line selection device to enter a collection state to collect zero-sequence current in each loop, and the zero-sequence current in each loop is processed, and first-stage zero-sequence current data of each loop is extracted; if arc light grounding occurs, an arc elimination device forcedly converts the arc light grounding into metal grounding, and the line selection device enters the collection state again to collect the zero-sequence current in each loop, so that second-stage zero-sequence current data can be obtained; corresponding first-stage zero-sequence current data are subtracted from the second-stage zero-sequence current data of each loop, so that incremental values can be obtained, and a line with the largest increment is a fault line; and one or more positioning methods are combined together to carry out fault interval positioning. The fast switching arc and harmonic elimination-based single-phase grounding fault line selection and location method of the invention is not affected by factors such as the magnitude of grounding resistance and the distance of a short-circuit point, and can select a fault line within 3ms after a grounding fault occurs. The method is stable and reliable and has high precision.

The invention discloses a repetitive controller, which comprises an internal model part, a cycle delay module, a compensation module and a frequency-specific gating module, wherein the input quantity of the repetitive controller is input from the input end of the internal model part; the internal model part, the cycle delay module and the compensation module are connected in series with one another; and the frequency-specific gating module is connected in series with the internal model part, the cycle delay module and the compensation module or is arranged on a forward channel of the internal model part. In the repetitive controller, the frequency-specific gating module is arranged, so that only a selected frequency-specific harmonic wave can be filtered out of an error signal, and the repetitive controller can perform harmonic elimination on the frequency-specific harmonic wave.

The invention discloses a quasi-PR grid-connected inverter optimization control method based on self-adaptive harmonic elimination. For the shortcomings of high parameter precision requirement, poor anti-disturbance capability, difficult realization and the like of an ideal PR controller in an actual system, a quasi-PR controller is applied to a single-phase photovoltaic inverter system; in view of factors such as the bandwidth limit of an inverter, the precision of a detection system, and the like, characteristic harmonic detection is adopted for selectively compensating 3rd, 5th and 7th harmonics with relatively high content and relatively low orders; and a self-adaptive learning rate and a steepest descent method of additional momentum factors are adopted for improving a BP neural network, so that while the training time is shortened, the shortcoming that the BP neural network easily obtains a local optimum solution is overcome, and the problems of inaccurate harmonic compensation,overlong system response time and the like are solved.

The invention relates to a method used for realizing two-level SHEPWM (specific harmonic eliminating pulse width modulation) on the basis of IGCT; corresponding switch pulse sequence is generated by modulation ratio m arranged from big to small; the forming format is memorized in a FLASH memory; a digital signal processor reads out the switch angle of 1 / 4 period corresponding to A phase in the FLASH memory according to the corresponding modulation ratio and the frequency parameter, symmetrically extends the angle to 360 DEG and constructs the switch angles for B phase and C phase; a timer is started after conversion calculation; in a timing breaking sub-program, the IGCT switch action time interval between three phases complies with the requirement after phase pulse width disposal. According to the switch characteristic of the IGCT, the design characteristic and the like of the output LC filter circuit, the method adopts specific harmonic elimination pulse width modulation to realize that the high-voltage frequency converter to have excellent output waveform in the whole output frequency section, and only needs to memory the switch angle data of 1 / 4 period of A phase at the same time, thus having small memory quantity.

The invention belongs to the technical field of power system, relating to a system resonance detector for monitoring resonant overvoltage in power system and a switched damping resistor mounted in the neutral point of the system. The technical proposal is that: an intelligent harmonic elimination apparatus is composed of a system resonance detector and a switched damping resistor mounted in the neutral point; the switched damping resistor is disposed between the neutral point and the earth by connecting with the fast thyristor switch in series; the value range of the damping resistance is between 1 to 1500 ohm; the dimension of the resistance value is selected according to the severity degree of the resonant overvoltage in specific power transmission and distribution system; if the resonant degree is more serious, the resistance is less. The system resonance detector can monitor resonant overvoltage caused by 1 / 3 harmonic, 1 / 2 harmonics, fundamental wave, second harmonic, triple-frequency harmonic and quintuple harmonic; simultaneously, according to the features that the line voltage is unbalanced when the fundamental wave is resonant, the invention exactly differentiates the fundamental wave resonant overvoltage or system single-phase grounding. When the system is normal, the fast thyristor switch is cut off; when the system resonant overvoltage is detected, the thyristor switch is closed; the neutral point is earthed through the damping resistor, thereby eliminating resonant overvoltage. Various damages caused by resonant overvoltage are prevented.

The invention discloses an optimal harmonic distribution SHEPWM switching angle calculation method and system. The method comprises the steps of: S1, determining amplitude expressions of fundamental wave and various sub-controlled harmonics; S2, determining the modulation ratio and the error values of the various sub-controlled harmonics, furthermore, determining the equation of the fundamental wave and the equations of the various sub-controlled harmonics according to the modulation ratio and the error values of the various sub-controlled harmonics, and constructing a nonlinear transcendental equation; and S3, constructing an objective function by using the amplitude expression of the lowest-order uncontrollable harmonic, and searching the solution of the nonlinear transcendental equation through a genetic algorithm, so that a satisfied result is obtained. By means of the optimal harmonic distribution SHEPWM switching angle calculation method and system disclosed by the invention, dependence on initial value determination in the traditional newton iteration method can be overcome; the fussy initial value trial and error process is greatly reduced; the universality of the solving method is improved; furthermore, the uncontrollable high-order harmonic distortion increasing problem in the specific harmonic elimination PWM technology can be overcome; and, on the premise that low-order harmonic elimination satisfies engineering requirements, the amplitude of the high-order harmonic is reduced, so that optimal harmonic distribution of the total THD is reduced.

The invention discloses a power equalization method and a modulator for modulation of a specific harmonic elimination multilevel radio frequency pulse width. The method comprises the steps of: decomposing a specific harmonic elimination multi-level RF-PWM signal into a plurality of 3-level RF-PWM signals with equal pulse areas by using the area equivalence principle based on a multi-level radio frequency pulse signal output from the specific harmonic elimination multi-level RF-PWM, according to the rise and fall of the pulse outputting the multi-level RF-PWM signal; driving a rear-stage SMPA unit, so that multi-level RF-PWM output pulse sequence specific harmonics are eliminated, while achieving the power equalization between the rear-stage SMPA units and between the power tubes in the unit. The radio frequency pulse width modulator is based on the power equalization method, and generates a phase shift control signal for driving a rear-stage 5-level SMPA unit by using a digital delay line unit, thereby realizing active cancellation of a 3X times specific harmonic. The power equalization method for modulation of a specific harmonic elimination multilevel radio frequency pulse widthdoes not need an additional power equalization control circuit, which simplifies the modulator structure.

The invention relates to a movable arc-suppression harmonic elimination device comprising a cabinet shell. A closed space formed by enclosing the cabinet shell is divided by a metal partition board into a main bus chamber, an earthed switch chamber, a voltage transformer chamber and a secondary meter chamber, wherein the main bus chamber is positioned behind the cabinet shell; the secondary meter chamber, the voltage transformer chamber and the earthed switch chamber are sequentially arranged in front of the cabinet shell from the top to bottom; and an isolated handcart is arranged in the voltage transformer chamber, provided with a voltage transformer and a high-voltage fuse and pushed into a cabinet body along a guide rail or pulled out of the cabinet body. By using a middle part of the front of a KYN28 type switch cabinet body as an isolated handcart chamber, arranging the isolated handcart which is provided with the voltage transformer and the high-voltage fuse and used as a movable component in the isolated handcart chamber and using an outgoing line cable chamber as the earthed switch chamber, the invention solves the problem of layout space of element which cannot be overstepped by a miniaturized protective device and simultaneously ensures normal play of protecting function.