Motor protection device suitable for frequency conversion working condition

Abstract

The utility model relates to a motor protection device suitable for a frequency conversion working condition. A three-phase voltage transformer TV1 and a one-path zero sequence voltage transformer TV2 are used for power frequency voltage protection. The three-phase outgoing line protection current transformer TA1 and the one-path zero sequence current transformer TA2 are used for power frequency current protection and the like; the bus-side current and voltage signals of the device are used for power frequency protection, the current TA3 is collected and measured at the same time and used for displaying the power consumption of the switch cabinet, and the device can be installed in the switch cabinet to serve as main protection of the interval and can also be installed in a high-voltage frequency converter control cabinet to serve as special protection of a motor. Dynamic protection and backup protection during power frequency operation are supported, the protection range is expanded, comprehensive protection during frequency conversion operation is supported, the selected CT is not prone to magnetic saturation, and the protection function can be achieved in the starting process of the motor. Linkage with the frequency converter is achieved, normal frequency output signals of the frequency converter are received, and protection mistaken starting caused by transmission errors of a mutual inductor outside the frequency range is prevented.

Description

Technical Field

[0001] The utility model relates to high-voltage variable-frequency motor protection, in particular to a motor protection device suitable for variable-frequency working conditions. Background Art

[0002] As my country's economy transforms towards green and low-carbon, the scale of industrial production continues to expand, and it is necessary to strengthen energy conservation and cost reduction management. Frequency converter speed regulation technology can improve processes and energy efficiency, and is increasingly widely used in all walks of life. The technical regulations for relay protection and safety automatic devices clearly point out the special requirements for the protection of variable frequency speed regulating motors. For motors, within the frequency range required by their working environment, the protection should adapt to the continuous change of frequency.

[0003] The traditional principle of motor differential protection is based on 50Hz current sampling and calculation, which cannot adapt to variable frequency operation. In addition, the traditional electromagnetic current transformer has low-frequency saturation. Therefore, the conventional motor protection and the configuration of traditional current transformers can no longer meet the actual operation requirements of variable frequency motor systems and the safe and reliable operation of electrical primary equipment. Summary of the invention

[0004] In order to solve the above technical problems, the utility model is a motor protection device suitable for variable frequency working conditions, and its technical solution is:

[0005] It includes a high-voltage frequency converter, a bypass switch, an analog-to-digital conversion sampling circuit, a 32-bit CPU processor, a voltage transformer TV1, a zero-sequence voltage transformer TV2, a current transformer TA1, a zero-sequence current transformer TA2, a current transformer TA3, a current transformer TA4 and a current transformer TA5. The device is equipped with a three-phase voltage transformer TV1 and a one-way zero-sequence voltage transformer TV2, and is connected to the power bus through a cable;

[0006] The 3-phase outgoing line protection current transformer TA1 and the 2-phase outgoing line measurement current transformer TA3 are connected to different secondary windings respectively, and the 1-way zero-sequence current transformer TA2 adopts a dedicated zero-sequence CT;

[0007] A 3-phase variable frequency current transformer TA4 is installed between the outlet end of the high-voltage inverter and the motor, and a 3-phase variable frequency current transformer TA5 is installed on the neutral point side of the motor;

[0008] The bypass switch is connected in parallel with the high-voltage inverter. The bypass switch position is collected through the switch quantity to determine whether the current motor is running through the high-voltage inverter or the industrial frequency.

[0009] Furthermore, the secondary side of the transformer is converted into an AC ±7.07V voltage signal for collection by the AD chip.

[0010] Furthermore, the analog-to-digital sampling conversion circuit uses two 16-bit AD chips, each with 8 sampling channels, and can collect 16 analog quantities simultaneously.

[0011] Furthermore, the 32-bit CPU processor performs FFT transformation on the AD sampling data to calculate the current and voltage amplitudes at the power frequency.

[0012] The beneficial effects of the utility model are as follows: the utility model is a motor protection device suitable for variable frequency working conditions, with 3-phase voltage transformer TV1 and 1-way zero-sequence voltage transformer TV2 as power frequency voltage protection; 3-phase outgoing line protection current transformer TA1 and 1-way zero-sequence current transformer TA2 as power frequency current protection; 2-phase outgoing line measurement current transformer TA3 and voltage transformer TV1 are used to measure power and power factor; 3-phase end-side variable frequency current transformer TA4 and 3-phase neutral point side variable frequency current transformer TA5 use wide-band CT, which can adapt to linear transmission within the range of 10Hz to 70Hz, prevent low-frequency saturation, and ensure current sampling accuracy. The bus side current and voltage signals of this device are used for power frequency protection, and the measured current is collected at the same time to display the power consumption of this switch cabinet. It can be installed in the switch cabinet as the main protection of this interval, and can also be installed in the high-voltage inverter control cabinet as a special protection for the motor. It supports differential protection and backup protection during power frequency operation, expands the protection range, and supports comprehensive protection during variable frequency operation. The selected CT is not prone to magnetic saturation, and the protection function can be realized during the motor startup process. The utility model realizes linkage with the frequency converter, receives the normal frequency output signal of the frequency converter, and prevents the transmission error of the mutual inductor outside the frequency range from causing the protection to start incorrectly. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the main wiring structure of the utility model. DETAILED DESCRIPTION

[0014] As shown in the figure, the utility model is a motor protection device suitable for variable frequency working conditions. In order to ensure that the differential protection can operate reliably under the variable frequency operation mode, the current transformer does not experience magnetic saturation, and the motor is always within the range of the main protection. A backup protection function is configured to achieve integrated protection and measurement control.

[0015] The utility model comprises an AC mutual inductor plug-in, switch quantity state acquisition, analog-to-digital conversion sampling circuit, a 32-bit CPU processor, an operation circuit outlet, and a human-computer interaction display.

[0016] Configure 3-phase voltage transformer TV1 and 1 zero-sequence voltage transformer TV2, collect the secondary side signals of bus voltage transformer TV1 and zero-sequence voltage transformer TV2 as power frequency voltage protection. Configure overvoltage protection, low voltage protection, zero-sequence overvoltage protection, PT disconnection detection and other functions.

[0017] Configure 3-phase outgoing line protection current transformer TA1 and 1-way zero-sequence current transformer TA2 as power frequency current protection. Collect outgoing line measurement 2-phase outgoing line measurement current transformer TA3, and voltage transformer TV1 to calculate the active power, reactive power, power factor and energy accumulation of this interval.

[0018] The 2-phase outgoing line measurement current transformer TA3 and the voltage transformer TV1 are used to measure power and power factor. The 3-phase phase end-side variable frequency current transformer TA4 and the 3-phase neutral point side variable frequency current transformer TA5 use wide-band CTs, which can adapt to linear transmission within the range of 10Hz to 70Hz. In other frequency bands, large sampling errors will be generated, causing abnormal startup. Therefore, when the inverter outputs within the range of 10Hz to 70Hz, a normal output signal contact is given, which is collected by the switch quantity. When the signal is collected, the protection function is automatically activated, otherwise the protection is locked. Prevent low-frequency saturation and ensure the accuracy of current sampling.

[0019] The analog-to-digital sampling conversion circuit uses two 16-bit AD chips, each with 8 sampling channels. The electrical quantities collected by the mutual inductor are all converted into voltage signals in the range of AC±7.07V for AD collection. 16 analog quantities can be collected simultaneously, and the calculation accuracy of measured current and voltage reaches 0.2 level.

[0020] The 32-bit CPU processor performs FFT transformation on the AD sampling data to calculate the current and voltage amplitude under the power frequency. In the variable frequency mode, the differential current is calculated using the sampling point differential principle, and the iterative method is used to track the system frequency and adjust the sampling point difference according to the relationship between the time difference and the phase angle difference. In the power frequency mode, the differential current is calculated using the phase differential principle, and the second harmonic blocking is adopted. The 32-bit CPU processor is configured to support floating-point operations, which improves the data processing speed and ensures the speed of the device.

[0021] It adopts AC and DC universal operating circuit to adapt to different power supply conditions on site. It is equipped with double-coil magnetic latching signal relay, which can be reset manually or remotely after the action occurs.

[0022] The human-computer interaction display uses a Chinese interface, showing the main wiring diagram of the system. The telemetry status can display both primary and secondary values. It has 16 fixed value areas for switching between fixed value areas under different operating conditions.

[0023] The 3-phase voltage transformer TV1, 1-way zero-sequence voltage transformer TV2, 3-phase outgoing line protection current transformer TA1, 1-way zero-sequence current transformer TA2, and 2-phase outgoing line measurement current transformer TA3 are all collected at the power frequency. There is no need for frequency tracking processing. The AD sampling data is directly transformed by FFT to calculate the current and voltage amplitudes at the power frequency. In the variable frequency mode, the differential current is calculated using the sampling point differential principle, and the iterative method is used to track the system frequency and adjust the sampling point difference according to the relationship between the time difference and the phase angle difference after the FFT transformation. In the power frequency mode, the differential current is calculated using the phasor differential principle, and the second harmonic interlocking is used to prevent the differential protection from malfunctioning.

[0024] Equipped with 3 Ethernet communication ports and 2 485 serial ports, it is easy to network and can be connected to the substation comprehensive background monitoring system. Equipped with RS232 printing port, it can be directly connected to the printer to print and record important parameters. Equipped with a special debugging interface, it can be connected to the computer through FTP file transfer to perform program upgrades, wave recording file export, operating parameter export and other operations.

[0025] The Ethernet interface of the utility model adopts an expansion stacking board method, can be embedded in an IED module, adopts a Linux operating system, realizes substation MMS message communication, and can also be embedded in a network chip to realize 103 communication, saving the cost of the whole machine.

[0026] Sampling value differential protection is configured under variable frequency conditions. The samples of all channels in the protection are the instantaneous values ​​of the current at the same time. Phase differential protection is configured under power frequency, and voltage-related protection, overcurrent protection, asymmetric protection, overheating protection, etc. are configured, providing complete and reliable protection measures for motors and inverters.

[0027] By collecting the bypass switch position through the switch quantity, it is determined whether the current motor is running through the high-voltage inverter or the industrial frequency operation. When the motor is running through the high-voltage inverter, the differential current is calculated by the variable frequency current transformer TA4 on the machine end side and the variable frequency current transformer TA5 on the neutral point side, and frequency tracking is required at this time; when the motor is running at industrial frequency, the differential current is calculated by the outgoing line protection current transformer TA1 and the variable frequency current transformer TA5 on the neutral point side, and frequency tracking is not required at this time.

[0028] The advantage of the utility model is that it collects the bus side current and voltage signals for power frequency protection, and collects the measured current to display the power consumption of the switch cabinet. It can be installed in the switch cabinet as the main protection of the interval, and can also be installed in the high-voltage inverter control cabinet as a special protection for the motor. It supports differential protection and backup protection during power frequency operation, expands the protection range, and supports comprehensive protection during variable frequency operation. The selected CT is not prone to magnetic saturation, and the protection function can be realized during the motor startup process. The device realizes linkage with the inverter, receives the normal frequency output signal of the inverter, and prevents the protection from being falsely started due to the transmission error of the mutual inductor outside the frequency range.

[0029] The above description is an explanation of the utility model, not a limitation of the utility model. The scope of the utility model is defined by the claims. Any form of modification can be made within the protection scope of the utility model.

Claims

1. A motor protection device suitable for variable frequency working conditions, comprising a high-voltage frequency converter, a bypass switch, an analog-to-digital conversion sampling circuit, a 32-bit CPU processor, a voltage transformer TV1, a zero-sequence voltage transformer TV2, a current transformer TA1, a zero-sequence current transformer TA2, a current transformer TA3, a current transformer TA4 and a current transformer TA5, characterized in that: The device is equipped with a 3-phase voltage transformer TV1 and a 1-way zero-sequence voltage transformer TV2, which are connected to the power bus through cables; The 3-phase outgoing line protection current transformer TA1 and the 2-phase outgoing line measurement current transformer TA3 are connected to different secondary windings respectively, and the 1-way zero-sequence current transformer TA2 adopts a dedicated zero-sequence CT; A 3-phase variable frequency current transformer TA4 is installed between the outlet end of the high-voltage inverter and the motor, and a 3-phase variable frequency current transformer TA5 is installed on the neutral point side of the motor; The bypass switch is connected in parallel with the high-voltage inverter. The bypass switch position is collected through the switch quantity to determine whether the current motor is running through the high-voltage inverter or the industrial frequency.

2. A motor protection device suitable for variable frequency working conditions as claimed in claim 1, characterized in that: The secondary side of the transformer is converted into AC ±7.07V voltage signal for collection by the AD chip.

3. A motor protection device suitable for variable frequency working conditions as claimed in claim 1, characterized in that: The analog-to-digital sampling conversion circuit uses two 16-bit AD chips, each with 8 sampling channels, which can collect 16 analog quantities simultaneously.

4. A motor protection device suitable for variable frequency working conditions as claimed in claim 1, characterized in that: The 32-bit CPU processor performs FFT transformation on the AD sampling data and calculates the current and voltage amplitudes at the power frequency.

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