CN204903656U - A device for arc suppressing coil ground system measuring circuit direct -to -ground capacitance - Google Patents

Abstract

The utility model relates to a device for measuring the line-to-ground capacitance in an arc-suppression coil grounding system, which comprises: an arc-suppression coil body, the A end of the arc-suppression coil body is connected to the neutral point of the power grid, and the X end is grounded. A current transformer is connected to the incoming line terminal, and injection voltage transformers and detection voltage transformers are connected in parallel at both ends of A and X; the control panel cabinet includes a PLC, and the PLC is connected with a frequency converter, a signal follower board, and an FPGA board; and a magnetic The control box is respectively connected with the arc suppression coil body and the control panel cabinet, controls the pulses sent by PLC, and performs corresponding shaping on the pulses, triggers the switching of the thyristors, and realizes the reactance control of the arc suppression coils. The utility model can accurately and quickly be used in the grounding system of the arc suppressing coil to measure the line-to-ground capacitance, and can automatically measure the capacitance current when the power grid is in normal operation, so that the grounding current can be quickly measured when a single-phase grounding fault occurs on a certain feeder line. compensate.

Description

A device for measuring line-to-ground capacitance in an arc-suppression coil grounding system

technical field

The utility model relates to the measurement of capacitance to ground, in particular to a device for measuring the capacitance of lines to ground in an arc suppressing coil grounding system.

Background technique

The electrical connection between the neutral point of the power system and the earth is called the neutral point grounding method of the power system. In my country's power system, according to the main operating characteristics, the corresponding grounding systems are divided into two categories: small current grounding systems (non-effective grounding) and large current grounding systems (effective grounding). In the power distribution system, small current grounding methods are widely used. There are three main types: 1. The neutral point is not grounded; 2. The neutral point is grounded through the arc suppression coil; 3. The neutral point is grounded through high resistance.

At present, the grounding form of my country's medium-voltage distribution network is mainly a small current grounding system (that is, the neutral point is grounded through the arc suppression coil). When the system is running for a long time, the single-phase grounding fault is the most common fault in the medium voltage distribution network system. After the grounding occurs, the small current grounding system can continue to operate with the fault. Because the non-fault relative ground voltage increases by 1.732 times, if not If it is dealt with in time, after long-term operation, it may develop into the threat of non-faulty phase insulation damage and secondary interphase short circuit. Therefore, quickly determining the grounding line when single-phase grounding is of great significance to the safe operation of the supply and distribution point system.

The actual system needs to accurately measure the capacitance current before the single-phase grounding line selection, because the size of the capacitance current is related to the system line, and the measurement of the capacitance current is related to the neutral point voltage (here refers to the neutral point displacement under normal operating conditions Therefore, it is difficult to measure the capacitance accurately. At the same time, the capacitance current of the measurement system is also an important basis for deciding whether to install the arc suppression coil in the resonant grounding system, and to select the capacity of the arc suppression coil. At the same time, it is also Under single-phase fault, it is a necessary precondition to quickly put the arc suppression coil into operation.

Contents of the invention

The purpose of the utility model is to overcome the shortcomings of the above-mentioned prior art and provide a device for measuring the line-to-ground capacitance in the arc-suppression coil grounding system. capacitance.

The technical solution adopted to achieve the purpose of this utility model is a device for measuring the line-to-ground capacitance in the arc-suppression coil grounding system, which includes:

The arc suppression coil body, the A terminal of the arc suppression coil body is connected to the neutral point of the power grid, the X terminal is grounded, the A incoming line terminal is connected with a current transformer, and the A and X ends are connected in parallel with an injection voltage transformer and a detection voltage transformer device;

The control panel cabinet includes a PLC, and the PLC is connected with a frequency converter, a signal follower board, and an FPGA board; and

The magnetic control box is equipped with a thyristor inside; the magnetic control box is respectively connected with the arc suppression coil body and the control panel cabinet, and the pulse sent by PLC is controlled, and the pulse is correspondingly shaped to trigger the switching of the thyristor to realize Reactance control for arc suppression coils.

In the above technical solution, the PLC is Siemens S-700PLC, and the frequency converter is Siemens MICROMASTER420 general-purpose frequency converter.

In the above technical solution, the frequency converter is connected to the PORT0 port of the PLC through an RS485 cable.

In the above technical scheme, the analog output port of the FPGA board is connected to the PLC analog input port A, B through a cable, the analog input port is connected to the PLC analog output port V through a 1.0 cable, and the digital output port Connect with the PLC digital quantity input port I0.1 through the cable, and connect the digital quantity input port with the PLC digital quantity output port Q0.2, Q0.6 through the cable.

In the above technical solution, the digital quantity output port of the signal following version is connected to the PLC digital quantity input port I0.0 through a cable, and the digital quantity input port is connected to the PLC digital quantity output ports Q0.3, Q0.4, Q0. 5 is connected by cable.

The utility model can accurately and quickly be used in the grounding system of the arc suppressing coil to measure the line-to-ground capacitance, and can automatically measure the capacitance current when the power grid is in normal operation, so that the grounding current can be quickly measured when a single-phase grounding fault occurs on a certain feeder line. compensate.

Description of drawings

Fig. 1 is a block diagram of the utility model for measuring the line-to-ground capacitance in the arc-suppression coil grounding system.

Fig. 2 is the schematic diagram of the connection relation of PLC and FPGA board used in the embodiment.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail.

The utility model is a device for measuring the line-to-ground capacitance in an arc-suppression coil grounding system, including an arc-suppression coil body, a control panel cabinet and a magnetic control box, wherein,

The arc-suppression coil body is installed between the neutral point and the ground of the three-phase distribution network. If the distribution network is star-connected, the neutral point needs to be led out through the grounding transformer, and the A terminal of the arc-suppression coil body is connected to the neutral point of the grid. , X terminal is grounded, A current transformer CT2 is connected to the incoming line terminal, and injection voltage transformer PT1 and detection voltage transformer PT2 are connected in parallel at both ends of A and X.

The control panel cabinet is the main control unit of the system, including frequency conversion signal injection, signal acquisition and processing, fault judgment, pulse transmission and other parts. The control panel cabinet includes PLC, and PLC is connected with frequency converter, signal follower board, and FPGA board. The PLC used in this embodiment is a Siemens S-700PLC, and the frequency converter is a Siemens MICROMASTER420 general-purpose frequency converter. The analog output port of the FPGA board is connected with the PLC analog input ports A and B through cables, and the analog input port is connected through 1.0 The cable is connected to the PLC analog output port V, the digital output port is connected to the PLC digital input port I0.1 through the cable, and the digital input port is connected to the PLC digital output port Q0.2 and Q0.6 through the cable . The digital output port of the signal following version is connected to the PLC digital input port I0.0 through a cable, and the digital input port is connected to the PLC digital output port Q0.3, Q0.4, and Q0.5 through a cable. The connection relationship between PLC and FPGA board is shown in Figure 2. As the core control unit, the PLC is mainly used to control the frequency converter, generate MCR pulse signals, and realize the measurement of capacitive current based on the frequency sweep method. The inverter adopts V/F linear control, and uses USS protocol to communicate with PLC to generate controllable variable frequency voltage signals. The FPGA board is mainly used for signal collection and processing. The collected signals mainly include neutral point voltage, useful frequency conversion signal and MCR current after power frequency offset. The frequency converter is connected to the PORT0 port of the PLC through an RS485 cable.

The magnetic control box is respectively connected with the arc suppression coil body and the control panel cabinet, and the pulses sent by the PLC are controlled, and the pulses are correspondingly shaped to trigger the on-off of the thyristor to realize the reactance control of the arc suppression coil. Make the reactor output the inductor current to compensate the capacitor current.

For the measurement system, the capacitor voltage under power frequency is an interference signal. Therefore, in the measurement system, it is necessary to process the capacitor voltage signal. The core is to filter out the power frequency and try to ensure that only the required signal exists in the measurement signal. Capacitor voltage signal at frequency.

As shown in Figure 2, since the input signal of the signal processing part is less, only the neutral point voltage, reactor current, and inverter current are needed, and the high-speed FPGA board is used for corresponding calculations, which solves the calculation problem of PLC.

When the power grid is in normal operation state, the control system is in the frequency sweep state, and the PLC controls the frequency converter through the USS protocol, so that the voltage output frequency of the frequency converter changes from 10HZ to 45HZ, and the frequency conversion voltage is boosted by PT1 and then input and output to the arc suppression coil Both ends inject a constant current signal linear signal with constant amplitude and frequency within a certain range. There is a measuring voltage transformer PT2 on the other side of the arc suppressing coil. This PT measures the capacitor voltage. The secondary side of PT2 is connected to the signal follower board. After being processed by the FPGA board, it is connected to the AIW0 port of the PLC. During the frequency sweep, because there are low-frequency sweep voltage and 50HZ power frequency voltage in the system at the same time, it is necessary to filter out the low-frequency voltage when measuring the actual capacitor voltage. Specifically, the collected resonance voltage is reversely output to the FPGA through the AQW0 port of the PLC. In the FPGA board, the power frequency voltage is obtained by removing the resonance voltage through the cancellation circuit. When the AIW0 port of the PLC detects the maximum voltage of the capacitor, the inductance of the arc suppression coil and the capacitance of the line to ground resonate at this time, and the PLC records the frequency at this time. The capacitance value of the line to ground is obtained by calculating the known arc suppression coil inductance value, capacitance voltage and frequency.

Claims (5)

1. A device for measuring line-to-ground capacitance in an arc suppression coil grounding system, characterized in that it comprises: The arc suppression coil body, the A terminal of the arc suppression coil body is connected to the neutral point of the power grid, the X terminal is grounded, the A incoming line terminal is connected with a current transformer, and the A and X ends are connected in parallel with an injection voltage transformer and a detection voltage transformer device; The control panel cabinet includes a PLC, and the PLC is connected with a frequency converter, a signal follower board, and an FPGA board; and The magnetic control box is equipped with a thyristor inside; the magnetic control box is respectively connected with the arc suppression coil body and the control panel cabinet, and the pulse sent by PLC is controlled, and the pulse is correspondingly shaped to trigger the switching of the thyristor to realize Reactance control for arc suppression coils. 2. The device for measuring line-to-ground capacitance in an arc-suppression coil grounding system according to claim 1, wherein the PLC is Siemens S-700PLC, and the frequency converter is Siemens MICROMASTER420 general-purpose frequency converter. 3. The device for measuring the line-to-ground capacitance in the arc-suppression coil grounding system according to claim 2, wherein the frequency converter is connected to the PORT0 port of the PLC through an RS485 cable. 4. The device for measuring line-to-ground capacitance in the arc-suppression coil grounding system according to claim 2, characterized in that: the analog output port of the FPGA board is connected to the PLC analog input port A, B through a cable , the analog input port is connected to the PLC analog output port V through a 1.0 cable, the digital output port is connected to the PLC digital input port I0.1 through a cable, and the digital input port is connected to the PLC digital output port Q0 through a cable .2, Q0.6 connection. 5. The device for measuring the line-to-ground capacitance in the arc-suppression coil grounding system according to claim 2, characterized in that: the signal follows the digital output port of the version and the PLC digital input port I0.0 through the cable Connection, digital input port and PLC digital output port Q0.3, Q0.4, Q0.5 are connected by cables.