CN203117256U - System for detecting bus capacitive current of medium voltage power grid - Google Patents

Abstract

The utility model relates to a system for detecting the bus capacitive current of a medium voltage power grid. The system is connected to a three-phase bus of the medium voltage power grid. The system comprises a voltage transformer, a signal generator, a zero-sequence voltage detection device and a processor, wherein the voltage transformer is connected with the three-phase bus of the medium voltage power grid, the signal generator and the zero-sequence voltage detection device are both connected with the voltage transformer, and the processor is connected with the signal generator and the zero-sequence voltage detection device. Compared with the prior art, the system provided by the utility model has the advantages of high safety and high detection precision.

Description

A system for detecting the capacitive current of the medium-voltage grid busbar

technical field

The utility model relates to a power grid detection system, in particular to a bus capacitance current detection system used in a medium-voltage power grid.

Background technique

With the expansion of the urban power grid and the increase of cable outlets, the system capacitive current increases greatly. When a single-phase grounding fault occurs in the system, the grounding arc cannot be self-extinguished, and it is easy to generate intermittent arcing grounding overvoltage. If it lasts for a long time, it will develop into a two-phase short circuit accident at the weak point of the line insulation. Therefore, when the network is large enough, it is necessary to use the arc suppression coil to compensate the capacitive current or directly act on the tripping through the resistance grounding method, which is an important technical measure to ensure the safe operation of the power system. In order to avoid threats to the safe operation of the power system caused by inappropriate grounding methods, the capacitive current value of the system must be correctly measured first, and then a reasonable neutral point operation method must be determined so as not to affect the selectivity and reliability of relay protection.

Utility model content

The purpose of the utility model is to provide a system for detecting the capacitive current of the medium-voltage grid busbar with high safety and high detection accuracy in order to overcome the above-mentioned defects in the prior art.

The purpose of this utility model can be achieved through the following technical solutions:

A system for detecting the capacitive current of a busbar of a medium-voltage power grid, which is connected to a three-phase busbar of a medium-voltage power grid, includes a voltage transformer, a signal generator, a zero-sequence voltage detection device, and a processor. The voltage transformer is connected to the three-phase bus of the medium-voltage grid, the signal generator and the zero-sequence voltage detection device are connected to the voltage transformer, and the processor is respectively connected to the signal generator and the zero-sequence voltage detection device.

The voltage transformer includes a primary winding and a secondary winding, the primary winding is directly connected to the three-phase busbar of the medium-voltage power grid, the secondary winding is coupled to the primary winding, and adopts an open triangle connection method, Both the signal generator and the zero-sequence voltage detection device are connected to the open delta end of the secondary winding.

The signal generator is a signal generator that can output a current signal with a frequency different from that of the power frequency voltage of the power grid.

Compared with the prior art, the utility model can accurately detect the current on the ground capacitance of each phase bus, because the voltage transformer connected to the power grid with the open delta connection method is used to realize the input of the measurement signal, and from the two The detection signal is collected on the secondary winding side, which avoids direct contact with the tester and the power grid, thus effectively improving safety.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is a schematic diagram of a voltage transformer connected to a power grid.

Detailed ways

The utility model will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example

As shown in Figure 1, a system for detecting the capacitive current of the medium-voltage grid busbar is connected to the three-phase busbar of the medium-voltage grid 5, including a voltage transformer 1, a signal generator 2, a zero-sequence voltage Detection device 3 and processor 4.

The voltage transformer 1 is connected to the three-phase busbar of the medium voltage grid 5, and its specific connection method is shown in Figure 2. Since the voltage transformer 1 includes a primary winding 11 and a secondary winding 12, the primary winding 11 is directly connected to the medium voltage grid The three-phase busbar of 5 is connected, while the secondary winding 12 is coupled with the primary winding 11, and the signal generator 2 and the zero-sequence voltage detection device 3 are connected by an open triangle connection. Both the signal generator 2 and the zero-sequence voltage detection device 3 are connected to the open triangle end 13 of the secondary winding 12, and the processor 4 is connected to the signal generator 2 and the zero-sequence voltage detection device 3 respectively.

The working principle of the utility model is:

First, the signal generator outputs a small current signal with a frequency different from the power frequency voltage of the power grid. This current signal will induce a current that is reduced in proportion to the number of winding turns on the primary winding side of the voltage transformer. Because the current signal cannot It circulates between the power supply and the grid load, so it can only form a loop through the ground capacitance on the three-phase bus, thus providing a theoretical basis for the utility model. Since the current induced by the primary winding side will generate a voltage drop on the winding resistance and leakage reactance of the voltage transformer and the ground capacitance of the grid wire, since the resistance and leakage reactance of each phase of the winding of the voltage transformer are basically symmetrical , and the ground capacitance of the three-phase bus is basically equal, the voltage drop generated by the current is also basically the same, so a zero-sequence voltage signal can be detected at the triangular open end of the secondary winding. Multiple sets of current signals of different frequencies are output by multiple sets of signal generators, and the corresponding zero-sequence voltage signals are detected. Multiple sets of these two signals are input to the processor, and the busbar in the medium-voltage network can be calculated according to the corresponding relationship. current in the capacitor to ground.

Claims (3)

1. system for detection of medium voltage network bus capacitor electric current, this system is connected on the three-phase bus of medium voltage network, it is characterized in that, comprise voltage transformer (VT), signal generator, zero sequence voltage detection device and processor, described voltage transformer (VT) connects the three-phase bus of medium voltage network, described signal generator all is connected with voltage transformer (VT) with the zero sequence voltage detection device, and described processor connects signal generator and zero sequence voltage detection device respectively.

2. a kind of system for detection of medium voltage network bus capacitor electric current according to claim 1, it is characterized in that, described voltage transformer (VT) comprises winding and Secondary Winding, a described winding directly is connected with the three-phase bus of medium voltage network, described Secondary Winding and a winding coupled, and adopt the mode of connection of open-delta, described signal generator and zero sequence voltage detection device all are connected the open delta end of Secondary Winding.

3. a kind of system for detection of medium voltage network bus capacitor electric current according to claim 1 is characterized in that, described signal generator is exportable and signal generator electrical network power-frequency voltage different frequency current signal.

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