CN105137152A - Ground lead current signal monitoring sensor for end screen of transformer bushing - Google Patents

Abstract

A transformer bushing end screen grounding wire current signal monitoring sensor, which consists of a conductive rod 1, a base 2, a bottom waterproof sealing ring 3, a coil 4, a coil 5, a coil 6, a casing 7, a waterproof cap 8, a conductive disc 9, and a top The waterproof sealing ring 10, the BNC connector 11, the BNC connector 12, and the BNC connector 13 are composed; the coil 4, the coil 5 and the coil 6 are sleeved on the conductive rod 1 side by side, and share the shell 7. The conductive rod 1 is cylindrical, and the shell 7 is cylindrical, and the two form a coaxial cylindrical structure; the base 2 is a cylindrical body, which forms a coaxial cylindrical structure with the conductive rod, and can transmit high-frequency signals in the range of 1MHz-40MHz without distortion. Small size and strong adaptability.

Description

A sensor for monitoring the current signal of the grounding wire at the end screen of the transformer bushing

technical field

The invention belongs to the field of on-line monitoring of transformer bushings in power systems, and relates to a current signal monitoring sensor for the grounding wire at the end screen of the transformer bushing.

Background technique

The failure rate of transformer bushings is high, so online monitoring of transformer bushings is very important. Usually, transformer bushing monitoring includes dielectric loss tangent tgδ and bushing partial discharge. When monitoring the above parameters, it is necessary to obtain the current signal from the lead-out line at the end screen of the transformer bushing.

1) Monitoring of transformer bushing dielectric loss tangent tgδ

The dielectric loss tangent tgδ value of the bushing reflects the damp condition of the bushing insulation, and the δ angle is the angle between the power frequency leakage current on the outlet line of the end screen of the bushing and the power frequency voltage signal on the high voltage guide rod of the bushing, very tiny. The on-line monitoring of transformer bushing power frequency leakage current belongs to the precision measurement category of high voltage, micro current and small angle. The phase angle difference of the current sensor used is a main factor affecting the measurement accuracy and stability of tgδ.

2) Partial discharge monitoring of transformer bushings

The transformer bushings above 110kV voltage level are mainly oil-paper capacitive bushings. During the manufacturing and long-term operation, partial discharges will occur in the bushings due to defects in the insulation structure, which will gradually destroy the insulation of the bushings. In order to grasp the insulation performance of the transformer bushing and the severity of the internal discharge of the insulation, it is one of the indispensable means to monitor the partial discharge through the grounding wire at the end of the transformer bushing. The partial discharge signal frequency of the transformer bushing is mainly concentrated in 20KHz-40MHz. In order to grasp the partial discharge information of the bushing, the current sensor needs to have a wide frequency band monitoring range to extract rich partial discharge signal features. Similarly, the current sensor needs to be placed on the ground wire connected to the lead wire at the end of the bushing.

3) Transformer overvoltage intrusion wave monitoring

When the transformer is attacked by lightning waves or operating overvoltage, the weak link in the transformer's internal insulation may be destroyed, and the transformer winding may be deformed. Therefore, it is an essential part of transformer state diagnosis to grasp the situation of the overvoltage shock suffered by the transformer. When the overvoltage invades the transformer, the lead wire at the end of the bushing will flow through the capacitive current caused by the overvoltage. According to the capacitive effect of the bushing, this current signal is the differential of the overvoltage signal. Accurately measure and integrate this current signal to obtain the overvoltage signal. Among them, the frequency range of the lightning overvoltage signal is mainly concentrated in 1K-1MHz, and the maximum magnitude of the current flowing through the grounding wire at the end screen of the transformer bushing can reach 1000A. The current sensor for monitoring the lightning overvoltage signal needs to be able to monitor low frequency signals and withstand large currents shock. At present, due to the lack of actual measurement technology, the waveform of the overvoltage of the power grid must be obtained by simulation calculation, and the error is large, which is not conducive to diagnosing the state of the transformer.

4) Problems existing in the current monitoring of the lead-out wire at the end screen of the transformer bushing

During the normal operation of the transformer, the lead-out wires at the end of the bushing must be reliably grounded, so the lead-out wires at the end of the bushing are often protected and grounded by a rainproof cap. When monitoring the insulation state of the bushing, the on-site personnel usually stop the transformer first, open the rainproof cap of the lead-out line at the end screen of the bushing, connect a relatively long grounding wire to the lead-out line at the end screen, and connect the other One end is connected to the transformer shell, and the lead-out wire of the last screen is reliably grounded through this grounding wire; the current sensor is set on this grounding wire. After the monitoring is completed, remove the sensor and restore the rainproof cap; or use a complex external sealing device to ensure that the grounding wire joint is not rusted and has a complicated structure.

Since this additional grounding wire is randomly placed and has different lengths, the inductance of the grounding wire itself changes accordingly, which in turn causes a measurement error of the current sensor on the current signal on the lead-out wire of the last screen. For the power frequency leakage current signal, since the grounding wire cannot always be in the center of the current sensor and is bent at will, the resulting phase error cannot meet the accuracy requirements of tgδ measurement. For the partial discharge pulse current signal, due to the non-coaxial cylindrical structure between the ground wire and the transformer shell, the frequency band of the ground wire is not wide enough, and the high frequency (above 1MHz) signal is distorted.

At the same time, the existing current sensor has a large volume, which increases the overall volume of the current monitoring device. For transformers with a voltage level of 110kV and above, considering the impact on the flashover voltage of the transformer bushing, the large-sized current sensor needs to be installed far away from the bushing for monitoring, and it cannot even be accepted by field personnel, so it is not practical. In addition, there are two parts that need to be sealed in the way of adding a grounding wire to the lead-out wire of the last screen, that is, the two ends of the grounding wire, so the requirements for the sealing structure are relatively high.

Contents of the invention

The content of the present invention is to propose a transformer bushing end screen grounding wire current signal monitoring sensor, which is characterized in that: the sensor is composed of a conductive rod 1, a base 2, a bottom waterproof sealing ring 3, a coil 4, a coil 5, a coil 6, Shell 7, waterproof cap 8, conductive disc 9, top waterproof sealing ring 10, BNC connector 11, BNC connector 12, BNC connector 13; conductive rod 1 is cylindrical, shell 7 is cylindrical, and the two form a coaxial Cylindrical structure; the base 2 is a cylinder, forming a coaxial cylindrical structure with the conductive rod; the bottom and top of the housing 7 are respectively provided with waterproof sealing rings 3 and 10, the waterproof cap 8 is installed on the top of the housing 7, and the inside of the current sensor is poured with epoxy resin seal; the conductive rod 1 and the base 2 are detachable and replaceable.

The purpose of the present invention is to provide a current signal monitoring sensor for the grounding wire of the transformer bushing end screen. The shell 7, the base 2 and the conductive rod 1 form a coaxial cylindrical structure, which can transmit the power frequency leakage current signal of 45Hz-55Hz and 20KHz without distortion. -40MHz partial discharge signal, 1K-2MHz overvoltage signal, frequency range 45Hz-40MHz. The two ends of the lead-out line at the end screen of the casing are sealed to prevent water from entering the interface at the end screen of the casing. The connection part between the sensor and the end screen interface and the coaxial lead wire of the end screen cylinder can be disassembled and replaced, and can adapt to different sizes of end screens.

The advantages of the present invention are:

(1) The conductive rod 1 is cylindrical, and the shell 7 is cylindrical, and the two form a coaxial cylindrical structure; the base 2 is cylindrical, and also forms a coaxial cylindrical structure with the conductive rod 1 . Then the sensor can transmit 45Hz-55Hz power frequency leakage current signal, 20KHz-40MHz partial discharge signal and 1K-2MHz overvoltage signal without distortion.

(2) The two ends of the conductive rod 1 and the inside of the sensor are waterproof and sealed, which can prevent water from entering the interface of the end screen of the casing and the inside of the sensor.

(3) The conductive rod 1 and the base 2 can be disassembled and replaced with different sizes, which are suitable for the lead-out wire interface of the end screen of the casing of different sizes, so that the sensor is easy to install and the lead-out wire of the end screen is grounded reliably.

Description of drawings

Fig. 1 is a schematic cross-sectional view of a sensor of the present invention.

Detailed ways

The present invention will be further described in conjunction with FIG. 1 .

As shown in Figure 1, a sensor for monitoring the current signal of the grounding wire at the end of the transformer bushing has a coaxial cylindrical structure as a whole. The current enters the conductive rod 1 from the lead-out line of the end screen of the bushing, flows into the shell 7 and the fixed base 2 of the sensor through the conductive disc 9, and finally flows into the grounding part of the lead-out line interface of the end screen of the transformer bushing along the base 2, so that the conductive rod and the conductive circle The loop formed by the disk 9, the casing 7 and the base 2 has a frequency band up to 100MHz, which is convenient for measuring partial discharge signals in a wide frequency range of 20KHz-40MHz. Coil 4, coil 5 and coil 6 are all ring-shaped, and are sleeved on the conductive rod 1 side by side, and are inside the shell 7, so the conductive rod 1 is on the central axis of the sensor, which ensures the accuracy of the phase angle of the power frequency leakage current measurement. Accuracy; Coil 4, Coil 5 and Coil 6 share a shell 7 and a conductive rod 1, so that the overall size of the sensor is small, and it can simultaneously monitor the intrusion wave impulse current signal, partial discharge signal and power frequency leakage current signal, with multiple Function.

The diameters of the conductive rod 1 and the base 2 depend on the diameter of the outlet wire interface of the transformer bushing end screen, which can be disassembled and replaced, so as to facilitate cooperation with the outlet wire interface of the end screen of the bushing with different diameters, while other parts of the sensor (such as coils) 4. Coil 5, coil 6, shell 7, conductive disk 9, waterproof cap 8) can remain unchanged.

The base 2 is installed and fixed in cooperation with the lead-out line interface of the end screen of the transformer bushing through the internal thread; the bottom and top of the shell 7 are joined with waterproof sealing rings 3 and 10; the shell 7 is fixed on the base 2 through the bottom screw; the conductive rod 1 penetrates from the center of the sensor, And connect with the tap of the end screen of the transformer bushing; then screw the conductive disc 9 from the top of the conductive rod 1, and contact with the sensor shell, connect the conductive disc 9 with the shell 7 by screws, and complete the installation.

In this example:

The conductive rod 1 is a cylindrical rod with a height of 97mm and a maximum diameter of 12mm; the base 2 has a height of 28mm and a maximum diameter of 68mm; the shell 7 is a cylinder with a height of 72mm and a maximum diameter of 72mm; the conductive disc 9 is A disc with a height of 5mm and a diameter of 36mm.

The number of turns of the coil is 80 turns, the integral resistance is 0.5Ω, and the monitoring frequency band is 1KHz-2MHz, which is used to monitor the impulse current signal, and the signal is output from the BNC connector 13; the number of turns of the coil is 30 turns, the integral resistance is 50Ω, and the monitoring frequency band is 20KHz-40MHz, used to monitor partial discharge signal, the signal is output from BNC connector 12; the number of 6 turns of the coil is 150 turns, the integral resistance is 20Ω, the monitoring frequency band is 45Hz-55Hz, used to monitor power frequency leakage current, the signal is output from BNC Connector 11 output.

The base 2, the shell 7, the waterproof cap 8, and the conductive disk 9 are made of iron with a conductivity of 9.71x10 ^-8 Ω·m and galvanized. The conductive rod 1 is made of copper material with a conductivity of 1.678x10 ^-8 Ω·m. The magnetic core materials of coil 4 , coil 5 and coil 6 are amorphous materials with a relative magnetic permeability greater than 10,000. The bottom waterproof sealing ring 3 and the top waterproof sealing ring 10 are made of fluorine rubber.

Claims (4)

1. A transformer bushing end screen grounding wire current signal monitoring sensor is characterized in that: the sensor consists of a conductive rod 1, a base 2, a bottom waterproof sealing ring 3, a coil 4, a coil 5, a coil 6, a casing 7, and a waterproof cap 8. It is composed of a conductive disc 9, a top waterproof sealing ring 10, a BNC connector 11, a BNC connector 12, and a BNC connector 13 (as shown in Figure 1). 2. The transformer bushing end screen grounding wire current signal monitoring sensor according to claim 1, characterized in that: the conductive rod 1 is cylindrical, the shell 7 is cylindrical, and the two form a coaxial cylindrical structure; the base 2 is The cylinder forms a coaxial cylindrical structure with the conductive rod. 3. The transformer bushing end screen grounding wire current signal monitoring sensor according to claim 2, characterized in that: the bottom and top of the casing 7 have waterproof sealing rings 3 and 10 respectively, the waterproof cap 8 is installed on the top of the casing 7, and the current sensor The interior is potted with epoxy resin pouring. 4. The current signal monitoring sensor of the transformer bushing end screen grounding wire according to claim 3, characterized in that: the conductive rod 1 and the base 2 are detachable and replaceable.