A device for measuring residual current in a three-phase four-wire supply line
By using series clamp-on current transformers and parallel shunt devices in overhead lines, the problem of measuring residual current in three-phase four-wire power supply lines, which is difficult to achieve with traditional methods, is solved, realizing simple and efficient current measurement and improving accuracy and applicability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- 余南雄
- Filing Date
- 2025-06-26
- Publication Date
- 2026-08-04
AI Technical Summary
In overhead lines, traditional clamp-on current transformers cannot simultaneously clamp all four conductors of a three-phase four-wire power supply line, making it difficult to accurately measure the residual current. Existing methods are cumbersome to operate, have low accuracy, or require line modifications, increasing costs and construction difficulty.
Four clamp-on current transformers are connected in series and connected in series with an ammeter. A shunt device is connected in parallel with the clamp-on current transformers. The current is measured by the principle of electromagnetic induction, and the appropriate shunt range is selected according to the current magnitude to achieve accurate measurement of the current in the four conductors.
It enables simple and accurate residual current measurement in overhead lines, reduces operational difficulty and cost, improves measurement sensitivity and accuracy, adapts to measurement needs of different current magnitudes, protects the ammeter, and reduces errors.
Smart Images
Figure CN224594727U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of circuit testing technology, specifically relating to a device for measuring the residual current of a three-phase four-wire power supply line. Background Technology
[0002] In today's power supply systems, the three-phase four-wire system is a very common and important power supply method. It consists of three live wires (A, B, and C phases) and one neutral wire (N wire), generally connected in a star configuration. This power supply method is widely used in various aspects of industrial production, commercial operations, and residential life, providing stable and reliable power support for various electrical equipment. Measuring the residual current in the conductors is crucial for ensuring the safe and stable operation of the power supply system. Residual current, also known as zero-sequence current, refers to the vector sum of the three-phase currents and the neutral current in a three-phase four-wire power supply line. Under normal circumstances, according to Kirchhoff's current law, the current flowing into and out of the same node is equal; therefore, the vector sum of the three-phase currents and the neutral current should be zero. However, when the conductor... When a fault such as leakage occurs in the circuit, an additional current is generated, causing the residual current to be non-zero. By accurately measuring the residual current, potential faults in the circuit can be detected in time, avoiding safety hazards such as electric shock accidents and electrical fires caused by leakage. At the same time, it also helps to improve the power quality and operating efficiency of the power supply system. Currently, clamp-on ammeters are commonly used to measure the residual current of conductors. Clamp-on ammeters have the advantages of being easy to use and measuring without power interruption. They can measure the residual current by clamping the conductors in the middle of a clamp-on current transformer and using the principle of electromagnetic induction to convert the current signal in the conductors into a measurable electrical signal. According to Kirchhoff's current law, when four conductors are clamped in a clamp-on current transformer at the same time, the presence of residual current in the circuit can be determined based on the measurement results.
[0003] However, in practical applications of overhead lines, due to their unique installation method, the distance between lines is very far. In low-voltage distribution lines, to meet the requirements of electrical safety distance and mechanical strength, the spacing between conductors may reach several meters. In this case, a single clamp-on current transformer cannot directly clamp all four conductors. The traditional method of measuring residual current with a single clamp-on current transformer becomes difficult to implement in the overhead line scenario, which brings great difficulties to line fault detection and maintenance. In existing technologies, although there are some attempts to measure current in overhead lines, most of them have limitations. For example, some methods use phase-by-phase measurement, measuring the current of each conductor separately, and then analyzing the residual current through complex calculations. This method is not only cumbersome to operate, requiring multiple measurements and calculations, but the measurement accuracy is also easily affected by external factors, such as inaccurate measurement positions and interference from environmental electromagnetic fields. In addition, some methods use special sensor arrangement methods, but these methods often require line modifications, increasing construction difficulty and cost, and may affect the normal operation of the line. Utility Model Content
[0004] The purpose of this invention is to provide a device for measuring the residual current of a three-phase four-wire power supply line, so as to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, this utility model provides the following technical solution:
[0006] A device for measuring the residual current in a three-phase four-wire power supply line, comprising:
[0007] An ammeter is provided, with four clamp-on current transformers connected to one side for measuring current in a conductor. The four clamp-on current transformers are connected in series, and the ammeter is connected in series with the four clamp-on current transformers. A current shunt device is connected to one side of the ammeter for shunting current, and the current shunt device is connected in parallel with the four clamp-on current transformers.
[0008] Preferably, the four clamp-on transformers are used to clamp the A-phase conductor, B-phase conductor, C-phase conductor, and neutral conductor in a three-phase four-wire power supply line.
[0009] Preferably, the diversion device comprises at least two metal sheets of different widths and thicknesses.
[0010] Compared with the prior art, the beneficial effects of this utility model are:
[0011] (1) This utility model sets up four clamp-on current transformers and connects them in series with each other and then in series with an ammeter. At the same time, the positive and negative poles of the four clamp-on current transformers are connected together and connected to the ammeter. This successfully constructs a measurement circuit that can measure the current of four conductors at the same time. This innovative design enables the effective measurement of the residual current of a three-phase four-wire power supply line in scenarios with large distances between lines, such as overhead lines, just like in ordinary lines. According to Kirchhoff's current law, the presence of residual current in the line can be determined by accurately measuring the vector sum of the currents of the four conductors. When the measurement result shows that the vector sum is not zero, it can be quickly determined that there is an abnormal residual current in the line, and then it can be determined that there may be a fault such as leakage in the line.
[0012] (2) The current shunt device of this utility model is connected in parallel with four clamp-on current transformers. By setting metal plates of different widths and thicknesses on the device, the current is reasonably shunted. In actual measurement, the operator can select the appropriate current shunt range according to the estimated current size. When the current is small, a smaller current shunt range is selected to allow more current to pass through the ammeter and improve the measurement sensitivity. When the current is large, a larger current shunt range is selected to shunt part of the current and avoid damage to the ammeter due to excessive current. This current shunt design not only effectively protects the ammeter and extends its service life, but also improves the measurement accuracy by reasonably distributing the current. At the same time, the multiple range selection provided by the current shunt device enables the device to adapt to the measurement needs of different current sizes and has a wider range of applicability.
[0013] (3) This utility model fully considers the convenience of actual use. Its overall structure is simple. The operator only needs to clamp the four pliers on the A, B, C phase conductors and the neutral line (N line) of the three-phase four-wire power supply line respectively, and then select the appropriate shunt range according to the estimated current size, and turn on the power of the ammeter to carry out the measurement. The entire operation process does not require complicated training and professional skills. Ordinary electricians can master it with simple guidance. This not only lowers the threshold for using the device and improves work efficiency, but also reduces measurement errors caused by improper operation. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the overall structure of this utility model.
[0015] In the diagram: 1. Ammeter; 2. Clamp-on current transformer; 3. Shunt device. Detailed Implementation
[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0017] Example 1:
[0018] Please see Figure 1 As shown, a device for measuring the residual current of a three-phase four-wire power supply line includes:
[0019] Ammeter 1 is connected to one side of clamp-on current transformer 2, which is used to measure the current in the conductor. There are four clamp-on current transformers 2 connected in series. Ammeter 1 is connected in series with the four clamp-on current transformers 2. A shunt device 3 is connected to one side of ammeter 1, which is used to shunt the current. The shunt device 3 is connected in parallel with the four clamp-on current transformers 2.
[0020] Specifically, the four clamp-on transformers 2 are used to clamp the A-phase conductor, B-phase conductor, C-phase conductor and neutral conductor in the three-phase four-wire power supply line, respectively, and the shunt device 3 includes at least two metal sheets of different widths and thicknesses.
[0021] As shown above, ammeter 1 and four clamp-on current transformers 2 are connected in series to form a series branch, constituting a complete measurement circuit. Ammeter 1 is used to receive and display the current value measured and superimposed by the four clamp-on current transformers 2. Under normal circumstances, according to Kirchhoff's current law, when the vector sum of the three-phase current and the neutral current is zero, the reading of ammeter 1 should be zero. When there is a residual current due to a fault such as leakage in the line, ammeter 1 displays the corresponding non-zero current value, thereby determining whether there is an abnormality in the line. Ammeter 1 can be a digital meter or a mechanical meter. The four clamp-on current transformers 2 are connected in series to form a current measurement series branch. Each clamp-on current transformer 2 is used to clamp the A-phase conductor, B-phase conductor, and C-phase conductor in the three-phase four-wire power supply line, respectively. The phase conductor, C-phase conductor, and neutral conductor (N-line) convert the alternating current in the conductor into an induced current in the secondary winding based on the principle of electromagnetic induction, thereby measuring the conductor current and transmitting the measured current signal to the subsequent measurement circuit. The current shunt device 3 is connected in parallel with four clamp-on current transformers 2. The current shunt device 3 includes at least two metal plates of different widths and thicknesses. By selecting metal plates of different widths and thicknesses to connect to the circuit, the current shunt ratio can be changed to achieve reasonable current shunt. When the measured current is large, part of the current is shunted to avoid damage to the ammeter 1 due to excessive current, thus protecting the ammeter 1. At the same time, reasonable current shunt improves the measurement accuracy and meets the measurement needs of different current sizes.
[0022] Working Principle: In a three-phase four-wire power supply system, according to Kirchhoff's current law, at the same node in the circuit, the sum of the currents flowing into that node is equal to the sum of the currents flowing out of that node. Ideally, in a three-phase four-wire power supply line, the vector sum of the three-phase currents (A, B, and C phases) and the neutral (N) current should be zero. This is because the three-phase currents are 120° out of phase and are in balance. The neutral current is the compensation current when the three-phase currents are unbalanced. Under normal circumstances, when the three phases are balanced, the neutral current is theoretically zero, and the overall vector sum is zero. The clamp-on transformer 2 works based on the principle of electromagnetic induction. When a conductor passes through the clamp of the clamp-on transformer 2, the current in the conductor... Alternating current generates alternating magnetic flux in the core of clamp-on transformer 2. According to the law of electromagnetic induction, this alternating magnetic flux induces an electromotive force in the secondary winding of clamp-on transformer 2, thereby generating an induced current. The magnitude of the induced current is proportional to the magnitude of the current in the conductor passing through the clamp. By measuring the induced current in the secondary winding, the current value in the conductor can be indirectly obtained. The positive and negative poles of the four clamp-on transformers 2 are connected together to form a closed loop. Three clamp-on transformers 2 clamp the three-phase conductors A, B, and C respectively, and the fourth clamp-on transformer 2 clamps the neutral line (N line). The four clamp-on transformers 2 measure the three-phase currents A, B, and C and the neutral line current respectively, and transmit these current signals. The current is transmitted to the measuring circuit. In this circuit, because the four clamp-on current transformers 2 are connected in series, the currents they measure are vector-superimposed. Under normal circumstances, according to Kirchhoff's current law, the vector sum of the currents in the four conductors is zero, and the reading of ammeter 1 should be zero. However, when a fault such as leakage occurs in the line, the balance between the three-phase current and the neutral current is broken, and the vector sum is no longer zero. Ammeter 1 will then display the corresponding current value, which is the residual current (zero-sequence current) in the line. The shunt device 3 is connected in parallel with the four clamp-on current transformers 2. Its function is to protect ammeter 1 and improve measurement accuracy. The shunt device 3 consists of two or three metal plates of different widths and thicknesses. These metal strips have different resistance values. When the measured current is large, by selecting metal strips with appropriate width and thickness, a portion of the current can be diverted to avoid damage to ammeter 1 due to excessive current. The current diversion principle is based on the characteristics of parallel circuits. In a parallel circuit, the voltage across each branch is equal, and the current is distributed according to the resistance. The metal strips of the current diversion device 3 are connected in parallel with the measurement circuit where ammeter 1 is located. When the metal strips are connected to the circuit, part of the current will be diverted through the metal strips, and only part of the current will pass through ammeter 1. By selecting metal strips with different resistance values, the current diversion ratio can be changed, thereby enabling the measurement of currents of different magnitudes and improving the accuracy and flexibility of the measurement.
[0023] In practical use, the operator should wear insulated gloves and use the insulated operating rod to clamp the four clamps onto the A, B, and C phase conductors and the neutral (N) line of the three-phase four-wire power supply line. When clamping, ensure the clamp jaws are clean and free of foreign objects, tightly closed, and without looseness. The conductor should be positioned as close to the center of the clamps as possible to ensure measurement accuracy. Turn on the power to ammeter 1 and select an appropriate shunt range based on the estimated current. If the line current is uncertain, a larger shunt range can be selected for preliminary measurement, and then the range can be adjusted based on the measurement results. For example, if the estimated current is large, a metal plate with a larger shunt ratio can be connected to the circuit initially. If the measurement result shows a small current, a metal plate with a smaller shunt ratio can be used to improve measurement accuracy. Observe the reading of ammeter 1 and record it after it stabilizes. Under normal circumstances, the reading of ammeter 1 should be close to zero. If the reading is not zero, it indicates the presence of residual current in the line, which may indicate a leakage fault. When recording the reading, pay attention to the unit and precision of the reading for subsequent analysis and processing.
[0024] The accompanying drawings of the embodiments disclosed in this utility model only involve the structures involved in the embodiments disclosed in this utility model. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this utility model can be combined with each other.
[0025] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A device for measuring the residual current in a three-phase four-wire power supply line, characterized in that, include: An ammeter (1) is connected to a clamp-on current transformer (2) on one side. The clamp-on current transformer (2) is used to measure the current in the conductor. There are four clamp-on current transformers (2) connected in series. The ammeter (1) is connected in series with the four clamp-on current transformers (2). A current shunt device (3) is connected to one side of the ammeter (1). The current shunt device (3) is used to shunt the current. The current shunt device (3) is connected in parallel with the four clamp-on current transformers (2).
2. The device for measuring the residual current of a three-phase four-wire power supply line according to claim 1, characterized in that, The four clamp-on transformers (2) are used to clamp the A-phase conductor, B-phase conductor, C-phase conductor and neutral line in the three-phase four-wire power supply line, respectively.
3. The device for measuring the residual current of a three-phase four-wire power supply line according to claim 1, characterized in that, The diversion device (3) includes at least two metal sheets of different widths and thicknesses.