Current transformer disconnection detection method, device and circuit breaker

Abstract

The application discloses a current transformer disconnection detection method. The current transformer comprises a measurement transformer for measuring load current of a main circuit and an energy transformer for extracting energy from the main circuit; the temperatures of the measurement transformer and the energy transformer are monitored in real time, and the measured temperature difference between the two is compared with a standard temperature difference range corresponding to the current load current; if the measured temperature difference is within the standard temperature difference range, it is determined that the measurement transformer and the energy transformer are normal; if the measured temperature difference is higher than the standard temperature difference range, it is determined that the measurement transformer is disconnected; and if the measured temperature difference is lower than the standard temperature difference range, it is determined that the energy transformer is disconnected. The application also discloses a current transformer disconnection detection device and a circuit breaker. Compared with the prior art, the application realizes accurate detection of the disconnection fault of the energy transformer for the first time, and has low implementation cost and simple operation.

Description

Technical Field

[0001] This invention relates to a method for detecting open circuits in current transformers. Background Technology

[0002] Circuit breakers are crucial components in low-voltage power distribution systems, playing a vital role in protecting the power distribution network and electrical equipment from faults such as overloads, short circuits, and leakage currents. Current transformers are commonly used components in circuit breakers, converting the primary current of the circuit breaker's main circuit into the secondary signal required by the intelligent controller. They have long held an irreplaceable position in current measurement and relay protection. Current transformers in existing intelligent circuit breakers typically include measuring transformers for measuring the load current of the main circuit and energy transformers for extracting electrical energy from the main circuit. Current transformers in intelligent circuit breakers operate for extended periods in complex environments, requiring high reliability to ensure normal circuit breaker operation. If a current transformer experiences a break, two serious consequences will occur depending on the location of the break: a broken measuring transformer will cause the measurement and control of the circuit breaker's electrical parameters to fail, leaving downstream equipment unprotected; a broken energy transformer will induce high voltage, causing discharge, arcing, and breakdown, potentially leading to fires and other safety accidents. Therefore, ensuring the accuracy of circuit breaker current measurement and monitoring the operating status of current transformers are crucial measures to improve the performance and reliability of smart circuit breakers. In existing technologies, most smart circuit breakers lack the function of detecting current transformer disconnections, and the few that do have this function only measure the disconnection. For example, Chinese invention patent CN201210461813 uses a digital-to-analog converter (DAC) to generate a continuous DC voltage, which is then superimposed on a current signal conditioning circuit. The microprocessor determines whether the current transformer is disconnected by detecting the output voltage of the current signal conditioning circuit. Another example is Chinese invention patent CN201110059748, which adds a grounding resistor between the current transformer and the current signal acquisition circuit, and the microprocessor determines whether the current transformer is disconnected by detecting the output voltage of the current signal conditioning circuit. However, none of these technical solutions achieve true disconnection detection of the current transformer. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a current transformer open circuit detection method that can accurately detect open circuit faults in energy transformers.

[0004] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0005] A method for detecting open circuit in a current transformer, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit and an energy transformer for extracting electrical energy from the main circuit; the method involves real-time monitoring of the temperatures of the measuring transformer and the energy transformer, and comparing the measured temperature difference between the two with a standard temperature difference range corresponding to the current load current: if the measured temperature difference is within the standard temperature difference range, the measuring transformer and the energy transformer are determined to be normal; if the measured temperature difference is higher than the standard temperature difference range, the measuring transformer is determined to be open circuit; if the measured temperature difference is lower than the standard temperature difference range, the energy transformer is determined to be open circuit.

[0006] Preferably, the standard temperature difference range corresponding to the current load current is determined in advance by the following method: when both the measuring transformer and the energy transformer of the current transformer are normal, temperature difference data between the measuring transformer and the energy transformer are collected under multiple different load currents; then, these temperature difference data are fitted to obtain the relationship curve between the standard temperature difference of the current transformer and the load current; the measurement error is superimposed on the relationship curve to obtain the standard temperature difference range.

[0007] Based on the same inventive concept, the following technical solutions can also be obtained:

[0008] A current transformer open circuit detection device, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit, and an energy transformer for extracting electrical energy from the main circuit; the current transformer open circuit detection device includes:

[0009] The temperature monitoring unit is used to monitor the temperature of the measuring transformer and the energy transformer in real time.

[0010] The judgment unit is used to compare the measured temperature difference between the measuring transformer and the energy transformer with the standard temperature difference range corresponding to the current load current: if the measured temperature difference is within the standard temperature difference range, the measuring transformer and the energy transformer are judged to be normal; if the measured temperature difference is higher than the standard temperature difference range, the measuring transformer is judged to be disconnected; if the measured temperature difference is lower than the standard temperature difference range, the energy transformer is judged to be disconnected.

[0011] Preferably, the standard temperature difference range corresponding to the current load current is determined in advance by the following method: when both the measuring transformer and the energy transformer of the current transformer are normal, temperature difference data between the measuring transformer and the energy transformer are collected under multiple different load currents; then, these temperature difference data are fitted to obtain the relationship curve between the standard temperature difference of the current transformer and the load current; the measurement error is superimposed on the relationship curve to obtain the standard temperature difference range.

[0012] A circuit breaker includes a current transformer, which includes a measuring transformer for measuring the load current of the main circuit and an energy transformer for extracting electrical energy from the main circuit; the circuit breaker also includes a current transformer open circuit detection device as described in any of the above technical solutions.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0014] This invention utilizes the significant temperature difference between the measuring transformer and the energy transformer under operating conditions, which is directly related to the load current. By monitoring the temperature difference between the two, it achieves the detection of open circuit faults, realizing accurate detection of open circuit faults in energy transformers for the first time. It can also detect open circuit faults in measuring transformers. The detection method of this invention is low in cost and simple to operate. Furthermore, it can be combined with other existing open circuit detection methods to obtain more accurate detection results through information fusion. Attached Figure Description

[0015] Figure 1 This is a circuit structure block diagram of a specific embodiment of the circuit breaker of the present invention;

[0016] Figure 2 The fitted curve shows the relationship between the temperature difference between the measurement transformer and the energy transformer and the load current.

[0017] Figure 3 The diagram shows an exploded view of the current transformer in a specific embodiment; where 1 is the front cover, 2 is the measuring transformer, 3 is the energy transformer, 4 is the adapter plate, 5 is the rear cover, 6 is the silicon steel sheet, 7 is the energy coil, 8 is the thermistor, and 9 is the thermistor. Detailed Implementation

[0018] To address the shortcomings of existing technologies, the present invention utilizes the significant temperature difference between the measuring transformer and the energy transformer under operating conditions, which is directly related to the load current, to detect open circuit faults by monitoring the temperature difference between the two.

[0019] The specific technical solution proposed in this invention is as follows:

[0020] A method for detecting open circuit in a current transformer, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit and an energy transformer for extracting electrical energy from the main circuit; the method involves real-time monitoring of the temperatures of the measuring transformer and the energy transformer, and comparing the measured temperature difference between the two with a standard temperature difference range corresponding to the current load current: if the measured temperature difference is within the standard temperature difference range, the measuring transformer and the energy transformer are determined to be normal; if the measured temperature difference is higher than the standard temperature difference range, the measuring transformer is determined to be open circuit; if the measured temperature difference is lower than the standard temperature difference range, the energy transformer is determined to be open circuit.

[0021] A current transformer open circuit detection device, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit, and an energy transformer for extracting electrical energy from the main circuit; the current transformer open circuit detection device includes:

[0022] The temperature monitoring unit is used to monitor the temperature of the measuring transformer and the energy transformer in real time.

[0023] The judgment unit is used to compare the measured temperature difference between the measuring transformer and the energy transformer with the standard temperature difference range corresponding to the current load current: if the measured temperature difference is within the standard temperature difference range, the measuring transformer and the energy transformer are judged to be normal; if the measured temperature difference is higher than the standard temperature difference range, the measuring transformer is judged to be disconnected; if the measured temperature difference is lower than the standard temperature difference range, the energy transformer is judged to be disconnected.

[0024] Preferably, the standard temperature difference range corresponding to the current load current is determined in advance by the following method: when both the measuring transformer and the energy transformer of the current transformer are normal, temperature difference data between the measuring transformer and the energy transformer are collected under multiple different load currents; then, these temperature difference data are fitted to obtain the relationship curve between the standard temperature difference of the current transformer and the load current; the measurement error is superimposed on the relationship curve to obtain the standard temperature difference range.

[0025] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment of the circuit breaker of the present invention, in conjunction with the accompanying drawings:

[0026] The structure of the circuit breaker in this embodiment is as follows: Figure 1 As shown, it includes a current transformer and an intelligent controller; as Figure 1As shown, the current transformer includes a measuring transformer and an energy transformer. The measuring transformer converts the primary current into a secondary voltage signal and sends it to the intelligent controller for processing. The energy transformer converts the primary current into a secondary current signal to power the intelligent controller. Thermistors 1 and 2 are respectively installed on the energy transformer and the measuring transformer to measure the temperature of the transformer's energy coil and measuring coil, respectively. The intelligent controller includes a signal conditioning circuit, a microprocessor circuit, a rectifier circuit, and a power conversion circuit. The signal conditioning circuit is responsible for integrating, restoring, and amplifying the secondary voltage signal from the measuring transformer and sending the processed signal to the microprocessor circuit. The rectifier circuit is responsible for rectifying and filtering the secondary current signal from the energy transformer and generating a system voltage after passing through the power conversion circuit to power the signal conditioning circuit and the microprocessor circuit. The microprocessor circuit processes the received output signals from the thermistors and the signal conditioning circuit, calculates the temperature difference ΔT between the transformer's energy coil temperature T1 and the measuring coil temperature T2, and determines whether the measuring transformer and the energy transformer are disconnected based on preset criteria.

[0027] When the circuit breaker is energized with its rated current and the current transformer is operating normally, both the energy transformer and the measuring transformer will experience temperature rises. Due to their different structures, the magnitude of these temperature rises differs significantly, with the energy transformer's temperature rise being much higher than that of the measuring transformer. Furthermore, the temperature difference between the two is related to the load current. If the energy transformer experiences a short circuit while the measuring transformer is functioning normally, the energy transformer's temperature rise will decrease sharply, and the temperature difference between the energy transformer and the measuring transformer will also decrease to below normal levels. Conversely, if the energy transformer is functioning normally but the measuring transformer experiences a short circuit, the operating current measured by the circuit breaker will drop sharply, approaching zero. The energy transformer's temperature rise will remain at a normal level, while the measuring transformer's temperature rise will change only slightly. Therefore, the temperature difference between the energy transformer and the measuring transformer will be higher than the temperature difference when the circuit breaker's operating current is close to zero. This invention utilizes this principle to achieve short circuit detection.

[0028] Give Figure 1 The circuit breaker shown is supplied with a working current I. The working current I is within 1.2 times the rated current. When the current transformer is working normally, the temperature of the energy transformer and the temperature of the current transformer at multiple current points are measured, and the temperature difference ΔT0 between the two is calculated. The data obtained are shown in Table 1.

[0029] Table 1 Temperature differences measured at different operating currents

[0030] Operating current I <![CDATA[Temperature difference △T0]]> 0.01In 3 0.1In 10 0.2In 18 0.5In 25 0.7In 31 1In 35 1.1In 38 1.2In 40

[0031] Then, by fitting the data in Table 1 using the polynomial fitting method, the following results can be obtained: Figure 2The fitted curve shown, along with the relationship between the temperature difference ΔT0 between the energy transformer and the measuring transformer and the load current I, i.e., the formula for temperature difference ΔT0 = f(I):

[0032] △T0=0.0208I 4 -0.4205I 3 +2.3428I 2 +2.7127I-1.6786

[0033] In actual operation of the circuit breaker, based on the measured temperatures T1 of the energy transformer and T2 of the measuring transformer, the temperature difference ΔT = T1 - T2 between the energy transformer and the measuring transformer during actual operation is calculated. According to ΔT0 = f(I), the standard temperature difference ΔT0 under the current load current when the coils of the energy transformer and the measuring transformer are normal is obtained. ΔT is compared with ΔT0. If the difference is within a reasonable measurement error range, it indicates that both the energy transformer and the measuring transformer are normal and no open circuit fault has occurred. Otherwise, it indicates an open circuit fault has occurred. If ΔT is higher than ΔT0 by a reasonable measurement error range, it can be determined that the measuring transformer has an open circuit fault; if ΔT is lower than ΔT0 by a reasonable measurement error range, it can be determined that the energy transformer has an open circuit fault. The intelligent controller will issue an alarm when an open circuit fault occurs based on the above detection results.

[0034] To ensure accurate test results, the energy transformer temperature T1 and the measured transformer temperature T2 should be obtained as accurately as possible. Figure 3 This shows a specific structure of a current transformer, such as... Figure 3 As shown, the current transformer includes a front cover 1, a measuring transformer 2, an energy transformer 3, an adapter plate 4, and a rear cover 5. The measuring transformer 2 and the energy transformer 3 are installed in parallel in the space formed by the combination of the front cover 1 and the rear cover 5. The energy transformer 3 is composed of a silicon steel sheet 6 and an energy coil 7. A thermistor 8 is installed on the surface of the energy coil 7, and a thermistor 9 is installed on the surface of the measuring transformer 2. The signal output leads of the measuring transformer 2, the energy transformer 3, thermistor 8, and thermistor 9 are soldered to the adapter plate 4 and connected to the intelligent controller through the adapter plate 4.

[0035] In summary, this invention detects open circuit faults by monitoring the temperature difference between the energy transformer and the measuring transformer, achieving accurate detection of open circuit faults in the energy transformer for the first time. It can also detect open circuit faults in the measuring transformer. The detection method of this invention is low in cost and simple to operate. Furthermore, it can be combined with other existing open circuit detection methods to obtain more accurate detection results through information fusion.

Claims

1. A method for detecting open circuit in a current transformer, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit, and an energy transformer for extracting electrical energy from the main circuit; characterized in that, The temperatures of the measuring current transformer and the energy transformer are monitored in real time, and the measured temperature difference between them is compared with the standard temperature difference range corresponding to the current load current. If the measured temperature difference is within the standard temperature difference range, the measuring current transformer and the energy transformer are considered to be normal. If the measured temperature difference is higher than the standard temperature difference range, the measuring current transformer is considered to be disconnected. If the measured temperature difference is lower than the standard temperature difference range, the energy transformer is considered to be disconnected. The standard temperature difference range corresponding to the current load current is determined in advance by the following method: under the condition that both the measuring current transformer and the energy transformer of the current transformer are normal, temperature difference data between the measuring current transformer and the energy transformer are collected under multiple different load currents. Then, these temperature difference data are fitted to obtain the relationship curve between the standard temperature difference of the current transformer and the load current. The measurement error is superimposed on the relationship curve to obtain the standard temperature difference range.

2. A current transformer open circuit detection device, wherein the current transformer includes a measuring transformer for measuring the load current of the main circuit, and an energy transformer for extracting electrical energy from the main circuit; characterized in that, The current transformer open circuit detection device includes: The temperature monitoring unit is used to monitor the temperature of the measuring transformer and the energy transformer in real time. The judgment unit is used to compare the measured temperature difference between the current transformer and the energy transformer with the standard temperature difference range corresponding to the current load current: if the measured temperature difference is within the standard temperature difference range, the current transformer and the energy transformer are judged to be normal; if the measured temperature difference is higher than the standard temperature difference range, the current transformer is judged to be disconnected; if the measured temperature difference is lower than the standard temperature difference range, the energy transformer is judged to be disconnected. The standard temperature difference range corresponding to the current load current is determined in advance by the following method: under the condition that both the current transformer and the energy transformer are normal, temperature difference data between the current transformer and the energy transformer are collected under multiple different load currents; then these temperature difference data are fitted to obtain the relationship curve between the standard temperature difference of the current transformer and the load current; the measurement error is superimposed on the relationship curve to obtain the standard temperature difference range.

3. A circuit breaker, comprising a current transformer, said current transformer including a measuring transformer for measuring the load current of the main circuit, and an energy transformer for extracting electrical energy from the main circuit; characterized in that, The circuit breaker also includes the current transformer open circuit detection device as described in claim 2.

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