Electronic transformer test circuit
By designing an electronic transformer test circuit for relay testers, the problem of low accuracy when relay testers output voltage signals below 1V is solved, high-precision measurement of electronic transformers is achieved, and overvoltage protection function is provided, which reduces costs.
Patent Information
- Application Number
- CN202420605673.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-27
- Publication Date
- 2025-03-14
- Estimated Expiration
- 2034-03-27
AI Technical Summary
The existing relay testers have low accuracy when outputting voltage signals below 1V, which cannot meet the debugging requirements of the 10KV distribution network switchgear. Relay testers with high-precision output on the market are expensive.
An electronic transformer test circuit is designed, including an overvoltage protection alarm circuit, a voltage conversion circuit and a passive first-order filter circuit. By reducing the high voltage output by the relay tester to a low voltage suitable for use in electronic transformers, the measurement accuracy is improved.
It realizes that the measurement accuracy of electronic transformers is improved at a low cost without the need for external power supply, and has an overvoltage protection function, avoiding safety hazards on high-voltage cabinets.
Smart Images
Figure CN222618771U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of electric power testing, in particular to an electronic mutual inductor testing circuit used in conjunction with an existing relay protection tester. Background Art
[0002] The distribution network switchgear is an electrical equipment mainly based on high-voltage switches. It assembles primary equipment such as busbars, insulators, transformers, lightning arresters, grounding switches, and secondary equipment for monitoring, controlling, measuring, adjusting and protecting the primary equipment in its closed metal cabinet. Its main function is to open, close, control and protect electrical equipment in the process of power generation, transmission, distribution and energy conversion in the power system. Before the high-voltage switchgear is put into production, it is necessary to test the functions and performance of the high-voltage switchgear. The test site is often outdoors, and it is impossible to pass the primary current generator (the equipment is large, and the high voltage and current are unsafe). It can only be tested by the relay protection tester (three-phase relay protection tester) to output voltage or current directly to the secondary side (output end) of the transformer to test the protection and measurement functions of the high-voltage cabinet.
[0003] The existing 10KV distribution network transformers mostly use electromagnetic transformers. If the secondary circuit of the electromagnetic transformer is open, high voltage will be generated, which will bring serious safety hazards. In order to solve the safety hazards caused by the secondary circuit of the electromagnetic transformer, the new 10KV distribution network switchgear has begun to use electronic transformers instead of electromagnetic transformers. Electronic transformers can convert primary current into secondary voltage, and will not generate high voltage when the secondary circuit is open.
[0004] The phase-to-phase ratio of an electronic transformer is generally 600A / 1V (when the primary side generates 600A current, the secondary side generates 1V voltage), and the zero-sequence ratio is 20A / 0.2V. During on-site commissioning or testing of switchgear, it is necessary to apply secondary quantities for testing. The rated voltage output of commonly used relay testers is generally between 100-150V. The output accuracy of relay testers can reach 0.2% at rated values. However, the output error is large below 1V, which cannot meet the commissioning requirements of switchgear. Relay testers that can achieve high-precision output below 1V are very rare and expensive on the market. Therefore, it is very urgent to design a module that can cooperate with existing relay testers to output voltage signals below 1V with high precision. Utility Model Content
[0005] In order to overcome the shortcomings of the prior art, the utility model provides an electronic transformer test module for use with an existing relay protection tester, which reduces the high voltage output by the relay protection tester to a low voltage that can be used by the electronic transformer, thereby solving the problems of low accuracy in directly testing electronic transformers with ordinary relay protection testers, and high price of relay protection instruments with high-precision output below 1V that are used in conjunction with electronic transformers.
[0006] To achieve the above-mentioned purpose, the utility model relates to an electronic transformer test circuit, comprising an overvoltage protection alarm circuit, a voltage conversion circuit and a passive first-order filter circuit connected in sequence. The overvoltage protection alarm circuit is used to ensure that the input voltage to the voltage conversion circuit does not exceed a set value. The voltage conversion circuit is used to convert the input large voltage into a small voltage suitable for electronic transformer measurement; the passive first-order filter circuit is used to filter out high-frequency noise or electromagnetic interference.
[0007] Specifically, the overvoltage protection alarm circuit includes a rectifier bridge B, a resistor R1, a capacitor C1, a diode D1, a relay K1, a resistor R3 and an LED lamp LED1; the voltage conversion circuit includes a resistor R2, a voltage transformer PT1 and an adjustable resistor R4; the passive first-order filter circuit includes a resistor R5 and a capacitor C2;
[0008] The UA end is connected to the second end of the rectifier bridge B and the second pin of the relay K1 respectively, the UN end is connected to the first end of the rectifier bridge B, one end of the LED lamp LED1 and the fourth pin of the voltage transformer PT1 respectively, the third end of the rectifier bridge B is connected to one end of the resistor R1, the other end of the resistor R1 is connected to one end of the capacitor C1, the cathode of the diode D1 and the first pin of the relay K1 respectively, the fourth end of the rectifier bridge B is connected to the other end of the capacitor C1, the anode of the diode D1 and the third pin of the relay K1 respectively, the fourth pin of the relay K1 is connected to the other end of the LED lamp LED1 through the resistor R3, the sixth pin of the relay K1 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the third pin of the voltage transformer PT1, the first pin of the voltage transformer PT1 is connected to one end of the adjustable resistor R4 and one end of the resistor R5 respectively, the other end of the resistor R5 is connected to one end of the capacitor C2 and the UAO end respectively, and the second pin of the voltage transformer PT1 is connected to the other end of the adjustable resistor R4, the other end of the capacitor C2 and the UNO end respectively.
[0009] The UA terminal and the UN terminal of the electronic transformer test circuit are respectively connected to the UA terminal and the UN terminal of the relay protection tester, and the UAO terminal and the UNO terminal of the electronic transformer test circuit are respectively connected to the output terminal of the electronic transformer.
[0010] The transformation ratio of the current type voltage transformer PT1 is 2000:2000, and the ratio of the resistor R2 and the adjustable resistor R4 is 100:1.
[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) It is low-cost and can be used in conjunction with conventional relay protection instruments, without the need to purchase test equipment with small signal output; (2) It has an overvoltage protection function. When the output voltage of the equipment is too high, it can automatically switch and prompt overvoltage to prevent the protection or instrumentation on the high-voltage cabinet from being burned out; (3) It does not require an external power supply and is easy and convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 This is a circuit diagram of the electronic transformer test module involved in Example 1. DETAILED DESCRIPTION
[0013] In order to more clearly illustrate the content of the utility model, the utility model is further described below in conjunction with the accompanying drawings and specific embodiments.
[0014] Example 1
[0015] For ease of use, this embodiment designs 4 groups of voltage input and output, corresponding to ABC three-phase voltages and zero-sequence voltage respectively. The design principles of the three-phase voltage and zero-sequence are the same, and the following description only focuses on one-phase voltage.
[0016] The utility model relates to an electronic transformer test circuit, comprising an overvoltage protection alarm circuit 1, a voltage conversion circuit 2 and a passive first-order filter circuit 3 which are connected in sequence. The overvoltage protection alarm circuit 1 is used to ensure that the input voltage to the voltage conversion circuit 2 does not exceed a set value (such as 1.5 times the rated voltage), and the voltage conversion circuit 2 is used to convert the input large voltage into a small voltage suitable for electronic transformer measurement; the passive first-order filter circuit 3 is used to filter out high-frequency noise or electromagnetic interference.
[0017] Specifically, the overvoltage protection alarm circuit 1 includes a rectifier bridge B, a resistor R1, a capacitor C1, a diode D1, a relay K1, a resistor R3 and an LED lamp LED1; the voltage conversion circuit 2 includes a resistor R2, a voltage transformer PT1 and an adjustable resistor R4; the passive first-order filter circuit 3 includes a resistor R5 and a capacitor C2;
[0018] The UA terminal (A phase input in the three-phase) is respectively connected to the second terminal of the rectifier bridge B and the second pin (contact) of the relay K1, the UN terminal (neutral line in the three-phase) is respectively connected to the first terminal of the rectifier bridge B, one end of the LED lamp LED1 and the fourth pin of the voltage transformer PT1, the third terminal of the rectifier bridge B is connected to one end of the resistor R1, the other end of the resistor R1 is respectively connected to one end of the capacitor C1, the cathode of the diode D1 and the first pin (control coil) of the relay K1, the fourth terminal of the rectifier bridge B is respectively connected to the other end of the capacitor C1, the anode of the diode D1 and the third pin (control coil) of the relay K1, the relay K1 The 4th pin (normally open switch) is connected to the other end of the LED lamp LED1 through the resistor R3, the 6th pin (normally closed switch) of the relay K1 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the 3rd pin of the voltage transformer PT1, the 1st pin of the voltage transformer PT1 is respectively connected to one end of the adjustable resistor R4 and one end of the resistor R5, the other end of the resistor R5 is respectively connected to one end of the capacitor C2 and the UAO end (the output positive pole of the A phase after the test module), the 2nd pin of the voltage transformer PT1 is respectively connected to the other end of the adjustable resistor R4, the other end of the capacitor C2 and the UNO end (the output negative pole after the test module).
[0019] The UA terminal and UN terminal of the electronic transformer test circuit are respectively connected to the UA terminal and UN terminal of the relay tester, and the UAO terminal and UNO terminal of the electronic transformer test circuit are respectively connected to the output terminal of the electronic transformer. By adding the electronic transformer test circuit between the electronic transformer and the relay tester, the high voltage output by the relay tester is reduced to a low voltage that can be used by the electronic transformer, thereby improving the measurement accuracy of the electronic transformer. The total power consumption of the overvoltage protection alarm circuit 1, the voltage conversion circuit 2 and the passive first-order filter circuit 3 does not exceed 2VA, and the voltage output capacity of the relay tester is generally above 30VA, which can fully meet the needs of the electronic transformer test circuit. Therefore, the device does not need an external power supply, and only needs to take power from the output of the relay tester to meet the working requirements.
[0020] The resistor R3 and LED1 form an overvoltage alarm circuit.
[0021] The transformation ratio of the current type voltage transformer PT1 is 2000:2000. By adjusting the resistance value of the adjustable resistor R4, the ratio of the resistor R2 to the adjustable resistor R4 can be 100:1.
[0022] The specific working process of an electronic transformer test circuit involved in the utility model is as follows:
[0023] (1) The AC input UA is converted into a DC signal after passing through the rectifier bridge B and the capacitor C1. The resistor R1 is a current limiting resistor. By setting the value of R1 reasonably, when the input is within 1.5 times the rated voltage, the second pin (contact) of the relay K1 contacts the sixth pin (normally closed switch). At this time, the relay K1 is in the default normally closed state, and the AC signal can flow into the voltage conversion circuit 2. When the input voltage exceeds 1.5 times the rated voltage, K1 acts, and the second pin (contact) of the relay K1 contacts the fourth pin (normally open switch). At this time, the K1 contact switches to pin 4, and the AC input cannot flow into the voltage conversion circuit 2. Through the resistor R3, LED1 forms a loop, and the LED1 lights up, indicating that there is an overvoltage. The measurement and collection device on the high-voltage cabinet can collect up to 1.5 times the rated voltage. The circuit can cut off the input and light up the indicator LED1 to indicate an overvoltage when the rated input voltage exceeds 1.5 times.
[0024] (2) The AC signal flows into the voltage conversion circuit 2, and the current-type voltage transformer PT1 reduces the input higher rated voltage to a lower voltage that can meet the measurement needs of the electronic transformer. For example, the transformation ratio of the current-type voltage transformer PT1 is 2000:2000. According to the transformer conversion formula, it can be deduced that the primary-secondary transformation ratio of the current-type voltage transformer PT1 is R2:R4. The input rated voltage is set to 100V, and the output rated voltage is set to 1V. It only needs to set R2:R4 to 100:1. R4 is set to an adjustable resistor. The output voltage can be calibrated by adjusting R4 during factory testing.
[0025] (3) The input lower voltage is filtered out by a first-order passive filter circuit to remove high-frequency noise or electromagnetic interference. The first-order passive filter circuit is a first-order RC low-pass filter circuit with a cut-off frequency of f=1 / (2πRC). Common high-frequency noise and electromagnetic interference frequencies are generally above 5KHz. When the cut-off frequency is set to 5KHz, the amplitude of the 50Hz signal is affected by 0.07‰, which is far lower than the output accuracy requirement of 2‰.
Claims
1. An electronic transformer test circuit, characterized in that: It includes an overvoltage protection alarm circuit, a voltage conversion circuit and a passive first-order filter circuit connected in sequence. The overvoltage protection alarm circuit is used to ensure that the input voltage to the voltage conversion circuit does not exceed the set value. The voltage conversion circuit is used to convert the input large voltage into a small voltage suitable for measurement by an electronic transformer; the passive first-order filter circuit is used to filter out high-frequency noise or electromagnetic interference.
2. The electronic transformer test circuit according to claim 1, characterized in that: The overvoltage protection alarm circuit includes a rectifier bridge B, a resistor R1, a capacitor C1, a diode D1, a relay K1, a resistor R3 and an LED lamp LED1; the voltage conversion circuit includes a resistor R2, a voltage transformer PT1 and an adjustable resistor R4; the passive first-order filter circuit includes a resistor R5 and a capacitor C2; The UA end is connected to the second end of the rectifier bridge B and the second pin of the relay K1 respectively, the UN end is connected to the first end of the rectifier bridge B, one end of the LED lamp LED1 and the fourth pin of the voltage transformer PT1 respectively, the third end of the rectifier bridge B is connected to one end of the resistor R1, the other end of the resistor R1 is connected to one end of the capacitor C1, the cathode of the diode D1 and the first pin of the relay K1 respectively, the fourth end of the rectifier bridge B is connected to the other end of the capacitor C1, the anode of the diode D1 and the third pin of the relay K1 respectively, the fourth pin of the relay K1 is connected to the other end of the LED lamp LED1 through the resistor R3, the sixth pin of the relay K1 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the third pin of the voltage transformer PT1, the first pin of the voltage transformer PT1 is connected to one end of the adjustable resistor R4 and one end of the resistor R5 respectively, the other end of the resistor R5 is connected to one end of the capacitor C2 and the UAO end respectively, and the second pin of the voltage transformer PT1 is connected to the other end of the adjustable resistor R4, the other end of the capacitor C2 and the UNO end respectively.
3. The electronic transformer test circuit according to claim 2, characterized in that: The UA terminal and the UN terminal of the electronic transformer test circuit are respectively connected to the UA terminal and the UN terminal of the relay protection tester, and the UAO terminal and the UNO terminal of the electronic transformer test circuit are respectively connected to the output terminal of the electronic transformer.
4. The electronic transformer test circuit according to claim 3, characterized in that: The transformation ratio of the current type voltage transformer PT1 is 2000:2000, and the ratio of the resistor R2 and the adjustable resistor R4 is 100:1.