An electronic passive overcurrent tripping relay

Abstract

The present invention provides an electronic passive overcurrent tripping relay, which relates to the field of high-voltage power grid relay protection and solves the problem of short-circuit protection failure caused by various reasons in the prior art. The tripping relay is provided with an overcurrent tripping control circuit, which is isolated and connected to the overcurrent tripping main circuit through the control relay and the sampling power transformer. In the overcurrent tripping main circuit, the current transformer, the normally closed node of the control relay, and the primary side coil of the sampling power transformer are connected in series to form a loop structure, and the current tripping electromagnet is connected in parallel with the normally closed node of the control relay. When the external power grid is short-circuited, the current transformer generates a corresponding short-circuit current, and the sampling power transformer feeds back the generation of the short-circuit current. The overcurrent tripping control circuit activates or resets the current tripping electromagnet through the control relay, so that the corresponding high-voltage switch is tripped when the external power grid is short-circuited. The present invention utilizes the energy of the short-circuit current itself to drive the protection tripping, thereby greatly improving the protection reliability.

Description

Technical Field

[0001] The present invention relates to the field of high-voltage power grid relay protection and electronic technology, is applied to the tripping process of a circuit breaker, and particularly relates to an electronic passive overcurrent tripping relay. Background Art

[0002] High-voltage circuit breakers are crucial components in power systems, controlling and protecting their normal operation. They not only effectively cut and close circuits but also quickly isolate fault areas in the event of short circuits or other abnormalities, ensuring the safety and reliability of the entire power grid.

[0003] To achieve these functions, a microcomputer protection system is typically used to monitor and control the operation of high-voltage circuit breakers. By monitoring changes in parameters such as voltage and current, the microcomputer protection system triggers appropriate protective actions upon detecting an abnormality, such as tripping the circuit breaker via a voltage-tripping electromagnet. However, this voltage-tripping electromagnet-based tripping method has certain limitations, including but not limited to the following:

[0004] 1. Auxiliary power supply reliability: Traditional microcomputer protection systems require an external power supply to power the voltage trip electromagnet. If the auxiliary power supply is unstable or fails, the circuit breaker may not trip in time, affecting the safe operation of the system.

[0005] 2. Inadequate equipment maintenance: In many remote or small power distribution stations, due to limited financial and technical resources, necessary maintenance is often lacking, which reduces the reliability of equipment. This may cause the protection system to malfunction in an emergency.

[0006] 3. Protection failure: In practice, it is found that protection failure often occurs at the power distribution terminal on the user side. The main reasons are failure of the protection device itself, problems with the control power supply, interruption of the control circuit, etc.

[0007] 4. Delayed response of the microcomputer protection system: For terminal stations using AC power, when power is suddenly restored, the microcomputer protection system requires time to start up and stabilize. This process may result in the system failing to respond in a timely manner when protection is most needed.

[0008] 5. Risk of false operation: In addition to protection failure, the microcomputer protection system may also have the risk of false operation. For example, it may be affected by interference, component aging or damage, etc., which may cause the system to mistakenly trigger the protection action.

[0009] It can be seen that although the existing high-voltage circuit breakers and their protection systems have met the basic needs of power systems to a certain extent, they still have many shortcomings in actual application. Therefore, it is necessary to develop a new protection technology to improve the reliability and safety of high-voltage circuit breakers under various conditions. Summary of the Invention

[0010] Based on the current status of the background technology, the purpose of the present invention is to solve the problem of short-circuit protection failure caused by various reasons, which are specifically reflected in the inaccurate starting value of the ordinary current tripping electromagnet, false operation caused by too small a starting current, insufficient small current starting force, false operation caused by inrush current, remote short-circuit skipping, and long-term heating of the current relay coil due to current passing through it. Therefore, an electronic passive overcurrent tripping relay is proposed.

[0011] The present invention utilizes the characteristics of short-circuit current tripping and adopts innovative electronic circuit technology, using the energy of the short-circuit current itself to drive the protection tripping; at the same time, the present invention is easy to cooperate with microcomputer protection to provide dual protection against short circuits, retaining the advantages of microcomputer protection and serving as a second independent passive tripping circuit for microcomputer overcurrent protection, thereby greatly improving protection reliability.

[0012] The present invention adopts the following technical solutions to achieve the purpose:

[0013] An electronic passive overcurrent tripping relay, wherein the tripping relay has an overcurrent tripping control circuit inside, and the overcurrent tripping control circuit is isolated and connected to the overcurrent tripping main circuit outside the tripping relay through the control relay and the sampling power transformer;

[0014] The overcurrent trip main circuit includes a current transformer and a current trip electromagnet. The current transformer, the normally closed node of the control relay, and the primary coil of the sampling power transformer are connected in series to form a loop structure. The current trip electromagnet is connected in parallel with the normally closed node of the control relay.

[0015] The overcurrent tripping control circuit includes a sampling power transformer, a sampling power circuit, a comparison circuit, an inverse time circuit, a quick-break circuit, a hysteresis holding circuit, a drive circuit and a control relay; the secondary side coil of the sampling power transformer is connected to the sampling power circuit, the comparison circuit, the inverse time circuit, the quick-break circuit, the hysteresis holding circuit, the drive circuit and the control relay in sequence;

[0016] The current transformer is used to generate the corresponding short-circuit current in the overcurrent tripping main circuit when the external power grid is short-circuited. The sampling power transformer is used to feed back the generation of the short-circuit current to the overcurrent tripping control circuit; the overcurrent tripping control circuit is used to change the bypass state of the short-circuit current in the overcurrent tripping main circuit by controlling the relay, so that the current tripping electromagnet is actuated or reset, and the corresponding high-voltage switch is tripped when the external power grid is short-circuited through the action of the current tripping electromagnet.

[0017] Preferably, the sampling power circuit in the overcurrent tripping control circuit is also connected to a gear circuit, which is used to increase the tripping action threshold of the tripping relay. The gear change can be achieved by direct short-circuiting or by control of the microcomputer protection system; the direct short-circuiting of the gear is used in very few places where the inrush current is extremely large to prevent false operation; the gear circuit is also used in conjunction with the microcomputer protection system to make the microcomputer protection system more sensitive, which is the main protection, and the overcurrent tripping relay is the backup protection, which is the failure protection of the microcomputer protection system.

[0018] Preferably, the power sources of the overcurrent trip main circuit and the overcurrent trip control circuit are both electric energy generated by the current transformer based on the external power grid, and can be independent of any other auxiliary power supply, thereby ensuring that when there is no power supply, such as a short circuit fault, the current trip electromagnet can be used to achieve tripping and ensure the safety of the distribution network.

[0019] The working power supply of the gear circuit, comparison circuit, inverse time circuit, quick-break circuit, hysteresis holding circuit, drive circuit and control relay in the overcurrent tripping control circuit is provided by the sampling power circuit in proportion from the overcurrent tripping main circuit through the sampling power transformer.

[0020] The microcomputer protection system has a separate control power supply and operating power supply. The current of the microcomputer protection system is connected in series to the overcurrent trip main circuit. The microcomputer protection system and the overcurrent trip relay are isolated and connected via a gear circuit. Apart from these two points, there is no other connection between the microcomputer protection and the overcurrent trip relay.

[0021] The control relay is a normally closed relay. Under normal circumstances, the current transformer outputs current, passing through the normally closed node of the control relay and then through the sampling current transformer to form a circuit. Because the current trip electromagnet is bypassed and short-circuited by the normally closed node of the control relay, it will not operate under normal circumstances.

[0022] The current transformer outputs AC current to the sampling power transformer, which is a special transformer designed with fixed parameters. Within the maximum inrush current range, the sampling power transformer isolates and transforms the output AC signal with power and voltage proportional to the current to the sampling power circuit. The sampling power circuit obtains the voltage signal and working power through linear transformation and uses them in the overcurrent tripping control circuit.

[0023] The voltage signal is compared with a reference (corresponding to the current threshold) by a comparator circuit. The comparison result is sent to the drive circuit, which amplifies the current and drives the control relay to open its normally closed node. The entire current in the overcurrent trip main circuit flows through the current trip electromagnet, which activates and removes the closing support of the high-voltage switch. The spring force causes the operating mechanism to open. This is the main operating principle of the electronic passive overcurrent trip relay.

[0024] When the current flowing through the sampling power transformer is greater than the maximum inrush current, the sampling power transformer will gradually saturate, limiting the voltage and protecting the electronic components; at the same time, it limits the capacitor charging current to prevent the capacitor voltage from always being higher than the reference voltage and locking out the re-operation.

[0025] Furthermore, if the electronic passive overcurrent tripping relay needs to be used in conjunction with microcomputer protection, when the gear position is used to control the current tripping, the microcomputer protection needs to output a passive node signal, which can be a photoelectric isolation output or a relay node output; its mechanism is that the gear position will not be increased when the microcomputer protection is in any abnormal state or when the overcurrent protection is activated (that is, the node output is in the disconnected state). The corresponding effect is that when the microcomputer protection is working normally, the microcomputer protection is the main one. When the microcomputer protection fails, the electronic passive overcurrent tripping relay automatically realizes the short-circuit protection tripping. That is, the tripping relay and the microcomputer protection constitute dual protection, and it is also the second tripping output of the microcomputer overcurrent protection to prevent the microcomputer protection tripping circuit from failing. The current tripping is output with a delay of less than 0.2s after the gear position is restored. The microcomputer protection can thus judge whether its own voltage tripping has failed based on the time when the current disappears.

[0026] Furthermore, the comparison circuit in the overcurrent tripping control circuit is used to compare the voltage corresponding to the electric energy extracted by the sampling power circuit from the overcurrent tripping main circuit with the reference voltage of the preset action current in the tripping relay, and use the comparison result as the basis for the action of the inverse time circuit, quick-break circuit, hysteresis holding circuit, drive circuit and control relay.

[0027] Furthermore, the inverse time circuit in the overcurrent tripping control circuit adopts a resistor current limiting capacitor charging circuit; the inverse time circuit is used to reflect the short-circuit current generated by the current transformer when the external power grid is short-circuited through a voltage delay method, and then delay the action output of the control relay, so that the tripping action time of the tripping relay and the short-circuit current present an inverse time relationship; the inverse time circuit can avoid normal inrush current and avoid the time for the remote short-circuit lower level to cut off the short-circuit point, thereby preventing false operation.

[0028] Furthermore, the quick-break circuit in the overcurrent tripping control circuit is used to stop the relay protection selectivity requirement of the inverse time circuit when the short-circuit current is greater than the preset maximum inrush current, directly control the comparison circuit, realize the flipping of the drive circuit, and make the tripping relay perform the tripping action to achieve the purpose of quick-break protection.

[0029] Furthermore, the hysteresis holding circuit in the overcurrent tripping control circuit adopts a positive feedback circuit to delay the impact of the comparison result after the large amount of energy consumed by driving the control relay, thereby allowing the control relay to maintain the action output for a certain period of time; the hysteresis holding circuit is used to maintain the action time of the control relay when the comparison circuit is actuated to flip the drive circuit, so that the current tripping electromagnet completes the action and prevents refusal to operate due to insufficient tripping kinetic energy.

[0030] Furthermore, the comparison circuit, inverse time circuit, hysteresis holding circuit, drive circuit and control relay in the overcurrent tripping control circuit together constitute a heavy-duty control unit; the heavy-duty control unit is used to start the charging capacitor and additional discharge circuit at the same time when the tripping relay performs the tripping action because the driving control relay consumes more energy, and the sampling power transformer enters the saturation zone when the short-circuit current is large. The superposition effect causes the voltage used for comparison to gradually drop below the holding voltage, and the comparison result is reversed, causing the control relay to stop operating. However, when the short-circuit current is still not cut off, the control relay's action is repeated, thereby causing the current tripping electromagnet to repeatedly operate to impact the tripping mechanism.

[0031] The heavy-duty control unit is also used to repeatedly operate the current tripping electromagnet to impact the tripping mechanism when the short-circuit current is lower than a specific threshold and the tripping impact force is insufficient, thereby achieving the tripping of the corresponding high-voltage switch, which is beneficial to prevent mechanical obstruction and improve the reliability of overcurrent protection tripping; the relationship between the repeated action time period of the heavy-duty control unit and the short-circuit current is an inverse time relationship.

[0032] Furthermore, the driving circuit in the overcurrent tripping control circuit is a nonlinear working circuit that flips based on a threshold value; the input signal of the driving circuit is the comparison result output by the comparison circuit, and the action control of the control relay is realized based on the amplification of the current in the working power supply; the driving circuit is also configured with an action indication circuit, and the action indication circuit is an LED indicator light connected in series in the driving circuit, and the lighting state of the LED indicator light corresponds to the action state of the control relay.

[0033] Furthermore, the control relay in the overcurrent trip control circuit is used to operate under the flip drive of the drive circuit according to the comparison result of the comparison circuit, disconnect its own normally closed node, and allow the short-circuit current of the overcurrent trip main circuit to flow through the current trip electromagnet. The current trip electromagnet will then operate and impact the tripping mechanism of the high-voltage switch, causing the high-voltage switch to complete tripping when the external power grid is short-circuited, thereby cutting off the short-circuit point of the external power grid.

[0034] Furthermore, the operating current of the current tripping electromagnet is calculated based on actual needs. Its operating current I is determined by the sampling transformer ratio, the charge-discharge comprehensive coefficient N, the sampling resistor value R, and the reference voltage V, where I = NV / R. Typically, the reference voltage V is fixed, and the needs of different operating values ​​can be met by changing the sampling resistor value R or the charge-discharge comprehensive coefficient N. The comprehensive coefficient N is primarily determined by the transformer ratio, the charge current limiting resistor, and the discharge resistor value. The transformer ratio setting also takes into account factors such as the transformer saturation zone and drive capability, so it is generally fixed. The charge current limiting resistor is closely related to the operating time and can only be selected differently in relays of different specifications. Therefore, gear control is generally achieved by changing the discharge resistor, and its impact on other parameters is relatively small.

[0035] Furthermore, the time from the moment the current suddenly rises from zero to the short-circuit current until the current trip electromagnet operates has an integral inverse time relationship with the short-circuit current. The overcurrent trip control circuit is a capacitor charging circuit with resistor current limiting. This results in a voltage delay reflecting the current transformer current, thus delaying the control relay output. This helps avoid normal inrush current and lower-level short-circuit tripping, meeting the relay protection selectivity requirements.

[0036] Furthermore, when the short-circuit current is greater than the maximum inrush current, there is no longer a requirement for relay protection selectivity. The short-circuit power pulse voltage is used to bypass the charging circuit to quickly control the action of the comparison circuit and flip the drive circuit to achieve a rapid protection action effect, meeting the relay protection speed requirements.

[0037] For the relevant functions of heavy-duty control, the relationship between the repetitive action time period and the short-circuit current also presents an integral inverse time relationship.

[0038] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows:

[0039] The electronic passive overcurrent trip relay of this invention provides short-circuit protection without the need for an external operating or control power supply. This innovative design utilizes purely electronic circuitry, eliminating the startup delay associated with microcomputer-based protection and ensuring an immediate response synchronized with overcurrent events, resulting in high reliability and rapid operation.

[0040] Before actuation, the electronic circuitry operates stably and consumes minimal energy, ensuring precise threshold setting and improving precision. The inverse time characteristic allows the present invention to determine based on inrush current and downstream short-circuit conditions, lowering the threshold to enhance sensitivity while ensuring rapid actuation in severe short-circuit conditions.

[0041] When a short circuit is detected, the present invention can quickly cut off the fault point to reduce damage. The design of the holding circuit avoids interference during the operation process and prevents multiple unnecessary tripping actions.

[0042] In actual short circuit situations, single tripping is successful in most short circuit situations. Under extreme conditions, the re-operation circuit further improves the tripping success rate.

[0043] This invention automatically and orderly executes hold, re-actuate, inverse time, and quick-break functions based on protection requirements, ensuring rapid action while maintaining strong anti-interference capabilities. Compared to traditional microcomputer protection, this invention significantly simplifies operating conditions, enhances environmental adaptability, and reduces failure rates.

[0044] The tripping electromagnet is controlled only in the bypass state, which does not cause the current loop to open, effectively avoiding secondary disasters that may be caused by the relay control process. At the same time, the present invention is easy to use with the microcomputer protection system, providing dual protection and significantly improving the overall reliability of the system.

[0045] By utilizing the energy of the short-circuit current to clear the fault, the present invention is not only environmentally friendly but also safe and reliable. High-voltage switches equipped with the present invention can provide reliable short-circuit protection under all conditions, resolving the issue of short-circuit protection failure and significantly improving the safety and stability of the power grid.

[0046] This invention provides reliable short-circuit protection for both complex and simplified distribution systems, and is particularly suitable for terminal distribution sites that do not require additional power supplies or microcomputer protection. Its widespread application will significantly enhance the overall safety, stability, and reliability of the power grid, reduce the scope of power outages, accelerate fault recovery, and ultimately improve power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the structure of the electronic passive overcurrent tripping relay of the present invention;

[0048] Figure 2 This is a schematic diagram of the structure of the trip relay in conjunction with the microcomputer protection system of the present invention;

[0049] Figure 3 The electrical schematic diagram of the electronic passive overcurrent tripping relay of the present invention;

[0050] Figure 4 This is a current inverse time action curve diagram of an example of the present invention;

[0051] Figure 5 This is a time dynamic curve diagram of the power supply voltage according to an example of the present invention. DETAILED DESCRIPTION

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0053] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0054] Example

[0055] like Figure 1 As shown, the electronic passive overcurrent trip relay of this embodiment has an overcurrent trip control circuit inside the trip relay. The overcurrent trip control circuit is isolated and connected to the overcurrent trip main circuit outside the trip relay through the control relay and the sampling power transformer;

[0056] The overcurrent trip main circuit includes a current transformer and a current trip electromagnet. The current transformer, the normally closed node of the control relay, and the primary coil of the sampling power transformer are connected in series to form a loop structure. The current trip electromagnet is connected in parallel with the normally closed node of the control relay.

[0057] The overcurrent tripping control circuit includes a sampling power transformer, a sampling power circuit, a comparison circuit, an inverse time circuit, a quick-break circuit, a hysteresis holding circuit, a drive circuit and a control relay; the secondary side coil of the sampling power transformer is connected to the sampling power circuit, the comparison circuit, the inverse time circuit, the quick-break circuit, the hysteresis holding circuit, the drive circuit and the control relay in sequence;

[0058] The current transformer is used to generate the corresponding short-circuit current in the overcurrent tripping main circuit when the external power grid is short-circuited. The sampling power transformer is used to feed back the generation of the short-circuit current to the overcurrent tripping control circuit; the overcurrent tripping control circuit is used to change the bypass state of the short-circuit current in the overcurrent tripping main circuit by controlling the relay, so that the current tripping electromagnet is actuated or reset, and the corresponding high-voltage switch is tripped when the external power grid is short-circuited through the action of the current tripping electromagnet.

[0059] like Figure 2As shown, the sampling power circuit in the overcurrent tripping control circuit is also connected to a gear circuit, which is used to increase the tripping action threshold of the tripping relay. The gear change can be achieved by direct short-circuiting or by control of the microcomputer protection system; the direct short-circuiting of the gear is used in very few places where the inrush current is extremely large to prevent false operation; the gear circuit is also used in conjunction with the microcomputer protection system to make the microcomputer protection system more sensitive. It is the main protection, and the overcurrent tripping relay is the backup protection. It is the failure protection of the microcomputer protection system.

[0060] In this embodiment, the power sources for the overcurrent trip main circuit and the overcurrent trip control circuit are both electric energy generated by the current transformer based on the external power grid; the working power sources for the gear circuit, comparison circuit, inverse time circuit, quick-break circuit, hysteresis holding circuit, drive circuit, and control relay in the overcurrent trip control circuit are all proportionally drawn from the overcurrent trip main circuit by the sampling power circuit through the sampling power transformer;

[0061] The microcomputer protection system has a separately configured control power supply and working power supply. The current of the microcomputer protection system is connected in series to the overcurrent tripping main circuit.

[0062] Combine Figure 3 The electrical principle diagram is given in this embodiment. This embodiment introduces a detailed description of an electrical form of the trip relay. The power supply of the overcurrent trip control circuit is Figure 3 The sampling power transformer CY1 is taken from the overcurrent trip main circuit, and then the DC is rectified by the resistor R1 and BR1 rectifier unit of the sampling power circuit. The first path is used to quickly store energy through the diode V1 and capacitor C3 to provide relay drive power; the second path is used to charge the capacitor C1 through the resistor R2, and the electric energy on the capacitor C1 is discharged through the resistor R3. The voltage on the capacitor C1 reflects the size of the transformer current with a delay. When the voltage on the capacitor C1 exceeds the conduction voltage of the Zener diode V5, the Zener diode V5 will be turned on, further driving the transistor Q2 to turn on and flip; when the transformer current is large enough, the rectifier output voltage of the BR1 rectifier unit is greater than the breakdown voltage of the diode V4, and the third path is used to quickly charge the capacitor C5 through the diode V4; further, when the transformer current is greater than the inrush current, the voltage on the capacitor C5 will be greater than the reference conduction voltage provided by the diode V5, thus achieving a fast action effect.

[0063] The inverse time control circuit is a capacitor charging circuit with resistor current limiting, mainly composed of Figure 3 The resistors R2, R3 and capacitor C1 are connected, that is, the voltage on capacitor C1 is determined by the charging current flowing through resistor R2 and the discharge speed of resistor R3. As a result, the voltage delay reflects the magnitude of the main circuit current I, thereby delaying the output of the control relay. Select appropriate values ​​of resistors R2, R3 and capacitor C1 to obtain the following: Figure 4The appropriate inverse time curve shown can avoid both normal inrush current and the time required for the downstream short-circuit cutoff point of the remote short-circuit to prevent false operation.

[0064] The comparison circuit compares the reference voltage with the aforementioned power supply voltage, mainly composed of Figure 3 The circuit is composed of diodes V3, V5, capacitor C5, resistors R6, R7, transistor Q2, and capacitor C7, wherein the sum of the conduction voltages of diodes V3, V5, and transistor Q2 constitutes a reference voltage, which corresponds to the action threshold of the main loop current. The parameter in this embodiment is 7.71A.

[0065] When the aforementioned power supply voltage is higher than the reference voltage, transistor Q2 is turned on, and through the positive feedback acceleration drive circuit, it drives the control relay to operate, thereby achieving the purpose of protection tripping; capacitor C5 is used for anti-interference filtering and providing the shortest holding time current; capacitor C7 is used for anti-interference filtering.

[0066] According to the principles of the aforementioned sampling power circuit and comparison circuit, the operating current of the tripping relay is calculated according to actual needs and determined by selecting the corresponding sampling resistors R1, R2, and R3 parameters. Assuming that the sampling power transformer ratio and the charge and discharge parameters constitute the comprehensive coefficient N, the sampling resistor resistance R, and the reference voltage V, the operating current of the overcurrent tripping relay I = NV / R. Usually V is fixed, and the needs of different operating values ​​can be met by changing the sampling resistor resistance R or the charge and discharge comprehensive coefficient N. The comprehensive coefficient N is mainly determined by the transformer ratio, the charging current limiting resistor R2, and the discharge resistor R3. The transformer ratio setting must also comprehensively consider factors such as the transformer saturation area and driving capability. Therefore, it is generally fixed. The charging current limiting resistor is closely related to the action time and can only be selected differently in relays of different specifications. Therefore, in principle, the gear control is achieved by changing the discharge resistor, and its impact on other parameters is relatively small. The operating current of the overcurrent tripping relay in this embodiment is 7.71A, which is generally about 2 times the rated load current and 1.5 times the 5A starting current of the current tripping electromagnet. For most short-circuit currents, the reliability coefficient is above 2.0.

[0067] The hysteresis holding circuit is mainly composed of Figure 3 The circuit is composed of resistor R8, transistor Q1, and resistor R5. When transistor Q2 is turned on and its collector voltage becomes low, a voltage difference is formed between the emitter and base of transistor Q1, and transistor Q1 is also turned on. In this way, a current is superimposed on the base of transistor Q2, prompting transistor Q2 to quickly saturate and turn on, and tripping action. In this way, when the aforementioned power-on voltage drops rapidly due to the discharge current of capacitor C1 being greater than the power-on charging current, capacitor C5 provides a period of positive feedback holding current through resistor R8, and transistor Q2 can also remain on for a period of time. See the holding and reset process for details. Figure 5The magnitude of the main circuit current I is different, and the action lag time determined by the current inverse time is different, but the holding time after the action is close.

[0068] The heavy-duty control unit is composed of a comparison circuit, an inverse time circuit, a hysteresis holding circuit, a drive circuit and a control relay. In the initial stage of transistor Q2's conduction, capacitors C1 and C5 provide holding current to ensure reliable transistor Q2 retention. As the relay operates, a larger current is required. Due to the internal impedance of the sampling transformer, the rectifier output voltage of the BR1 rectifier unit drops. In addition, as current flows through the electromagnet, the electromagnet impedance also slightly reduces the main circuit current, further reducing the rectifier output voltage of the BR1 rectifier unit. To ensure reliable restart, when the drive control relay operates, a discharge circuit for capacitor C1 is added through resistor R10 and diode V2. These factors combine to reduce the voltage on capacitor C1 to below the minimum holding voltage. Capacitor C5 will only discharge without charging. The positive feedback current through transistor Q1 gradually decreases, and eventually the base current of transistor Q2 gradually decreases, causing its collector voltage to rise. Transistor Q1 begins to turn off, and the base current of transistor Q2 further decreases. This positive feedback causes transistor Q2 to quickly turn off, and the relay stops operating and resets.

[0069] If the tripping fails at this time and the main circuit current I is maintained, the process of inverse time charging, comparison, transistor Q2 conduction, maintenance, and relay driving is repeated, forming a heavy trip, controlling the relay to operate repeatedly, so that the current tripping electromagnet repeatedly impacts the tripping mechanism. When the short-circuit current is relatively small, it is beneficial to tripping and also helps to prevent refusal to operate caused by mechanical resistance.

[0070] The gear circuit provides an external way to increase the action threshold of the electronic passive overcurrent trip relay. Figure 3 It is composed of resistor R9 and two terminals. The principle is to increase the discharge resistance of the integral capacitor. Therefore, the external gear control method is to provide a passive node. Optoelectronic isolation output can also be used. When closed, the action threshold is increased by about 40%, and when disconnected, it is the basic gear.

[0071] When the trip relay in this embodiment is used in conjunction with microcomputer protection, the position control node closes when the microcomputer protection is operating normally, raising the trip relay's operating threshold by approximately 40% and delaying its actuation time. This effectively establishes the microcomputer protection as primary protection, with the trip relay serving as backup. If the microcomputer protection triggers an overcurrent, the position control node immediately opens. When the trip relay is used independently and malfunctions due to inrush current, the position input terminals can be short-circuited to raise the actuation threshold by approximately 40%.

[0072] In this embodiment, an action indication circuit is connected in series with the driving circuit, that is, an LED indicator light represented by the light emitting diode D1, which lights up synchronously with the tripping action to facilitate test observation.

[0073] The driving circuit is Figure 3 Chip U1, resistor R4, and LED D1 are shown. Chip U1 is an optocoupler driver chip with an output current of up to 300mA, an isolation withstand voltage of up to 3kV, and a withstand voltage of up to 300V between the output terminals when closed. A freewheeling diode is configured in reverse order, making it suitable for inductive loads. The nonlinear conduction characteristics of chip U1 and LED D1 also significantly contribute to the aforementioned re-operation effect, making the operating hysteresis parameters more reasonable.

[0074] The control relay is Figure 3 Relay J1 has a rated coil voltage of DC5V, a coil operating current of 56mA, a minimum holding current of 8mA, is a normally closed node relay, has a contact rated load of 16A / AC250V, and a maximum switching power of 2000VA.

[0075] The working process of the electronic passive overcurrent tripping relay of this embodiment can be summarized as follows: the current transformer outputs AC current to the sampling power transformer, which is isolated and transformed by the sampling power transformer to output an AC signal with power and voltage proportional to the short-circuit current to the sampling power circuit, which is linearly converted into a voltage signal and a working power supply by the sampling power circuit. The working power supply is used as a working power supply for the control relay. The voltage signal is compared with a reference (representing the current threshold) by a comparison circuit, and the comparison result is sent to the drive circuit. Once the current flowing through the sampling power transformer exceeds the action threshold, the comparison circuit outputs an action signal to the control circuit and the drive circuit, which is amplified by the drive circuit to drive the control relay to act, and the normally closed node of the control relay is disconnected, so that all current flows through the tripping electromagnet coil, the tripping electromagnet is actuated, and the closing fulcrum of the circuit breaker is triggered and removed. Under the action of the spring force, the operating mechanism is opened.

[0076] for Figure 3 The electrical principle structure of the trip relay of this embodiment and its related performance parameters are introduced as follows:

[0077] Passive tripping operating current: 7.71A±0.2A;

[0078] The time from when the current rapidly rises from 0 to the short-circuit current to when the current trip electromagnet operates is in an integral inverse time relationship with the short-circuit current. For an overcurrent trip main circuit current of 8.10A, the corresponding operating time is 0.65±0.02 seconds, and for an overcurrent trip main circuit current of 22.00A, the corresponding operating time is 0.15±0.02 seconds. In the quick-break operating range, for an overcurrent trip main circuit current of 27A, the corresponding operating time is 0.07±0.01 seconds, and for an overcurrent trip main circuit current of 40A, the corresponding operating time is 0.03±0.01 seconds.

[0079] The repetitive action time period of the current tripping protection circuit is in an integral inverse time relationship with the short-circuit current. The repetitive action time period of the overcurrent tripping main circuit with a current of 8.10A is 0.48±0.10 seconds, the repetitive action time period of 16A is 0.28±0.02 seconds, and the repetitive action time period of 40A is 0.2±0.02 seconds.

[0080] If used in conjunction with microcomputer protection, the microcomputer short-circuit protection output will simultaneously disconnect the gear control, and the relay output delay is less than 0.2s. The microcomputer protection can determine whether its own voltage tripping has failed based on the current disappearance time.

[0081] According to the above mechanism, if a short circuit occurs at any time, under any conditions, or for any reason, the short-circuit current activates the control relay coil and the current trip electromagnet, ensuring fault clearance. When used in conjunction with microcomputer protection, the trip relay of this embodiment serves as a secondary tripping protection outlet for the microcomputer overcurrent protection, operating independently and independent of the power supply, thereby enhancing operational reliability.

Claims

1. An electronic passive overcurrent tripping relay, characterized in that: The trip relay has an overcurrent trip control circuit inside, and the overcurrent trip control circuit is isolated and connected to the overcurrent trip main circuit outside the trip relay through the control relay and the sampling power transformer; The overcurrent trip main circuit includes a current transformer and a current trip electromagnet. The current transformer, the normally closed node of the control relay, and the primary coil of the sampling power transformer are connected in series to form a loop structure. The current trip electromagnet is connected in parallel with the normally closed node of the control relay. The overcurrent tripping control circuit includes a sampling power transformer, a sampling power circuit, a comparison circuit, an inverse time circuit, a quick-break circuit, a hysteresis holding circuit, a drive circuit and a control relay; the secondary side coil of the sampling power transformer is connected to the sampling power circuit, the comparison circuit, the inverse time circuit, the quick-break circuit, the hysteresis holding circuit, the drive circuit and the control relay in sequence; The current transformer is used to generate a corresponding short-circuit current in the overcurrent trip main circuit when the external power grid is short-circuited. The sampling current transformer is used to feed back the generation of the short-circuit current to the overcurrent trip control circuit. The overcurrent trip control circuit is used to change the bypass state of the short-circuit current in the overcurrent trip main circuit by controlling the relay, so as to activate or reset the current trip electromagnet. The action of the current trip electromagnet causes the corresponding high-voltage switch to complete tripping when the external power grid is short-circuited. The sampling power circuit in the overcurrent tripping control circuit is also connected to a gear circuit, which is also connected to the microcomputer protection system. The gear circuit is composed of a resistor R9 and two terminals. The gear circuit is used to cooperate with the tripping relay and the microcomputer protection system to increase the tripping action threshold of the tripping relay, so that the microcomputer protection is the main protection. The quick-break circuit in the overcurrent trip control circuit is used to stop the relay protection selectivity requirement of the inverse time circuit when the short-circuit current is greater than the preset maximum inrush current, directly control the comparison circuit, realize the flipping of the drive circuit, and make the trip relay perform the tripping action; when the short-circuit current feedback from the sampling power transformer is greater than the preset maximum inrush current, the quick-break circuit makes the rectifier output voltage of the rectifier unit BR1 greater than the breakdown voltage of the diode V4, and quickly charges the capacitor C5 through the diode V4.

2. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The power supplies for the overcurrent tripping main circuit and the overcurrent tripping control circuit are both the electric energy generated by the current transformer based on the external power grid; the working power supplies for the gear circuit, comparison circuit, inverse time circuit, quick-break circuit, hysteresis holding circuit, drive circuit and control relay in the overcurrent tripping control circuit are all provided by the sampling power circuit in proportion through the sampling power transformer from the overcurrent tripping main circuit.

3. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The comparison circuit in the overcurrent tripping control circuit is used to compare the voltage corresponding to the electric energy extracted by the sampling power circuit from the overcurrent tripping main circuit with the reference voltage of the preset action current in the tripping relay, and use the comparison result as the basis for the action of the inverse time circuit, quick-break circuit, hysteresis holding circuit, drive circuit and control relay.

4. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The inverse time circuit in the overcurrent trip control circuit adopts a resistor current limiting capacitor charging circuit; the inverse time circuit is used to reflect the short-circuit current generated by the current transformer when the external power grid is short-circuited through voltage delay, thereby delaying the action output of the control relay; the inverse time circuit is also used to make the relationship between the tripping action of the tripping relay and the short-circuit current present an inverse time relationship.

5. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The hysteresis holding circuit in the overcurrent tripping control circuit adopts a positive feedback circuit; the hysteresis holding circuit is used to maintain the action time of the control relay when the comparison circuit operates to flip the drive circuit, so that the current tripping electromagnet completes the action.

6. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The comparison circuit, hysteresis holding circuit, drive circuit and control relay in the overcurrent tripping control circuit together constitute the heavy-duty control unit; The heavy-acting control unit is used to repeatedly execute the action of the control relay when the tripping relay performs the tripping action, and as the positive feedback effect of the hysteresis holding circuit decreases, causing the control relay to stop operating, but the short-circuit current is still not cut off, thereby causing the current tripping electromagnet to repeatedly operate to impact the tripping mechanism; the heavy-acting control unit is also used to repeatedly operate the current tripping electromagnet to impact the tripping mechanism when the short-circuit current is lower than the threshold value and the tripping impact force is insufficient, thereby realizing the tripping of the corresponding high-voltage switch; the relationship between the repeated action time period of the heavy-acting control unit and the short-circuit current is an inverse time relationship.

7. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The driving circuit in the overcurrent tripping control circuit is a nonlinear working circuit that flips based on a threshold value; the input signal of the driving circuit is the comparison result output by the comparison circuit, and the action control of the control relay is realized based on the amplification of the current in the working power supply; the driving circuit is also equipped with an action indication circuit, which is an LED indicator light connected in series in the driving circuit, and the lighting state of the LED indicator light corresponds to the action state of the control relay.

8. The electronic passive overcurrent trip relay according to claim 1, characterized in that: The control relay in the overcurrent trip control circuit is used to operate under the flip drive of the drive circuit according to the comparison result of the comparison circuit, disconnect its own normally closed node, and make the short-circuit current of the overcurrent trip main circuit flow through the current trip electromagnet. The current trip electromagnet will then operate and impact the tripping mechanism of the high-voltage switch, so that the high-voltage switch will complete tripping when the external power grid is short-circuited, and the short-circuit point of the external power grid will be cut off.

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