PT protector suitable for secondary resonance elimination device

Abstract

The invention discloses a PT protector suitable for a secondary resonance elimination device, and relates to the technical field of power system protection. The PT protector is connected in series between a PT opening secondary winding and a secondary resonance elimination device, and comprises a protection resistor, an alternating current starting type relay, a time relay and an intermediate relay, and all the parts work cooperatively, so that the normal action and the short circuit fault of the secondary resonance elimination device are accurately distinguished, and mistaken cut-off is avoided; and when the working power supply loses power, the current can still be limited through the protection resistor, so that the problem of short-circuit protection deficiency of the secondary winding of the PT opening is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system protection, and in particular to a PT protector suitable for secondary harmonic elimination device. BACKGROUND

[0002] In the power system, secondary harmonic elimination device is often used to prevent overvoltage hazards caused by ferroresonance. The device connects a small resistance in parallel with the PT open secondary winding through a high-frequency switch to break the system resonance condition, thereby achieving harmonic elimination and reducing overvoltage. However, when the high-frequency switch fails (such as contact burning and sticking, breakdown), it will cause the PT open secondary winding to be connected with the small resistance for a long time, resulting in a short circuit of the PT open secondary circuit.

[0003] In the prior art, the protection of the PT mainly relies on the primary side high-voltage fuse and the secondary side small air switch. However, since the voltage of the PT open secondary winding is almost zero during normal operation of the system, there is no obvious indication of secondary short circuit, and if a small air switch is installed at this location, it cannot be monitored through voltage abnormality after tripping, resulting in the lack of short circuit protection function on the PT secondary open winding. When the secondary harmonic elimination device fails to form a persistent short circuit, if abnormal conditions such as single-phase grounding and PT fuse damage occur in the system, a large current will be generated instantaneously, eventually leading to PT burning and even causing a fire.

[0004] The existing secondary harmonic elimination device only configures PT open secondary winding breakage monitoring, which cannot deal with the short circuit problem caused by high-frequency switch failure; and the conventional PT protector (primary high-voltage fuse, secondary small air switch) cannot adapt to the special conditions (no voltage during normal operation, instantaneous high voltage and large current during failure) of the PT open secondary winding, resulting in a protection blind area. Therefore, there is an urgent need for a special protector that can detect and cut off the short circuit fault of the PT open secondary winding without affecting the normal operation of the secondary harmonic elimination device. SUMMARY

[0005] The present application provides a PT protector suitable for secondary harmonic elimination device, which is applied between the PT open secondary winding and the secondary harmonic elimination device, can effectively detect and cut off the short circuit fault of the PT open secondary winding, and avoid misoperation when the secondary harmonic elimination device operates normally, solving the problem of lack of short circuit protection function on the PT secondary open winding.

[0006] The present application is implemented by the following technical solutions:

[0007] The present application provides a PT protector suitable for secondary harmonic elimination device, which is applied between the PT open secondary winding and the secondary harmonic elimination device, can effectively detect and cut off the short circuit fault of the PT open secondary winding, and avoid misoperation when the secondary harmonic elimination device operates normally, solving the problem of lack of short circuit protection function on the PT secondary open winding.

[0008] A protection resistor is connected in series in the main circuit between the first end of the PT open secondary winding and the input end of the secondary harmonic elimination device;

[0009] An AC current starting type relay, whose coil is connected in series in the main circuit, is used to monitor the current in the main circuit; the AC current starting type relay is also provided with at least one pair of normally open contacts;

[0010] A time relay, whose coil is connected to the working power supply through the normally open contacts of the AC current starting type relay, is powered and starts to delay when the coil of the AC current starting type relay is powered;

[0011] The time relay is also provided with a pair of delay closing contacts and at least one pair of delay opening contacts; the delay closing contacts are connected in series to the coil of the time relay and then connected to the working power supply, forming a self-holding circuit; the delay opening contacts are connected in series in the main circuit to cut off the main circuit when the delay setting value is reached;

[0012] An intermediate relay, whose coil is connected to the working power supply, is also provided with a pair of normally open contacts; the normally open contacts are connected in parallel to the protection resistor and then connected in series in the main circuit; the normally open contacts of the intermediate relay are closed to short the protection resistor when the working power supply is normal; the normally open contacts are opened to connect the protection resistor in series in the main circuit when the working power supply is powered off.

[0013] Further, the PT protector is also provided with a first jumper and a second jumper; the first jumper is connected in parallel to both ends of the protection resistor, and the second jumper is connected in series in the parallel branch of the normally open contacts of the intermediate relay and the protection resistor, for selecting the access mode of the protection resistor.

[0014] Further, the PT protector also includes a control module and a controlled switch assembly; the controlled switch assembly includes a first controlled switch and a second controlled switch; the first controlled switch connects both terminals of the first jumper, and the second controlled switch connects both terminals of the second jumper, for electrically simulating the short-circuit and open states of the jumper;

[0015] The control module is configured to output a control signal to the controlled switch assembly to automatically switch the access mode of the protection resistor.

[0016] Further, when the first jumper is short-circuited, the protection resistor is continuously short-circuited, and the main circuit impedance is the lowest, to adapt to the scenario where the secondary harmonic elimination device has high reliability and no power supply failure risk;

[0017] When the second jumper is short-circuited, the normally open contact of the intermediate relay is closed to short-circuit the protection resistor when the working power supply is normal, and is opened to connect the protection resistor into the main circuit when the working power supply is lost, so as to adapt to a scene with the risk of power loss.

[0018] When neither the first jumper nor the second jumper is short-circuited, the protection resistor is continuously connected into the main circuit to limit the current in the main circuit, so as to adapt to a scene with high sensitivity requirement for short-circuit fault.

[0019] Further, the PT protector further comprises a detection circuit for collecting at least one of a PT open secondary winding voltage, an input end voltage of a secondary harmonic elimination device, and a protection resistor circuit voltage.

[0020] The control module is connected with the detection circuit and is configured to judge a system state according to the voltage signal collected by the detection circuit, and output a corresponding control signal to the controlled switch assembly based on the system state, so as to automatically switch the connection mode of the protection resistor.

[0021] Further, the control module is further configured to dynamically adjust the action current setting value of the alternating current starting type relay and / or the delay setting value of the time relay based on the signal collected by the detection circuit.

[0022] Further, the PT protector further comprises a remote communication module, which is in communication connection with the control module, for uploading at least one of the voltage signal collected by the detection circuit, the system state judgment result, and the current connection mode of the protection resistor to a remote monitoring center.

[0023] Further, the PT protector further comprises a reset button, which is connected in series in a self-holding circuit of the time relay, for manually cutting off the self-holding circuit of the time relay after the time relay is actuated, so as to reset the time relay.

[0024] Further, the remote communication module is further configured to receive a remote instruction from the remote monitoring center.

[0025] The control module is further configured to perform at least one of switching the connection mode of the protection resistor, resetting the time relay, adjusting the action current setting value of the alternating current starting type relay, or adjusting the delay setting value in response to the remote instruction.

[0026] Further, the PT protector further comprises a fault alarm unit; the fault alarm unit comprises a buzzer and a fault output contact, and when the time relay is actuated to cut off the main circuit, the buzzer sounds an alarm, and the fault output contact is closed and outputs a fault signal.

[0027] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0028] By connecting the AC current starting type relay in series in the circuit, the instantaneous current generated by the normal operation of the secondary harmonic elimination device and the continuous current generated by the fault can be sensed, and the time relay is triggered to start timing through the current signal. If the harmonic elimination operation ends before the delay setting value is reached, the normally open contact of the AC current starting type relay is disconnected, so that the intermediate relay is reset, the delay opening contact does not operate, the circuit is not cut off, the normal operation of the secondary harmonic elimination device is not affected, and false operation is avoided.

[0029] However, when the AC current starting type relay is continuously attracted and exceeds the delay setting value, the delay opening contact of the time relay will cut off the main circuit after completing the predetermined timing operation, so as to avoid the continuous existence of the short-circuit current, thereby playing a role in protecting the PT secondary winding.

[0030] At the same time, the protection resistor is connected in series in the circuit. When the working power supply is normal, the intermediate relay is attracted, and the normally open contact connected in parallel across the protection resistor is short-circuited, so as to ensure that the secondary harmonic elimination device can obtain sufficient voltage signals to normally start and work. When the working power supply is lost, the normally open contact of the intermediate relay is disconnected, and the protection resistor is connected to the main circuit. Even in the case of power loss of the PT protector, the protection resistor can still limit the current to provide basic protection and reduce the risk of PT explosion and fire. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0032] Figure 1 It is an electrical schematic diagram of the PT protector;

[0033] Figure 2 It is a schematic diagram of installation and use of the PT protector;

[0034] Figure 3 It is a schematic diagram of installation of the reset button and the power indicator light;

[0035] Figure 4 It is a schematic diagram of jumper connection.

[0036] Marked in the drawings:

[0037] L600: PT open winding first end; L601: voltage input end of secondary harmonic elimination device; N600: PT open winding tail end / secondary harmonic elimination device common end connection terminal; R: protection resistor; ZJ1: AC current starting type relay (coil + normally open contact ZJ1-1); ZJ2: intermediate relay (coil + normally open contact ZJ2-1); KT1: time relay (coil + time delay opening contact KT1-1 + time delay closing contact KT1-2); 1-2: first jumper; 3-4: second jumper. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with embodiments and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application and not as limitation to the present application.

[0039] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application and the above-described drawings are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to or inherent to other steps or units.

[0040] The terms used in various embodiments of the present application are only used for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly dictates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present application belong. The terms (such as those defined in a generally used dictionary) will be interpreted to have the same meaning as the contextual meaning in the relevant technical field and will not be interpreted to have an idealized meaning or an overly formal meaning, unless clearly defined in various embodiments of the present application.

[0041] The present application proposes a PT protector applied to the PT of a secondary harmonic elimination device, aiming to solve the problem of the lack of short circuit protection function on the secondary open winding of the existing PT, to realize the cutting off of the PT open loop when the secondary harmonic elimination device fails, and the connection of the PT open loop when the secondary harmonic elimination device operates normally, to prevent explosion and fire accidents.

[0042] Reference Figure 1 , Figure 1The electrical schematic of the PT protector is shown, including a protection resistor R, an alternating current starting type relay ZJ1, an intermediate relay ZJ2 and a time relay KT1. The time relay KT1, the coil of the alternating current starting type relay ZJ1 and the protection resistor R are connected in series; the normally open contact ZJ1-1 of the alternating current starting type relay ZJ1 and the coil of the time relay KT1 are connected in series, forming linkage, and are connected to the positive and negative power supply; one end of the coil of the intermediate relay ZJ2 is connected to the positive power supply and the other end is connected to the negative power supply, and the normally open contact ZJ2-1 of the intermediate relay ZJ2 is connected in parallel with the protection resistor R; the time delay closing contact KT1-2 of the time relay is connected to the positive and negative power supply and is connected in series with the coil thereof.

[0043] The alternating current starting type relay ZJ1 adopts a current drive mode, and the coil thereof is connected in series in the main circuit to sense the loop current. When the current reaches or exceeds the preset action value, the normally open contact ZJ1-1 thereof is closed to turn on the rear circuit. This feature enables the instantaneous current pulse generated when the secondary harmonic elimination device acts to be accurately captured. The time relay KT1 adopts a voltage drive mode, and the coil thereof starts to delay after being powered on, and the contact state thereof changes after the delay ends. In the present scheme, the time delay opening contact KT1-1 is used to disconnect the main circuit and is the executor of the protection action, and the time delay closing contact KT1-2 is used to form a self-holding circuit after the action to ensure that the fault state is locked until manual reset. The intermediate relay ZJ2 is also voltage driven, and its action is directly controlled by the presence or absence of the working power supply. The on-off of the normally open contact ZJ2-1 realizes the intelligent access and bypass of the protection resistor R,

[0044] The working power supply adopts the DC 24V voltage commonly used in the secondary loop of the power system, adapts to the power supply standard of conventional relay protection equipment, and the power supply fluctuation range is ±10%, which ensures stable work in the power system voltage fluctuation scene.

[0045] Referring to Figure 2 , Figure 2The installation and use of the PT protector is shown. The PT protector is connected in series between the PT opening secondary winding and the secondary harmonic elimination device (L600-L601). The tail end N600 of the PT opening winding is directly connected to the common end of the secondary harmonic elimination device. The protection resistor R, the coil of the alternating current starting relay ZJ1 and the time relay KT1 are connected in series in the main circuit between the head end L600 of the PT opening secondary winding and the voltage input end L601 of the secondary harmonic elimination device. The coil of the alternating current starting relay ZJ1 can monitor the current in the main circuit. When the secondary harmonic elimination device works normally, a small resistor is intermittently connected to the main circuit. When the small resistor is connected, the main circuit generates a transient current. The coil of ZJ1 is powered, the normally open contact ZJ1-1 of ZJ1 is attracted, and the power supply circuit is turned on. The coil of the time relay KT1 is connected to the working power supply through the normally open contact ZJ1-1 of ZJ1. When the power supply circuit is turned on, the coil of the time relay KT1 is powered, and the time delay starts. If the secondary harmonic elimination device is disconnected and connected with a small resistor (for example, the connection time of the small resistor is less than 0.1s) before the time delay of KT1 acts (for example, the set time delay is 0.5s), the transient current disappears after the reset of ZJ1, the coil of KT1 loses power and resets, and the time delay opening contact KT1-1 remains closed, which does not affect the normal work of the secondary harmonic elimination device, thereby destroying the resonance condition and limiting the overvoltage. If the secondary harmonic elimination device is not disconnected and connected with a small resistor (the duration is greater than or equal to 0.5s) before KT1 reaches the set time delay, ZJ1 is continuously attracted, the time delay of 0.5s is completed, and the time delay closing contact KT1-2 is closed to form a self-holding circuit with the coil of KT1 (even if ZJ1 resets subsequently, KT1 remains in the action state), and the time delay opening contact KT1-1 acts to disconnect the main circuit of the PT opening secondary winding, thereby avoiding that the PT bears the short-circuit current for a long time.

[0046] The coil of the intermediate relay ZJ2 is connected to the working power supply. The normally open contact ZJ2-1 is connected in parallel with the protection resistor R and then connected in series in the main circuit. When the working power supply is powered, the normally open contact ZJ2-1 is closed, the protection resistor R is short-circuited, and the impedance of the main circuit is extremely low (only the inherent impedance of the wire and the relay contact), which ensures that the secondary harmonic elimination device can normally obtain the PT opening voltage signal. If the line resonates abnormally, a small resistor is continuously connected to the PT opening secondary winding. At this time, the coil of ZJ1 is started, the time relay KT1 is started again, and the time delay is started. When KT1 acts, KT1 realizes self-holding through the time delay closing contact KT1-3, and the time delay opening contact KT1-1 acts to disconnect the PT opening circuit, thereby realizing the PT short-circuit fault protection. If the working power supply loses power, the time relay KT1 cannot be started, and the PT opening circuit cannot be disconnected. However, at this time, the protection resistor R is always connected in the main circuit. Even if the secondary harmonic elimination device incorrectly acts and continuously connects the small resistor, the main circuit current can be reduced due to the protection resistor R, thereby playing a power loss protection role.

[0047] In which, the time delay disconnecting contact KT1-1 is preferably set to two, to prevent one contact failure (such as arc sticking, mechanical jamming, resulting in failure to disconnect) while the other contact still ensures reliable disconnection of the main circuit.

[0048] Further, referring to Figure 3 When KT1 completes the time delay action, the time delay closing contact KT1-2 is closed, forming a power supply circuit independent of ZJ1-1, that is, the working power supply positive - KT1-2 - KT1 coil - reset button - working power supply negative power supply circuit, to ensure that KT1 continues to act, avoiding the main circuit misdirected on when the fault is not eliminated.

[0049] After troubleshooting, maintenance personnel can press the reset button to disconnect the self-holding circuit of KT1, the time delay disconnecting contact KT1-1 in the main circuit is reset, and the main circuit is restored to be on, and the PT protector and the secondary harmonic elimination device are put into use again.

[0050] Further, the PT protector further includes a power supply state indicator light. The power supply state indicator light is connected in parallel with the intermediate relay coil, and is used to indicate the state of the working power supply.

[0051] Further, a first jumper 1-2 is connected in parallel across the protection resistor R, and a second jumper 3-4 is connected in series in the parallel branch of the normally open contact ZJ2-1 of the intermediate relay and the protection resistor R, as shown in Figure 4 By selectively short-circuiting the first jumper 1-2 or the second jumper 3-4, the access mode of the protection resistor R can be switched.

[0052] When the first jumper 1-2 is short-circuited, the protection resistor R is short-circuited, and in this mode, the impedance of the main circuit is the lowest, which is suitable for scenarios where the secondary harmonic elimination device has high reliability and no power supply loss risk. When the second jumper 3-4 is short-circuited, the intermediate relay ZJ2 participates in the work, and when the working power supply is powered, the normally open contact ZJ2-1 is closed, and the protection resistor R is short-circuited. When the working power supply is lost, the protection resistor R is connected to the main circuit, and even if the secondary harmonic elimination device continuously connects a small resistor in parallel on the PT open secondary winding, due to the action of the protection resistor R, the resonance condition can also be destroyed, while greatly reducing the short-circuit current, protecting the PT, and adapting to scenarios where the harmonic elimination device has relatively high reliability but has power supply loss risk. When neither the first jumper 1-2 nor the second jumper 3-4 is short-circuited, the protection resistor is fixedly connected to the main circuit, limiting the current in the main circuit, and is suitable for scenarios with high requirements for short-circuit fault sensitivity.

[0053] Further, the PT protector is also provided with a control module and a controlled switch assembly. The controlled switch assembly includes a first controlled switch K1 and a second controlled switch K2, the first controlled switch K1 is connected to the two terminals of the first jumper 1-2, and the second controlled switch K2 is connected to the two terminals of the second jumper 3-4, for simulating the short-circuit and open-circuit states of the jumper.

[0054] The control module is configured to output a control signal to the controlled switch assembly to control K1 and K2 respectively, so as to automatically switch the access mode of the protection resistor R.

[0055] The control module can adopt an STM32F103 series MCU, and the controlled switch assembly can adopt electromagnetic normally open relays. The coils of the two electromagnetic normally open relays are respectively connected to the GPIO ports of the control module, and the normally open contacts are respectively connected to the first jumper and the second jumper. The control module outputs a high-level control signal to the coils of the two electromagnetic normally open relays, and the coils are attracted to the normally open contacts to simulate the short-circuit of the jumper. When a low-level signal is output, the coils lose power, the contacts are opened, and the jumper is not short-circuited.

[0056] Further, the PT protector also includes a fault alarm unit. The fault alarm unit includes a buzzer and a fault output contact. When the time relay KT1 acts to cut off the main circuit, the buzzer sounds an alarm, and the fault output contact is closed and outputs a fault signal.

[0057] The buzzer is connected in series with the time delay closing contact of KT1; the fault output contact and the buzzer act synchronously, and the closed fault output contact outputs an on-off signal. The on-off signal output contact can be connected to a local monitoring screen or uploaded to a power system monitoring center through a remote communication module to realize visual fault alarm.

[0058] Further, the PT protector is also provided with a detection circuit. The detection circuit is used to collect at least one of the PT open secondary winding voltage, the input end voltage of the secondary harmonic elimination device, and the protection resistor circuit voltage.

[0059] Specifically, the detection circuit can include three voltage sampling points and corresponding voltage sensors.

[0060] The first voltage sampling point (A+ / A-): is set at the two ends L600-N600 of the PT open secondary winding, and a voltage divider type voltage sensor (resistance division ratio 100:1, input voltage 0-200V, output 0-2V) is used to collect the open voltage signal output by the PT to determine whether the PT side is abnormal.

[0061] Second voltage sampling point (B+ / B-): Set at the input end L601-N600 of the secondary harmonic elimination device, a Hall voltage sensor (ACS712 series, measurement range 0-200V, accuracy ±0.5%) is used to collect the input voltage signal of the secondary harmonic elimination device to determine whether the harmonic elimination device is short-circuited.

[0062] Third voltage sampling point (C+ / C-): Set at both ends of the protection resistor R, a voltage divider sensor (voltage division ratio 1000:1, input voltage 0-100V, output 0-0.1V) is used to collect the voltage signal of the protection resistor R to determine whether R is connected to the circuit.

[0063] The sensor sampling frequency is set to no less than 1kHz, and after the collected signal is filtered by a sliding average filter, it is converted into a digital signal by the ADC module of the MCU.

[0064] The control module realizes fault diagnosis and mode switching based on the sampling signal, the current signal of the AC current starting relay ZJ1, and the working power supply monitoring voltage. The fault types include PT side abnormality, secondary harmonic elimination device fault, system resonance, and working power supply power failure.

[0065] (1) System resonance fault: If the voltage at the first sampling point fluctuates periodically, and the voltage at the second sampling point changes synchronously with the voltage at the first sampling point, and the current starting relay generates intermittent current consistent with the period of the small resistance connected to the secondary harmonic elimination device, it can be determined as a system resonance fault.

[0066] (2) PT side abnormality: If the voltage at the first sampling point is zero sequence voltage or the voltage amplitude exceeds the preset voltage threshold, the voltage at the second sampling point synchronously deviates abnormally, and the current amplitude of the AC current starting relay ZJ1 exceeds the preset current threshold, it can be determined as a PT side abnormality fault.

[0067] (3) Secondary harmonic elimination device fault: If the voltage signal at the second sampling point is lower than the preset short-circuit voltage threshold, and the duration exceeds the preset time, the voltage signal at the first sampling point is within the normal range, the AC current starting relay ZJ1 is continuously powered, and the current amplitude is stable above the preset current threshold, it can be determined as a secondary harmonic elimination device fault.

[0068] (4) Working power supply power failure fault: If the working power supply monitoring signal disappears (the middle relay coil loses power), the voltage signal at the third sampling point changes from near 0 to a non-zero value (the protection resistor is connected to the circuit), and the AC current starting relay ZJ1 has a continuous current or A, B point voltage abnormality, it can be determined as a working power supply power failure fault.

[0069] Further, the control module is connected with the detection circuit and is configured to determine the system state according to the voltage signal collected by the detection circuit, and output a corresponding control signal to the controlled switch assembly based on the system state, so as to automatically switch the access mode of the protection resistor.

[0070] In the control module, detection logic is configured to output different fault type detection results through threshold comparison and logical judgment, and convert the detection results into corresponding control signals and output the control signals to the controlled switch assembly to control the state of the first jumper 1-2 and the second jumper 2-3 and switch the access mode of the protection resistor. Wherein, the fault type and the corresponding protection mode are shown in Table 1.

[0071] Table 1

[0072] Fault type / system status Sampled signal features Corresponding protection mode Control module output (K1 / K2 status) Loop normal A+ / A- voltage normal (0V / 33V zero sequence voltage), B+ / B- voltage fluctuates with the action of eliminating the harmonic, C+ / C- voltage ≈0 (ZJ2-1 closed), ZJ1 intermittent power Protection resistance forced not to access K1 attracted, K2 open (simulated first jumper short circuit) System resonance A+ / A- voltage periodic fluctuation (10V-100V, frequency 50Hz-1kHz), B+ / B- voltage synchronous fluctuation, ZJ1 intermittent power Protection resistance delay access K1 open, K2 attracted (simulated second jumper short circuit) PT side abnormal (single-phase grounding / PT fuse damage) A+ / A- voltage is zero sequence voltage (33V) or overvoltage (>100V), B+ / B- point voltage synchronous abnormal, ZJ1 current >500mA Protection resistance forced access K1 open, K2 open (both jumpers are not shorted) Secondary harmonic elimination device failure (continuous short circuit) B+ / B- voltage < 0.5 V (close to short circuit), duration > 0.5 s, A+ / A- voltage normal, ZJ1 persistent power-on Protection resistance forced access + fast break loop K1 open, K2 open Power supply power loss + abnormal Working power monitoring signal (ZJ2 coil voltage <18V), C+ / C- voltage >10V (R connection), A+ / A-, B+ / B- abnormal Protection resistance forced access K1 open, K2 open

[0073] Further, the control module is further configured to dynamically adjust the action current setting value of the alternating current starting type relay ZJ1 and / or the delay setting value of the time relay KT1 based on the signal collected by the detection circuit.

[0074] Specifically, the control module dynamically adjusts the action current of ZJ1 and the delay time of KT1 by the following way to adapt to different PT models (such as JDZ-10, JSZV-10) and system working conditions:

[0075] (1) ZJ1 action current adjustment: The ZJ1 coil loop is connected in series with an adjustable resistance assembly (such as a digital potentiometer AD5242 with a resistance range of 0-10kΩ), and the control module adjusts the resistance value by sending instructions through the I2C bus to change the power supply current of the ZJ1 coil.

[0076] When the system resonates, the adjustable resistance value can be increased to increase the ZJ1 action current threshold to avoid false triggering by the instantaneous current of the resonance elimination; when the PT side is abnormal / elimination device fails, the adjustable resistance value can be reduced to reduce the action current threshold to improve the fault response sensitivity.

[0077] (2) KT1 delay adjustment: The KT1 is a programmable time relay (such as H3Y-4 series, supporting 0.1s-10s adjustable), and the control module outputs different duty cycle PWM signals to control and adjust the delay setting value. The control module dynamically adjusts the duty cycle of the PWM signal according to the fault type, and the PWM duty cycle is positively correlated with the delay time, thereby changing the delay setting value.

[0078] Preferably, the alternating current starting type relay is an undercurrent starting type relay with a starting current threshold range of 50mA-5A, and the time relay is a programmable time relay with a delay time range of 0.1s-10s.

[0079] Further, the PT protector further comprises a remote communication module, which is in communication connection with the control module, and is configured to upload at least one of the voltage signal collected by the detection circuit, the system state judgment result, and the current access mode of the protection resistor to the remote monitoring center.

[0080] Further, the remote communication module is further configured to receive a remote instruction from the remote monitoring center and transmit the remote instruction to the control module, and the control module is further configured to perform a corresponding action in response to the remote instruction.

[0081] The remote instruction can be a time relay reset instruction, an instruction for switching the access mode of the protection resistor R, an instruction for adjusting the action current setting value of the alternating current starting type relay and the delay setting value of the time relay, and the control module performs a corresponding action according to the control to realize remote control.

[0082] The communication module can adopt a LoRa module or a 5G module, support RS485 / LoRa / 5G protocols, and can upload the voltage signal (A / B / C points) of the detection circuit, the fault type judgment result, the protection resistor access mode, the relay action state and other data in real time. And receive the monitoring center instruction, realize the protection mode switching, the time relay reset, the dynamic threshold adjustment and other operations.

[0083] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A PT protector suitable for a secondary harmonic suppression device, characterized in that, Connected in series between the open-ended secondary winding of the PT and the secondary harmonic suppression device, the PT protector is used to protect the open-ended secondary winding of the PT. The PT protector includes: The protection resistor is connected in series in the main circuit between the first end of the open secondary winding of the PT and the voltage input terminal of the secondary harmonic suppression device. An AC current-starting relay has its coil connected in series in the main circuit for monitoring the current in the main circuit; the AC current-starting relay also has at least one pair of normally open contacts. A time relay, the coil of which is connected to the working power supply through the normally open contact of the AC current-starting type relay. When the coil of the AC current-starting type relay is energized, the coil of the time relay is energized and begins to delay. The time relay is also provided with a pair of delayed closing contacts and at least a pair of delayed opening contacts. The delayed closing contacts are connected in series with the coil of the time relay and then connected to the working power supply to form a self-holding circuit. The delayed opening contacts are connected in series in the main circuit to cut off the main circuit when the delay set value is reached. An intermediate relay, the coil of which is connected to the working power supply, is also provided with a pair of normally open contacts, which are connected in parallel with the protective resistor and then in series in the main circuit; the normally open contacts of the intermediate relay are closed when the working power supply is normal to short-circuit the protective resistor; when the working power supply is de-energized, they are opened to connect the protective resistor in series in the main circuit.

2. The PT protector for a secondary harmonic suppression device according to claim 1, characterized in that, The PT protector is also provided with a first jumper and a second jumper; the first jumper is connected in parallel across the two ends of the protection resistor, and the second jumper is connected in series in the parallel branch of the normally open contact of the intermediate relay and the protection resistor, for selecting the connection mode of the protection resistor.

3. The PT protector for a secondary harmonic suppression device according to claim 2, characterized in that, The PT protector also includes a control module and a controlled switch assembly. The controlled switch assembly includes a first controlled switch and a second controlled switch. The first controlled switch is connected to two terminals of the first jumper, and the second controlled switch is connected to two terminals of the second jumper, for electrically simulating the short-circuit and open states of the jumper. The control module is configured to output a control signal to the controlled switch assembly to automatically switch the connection mode of the protection resistor.

4. The PT protector for a secondary harmonic suppression device according to claim 3, characterized in that, When the first jumper is shorted, the protection resistor is continuously shorted, and the main circuit impedance is at its lowest, so as to adapt to the scenario where the secondary harmonic elimination device has high reliability and no risk of power failure. When the second jumper is shorted, the normally open contact of the intermediate relay closes to short-circuit the protection resistor when the working power supply is normal, and opens when the working power supply fails. The protection resistor is connected in series in the main circuit to adapt to scenarios with power failure risk. When neither the first jumper nor the second jumper is short-circuited, the protective resistor is continuously connected to the main circuit to limit the current in the main circuit, thus adapting to scenarios with high sensitivity requirements for short-circuit faults.

5. The PT protector for a secondary harmonic suppression device according to claim 3, characterized in that, The PT protector also includes a detection circuit and a control module. The detection circuit is used to collect at least one of the following: the voltage of the open secondary winding of the PT, the input voltage of the secondary harmonic elimination device, and the voltage of the protection resistor circuit. The control module is connected to the detection circuit and is configured to determine the system status based on the voltage signal collected by the detection circuit, and output a corresponding control signal to the controlled switch component based on the system status to automatically switch the access mode of the protection resistor.

6. The PT protector for a secondary harmonic suppression device according to claim 5, characterized in that, The control module is also configured to dynamically adjust the operating current setting value of the AC current-activated relay and / or the delay setting value of the time relay based on the signal acquired by the detection circuit.

7. The PT protector for a secondary harmonic suppression device according to claim 5, characterized in that, The PT protector also includes a remote communication module, which is communicatively connected to the control module and is used to upload at least one of the following data to the remote monitoring center: the voltage signal collected by the detection circuit, the system status judgment result, and the current access mode of the protection resistor.

8. The PT protector for a secondary harmonic suppression device according to any one of claims 1-7, characterized in that, The PT protector also includes a reset button, which is connected in series in the self-holding circuit of the time relay and is used to manually disconnect the self-holding circuit after the time relay is activated, so as to reset the time relay.

9. The PT protector for a secondary harmonic suppression device according to claim 7, characterized in that, The remote communication module is also configured to receive remote commands from the remote monitoring center. The control module is also configured to, in response to the remote command, perform at least one of the following operations: switching the access mode of the protection resistor, resetting the time relay, adjusting the operating current setting value of the AC current-activated relay, or adjusting the delay setting value.

10. The PT protector for a secondary harmonic suppression device according to claim 8, characterized in that, The PT protector also includes a fault alarm unit; the fault alarm unit includes a buzzer and a fault output contact. When the time relay operates to cut off the main circuit, the buzzer sounds an alarm, and the fault output contact closes and outputs a fault signal.

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