Gas relay contact performance detection device

Abstract

The invention relates to the technical field of electrical equipment detection, and discloses a gas relay contact performance detection device, which comprises a main control unit, a power supply unit, an excitation source unit, an electronic load unit and an acquisition unit. The excitation source unit is of a voltage competition type parallel topological structure, and passive automatic switching between high-voltage cleaning output and low-voltage constant-current output is achieved through a one-way blocking assembly by means of potential changes of a common injection node. The electronic load unit is based on a negative feedback control loop, clamps the loop current in a cleaning mode, and maintains the current constant in a high-frequency response step scanning mode. And the main control unit operates a contact resistance dynamic analysis algorithm, and calculates an intrinsic zero-current resistance value and a thermal drift coefficient by using a least square method. The problem of switching delay between contact oxidation film cleaning and precision measurement is effectively solved, the interference of the test current heat effect on resistance measurement is eliminated, and the accuracy of contact health state diagnosis is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of power equipment testing technology, specifically to a gas relay contact performance testing device. Background Technology

[0002] Gas relays are core non-electrical protection components of oil-immersed transformers, used to trip or alarm when a fault occurs inside the transformer, causing gas or oil flow surges. During long-term operation, the metal contacts inside the gas relay are exposed to insulating oil or air, and an oxide film or oil film gradually forms on the contact surface. In power system maintenance, operators determine the reliability of the gas relay based on the contact resistance value. Existing general-purpose contact resistance testing instruments use a low-voltage constant current source for loading tests.

[0003] Due to the presence of an insulating film on the contact surface, the low driving voltage output by general-purpose testing instruments cannot break down this insulating layer, causing the testing instruments to display the contacts as open circuits or in a high-resistance state, resulting in misjudgments. To solve this problem, the industry has adopted high-voltage cleaning-assisted measurement technology, which involves applying a high-voltage pulse before precision measurement to break down the insulating film on the contact surface. Existing testing equipment with high-voltage cleaning capabilities uses mechanical relays or contactors to internally switch between the high-voltage cleaning circuit and the low-voltage precision measurement circuit.

[0004] The inherent time delay in the physical action of mechanical switching components creates a timing gap between the end of high-voltage breakdown and the start of precision constant current measurement. During this gap, the conductive channels of the contacts cool, and the physical state of the microscopic conductive spots retracts, causing subsequent measurement data to fail to accurately reflect the contact's conductivity at the moment of action. Furthermore, existing technologies employ static resistance measurement with a single current value, neglecting the Joule heating effect generated by the test current on the contact resistance. The temperature rise caused by the test current flowing through the tiny contact surface leads to thermal drift in the resistance value, resulting in temperature errors in the final measurement results. This makes it impossible to obtain the intrinsic zero-current resistance value of the tested contact and to effectively assess the contact's thermal stability. Therefore, this invention proposes a gas relay contact performance testing device to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a gas relay contact performance testing device, which solves the problems of timing breaks in the testing process caused by using mechanical switches to switch between high-pressure cleaning and precision measurement circuits, and insufficient accuracy of resistance measurement results due to ignoring the Joule heating effect of the test current when using a single static current measurement.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a gas relay contact performance testing device, comprising: a main control unit;

[0007] The power supply unit is used to convert external AC power into DC operating voltage;

[0008] A switching matrix unit, located between the common injection node and the contact under test, is used to establish a current path between the excitation source unit and the contact under test.

[0009] An excitation source unit is connected between the power supply unit and the switching matrix unit. The excitation source unit includes a high-voltage output branch and a low-voltage constant current output branch that converge at the common injection node. It is used to switch the output of a high-voltage signal or a constant current signal to the measured contact under the control of the main control unit.

[0010] An electronic load unit, connected to the load terminal of the tested contact, is used as a controlled current regulating component to regulate the loop current flowing through the tested contact.

[0011] The acquisition unit has its input terminal connected in parallel across the two ends of the contact under test, and is used to acquire the voltage drop signal of the contact under test and send it to the main control unit;

[0012] The main control unit is used to control the excitation source unit and the electronic load unit to work together to perform contact performance detection.

[0013] Preferably, the excitation source unit adopts a voltage-competitive parallel topology. One end of the high-voltage output branch is connected to the high-voltage DC bus provided by the power supply unit, and the other end of the high-voltage output branch is connected to the common injection node. A high-voltage isolation control switch is connected in series in the high-voltage output branch. The low-voltage constant current output branch includes a precision constant current source module and a unidirectional blocking component. The positive output terminal of the precision constant current source module is connected to the anode of the unidirectional blocking component, and the cathode of the unidirectional blocking component is connected to the common injection node. The common injection node serves as the output terminal of the excitation source unit and is connected to the switching matrix unit.

[0014] Preferably, the unidirectional blocking component is used to automatically control the switching of the current path by utilizing the potential change of the common injection node. When the high-voltage isolation control switch is closed, the potential of the common injection node rises to the voltage of the high-voltage DC bus, and the unidirectional blocking component is in a reverse biased state and is in a cutoff state, blocking the high voltage from entering the precision constant current source module. When the high-voltage isolation control switch changes from closed to open and the electronic load unit remains in a current-absorbing state, the potential of the common injection node drops. When the potential of the common injection node drops to below the difference between the output compliance voltage of the precision constant current source module and the forward conduction voltage drop of the unidirectional blocking component, the unidirectional blocking component changes from a cutoff state to a forward conduction state, and the precision constant current source module injects current into the common injection node through the unidirectional blocking component.

[0015] Preferably, a positive temperature coefficient thermistor is connected in series in the high-voltage output branch, and the positive temperature coefficient thermistor is used as a self-resetting current limiting element. A metal oxide varistor is connected in parallel at the common injection node, and the metal oxide varistor is used to suppress switching surge voltage. The high-voltage isolation control switch is a power relay with reinforced insulation structure, and the dielectric withstand voltage of the power relay in the open contact state is greater than the maximum operating voltage of the high-voltage DC bus. The low-voltage constant current output branch is provided with a crowbar protection circuit, which includes a fast-acting fuse and a transient voltage suppression diode. The fast-acting fuse is connected in series between the positive output terminal of the precision constant current source module and the anode of the unidirectional blocking component. The transient voltage suppression diode is connected in parallel between the anode of the unidirectional blocking component and the circuit ground. The breakdown voltage of the transient voltage suppression diode is between the maximum output compliance voltage of the precision constant current source module and the absolute maximum rated voltage of the internal components of the precision constant current source module.

[0016] Preferably, the main circuit of the electronic load unit includes a power MOSFET, a precision current sampling resistor, and an operational amplifier. The drain of the power MOSFET is connected to the load terminal of the contact under test, and the source of the power MOSFET is connected to ground in series with the precision current sampling resistor. The operational amplifier forms a negative feedback control loop. The non-inverting input of the operational amplifier receives the analog control voltage from the main control unit, the inverting input of the operational amplifier acquires the voltage signal to ground across the precision current sampling resistor, and the output of the operational amplifier drives the gate of the power MOSFET.

[0017] Preferably, the main control unit controls the electronic load unit to execute a constant current limiting cleaning mode and a high-frequency response stepped scanning mode. In the constant current limiting cleaning mode, the electronic load unit clamps the loop current to a preset cleaning limiting current value when the excitation source unit outputs a high voltage signal. In the high-frequency response stepped scanning mode, the electronic load unit changes the analog control voltage in a time sequence to perform stepped current scanning, and is used to adjust the gate voltage of the power metal-oxide-semiconductor field-effect transistor to maintain a constant loop current at the instant when the excitation source unit switches between outputting a high voltage signal or a constant current signal.

[0018] Preferably, the acquisition unit adopts a Kelvin four-wire connection structure, and the two voltage sampling leads from the acquisition unit are connected to the two ends of the contact under test. The physical connection point of the voltage sampling leads inside the gas relay contact performance testing device is located between the cathode of the unidirectional blocking component and the contact under test. The front-end circuit of the acquisition unit adopts a high input impedance instrumentation amplifier, and the acquisition unit is used to perform multi-point oversampling at each current step of the stepped current scan.

[0019] Preferably, the main control unit internally runs a contact resistance dynamic analysis algorithm. The main control unit performs numerical analysis on the current and voltage dataset collected by the acquisition unit based on a physical temperature rise model of conductor resistance. The numerical analysis process includes: using the least squares method to perform linear regression calculation on the square of the current value and the resistance value, calculating the intrinsic zero-current resistance value as the linear regression intercept and the thermal drift coefficient as the linear regression slope. The main control unit calculates the ratio of the thermal drift coefficient to the intrinsic zero-current resistance value to obtain the relative thermal drift rate. Based on the intrinsic zero-current resistance value, the thermal drift coefficient, and the relative thermal drift rate, the main control unit performs a multi-dimensional classification judgment on the health status of the tested contact.

[0020] Preferably, the device further includes an interaction unit connected to the main control unit. The interaction unit includes a display screen, buttons, and a voice module. The interaction unit receives test configuration parameters input by the user, including high-voltage cleaning voltage threshold, cleaning limiting current, high-voltage holding time, and thermal stress scanning current sequence. The interaction unit also displays a contact health diagnostic report generated by the main control unit.

[0021] This invention provides a device for testing the performance of gas relay contacts. It has the following advantages:

[0022] 1. This invention employs a voltage-competitive parallel topology in conjunction with a unidirectional blocking component. By monitoring the potential change of the common injection node, the passive automatic switching between high-voltage cleaning output and low-voltage constant current output is achieved using the physical characteristics of the unidirectional blocking component. This method avoids the action delay and contact bounce caused by using mechanical relays for mode switching, and also eliminates the need for complex active logic control circuits. While ensuring that high voltage cannot backflow and damage the precision constant current source module, it ensures that the tested contact can immediately transition to a stable constant current measurement state after oxide film breakdown, thus improving the continuity of the detection process and the reliability of the hardware system.

[0023] 2. This invention utilizes an electronic load unit as a controlled current regulation component with a negative feedback control loop. During high-pressure cleaning, the electronic load unit can strictly clamp the loop current to a preset cleaning limit current value, preventing excessive arc erosion of the test contact surface caused by the surge current generated at the moment of oxide film breakdown. Simultaneously, during the measurement phase, the electronic load unit can quickly respond to changes in the analog control voltage of the main control unit, performing high-frequency response stepped scanning. This solves the technical problems of traditional resistive loads in achieving precise current regulation and suppressing current overshoot, thereby protecting the test contact while acquiring richer current and voltage response data.

[0024] 3. This invention applies a contact resistance dynamic analysis algorithm based on a physical temperature rise model. By performing least squares linear regression analysis on multiple sets of voltage and current data collected during the step-current scanning process, it can calculate the intrinsic zero-current resistance value stripped of Joule thermal effects and the thermal drift coefficient reflecting the micro-contact condition of the contact. This analysis method overcomes the shortcomings of traditional single-point static resistance measurement, which is easily affected by the thermal effect of the test current and leads to misjudgment. It can comprehensively evaluate the aging degree of the tested contact from two dimensions: resistance amplitude and thermal stability, thus improving the accuracy and foresight of contact health status diagnosis. Attached Figure Description

[0025] Figure 1 This is a perspective view of the present invention;

[0026] Figure 2 This is a schematic diagram of the system architecture of the present invention;

[0027] Figure 3 This is a schematic diagram of the overall method flow of the present invention;

[0028] Figure 4 This is a schematic diagram comparing the power switching transient response of the present invention;

[0029] Figure 5 This is a schematic diagram of the contact resistance regression analysis of the present invention.

[0030] Among them, 100 is the main control unit; 200 is the power supply unit; 300 is the switching matrix unit; 400 is the excitation source unit; 401 is the high-voltage isolation control switch; 402 is the precision constant current source module; 403 is the unidirectional blocking component; 500 is the electronic load unit; 600 is the acquisition unit; 700 is the interaction unit; and 800 is the contact under test. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] See attached document Figure 1 and Figure 2 The gas relay contact performance testing device provided by this invention integrates hardware and embedded control logic. A gas relay contact performance testing device includes: a main control unit 100, a power supply unit 200, a switching matrix unit 300, an excitation source unit 400, an electronic load unit 500, a data acquisition unit 600, and an interaction unit 700. All units are integrated within the same chassis and connected via an internal bus.

[0033] The main control unit 100 establishes connections with the switching matrix unit 300, the excitation source unit 400, the electronic load unit 500, and the acquisition unit 600. The main control unit 100 sends timing control commands to coordinate the actions of each hardware module and receives digital sampling signals from the acquisition unit 600. Internally, the main control unit 100 runs a detection algorithm program, performing contact resistance calculations, thermal drift rate analysis, and fault logic determination.

[0034] The power supply unit 200 is connected to an external AC power source. The power supply unit 200 converts AC power into DC operating voltage to provide test voltage to the excitation source unit 400.

[0035] The excitation source unit 400 is connected between the power supply unit 200 and the switching matrix unit 300. The excitation source unit 400 integrates a high-voltage output branch and a low-voltage constant current output branch. The excitation source unit 400 is controlled by the main control unit 100 and selectively outputs a high-voltage signal or a constant current signal.

[0036] The switching matrix unit 300 is located between the excitation source unit 400 and the contact under test 800. The switching matrix unit 300 includes a relay routing circuit. According to the channel selection command, the switching matrix unit 300 establishes a connection channel between different terminals of the excitation source unit 400 and the contact under test 800.

[0037] The electronic load unit 500 is connected to the load terminal of the contact under test 800. The electronic load unit 500 is connected to the main control unit 100 as a controlled current regulation component. The electronic load unit 500 operates in constant current mode, regulates the loop current flowing through the contact under test 800, and performs a stepped current scan according to a preset sequence.

[0038] The acquisition unit 600 uses a four-wire connection, with its input terminal connected in parallel across the two ends of the measured contact 800. The acquisition unit 600 acquires the voltage drop signal of the measured contact 800 in real time. The acquisition unit 600 converts the analog voltage signal into a digital signal and sends it to the main control unit 100.

[0039] The interaction unit 700 is connected to the main control unit 100. The interaction unit 700 includes a display screen, buttons, and a voice module for command input and result output.

[0040] During the testing process, the main control unit 100 selects the contact 800 under test via the switching matrix unit 300. The main control unit 100 controls the excitation source unit 400 and the electronic load unit 500 to apply high-voltage cleaning excitation and low-voltage measurement excitation sequentially. Current flows sequentially through the excitation source unit 400, the switching matrix unit 300, the contact 800 under test, and the electronic load unit 500. The acquisition unit 600 simultaneously acquires data, and the main control unit 100 completes the contact performance evaluation.

[0041] See attached document Figure 2 The excitation source unit 400 adopts a voltage-competitive parallel topology based on unidirectional conducting devices. This topology automatically controls the switching of the current path by utilizing changes in the circuit node potential, thereby achieving dead-time-free logic switching between the high-voltage energy cleaning circuit and the low-voltage precision measurement circuit. The excitation source unit 400 includes a high-voltage output branch, a low-voltage constant current output branch, and a common injection node.

[0042] One end of the high-voltage output branch is connected to the high-voltage DC bus provided by the power supply unit 200, and the other end is connected to the common injection node. The high-voltage output branch is used to provide instantaneous high potential energy to the common injection node. A high-voltage isolation control switch 401 is connected in series in this branch. The high-voltage isolation control switch 401 is an electromagnetic relay or solid-state relay with high insulation withstand voltage characteristics. The insulation resistance of the high-voltage isolation control switch 401 in the open state must be greater than 100MΩ, and the dielectric withstand voltage between the contacts is designed to be 1.5 to 2 times greater than the rated voltage of the high-voltage DC bus to prevent arcing or leakage current generated on the high-voltage side from entering the common injection node.

[0043] The low-voltage constant current output branch includes a precision constant current source module 402 and a unidirectional blocking component 403. The input terminal of the precision constant current source module 402 is connected to a low-voltage DC power supply, and its positive output terminal is connected to the anode of the unidirectional blocking component 403. The cathode of the unidirectional blocking component 403 is connected to a common injection node. The precision constant current source module 402 employs a linear regulated constant current circuit architecture and is configured to output a preset constant measurement current. The precision constant current source module 402 has an inherent maximum output compliance voltage. The compliance voltage refers to the highest port voltage that a constant current source can provide to maintain a constant current output when the load resistance is too high or the circuit is open.

[0044] The unidirectional blocking component 403 utilizes the unidirectional conductivity of a diode to achieve branch isolation and automatic connection. The unidirectional blocking component 403 uses a high-voltage fast recovery diode. Its reverse blocking logic is based on the node potential difference principle: when the high-voltage isolation control switch 401 is closed, the potential of the common injection node is forcibly pulled up to the high-voltage DC bus voltage. Due to system design guarantees Much greater than the maximum output compliance voltage of the precision constant current source module 402 The unidirectional blocking component 403 is in the off state due to reverse bias voltage. At this time, the precision constant current source module 402 is in the voltage saturation output state because the output circuit is open, and its output voltage is clamped at... It is in a state of energy storage awaiting connection.

[0045] To ensure circuit safety during frequent switching, the reverse breakdown voltage parameter of the unidirectional blocking component 403 is... It needs to be determined based on the following inequality:

[0046] ;

[0047] in, This is the DC reverse withstand voltage of the unidirectional blocking component 403; This refers to the high-voltage DC bus voltage of the high-voltage output branch (e.g., 220V). This is an estimated value for the parasitic inductive voltage spikes that may occur during circuit switching. This is a safety margin factor, taking into account the effects of relay operation jitter and power supply ripple. The value range is usually set to 1.2 to 1.5.

[0048] When the high-voltage isolation control switch 401 is open, the potential of the common injection node drops rapidly due to load energy consumption. Once the potential of the common injection node drops below... (in (For the forward conduction voltage drop of the unidirectional blocking component 403), the unidirectional blocking component 403 immediately switches from cutoff to conduction, and the precision constant current source module 402 can inject current into the common injection node without a start-up delay, thereby maintaining the continuity of the load circuit current.

[0049] For the specific circuit of the precision constant current source module 402, those skilled in the art can use an operational amplifier combined with a power MOSFET to form a voltage-controlled current source (VCCS) circuit. Its current stabilization accuracy and temperature drift index are well known in the art and will not be described in detail here.

[0050] See attached document Figure 3 The passive automatic connection mechanism described in this embodiment refers to the circuit behavior of automatically triggering the low-voltage circuit to conduct by utilizing the potential change rate of the circuit node during the process of disconnecting the high-voltage circuit, thereby maintaining the continuity of the load current.

[0051] The passive automatic connection mechanism is based on the voltage competition principle of parallel branches. Physically, the high-voltage and low-voltage branches converge at the same point. The system controls the on / off state of the high-voltage branch, forcing the potential of the common injection node to switch between a high-voltage clamping state and a low-voltage sustaining state. During this process, the electronic load unit 500 maintains a current-drawing state, and its continuous energy consumption is the driving force behind the rapid drop in node potential and triggering the conduction of the low-voltage branch.

[0052] The specific working logic is executed according to the following electrical state transition steps:

[0053] Reverse bias isolation state: The main control unit 100 controls the high-voltage isolation control switch 401 to be in the closed state. The ground potential of the common injection node is forcibly pulled up to the high-voltage DC bus voltage. This voltage value is much higher than the open-circuit compliance voltage of the precision constant current source module 402. Therefore, the unidirectional blocking component 403 is subjected to a deep reverse bias voltage, its internal carriers are depleted, and it is in a high-impedance cutoff state. At this time, although the precision constant current source module 402 is enabled, because the output path is blocked, it automatically operates in voltage saturation mode, waiting for the external potential conditions to allow it to release current.

[0054] Potential drop transition state: The main control unit 100 controls the high-voltage isolation control switch 401 to open. High-voltage energy supply is interrupted. Because the electronic load unit 500 continues to draw current, the charge stored in the parasitic capacitance at the common injection node and the distributed capacitance of the lines is rapidly discharged. Instantaneous value of the voltage to ground at the common injection node. It decreased sharply over time.

[0055] Forward conduction state: When the potential of the common injection node drops below the potential threshold of the low-voltage branch, the voltage polarity across the unidirectional blocking component 403 reverses, establishing a forward bias. The precision constant current source module 402 then exits the voltage saturation mode, and the output current is injected into the common injection node via the unidirectional blocking component 403. Since the conduction time of the unidirectional blocking component 403 (such as a Schottky diode) is on the order of nanoseconds, much faster than the action time of a mechanical relay and the contact cooling time, in the microscopic time domain, the current flowing through the measured contact 800 does not experience a zero-value break, achieving seamless transfer of the current loop.

[0056] To ensure the effectiveness of the connection process, the critical voltage criterion for the unidirectional blocking component 403 to switch from cutoff to conduction is as follows: ;

[0057] in, For public injection nodes The instantaneous value of the voltage to ground at a given moment; The maximum output compliance voltage designed for the precision constant current source module 402 is typically set between 12V and 30V to cover the voltage drop requirements of conventional contact resistance testing. This is the forward voltage drop of the unidirectional blocking component 403, which is typically 0.3V to 0.7V for a Schottky diode.

[0058] In circuit parameter design, to prevent brief current drops during switching, the current loop response bandwidth of the electronic load unit 500 must match the voltage sag rate. Ideal passive automatic switching should meet the following current continuity conditions:

[0059] ;

[0060] in, The actual load current flowing through the tested contact 800 at the moment of switching; To maintain the minimum wetting current required to prevent the micro-metallic bridges at the contact from solidifying and shrinking, keeping the actual load current greater than the minimum wetting current is a key physical condition to prevent the insulating film from re-covering the conductive spots before testing.

[0061] For the selection of the unidirectional blocking component 403, those skilled in the art should select the reverse recovery time (…). Fast recovery diodes or Schottky diodes with a ns of less than 100ns are used to ensure that a conduction path can be quickly established after the high voltage pulse is removed.

[0062] See attached document Figure 2To ensure the safe operation of precision measurement circuits in mixed voltage environments, the system implements a multi-level protection strategy in terms of physical connections and electrical topology. The safety isolation and protection design mainly includes the insulation selection of high-voltage switching actuators, overvoltage crowbar protection circuits on the low-voltage side, and surge suppression networks for common nodes.

[0063] The high-voltage isolating control switch 401 is the actuator connecting the high-voltage DC bus to the common injection node. In the open state, the high-voltage isolating control switch 401 must be able to completely block the coupling of the high-voltage side potential to the common injection node. For hardware selection, a power relay with reinforced insulation is used for the high-voltage isolating control switch 401. The electrical clearance and creepage distance between the relay contacts must meet the withstand voltage requirements for pollution degree 2 in IEC 60664 or similar safety standards. The specific withstand voltage selection is determined according to the following formula:

[0064] ;

[0065] in, This refers to the dielectric withstand voltage index when the relay contacts are open. The highest operating voltage of the high voltage DC bus (e.g., 300V). The safety margin voltage is used to cover power supply ripple and switching transient overshoot, and is usually not less than 500V.

[0066] This high-voltage design aims to prevent continuous arcing when the relay disconnects, ensuring that the leakage current on the high-voltage side is limited to below microamperes after the contacts are physically separated, so as not to affect subsequent precision resistance measurements.

[0067] In the low-voltage constant current output branch, to prevent high voltage from being directly applied to the precision constant current source module 402 due to the failure of the unidirectional blocking component 403 (such as short-circuit breakdown), a crowbar protection circuit based on a combination of a fuse and a transient voltage suppression diode is set in the circuit. The specific connection method of this protection circuit is as follows: the fast-acting fuse is connected in series between the positive output terminal of the precision constant current source module 402 and the anode of the unidirectional blocking component 403; the transient voltage suppression diode is connected in parallel between the anode of the unidirectional blocking component 403 and the circuit ground.

[0068] Its protection principle is as follows: Under normal operation, the transient voltage suppressor diode presents a high-resistance state. When the unidirectional blocking component 403 fails, causing a high voltage intrusion, the branch voltage rises rapidly and exceeds the breakdown voltage of the transient voltage suppressor diode. The transient voltage suppressor diode rapidly transitions from a high-resistance state to a low-resistance conducting state, clamping the intruding high voltage to a safe level and providing a low-resistance discharge path to ground for the high-voltage source. At this time, the current flowing through the fast-acting fuse increases sharply and exceeds its fusing threshold, causing the fuse to physically melt within milliseconds, thereby permanently severing the connection between the fault source and the precision constant current source module 402.

[0069] Breakdown voltage of transient voltage suppressor diode The following matching relationship must be satisfied:

[0070] ;

[0071] in, This is the maximum output compliance voltage of the precision constant current source module 402; This is the absolute maximum rated voltage of the internal output stage components of the precision constant current source module 402.

[0072] To suppress the switching surge caused by the parasitic inductance of the line during the operation of the high-voltage isolation control switch 401, a metal oxide varistor is connected in parallel with ground at the common injection node. This varistor is used to absorb operational overvoltages and limit the peak node voltage to the reverse withstand voltage range of the unidirectional blocking component 403.

[0073] In addition, a positive temperature coefficient thermistor is connected in series in the high-voltage output branch as a self-resetting current-limiting element. This thermistor has a low cold-state resistance at room temperature (typically less than 10Ω), which does not affect the current output capability during high-voltage cleaning. When the circuit current continuously exceeds the protection threshold due to a short-circuit fault... At this time, the resistance of the thermistor increases exponentially due to the self-heating effect, limiting the fault current to a safe range in the milliampere level.

[0074] For the specific parameters of the above-mentioned protection devices, those skilled in the art can refer to the relevant electronic component specifications for selection based on the voltage level and current capacity of the actual circuit, and will not be elaborated here.

[0075] See attached document Figure 2 In this embodiment, an electronic load with a linearly adjustable topology is used in conjunction with a high-impedance differential sampling circuit to achieve the energy dissipation required for high-pressure cleaning and the precise current stabilization function required for contact resistance testing on the same physical port.

[0076] The electronic load unit 500 is connected to the load terminal of the measured contact 800 of the gas relay under test, forming the controlled terminal of the current loop. The circuit architecture of this unit is based on a voltage-controlled current source (VCCS) closed-loop system. The main hardware components include power metal-oxide-semiconductor field-effect transistors (MOSFETs) and precision current sampling resistors. And operational amplifiers. The drain of the power MOSFET is directly connected to the load terminal of the contact, and the source is grounded after being connected in series with a precision current sampling resistor. The operational amplifier forms a negative feedback control loop, and its non-inverting input receives the analog control voltage output from the main control unit 100 via a digital-to-analog converter (DAC). The inverting input terminal acquires the voltage signal to ground on the precision current sampling resistor.

[0077] During operation, the operational amplifier adjusts the gate drive voltage of the power MOSFET, forcing the power MOSFET to operate in the linear amplification region. At this time, the power MOSFET exhibits variable resistance characteristics, dynamically adjusting the channel resistance according to the control voltage to control the flow of the loop current. The following linear relationship is satisfied: ;

[0078] in, The loop current flowing through the tested contact 800 and the electronic load; This is the analog control voltage corresponding to the target current value; This is a precision current sampling resistor, made of an alloy resistor with a temperature coefficient of less than 20ppm / ℃, to suppress resistance drift caused by high current heating.

[0079] The electronic load unit 500 executes two operating modes according to the instructions of the main control unit 100:

[0080] Mode 1: Constant current limiting cleaning mode. During the high voltage source connection stage, the main control unit 100 is set. Corresponding to the preset cleaning current (Typically set to 50mA to 200mA). When high voltage is applied to the contacts, the power MOSFET must simultaneously withstand the high voltage drop (e.g., above 200V) and the cleaning current. To prevent thermal failure of devices, the selection of power MOSFETs must be determined based on their forward bias safe operating area curve to ensure that the transient thermal resistance of the device can withstand the corresponding pulse power impact within the duration (milliseconds) of the high voltage pulse.

[0081] Mode 2: High-frequency response stepped scan mode. During the thermal stress test phase, the main control unit 100 changes according to the time sequence. To complement the passive automatic switching mechanism, the control loop bandwidth of the electronic load is designed to be greater than 10kHz. This high-frequency response characteristic allows the electronic load to quickly adjust the gate voltage of the power MOSFET to compensate for changes in power supply internal resistance and maintain the loop current the instant the excitation source unit 400 switches from a high-voltage source to a low-voltage source. The current is kept constant to prevent it from dropping.

[0082] The measurement circuit adopts a Kelvin four-wire connection topology. The acquisition unit 600 is connected to both ends of the measured contact 800 via two independent voltage sampling leads (Sense+ and Sense-). Crucially, the physical connection point of the voltage sampling leads is located downstream of the unidirectional blocking component 403 (diode) in the excitation source unit 400, i.e., directly connected in parallel to the root of the metal spring of the measured contact 800.

[0083] The front end of the acquisition unit 600 uses a high-precision instrumentation amplifier with an input impedance of The design is for an impedance greater than 10⁹ Ω. Based on the voltage divider principle, the measurement relationship of the voltage sampling circuit is as follows:

[0084] ;

[0085] in, The voltage value measured by the acquisition unit 600; This represents the actual contact voltage drop across the two ends of the contact point; This is the bias current flowing into the instrumentation amplifier; To test the equivalent resistance of the leads.

[0086] because Extremely large, leading to In the nanoampere (nA) range, the voltage drop across the lead resistance is... This is negligible. Furthermore, since the sampling point is located after the diode, the forward voltage drop (approximately 0.7V) generated by the unidirectional blocking component 403 exists only in the current drive circuit and does not enter the voltage sampling circuit. Therefore, the voltage value output by the acquisition unit 600 essentially only reflects the voltage drop generated by the contact resistance of the contact point. According to Ohm's law, the contact resistance of the measured contact 800... The calculation is as follows: ;

[0087] This calculation formula shows that the measurement accuracy of contact resistance depends only on the voltage sampling accuracy, the sampling resistor accuracy, and the DAC output accuracy, and is independent of the nonlinear voltage drop characteristics of the high-voltage protection diode.

[0088] See attached document Figure 3 The method in this embodiment relies on the timing scheduling of hardware circuits by the main control unit 100. By synchronizing the states of the voltage source, current source, and electronic load at a microscopic time scale, it achieves continuous operation of oxide film cleaning and contact resistance thermal stress measurement on the contact surface. The core logic of this process is to utilize the electrical inertia and state preset of the circuit to ensure that the current flowing through the contact remains above the wetting threshold during the transition from the high-voltage breakdown state to the low-voltage measurement state, thereby physically inhibiting the regeneration of the oxide film in the measurement gap.

[0089] The detection process is based on a strict sequential state machine operation, and the specific control steps are described below:

[0090] The main control unit 100 reads the preset test configuration file and locks the key control parameters, including the high-voltage cleaning voltage threshold. (e.g., 200V), cleaning limiting current High pressure maintenance time Initiation current of thermal stress scanning Termination current and current step size The main control unit 100 simultaneously performs zero-point offset calibration on the acquisition unit 600 and sends a command to the power supply unit 200 to activate the high-voltage DC bus.

[0091] Channel selection and trunk line establishment are initiated by the main control unit 100 sending a channel address command to the switching matrix unit 300. Before executing the switching action, the main control unit 100 performs trunk switching logic, confirming that the excitation source unit 400 is in an output-disabled state and the electronic load unit 500 is in a high-blocking-open state. This operation ensures that the relay contacts close under no-current conditions, eliminating the risk of arcing and burning. After sending the switching command, the main control unit 100 executes a fixed mechanical stabilization delay (typically 20ms to 50ms) to wait for the mechanical contacts in the switching matrix unit 300 to fully engage and for the jitter to be eliminated, thereby establishing a stable physical test channel.

[0092] During the high-voltage clamping cleaning phase, the main control unit 100, equipped with the electronic load unit 500, enters constant current operating mode and sets the current setpoint to the cleaning limiting current. Subsequently, the main control unit 100 controls the high-voltage isolation control switch 401 to close. The high-voltage DC bus voltage is applied to both ends of the tested contact 800 of the gas relay. If a high-resistance insulating film exists on the contact surface, the high voltage will break down the film within microseconds. Once breakdown occurs, the loop current rises rapidly, and the hardware closed-loop circuit of the electronic load unit 500 responds quickly, clamping the loop current at a specific voltage level by adjusting the impedance of the internal power transistor. The duration of this state is determined by the high-voltage maintenance time. The timeframe is typically set to 50ms to 100ms to ensure that the conductive spots form a stable metal contact surface under the thermal effect of the current.

[0093] During the preset bias and loop switching phase, as the cleaning phase is about to end, the main control unit 100 first controls the precision constant current source module 402 to turn on its output. At this time, since the high-voltage branch is still in the conducting state, the common node potential is higher than the output potential of the precision constant current source module 402, and the one-way blocking component 403 is in the reverse cut-off state. The precision constant current source module 402 enters the voltage saturation output mode and is in a hot standby state. Subsequently, the main control unit 100 controls the high-voltage isolation control switch 401 to open. As the common node potential drops, the pre-turned precision constant current source module 402 automatically takes over the loop current through the one-way blocking component 403. During this switching process, the main control unit 100 maintains the set value of the sink current of the electronic load unit 500 at [value missing]. This process remains unchanged until the switchover is confirmed to be complete. This "on-then-off" logic ensures that the actual load current is controlled. The following continuity conditions must be met:

[0094] , ;

[0095] in, This refers to the moment when the high-voltage switch is disconnected; The switching transition time (depends on the diode's reverse recovery characteristics, typically less than 1 microsecond) This is the minimum wetting current of the contact. For any time ; It indicates that it belongs to.

[0096] During the stepped thermal stress scanning phase, after confirming that the circuit has switched to the low-voltage precision measurement circuit, the main control unit 100 controls the electronic load unit 500 to enter the sequence scanning mode. The electronic load follows a preset stepped sequence. Adjust the loop current step by step. At each current step... First, the main control unit 100 executes a thermal equilibrium delay (e.g., 10ms) to wait for the Joule heat generated by the current to reach local thermal equilibrium on the microscopic spots of the contact. Then, the acquisition unit 600 is triggered to perform multi-point oversampling to acquire the contact voltage drop data under the corresponding current. .

[0097] After data processing and status reset, and completing the scan of all current steps, the main control unit 100 sequentially shuts down the electronic load unit 500 and the precision constant current source module 402, and disconnects the switching matrix unit 300. The main control unit 100 then utilizes the acquired current and voltage datasets... Based on the resistance-temperature relationship model, contact resistance is calculated and thermal drift characteristics are extracted, ultimately generating a contact health diagnostic report.

[0098] See attached document Figure 3This embodiment details how, during the cleaning phase, the system utilizes the tunneling effect of the high-voltage electric field and the constant current characteristics of the electronic load to collaboratively complete the physical breakdown of the oxide film on the contact surface and the reconstruction of the conductive channels. Physically, this process corresponds to the transient process in electrical contact theory where the insulating film breaks down into spot expansion, and is specifically achieved through the following control steps.

[0099] The electronic load is preset in open loop and prepared for low resistance. Before applying high voltage, the main control unit 100 initializes the electronic load unit 500 and sets the cleaning limiting current. At this point, since the high-voltage side switch is not yet closed, the loop current is zero. Because the error amplifier inside the electronic load has zero voltage at its negative input terminal (current sampling feedback) and is lower than the reference voltage at its positive input terminal, its output voltage automatically saturates to the positive rail of the power supply. This high-level drive signal is applied to the gate of the power MOSFET, forcing the power MOSFET into the deep linear region, exhibiting minimal on-resistance. (Typically in the milliohm range). The physical significance of this hardware preset state is to ensure that the electronic load presents extremely low impedance at the moment of subsequent high voltage connection, so that the power supply voltage is fully applied to the two ends of the tested contact 800 with almost no loss, so as to obtain the maximum breakdown field strength.

[0100] High voltage establishment and field-induced breakdown occur; the main control unit 100 closes the high-voltage isolation control switch 401. High-voltage DC bus voltage. A load is instantaneously applied to the series branch consisting of the tested contact 800 and the electronic load unit 500. At this time, the circuit is in a high-voltage, low-current standby state. Because the surface of the tested contact 800 is covered with a high-impedance insulating oxide film, according to the series voltage division principle, the contact gap bears most of the system voltage. The electric field strength within the insulating film... The following breakdown criteria must be met:

[0101] ;

[0102] in, This is the high voltage DC bus voltage, which needs to be set to a value higher than the breakdown voltage of common contact diaphragm layers (usually selected as above 200V). The physical thickness of the oxide film on the contact surface; This represents the intrinsic dielectric breakdown field strength of the oxide film material. For silver sulfide or copper oxide films, this value is typically in the range of 10. 5 Up to 10 6 On the order of V / cm.

[0103] Microsecond-level transient response and current clamping: When the electric field strength exceeds a critical value, the insulating film undergoes electrical breakdown, and the contact impedance drops by orders of magnitude within a nanosecond time. At this time, the loop current exhibits a sharp increasing trend determined by the power supply voltage divided by the residual line resistance. The error amplifier in the electronic load unit 500 detects the rapid rise in voltage drop across the sampling resistor and its proximity to the set threshold, then exits the positive-track saturation state and rapidly reduces the gate voltage of the power MOSFET. The operating point of the power MOSFET quickly shifts from the linear region to the saturation region. To prevent excessive inrush current during the feedback loop response delay, the operational amplifier selected in this embodiment must have high slew rate characteristics. After steady-state establishment, the drain-source voltage of the power MOSFET... The voltage automatically rises, absorbing the high voltage originally applied to the contacts and limiting the circuit current. The voltage balance equation under this condition is:

[0104] ;

[0105] in, This is the residual voltage drop across the contacts after breakdown (typically less than 1V). This is the dynamic voltage across the drain and source of the power MOSFET. This voltage is automatically adjusted according to the contact impedance, thus serving as an active current limiter. This refers to the fixed line resistance in the circuit.

[0106] Electrothermal wetting and spot stabilization. When the current is limited to... Under these conditions, the system maintains high voltage for a specified time. This stage corresponds to the spot enlargement process, where the Joule heating generated by a constant current flowing through the microscopic breakdown channels softens or partially melts the microscopic metal bumps on the contact surface, thereby increasing the effective conductive area. This process is called electrowetting. The effective energy density injected into the contacts during the cleaning process... Represented as:

[0107] ;

[0108] in, This represents the instantaneous value of the contact resistance, which changes dynamically over time. The main control unit 100 controls the high-voltage holding time. (Typically set to 50ms to 100ms) ensure that energy injection stops immediately after a stable metal contact spot has formed. For cleaning, limit the current. The selection of the current should be lower than the macroscopic fusion welding threshold of the contact material, usually set to 10% to 20% of the rated operating current of the contact.

[0109] See attached document Figure 3This embodiment details the physical mechanism by which the load current continuity is achieved during the process of cutting off a high-voltage source and connecting a low-voltage precision constant current source, utilizing the potential gradient of the circuit node and the unidirectional conductivity of the unidirectional blocking component 403, combined with the energy storage effect of the line parasitic capacitance. This process is a passive commutation process based on the characteristics of analog circuits, and is specifically implemented through the following control steps.

[0110] Precision constant current source pre-activation and reverse isolation: Before the main control unit 100 performs the high-voltage disconnection action, the precision constant current source module 402 in the power supply unit 200 is first activated. At this time, the high-voltage isolation control switch 401 is in the closed conducting state, and the ground potential of the common injection node is... Clamped to the voltage of the high voltage DC bus (e.g., 200V). At this time, the unidirectional blocking component 403 connected in series in the output path of the precision constant current source is subjected to a reverse bias voltage. :

[0111] ;

[0112] in, The instantaneous potential of the common injection node; This is the internal potential of the positive output terminal of the precision constant current source module 402; The maximum open-circuit compliance voltage is set for the precision constant current source module 402. This voltage setting must meet the voltage drop requirements of the subsequent low-voltage circuit.

[0113] In this state, the unidirectional blocking component 403 is in the reverse cutoff region, isolating the high-voltage bus from the low-voltage output stage of the precision constant current source. Simultaneously, due to the blocked output circuit, the internal control loop of the precision constant current source module 402 saturates the output voltage to... It is in voltage standby mode.

[0114] The high-voltage source is physically disconnected, and the capacitor discharge buffer is activated. The main control unit 100 controls the high-voltage isolation control switch 401 to open. With the separation of the mechanical contacts, the high-voltage DC bus stops supplying power to the common injection node. At this time, although the external power supply is cut off, due to the distributed capacitance (including line stray capacitance and electronic load input capacitance) between the common injection node and ground, the charge stored in this distributed capacitance is discharged through the electronic load unit 500, which is in a constant current absorption state. This distributed capacitance acts as a transient energy buffer, reducing the voltage at the common injection node. It is not a vertical mutation that occurs, but rather follows... The discharge pattern exhibits an exponential decrease. In the initial stage of the voltage drop, the capacitor discharge current maintains its flow through the contacts. The system does not reset to zero temporarily, allowing physical time for power switching.

[0115] Automatic commutation based on potential difference, when the voltage of the common injection node... When the voltage drops to the critical threshold, the bias state of the unidirectional blocking component 403 flips from reverse cutoff to forward conduction. The critical condition for this physical commutation is:

[0116] ;

[0117] in, This is the forward conduction voltage drop of the unidirectional blocking component 403.

[0118] When this condition is met, the precision constant current source module 402 immediately injects current into the common injection node through the conducting unidirectional blocking component 403. To ensure seamless current connection, a Schottky diode or ultrafast recovery diode with an extremely short forward recovery time (typically less than 50ns) must be selected as the unidirectional blocking component 403 to ensure that the diode can quickly establish a conduction path at the moment of voltage reversal. At this time, the total current flowing through the measured contact 800... It is composed of the superposition of capacitor discharge current and low-voltage source injection current, and is completely switched to low-voltage source power supply in a very short time.

[0119] To ensure the current stability and voltage margin of the electronic load, the circuit enters a low-voltage steady state after power switching. To ensure that the electronic load unit 500 can maintain its set constant current sinking capacity under low voltage without saturation distortion, the system voltage design must meet the following voltage margin constraints:

[0120] ;

[0121] in, The minimum terminal voltage required to maintain linear constant current control of the electronic load unit 500 (typically 1V to 3V, depending on the conduction characteristics of the power MOSFET and the voltage drop across the sampling resistor).

[0122] Provided the above constraints are met, the electronic load unit 500 can utilize its high-bandwidth control loop to compensate for voltage fluctuations during the switching process, ensuring the total current flowing through the measured contact 800. Always above the critical current required to maintain the metallic conductive spot (Usually set to 10mA or higher), thus physically preventing the regeneration of the oxide film.

[0123] See attached document Figure 3In the low-voltage precision measurement stage, the method of this embodiment utilizes a programmable load to generate a monotonically increasing current sequence. By applying a quantized current excitation to the measured contact 800, the dynamic response characteristics of the contact resistance as a function of current density are analyzed. This process distinguishes between clean metal contacts and residual oxide film contacts based on the difference between the positive temperature coefficient characteristics of the metal conductor and the negative differential resistance characteristics of the semiconductor film. This control process is implemented through the following specific control steps.

[0124] The scan sequence list is generated, the main control unit 100 reads the test configuration parameters, and constructs the current control sequence in the register. The sequence is an arithmetic progression, where the nth... Target current value at each test point The calculation is as follows:

[0125] , ;

[0126] in, To construct the current control sequence in the register, it is set to be greater than the minimum wetting current of the contact (usually 10mA) to ensure the stability of the measurement base; The current step size must satisfy the following conditions: ,in Program the resolution of the current for the electronic load; To determine the total number of steps scanned, the termination current is used. constraint.

[0127] Current loading and thermal balance establishment: The main control unit 100 will display the current target current value. The signal is sent to the electronic load unit 500. The electronic load adjusts the conduction level of the power MOSFET to stabilize the loop current. After the current is established, the main control unit 100 performs a delay operation for a duration of [duration missing]. (Dwell time). This time is set based on the thermal time constant of the measured contact at 80°C, with the aim of waiting for the Joule heat generated by the current. The heat conduction from the contacts to the spring substrate reaches a dynamic balance, stabilizing the contact spot temperature. For conventional signal relays, to avoid excessive local temperature rise leading to softening voltage drift, Set to 10ms to 50ms.

[0128] Synchronous integration oversampling is employed. After thermal equilibrium is established, the main control unit 100 triggers the acquisition unit 600 to perform voltage sampling. To eliminate common-mode interference from the 50Hz / 60Hz power frequency electromagnetic field on the microvolt-level voltage signal, the sampling window time is... Strictly designed to be an integer multiple of the power frequency cycle:

[0129] ;

[0130] in, It is a positive integer (usually 1, 5, 10); The power grid frequency (50Hz or 60Hz).

[0131] The acquisition unit 600 performs continuous integration or high-speed multi-point averaging within this time window to calculate the effective voltage measurement value. It can suppress periodic noise components to the greatest extent.

[0132] Contact resistance calculation and differential characteristic determination, based on the main control unit 100. The current contact resistance is calculated. Then, the main control unit 100 calculates the differential rate of change of resistance with respect to current (i.e., differential resistance characteristic), as a physical criterion for judging the state of the contact surface.

[0133] ;

[0134] The judgment logic is as follows:

[0135] like This indicates that the contact exhibits the positive temperature coefficient of resistance characteristic of a metallic conductor. With the target current value... Increased temperature of the spot leads to increased lattice vibrations, resulting in increased electron scattering and contact resistance. It shows a slight upward trend. This corresponds to a clean metal contact state.

[0136] like (in A negative threshold indicates that the contact exhibits negative resistance characteristics. This is typically due to the reduced potential barrier of the residual semiconductor oxide film under the influence of electric and thermal fields, leading to enhanced tunneling effects. This corresponds to the residual state of the oxide film.

[0137] If detected ( Set to 1.5 times the maximum contact resistance value specified in the contact product manual) or If the value remains negative, the main control unit 100 determines that the test is unqualified and terminates the scan prematurely.

[0138] Sequence iteration, main control unit 100 judges test points Has it been achieved? If it is not achieved, then... It then returns to the current loading and thermal equilibrium establishment steps; if all step tests have been completed, it generates a complete... The dataset's test report, and the electronic load and power module are shut down according to the timing sequence. Analysis of this dataset... The slope of the curve in the coordinate system can be used to quantitatively characterize the microscopic physical properties of the contact point.

[0139] See attached document Figure 3 The main control unit 100 uses the acquired current and voltage dataset By employing numerical regression analysis, the influence of current-induced thermal effects on resistance measurement is decoupled, and the intrinsic physical parameters of the contact are extracted. This process is based on a physical temperature rise model of conductor resistance and is implemented through the following algorithmic steps.

[0140] Data filtering and monotonicity pre-detection: The main control unit 100 first checks the contact resistance. Perform a moving average filter to suppress random electromagnetic noise. Set the filter window length to [value]. (Usually an odd number, such as 3 or 5). For the center data point within the window, calculate its deviation from the window mean. If the deviation exceeds a preset noise tolerance (e.g., 3 times the local standard deviation), replace the outlier with the linear interpolation result of the neighboring points within the window. Subsequently, the algorithm performs a physical monotonicity check. Since pure metals have a positive temperature coefficient, the resistance should theoretically increase monotonically when the temperature rises due to increased current. If a continuous decreasing trend appears in the data sequence (i.e., the differential derivative...), the algorithm will perform a physical monotonicity check. If the amplitude exceeds the noise floor of the measurement system, the main control unit 100 marks that the data segment has semiconductor tunneling characteristics, indicating that there is still an unbroken oxide film remaining on the contact surface. At this time, the test result is directly determined to be a cleaning failure, and no further fitting is performed.

[0141] An electrothermal coupling physical model is established. For thoroughly cleaned metal contacts, the microscopic temperature rise in the contact area follows the Kohlausch relationship (voltage-temperature relationship) in physics. According to the Wiedemann-Franz law, the highest temperature of the conductive spot... Voltage drop across the contact There exists a definite functional relationship. Because within a small temperature rise range, the resistivity of the metal changes linearly with temperature, and... The contact resistance of the contact point can be derived. With test current The two sides satisfy a second-order parabolic relationship:

[0142] ;

[0143] in, To test current Theoretical resistance value under action; The intrinsic zero-current resistance is the cold-state contact resistance after removing the influence of current heating effect. This value truly reflects the physical contact area of ​​the contact point. The thermal drift coefficient is determined by the temperature coefficient of resistance, thermal conductivity, and geometry of the contact material, and characterizes the sensitivity of the contact resistance to the square of the current. To measure the residual.

[0144] Least square regression and goodness-of-fit verification: The main control unit 100 uses the least squares method to perform regression on the preprocessed data pairs. Perform linear regression. Construct a system of normal equations with the objective of minimizing the sum of squared errors, and solve for the model parameters:

[0145] ;

[0146] ;

[0147] Among them, the transformation variable , ; This represents the total number of data points. For the first The values ​​of the independent variable for each data point; For the first The values ​​of the dependent variable for each data point; In all data points and The sum of the products; For all independent variables The sum of the values ​​of ; For all dependent variables The sum of the values ​​of; All independent variables The sum of the squares of the values; For the regression line in the dependent variable The intercept on the independent variable, which represents the value when the independent variable... When, dependent variable The predicted value.

[0148] To ensure the physical reliability of the calculation results, the main control unit 100 further calculates the fitting determination coefficients. :

[0149] ;

[0150] in, The average of the values ​​of all independent variables; Take values ​​for all dependent variables The average value; for and The sum of the products of the deviations from the mean reflects the degree of linear correlation between the two. for The sum of squared deviations from the mean reflects the independent variable The degree of dispersion; for The sum of squared deviations from the mean reflects the dependent variable The overall degree of fluctuation.

[0151] If calculated If the measurement data is below the preset confidence threshold (e.g., 0.95), it indicates that the measurement data does not conform to the physical temperature rise law, which may be caused by mechanical vibration of the contact or unstable contact. The main control unit 100 will output a fitting divergence alarm and mark the measurement as invalid.

[0152] The thermal stability index is quantified, and under the premise of effective fitting, the main control unit 100 uses the calculated... Value calculation of relative thermal drift rate :

[0153] ;

[0154] in, The maximum current setting in the scan sequence, relative thermal drift rate The maximum percentage of resistance drift caused by Joule heating of the contact under full load operating conditions is quantified. The smaller the value, the more stable the conductive spots of the contact and the stronger its resistance to thermal shock.

[0155] Multi-dimensional hierarchical judgment, with 100 bases for the main control unit. , and The system comprehensively assesses the health status of the contacts. It retrieves pre-stored threshold values, including the upper limit of static resistance. With thermal drift limit The method for determining these two thresholds is as follows: Statistical modeling is performed on at least 30 qualified relays from the same batch, and the threshold value is taken as... The mean of the distribution plus three standard deviations ( As Take it The 99th percentile of the distribution is used as The decision logic is as follows:

[0156] like The failure was determined to be due to residual oxide film, and the physical mechanism was dominated by the negative temperature coefficient effect of semiconductors.

[0157] like The failure was determined to be due to excessive contact resistance, indicating insufficient effective contact area.

[0158] like and The result was determined to be a potential risk of thermal stability degradation, indicating that although the static resistance of the contacts was qualified, there was a risk of local overheating under high current.

[0159] like and and The condition was determined to be healthy.

[0160] The main control unit 100 will finally extract the feature parameters ( The diagnosis conclusions should be written into the test report.

[0161] This embodiment was applied to the annual maintenance of a QJ-80 type gas relay on the main transformer of a 110kV substation. The object of the inspection was the normally open reed switch contact inside the relay. Because this contact was in an open state for a long time in an oil-filled environment, there was a risk of silver sulfide oxide film forming on its surface.

[0162] Test parameter settings: Connect the detection device of this invention to both ends of the relay contacts via a four-wire test clip. The system configuration is as follows:

[0163] High-pressure cleaning stage: Set the cleaning voltage to 48V DC and the current limit to 100mA.

[0164] Low-voltage measurement phase: Set the constant current source output current to 50mA (for transient switching test) and 100mA to 500mA (for dynamic resistance scanning).

[0165] Judgment threshold: The minimum wetting current threshold is set to 10mA (i.e., attached). Figure 4 (The boundary of the gray shaded area in the text).

[0166] Transient response analysis of power switching (corresponding appendix) Figure 4 After high-pressure cleaning is completed, the system controls the high-pressure source to disconnect and connect a low-voltage constant current source. The contact circuit current waveform acquired by the oscilloscope is shown in the attached figure. Figure 4 As shown:

[0167] Traditional testing methods (shown by dashed lines): In The high-voltage source was immediately disconnected, and the circuit current instantly dropped from 100mA to 0mA. Subsequently, to Within this range, the current remains at zero, creating a dead zone lasting approximately 15 microseconds. During this period, the contacts completely lose current support, posing a very high risk of regeneration of the surface oxide film. Afterwards, the relay mechanically closes, and the current waveform shows obvious overshoot and oscillation (mechanical contact bounce), approximately at... It then gradually stabilized at 50mA.

[0168] Embodiment of the present invention (shown by solid lines): In With the high-voltage source constantly disconnected, the current did not experience a sudden drop due to the automatic freewheeling circuit design; instead, it exhibited a smooth exponential decay characteristic. Throughout the transition process, the loop current remained above 50mA, far exceeding the 10mA threshold for the power outage danger zone, achieving seamless switching. This process avoided secondary oxidation of the contact surfaces caused by current interruption, ensuring the accuracy of subsequent measurement data.

[0169] Contact resistance dynamic characteristic diagnosis (corresponding appendix) Figure 5 After the current stabilizes, the device controls the constant current source to perform a step scan within the range of 100mA to 500mA, with a step size of 50mA. The contact resistance is calculated based on the collected voltage and current data, and linear regression analysis is performed. The results are shown in the attached figure. Figure 5 As shown:

[0170] Scenario A: Qualified contact (above image). The measured data points (solid black circles) are closely distributed near the theoretical fitting curve. As the scanning current increases from 100mA to 500mA, the contact resistance value slowly rises from approximately 10.5mΩ to approximately 10.7mΩ. This characteristic of resistance increasing slightly with current is consistent with the Joule heating effect (positive temperature coefficient) of pure metallic conductors, and the data dispersion is extremely small, indicating good metal contact on the contact surface and that the oxide film has been completely removed. The result is deemed qualified.

[0171] Scenario B: Failed contact (see image below). The measured data points (hollow cubes) show a clear discrete distribution. As the scanning current increases, the contact resistance actually decreases, from approximately 13.5 mΩ at 100 mA to approximately 11.5 mΩ at 500 mA. This negative differential resistance characteristic of high resistance at low current and low resistance at high current is a typical feature of semiconductor tunneling, indicating that unbroken insulating oxide film still remains on the contact surface. Combined with the large data dispersion, the contact is determined to have a potential contact defect, resulting in failure.

Claims

1. A gas relay contact performance testing device, characterized in that, Including the main control unit (100); A power supply unit (200) is used to convert an external AC power supply into a DC operating voltage; A switching matrix unit (300) is located between the common injection node and the test contact (800) to establish a current path between the excitation source unit (400) and the test contact (800); An excitation source unit (400) is connected between the power supply unit (200) and the switching matrix unit (300). The excitation source unit (400) includes a high-voltage output branch and a low-voltage constant current output branch converging at the common injection node. It is used to switch the output of a high-voltage signal or a constant current signal to the measured contact (800) under the control of the main control unit (100). An electronic load unit (500) is connected to the load terminal of the test contact (800) and is used as a controlled current regulating component to regulate the loop current flowing through the test contact (800). The acquisition unit (600) has its input terminal connected in parallel to both ends of the test contact (800) and is used to acquire the voltage drop signal of the test contact (800) and send it to the main control unit (100). The main control unit (100) is used to control the excitation source unit (400) and the electronic load unit (500) to work together to perform contact performance detection.

2. The gas relay contact performance testing device according to claim 1, characterized in that, One end of the high-voltage output branch is connected to the high-voltage DC bus provided by the power supply unit (200), and the other end of the high-voltage output branch is connected to the common injection node. A high-voltage isolation control switch (401) is connected in series in the high-voltage output branch. The low-voltage constant current output branch includes a precision constant current source module (402) and a one-way blocking component (403); the positive output terminal of the precision constant current source module (402) is connected to the anode of the one-way blocking component (403), and the cathode of the one-way blocking component (403) is connected to the common injection node; The common injection node is connected to the switching matrix unit (300) as the output terminal of the excitation source unit (400).

3. The gas relay contact performance testing device according to claim 2, characterized in that, The unidirectional blocking component (403) is used to automatically control the switching of the current path by utilizing the potential change of the common injection node; When the high-voltage isolation control switch (401) is closed, the potential of the common injection node rises to the voltage of the high-voltage DC bus, and the unidirectional blocking component (403) is subjected to reverse bias voltage and is in the cut-off state. The unidirectional blocking component (403) blocks the high voltage from entering the precision constant current source module (402). When the high-voltage isolation control switch (401) changes from closed to open and the electronic load unit (500) maintains the current-absorbing state, the potential of the common injection node drops. When the potential of the common injection node drops to below the difference between the output compliance voltage of the precision constant current source module (402) and the forward conduction voltage drop of the unidirectional blocking component (403), the unidirectional blocking component (403) changes from the cut-off state to the forward conduction state, and the precision constant current source module (402) injects current into the common injection node through the unidirectional blocking component (403).

4. The gas relay contact performance testing device according to claim 2, characterized in that, A positive temperature coefficient thermistor is connected in series in the high voltage output branch, and the positive temperature coefficient thermistor is used as a self-recovering current limiting element. A metal oxide varistor is connected in parallel at the common injection node, and the metal oxide varistor is used to suppress switching surge voltage. The high-voltage isolation control switch (401) is a power relay with reinforced insulation structure. The dielectric withstand voltage of the power relay in the open contact state is greater than the highest operating voltage of the high-voltage DC bus.

5. The gas relay contact performance testing device according to claim 2, characterized in that, The low-voltage constant current output branch is equipped with a crowbar protection circuit, which includes a fast-acting fuse and a transient voltage suppression diode. The fast-acting fuse is connected in series between the positive output terminal of the precision constant current source module (402) and the anode of the unidirectional blocking component (403); The transient voltage suppression diode is connected in parallel between the anode of the unidirectional blocking component (403) and the circuit ground; The breakdown voltage of the transient voltage suppressor diode is between the maximum output compliance voltage of the precision constant current source module (402) and the absolute maximum rated voltage of the internal components of the precision constant current source module (402).

6. The gas relay contact performance testing device according to claim 1, characterized in that, The main circuit of the electronic load unit (500) includes a power metal-oxide-semiconductor field-effect transistor, a precision current sampling resistor, and an operational amplifier. The drain of the power metal-oxide-semiconductor field-effect transistor is connected to the load terminal of the contact under test (800), and the source of the power metal-oxide-semiconductor field-effect transistor is connected in series with the precision current sampling resistor and then grounded. The operational amplifier forms a negative feedback control loop. The non-inverting input of the operational amplifier receives the analog control voltage from the main control unit (100). The inverting input of the operational amplifier acquires the voltage signal to ground on the precision current sampling resistor. The output of the operational amplifier drives the gate of the power metal-oxide-semiconductor field-effect transistor.

7. The gas relay contact performance testing device according to claim 6, characterized in that, The main control unit (100) controls the electronic load unit (500) to execute the constant current limiting cleaning mode and the high frequency response step scan mode; In the constant current limiting cleaning mode, the electronic load unit (500) clamps the loop current to a preset cleaning limiting current value when the excitation source unit (400) outputs a high voltage signal; In the high-frequency response stepped scanning mode, the electronic load unit (500) changes the analog control voltage in a time sequence to perform stepped current scanning, and is used to adjust the gate voltage of the power metal oxide semiconductor field-effect transistor to maintain a constant loop current at the instant when the excitation source unit (400) switches to output a high voltage signal or a constant current signal.

8. The gas relay contact performance testing device according to claim 2, characterized in that, The acquisition unit (600) adopts a Kelvin four-wire connection structure, and the two voltage sampling leads of the acquisition unit (600) are connected to the two ends of the contact under test (800); The physical connection point of the voltage sampling lead inside the gas relay contact performance testing device is located between the cathode of the unidirectional blocking component (403) and the contact under test (800). The front-end circuit of the acquisition unit (600) employs a high input impedance instrumentation amplifier, and the acquisition unit (600) is used to perform multi-point oversampling at each current step of the stepped current scan.

9. The gas relay contact performance testing device according to claim 1, characterized in that, The main control unit (100) runs a contact resistance dynamic analysis algorithm; The main control unit (100) is used to perform numerical analysis on the current and voltage datasets collected by the acquisition unit (600) based on the physical temperature rise model of conductor resistance. The numerical analysis process includes: using the least squares method to perform linear regression calculation on the square of the current value and the resistance value, and calculating the intrinsic zero current resistance value as the linear regression intercept and the thermal drift coefficient as the linear regression slope. The main control unit (100) is used to calculate the ratio of the thermal drift coefficient to the intrinsic zero current resistance value to obtain the relative thermal drift rate; The main control unit (100) makes a multi-dimensional classification judgment on the health status of the tested contact (800) based on the intrinsic zero current resistance value, the thermal drift coefficient and the relative thermal drift rate.

10. A gas relay contact performance testing device according to claim 1, characterized in that, The device further includes an interaction unit (700), which is connected to the main control unit (100). The interaction unit (700) includes a display screen, buttons, and a voice module. The interactive unit (700) is used to receive test configuration parameters input by the user. The test configuration parameters include high-voltage cleaning voltage threshold, cleaning limiting current, high-voltage holding time, and thermal stress scanning current sequence. The interactive unit (700) is used to display the contact health diagnostic report generated by the main control unit (100).

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