A method and system for electrical safety assessment of a distribution box

Abstract

The application discloses a power distribution box electric safety evaluation method and system, and belongs to the technical field of electrical parameter measurement and electrical fault detection. In view of the fact that the real micro-voltage drop of the to-be-evaluated electric connection section and the equivalent additive zero offset of the micro-voltage drop difference collection channel are in the same order of magnitude when the power distribution box is in low-load operation, and obvious errors are caused when the connection resistance is directly converted according to the micro-voltage drop and the loop current, the application establishes a first measurement window and a second measurement window before and after the load step, respectively, when the target loop naturally generates a load step, and screens an effective self-calibration step which is stable on the power supply side, ends the switch transient state and meets the quasi-isothermal condition. The application can weaken the influence of the measurement channel zero offset on the low-load connection state evaluation without power interruption and without the need of actively injecting a special test current, and can assist in distinguishing the zero point drift of the collection channel and the actual electric connection deterioration.

Description

Technical Field

[0001] This invention relates to the fields of electrical parameter measurement, electrical performance testing, and electrical fault detection, specifically to a method and system for assessing the electrical safety of distribution boxes. Background Technology

[0002] Low-voltage distribution boxes distribute electrical energy to end loads through circuit breakers, busbars, terminals, and branch conductors. Besides overcurrent, over / undervoltage, and residual current anomalies, deterioration of electrical connections, such as circuit breaker contact oxidation, loose terminals, and decreased contact pressure at busbar lap joints, can also pose electrical safety risks. Deterioration in electrical connections typically manifests first as increased contact resistance at the connection points, further leading to increased voltage drop and localized Joule heating.

[0003] For online detection of electrical connection status, the connection resistance can be calculated by simultaneously acquiring the voltage difference across the connection point and the loop current flowing through that connection point. Alternatively, the connection status can be inferred by combining the load current and the temperature rise at the connection point. This method can, to a certain extent, determine whether there are significant abnormalities in the contact resistance of the electrical connection.

[0004] However, under the special operating conditions of low-load operation of the distribution box, the actual connection resistance of normal circuit breaker contacts, busbar connection points, and well-tightened terminals is usually in the micro-ohm range. When the load current of the target circuit is small, the actual resistance voltage drop formed by the electrical connection section to be evaluated may be only in the millivolt or even sub-millivolt range.

[0005] At the same time, errors such as differential amplifier input offset, isolation measurement link zero drift, analog-to-digital converter zero error, sampling wire thermoelectric potential, and residual differential components after high common-mode voltage coupling in the micro-dropout differential acquisition channel will combine to form an approximately additive equivalent additive zero bias.

[0006] When the connection resistance is determined by directly dividing the measured micro-voltage drop of the connection segment by the current loop current, under low load conditions, the equivalent additive zero bias is also divided by the smaller loop current, thus being converted into a larger apparent resistance error.

[0007] For example, when the actual connection resistance of a healthy electrical connection segment is 80 μΩ and the loop current is 5 A, the actual resistance voltage drop is approximately 0.4 mV. If the micro-voltage drop differential acquisition channel forms an equivalent additive zero bias of 0.9 mV under this operating condition, the measured connection segment micro-voltage drop will be approximately 1.3 mV. If 1.3 mV is directly divided by 5 A, an apparent connection resistance of approximately 260 μΩ is obtained, which deviates significantly from the actual connection resistance. Furthermore, when the direction of the equivalent additive zero bias is opposite to the direction of the actual resistance voltage drop, it may mask the actual early increase in connection resistance.

[0008] While power-off zero-current calibration of the micro-voltage drop acquisition channel can obtain a static zero point, the distribution box typically provides continuous power, and the temperature, common-mode voltage, and electromagnetic environment of the micro-voltage drop acquisition channel during actual operation may differ significantly from the power-off zero-calibration state. Actively injecting a dedicated test current into the operating target circuit requires additional test hardware or altering the user's normal load conditions.

[0009] Furthermore, if two load states with a long interval are arbitrarily selected for two-point calculations, the Joule heating generated by the change in load current will alter the temperature of the electrical connection segment being evaluated, thus changing its actual connection resistance. In this case, the difference between the two operating points simultaneously includes both measurement channel error and changes in the thermal state of the connection segment, making it unsuitable for direct channel self-calibration.

[0010] Therefore, the technical problem that this invention needs to solve is: under the operating conditions of the distribution box without power interruption and without actively applying a dedicated test current, how to utilize the load changes that naturally occur during the normal operation of the target circuit to form two comparable operating points in a short period of time before the thermal state of the connection section changes significantly, so as to reduce the influence of the equivalent additive zero bias on the connection resistance evaluation results in the low load micro voltage drop measurement. Summary of the Invention

[0011] The purpose of this invention is to provide a method and system for assessing the electrical safety of distribution boxes. This method establishes two quasi-isothermal operating points by utilizing the naturally formed load step of the target circuit. Based on the changes in micro-voltage drop and current at the two operating points using the same micro-voltage drop differential acquisition channel, the incremental connection resistance is determined. Furthermore, the equivalent additive zero bias is calculated to correct the micro-voltage drop under subsequent low-load conditions. To achieve the above objective, this invention adopts the following technical solution:

[0012] This invention first simultaneously collects the loop current, supply voltage, residual current of the target loop, and the micro voltage drop of the connection section at both ends of the electrical connection section to be evaluated.

[0013] The micro voltage drop of the connection section is preferably obtained by directly bridging the current inflow side and the current outflow side of the electrical connection section to be evaluated by the same micro voltage drop differential acquisition channel, so as to avoid obtaining the millivolt-level voltage drop by subtracting the measurement results of two independent high-voltage measurement channels.

[0014] During the operation of the target circuit, the load step naturally formed by the start-up, stop, power level change or production cycle change of the electrical equipment is detected.

[0015] When the current change before and after a load step reaches the preset minimum self-calibration current difference, further determine whether the power supply side is stable before and after the step, whether the step transient has ended, and whether the two measurement windows before and after the step meet the quasi-isothermal conditions.

[0016] Set the first measurement window in the stable operating range before the load step occurs. A second measurement window is set during the stable operating interval after the transient shielding period following the load step. .

[0017] For the AC target circuit, in the first measurement window Second measurement window Within each sample, synchronous sampling points are selected near the peak value of the same current polarity and whose rate of change of current satisfies the following formula: ;

[0018] in, Represents the instantaneous loop current of the target loop; Indicates time; Represents the differential operator; Represents loop current The differential; Indicates time The differential; Represents loop current Relative to time The instantaneous rate of change; This indicates the preset current change rate threshold.

[0019] For the first measurement window Statistical processing is performed on multiple synchronous micro-voltage drop samples and loop current samples that meet the aforementioned conditions to obtain the first micro-voltage drop characteristic. and first current characteristics For the second measurement window Statistical processing was performed on multiple synchronous micro-voltage drop samples and loop current samples that met the corresponding conditions to obtain the second micro-voltage drop characteristic. Second current characteristics .

[0020] First measurement window Second measurement window When the quasi-isothermal condition is met, and the equivalent additive zero bias of the micro-pressure drop differential acquisition channel remains approximately stable between the two windows, the two operating points respectively satisfy: ; ;

[0021] in: Indicates the first measurement window With the second measurement window The equivalent connection resistance of the electrical connection segment to be evaluated during the corresponding quasi-isothermal period, in units of ;

[0022] This indicates the equivalent additive zero bias of the micro-voltage drop differential acquisition channel during the current calibration period, expressed in V.

[0023] Subtracting the two equations above, determine the incremental connection resistance: ;

[0024] in: Indicates incremental connection resistance, in units of ;

[0025] This represents the characteristic change in micro-voltage drop between two operating points before and after a load step, expressed in V;

[0026] This represents the characteristic change in loop current between two operating points before and after a load step change, expressed in amperes (A).

[0027] To reduce the amplification of random errors caused by an excessively small denominator, only when the following condition is met:

[0028] When the load step is used, the corresponding self-calibration step is taken as the effective self-calibration step.

[0029] in, This indicates the preset minimum self-calibration current difference, in amperes (A).

[0030] Obtain incremental connection resistance Then, based on the first operating point, the equivalent additive zero bias within the current calibration period is calculated: ;

[0031] Alternatively, consistency can be checked using the following formula based on the second working point: In equivalent additive zero bias During the validity period, for the first A stable measurement window yields micro-pressure drop characteristics. and current characteristics The corrected connection resistance is determined according to the following formula: ;

[0032] in: Indicates the first The connection resistance after zero bias correction corresponding to each stable measurement window, in units of ;

[0033] Indicates the first The micro-voltage drop characteristics obtained within a stable measurement window, in units of V;

[0034] Indicates the first The loop current characteristics obtained within a stable measurement window, in A;

[0035] Indicates the sequence number of the stable measurement window. It is a positive integer;

[0036] Subscript Indicates correction.

[0037] When the following conditions are met: When not using a corrected connection resistor Update on safety risks.

[0038] in, This indicates the preset minimum effective measurement current, in amperes (A).

[0039] The quasi-isothermal condition can be determined using either a time criterion or a temperature criterion. When using the time criterion, the second measurement window... The end time is earlier than the quasi-isothermal cutoff time determined based on the thermal inertia of the electrical connection segment to be evaluated. .

[0040] When using temperature criteria, the temperature of the electrical connection section to be evaluated is acquired by the temperature acquisition unit, and the temperature is measured within the first measurement window. With the second measurement window When the temperature change between the two conditions does not exceed the preset temperature change threshold, the quasi-isothermal condition is determined to be met.

[0041] For AC circuits, the selected synchronous sampling point is preferably close to the peak value of the circuit current to reduce the influence of the inductive voltage component generated by the equivalent distributed inductance of the electrical connection section to be evaluated.

[0042] The inductive voltage component can be expressed as: ;

[0043] in: This represents the inductive voltage component of the electrical connection segment to be evaluated, in units of V; This represents the equivalent distributed inductance of the electrical connection segment to be evaluated under the current measurement path, in H. Indicates the instantaneous loop current of the target loop, in amperes (A). Indicates time, in seconds;

[0044] It represents the instantaneous rate of change of the loop current relative to time, with units of A / s.

[0045] For each new valid self-calibration step obtained, the corresponding incremental connection resistance is re-obtained. and equivalent additive zero bias .

[0046] When the equivalent additive zero bias Significant changes have occurred, and the incremental connection resistance... When maintaining within the healthy connection reference boundary, the zero-point drift of the micro-dropout differential acquisition channel is preferentially identified, and the new equivalent additive zero bias is utilized. Updated for subsequent low-load, low-voltage drop correction.

[0047] When the equivalent additive zero bias Maintaining within the zero-bias stability boundary, while incrementally connecting the resistance. When a series of effective self-calibration steps continuously increase or exceed the healthy connection reference boundary, it is considered evidence of actual degradation of the electrical connection segment to be evaluated.

[0048] Among them, the zero-bias stability boundary is used to characterize the allowable range of equivalent additive zero bias during the healthy operation phase, and the zero-bias drift boundary is used to characterize the upper limit of the allowable change in equivalent additive zero bias between consecutive effective self-calibration steps; the zero-bias stability boundary and the zero-bias drift boundary can be determined according to the equivalent additive zero bias sequence corresponding to multiple consecutive effective self-calibration steps when the electrical connection segment to be evaluated is in a healthy connection state.

[0049] The basic electrical safety risk items are determined based on circuit current, supply voltage, and residual current; the contact safety risk items are determined based on incremental connection resistance. Correcting connection resistance Its changing state is determined.

[0050] The safety level output module outputs the electrical safety level of the distribution box based on the basic electrical risk items and contact safety risk items. The electrical safety level can include normal level, attention level, warning level, and danger level.

[0051] The present invention has the following beneficial effects:

[0052] 1. Under low load conditions, the incremental connection resistance is determined by using the differential relationship between the same micro-voltage drop differential acquisition channel at two quasi-isothermal operating points. This allows the additive zero bias, which remains essentially unchanged between the two operating points, to be canceled out during the differential process, reducing the impact of the additive zero bias being amplified by the division of the smaller load current.

[0053] 2. The two operating points used for self-calibration are derived from the load step that naturally forms during the normal operation of the target circuit, without interrupting the power supply or actively injecting a dedicated test current into the target circuit;

[0054] 3. Limit the first measurement window by using quasi-isothermal conditions. With the second measurement window The time interval or temperature change between them reduces the actual change in connection resistance caused by Joule heating in the connection section, thus minimizing the mixing of self-calibration calculation results.

[0055] 4. Obtaining incremental connection resistance Simultaneously, inversely calculate the equivalent additive zero bias. And utilizing the equivalent additive zero bias Correcting the micro-voltage drop in the connection section during subsequent stable operation enables an effective self-calibration step to serve subsequent continuous low-load contact status monitoring;

[0056] 5. Connect resistors incrementally With equivalent additive zero bias Different combinations of variations can help distinguish between drift in the micro-voltage drop differential acquisition channel and actual degradation of the electrical connection section to be evaluated, reducing the possibility that drift in the measurement channel may directly enter the contact safety risk assessment results. Attached Figure Description

[0057] Figure 1 This is a flowchart illustrating the electrical safety assessment method for distribution boxes according to the present invention.

[0058] Figure 2 This is a schematic diagram of the electrical connection relationship between the target circuit, the electrical connection segment to be evaluated, and each acquisition unit in this invention.

[0059] Figure 3 This invention provides an effective self-calibrating step and a first measurement window. Transient shielding area, second measurement window and the quasi-isothermal cutoff time The timing diagram.

[0060] Figure 4 This is the first quasi-isothermal operating point of the present invention. Second quasi-isothermal operating point and incremental connection resistors Equivalent additive zero bias A schematic diagram illustrating the two-point self-calibration principle of the relationship between them.

[0061] Figure 5 This is a schematic diagram of the functional modules of the power distribution box power safety assessment system of the present invention.

[0062] In the diagram: 10. Power supply side; 11. Circuit breaker; 12. Electrical connection section to be evaluated; 13. Branch load; 20. Current acquisition unit; 30. Micro-voltage drop differential acquisition unit; 40. Power supply voltage acquisition unit; 50. Residual current acquisition unit; 60. Safety assessment processor; 70. Temperature acquisition unit; 101. Electrical quantity acquisition module; 102. Load step identification module; 103. Valid event filtering module; 104. Incremental impedance calculation module; 105. Zero bias self-calibration module;

[0063] 106. Exposure Risk Assessment Module; 107. Basic Risk Assessment Module; 108. Safety Level Output Module Detailed Implementation

[0064] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are used to illustrate the implementation of the technical solution of the present invention and are not intended to unduly limit the scope of protection of the present invention.

[0065] like Figure 2 As shown, in the target outgoing circuit of a low-voltage distribution box, the power supply side 10 supplies power to the branch load 13 via the circuit breaker 11 and the electrical connection section 12 to be evaluated.

[0066] The electrical connection section 12 to be evaluated can be the closed contact of the circuit breaker 11, the circuit breaker terminal block, the busbar bolt lap position, the neutral busbar connection position, or the terminal block of the key branch line conductor.

[0067] The micro voltage drop differential acquisition unit 30 has a first micro voltage drop sampling terminal and a second micro voltage drop sampling terminal. The first micro voltage drop sampling terminal is connected to the current inflow side of the electrical connection segment 12 to be evaluated, and the second micro voltage drop sampling terminal is connected to the current outflow side of the electrical connection segment 12 to be evaluated, thereby directly obtaining the small potential difference between the two ends of the electrical connection segment 12 to be evaluated.

[0068] The current acquisition unit 20 is set in the phase current path of the target circuit to acquire the instantaneous circuit current flowing through the target circuit.

[0069] The power supply voltage acquisition unit 40 is connected upstream of the target circuit to acquire the upstream power supply voltage of the target circuit in order to determine whether there is a power supply side disturbance when the target circuit experiences a load step change.

[0070] The residual current acquisition unit 50 preferably adopts a zero-sequence current transformer, in which the phase line and neutral line of the target circuit pass through its magnetic core to obtain the residual current of the target circuit.

[0071] Temperature acquisition unit 70 is located near the electrical connection section 12 to be evaluated, and is used to acquire the temperature of the electrical connection section 12 to be evaluated when the quasi-isothermal conditions are determined using temperature criteria.

[0072] The current acquisition unit 20, the micro voltage drop differential acquisition unit 30, the power supply voltage acquisition unit 40, the residual current acquisition unit 50, and the temperature acquisition unit 70 are all connected to the safety assessment processor 60 and acquire data according to a unified time reference.

[0073] The low voltage drop differential acquisition unit 30 preferably includes an input protection circuit, a high common-mode differential amplifier circuit or an isolated differential amplifier circuit, and an analog-to-digital conversion circuit.

[0074] The measurement range of the micro-voltage drop differential acquisition unit 30 is determined based on the voltage drop range that the electrical connection segment 12 to be evaluated may experience under normal connection and expected deterioration conditions. The two micro-voltage drop sampling leads are preferably arranged symmetrically to bring the sampling positions as close as possible to both ends of the electrical connection segment 12 to be evaluated, minimizing the input of voltage drop from branch conductors unrelated to the evaluation object into the measurement results.

[0075] like Figure 1 and Figure 3 As shown, the safety assessment processor 60 continuously acquires the loop current of the target loop. When the target loop current of the branch load 13 jumps from the first stable level to the second stable level due to equipment startup, shutdown, or power level change, the load step identification module 102 generates a candidate load step event.

[0076] The first and second stability levels can be determined by whether the fluctuation range of the circuit current statistical characteristics within multiple consecutive power frequency cycles is lower than the stability threshold.

[0077] The moment when the load step occurs is denoted as .exist The first measurement window is established within the interval corresponding to the previous first stable level. .

[0078] exist A transient shielding zone is then set up to eliminate circuit breaker operating spikes, contactor operating transients, motor starting impacts, and the rapid adjustment process of frequency converters.

[0079] When the loop current enters the second stable level after the transient shielding region, a second measurement window is established within this stable operating range. .

[0080] First, determine whether the current characteristic difference corresponding to the two steady-state levels satisfies:

[0081] ;

[0082] in, This is the minimum self-calibrating current difference.

[0083] If the above conditions are not met, it is considered that the current change between the two operating points is insufficient to ensure that the two-point differential calculation has a sufficient signal-to-noise ratio, and the corresponding candidate step is not used for micro-voltage drop channel self-calibration.

[0084] Secondly, the power supply voltage acquisition unit 40 compares the power supply voltage before and after the load step occurs.

[0085] When the change in power supply voltage exceeds the preset power supply stability threshold, or when multiple reference circuits in the distribution box that are not directly related to the target load step experience sudden changes in electrical parameters in the same direction during the same period, it is considered that the corresponding candidate step may be affected by upstream power supply disturbances, and the candidate step will not be used for self-calibration.

[0086] Next, for the first measurement window Second measurement window Whether the quasi-isothermal condition is met is used to determine this.

[0087] When using the time criterion, the quasi-isothermal cutoff time is pre-determined based on the thermal inertia of the electrical connection segment 12 to be evaluated. The second measurement window is required. The end time is earlier than .

[0088] When using temperature criteria, the temperature acquisition unit 70 acquires data from the first measurement window. Second measurement window The corresponding connection segment temperature is considered to meet the quasi-isothermal condition when the temperature change between the two windows does not exceed the temperature change threshold.

[0089] For a 50 Hz AC target circuit, in the first measurement window Second measurement window Within the circuit, the zero-crossing position of the loop current is used to determine the phase of the power frequency cycle.

[0090] A synchronous sampling region is set up near the peak value of the same current polarity, and only samples that meet the following criteria are selected: The synchronous sampling points. Where, The instantaneous loop current of the target loop; For time; It is a differential operator; It is the differential of the loop current; The derivative of time; The instantaneous rate of change of the target loop current with respect to time; This is a preset threshold for the rate of change of current.

[0091] Choosing a synchronous sampling point near the current peak can reduce the inductive voltage component generated by the equivalent distributed inductance of the electrical connection segment 12 being evaluated. This inductive voltage component can be expressed as:

[0092] ;

[0093] In the formula, Represents the inductive voltage component; This represents the equivalent distributed inductance of the electrical connection segment 12 to be evaluated under the current measurement path; It represents the instantaneous rate of change of the loop current relative to time.

[0094] Due to the proximity of the peak value of the sinusoidal alternating current Smaller, therefore able to reduce The proportion of the results in the micro-pressure drop measurement.

[0095] For the first measurement window respectively Second measurement window The synchronous micro-voltage drop samples and current samples from multiple power frequency cycles are processed by median value processing or truncated averaging.

[0096] First measurement window The corresponding processing result is the first micro-voltage drop characteristic. and first current characteristics Second measurement window The corresponding processing results are the second micro-voltage drop characteristic U_{2} and the second current characteristic. .

[0097] like Figure 4 As shown, the first quasi-isothermal operating point is represented as: ;

[0098] The second quasi-isothermal operating point is represented as: ;

[0099] First measurement window Second measurement window When the quasi-isothermal condition is met, and the equivalent additive zero bias of the micro-pressure drop differential acquisition unit 30 remains approximately constant between the two windows, we have: In the formula This indicates the equivalent connection resistance of the electrical connection segment 12 to be evaluated during the quasi-isothermal period; This indicates that the micro-voltage drop differential acquisition unit 30 has an equivalent additive zero bias during the current calibration period.

[0100] Subtracting the two equations, we get the equivalent additive zero bias. It is eliminated, therefore we get: ;

[0101] in, This represents the incremental connection resistance. Further, based on the first operating point, the equivalent additive zero bias within the current calibration period is calculated: ;

[0102] The equivalent additive zero bias can also be verified using the following formula based on the second operating point: ;

[0103] When the deviation between the equivalent additive zero biases determined by the two operating points does not exceed the preset zero bias consistency threshold, the calibration result corresponding to the effective self-calibration step can be further confirmed as valid.

[0104] Taking a set of illustrative operating parameters as an example, assume that the actual connection resistance of the electrical connection segment 12 to be evaluated is approximately The current equivalent additive zero bias It is 0.9 mV.

[0105] Before the load step occurs:

[0106] The actual resistance voltage drop is approximately 0.4 mV. After superimposing the equivalent additive zero bias:

[0107] After the load step occurs, the target circuit enters a second stable level of approximately 20 A within the quasi-isothermal range. The corresponding actual resistance voltage drop is approximately 1.6 mV, after superimposing the same equivalent additive zero bias: .

[0108] therefore: ;

[0109] Then calculate based on the first working point: Therefore, the approximately constant 0.9 mV equivalent additive zero bias between the two operating points does not enter the incremental connection resistance. The calculation results.

[0110] In equivalent additive zero bias Within the validity period, when the target circuit re-enters a certain stable measurement window, the corresponding micro-voltage drop characteristics are obtained. and loop current characteristics .

[0111] according to: ;

[0112] Determine the first The corrected connection resistance corresponding to each stable measurement window. When:

[0113] At that time, it is not necessary to use the correction connection resistance. Update the contact safety risk items to avoid the amplification of division errors again when the current is close to zero.

[0114] Equivalent additive zero bias The shelf life can be determined based on both time and temperature conditions.

[0115] For example, if the cumulative runtime after the self-calibration step does not exceed the preset effective duration, and the change in the operating temperature of the micro-voltage drop differential acquisition unit 30 relative to the calibration time does not exceed the allowable temperature change range, the equivalent additive zero bias is achieved. Stay effective.

[0116] If any of the above conditions are not met, the use of the old equivalent additive zero bias is suspended. Update and correct the connection resistor, and wait for a new effective self-calibration step.

[0117] For contact status assessment, a healthy connection reference boundary can be established in the early stage of the distribution box commissioning through multiple effective self-calibration steps, or the healthy connection reference boundary can be determined based on the allowable connection resistance of the circuit breaker, connector or busbar connection structure to be evaluated.

[0118] When a certain incremental connection resistor If the contact risk slightly exceeds the healthy connection reference boundary, a level of concern-level contact risk can be output first.

[0119] Incremental connection resistance obtained from multiple effective self-calibration steps A continuous increase or continuous exceedance of the healthy connectivity reference boundary, while with equivalent additive zero bias. When kept within the zero bias stability boundary, evidence of degradation of the electrical connection segment 12 to be evaluated is formed, and the contact safety risk level is increased.

[0120] When changes in ambient temperature or aging of the micro-voltage drop differential acquisition unit 30 cause zero-point drift in the acquisition channel, the newly obtained effective self-calibration step may exhibit a significantly altered equivalent additive zero bias. .

[0121] If the incremental connection resistor is then... If it remains within the healthy connectivity reference boundary, then an "equivalent additive zero bias" is formed. Change and incremental connection resistance A stable combination of states.

[0122] The security assessment processor 60 updates the equivalent additive zero bias accordingly. It also records the drift status of the acquisition channel, and does not directly determine the zero-point drift of the acquisition channel as contact degradation.

[0123] like Figure 5 As shown, the system of the present invention includes an electrical quantity acquisition module 101, a load step identification module 102, a valid event screening module 103, an incremental impedance calculation module 104, a zero bias self-calibration module 105, a contact risk assessment module 106, a basic risk assessment module 107, and a safety level output module 108.

[0124] The electrical quantity acquisition module 101 provides synchronous data of loop current and micro voltage drop to the load step identification module 102, and provides data of loop current, supply voltage and residual current to the basic risk assessment module 107.

[0125] The load step identification module 102 identifies the natural load step of the target circuit, and the effective event screening module 103 further excludes load steps that are disturbed by the power supply side, do not meet the minimum current change requirement, do not meet the quasi-isothermal condition, or cannot be approximately kept stable by the equivalent additive zero bias between the two measurement windows.

[0126] The incremental impedance calculation module 104 calculates the impedance based on the effective self-calibration step. as well as Determine the incremental connection resistance .

[0127] Zero bias self-calibration module 105 connects to the incremental resistor. And the equivalent additive zero bias is calculated inversely at the first and second operating points respectively. The equivalent additive zero bias obtained from the two operating points is then subjected to a consistency check; after the check passes, the equivalent additive zero bias is... Within the validity period, correct the slight pressure drop of subsequent connection sections.

[0128] Contact risk assessment module 106 based on incremental connection resistance Correcting connection resistance And determine the contact safety risk items based on the corresponding historical changes.

[0129] The basic risk assessment module 107 identifies overcurrent risk, over / undervoltage risk, and residual current risk based on loop current, supply voltage, and residual current.

[0130] The safety level output module 108 determines the final electrical safety level by comprehensively considering contact safety risk items and basic electrical risk items.

[0131] Preferably, the final electrical safety level can be determined by prioritizing the highest risk item. When any basic risk item reaches the danger level, the danger level is output; when the basic risk item does not reach the danger level but the safety risk reaches the warning level or danger level, the current electrical safety level is determined according to the safety risk level.

[0132] In a three-phase distribution box, independent micro-voltage drop differential acquisition units 30 can be arranged at the key circuit breaker contacts, busbar connection points, or outgoing terminal terminals of phases A, B, and C, respectively, and corresponding natural load step and incremental connection resistance can be established for each phase. and equivalent additive zero bias .

[0133] For target circuits that have not generated a natural load step that meets requirements for an extended period, the risk assessment of basic overcurrent, over / undervoltage, and residual current continues to operate, relying on the expired equivalent additive zero bias. The fine-tuning of the connection resistance correction is paused until a new effective self-calibration step is obtained.

[0134] The load step in this invention does not need to be actively generated by the safety assessment system; it is sufficient as long as the target circuit naturally forms two identifiable stable load levels during normal operation.

[0135] The equivalent additive zero bias This refers to the result of comprehensively and equivalently converting errors such as differential amplifier input offset, analog-to-digital converter zero-point error, sampling wire thermoelectric potential, and residual common-mode coupling into additive quantities in the micro-voltage drop characteristics within the specified sampling polarity, specified synchronization feature extraction method, and current effective calibration period, without needing to identify each error source separately.

[0136] The above embodiments demonstrate that the present invention can achieve online correction of zero bias in low-load micro-voltage drop measurement by utilizing natural load step under the condition that the distribution box is operating normally without power interruption, and obtain contact safety risk information based on the correction results.

[0137] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for assessing the electrical safety of a distribution box, characterized in that, The process includes the following: The circuit current, supply voltage, residual current, and micro voltage drop of the connection section at both ends of the electrical connection section to be evaluated are collected synchronously from the target circuit of the distribution box. The micro voltage drop of the connection section is obtained by the same micro voltage drop differential acquisition channel. The system detects load steps that naturally occur in the target circuit due to changes in load operating conditions, and filters out valid self-calibrating steps from these load steps. A valid self-calibrating step must at least satisfy the following conditions: the change in step current reaches a preset minimum self-calibrating current difference; the change in supply voltage before and after the step does not exceed a supply stability threshold; the transient process after the step has ended; and the first measurement window before the step has been reached. With the second measurement window after the step jump The measurement range is within the quasi-isothermal range of the electrical connection section to be evaluated, and the equivalent additive zero bias of the micro-voltage drop differential acquisition channel remains approximately stable between the first measurement window and the second measurement window; First measurement window Second measurement window Extract the first micro-voltage drop feature from the internal components respectively. Second micro-pressure drop characteristics First current characteristics Second current characteristics The incremental connection resistance is determined according to the following formula. : ; in, This indicates the incremental connection resistance. Indicates the first measurement window The micro-pressure drop characteristics obtained internally, Indicates the second measurement window The micro-pressure drop characteristics obtained internally, Indicates the first measurement window The loop current characteristics obtained internally, Indicates the second measurement window The characteristics of the loop current obtained within the loop; The equivalent additive zero bias of the micro-voltage differential acquisition channel during the current calibration period can be calculated using the following formula. : ; And the equivalent additive zero bias is calculated inversely based on the operating point corresponding to the second measurement window. A consistency check is performed. If the deviation between the equivalent additive zero biases calculated from the two operating points does not exceed a preset zero bias consistency threshold, the calibration result corresponding to the effective self-calibration step is confirmed to be valid. During the validity period, based on the equivalent additive zero bias... Correct the micro voltage drop across the connection section in the subsequent stable measurement window and determine the corrected connection resistance; The contact safety risk items are determined based on the deviation of the incremental connection resistance and the corrected connection resistance from the healthy connection reference boundary. Combined with the basic power consumption risk items determined based on the circuit current, supply voltage and residual current, the power consumption safety level of the distribution box is determined.

2. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that, The electrical connection section to be evaluated is at least one of the following: circuit breaker contact, circuit breaker terminal block, busbar connection point, neutral busbar connection point, or branch conductor terminal block. The first and second sampling terminals of the micro-voltage drop differential acquisition channel are electrically connected to the current inflow side and current outflow side of the electrical connection segment to be evaluated, respectively, so as to directly obtain the micro-voltage drop of the connection segment at both ends of the electrical connection segment to be evaluated.

3. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that, Screening for the effective self-calibrating step also includes: Compare the changes in the upstream supply voltage of the target circuit before and after the load step occurs, and detect whether there are sudden changes in synchronous electrical parameters in multiple reference circuits; When the change in the supply voltage exceeds the supply stability threshold, or when multiple reference circuits experience sudden changes in electrical parameters in the same direction within a corresponding time interval, the corresponding load step is identified as a supply-side disturbance event, and the incremental connection resistance is not updated using the supply-side disturbance event. and equivalent additive zero bias .

4. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that: First measurement window Located in the stable operating range before the load step occurs; Second measurement window Located in the stable operating range after the transient shielding period following a load step; Second measurement window The end time is earlier than the quasi-isothermal cutoff time. ; Alternatively, the temperature of the electrical connection section to be evaluated can be detected by the temperature acquisition unit, during the first measurement window. With the second measurement window When the temperature change between the two values ​​does not exceed a preset temperature change threshold, the first measurement window is determined. Second measurement window The quasi-isothermal condition is satisfied; in, This indicates the quasi-isothermal cutoff time predetermined based on the thermal inertia of the electrical connection segment to be evaluated.

5. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that, For the first measurement window Second measurement window Synchronous phase positioning is performed on the loop current waveform within the circuit, and synchronous sampling points satisfying the following formula are selected near the current peaks of the same polarity: ; in, Represents the instantaneous loop current of the target loop; Indicates time; Represents the differential operator; Represents loop current The differential; Indicates time The differential; Represents loop current Relative to time The instantaneous rate of change; Indicates the preset current change rate threshold; For the first measurement window respectively Second measurement window Multiple synchronous micro-voltage drop samples and current samples that meet the aforementioned conditions are subjected to median value processing or truncated averaging to obtain the first micro-voltage drop characteristic. Second micro-pressure drop characteristics First current characteristics Second current characteristics .

6. The method for assessing the electrical safety of a distribution box according to claim 1 or 5, characterized in that, In equivalent additive zero bias During the validity period, for the first A stable measurement window yields micro-pressure drop characteristics. and current characteristics The corrected connection resistance is determined according to the following formula. : ； in, Indicates the first The connection resistance after zero bias correction corresponding to each stable measurement window; Indicates the first Micro-pressure drop characteristics obtained within a stable measurement window; Indicates the first Loop current characteristics obtained within a stable measurement window; Indicates the sequence number of the stable measurement window; subscript Indicates correction; When the following formula is satisfied, it is not necessary to use the correction connection resistance. Update the access safety risk items: ； in, This indicates the preset minimum effective measurement current.

7. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that, The incremental connection resistance is redefined each time a new valid self-calibration step is obtained. and equivalent additive zero bias ; When the equivalent additive zero bias corresponds to a continuous effective self-calibration step. The change exceeds the zero bias drift boundary, while the incremental connection resistance When remaining within the healthy connection reference boundary, the corresponding change is identified as a micro-dropout differential acquisition channel drift, and the equivalent additive zero bias is updated without increasing the contact safety risk; When the equivalent additive zero bias Maintaining within the zero-bias stability boundary, while incrementally connecting the resistance. When the healthy connection reference boundary is exceeded consecutively in multiple effective self-calibration steps, the corresponding change is identified as a degradation of the electrical connection segment to be evaluated and an increase in contact safety risk; the zero-bias stability boundary and the zero-bias drift boundary are determined based on the equivalent additive zero-bias sequence corresponding to multiple consecutive effective self-calibration steps when the electrical connection segment to be evaluated is in a healthy connection state.

8. The method for assessing the electrical safety of a distribution box according to claim 1, characterized in that, The equivalent additive zero bias The validity period is determined at least based on the cumulative duration after the effective self-calibration step occurs and the change in the operating temperature of the micro-voltage drop differential acquisition channel. When the validity period expires and no new valid self-calibration step is obtained, the old equivalent additive zero bias should be discontinued. Update and correct the connection resistors, and continue to conduct basic power risk assessments based on loop current, supply voltage, and residual current.

9. A power distribution box electrical safety assessment system, characterized in that, It includes an electrical quantity acquisition module, a load step identification module, a valid event screening module, an incremental impedance calculation module, a zero bias self-calibration module, a contact risk assessment module, a basic risk assessment module, and a safety level output module; The electrical quantity acquisition module includes a micro-voltage drop differential acquisition channel set at both ends of the electrical connection section to be evaluated, as well as a current acquisition unit, a power supply voltage acquisition unit, and a residual current acquisition unit corresponding to the target circuit. The load step identification module is used to identify load steps that are naturally formed in the target circuit. The effective event filtering module is used to filter effective self-calibration steps that are stable on the power supply side, have ended transiently, meet quasi-isothermal conditions, and whose equivalent additive zero bias of the micro-voltage drop differential acquisition channel remains approximately stable between the first and second measurement windows. The incremental impedance calculation module is used to calculate based on the first measurement window. Second measurement window The incremental connection resistance is determined by the difference in voltage drop characteristics and the difference in current characteristics. ; The zero-bias self-calibration module is used to connect the resistor according to the incremental connection resistance. The equivalent additive zero bias of the micro-voltage drop differential acquisition channel is calculated by reversing the working points corresponding to the first and second measurement windows. The equivalent additive zero bias obtained from the two operating points is then subjected to a consistency check. After the check passes, the equivalent additive zero bias is used. Correcting the slight voltage drop in subsequent connection sections; The contact risk assessment module is used to assess the incremental connection resistance. Correcting connection resistance Identify safety risks associated with contact; The basic risk assessment module is used to determine basic power consumption risk items based on circuit current, supply voltage and residual current; The safety level output module is used to determine the electrical safety level of the distribution box based on the contact safety risk items and the basic electrical risk items.

10. The electrical safety assessment system for distribution boxes according to claim 9, characterized in that, The zero-bias self-calibration module is also used to store the equivalent additive zero bias corresponding to continuous effective self-calibration steps. Sequential and incremental connection resistors sequence; The contact risk assessment module is based on the equivalent additive zero bias. Sequence and Incremental Connection Resistors The sequence variation combination distinguishes between drift in the micro-voltage drop differential acquisition channel and degradation of the electrical connection section to be evaluated.

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