Three-phase heating cycle test apparatus and method

Abstract

This application relates to the field of cable technology, specifically providing a three-phase heating cycle test apparatus and method. The three-phase heating cycle test apparatus includes a simulation circuit and a test circuit, both employing independent three-phase current control. Both the simulation and test circuits are equipped with an automatic capacitor compensation system to achieve balanced three-phase thermal power input to the cable within their respective circuits. It also includes a measurement sensing unit that achieves multi-dimensional temperature fusion sensing, comprehensive monitoring of the temperature field without dead zones, and diagnosis of early-stage insulation degradation in the test cable. The automatic capacitor compensation system eliminates voltage fluctuations caused by three-phase impedance differences in real time, eliminating interference from the asymmetry of the test sample itself and improving the reliability of test data. The measurement sensing unit accurately captures insulation degradation caused by interphase thermal stress, automatically terminating the test at the initial stage of damage, significantly improving safety.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cables, and particularly relates to a three-phase heating cycle test device and method. BACKGROUND

[0002] When a cable is subjected to electrical tests, the cable needs to be heated according to requirements. Currently, a 10kV cable heat cycle test device system is traditionally composed of a test loop and a simulation loop. The test loop current is adjusted by following the current of the simulation loop temperature measuring device to measure the same temperature, so that the cable temperature reaches the standard requirements.

[0003] The traditional cable heat cycle test device system usually adopts single-phase independent experiments. The traditional single-phase test cannot simulate the real three-phase coupling effect problem. There is also research on three-phase heat cycle tests in the prior art to realize three-phase collaborative control and multi-dimensional monitoring to solve the electromagnetic-thermal coupling effect problem that cannot be simulated by the traditional single-phase test. However, the prior art cannot deal with the inherent impedance imbalance of the test sample, resulting in uneven three-phase heat generation, additional and unexpected thermal stress, and the test is not to examine the heat aging resistance of the insulation material, but to examine the mixed effect of the test sample structure imbalance + heat aging. It is easy to cause damage to good quality test samples or cover up the defects of poor quality test samples.

[0004] In addition, in the prior art, whether it is qualified is usually judged by offline testing (such as measuring DC resistance, making a ratio test, and performing no-load loss test) after the test is completed. The failure process and specific reasons cannot be known, there is a lack of effective early termination mechanism, the test sample may be irreversibly severely damaged or even burst into fire in an unbalanced process, and the risk is high. SUMMARY

[0005] In order to solve the technical problems that the three-phase heat cycle test device in the prior art cannot deal with the inherent impedance imbalance of the test sample, resulting in uneven three-phase heat generation, and the technical problem that the electrical performance of the three-phase cable cannot be monitored in real time, the application provides a three-phase heat cycle test device and method to improve the accuracy and reliability of the three-phase heat cycle test.

[0006] Firstly, the application embodiment provides a three-phase heat cycle test device, which comprises a simulation loop and a test loop. The simulation loop comprises a sample cable, and the test loop comprises a test sample cable. The simulation loop and the test loop both adopt three-phase independent current regulation.

[0007] An automatic capacitor compensation system is installed in both the simulation circuit and the test circuit. The automatic capacitor compensation system includes a detection unit, a control unit, and an execution unit. The detection unit detects the three-phase current value of the cable in the circuit in real time. The control unit is equipped with a current rebalancing algorithm to calculate the current imbalance and calculate the required capacitor compensation amount based on the current imbalance. The execution unit is used to perform capacitor compensation based on the capacitor compensation amount calculated by the control unit, thereby achieving the balance of the three-phase thermal power input of the cable in the circuit.

[0008] It also includes a measurement sensing unit, which includes an insulation resistance tester and a Schering bridge installed on the test cable in the test circuit, to detect the insulation resistance and tanδ value of the test cable respectively, so as to realize the deterioration diagnosis of the test cable.

[0009] In some embodiments, the detection unit includes a current transformer, a voltage transformer, and a signal conditioning and analog-to-digital converter. The current transformer detects the three-phase current values ​​of the cable in the circuit, including the effective current value and phase angle. The voltage transformer is installed in the circuit of the built-in compensation capacitor bank in the switchgear of the circuit to collect the compensation circuit voltage. The signal conditioning and analog-to-digital converter converts the three-phase current values ​​and the compensation circuit voltage into digital signals and transmits them to the control unit in the circuit.

[0010] In some embodiments, the execution unit includes a thyristor switching switch and a built-in compensation capacitor bank disposed in the switch cabinet. The thyristor switching switch receives a capacitor compensation command from the control unit to control the switching of the compensation capacitor bank in the circuit.

[0011] In some embodiments, the measurement sensing unit further includes a first temperature measuring device disposed in the simulation loop, a second temperature measuring device disposed in the test loop, and an infrared imager that simultaneously measures the temperature of the simulation loop and the test loop. The first temperature measuring device includes a first temperature controller, a first thermocouple, and a first distributed optical fiber DIS. The first temperature controller receives first temperature data collected by the first thermocouple and the first distributed optical fiber DIS and transmits the first temperature data to the control host. The second temperature measuring device includes a second temperature controller, a second thermocouple, and a second distributed optical fiber DIS. The second temperature controller receives second temperature data collected by the second thermocouple and the second distributed optical fiber DIS and transmits the second temperature data to the control host.

[0012] This application embodiment also provides a three-phase heating cycle test method, which simultaneously performs heating cycle tests on sample cables and test cables. Each heating cycle includes three stages: heating, heat preservation, and cooling. Each heating cycle is implemented using the above-mentioned three-phase heating cycle test device.

[0013] The entire heating cycle test also includes the use of an automatic capacitor compensation system in the simulation circuit and the test circuit to periodically balance the three-phase thermal power input of the cable in the circuit. The process of balancing the three-phase thermal power input of the cable in the circuit mainly includes: detecting the three-phase current value of the cable in the circuit and the voltage of the compensation circuit, calculating the current imbalance based on the three-phase current value, calculating the required capacitor compensation amount based on the current imbalance and the voltage of the compensation circuit, and supplementing the capacitor based on the capacitor compensation amount.

[0014] It also includes the step of using a measurement sensing unit to evaluate the insulation aging of each phase of the test cable at each stage, and setting up an early warning and termination mechanism based on the insulation aging evaluation results of the test cable.

[0015] In some embodiments, the step of balancing the three-phase thermal power input of the cable in the circuit includes:

[0016] Step 1: Initialization and target value setting: The system is powered on, and all compensation capacitors are in the open state, which is the initial state. The control unit reads the target value of the current imbalance.

[0017] Step 2, Data Acquisition and Deviation Calculation of Current Unbalance: The detection unit continuously acquires the three-phase current values ​​of the cable in the circuit. The three-phase current values ​​include the effective current value and phase. The control unit calculates the current unbalance value and compares it with the target value of the current unbalance. The deviation between the current unbalance value and the target value is calculated. When the deviation exceeds the specified value range, proceed to Step 3.

[0018] Step 3, calculate the capacitance compensation: Based on the effective value of the current and the phase measured in Step 2, select the phase with the middle effective value of the current as the reference phase. The control unit calculates the capacitive current value ΔI that needs to be increased or decreased in each of the two adjacent phases when the current reaches balance. According to the formula ΔI = ωCΔU, the required ΔI is converted into the capacitance ΔC that needs to be switched.

[0019] Where ω is the angular frequency and ΔU is the voltage of the compensation circuit;

[0020] Step 4: Switching the compensation capacitor bank. Based on the capacitor compensation amount calculated in Step 3, the control unit calculates the number of compensation capacitor banks to be switched corresponding to the capacitor compensation amount, and the execution unit completes the switching action.

[0021] In some embodiments, in step 4, after the control unit calculates the number of compensation capacitor group switching combinations corresponding to the capacitor compensation amount, the control unit sends a switching command to the execution unit to complete the automatic switching action of the compensation capacitor group.

[0022] In some embodiments, if the automatic switching of the compensation capacitor bank by the execution unit still does not meet the capacitance compensation amount, the manual switching of the manual capacitor bank is further performed by the manual switch of the transformer in the circuit to complete the manual switching action of the compensation capacitor bank.

[0023] In some embodiments, after completing step 4, wait for a settling time T, jump to step 2, remeasure the effective value and phase angle of the three-phase current in the circuit, recalculate the current unbalance degree, and then calculate the deviation between the current unbalance degree and the target value. When the deviation value does not exceed the specified value range, or when the current unbalance degree does not exceed the threshold, the loop ends.

[0024] In some embodiments, the insulation aging assessment method includes: testing the phase-to-phase insulation resistance and tanδ value of the test cable in each heating cycle, recording the test data in all heating cycles, calculating the difference in in-phase insulation resistance of the same phase cable in the first and last heating cycles, and comparing whether the insulation resistance difference and tanδ exceed the threshold, thereby assessing the insulation aging of each phase of the test cable.

[0025] In some embodiments, the insulation aging assessment method further includes: in the same heating cycle, detecting multiple sets of insulation resistance values ​​and tanδ values ​​at specified time intervals, comparing the phase-to-phase insulation resistance difference and tanδ value in the same heating cycle, and analyzing the insulation changes of each phase of each test cable at different temperatures in each heating cycle.

[0026] In some embodiments, the insulation aging assessment method further includes measuring and recording the conductor length at specified time intervals within each heating cycle, and assessing the insulation shrinkage based on multiple measurements of the conductor length within each heating cycle, thereby assessing the insulation aging of the test cable.

[0027] In some embodiments, the method further includes using a measurement sensing unit to comprehensively monitor the temperature of the sample cable and the test cable, using a first temperature measuring device and a second temperature measuring device to form continuous one-dimensional monitoring of the temperature of the sample cable and the test cable respectively, using an infrared imager to form two-dimensional monitoring of the surface of the sample cable and the test cable, and investigating local overheating faults of the sample cable and the test cable.

[0028] Compared with the prior art, the beneficial effects that this application can achieve are:

[0029] 1. A true three-phase current simulation was achieved by using a multi-magnetic-circuit transformer. Combined with thermocouples, distributed fiber optic DTS full-path temperature control and infrared dynamic thermal compensation, the electromagnetic-thermal-mechanical multi-field coupling effect in power grid operation was reproduced in the experimental environment.

[0030] 2. The automatic capacitor compensation system eliminates voltage fluctuations caused by three-phase impedance differences in real time, ensuring absolute balance of three-phase thermal power input. It also eliminates interference caused by the asymmetry of the test sample itself, making the test results purely reflect the performance of the insulating material under the expected thermal stress and improving data reliability.

[0031] 3. It pioneered the use of phase-to-phase insulation resistance difference criteria. Based on the insulation resistance difference and tanδ value, it accurately captures insulation degradation caused by phase-to-phase thermal stress. It can automatically terminate the test at the initial stage of damage, protecting expensive test samples and test equipment, and greatly improving safety.

[0032] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A schematic diagram of the cable short-circuiting method in this application is shown;

[0035] Figure 2 A schematic diagram of the three-phase heating cycle test apparatus in this application is shown;

[0036] Figure 3 A schematic diagram of the automatic capacitor compensation system in this application is shown;

[0037] Figure 4 A flowchart illustrating the three-phase thermal power input balance in this application is shown.

[0038] Figure 5 The flowchart of the insulation aging assessment in this application is shown. Detailed Implementation

[0039] The term "comprising" in this application specification is synonymous with "including," "containing," or "characterized in," and is inclusive or open-ended, and does not exclude additional undescribed elements or method steps.

[0040] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0042] The present application will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] This embodiment provides a three-phase heating cycle test device, including a simulation circuit and a test circuit. The simulation circuit includes a sample cable, and the test circuit includes a test cable. Both the simulation circuit and the test circuit draw power from the distribution cabinet through a voltage regulator and a switch cabinet. The sample cable, the test cable, the simulation circuit, and the test circuit are all equipped with current transformers to collect the electrical parameters of the cables in their respective circuits and feed the corresponding electrical parameters back to the control host. The control unit of the control host calculates and processes the relevant electrical parameters to control the cable parameters in each circuit. The human-machine interface of the control host displays and operates the relevant parameters in each circuit.

[0045] In this embodiment, the voltage regulator uses a Δ / YN-11 connected transformer to achieve independent three-phase current regulation (error <2%), simulating the phase difference and unbalanced conditions of a real power grid.

[0046] The sample cable is longer than 5 meters, and the test cable is longer than 10 meters. Both the simulation circuit and the test circuit use three-phase independent current control, and both circuits use open-type feedthrough transformers. The two ends of the sample cable and the test cable are short-circuited together using fixtures. The feedthrough transformer and the test cable form a primary and secondary coil. Short-circuiting the test cable (equivalent to the secondary coil) creates a large short-circuit current. The short-circuiting method for the sample cable and the test cable is as follows: Figure 1As shown. The test circuit current is adjusted to follow the simulation circuit current. The synchronization standard for current adjustment is that the temperature of the test cable in the test circuit measured by the temperature measuring device is the same as the temperature of the sample cable in the simulation circuit, thus ensuring that the cable temperature meets the standard requirements.

[0047] Specifically, such as Figure 2 As shown, in the simulation circuit, the sample cable passes through the sample transformer and draws power from the distribution cabinet via the sample voltage regulator and sample switch cabinet. Each phase end of the sample cable is equipped with a sample current transformer to collect the three-phase current values ​​of the sample cable, including the effective current value and phase angle, and feeds the three-phase current data of the sample cable back to the control host for current control and capacitor compensation control of the sample cable. Similarly, in the test circuit, the test cable passes through the test transformer and draws power from the distribution cabinet via the test voltage regulator and test switch cabinet. Each phase end of the test cable is equipped with a test current transformer to collect the three-phase current data of the test cable, retain the effective current value and phase angle, and feeds the three-phase current data of the test cable back to the control host for current control and capacitor compensation control of the test cable.

[0048] An automatic capacitor compensation system is installed in both the simulation circuit and the test circuit to achieve three-phase thermal power input balance for the sample cable and the test cable. The automatic capacitor compensation system includes a detection unit, a control unit, and an execution unit. The detection unit is used to detect the three-phase current value of the cable in the circuit in real time. The control unit is equipped with a current rebalancing algorithm to calculate the current imbalance based on the three-phase current value detected by the detection unit and to calculate the required capacitor compensation amount based on the current imbalance. The execution unit performs capacitor compensation based on the capacitor compensation amount calculated by the control unit, thereby achieving three-phase thermal power input balance for the cable in the circuit.

[0049] The detection unit includes a current transformer, a voltage transformer, and a signal conditioning and analog-to-digital converter. The current transformer detects the three-phase current values ​​of the cable in the circuit, including the effective current value and phase angle. The voltage transformer is installed in the circuit of the compensation capacitor bank built into the switch cabinet in the circuit to collect the compensation circuit voltage. The signal conditioning and analog-to-digital converter converts the three-phase current values ​​and the compensation circuit voltage into digital signals and transmits them to the control unit in the circuit.

[0050] The execution unit includes a thyristor switching switch and a built-in compensation capacitor bank installed in the switch cabinet. The built-in compensation capacitor bank is a 120kVAR capacitor bank. The thyristor switching switch receives the capacitor compensation command from the control unit to control the switching of the compensation capacitor bank in the circuit.

[0051] In some embodiments, the execution unit further includes a manually compensated capacitor bank disposed on the through-core transformer, and the switching of the manually compensated capacitor bank is realized by manually opening and closing the circuit breaker. The manually compensated capacitor bank is also a 120kVAR capacitor bank.

[0052] The automatic capacitance compensation system in the simulation circuit and the test circuit has the same structure, the only difference being that the detection unit and the execution unit in each circuit have separately controlled components. Specifically, taking the test circuit as an example, the automatic capacitance compensation system... Figure 3 As shown, the detection unit includes a test current transformer installed in the test circuit, a voltage transformer installed in the built-in compensation capacitor bank circuit of the test switchgear, and a signal conditioning and analog-to-digital converter. The test current transformer is used to collect the current parameters of each phase from the test cable, and the voltage transformer is used to collect the voltage of the compensation circuit and transmit it to the signal conditioning and analog-to-digital converter. The analog signal is modulated and converted into a digital signal before being transmitted to the control unit. The control unit includes a core processor and a memory storing the current balance algorithm. The core processor is used to execute the current balance algorithm and send capacitor compensation commands to the execution unit. The execution unit includes a thyristor switching switch and a built-in compensation capacitor bank installed in the test switchgear. The capacitor compensation command controls the opening and closing of the thyristor switching switch, thereby controlling the switching of the built-in compensation capacitor bank.

[0053] In some embodiments, the execution unit further includes a manually operated compensation capacitor bank disposed on the through-core transformer, which is switched on and off manually. The manually operated compensation capacitor bank is used as a backup capacitor bank to perform capacitor compensation by manual switching when the built-in compensation capacitor bank is completely switched off and still cannot meet the capacitor compensation requirements.

[0054] Because three-phase cables inherently possess unbalanced impedance, unbalanced currents are generated, leading to uneven heat generation across the three phases and creating additional, unexpected thermal stress. If this unbalanced current is not balanced, the thermal cycling test of the three-phase cable will not assess the "heat aging resistance of the insulation material," but rather the mixed performance of "three-phase cable structural imbalance + thermal aging," potentially damaging high-quality test cables or masking defects in low-quality test cables. The three-phase heating cycling test device of this application incorporates an automatic capacitor compensation system to ensure absolutely balanced three-phase thermal power input, eliminating interference from the inherent asymmetry of the three-phase cables. This allows the test results to purely reflect the performance of the cable insulation material under expected thermal stress, greatly improving the reliability and accuracy of the test data.

[0055] It also includes a measurement sensing unit, which detects the temperature of the sample cable in the simulation circuit and the test cable in the test circuit, such as... Figure 2As shown, the measurement sensing unit also includes a first temperature measuring device disposed in the simulation circuit, a second temperature measuring device disposed in the test circuit, and an infrared imager that simultaneously measures the temperature of the simulation circuit and the test circuit. The first temperature measuring device includes a first temperature controller, a first thermocouple, and a first distributed optical fiber DIS. The first temperature controller receives the first temperature data collected by the first thermocouple and the first distributed optical fiber DIS and transmits the first temperature data to the control host. The second temperature measuring device includes a second temperature controller, a second thermocouple, and a second distributed optical fiber DIS. The second temperature controller receives the second temperature data collected by the second thermocouple and the second distributed optical fiber DIS and transmits the second temperature data to the control host.

[0056] The first temperature data includes the conductor temperature and sheath temperature of the sample cable. A first thermocouple simultaneously measures both the conductor and sheath temperatures, while a first distributed optical fiber measures the sheath temperature. The second temperature data is the sheath temperature of the test cable. Both the second thermocouple and the connected distributed optical fiber measure the sheath temperature of the test cable. Because the first thermocouple, which measures the conductor temperature, would damage the cable insulation during installation, and the test cable requires high-voltage electrical testing, the second thermocouple measures the sheath temperature to ensure the integrity of the test cable and meet the requirements of high-voltage electrical testing. When the test environment and applied current are the same, and the sheath temperature of the test cable is the same as that of the sample cable, it can be assumed that the conductor temperatures of the test cable and the sample cable are also the same.

[0057] The first and second distributed optical fiber DIS are deployed along the full length of the sample cable and the test cable, respectively, to synchronously capture the axial / radial temperature gradient of the three-phase conductors (single-phase only requires point monitoring). During the cooling phase, the forced air circulation system must maintain a synchronous cooling rate of three phases (±0.5℃ / min). In some embodiments, the first thermocouple uses a 12-channel thermocouple, and the second thermocouple uses a 24-channel thermocouple, for a total of 36 channels, which are synchronously triggered with the infrared imager, which typically uses a 12-channel infrared imager.

[0058] When simulating actual operating conditions, the cable experiences periodic temperature changes (typically ΔT≥70℃ or ΔT≥95℃) under load fluctuations. This leads to differences in the coefficients of thermal expansion between the conductor and the insulation layer (XLPE insulation ≈ 200 × 10⁻⁶). -6 / K, copper conductor ≈17×10 -6The shear stress generated by cross-linked polyethylene (XLPE) can lead to insulation delamination, accessory sealing failure, or partial discharge over time. Furthermore, XLPE is prone to molecular chain breakage under repeated thermal cycling, especially during the cooling phase (<50℃), where the material shrinkage rate accelerates, inducing microcracks and reducing breakdown strength. At the cable joint, the insulation-semiconductor interface is susceptible to air gaps or slippage under cyclic stress due to thermal expansion mismatch, resulting in local electric field distortion. The measurement sensing unit in this application uses a first and a second temperature controller to continuously monitor the temperature of the sample cable and the test cable in one dimension, and an infrared imager to monitor the surfaces of the sample cable and the test cable in two dimensions. Through multi-dimensional temperature fusion sensing, it achieves comprehensive monitoring of local overheating faults, microcracks, gaps, and other conditions in the sample cable and the test cable without blind spots.

[0059] The measurement sensing unit also includes an insulation resistance tester and a Schering bridge installed on the test cable in the test circuit, which respectively detect the insulation resistance value and tanδ value of the test cable to realize the deterioration diagnosis of the test cable.

[0060] Traditional testing equipment lacks the means to diagnose and monitor the test cable during the testing process. It is usually result-oriented, and after the test, offline tests such as measuring DC resistance, performing turns ratio tests, and no-load loss tests are used to determine whether the quality or performance of the test cable is up to standard. If the test results show that the cable quality or performance is unqualified, the failure process and specific cause cannot be known. The problem may not be discovered until the insulation is completely broken down or severe deformation occurs.

[0061] In the three-phase heating cycle test apparatus of this application, the insulation resistance tester and Schering bridge on the test cable in the test circuit can be used for both deformation testing and electrical testing. In deformation testing, since no specific high voltage is applied, the insulation resistance tester and Schering bridge can be connected to the test circuit throughout the entire test process, allowing for real-time monitoring of the insulation resistance and tanδ value at each stage.

[0062] The insulation resistance and tanδ values ​​of the three-phase cable are tested and recorded in each heating cycle. The difference in insulation resistance of the same phase in the first and last heating cycles is calculated, and the difference in insulation resistance and tanδ are compared to see if they exceed the threshold, thus obtaining the insulation change of the same phase cable under different thermal cycles. The phase-to-phase insulation resistance difference and tanδ difference threshold are extremely sensitive early diagnostic indicators, capable of issuing an alarm when the insulation undergoes minor but differentiated degradation, accurately locating which phase has a problem due to mechanical and thermal stress. It not only tells us that the test cable "failed," but also when it began to fail, why it failed, and where it failed first, demonstrating strong predictive and diagnostic capabilities.

[0063] In electrical testing, a specific high voltage is applied to the test circuit. This voltage can be stopped for a period of time during each heating cycle, and an insulation resistance tester and a Schering bridge can be connected to the test circuit to detect the insulation resistance and tanδ values. For example, at the end of each heating cycle, or at a designated stage within each heating cycle, such as before heating, during heat preservation, or after heat preservation, the specific voltage can be stopped for 10-30 minutes. An insulation resistance tester and a Schering bridge can then be connected to the test circuit to detect and record the insulation resistance and tanδ values, thereby comparing the insulation changes of the same phase cable under different thermal cycles.

[0064] The three-phase heating cycle test device also includes air-cooling equipment. A first air cooler is set in the simulation circuit and a second air cooler is set in the test circuit. Both the first and second air coolers adopt a three-channel independent air duct design, so as to keep the cables in the test circuit and the simulation circuit at three-phase synchronous cooling during the cooling stage.

[0065] Example 2

[0066] This application also provides a three-phase heating cycle test method, which uses the aforementioned three-phase heating cycle test device to conduct a three-phase cable thermal cycle test. This includes simultaneously heating cycle tests on both the sample cable and the test cable. Each heating cycle includes three stages: heating, heat preservation, and cooling. Both the simulation circuit and the test circuit employ independent three-phase current control. The test circuit current is adjusted following the simulation circuit current. The synchronization standard for current adjustment is that, under the condition of ensuring the same test ambient temperature, if the temperature measuring device measures that the sheath temperature of the test cable in the test circuit is the same as the sheath temperature of the sample cable in the simulation circuit, it can be considered that the conductor temperatures of the sample cable and the test cable are the same, thus ensuring that the cable temperature meets the standard requirements.

[0067] The three-phase heating cycle test method of this application also includes the step of periodically balancing the three-phase thermal power input of the cable in the circuit using an automatic capacitor compensation system in the simulation circuit and the test circuit. The process of balancing the three-phase thermal power input of the cable in the circuit mainly includes the following steps: the automatic capacitor compensation system detects the unbalanced current of the cable in the circuit, then calculates the required capacitor compensation amount based on the unbalanced current, and finally supplements the capacitor based on the capacitor compensation amount.

[0068] Specifically, the method by which an automatic capacitor compensation system balances the three-phase thermal power input of the cables in its circuit is as follows: Figure 4 As shown, it includes the following steps:

[0069] Step 1, Initialization and Target Value Setting. Before powering on the system, ensure all compensation capacitors are disconnected to complete initialization. The control unit then reads the target value for the current imbalance.

[0070] The initialization process includes disconnecting the manual compensation capacitor bank and the built-in compensation capacitor bank. The target value for current imbalance is input through the human-machine interface. Assuming the target value for current imbalance is... In some embodiments, the target value of current imbalance is... The value can range from 0.5% to 1%.

[0071] Step 2: Data Acquisition and Current Unbalance Calculation. The detection unit continuously acquires the three-phase current values ​​of the cable in its circuit, including the effective value and phase angle, as well as the compensation circuit voltage. The control unit calculates the current unbalance value. and the target value of current imbalance Compare and calculate the current value of the current imbalance. Target value of current imbalance Deviation between If the deviation value exceeds the specified range, proceed to step 3. For example, -1% ≤ If ≤1%, proceed to step 3;

[0072] Wherein, the unbalance degree = (maximum phase current - minimum phase current) / average current × 100%. Specifically, the detection unit detects the three-phase current (Ii) for the i-th time in its circuit. , I , I When I >I >I Then it can be calculated =( I - I / × 100% (1); Let be the average value of the three-phase current detected in the i-th time, where i is the number of current detections during the balancing cycle of the same three-phase thermal power input, i = 0, 1, 2...n.

[0073] Step 3: Calculate the capacitance compensation. Based on the measured effective current value and phase in Step 2, select the phase with the middle effective current value as the reference phase. The control unit calculates the capacitive current value ΔI that needs to be increased or decreased for each of the two adjacent phases when the current reaches equilibrium, according to the formula:

[0074] ΔI = ωΔCΔU (2); Convert the required ΔI into the capacitance ΔC that needs to be switched; where ω is the angular frequency and ΔU is the voltage of the compensation circuit.

[0075] Specifically, for example, phase B of I If I is the reference phase, then adjust I. and I To align with Ib_i, calculate the current difference ΔIa between phase A and phase B, and the current difference ΔIc between phase B and phase C. Then, calculate the required capacitance compensation ΔCa for phase A and the required capacitance compensation ΔCc for phase C according to formula (2).

[0076] Step 4: Switching the compensation capacitor bank. Based on the capacitance compensation amount calculated in Step 3, the control unit calculates the number of compensation capacitor banks that are closest to the capacitance compensation amount to switch, such as 1μF, 2μF, 4μF, etc., and completes the switching action.

[0077] Specifically, after the control unit calculates the number of compensation capacitor groups that are closest to the capacitance compensation amount, it sends a switching command to the execution unit to complete the automatic switching action of the compensation capacitor groups. If the capacitance compensation amount is still not met after the execution unit completes the automatic switching of the compensation capacitor groups, the manual switching of the compensation capacitor groups is further performed through the manual switch of the transformer in the circuit to complete the manual switching action of the compensation capacitor groups.

[0078] The manual compensation capacitor group serves as a backup capacitor compensation group. Once the automatic switching of the built-in compensation capacitor group is completed and the capacitor compensation amount is met, the switching of the manual compensation capacitor group will not be performed. If the automatic switching of the built-in compensation capacitor group is completed but the capacitor compensation amount is not met, then the manual compensation capacitor group can be switched to perform superimposed compensation.

[0079] After completing step 4, wait for a settling time T, then proceed to step 2 to remeasure the effective value and phase angle of the three-phase current in the circuit, and calculate the new current imbalance value. Compare this new current imbalance value with the target current imbalance value, and if the deviation value is met... Not exceeding the specified value range, such as -1%≤ When the current imbalance is less than 1%, or when the current imbalance value does not exceed the first threshold K1, the first threshold K1 can be set to 1.5%-2%. If the current imbalance value is less than 2% in the nth cycle, the current imbalance will no longer improve significantly, and the switching limit of the compensation capacitor bank has been reached. The calculation cycle of the capacitor compensation amount ends, and the three-phase thermal power input balancing process of the cable is completed.

[0080] The balancing process of the three-phase thermal power input of the cable in an automatic capacitance compensation system is dynamically adjusted. During prolonged thermal cycling tests, which may last for days or even weeks, the cable temperature and the dielectric constant of the insulation material will change, leading to changes in its inherent capacitance and disrupting the established balance. Therefore, the automatic capacitance compensation system needs to periodically, for example every 30-60 minutes, or triggered, such as when the current imbalance exceeds a first threshold K1, restart the iterative process of steps 2 to 4 to achieve continuous, adaptive balancing.

[0081] Furthermore, after the heating cycle test is started, the initialization process only occurs during the first balancing step of the automatic capacitor compensation system on the three-phase thermal power input of the cable in the circuit. That is, in the first three-phase thermal power input step, step 3 records that the total capacitance of each phase is currently 0. In the subsequent periodic dynamic adjustment, step 3 records the total capacitance of each phase, including the sum of the compensation capacitance automatically switched and manually switched in the previous three-phase thermal power input balancing step.

[0082] The automatic capacitor compensation system ensures absolute balance of three-phase thermal power input, eliminates interference caused by the asymmetry of the test sample itself, and makes the test results purely reflect the performance of the insulating material under the expected thermal stress, with extremely high data reliability.

[0083] The three-phase heating cycle test method of this application also includes using a measurement sensing unit to evaluate the insulation aging of each phase of the test cable in each stage, and setting an early warning and termination mechanism based on the insulation aging evaluation results of the test cable.

[0084] Cable insulation aging assessment methods analyze insulation resistance differences, tanδ values, and insulation shrinkage. The analysis of conductor insulation resistance differences and tanδ values ​​in the cable insulation aging assessment methods for test samples includes, for example... Figure 5 As shown, it includes:

[0085] The insulation resistance and tanδ values ​​of the test cable were tested in each heating cycle, and the test data in all heating cycles were recorded. Then, the difference in insulation resistance between the first and last heating cycles of the same phase cable was calculated to evaluate the insulation aging of each phase of the test cable.

[0086] During deformation testing, since no specific high voltage is applied, the insulation resistance tester and Schering bridge can be connected to the test circuit throughout the entire test process, and the insulation resistance value and tanδ value can be monitored in real time at each stage.

[0087] In electrical testing, because a specific high voltage is applied in the test circuit, the application of this specific voltage can be stopped for a period of time during each heating cycle. An insulation resistance tester and a Schering bridge are then connected to the test circuit to detect the insulation resistance and tanδ values. For example, at the end of each heating cycle, or at a designated stage within each heating cycle, such as before heating, during heat preservation, or after heat preservation, the application of the specific voltage is stopped for 10-30 minutes, and an insulation resistance tester and a Schering bridge are connected to the test circuit to detect and record the insulation resistance and tanδ values.

[0088] Calculate the difference in insulation resistance of the same phase cable during the first and last heating cycles, and determine whether the difference in insulation resistance and tanδ value exceed the threshold. Evaluate the insulation change of the same phase cable after multiple heating cycles.

[0089] Formula for calculating insulation resistance difference: (Formula 3), where, It is the larger resistance value among the two adjacent phases. It is the smaller resistance value among the two adjacent phases.

[0090] The difference in insulation resistance between the same phase cable during the initial and final heating cycles is calculated using formula (3). First, the insulation resistance values ​​measured during the initial and final heating cycles of the same phase cable are determined, and then calculated using formula (3). For example, taking phase A as an example, the insulation resistance value measured during the initial heating cycle is... The insulation resistance value measured during the final heating cycle was [value missing]. After assessment, < Then the difference in insulation resistance between phases A is _____. Similarly, the difference in in-phase insulation resistance of B can be calculated. The difference in in-phase insulation resistance between C and C Then , , Compare with the second threshold K2; if it exceeds the second threshold K2, or When the value exceeds the third threshold K3, an alarm is triggered, indicating that the test cable has deteriorated. Here, j represents the number of tests for insulation resistance and tanδ, K2 is the specified value for the difference in insulation resistance between phases, and K3 is the specified value for the tanδ threshold. The value of K3 is... between.

[0091] Furthermore, in some embodiments, the method also includes in-phase insulation resistance difference analysis: that is, after the three-phase insulation resistance values ​​are measured, the insulation resistance values ​​of each phase are sorted by size, and then the interphase insulation resistance values ​​are calculated according to formula (3). Then, the interphase insulation resistance values ​​are compared with the fourth threshold K4. If the interphase insulation resistance value exceeds the fourth threshold, an early warning signal is issued. The value of K4 is between 10% and 20%.

[0092] For example, under a certain heating cycle, the insulation resistance of phase A is measured. The insulation resistance of phase B is 1000 GΩ. The insulation resistance of phase C is 900 GΩ. Given a resistance of 850 GΩ, the difference in interphase insulation resistance between phase A and phase B can be calculated as follows: The interphase insulation resistance difference between phase A and phase C is approximately 11.11%. ≈17.64%, the difference in interphase insulation resistance between phase B and phase C is: ≈5.88%. If K1 is set to 15%, then during this heating cycle, the difference in interphase insulation resistance between phase A and phase C is approximately 5.88%. If the insulation resistance difference is greater than 15%, it can be determined that the insulation performance of phase C has failed, issuing an early warning. The test can be automatically terminated at the initial stage of damage, protecting expensive test samples and equipment, and greatly improving safety. By calculating the insulation resistance difference between phases, not only can the insulation failure of the test resistor be determined, but also which phase of the cable has failed, allowing for precise location of the failure.

[0093] Further deformation testing can be conducted by measuring multiple sets of insulation resistance and tanδ values ​​at regular time intervals within the same heating cycle. The interphase insulation resistance difference between adjacent phases is then calculated, and the difference in interphase insulation resistance and tanδ are compared to determine if they exceed threshold values. This allows for analysis of the insulation changes of each phase of the test cable at different temperatures during each heating cycle. For example, the interphase insulation resistance and tanδ values ​​can be measured and recorded at different stages within the same heating cycle: before heating, during heat preservation, and after heat preservation. Alternatively, at regular time intervals (e.g., 2h, 3h, 4h, 5h, 6h), the interphase insulation resistance and tanδ values ​​can be measured and recorded. These time intervals can be uniform or non-uniform. The interphase insulation resistance difference is then calculated, and it is determined whether the difference in interphase insulation resistance and tanδ exceed threshold values ​​within the same heating cycle. This allows for analysis of the insulation changes of each phase of the test cable at different temperatures during each heating cycle, providing a more detailed assessment of the insulation aging of the test cable. Especially in the later stages of the test, the aging or failure time of the test cable can be more clearly identified, improving the safety performance of the test.

[0094] Insulation resistance difference and tanδ value are extremely sensitive early diagnostic indicators. Whether the phase-to-phase insulation resistance difference exceeds the second threshold K2, the phase-to-phase insulation resistance difference exceeds the third threshold K3, or the tanδ value exceeds the fourth threshold K4, an alarm can be triggered when the insulation shows minor but differentiated deterioration, accurately pinpointing which phase is experiencing problems due to mechanical and thermal stress. It not only knows that the test cable has "failed," but also when it began to fail, why it failed, and where it failed first, demonstrating strong predictive and diagnostic capabilities. It can automatically terminate the test in the initial stage of damage, protecting expensive test samples and equipment, and greatly improving safety.

[0095] In the method for evaluating the insulation aging of test cables, the analysis of insulation shrinkage includes: measuring and recording the conductor length every 2 hours in each heating cycle; and evaluating the insulation shrinkage based on the multiple measurements of the conductor length in each heating cycle, thereby assessing the insulation aging of the test cable.

[0096] The calculation process is stored in the control host through the memory. During the test, the test personnel only need to input the measured insulation resistance value and tanδ value of each phase into the control host. After the control host calculates and evaluates, it issues a warning on the human-machine interface and issues an early warning sound.

[0097] The three-phase heating cycle test method of this application also includes comprehensive monitoring of the temperature of the sample cable and the test cable by using a measuring sensor unit, continuous one-dimensional monitoring of the temperature of the sample cable and the test cable by using a first temperature measuring device and a second temperature measuring device respectively, two-dimensional monitoring of the surface of the sample cable and the test cable by using an infrared imager, and troubleshooting local overheating faults of the sample cable and the test cable.

[0098] By using multi-dimensional temperature fusion sensing, the technology achieves comprehensive monitoring of local overheating faults, micro-cracks, gaps, and other conditions in sample cables and test cables without any blind spots.

[0099] Verification of Examples

[0100] A three-phase thermal cycling verification system for 110kV cross-linked cables. The three-phase heating cycle test apparatus and method described in this application were used to conduct three-phase thermal cycling tests on 110kV cross-linked cables. Both the sample voltage regulator and the test voltage regulator used Δ / YN-11 connected transformers (3×6000A / 35kV), and the built-in compensation capacitor banks were all +120kVAR capacitor banks. The first temperature controller had 12 channels, and the second temperature controller had 24 channels. The infrared imager had a resolution of 640×512 and a positioning accuracy of 0.1mm. A three-channel independent air-cooling unit was used for air cooling.

[0101] The automatic capacitor compensation system achieves an axial temperature difference of ≤1.3℃ for the three-phase conductors (national standard requires ≤2℃); it successfully detects the 0.15mm micro-gap caused by thermal expansion at the B-phase joint, which cannot be detected by traditional single-phase tests; the test cycle is shortened to 7.5h (the traditional method requires 9h).

[0102] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A three-phase heating cycle test device, comprising a simulation circuit and a test circuit, wherein the simulation circuit includes a sample cable and the test circuit includes a test specimen cable, and both the simulation circuit and the test circuit employ three-phase independent current control, characterized in that, An automatic capacitor compensation system is installed in both the simulation circuit and the test circuit. The automatic capacitor compensation system includes a detection unit, a control unit, and an execution unit. The detection unit detects the three-phase current value of the cable in the circuit in real time. The control unit is equipped with a current rebalancing algorithm to calculate the current imbalance and calculate the required capacitor compensation amount based on the current imbalance. The execution unit is used to perform capacitor compensation based on the capacitor compensation amount calculated by the control unit, thereby achieving the balance of the three-phase thermal power input of the cable in the circuit. It also includes a measurement sensing unit, which includes an insulation resistance tester and a Schering bridge installed on the test cable in the test circuit, to detect the insulation resistance value and tanδ value of the test cable respectively, so as to realize the deterioration diagnosis of the test cable.

2. The three-phase heating cycle test apparatus according to claim 1, characterized in that, The detection unit includes a current transformer, a voltage transformer, and a signal conditioning and analog-to-digital converter. The current transformer detects the three-phase current values ​​of the cable in the circuit, including the effective current value and phase angle. The voltage transformer is installed in the circuit of the compensation capacitor bank built into the switch cabinet in the circuit to collect the compensation circuit voltage. The signal conditioning and analog-to-digital converter converts the three-phase current values ​​and the compensation circuit voltage into digital signals and transmits them to the control unit in the circuit.

3. The three-phase heating cycle test apparatus according to claim 1, characterized in that, The execution unit includes a thyristor switching switch and a built-in compensation capacitor bank installed in the switch cabinet. The thyristor switching switch receives the capacitor compensation command from the control unit to control the switching of the compensation capacitor bank in the circuit.

4. The three-phase heating cycle test apparatus according to claim 1, characterized in that, The execution unit also includes a manually compensated capacitor bank installed on the through-core transformer, which can be switched on and off by manual opening and closing of the circuit breaker.

5. The three-phase heating cycle test apparatus according to claim 1, characterized in that, The measurement sensing unit also includes a first temperature measuring device installed in the simulation loop, a second temperature measuring device installed in the test loop, and an infrared imager that simultaneously measures the temperature of the simulation loop and the test loop. The first temperature measuring device includes a first temperature controller, a first thermocouple, and a first distributed optical fiber DIS. The first temperature controller receives the first temperature data collected by the first thermocouple and the first distributed optical fiber DIS and transmits the first temperature data to the control host. The second temperature measuring device includes a second temperature controller, a second thermocouple, and a second distributed optical fiber DIS. The second temperature controller receives the second temperature data collected by the second thermocouple and the second distributed optical fiber DIS and transmits the second temperature data to the control host.

6. A three-phase heating cycle test method, wherein a heating cycle test is simultaneously performed on a sample cable and a test cable, each heating cycle comprising three stages: heating, heat preservation, and cooling, characterized in that, Each heating cycle is achieved using the three-phase heating cycle test apparatus as described in any one of claims 1-5; The entire heating cycle test also includes the use of an automatic capacitor compensation system in the simulation circuit and the test circuit to periodically balance the three-phase thermal power input of the cable in the circuit. The process of balancing the three-phase thermal power input of the cable in the circuit mainly includes: detecting the three-phase current value of the cable in the circuit and the voltage of the compensation circuit, calculating the current imbalance based on the three-phase current value, calculating the required capacitor compensation amount based on the current imbalance and the voltage of the compensation circuit, and supplementing the capacitor based on the capacitor compensation amount. It also includes the step of using a measurement sensing unit to evaluate the insulation aging of each phase of the test cable at each stage, and setting up an early warning and termination mechanism based on the insulation aging evaluation results of the test cable.

7. The three-phase heating cycle test method according to claim 6, characterized in that, The steps for balancing the three-phase thermal power input of the cables in the circuit include: Step 1, Initialization and Target Value Setting: The system is powered on, and all compensation capacitors are in the open state, which is the initial state. The control unit reads the target value of the current imbalance. Step 2, Data Acquisition and Deviation Calculation of Current Unbalance: The detection unit continuously acquires the three-phase current values ​​of the cable in the circuit. The three-phase current values ​​include the effective current value and phase. The control unit calculates the current unbalance value and compares it with the target value of the current unbalance. The deviation between the current unbalance value and the target value is calculated. When the deviation exceeds the specified value range, proceed to Step 3. Step 3, calculate the capacitance compensation: Based on the effective current value and phase measured in Step 2, select the phase with the middle effective current value as the reference phase. The control unit calculates the capacitive current value ΔI that needs to be increased or decreased in each of the two adjacent phases when the current reaches balance. According to the formula ΔI = ωΔCΔU, the required ΔI is converted into the capacitance ΔC that needs to be switched. Where ω is the angular frequency and ΔU is the voltage of the compensation circuit; Step 4, Switching the compensation capacitor bank: Based on the capacitor compensation amount calculated in Step 3, the control unit calculates the number of compensation capacitor banks to be switched corresponding to the capacitor compensation amount, and the execution unit completes the switching action.

8. The three-phase heating cycle test method according to claim 7, characterized in that, In step 4, after the control unit calculates the number of compensation capacitor groups to be switched corresponding to the capacitance compensation amount, the control unit sends a switching command to the execution unit to complete the automatic switching action of the compensation capacitor groups.

9. The three-phase heating cycle test method according to claim 8, characterized in that, If the automatic switching of the compensation capacitor bank by the execution unit still does not meet the capacitor compensation requirement, the manual switching of the manual capacitor compensation bank is further performed through the manual switch of the transformer in the circuit to complete the manual switching action of the compensation capacitor bank.

10. The three-phase heating cycle test method according to claim 7, characterized in that, After completing step 4, wait for a settling time T, then jump to step 2, remeasure the effective value and phase angle of the three-phase current in the circuit, and recalculate the current unbalance value. Then calculate the deviation between the current unbalance value and the target value. When the deviation value does not exceed the specified value range, or when the current unbalance value does not exceed the threshold, the loop ends.

11. The three-phase heating cycle test method according to claim 6, characterized in that, The insulation aging assessment method includes: testing the insulation resistance and tanδ values ​​of the test cable in each heating cycle, recording the test data in all heating cycles, calculating the difference in insulation resistance of the same phase cable in the first and last heating cycles, and comparing whether the difference in insulation resistance and tanδ exceed the threshold, thereby assessing the insulation aging of each phase of the test cable.

12. The three-phase heating cycle test method according to claim 11, characterized in that, The insulation aging assessment method also includes: in the same heating cycle, testing multiple sets of insulation resistance values ​​and tanδ values ​​at specified time intervals, comparing the phase-to-phase insulation resistance difference and tanδ value in the same heating cycle, and analyzing the insulation changes of each phase of each test cable at different temperatures in each heating cycle.

13. The three-phase heating cycle test method according to claim 6, characterized in that, The insulation aging assessment method also includes: measuring and recording the conductor length at specified time intervals during each heating cycle, and assessing the insulation shrinkage based on multiple measurements of the conductor length during each heating cycle, thereby assessing the insulation aging of the test cable.

14. The three-phase heating cycle test method according to claim 6, characterized in that, It also includes comprehensive monitoring of the temperature of the sample cable and the test cable using a measurement sensing unit, continuous one-dimensional monitoring of the temperature of the sample cable and the test cable using a first temperature measuring device and a second temperature measuring device respectively, two-dimensional monitoring of the surface of the sample cable and the test cable using an infrared imager, and troubleshooting of local overheating faults in the sample cable and the test cable.

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