Device and method for checking wiring of secondary circuit of voltage transformer of high-altitude transformer substation

Abstract

The invention relates to a high-altitude substation voltage transformer secondary circuit wiring inspection device and method, and relates to the technical field of secondary circuit wiring inspection, and the method comprises the steps: constructing a detection system which comprises a control unit, a detection unit, a voltage reduction unit, a power supply unit, a communication unit and a signal maintaining unit; the communication unit realizes bidirectional data communication between the detection unit and the control unit based on a Modbus communication protocol; the signal holding unit comprises a plurality of capacitors which are connected in parallel between a, b, c and l terminals and an n terminal of the secondary side of the voltage transformer; the invention provides a rapid detection method for secondary side wiring of a voltage transformer, the method can be compatible with various wiring faults including PT polarity errors, open-phase errors, open-delta errors and the like, and secondly, the designed power supply module adopts a self-power supply mode, and internal power taking can be performed through a self-induction mode without an external power supply.

Description

Technical Field

[0001] This invention relates to the field of secondary circuit wiring inspection technology, and in particular to a device and method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations. Background Technology

[0002] Voltage transformers are important primary equipment used in power plants, substations, and user substations. Their secondary circuits provide secondary voltage for metering, measuring instruments, relay protection, and other systems throughout the station. The correctness of the secondary wiring of the voltage transformer directly affects the safety of the load and even the entire circuit. If the secondary wiring of the voltage transformer is incorrect, it will cause inaccurate energy metering, malfunction or failure of relay protection devices, and may even burn out the high-voltage voltage transformer or cause power outage.

[0003] In the operation of substation power systems, voltage transformers are key electrical measurement and protection devices. The correctness of their secondary circuit wiring directly affects the accuracy of power grid metering, the reliability of protection device operation, and the safe and stable operation of the entire power system. Currently, the inspection of secondary wiring of voltage transformers in the industry still largely relies on traditional manual inspection methods. This method mainly depends on the professional experience of staff to complete the inspection by checking each terminal, measuring the continuity of the line, and comparing with drawings. This process is not only cumbersome and time-consuming, but also extremely inefficient, making it difficult to meet the high-efficiency requirements of large-scale construction and operation and maintenance of high-altitude substations. Furthermore, it poses significant quality risks. Secondly, the core shortcoming of manual inspection is the low detection rate of incorrect wiring. Due to the complexity of the secondary circuit wiring of voltage transformers, involving multiple circuit branches, a large number of terminals and cables, manual inspection is prone to overlooking hidden incorrect wiring problems, such as misconnections, loose connections, short circuits, and reversed polarity, due to factors such as visual fatigue, lack of experience, and misunderstanding of drawings. These undetected incorrect wiring risks may cause a series of consequences during power grid operation. Based on this, this paper proposes an inspection device and method for the secondary circuit wiring of voltage transformers in high-altitude substations. Summary of the Invention

[0004] To overcome the problems existing in related technologies, this invention provides a device and method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations. The proposed method is compatible with various wiring faults, including PT polarity errors, phase loss errors, and open delta errors.

[0005] To achieve the above objectives, this invention provides a method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, comprising the following steps: S1. Construct a detection system, which includes a control unit, a detection unit, a step-down unit, a power supply unit, a communication unit, and a signal holding unit. The control unit uses a programmable logic controller as the main control device to improve anti-interference capability in strong magnetic and electric field environments. The communication unit realizes bidirectional data communication between the detection unit and the control unit based on the Modbus communication protocol. The signal holding unit includes multiple capacitors connected in parallel between terminals a, b, c, l and terminal n on the secondary side of the voltage transformer. S2. The power supply unit adopts a self-powered mode, drawing power internally through self-induction mode, and converting the external mains power of 220V / 50Hz into 24VDC and 12VDC to power the control unit, detection unit, communication unit and step-down unit respectively. S3. Apply a 220V AC signal to the high-voltage terminal of the voltage transformer. After the voltage signal at the high-voltage terminal is stepped down by the step-down unit, it is transmitted to the detection unit. S4. The detection unit performs real-time measurement of the low-voltage side voltage of the voltage transformer, and adopts a weak signal measurement method based on micro-capacitance detection to acquire instantaneous weak voltage data and upload it to the data register of the control unit. S5. The control unit calls the pre-stored standard voltage parameter library, compares and analyzes the real-time measurement data with the standard parameters, and calculates the voltage deviation value, phase difference, polarity consistency and on / off status indicators. S6. Based on the calculation results of step S5, perform a comprehensive verification of the polarity, ratio, phase sequence and on / off status of the secondary circuit wiring of the voltage transformer, and identify abnormal situations including PT polarity error, phase loss error, open delta connection error and open circuit fault. S7. Display the wiring inspection results through the touch screen configuration interface. The results include the wiring correctness judgment, fault type and location information. If a wiring error is detected, the control unit automatically locates the fault type and the corresponding wiring location and generates a fault diagnosis report.

[0006] Preferably, the capacitor of the signal holding unit in step 1 is a high-frequency anti-interference capacitor with a capacitance range of 0.01μF-0.1μF, used to suppress the influence of electromagnetic interference in the industrial field on the voltage measurement signal.

[0007] Preferably, in step 2, the self-induction power supply mode of the power supply unit provides emergency power to the core unit of the equipment by coupling the electromagnetic energy of the voltage transformer circuit through the electromagnetic induction coil, and after rectification, filtering and voltage stabilization, the emergency power supply duration is not less than 4 hours.

[0008] Preferably, in step 4, the weak signal voltage measurement method based on microcapacitor detection captures weak instantaneous voltage signals through the principle of capacitive coupling, and achieves accurate measurement after signal amplification and filtering.

[0009] Preferably, the standard voltage parameter library in step 5 includes standard voltage values, phase angle ranges, and polarity identifiers for the secondary side of voltage transformers of different models and ratios, and supports parameter updates and expansions through a touch screen configuration interface.

[0010] Preferably, in step S6: The criterion for determining PT polarity error is: the difference between the measured voltage phase and the standard phase exceeds ±180°; The criteria for determining a phase loss error are: the measured voltage value of any phase is lower than 50% of the standard value, and the duration exceeds 1 second; Preferably, the criterion for determining an error in the open delta connection is: the deviation of the measured voltage values ​​at both ends of the open delta from the standard value exceeds ±20%.

[0011] Preferably, the fault diagnosis report in step 7 includes the fault occurrence time, fault type, fault location coordinates, measurement data details and rectification suggestions, and supports exporting and storing it in document format.

[0012] Preferably, the voltage sampling frequency of the detection unit is not less than 10kHz, and the data analysis and processing delay of the control unit is not greater than 100ms.

[0013] Preferably, the power supply unit has overvoltage, overcurrent and short-circuit protection functions. When the input voltage exceeds 220V±10% or the output current exceeds 1.2 times the rated value, the power supply is automatically cut off and an alarm signal is triggered.

[0014] The present invention also provides a device for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, including the aforementioned method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations.

[0015] The technical solution provided by this invention may include the following beneficial effects: 1. This invention proposes a rapid detection method for the secondary side wiring of voltage transformers. This method is compatible with various wiring faults, including PT polarity error, phase loss error, and open delta error.

[0016] 2. The power supply module of the instrument of this invention adopts a self-powered mode, which can draw power internally through self-induction mode without external power supply. It is suitable for power-free modes in various occasions. The display adopts a touch screen mode, which provides a better configuration interface and facilitates operation by on-site technicians.

[0017] 3. This invention proposes a weak signal voltage measurement method based on microcapacitance detection. This method can ensure the accurate measurement of weak instantaneous voltage, thereby improving the accuracy of voltage measurement.

[0018] 4. This invention can quickly check the secondary side wiring of voltage transformers, effectively avoiding commissioning failures caused by incorrect secondary side wiring of voltage transformers. It can save engineering installation and commissioning time, improve the success rate of first-time power supply, save manpower and reduce the professional requirements of operators, reduce labor intensity, improve work efficiency, and save costs.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0020] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same parts in the exemplary embodiments of the invention.

[0021] Figure 1 This is a flowchart of the method steps of the present invention; Figure 2 This is a block diagram of the overall composition of the detection system of the present invention; Figure 3 This is a power supply logic block diagram of the power supply unit of the present invention; Figure 4 This is a block diagram of the internal logic of the detection unit of the present invention; Figure 5 This is a logic block diagram for fault determination in this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention 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 invention, and not all of them. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention. Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. Although preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention more thorough and complete, and to fully convey the scope of the invention to those skilled in the art.

[0023] The technical solutions of the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] See Figures 1-5 As shown, this invention proposes a method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, including the following steps: S1. Construct a detection system, which includes a control unit, a detection unit, a step-down unit, a power supply unit, a communication unit, and a signal holding unit. The control unit uses a programmable logic controller (PLC) as the main control device, and its core chip adopts a shielded packaging design, which can work stably in industrial environments with electric field strength ≤10kV / m and magnetic field strength ≤100mT, thereby improving the anti-interference capability in strong magnetic field and strong electric field environments. The communication unit realizes bidirectional data communication between the detection unit and the control unit based on the Modbus communication protocol. The signal holding unit includes multiple capacitors connected in parallel between terminals a, b, c, l and n on the secondary side of the voltage transformer. S2. The power supply unit adopts a self-powered mode, drawing power internally through self-induction mode, and converting the external 220V / 50Hz mains power into 24VDC and 12VDC to power the control unit, detection unit, communication unit and step-down unit respectively. The power supply unit has overvoltage, overcurrent and short circuit protection functions. When the input voltage exceeds the range of 220V±10% or the output current exceeds 1.2 times the rated value, the power supply is automatically cut off and an alarm signal is triggered. S3. Apply a 220V AC signal to the high-voltage terminal of the voltage transformer. After the voltage signal at the high-voltage terminal is stepped down by the step-down unit, it is transmitted to the detection unit. S4. The detection unit performs real-time measurement of the low-voltage side voltage of the voltage transformer. It adopts a weak signal measurement method based on micro-capacitance detection to acquire instantaneous weak voltage data and upload it to the data register of the control unit. The voltage sampling frequency of the detection unit is not less than 10kHz, and the data analysis and processing delay of the control unit is not greater than 100ms. S5. The control unit calls the pre-stored standard voltage parameter library, compares and analyzes the real-time measurement data with the standard parameters, and calculates the voltage deviation value, phase difference, polarity consistency and on / off status indicators. S6. Based on the calculation results of step S5, perform a comprehensive verification of the polarity, ratio, phase sequence and on / off status of the secondary circuit wiring of the voltage transformer, and identify abnormal situations including PT polarity error, phase loss error, open delta connection error and open circuit fault. S7. Display the wiring inspection results through the touch screen configuration interface. The results include the judgment of wiring correctness, fault type and location information. If a wiring error is detected, the control unit automatically locates the fault type and the corresponding wiring location and generates a fault diagnosis report.

[0025] In step 1, the signal holding unit includes four high-frequency anti-interference capacitors, which are connected in parallel between terminals a, b, c, l and n on the secondary side of the voltage transformer. The capacitors are selected as ceramic high-frequency capacitors with a capacitance range of 0.01μF-0.1μF, preferably 0.05μF capacitors. This type of capacitor has good high-frequency characteristics and anti-electromagnetic interference capability, which can effectively suppress the influence of electromagnetic interference in the industrial field on the voltage measurement signal, and ensure the stability and measurement accuracy of the signal voltage when testing whether there is a break in the secondary side of the voltage transformer.

[0026] In step 2, the self-induction power supply mode of the power supply unit couples the electromagnetic energy of the voltage transformer circuit through the electromagnetic induction coil, and after rectification, filtering and voltage stabilization, it provides emergency power supply to the core unit of the equipment. The emergency power supply duration is not less than 4 hours.

[0027] In step 4, the weak signal voltage measurement method based on microcapacitor detection captures weak instantaneous voltage signals through the principle of capacitive coupling, and achieves accurate measurement after signal amplification and filtering.

[0028] The standard voltage parameter library in step 5 contains standard voltage values, phase angle ranges, and polarity markings for the secondary side of voltage transformers of different models and ratios, and supports parameter updates and expansions through a touch screen configuration interface.

[0029] In step S6: A comprehensive verification of the secondary circuit wiring of the voltage transformer is performed. PT polarity error determination: If the difference between the measured voltage phase and the standard phase Δφ exceeds ±180°, it is determined that the PT polarity is incorrect; Phase loss error judgment: If the measured voltage value U of any one of the three phases a, b, and c is lower than 50% of the standard value U_standard, and this state lasts for more than 1 second, it is judged as a phase loss error; Open delta connection error judgment: If the deviation of the measured voltage value at both ends of the open delta exceeds ±20% from the standard value, it is judged as an open delta connection error; Open circuit fault determination: If the voltage measurement value between a certain terminal (a, b, c, l) and terminal n is 0 (or lower than 0.5V) for a continuous period of more than 2 seconds, it is determined that the corresponding line is open circuit fault.

[0030] The fault diagnosis report in step 7 includes the fault occurrence time, fault type, fault location coordinates, detailed measurement data, and rectification suggestions. It supports exporting and storing the report in document format. Specifically, the PLC transmits the wiring inspection results to the touchscreen for intuitive display through the configuration interface. Wiring correctness assessment: indicated by a green "pass" or a red "fail" mark; Fault information: If a fault exists, the fault type (such as PT polarity error, phase loss error, etc.) and fault location coordinates (such as "phase A line open" or "open delta 3-terminal wiring error"). Measurement data details: Displays the measured voltage values, phase angles, voltage deviations, and other data for each phase.

[0031] Meanwhile, the PLC automatically generates a fault diagnosis report, which includes the fault occurrence time (accurate to the second), fault type, fault location coordinates, detailed measurement data, and rectification suggestions (such as "adjust PT polarity wiring to ensure corresponding terminals" and "check phase A wiring to eliminate break points"). It supports the report export function via the touch screen and can save the report to a USB flash drive in PDF or other formats.

[0032] Specifically, the aforementioned detection unit uses a high-precision voltage acquisition module as its core detection component. Its voltage sampling frequency is no less than 10kHz, which can accurately capture the instantaneous weak voltage signal on the low-voltage side of the voltage transformer. This detection unit is based on the weak signal measurement method of micro-capacitance detection. It extracts the weak voltage signal through the capacitive coupling principle, and processes it through the built-in signal amplification circuit (the amplification factor is adjustable from 100 to 1000 times) and low-pass filter circuit (the cutoff frequency is 1kHz) to effectively filter out electromagnetic interference signals in the industrial field and ensure the accuracy of the measurement data. The detection unit and the control unit realize data transmission through a communication interface, and upload the real-time measured voltage data to the data register of the control unit.

[0033] The step-down unit uses a high-precision step-down transformer as its core component. Its input voltage range is 0-250VAC, and its output voltage range is 0-10VAC, with a transformation ratio error not exceeding ±0.5%. When a 220V AC signal is applied to the high-voltage terminal of the voltage transformer, the step-down unit can smoothly reduce the voltage signal to a range measurable by the detection unit, while ensuring that the phase of the stepped-down voltage signal is consistent with the original signal, avoiding phase distortion caused by the step-down process and affecting subsequent phase difference judgment. The step-down unit has an internal overvoltage protection circuit that automatically cuts off the circuit when the input voltage exceeds the set range to prevent equipment damage.

[0034] It also includes a display unit, which uses a 10-inch touchscreen as the display and operation interface. Operators can use the touchscreen to perform operations such as parameter setting, detection start / stop, and parameter library update. At the same time, the touchscreen can display the wiring inspection results in real time, including wiring correctness judgment, fault type, fault location information, and measurement data details. In addition, the touchscreen supports viewing and exporting fault diagnosis reports, which can be stored in PDF or other formats to a USB flash drive or the device's built-in storage module.

[0035] The present invention also proposes a device for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, including the above-mentioned method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations.

[0036] The following examples illustrate the application scenarios: (I) Wiring and commissioning scenario for newly built high-altitude substations: In a newly constructed 220kV substation at an altitude of 4000m, the secondary circuit wiring of a 10kV voltage transformer (10kV / 100V ratio) was inspected. Following the above operating procedures, the detection device was activated, and a 220V AC signal was applied to the high-voltage end of the voltage transformer. The detection unit collected low-voltage side voltage data in real time. After PLC comparison and analysis, the touchscreen displayed "phase loss error," with the fault location coordinates as "phase b line." The measurement data details showed that the measured value of phase b voltage was 25V (standard value 57.735V), lasting for 1.5 seconds. Based on the rectification suggestions, technicians checked the phase b wiring and found that the connection between the secondary side phase b terminal and the detection line was loose. After tightening, the test was repeated, and the result was "qualified," ensuring the correctness of the voltage transformer secondary circuit wiring and avoiding inaccurate subsequent metering or malfunctioning protection devices due to phase loss errors.

[0037] (II) Substation maintenance and repair scenarios: During maintenance at a 110kV substation at an altitude of 2800m, the secondary circuit wiring of a voltage transformer (model JSZV-10, transformation ratio 10kV / 100V) in operation needed to be checked. Since there was no stable mains power supply at the maintenance site, the testing device switched to self-induction power supply mode, using the electromagnetic energy coupled to the voltage transformer circuit for emergency power supply. During the test, the touchscreen displayed "Open delta wiring error," and the fault diagnosis report showed that the measured voltage across the open delta was 15V (standard value 100V), with a deviation rate of 85%. Based on the fault location coordinates in the report, technicians checked the open delta terminals and found that the terminal wiring sequence was reversed. After adjusting the wiring and retesting, the measured voltage across the open delta was 98V, with a deviation rate of 2%, meeting the requirements and ensuring the safe operation of the voltage transformer.

[0038] This method can quickly detect wiring errors on the secondary side of voltage transformers, reduce the workload of wiring inspectors, improve the success rate of initial power supply, and increase the safety margin of electrical equipment and instruments.

[0039] The present invention has been described in detail above with reference to the accompanying drawings. In the above embodiments, the descriptions of each embodiment have their own emphasis; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. Those skilled in the art should also understand that the actions and modules involved in the specification are not necessarily essential to the present invention. Furthermore, it is understood that the steps in the method of the embodiments of the present invention can be adjusted, combined, and deleted according to actual needs, and the structure in the device of the embodiments of the present invention can be combined, divided, and deleted according to actual needs.

[0040] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, characterized in that... Includes the following steps: S1. Construct a detection system, which includes a control unit, a detection unit, a step-down unit, a power supply unit, a communication unit, and a signal holding unit. The control unit uses a programmable logic controller as the main control device to improve anti-interference capability in strong magnetic and electric field environments. The communication unit realizes bidirectional data communication between the detection unit and the control unit based on the Modbus communication protocol. The signal holding unit includes multiple capacitors connected in parallel between terminals a, b, c, l and terminal n on the secondary side of the voltage transformer. S2. The power supply unit adopts a self-powered mode, drawing power internally through self-induction mode, and converting the external mains power of 220V / 50Hz into 24VDC and 12VDC to power the control unit, detection unit, communication unit and step-down unit respectively. S3. Apply a 220V AC signal to the high-voltage terminal of the voltage transformer. After the voltage signal at the high-voltage terminal is stepped down by the step-down unit, it is transmitted to the detection unit. S4. The detection unit performs real-time measurement of the low-voltage side voltage of the voltage transformer, and adopts a weak signal measurement method based on micro-capacitance detection to acquire instantaneous weak voltage data and upload it to the data register of the control unit. S5. The control unit calls the pre-stored standard voltage parameter library, compares and analyzes the real-time measurement data with the standard parameters, and calculates the voltage deviation value, phase difference, polarity consistency and on / off status indicators. S6. Based on the calculation results of step S5, perform a comprehensive verification of the polarity, ratio, phase sequence and on / off status of the secondary circuit wiring of the voltage transformer, and identify abnormal situations including PT polarity error, phase loss error, open delta connection error and open circuit fault. S7. Display the wiring inspection results through the touch screen configuration interface. The results include the wiring correctness judgment, fault type and location information. If a wiring error is detected, the control unit automatically locates the fault type and the corresponding wiring location and generates a fault diagnosis report.

2. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, The capacitor selected for the signal holding unit in step 1 is a high-frequency anti-interference capacitor with a capacitance range of 0.01μF-0.1μF, used to suppress the influence of electromagnetic interference in the industrial environment on the voltage measurement signal.

3. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, In step 2, the self-induction power supply mode of the power supply unit provides emergency power to the core unit of the equipment by coupling the electromagnetic energy of the voltage transformer circuit through the electromagnetic induction coil, and after rectification, filtering and voltage stabilization, the emergency power supply duration is not less than 4 hours.

4. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, In step 4, the weak signal voltage measurement method based on microcapacitance detection captures weak instantaneous voltage signals through the principle of capacitive coupling, and achieves accurate measurement after signal amplification and filtering.

5. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, The standard voltage parameter library mentioned in step 5 contains standard voltage values, phase angle ranges, and polarity identifiers for the secondary side of voltage transformers of different models and ratios, and supports parameter updates and expansions through a touch screen configuration interface.

6. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, In step S6: The criterion for determining PT polarity error is: the difference between the measured voltage phase and the standard phase exceeds ±180°; The criteria for determining a phase loss error are: the measured voltage value of any phase is lower than 50% of the standard value, and the duration exceeds 1 second; The criterion for determining an error in an open delta connection is: the deviation of the measured voltage value at both ends of the open delta from the standard value exceeds ±20%.

7. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, The fault diagnosis report in step 7 includes the fault occurrence time, fault type, fault location coordinates, measurement data details, and rectification suggestions, and supports exporting and storing it in document format.

8. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, The voltage sampling frequency of the detection unit is not less than 10kHz, and the data analysis and processing delay of the control unit is not greater than 100ms.

9. The method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations according to claim 1, characterized in that, The power supply unit has overvoltage, overcurrent and short circuit protection functions. When the input voltage exceeds 220V±10% or the output current exceeds 1.2 times the rated value, the power supply will be automatically cut off and an alarm signal will be triggered.

10. A device for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, characterized in that... This includes the method for inspecting the secondary circuit wiring of voltage transformers in high-altitude substations, as described in any one of claims 1-9.

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