Long-term voltage test system for AC cable operating in DC mode

Abstract

The application discloses an AC cable long-term voltage test system for DC operation, and relates to the field of power transmission. A DC source cannot bear high voltage for cable test, in order to approach AC direct operation working condition, how to simultaneously apply DC voltage and DC current to the test cable to eliminate the influence of eddy current on the maximum temperature difference of the cable insulation layer becomes a technical problem that needs to be broken through at present. The system comprises a test loop and a simulation loop series cable system, a DC high-voltage generator, a large-current DC generator, an isolation transformer connected with an AC power supply at an input end, and a controller. The simulation loop cable conductor and outer sheath, the large-current DC generator, and the wireless temperature measurement module of the simulation loop are connected with the DC high-voltage generator through an insulation support table to realize the same potential. The simulation loop is provided with a current and voltage measurement sensor device and a wireless cable temperature sensor. The current and voltage signals are transmitted to an upper computer through the controller, and the upper computer is used for real-time monitoring and control. The system can effectively realize long-term voltage test for AC cable operation in the DC mode.

Description

Technical Field

[0001] The present invention relates to the field of power transmission, and in particular to a long-term voltage test system for converting AC cables to DC operation. Background Art

[0002] As the selection of urban transmission corridors becomes increasingly difficult and the demand for power supply reliability continues to rise, XLPE cables are gaining increasing popularity in urban distribution networks due to their excellent electrical, mechanical, and physical and chemical properties. Compared to AC transmission, DC transmission offers higher transmission efficiency and lower line losses. It also facilitates current regulation and power transfer direction changes. It requires fewer wires and has lower investment costs, making it more economical for long-distance transmission than AC. DC cable length is not limited by capacitive current, making it advantageous for applications such as sea crossings and island transmission. It can connect two power grids, even when the frequencies differ, and can reduce short-circuit currents between the main line and the grid. Current industry experience suggests that direct conversion of AC cables at voltages of 110 kV and below to DC operation is possible and feasible. However, direct conversion of cables at voltages of 220 kV and above from AC to DC carries significant risks due to the space charge effect in strong electric fields and the temperature effects of thick insulation, making this practice not recommended. DC cables operating at ultra-high voltage levels should utilize specialized DC insulation and shielding materials. Therefore, through appropriate design of operating parameters and methods, AC cables can be used for DC transmission.

[0003] The existing traditional long-term voltage test of DC cables uses two cable circuits. AC current is applied to the two cable circuits through multiple sets of through-hole transformers to increase the temperature. The simulation circuit and multiple sets of through-hole transformers are not subjected to the test voltage. The existing traditional long-term voltage test of DC cables uses different currents in the test circuit and simulation circuit, making the current values ​​of the test circuit and simulation circuit similar. The simulation circuit is used as a temperature measurement reference, and the temperature signal is collected by thermocouples and the data is transmitted using optical fiber.

[0004] When the voltage level of the cable itself is low, the AC current generates an induced current in the cable insulation sheath, forming eddy currents. Eddy currents, like normal currents, will produce thermal effects. For DC cables, during long-term voltage tests, it is necessary to measure the maximum temperature difference between the cable conductor temperature and the insulation layer. Therefore, the use of traditional heating methods will affect the maximum temperature difference of the insulation layer of low-voltage cables. , which affects the temperature rise of the cable. In this case, it is necessary to establish a new way to apply load to the cable conductor to eliminate the influence of eddy current on the maximum temperature difference of the cable insulation layer.

[0005] Therefore, how to simultaneously apply DC voltage and DC current to the test cable to eliminate the influence of eddy current on the maximum temperature difference of the cable insulation layer has become a technical problem that needs to be overcome at this stage. SUMMARY

[0006] The technical problem to be solved and the technical task proposed by the present application are to perfect and improve the prior art, and provide an alternating current cable long-term voltage test system for direct current operation, so as to realize long-term voltage test on the alternating current cable for direct current transmission. To this end, the present application adopts the following technical solutions.

[0007] The alternating current cable long-term voltage test system for direct current operation comprises a cable system, a direct current high-voltage generator, a large-current direct current generator, an isolation transformer, a controller and an insulation support platform. The cable system comprises a test loop and a simulation loop as a cable test sample, and the test loop and the simulation loop are connected in series. The input end of the isolation transformer is connected with an alternating current power supply, the output end is connected with the input end of the large-current direct current generator, and the neutral point is connected with the insulation support platform. The output end of the large-current direct current generator is connected with the terminal end of the simulation loop, and the other end is connected with the terminal end of the test loop. One end of the direct current high-voltage generator is connected with the test loop and the insulation support platform, and the other end is connected with the ground. A plurality of wireless cable temperature measurement sensors are arranged at a plurality of temperature measurement points in the simulation loop, and a current and voltage measurement sensing device is further arranged on the simulation loop. The wireless cable temperature measurement sensors and the current and voltage measurement sensing device are connected to the controller, and the controller is connected to an upper computer to realize monitoring and control. The test loop and the simulation loop are connected in series in the 1-back cable line, the test loop and the simulation loop are simultaneously subjected to direct current by the large-current direct current generator to achieve temperature rise, the test loop and the simulation loop are subjected to the same current, the direct current high-voltage generator simultaneously applies voltage to the test loop, the cable conductor temperature is converted into an electrical signal by the wireless cable temperature measurement sensor, the temperature signal is transmitted to the upper computer through the controller, the current and voltage signals are transmitted to the upper computer through the controller by the current and voltage measurement sensing device, and real-time monitoring and control are realized by the upper computer. The long-term voltage test on the alternating current cable for direct current operation can be realized, the technical problem that the direct current voltage and the direct current are simultaneously applied to the test cable in the long-term voltage test of the alternating current cable for direct current transmission to eliminate the influence of eddy current on the maximum temperature difference of the cable insulation layer is solved, and the test basis for the reliability of the original alternating current line directly changed to direct current operation is provided, thereby providing technical support for the safe operation of the cable.

[0008] As a preferred technical means, the grounding point of the large-current direct current generator is connected with the insulation support platform, and the simulation loop and the wireless cable temperature measurement sensor are placed on the insulation support platform. The simulation loop cable conductor and the outer sheath, the large-current direct current generator, the wireless temperature measurement module of the simulation loop and the direct current high-voltage generator are at the same potential and can withstand the test direct current high voltage.

[0009] As a preferred technical means, the test loop is wound around the test site once, and the test loop is not connected with the insulation support platform. The simulation loop is long enough to make the test closer to the actual situation of the alternating current line.

[0010] As a preferred technical means: the distance between every two adjacent radio cable temperature sensor temperature measuring points is between 0.5-2m, and the temperature measuring points are arranged along the analog circuit with equal length. The distance is appropriate, the distribution is uniform, and the temperature monitoring reliability is good.

[0011] As a preferred technical means: the isolation transformer comprises a primary winding and a secondary winding, the input voltage of the primary winding is AC380V, and the secondary winding outputs AC380V connected to the input end of the large-current direct current generator. The use of 380V alternating current conforms to the current low-voltage distribution network, and compared with connecting to a medium-high voltage distribution network, the technical difficulty is lower, the connection operation is more convenient, and the safety is better.

[0012] As a preferred technical means: the large-current direct current generator adopts a three-phase bridge rectifier circuit and an LC filter circuit. Three-phase 380V alternating current passes through an air switch, a contactor, and a silicon controlled rectifier, is input to the three-phase bridge rectifier circuit after voltage regulation by the silicon controlled rectifier, and is output as a pulsating direct current. After filtering by the LC filter circuit composed of an inductor and a capacitor, a relatively stable small-ripple direct current power supply is obtained at the output end of the power supply and is at the same potential as the insulation support platform. The alternating current to direct current conversion can be conveniently realized, and the output power supply is stable and reliable.

[0013] As a preferred technical means: the controller and the upper computer system are both provided with a wireless transmission module. The wireless transmission of signals can be conveniently realized.

[0014] As a preferred technical means: the upper computer is provided with a monitoring module for monitoring the current, voltage, temperature rise of the cable test sample and automatically generating a report, and a control module for remote control and on-site remote control protection. Comprehensive monitoring and safety control of the test system can be realized.

[0015] As a preferred technical means: the temperature measuring range of the radio cable temperature sensor is 0-110℃, and the temperature signal conversion electric signal current is between 4-20mA. The temperature rise range of the conductor can be effectively covered, and the signal current range of 4-20mA is clear and stable enough.

[0016] As a preferred technical means: the test system is provided with a wireless environment temperature sensor for monitoring the ambient temperature, and the environment temperature sensor is connected to the upper computer through the controller. The upper computer can control and adjust the conductor current according to the change of the ambient temperature. The ambient temperature monitoring and the current control and adjustment of the conductor circuit can be effectively realized.

[0017] Beneficial effects: It can effectively realize long-term voltage testing of AC cables converted to DC operation, solve the technical problem of simultaneously applying DC voltage and DC current to the test cable in the long-term voltage test of AC cables converted to DC operation to eliminate the influence of eddy current on the maximum temperature difference of the cable insulation layer. For the transformation of existing distribution networks, it provides a test basis for the reliability of directly converting the original AC lines to DC operation, and provides technical guarantee for the safe operation of cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the principle of the present invention.

[0019] In the figure: 1- high current DC generator; 2- isolation transformer; 3- DC high voltage generator; 4- test circuit; 5- simulation circuit; 6- insulation support platform; 7- AC power supply. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings.

[0021] like Figure 1 As shown, a long-term voltage test system for converting AC cables to DC operation includes a cable system, a set of DC high-voltage generators 3, a set of high-current DC generators 1, an isolation transformer 2, a controller and an insulating support platform 6. The cable system includes a test loop 4 and a simulation loop 5 as a cable test piece, and the test loop 4 and the simulation loop 5 are connected in series; the input end of the isolation transformer 2 is connected to the AC power supply 7, the output end is connected to the input end of the high-current DC generator 1, and the neutral point is connected to the insulating support platform 6; the output end of the high-current DC generator 1 is connected to the terminal of the simulation loop 5, and the other end is connected to the terminal of the test loop 4; one end of the DC high-voltage generator 3 is connected to the test loop 4 and the insulating support platform 6, and the other end is grounded; multiple temperature measuring points are set on the simulation loop 5 to arrange wireless cable temperature sensors, and the simulation loop 5 is also provided with a current and voltage measurement sensor device. The wireless cable temperature sensor and the current and voltage measurement sensor device are connected to the controller, and the controller is connected to the host computer to achieve monitoring and control.

[0022] To withstand the high DC voltage test, the grounding point of the high-current DC generator 1 is connected to an insulating support platform 6, and the simulation loop 5 and the wireless cable temperature sensor are placed on the insulating support platform 6. This ensures that the cable conductor and outer sheath of the simulation loop 5, the high-current DC generator 1, the wireless temperature measurement module of the simulation loop 5, and the DC high-voltage generator 3 are at the same potential, allowing them to withstand the high DC voltage test.

[0023] To make the test closer to the actual conditions of an actual AC line, the test loop 4 makes a circle around the test site and is not connected to the insulating support platform 6. A sufficiently long simulation loop 5 is ensured to make the test closer to the actual conditions of an actual AC line.

[0024] In order to achieve comprehensive and reliable temperature monitoring, the distance between every two adjacent wireless cable temperature sensor temperature measuring points is 0.8m, and the temperature measuring points are arranged along the simulation circuit 5 with equal length. The distance is appropriate, the distribution is uniform, and the temperature monitoring is comprehensive and reliable.

[0025] In order to facilitate connection, the isolation transformer 2 includes a primary winding and a secondary winding, the input voltage of the primary winding is AC380V, and the output AC380V of the secondary winding is connected to the input end of the large current DC generator 1. The use of 380V AC conforms to the current AC low voltage distribution network, and compared with the connection of high voltage distribution network, the technical difficulty is lower, the connection operation is more convenient, and the safety is better.

[0026] In order to realize stable and reliable AC-DC conversion, the large current DC generator 1 adopts a three-phase bridge rectifier circuit and an LC filter circuit. The three-phase 380V AC power is input to the three-phase bridge rectifier circuit through the air switch, contactor and thyristor after voltage regulation by the thyristor. The rectified output pulse DC power is filtered by the LC filter circuit composed of inductance and capacitance, and then a relatively stable small ripple DC power is obtained at the output end of the power supply, and the power supply is at the same potential as the insulation support platform 6. The AC-DC conversion can be easily realized, and the output power supply is stable and reliable.

[0027] In order to realize wireless transmission of signals, the controller and the upper computer system are both provided with wireless transmission modules. The wireless transmission of signals can be easily realized.

[0028] In order to realize comprehensive monitoring and safety control, the upper computer is provided with a monitoring module for monitoring the current, voltage, temperature rise of the cable test sample and automatically generating a report, and a control module for remote control and on-site remote control protection. The comprehensive monitoring and safety control of the test system can be realized.

[0029] In order to realize the monitoring of cable temperature rise, the temperature measuring range of the wireless cable temperature sensor is 0-110℃, and the temperature signal conversion electric signal current is between 4-20mA. During the test, the test circuit 4 and the simulation circuit 5 are heated simultaneously by the DC large current generator, the cable conductor temperature reaches 70-75℃, the temperature measuring range is 0-110℃, which can effectively cover the conductor temperature rise range and the 4-20mA signal current range, and it is clear and stable enough.

[0030] In order to realize current control and adjustment, the test system is provided with a wireless environment temperature sensor for monitoring the ambient temperature. The environment temperature sensor is connected to the upper computer through the controller, and the upper computer can control and adjust the conductor current through the change of the ambient temperature. The ambient temperature monitoring and the current control and adjustment of the conductor circuit are effectively realized.

[0031] The same DC current is applied to the test loop 4 and the simulation loop 5 through the large-current DC generator 1 via a 1-back cable line, the temperature rise is achieved, the test loop 4 and the simulation loop 5 are the same current, the DC high-voltage generator 3 simultaneously applies voltage to the test loop 4, the cable conductor of the simulation loop 5 is at the same potential with the outer sheath and the large-current DC generator 1 and the insulation support table 6, and can bear the test voltage, the temperature signal of the cable conductor is converted into an electric signal by the wireless cable temperature sensor, the electric signal is transmitted to the upper computer through the controller, the current and voltage signals are transmitted to the upper computer through the controller by the current and voltage measuring sensor device, and real-time monitoring and control are performed by the upper computer, so that the long-term voltage test on the AC cable for DC power transmission can be effectively realized.

[0032] The above Figure 1 The long-term voltage test system for AC cable converted to DC operation is a specific embodiment of the present application, has embodied the outstanding substantial characteristics and significant progress of the present application, and can be modified in shape, structure and the like according to actual use needs under the guidance of the present application, and all within the protection scope of the present application.

Claims

1. A long-term voltage test system for converting AC cables to DC operation, characterized by: The invention comprises a cable system, a DC high-voltage generator (3), a high-current DC generator (1), an isolation transformer (2), a controller and an insulating support platform (6), wherein the cable system comprises a test loop (4) and a simulation loop (5) as a cable test piece, wherein the test loop (4) and the simulation loop (5) are connected in series; the input end of the isolation transformer (2) is connected to a 380V AC power supply (7), the output end is connected to the input end of the high-current DC generator (1), and the neutral point is connected to the insulating support platform (6); the output end of the high-current DC generator (1) is connected to the terminal of the simulation loop (5), and the other end is connected to the terminal of the test loop (4); one end of the DC high-voltage generator (3) is connected to the test loop (4) and the insulating support platform (6), and the other end is grounded; a plurality of temperature measuring points are provided in the simulation loop (5) and wireless cable temperature sensors are arranged; a current and voltage measuring sensor device is also provided on the simulation loop (5); the wireless cable temperature sensor and the current and voltage measuring sensor device are connected to the controller, and the controller is connected to a host computer to realize monitoring and control; The grounding point of the high-current DC generator (1) is connected to the insulating support platform (6), and the simulation loop (5) and the wireless cable temperature sensor are placed on the insulating support platform (6); the simulation loop cable conductor and the outer sheath, the high-current DC generator, the wireless temperature measurement module of the simulation loop and the DC high-voltage generator are at the same potential and can withstand the test DC high voltage.

2. The long-term voltage test system for converting AC cables to DC operation according to claim 1, characterized in that: The test loop (4) makes a circle around the test site, and the test loop (4) is not connected to the insulating support platform (6).

3. The long-term voltage test system for converting AC cables to DC operation according to claim 1, characterized in that: The distance between each two adjacent temperature measurement points of the wireless cable temperature sensors is between 0.5 and 2 meters, and the temperature measurement points are arranged along the analog loop (5) with equal lengths.

4. The long-term voltage test system for converting AC cables to DC operation according to claim 1, characterized in that: The isolation transformer (2) comprises a primary winding and a secondary winding. The input voltage of the primary winding is AC380V, and the output voltage of the secondary winding is AC380V connected to the input end of the high current DC generator (1).

5. The long-term voltage test system for converting AC cables to DC operation according to claim 4, characterized in that: The high current DC generator (1) adopts a three-phase bridge rectifier circuit and an LC filter circuit. The three-phase 380V AC power passes through the circuit breaker and the contactor to the thyristor, and is input into the three-phase bridge rectifier circuit after the thyristor voltage regulation. The rectifier outputs pulsating DC power, which is then filtered by the LC filter circuit composed of inductors and capacitors to obtain a relatively stable DC power supply with small ripple at the output end of the power supply, and the DC power supply has the same potential as the insulating support platform (6).

6. The long-term voltage test system for converting AC cables to DC operation according to claim 1, characterized in that: The controller and the host computer system are both provided with wireless transmission modules.

7. The long-term voltage test system for converting AC cables to DC operation according to claim 6, characterized in that: The host computer is provided with a monitoring module for monitoring the current, voltage, temperature rise of the cable test product and automatically generating reports, and has a control module for remote control and local remote control protection.

8. The long-term voltage test system for converting AC cables to DC operation according to claim 1, characterized in that: The temperature measuring range of the wireless cable temperature measuring sensor is 0-110°C; the electric signal current converted from the temperature signal is between 4-20mA.

9. The long-term voltage test system for converting AC cables to DC operation according to claim 7, characterized in that: The test system is provided with a wireless ambient temperature sensor for monitoring ambient temperature. The ambient temperature sensor is connected to a host computer via a controller. The host computer can control and adjust the conductor current according to the change of ambient temperature.

Images