CN115800224B - Superconducting cable direct-current transmission system and direct-current fault rapid isolation method - Google Patents
Superconducting cable direct-current transmission system and direct-current fault rapid isolation method Download PDFInfo
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Abstract
The invention discloses a superconducting cable direct current transmission system which comprises an alternating current switch, a transformer, a rectifier, a current limiter, a superconducting cable and a direct current switch which are connected in sequence; the current limiter comprises two power devices Q1 and Q2, a capacitor and two current limiting inductors, wherein the negative electrode of the power device Q1 is connected with the positive electrode of the power device Q2, one end of the capacitor is connected with the positive electrode of the power device Q1, the other end of the capacitor is connected with the negative electrode of the power device Q2, the positive electrode of the power device Q1 and the negative electrode of the power device Q2 are respectively led out to serve as direct current ports of the current limiter, the direct current ports are connected with the rectifier in parallel, the positive electrode and the negative electrode of the power device Q2 are respectively connected with one ends of the two current limiting inductors, and the other ends of the two current limiting inductors are respectively connected with the superconducting cable. The scheme can prevent equipment from being damaged due to overlarge fault current, can also ensure the duration time of the fault, and is favorable for positioning the fault and grading matching of direct current protection.
Description
Technical Field
The invention relates to the field of direct current power transmission and distribution and high-power direct current sources, in particular to a superconducting cable direct current transmission system and a direct current fault quick isolation method.
Background
The urban power grid is one of important infrastructure of urban modern construction, is a main load center of a power system, and has the characteristics of large power consumption, high load density, safety, reliability, high power supply quality requirement and the like. With the improvement of the electricity consumption of residents and the large-scale access of new energy automobiles to a power grid, the problems of insufficient urban power supply capacity, unbalanced power supply and tension of a power supply corridor are increasingly outstanding. There is a need for a new power transmission system that has sufficient system reliability while improving power transmission capability and reducing system complexity.
The superconducting cable transmits large current without resistance, the conductor loss is less than one tenth of that of the conventional cable, and the current transmission capacity of the superconducting cable with the same section is 3-5 times that of the conventional cable, so that the occupied area and the space of a power transmission system can be saved by using the superconducting cable, and a large amount of precious land resources can be saved.
However, during the duration of the dc short-circuit fault, the superconducting cable generates a large amount of heat, which causes a temperature rise, so that the superconducting cable is converted from a superconducting state to a normal state, which has an influence on the current-carrying performance of the superconducting cable, and in severe cases, may cause an expensive superconducting cable fault.
Disclosure of Invention
Aiming at the technical problems, the invention provides a superconducting cable direct current transmission system, which is used for improving the power transmission capacity, reducing the complexity and improving the reliability of a system by applying a superconducting cable to a high-current power transmission and distribution system.
In order to achieve the above purpose, the invention adopts the following technical scheme:
As a first aspect of the present application, there is provided a superconducting cable dc power transmission system including an ac switch, a transformer, a rectifier, a current limiter, a superconducting cable, and a dc switch connected in this order; the current limiter comprises two power devices Q1 and Q2, a capacitor and two current limiting inductors, wherein the negative electrode of the power device Q1 is connected with the positive electrode of the power device Q2, one end of the capacitor is connected with the positive electrode of the power device Q1, the other end of the capacitor is connected with the negative electrode of the power device Q2, the positive electrode of the power device Q1 and the negative electrode of the power device Q2 are respectively led out to serve as direct current ports of the current limiter, the direct current ports are connected with the rectifier in parallel, the positive electrode and the negative electrode of the power device Q2 are respectively connected with one ends of the two current limiting inductors, and the other ends of the two current limiting inductors are respectively connected with the superconducting cable.
In a preferred embodiment, the current limiter is configured with an In-situ controller to collect a dc voltage and a dc current, and after a dc fault is detected, the current limiter is controlled to chop, and the amplitude of the fault current is limited to a target value Ig, ig > In, and In is a rated dc current.
In a preferred embodiment, the dc switch is configured with a dc switch protection device, and the dc switch is tripped when the dc current flowing through the switch exceeds a preset current threshold Ik of the switch for a first preset period of time T1.
As a second aspect of the present application, a method for quickly isolating a dc fault of a superconducting cable dc transmission system is provided, including:
During normal operation, the current limiter power device Q1 is turned on, and the current limiter power device Q2 is turned off;
when the direct current is detected to be larger than a current limiting action value I1, the current limiter enters a chopping mode, Q1 is turned on or off according to a duty ratio M, Q2 is turned off, and the amplitude of fault current is limited to a target value Ig;
When the direct current is detected to be smaller than the current limiting action return value I2, the current limiter exits from the chopping mode and enters into the normal operation mode, and the current limiter power device Q1 is turned on and the current limiter power device Q2 is turned off; wherein In < I2< Ig < I1, in is the rated DC current;
the chopper mode duration of the current limiter exceeds a second preset duration T2, the power device Q1 of the current limiter is turned off, the power device Q2 of the current limiter is turned off, and the alternating current switch and the direct current switch are tripped; wherein T2< T1, T1 is the time constant of the DC switch protection device.
In a preferred embodiment, the ac switch and the dc switch are used as backup protection switches of a current limiter, and when the dc is shorted, the current limiter enters a chopping mode to limit fault current; when the current limiter fails or is a direct current permanent short circuit fault, the alternating current switch and the direct current switch are tripped.
In a preferred embodiment, the current of the current limiter is directional, the current flowing from the current limiter to the direct current switch is positive, and the current value is positive.
Compared with the prior art, the technical scheme of the application has the following technical effects:
the invention provides a scheme of adopting the cooperation of the current limiter and the direct current switch to isolate direct current faults for the first time. If the rectifier is directly connected into the superconducting cable, the impedance of the superconducting cable is particularly small, the existing direct current switch is slower, when a load has a short-circuit fault, the short-circuit current rising speed is particularly high, and the short-circuit current is particularly high, so that the overcurrent damage and the open and the break damage of the direct current switch of the superconducting cable can be caused. The invention adopts the current limiter to quickly limit the rising of fault current, ensures the reliable action of the direct current switch and protects the safety of the superconducting cable.
Drawings
Fig. 1 is a schematic diagram of a specific embodiment of a superconducting cable dc transmission system and a dc fault rapid isolation method according to the present application;
FIG. 2 is a schematic representation of a current limiting embodiment provided by the present application;
fig. 3 is a schematic flow chart of a method for quickly isolating a dc fault provided by the application.
The reference numerals in the figures illustrate:
1. An alternating current switch; 2. a transformer; 3. a rectifier; 4. a flow restrictor; 5. a superconducting cable; 6. a DC switch; 41. a capacitor; 42. a power circuit; 43. a current limiting inductor.
Detailed Description
The following describes the embodiments of the present invention in further detail with reference to the drawings.
The direct current transmission technology has the functions of large transmission radius, strong transmission capacity, control of the system tide direction, maintenance of the voltage and frequency stability of the interconnected alternating current system and the like, and is widely applied to power grids. In the urban load dense area, the high-capacity transmission capacity of the superconducting cable can reduce the number of central substations, further greatly simplify the urban transmission and distribution network structure, reduce the complexity of the system and improve the reliability of the system. Compared with the original conventional power transmission network, the novel power grid based on the superconducting cable can omit various devices such as conventional high-voltage lines, step-up and step-down transformers, high-voltage line switches, high-voltage transformer switches, high-voltage compensation and the like. However, superconducting cables are rarely applied to high-current power transmission and distribution, and related electric protection is rarely performed. The application provides a superconducting cable direct-current transmission system by combining a direct-current transmission technology and high-capacity transmission capacity of a superconducting cable.
Fig. 1 is a schematic diagram of a dc power transmission system of a superconducting cable according to an embodiment of the present application, and fig. 2 is a schematic diagram of a current limiter. The superconducting cable direct current transmission system comprises an alternating current switch 1, a transformer 2, a rectifier 3, a current limiter 4, a superconducting cable 5 and a direct current switch 6 which are connected in sequence. The current limiter 4 comprises two power devices Q1 and Q2, a capacitor 41 and two current limiting inductors 43, wherein the negative electrode of the power device Q1 is connected with the positive electrode of the power device Q2, one end of the capacitor 41 is connected with the positive electrode of the power device Q1, the other end of the capacitor 41 is connected with the negative electrode of the power device Q2, the positive electrode of the power device Q1 and the negative electrode of the power device Q2 are respectively led out to serve as direct current ports of the current limiter, the direct current ports are connected with the rectifier 3 in parallel, the positive electrode and the negative electrode of the power device Q2 are respectively connected with one ends of the two current limiting inductors 43, and the other ends of the two current limiting inductors 43 are respectively connected with the superconducting cable 5. In the scheme, the direct current fault is isolated by adopting a scheme of matching the current limiter and the direct current switch. If the rectifier is directly connected into the superconducting cable, the impedance of the superconducting cable is particularly small, the existing direct current switch is slower, when a load has a short-circuit fault, the short-circuit current rising speed is particularly high, and the short-circuit current is particularly high, so that the overcurrent damage and the open and the break damage of the direct current switch of the superconducting cable can be caused. The application adopts the current limiter to quickly limit the rising of fault current, ensures the reliable action of the direct current switch and protects the safety of the superconducting cable.
In some embodiments, the current limiter is configured with an In-situ controller to collect a dc voltage and a dc current, and after a dc fault is detected, the current limiter is controlled to chop, and the amplitude of the fault current is limited to a target value Ig, ig > In, and In is a rated dc current. Ig=1.2in was taken In this example. The existing direct current protection scheme has large direct current fault current and short fault duration, and is not beneficial to the positioning of the direct current fault and the hierarchical coordination of direct current protection. The amplitude of fault current is limited by chopper operation of the current limiter after detecting all direct current faults. The scheme can prevent equipment from being damaged due to overlarge fault current, can also ensure the duration of the fault, and is used for positioning the fault and grading matching of direct current protection.
In some embodiments, the dc switch is configured with a dc switch protection device, and the dc switch is tripped when the dc current flowing through the switch exceeds the switch preset current threshold Ik for a first preset period of time T1. In this embodiment, when the dc current flowing through the switch exceeds the switch preset current threshold ik=1.15in, and the first preset time period t1=2 s is continued, the dc switch is turned off.
Fig. 3 shows a method for quickly isolating a dc fault of the dc power transmission system of a superconducting cable according to an embodiment of the present application, which specifically includes the following steps:
During normal operation, the current limiter power device Q1 is turned on, and the current limiter power device Q2 is turned off;
when the direct current is detected to be larger than a current limiting action value I1, the current limiter enters a chopping mode, Q1 is turned on or off according to a duty ratio M, Q2 is turned off, and the amplitude of fault current is limited to a target value Ig;
When the direct current is detected to be smaller than the current limiting action return value I2, the current limiter exits from the chopping mode and enters into the normal operation mode, and the current limiter power device Q1 is turned on and the current limiter power device Q2 is turned off; wherein In < I2< Ig < I1, in is the rated DC current;
the chopper mode duration of the current limiter exceeds a second preset duration T2, the power device Q1 of the current limiter is turned off, the power device Q2 of the current limiter is turned off, and the alternating current switch and the direct current switch are tripped; wherein T2< T1, T1 is the time constant of the DC switch protection device.
The direct current fault quick isolation method of the superconducting cable direct current transmission system of the application is described with reference to a specific embodiment, and comprises the following steps: in normal operation, the current limiter power device Q1 is on, and Q2 is off. When the direct current is detected to be larger than the current limiting action value I1, I1=1.5In, the current limiter enters a chopping mode, Q1 is turned on or off according to the duty ratio M, Q2 is turned off, and the amplitude of the fault current is limited to a target value Ig, and Ig=1.2In. When the detected direct current is smaller than the current limiting action return value I2, i2=1.1in. The current limiter exits from the chopping mode, enters into the normal operation mode, and the current limiter power device Q1 is turned on and the current limiter power device Q2 is turned off; the current limiter chopping mode duration exceeds a second preset time period T2, t2=1s, the current limiter power device Q1 is turned off, Q2 is turned off, and the ac switch and the dc switch are tripped.
In some embodiments, the ac switch and the dc switch are used as backup protection switches of the current limiter, and when the dc is shorted, the current limiter enters a chopping mode to limit the fault current. When the current limiter fails or is a direct current permanent short circuit fault, the alternating current switch and the direct current switch are tripped.
In some embodiments, the current of the current limiter is directional, the current flowing from the current limiter to the direct current switch is positive, and the current value is positive.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.
Claims (5)
1. The superconducting cable direct current transmission system is characterized by comprising an alternating current switch, a transformer, a rectifier, a current limiter, a superconducting cable and a direct current switch which are connected in sequence; the current limiter comprises two power devices Q1 and Q2, a capacitor and two current limiting inductors, wherein the negative electrode of the power device Q1 is connected with the positive electrode of the power device Q2, one end of the capacitor is connected with the positive electrode of the power device Q1, the other end of the capacitor is connected with the negative electrode of the power device Q2, the positive electrode of the power device Q1 and the negative electrode of the power device Q2 are respectively led out to serve as direct current ports of the current limiter, the direct current ports are connected with the rectifier in parallel, the positive electrode and the negative electrode of the power device Q2 are respectively connected with one ends of the two current limiting inductors, and the other ends of the two current limiting inductors are respectively connected with the superconducting cable;
the direct current fault quick isolation method of the superconducting cable direct current transmission system comprises the following steps:
During normal operation, the current limiter power device Q1 is turned on, and the current limiter power device Q2 is turned off;
when the direct current is detected to be larger than a current limiting action value I1, the current limiter enters a chopping mode, Q1 is turned on or off according to a duty ratio M, Q2 is turned off, and the amplitude of fault current is limited to a target value Ig;
When the direct current is detected to be smaller than the current limiting action return value I2, the current limiter exits from the chopping mode and enters into the normal operation mode, and the current limiter power device Q1 is turned on and the current limiter power device Q2 is turned off; wherein In < I2< Ig < I1, in is the rated DC current;
the chopper mode duration of the current limiter exceeds a second preset duration T2, the power device Q1 of the current limiter is turned off, the power device Q2 of the current limiter is turned off, and the alternating current switch and the direct current switch are tripped; wherein T2< T1, T1 is the time constant of the DC switch protection device.
2. The superconducting cable dc transmission system of claim 1 wherein the current limiter is configured with an In-situ controller to collect dc voltage and dc current, and after a dc fault is detected, to control the current limiter to chop, to limit the magnitude of the fault current to a target value Ig, ig > In, in being the rated dc current.
3. The superconducting cable dc power transmission system of claim 1 wherein the dc switch is configured with a dc switch protection device to trip the dc switch when the dc current flowing through the switch exceeds a switch preset current threshold Ik for a first preset period of time T1.
4. The superconducting cable dc power transmission system of claim 1 wherein the ac switch and dc switch act as backup protection switches for the current limiter, the current limiter entering a chopping mode to limit fault current after dc short-circuiting; when the current limiter fails or is a direct current permanent short circuit fault, the alternating current switch and the direct current switch are tripped.
5. The superconducting electrical cable dc power transmission system of claim 1 wherein the current of the current limiter is directional and the current flowing from the current limiter to the dc switch is positive and the current value is positive.
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| CN109119981A (en) * | 2018-09-29 | 2019-01-01 | 南京南瑞继保电气有限公司 | A kind of DC Line Fault current-limiting apparatus and system and its Current limited Control method |
| CN210744758U (en) * | 2019-08-29 | 2020-06-12 | 南京理工大学 | Multi-terminal direct-current transmission system based on superconducting current limiter |
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| CN101951148A (en) * | 2010-09-13 | 2011-01-19 | 东南大学 | Low-voltage inversion superconductive transmission and distribution method of multi-DC voltage grades |
| CN106253322B (en) * | 2016-09-11 | 2019-07-02 | 浙江大学 | A kind of current transformer of the high-temperature superconductor DC bus for wind-driven generator |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109119981A (en) * | 2018-09-29 | 2019-01-01 | 南京南瑞继保电气有限公司 | A kind of DC Line Fault current-limiting apparatus and system and its Current limited Control method |
| CN210744758U (en) * | 2019-08-29 | 2020-06-12 | 南京理工大学 | Multi-terminal direct-current transmission system based on superconducting current limiter |
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