CN111736011A - Controllable zero sequence current transformer - Google Patents
Controllable zero sequence current transformer Download PDFInfo
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- CN111736011A CN111736011A CN202010424678.8A CN202010424678A CN111736011A CN 111736011 A CN111736011 A CN 111736011A CN 202010424678 A CN202010424678 A CN 202010424678A CN 111736011 A CN111736011 A CN 111736011A
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- controlled rectifier
- silicon controlled
- zero sequence
- transformer
- current
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
- G01R15/183—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core
- G01R15/185—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core with compensation or feedback windings or interacting coils, e.g. 0-flux sensors
Abstract
The invention discloses a controllable zero sequence current transformer, which comprises: the device comprises a current transformer, a first silicon controlled rectifier, a second silicon controlled rectifier, a voltage transformer, an APC voltage conversion module, a photoelectric isolation element, an MCU and a relay protection device; the current transformer comprises a primary wire turn and a secondary wire turn which are respectively wound on the coupling iron core; the voltage transformer comprises an adaptive transformer and a secondary side small resistor; the APC voltage conversion module is connected with the voltage transformer; the photoelectric isolation element is connected between the APC voltage conversion module and the MCU; the MCU is used for monitoring and storing the output digital voltage signal and controlling the silicon controlled rectifier to adjust the measurement gear of the current transformer; the MCU is connected with the relay protection device through a serial port communication interface; the relay protection device is used for monitoring the zero sequence current amplitude and isolating fault points. The invention can greatly enlarge the measurement range of the zero sequence current, identify the high resistance grounding fault in a wider range and meet the requirement of multiple functions.
Description
Technical Field
The invention relates to the technical field of power transformers, in particular to a controllable zero-sequence current transformer used in a mode that arc suppression coils are connected in parallel and low-resistance grounding.
Background
At present, arc suppression coil parallel low-resistance grounding devices are more and more widely applied to power systems. The arc suppression coil parallel low-resistance grounding device has the advantages that the arc suppression coil and the low-resistance grounding resistor can be compatible, namely, partial arc type faults can be eliminated by the arc suppression coil, zero sequence current protection actions can be triggered by the input of the low-resistance grounding resistor, and low-transition resistance fault points can be isolated.
In a power distribution network with a neutral point grounded through an arc suppression coil and a low resistance in the prior art, the single-phase ground fault is complex in fault type, the occurrence frequency of the high-resistance ground fault is high, the range of a grounding transition resistance value can reach thousands of ohms, and the corresponding zero-sequence current is 0-500A. When the transformer substation adopts a grounding mode that arc suppression coils are connected with low-resistance grounding resistors in parallel, the zero-sequence current transformer generally mainly meets the requirements of a zero-sequence overcurrent protection device, the selection type is generally 10p10, the measurement range of the zero-sequence current transformer meeting the measurement accuracy is 0.1 Ie-10 Ie, wherein Ie is rated current and is generally about 500A; from the analysis, the accurate measurement range is 50A-5000A, and the corresponding grounding point transition resistance value is 0-100 omega.
The inventor finds that the following technical problems exist in the prior art in the process of implementing the invention:
the conventional zero sequence current transformer cannot meet the measurement requirement of zero sequence current when high-resistance ground faults occur, and when the high-resistance ground faults occur and a line selection device is required to select lines, line selection is usually wrong or cannot be started due to the problem of measurement accuracy of the zero sequence current transformer.
Disclosure of Invention
The invention provides a controllable zero sequence current transformer which can greatly enlarge the measurement range of zero sequence current, identify high-resistance grounding faults in a wider range and meet the requirement of multiple functions.
The embodiment of the invention provides a controllable zero sequence current transformer, which comprises:
the device comprises a current transformer, a first silicon controlled rectifier, a second silicon controlled rectifier, a voltage transformer, an APC voltage conversion module, a photoelectric isolation element, an MCU and a relay protection device;
the current transformer comprises a primary wire turn and a secondary wire turn, wherein the primary wire turn and the secondary wire turn are respectively wound on a coupling iron core to form a current conversion relation; the voltage transformer comprises an adaptive transformer and a secondary side small resistor and is used for converting a current signal into a voltage signal; the adaptive transformer comprises a first winding and a second winding, and the secondary side small resistor is connected in parallel at two ends of the second winding;
wherein the secondary turns have taps connected to the input of the first silicon controlled rectifier; one end of the secondary turn is connected with the input end of the second silicon controlled rectifier, and the other end of the secondary turn is connected with one end of the first winding; the output ends of the first silicon controlled rectifier and the second silicon controlled rectifier are respectively connected with the other end of the first winding;
the APC voltage conversion module is connected with the voltage transformer and is used for converting an analog voltage signal into a PWM pulse digital signal;
the photoelectric isolation element is connected between the APC voltage conversion module and the MCU;
the MCU is used for monitoring and storing the output digital voltage signal, and is also used for sending a control instruction to the first silicon controlled rectifier and the second silicon controlled rectifier when the current amplitude is monitored to meet an abnormal condition, so as to control the first silicon controlled rectifier and the second silicon controlled rectifier to be switched on or off, so as to adjust the measurement gear of the current transformer;
the MCU is connected with the relay protection device through a serial port communication interface;
the relay protection device is used for monitoring the zero sequence current amplitude and judging whether the line has a ground fault according to the zero sequence current amplitude; if the device judges that the ground fault occurs, a switch opening command is generated, a fault line is opened, and a fault point is isolated.
As an improvement of the above scheme, the method further comprises the following steps: a fault line selection device;
the MCU is connected with the fault line selection device through a serial port communication interface;
the fault line selection device is used for monitoring the zero sequence voltage and the zero sequence current of the fault line, judging the fault line according to the monitored zero sequence voltage and the monitored zero sequence current of the fault line and giving an alarm.
As an improvement of the above scheme, when it is monitored that the current amplitude satisfies the abnormal condition, the method specifically includes:
when the current amplitude exceeds a preset limit value or an abnormal working condition occurs;
the abnormal operating condition includes current topping.
As an improvement of the above scheme, the method further comprises the following steps:
when the current transformer normally operates, the first silicon controlled rectifier is switched on, the second silicon controlled rectifier is switched off, and the current transformer operates at a low-current measuring gear;
when the MCU monitors that the current amplitude meets the abnormal condition, a control instruction is sent out to disconnect the first silicon controlled rectifier and connect the second silicon controlled rectifier, so that the mutual inductor operates at a high-current measuring gear.
The controllable zero sequence current transformer provided by the embodiment of the invention has the following beneficial effects:
the measurement of large current (metallic grounding fault and low transition resistance grounding fault zero-sequence current) and small current (high resistance grounding fault zero-sequence current) is realized by changing the number of turns corresponding to the tap; monitoring and storing the output digital voltage signal through the MCU, and controlling the conduction and the disconnection of the first silicon controlled rectifier and the second silicon controlled rectifier; the conversion of different current amplitude measurement gears is realized through the connection and disconnection of the first silicon controlled rectifier and the second silicon controlled rectifier; monitoring the zero sequence current amplitude value through a relay protection device, judging whether the line has a ground fault according to the zero sequence current amplitude value, and generating a switch opening command when the device judges that the ground fault occurs, opening the fault line and isolating a fault point; monitoring zero sequence voltage and zero sequence current of a fault line through a fault line selection device, selecting the fault line and giving an alarm; the method can greatly enlarge the measurement range of the zero sequence current, identify the high-resistance earth fault in a wider range and meet the requirement of multiple functions, thereby improving the safety and stability of the power system.
Drawings
Fig. 1 is a schematic structural diagram of a controllable zero sequence current transformer according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of an embodiment of the present invention.
Fig. 3 is a schematic diagram of a connection structure of a relay protection device and a fault line selection device according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of an arc suppression coil parallel low-resistance grounding device of a controllable zero-sequence current transformer according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a schematic structural diagram of a controllable zero sequence current transformer provided in an embodiment of the present invention includes: the device comprises a current transformer 1, a first silicon controlled rectifier 2, a second silicon controlled rectifier 3, a voltage transformer 4, an APC voltage conversion module 5, a photoelectric isolation element 6, an MCU7 and a relay protection device 8;
the current transformer 1 comprises a primary turn 11 and a secondary turn 12, wherein the primary turn 11 and the secondary turn 12 are respectively wound on a coupling iron core to form a current conversion relation; the voltage transformer 4 comprises an adaptive transformer and a secondary side small resistor 43, and is used for converting a current signal into a voltage signal; the adaptive transformer comprises a first winding 41 and a second winding 42, and the secondary side small resistor 43 is connected in parallel at two ends of the second winding 42;
wherein the secondary turns 12 are provided with a tap 121, the tap 121 being connected to the input of the first silicon controlled rectifier 2; one end of the secondary turn 12 is connected to the input terminal of the second silicon controlled rectifier 3, and the other end of the secondary turn 12 is connected to one end of the first winding 41; the output ends of the first silicon controlled rectifier 2 and the second silicon controlled rectifier 3 are respectively connected with the other end of the first winding 41;
the APC voltage conversion module 5 is connected with the voltage transformer 4 and is used for converting an analog voltage signal into a PWM pulse digital signal;
the photoelectric isolation element 6 is connected between the APC voltage conversion module 5 and the MCU 7;
the MCU7 is used for monitoring and storing the output digital voltage signal, and is also used for sending a control instruction to the first silicon controlled rectifier 2 and the second silicon controlled rectifier 3 when the current amplitude is monitored to meet the abnormal condition, and controlling the first silicon controlled rectifier 2 and the second silicon controlled rectifier 3 to be switched on or switched off so as to adjust the measurement gear of the current transformer 1;
the MCU7 is connected with the relay protection device 8 through a serial port communication interface;
the relay protection device 8 is used for monitoring the zero sequence current amplitude and judging whether the line has a ground fault according to the zero sequence current amplitude; if the device judges that the ground fault occurs, a switch opening command is generated, a fault line is opened, and a fault point is isolated.
Specifically, the primary wire turns 11 of the current transformer 1 are generally 1 turn; the secondary turns 12 are provided with taps 121 to enable the switching of different current amplitude measurement steps by switching a first silicon controlled rectifier 2(SCR1) and a second silicon controlled rectifier 3(SCR2) on and off.
Specifically, the photoelectric isolation element 6 is connected between the APC voltage conversion module 5 and the MCU 7; can realize isolation and prevent electromagnetic interference.
Specifically, the current transformer 1 has more turns corresponding to the taps 121, and is mainly used for measuring large current (zero-sequence current of metallic ground fault and low-transition-resistance ground fault); the tap 121 has a small number of turns and is mainly used for small current (zero sequence current of high resistance ground fault) measurement.
When the current transformer runs normally, the SCR1 is switched on, the SCR2 is switched off, and the current transformer 1 runs at a low-current measuring gear; when the MCU7 monitors that the current exceeds a certain limit value or abnormal working conditions such as topping occur, the MCU7 sends a control command to disconnect the SCR1 and connect the SCR2, so that the current transformer 1 operates in a high-current measuring gear. Thus, accurate measurement of large current and small current can be simultaneously realized. The large current measuring signal is used for triggering the relay protection device 8 to act, and the small current measuring signal is used for triggering the fault line selection device 9 to conduct grounding line selection.
Further, still include: a fault line selection device 9;
the MCU7 is connected with the fault line selection device 9 through a serial port communication interface;
the fault line selection device 9 is used for monitoring the zero sequence voltage and the zero sequence current of the fault line, judging the fault line according to the monitored zero sequence voltage and the zero sequence current of the fault line and giving an alarm.
Specifically, referring to fig. 2, it is a schematic structural diagram of an embodiment of the present invention.
Fig. 3 is a schematic diagram of a connection structure of the relay protection device 8 and the fault line selection device 9 according to an embodiment of the present invention. The relay protection device 8 is respectively connected with a current transformer in the line, so that the zero sequence current amplitude in the line is monitored, and whether the line has a ground fault is judged according to the zero sequence current amplitude; if the device judges that the ground fault occurs, a switch opening command is generated, a fault line is opened, and a fault point is isolated; the fault line selection device 9 is connected with a current transformer and a voltage transformer in the line respectively, so that the zero sequence voltage in the line and the zero sequence current of the fault line are monitored, and the fault line is judged according to the monitored zero sequence voltage and the monitored zero sequence current of the fault line and is alarmed.
Further, when it is monitored that the current amplitude satisfies the abnormal condition, the method specifically includes:
when the current amplitude exceeds a preset limit value or an abnormal working condition occurs;
the abnormal operating condition includes current topping.
Further, still include:
when the current transformer operates normally, the first silicon controlled rectifier 2 is switched on, the second silicon controlled rectifier 3 is switched off, and the current transformer 1 operates at a low-current measuring gear;
when the MCU7 monitors that the current amplitude meets the abnormal condition, a control instruction is sent to disconnect the first silicon controlled rectifier 2 and connect the second silicon controlled rectifier 3, so that the transformer operates at a high-current measuring gear.
In particular, this allows for accurate measurement of both large and small currents. The large current measuring signal is used for triggering the relay protection device 8 to act, and the small current measuring signal is used for triggering the fault line selection device 9 to conduct grounding line selection.
Referring to fig. 4, when the system detects that the zero sequence voltage amplitude exceeds the threshold value, the damping resistor of the arc suppression coil is short-circuited and enters the compensation state of the arc suppression coil. After the compensation state lasts for a certain time T0, if the system finds that the system is not cleared, a low-resistance grounding resistor is put into use to trigger the zero-sequence overcurrent protection action.
In the process, when a low-resistance grounding resistor is put into use, if zero-sequence overcurrent protection is triggered, the transition resistance value of a fault grounding point is not more than 200 ohms, otherwise, zero-sequence overcurrent protection sensitivity is insufficient, the fault point cannot be tripped if the line fault point is a grounding fault caused by personal electric shock (human body transition resistance is about 500-1000 ohms), and great safety risk is caused.
Therefore, when the arc suppression coil operates in a parallel low-resistance grounding mode, a line selection device needs to be arranged for matching. The line selection device is characterized in that a high-resistance grounding fault can be identified and a fault line can be selected as long as a proper measurement current is given, and judgment by an operator on duty is facilitated. The premise that the line selection device can reliably judge is that the zero sequence current transformer 1 needs to have enough measurement accuracy when the current is small.
In a power distribution network with a neutral point grounded through an arc suppression coil and a low resistance, the fault type of a single-phase ground fault is complex, the occurrence frequency of a high-resistance ground fault is high, the range of a grounding transition resistance value can reach several k omega, and the corresponding zero-sequence current is 0-500A. When the transformer substation adopts the grounding mode that arc suppression coils are connected with low-resistance grounding resistors in parallel, the zero-sequence current transformer 1 generally meets the requirements of a zero-sequence overcurrent protection device, the selection type is generally 10p10, the measurement range of the measurement accuracy is 0.1 Ie-10 Ie (Ie is rated current and generally about 500A), namely the accurate measurement range is 50A-5000A, and the corresponding grounding point transition resistance value is 0-100 omega. From the above analysis, it can be seen that the conventional zero sequence current transformer 1 cannot meet the measurement requirement of the zero sequence current when the high resistance ground fault occurs, and when the line selection device is required to select the line due to the high resistance ground fault, the line selection is often wrong or the starting cannot be performed due to the problem of the measurement accuracy of the zero sequence current transformer 1.
By adopting the zero-sequence current transformer 1 provided by the embodiment of the invention, the measurement of the zero-sequence current in a wider range can be realized by adjusting the measurement gear, the identification of the high-resistance grounding fault in the wider range is included, and the method has very positive significance.
The controllable zero sequence current transformer provided by the embodiment of the invention has the following beneficial effects:
the measurement of large current (metallic grounding fault and low transition resistance grounding fault zero-sequence current) and small current (high resistance grounding fault zero-sequence current) is realized by changing the number of turns corresponding to the tap; monitoring and storing the output digital voltage signal through the MCU, and controlling the conduction and the disconnection of the first silicon controlled rectifier and the second silicon controlled rectifier; the conversion of different current amplitude measurement gears is realized through the connection and disconnection of the first silicon controlled rectifier and the second silicon controlled rectifier; monitoring the zero sequence current amplitude value through a relay protection device, judging whether the line has a ground fault according to the zero sequence current amplitude value, and generating a switch opening command when the device judges that the ground fault occurs, opening the fault line and isolating a fault point; monitoring zero sequence voltage and zero sequence current of a fault line through a fault line selection device, selecting the fault line and giving an alarm; the method can greatly enlarge the measurement range of the zero sequence current, identify the high-resistance earth fault in a wider range and meet the requirement of multiple functions, thereby improving the safety and stability of the power system.
It should be noted that the above-described system embodiments are merely illustrative, where the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. In addition, in the drawings of the embodiment of the system provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, and may be specifically implemented as one or more communication buses or signal lines. One of ordinary skill in the art can understand and implement it without inventive effort.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (4)
1. A controllable zero sequence current transformer, characterized by comprising: the device comprises a current transformer, a first silicon controlled rectifier, a second silicon controlled rectifier, a voltage transformer, an APC voltage conversion module, a photoelectric isolation element, an MCU and a relay protection device;
the current transformer comprises a primary wire turn and a secondary wire turn, wherein the primary wire turn and the secondary wire turn are respectively wound on a coupling iron core to form a current conversion relation; the voltage transformer comprises an adaptive transformer and a secondary side small resistor and is used for converting a current signal into a voltage signal; the adaptive transformer comprises a first winding and a second winding, and the secondary side small resistor is connected in parallel at two ends of the second winding;
wherein the secondary turns have taps connected to the input of the first silicon controlled rectifier; one end of the secondary turn is connected with the input end of the second silicon controlled rectifier, and the other end of the secondary turn is connected with one end of the first winding; the output ends of the first silicon controlled rectifier and the second silicon controlled rectifier are respectively connected with the other end of the first winding;
the APC voltage conversion module is connected with the voltage transformer and is used for converting an analog voltage signal into a PWM pulse digital signal;
the photoelectric isolation element is connected between the APC voltage conversion module and the MCU;
the MCU is used for monitoring and storing the output digital voltage signal, and is also used for sending a control instruction to the first silicon controlled rectifier and the second silicon controlled rectifier when the current amplitude is monitored to meet an abnormal condition, so as to control the first silicon controlled rectifier and the second silicon controlled rectifier to be switched on or off, so as to adjust the measurement gear of the current transformer;
the MCU is connected with the relay protection device through a serial port communication interface;
the relay protection device is used for monitoring the zero sequence current amplitude and judging whether the line has a ground fault according to the zero sequence current amplitude; if the device judges that the ground fault occurs, a switch opening command is generated, a fault line is opened, and a fault point is isolated.
2. The controllable zero sequence current transformer of claim 1, further comprising: a fault line selection device;
the MCU is connected with the fault line selection device through a serial port communication interface;
the fault line selection device is used for monitoring the zero sequence voltage and the zero sequence current of the fault line, judging the fault line according to the monitored zero sequence voltage and the monitored zero sequence current of the fault line and giving an alarm.
3. The controllable zero sequence current transformer of claim 1, wherein when the monitored current amplitude satisfies the abnormal condition, specifically comprising:
when the current amplitude exceeds a preset limit value or an abnormal working condition occurs;
the abnormal operating condition includes current topping.
4. The controllable zero sequence current transformer of claim 1, further comprising:
when the current transformer normally operates, the first silicon controlled rectifier is switched on, the second silicon controlled rectifier is switched off, and the current transformer operates at a low-current measuring gear;
when the MCU monitors that the current amplitude meets the abnormal condition, a control instruction is sent out to disconnect the first silicon controlled rectifier and connect the second silicon controlled rectifier, so that the mutual inductor operates at a high-current measuring gear.
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| CN202010424678.8A CN111736011A (en) | 2020-05-19 | 2020-05-19 | Controllable zero sequence current transformer |
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| CN202010424678.8A CN111736011A (en) | 2020-05-19 | 2020-05-19 | Controllable zero sequence current transformer |
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Application publication date: 20201002 |