CN113267670A - Fault phase current acquisition circuit of feeder terminal device - Google Patents

Fault phase current acquisition circuit of feeder terminal device Download PDF

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Publication number
CN113267670A
CN113267670A CN202110507503.8A CN202110507503A CN113267670A CN 113267670 A CN113267670 A CN 113267670A CN 202110507503 A CN202110507503 A CN 202110507503A CN 113267670 A CN113267670 A CN 113267670A
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China
Prior art keywords
current transformer
primary side
terminal device
current
acquisition circuit
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Pending
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CN202110507503.8A
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Chinese (zh)
Inventor
冷春田
於凡枫
王晶
高敏
陈致远
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Shanghai Holystar Information Technology Co ltd
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Shanghai Holystar Information Technology Co ltd
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Priority to CN202110507503.8A priority Critical patent/CN113267670A/en
Publication of CN113267670A publication Critical patent/CN113267670A/en
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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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
    • G01R1/36—Overload-protection arrangements or circuits for electric measuring instruments
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
    • G01R35/02—Testing or calibrating of apparatus covered by the other groups of this subclass of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The invention relates to the technical field of feeder line terminal devices, in particular to a fault phase current acquisition circuit of a feeder line terminal device, which comprises: the first current transformer is provided with a first preset transformation ratio, is arranged on the secondary side of the feeder line terminal device and is used for providing a wave recording requirement for the analog-digital converter when a circuit fails; and the second current transformer is provided with a second preset transformation ratio, is arranged on the secondary side of the feeder line terminal device and is connected with the first current transformer in parallel, and is used for measuring the sudden change current generated by high-impedance grounding. The technical scheme of the invention has the beneficial effects that: the double-range CT fault phase current acquisition circuit is provided for a feeder line terminal device, can meet the 20-time wave recording requirement when a short circuit fault occurs in a line, and can accurately measure a sudden change signal of 350mA current magnitude under the condition of non-line fault, so that a high-resistance grounding fault generated by any phase line of a 10KV system can be accurately judged.

Description

Fault phase current acquisition circuit of feeder terminal device
Technical Field
The invention relates to the technical field of feeder line terminal devices, in particular to a fault phase current acquisition circuit of a feeder line terminal device.
Background
The standardized electronic distribution switch monitoring Terminal device (FTU) of state network, primary side CT (Current transformer) adopts 600A:1V Current collection CT conversion to obtain small voltage signals, and the Current transformer has the function of converting primary Current with larger value into secondary Current with smaller value through a certain transformation ratio for protection, measurement and other purposes. The circuit requires to satisfy 20 times overload's record ripples demands when short-circuit fault, and the inside 20V that will use of general FTU device: the load current conversion small signal is converted by the secondary side small CT of 3.25V and enters a 16-bit ADC (Analog-to-Digital Converter) for wave recording processing. When the load current signal of the rated 600A is tested by the transformation ratio device, an analog quantity signal of +/-229.775 mV can be generated at the input end of the ADC.
In the prior art, in a 10KV neutral point ungrounded line system, distributed capacitance and distributed resistance exist. When 2K omega high impedance grounding on any line occurs, the minimum current mutation amount after grounding of a fault phase under an equivalent model is about 350 mA. If the traditional single-range CT is adopted, because the range of the secondary side small CT meeting the recording requirement is larger (i.e. the transformation ratio is large), the fault phase current variation of 350mA can only generate an analog quantity mutation of ± 0.134035mV at the input end of the ADC. Because the ADC adopts 16 bits, the test range of the ADC is ± 10V, that is, the minimum ADC scale 1LBS is 20V/65535 mV-0.305180 mV, and in addition, the ADC itself has a noise problem, so that the sudden change signal of 350mA current magnitude cannot be accurately measured at all, and whether the line has a high-impedance ground fault cannot be determined because the transient sudden change current signal cannot be accurately measured.
Disclosure of Invention
To solve the above problems in the prior art, a fault phase current acquisition circuit of a feeder terminal device is provided.
The specific technical scheme is as follows:
the invention includes a fault phase current acquisition circuit of a feeder terminal device, comprising:
a first current transformer having a first predetermined transformation ratio and disposed on the secondary side of the feeder terminal device, wherein a first input terminal of a primary side of the first current transformer is connected to a first output terminal of a primary side of the feeder terminal device, and a second input terminal of the primary side of the first current transformer is connected to a second output terminal of the primary side of the feeder terminal device;
a second current transformer having a second predetermined transformation ratio, disposed on the secondary side of the feeder terminal device and connected in parallel with the first current transformer, wherein a first input terminal on the primary side of the second current transformer is connected to a first output terminal on the primary side of the feeder terminal device, and a second input terminal on the primary side of the second current transformer is connected to a second output terminal on the primary side of the feeder terminal device;
the first input end of the analog-to-digital converter is connected with the first output end of the secondary side of the first current transformer, the second input end of the analog-to-digital converter is connected with the second output end of the secondary side of the first current transformer, and the first current transformer is used for providing wave recording requirements for the analog-to-digital converter when a circuit fails;
the third input end of the analog-to-digital converter is connected with the first output end of the secondary side of the second current transformer, the fourth input end of the analog-to-digital converter is connected with the second output end of the secondary side of the second current transformer, and the second current transformer is used for measuring the sudden change current generated by high-impedance grounding.
Preferably, the method further comprises the following steps:
and the overload protection device is arranged between a first output end on the primary side of the feeder terminal device and a first input end on the primary side of the second current transformer and is used for monitoring an output signal on the primary side of the feeder terminal device, and when the output signal exceeds a preset threshold value, the overload protection device automatically cuts off the primary side of the second current transformer.
Preferably, the overload protection apparatus specifically includes:
a first input end of the rectifier bridge is connected with a first output end of a primary side of the feeder terminal device, and a second input end of the rectifier bridge is connected with a second input end of a primary side of the second current transformer;
the first output end and the second output end of the rectifier bridge are respectively connected to two sides of a coil of the relay;
the relay further includes a contact connected between a first input terminal on the primary side of the second current transformer and a first output terminal on the primary side of the feeder terminal device.
Preferably, the overload protection apparatus further includes:
the grid electrode of the switch tube is connected with the first output end of the rectifier bridge through a first resistor, the source electrode of the switch tube is grounded, and the drain electrode of the switch tube is connected with the relay coil;
the first capacitor is connected between the first resistor and the second output end of the rectifier bridge;
the second resistor is connected between the first resistor and the second output end of the rectifier bridge and is connected with the first capacitor in parallel;
and the voltage stabilizing diode is connected between the first resistor and the second output end of the rectifier bridge and is connected with the first capacitor and the second resistor in parallel.
Preferably, the overload protection device further includes an isolated dc power supply connected to the relay coil for supplying current to the relay coil.
Preferably, the first preset transformation ratio is 20V: 3.25V.
Preferably, the second preset transformation ratio is 1V: 3.25V.
Preferably, the feeder terminal device further comprises a third current transformer having a third predetermined transformation ratio and disposed on the primary side of the feeder terminal device, and the first output terminal and the second output terminal on the secondary side of the third current transformer are respectively used as the first output terminal and the second output terminal on the primary side of the feeder terminal device.
Preferably, the third preset transformation ratio is 600A: 1V.
Preferably, the first resistor is a current limiting resistor.
The technical scheme of the invention has the following advantages or beneficial effects: the double-range CT fault phase current acquisition circuit is provided for a feeder line terminal device, can meet the 20-time wave recording requirement when a short circuit fault occurs in a line, and can accurately measure a sudden change signal of 350mA current magnitude under the condition of non-line fault, so that a high-resistance grounding fault generated by any phase line of a 10KV system can be accurately judged.
Drawings
Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings. The drawings are, however, to be regarded as illustrative and explanatory only and are not restrictive of the scope of the invention.
Fig. 1 is a structural view of a fault phase current acquisition circuit of a feeder terminal device in a first embodiment of the present invention;
fig. 2 is a structural diagram of a fault phase current acquisition circuit of a feeder terminal device according to a second 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.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.
The present invention includes a fault phase current acquisition circuit of a feeder terminal device, as shown in fig. 1 and 2, including:
a first current transformer CT1 having a first predetermined transformation ratio and disposed on the secondary side of the feeder terminal unit FTU, a first input terminal on the primary side of the first current transformer CT1 being connected to a first output terminal on the primary side of the feeder terminal unit, a second input terminal on the primary side of the first current transformer CT1 being connected to a second output terminal on the primary side of the feeder terminal unit;
a second current transformer CT2 having a second predetermined transformation ratio, disposed on the secondary side of the feeder terminal device and connected in parallel with the first current transformer CT1, wherein a first input terminal of the primary side of the second current transformer CT2 is connected to a first output terminal of the primary side of the feeder terminal device, and a second input terminal of the primary side of the second current transformer CT2 is connected to a second output terminal of the primary side of the feeder terminal device;
the first input end of the analog-to-digital converter is connected with the first output end of the secondary side of the first current transformer CT1, the second input end of the analog-to-digital converter is connected with the second output end of the secondary side of the first current transformer CT1, and the first current transformer CT1 is used for providing wave recording requirements for the analog-to-digital converter when a circuit fails;
the third input end of the analog-to-digital converter is connected with the first output end of the secondary side of the second current transformer CT2, the fourth input end of the analog-to-digital converter is connected with the second output end of the secondary side of the second current transformer CT2, and the second current transformer CT2 is used for measuring the sudden change current generated by high-impedance grounding.
Specifically, in this embodiment, the secondary side of the FTU device includes two current transformers with different ranges connected in parallel, where the first current transformer has a larger range and is used to meet the recording requirement of the ADC when a short-circuit fault occurs in the line, and the second current transformer has a smaller range but a higher precision and can capture a 350mA sudden change current generated by high impedance grounding of 2K Ω under a rated load current of 600A, so as to accurately determine a high impedance grounding fault generated by any phase line of the line.
In a preferred embodiment, as shown in fig. 1 and 2, the method further comprises:
and the overload protection device K is arranged between the first output end on the primary side of the feeder terminal device and the first input end on the primary side of the second current transformer CT2 and is used for monitoring the output signal on the primary side of the feeder terminal device, and when the output signal exceeds a preset threshold value, the overload protection device automatically cuts off the primary side of the second current transformer.
Specifically, the overload protection device in this embodiment is configured to monitor an output signal of the primary-side CT, and when the output signal of the primary-side CT exceeds a preset threshold, the overload protection device automatically cuts off the small-range high-precision CT, that is, cuts off the input primary side of the CT2, so as to achieve the purpose of protecting the small-range high-precision CT.
In a preferred embodiment, as shown in fig. 2, the overload protection apparatus specifically includes:
a first input end of the rectifier bridge is connected with a first output end of a primary side of the feeder terminal device, and a second input end of the rectifier bridge is connected with a second input end of a primary side of the second current transformer CT 2;
the first output end and the second output end of the rectifier bridge are respectively connected to two sides of a coil K1A of the relay;
the relay further comprises a contact K1B connected between a first input terminal on the primary side of the second current transformer and a first output terminal on the primary side of the feeder terminal device;
a switch tube Q1, wherein the grid of the switch tube G1 is connected with the first output end of the rectifier bridge through a first resistor R1, the source of the switch tube Q1 is grounded, and the drain of the switch tube Q1 is connected with a coil K1A of the relay;
the first capacitor C1 is connected between the first resistor R1 and the second output end of the rectifier bridge;
the second resistor R2 is connected between the first resistor R1 and the second output end of the rectifier bridge and is connected with the first capacitor C1 in parallel;
and the voltage stabilizing diode D5 is connected between the first resistor R1 and the second output end of the rectifier bridge, and is connected with the first capacitor C1 and the second resistor R2 in parallel.
Specifically, the rectifier bridge in this embodiment is composed of four diodes (D1-D4 shown in fig. 2) connected end to end for converting the ac power output by the primary side CT into dc power. The FTU device in this embodiment adopts two parallel small-range current transformers, the first current transformer CT1 is a wide-range small signal, the second current transformer CT2 is a narrow-range high-precision small signal, the primary sides of CT1 and CT2 are both connected to the secondary side of CT3, and the secondary sides of CT1 and CT2 are both connected to the input end of an analog-to-digital converter ADC (AD 1P, AD1N, AD2P, AD2N shown in fig. 2). When the load current of the line is short-circuited, in order to prevent the second current transformer CT2 from being damaged due to overload caused by the overranging of an input signal, a relay K is additionally arranged in the embodiment, the type of the relay is preferably G5V-2-H1-5VDC, and a coil K1A of the relay adopts an isolated 5V power supply for supplying power. When the primary side current is in short circuit overload, the normally closed contact K1B of the relay is opened timely, and the function of protecting the second current transformer CT2 is achieved.
As shown in fig. 2, when the current on the primary side is smaller than the rated current, the input signal at the PN end is smaller than an ac signal of ± 1V, the ac voltage small signal first passes through the rectifier bridge, the rectifier bridges D1 to D4 adopt diodes of the type 1N4448, the forward conduction voltage drop of a single diode is 0.65V, the diode is not enough to generate enough conduction voltage in the rated range, the protection circuit cannot be started to work, the coil of the relay cannot be excited, so that the second current transformer CT2 is always in a signal access state, and the high-resistance abrupt-change current signal is monitored in real time.
When the current on the primary side has a short-circuit fault, the current on the primary side is increased by a plurality of times compared with 600A, in this case, a PN port can generate an alternating current small signal of +/-4-20V, the signal firstly passes through rectifier bridges D1-D4 and a current-limiting resistor R1 to charge a first capacitor C1, when the voltage on two ends of the C1 rises to 1.5V or above, a switching tube Q1 starts to be conducted, and the Q1 is preferably an N-mos tube with the model number of SI 2302. Then, a coil K1A of the relay is electrified and excited, a contact K1B of the relay is disconnected, and the second current transformer CT2 is disconnected with a PN port, so that the second current transformer CT2 is protected, the CT2 cannot be damaged due to the fact that CT2 inputs over-range, if short-circuit current is too large, the voltage of the PN port is too high, a voltage stabilizing diode D5 and a current limiting resistor R1 are arranged for preventing the grid of a switching tube Q1 from being broken down, the grid voltage of a clamping switching tube Q1 is clamped, and the grid voltage of the Q1 is always kept not more than 5.1V.
When the fault short-circuit current of the line disappears, the rectifier bridges D1-D4 enter a cut-off state again, the residual charge of the first capacitor C1 is discharged through the second resistor R2, the grid voltage of the switching tube Q1 is lower than the opening voltage after the discharge is finished, the Q1 enters the cut-off state and is not conducted any more, the relay coil K1A loses the excitation voltage, and the relay contact K1B is restored to the normally closed state again. The second current transformer CT2 resumes connection with the PN signal port and continues to acquire current readings within the nominal range.
Through the technical scheme, the FTU fault phase current acquisition circuit in the embodiment can effectively acquire the short-circuit current with the highest recording wave of 12KA, and can accurately measure the sudden change signal of the 350mA current amount under the condition that the rated load current is less than or equal to 600A; in addition, the current transformer aiming at small range can be effectively and automatically switched on and off for protection, and the current acquisition circuit is prevented from being damaged.
In a preferred embodiment, as shown in fig. 2, the overload protection apparatus further comprises an isolated DC power source DC connected to the relay coil K1A for supplying current to the relay coil K1A.
As a preferred embodiment, the first preset transformation ratio is 20V: 3.25V, the first current transformer CT1 is integrated in the FTU, has a large measuring range, can meet the wave recording requirement of 20 times of short-circuit current, can output an analog quantity signal with an effective value of 3.25V when the current is 12KA, and can be used for current wave recording when the analog-to-digital converter ADC has a short-circuit fault on a circuit; the second preset transformation ratio is 1V: 3.25V, the second current transformer CT2 is integrated in the FTU, and can collect 350mA abrupt current generated by 2K omega high-impedance grounding under the load current of 600A, so that the high-impedance grounding fault generated by any phase line of the 10KV system can be accurately judged.
In a preferred embodiment, as shown in fig. 1, the FTU further comprises a third current transformer CT3 having a third predetermined transformation ratio of 600A:1V, CT3 is disposed on the primary side of the FTU, and the first output terminal and the second output terminal on the secondary side of the third current transformer CT3 are respectively used as the first output terminal and the second output terminal on the primary side of the feeder terminal device.
The embodiment of the invention has the beneficial effects that: the double-range CT fault phase current acquisition circuit is provided for a feeder line terminal device, can meet the 20-time wave recording requirement when a short circuit fault occurs in a line, and can accurately measure a sudden change signal of 350mA current magnitude under the condition of non-line fault, so that a high-resistance grounding fault generated by any phase line of a 10KV system can be accurately judged.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims (10)

1. A fault phase current acquisition circuit for a feeder termination device, comprising:
a first current transformer having a first predetermined transformation ratio and disposed on the secondary side of the feeder terminal device, wherein a first input terminal of a primary side of the first current transformer is connected to a first output terminal of a primary side of the feeder terminal device, and a second input terminal of the primary side of the first current transformer is connected to a second output terminal of the primary side of the feeder terminal device;
a second current transformer having a second predetermined transformation ratio, disposed on the secondary side of the feeder terminal device and connected in parallel with the first current transformer, wherein a first input terminal on the primary side of the second current transformer is connected to a first output terminal on the primary side of the feeder terminal device, and a second input terminal on the primary side of the second current transformer is connected to a second output terminal on the primary side of the feeder terminal device;
the first input end of the analog-to-digital converter is connected with the first output end of the secondary side of the first current transformer, the second input end of the analog-to-digital converter is connected with the second output end of the secondary side of the first current transformer, and the first current transformer is used for providing wave recording requirements for the analog-to-digital converter when a circuit fails;
the third input end of the analog-to-digital converter is connected with the first output end of the secondary side of the second current transformer, the fourth input end of the analog-to-digital converter is connected with the second output end of the secondary side of the second current transformer, and the second current transformer is used for measuring the sudden change current generated by high-impedance grounding.
2. The faulty phase current acquisition circuit of claim 1, further comprising:
and the overload protection device is arranged between a first output end on the primary side of the feeder terminal device and a first input end on the primary side of the second current transformer and is used for monitoring an output signal on the primary side of the feeder terminal device, and when the output signal exceeds a preset threshold value, the overload protection device automatically cuts off the primary side of the second current transformer.
3. The faulty phase current acquisition circuit of claim 2, wherein said overload protection device comprises in particular:
a first input end of the rectifier bridge is connected with a first output end of a primary side of the feeder terminal device, and a second input end of the rectifier bridge is connected with a second input end of a primary side of the second current transformer;
the first output end and the second output end of the rectifier bridge are respectively connected to two sides of a coil of the relay;
the relay further includes a contact connected between a first input terminal on the primary side of the second current transformer and a first output terminal on the primary side of the feeder terminal device.
4. The faulty phase current acquisition circuit of claim 3, wherein said overload protection device further comprises:
the grid electrode of the switch tube is connected with the first output end of the rectifier bridge through a first resistor, the source electrode of the switch tube is grounded, and the drain electrode of the switch tube is connected with the relay coil;
the first capacitor is connected between the first resistor and the second output end of the rectifier bridge;
the second resistor is connected between the first resistor and the second output end of the rectifier bridge and is connected with the first capacitor in parallel;
and the voltage stabilizing diode is connected between the first resistor and the second output end of the rectifier bridge and is connected with the first capacitor and the second resistor in parallel.
5. The fault phase current acquisition circuit of claim 3, wherein said overload protection device further comprises an isolated DC power source coupled to said relay coil for supplying current to said relay coil.
6. The failed phase current acquisition circuit of claim 1, wherein said first preset transformation ratio is 20V: 3.25V.
7. The faulty phase current acquisition circuit of claim 1 wherein said second preset transformation ratio is 1V: 3.25V.
8. The fault phase current collecting circuit of claim 1, further comprising a third current transformer having a third predetermined transformation ratio and disposed on the primary side of the feeder terminal device, wherein the first output terminal and the second output terminal of the secondary side of the third current transformer are respectively the first output terminal and the second output terminal of the primary side of the feeder terminal device.
9. The faulty phase current acquisition circuit of claim 8, wherein said third preset transformation ratio is 600A: 1V.
10. The faulty phase current acquisition circuit of claim 4 in which said first resistor is a current limiting resistor.
CN202110507503.8A 2021-05-10 2021-05-10 Fault phase current acquisition circuit of feeder terminal device Pending CN113267670A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202110507503.8A CN113267670A (en) 2021-05-10 2021-05-10 Fault phase current acquisition circuit of feeder terminal device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202110507503.8A CN113267670A (en) 2021-05-10 2021-05-10 Fault phase current acquisition circuit of feeder terminal device

Publications (1)

Publication Number Publication Date
CN113267670A true CN113267670A (en) 2021-08-17

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CN202110507503.8A Pending CN113267670A (en) 2021-05-10 2021-05-10 Fault phase current acquisition circuit of feeder terminal device

Country Status (1)

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CN (1) CN113267670A (en)

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