Medium and low voltage power distribution network capacitance current on-line measurement method and system

Abstract

According to the method, two ends of a damping resistor of the medium and low voltage power distribution network are connected in parallel with an adjustable voltage device; the method comprises the following steps: starting to inject a voltage Uim by an adjustable voltage device, measuring the amplitude change of a neutral point voltage U0 in real time, increasing the starting injection voltage Uim to an injection voltage Uim1, increasing the neutral point voltage U0 to U01, injecting a voltage Uim2 by the adjustable voltage device again, measuring the neutral point voltage U02, and setting the neutral point current of the two times as I01 and I02; and calculating to obtain a system capacitance XC and a capacitance current If.

Description

Technical Field

[0001] The present invention relates to the technical field of medium and low voltage distribution network measurement, and in particular to a method and system for online measurement of capacitance current in medium and low voltage distribution networks. Background Art

[0002] At present, the neutral point grounding method through arc suppression coil is still widely used in my country's medium and low voltage distribution network (6-66kV), which can significantly improve the reliability and safety of system operation. After a single-phase grounding occurs in the system, the arc suppression coil connected to the neutral point provides "reactive current" to the grounding point to offset the "capacitive current" flowing into the grounding point, thereby achieving the effect of extinguishing the grounding arc. At present, most systems use pre-debugging automatic compensation arc suppression coils, which calculate the system capacitive current in advance through the built-in algorithm. After a grounding fault occurs in the system, the damping resistor is quickly removed to achieve reliable compensation.

[0003] As the medium and low voltage distribution networks continue to carry out cable transformation, after a high proportion of cables are connected, the three-phase imbalance of the system is rapidly reduced, often less than 0.2%. For such a three-phase overly balanced system, the arc suppression coil often cannot sense the change of the unbalanced voltage value in time, resulting in dynamic tracking failure, and cannot accurately compensate after a ground fault occurs. At the same time, since traditional online capacitance current measurement methods such as the equivalent resonance method and the two-point calculation method all rely on the distribution network's own zero-sequence electrical quantity as the calculation basis for real-time measurement algorithms, the neutral point voltage is too low, resulting in a decrease in online measurement accuracy, making it difficult to provide an accurate basis for the controller to adjust the gear. In actual operation, the system is interfered by other power frequency signals, and the arc suppression coil may have frequent gear adjustment failures. In extreme cases, the number of gear adjustments in a single month reaches tens of thousands of times, which seriously affects the stability and reliability of the system.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0005] The present invention provides a method and system for online measurement of capacitance current in medium and low voltage distribution networks, which improves online measurement accuracy and avoids frequent gear adjustment failures of arc suppression coils.

[0006] A method for online measurement of capacitance current in a medium and low voltage distribution network comprises:

[0007] Connect an adjustable voltage device in parallel across the damping resistor of the medium and low voltage distribution network;

[0008] Adjustable voltage device starting injection voltage U im , real-time measurement of the neutral point voltage U0 amplitude change, where the initial injection voltage U im To the injection voltage U im1, the neutral point voltage U0 is increased to U 01 , the adjustable voltage device injects voltage U again im2 , measure the neutral point voltage U 02 , the neutral point current before and after is I 01 ,I 02 ;

[0009] According to the system phase voltage E a , calculate the system capacitance X C and capacitor current I f for:

[0010] X C =(U 01 -U 02 ) / (I 02 -I 01 )

[0011] I f =E a / X C .

[0012] In the online measurement method for capacitance current of medium and low voltage distribution network, the system capacitance X is measured and calculated multiple times. C and capacitor current I f , the weighted average is used as the final system capacitance and capacitor current.

[0013] In the online measurement method of the capacitance current in the medium and low voltage distribution network, the neutral point voltage U 01 It is 90-100V.

[0014] In the online measurement method of the capacitance current of the medium and low voltage distribution network, the injected voltage U im2 The amplitude is the injected voltage U im1 1.2 times the amplitude.

[0015] In the online measurement method of the capacitance current in the medium and low voltage distribution network, the neutral point is injected with a double-segment power frequency voltage signal.

[0016] In the online measurement method of capacitor current in medium and low voltage distribution networks, when the arc suppression coil operates normally, the control device detection circuit detects in real time that the neutral point voltage or current changes exceeding the set value and then starts the adjustable voltage device.

[0017] In the online measurement method of the capacitance current of a medium and low voltage distribution network, the adjustable voltage device is started when the measurement time meets the time requirement. After the measurement is completed, it is determined whether the arc suppression coil position needs to be adjusted according to the result to ensure reliable compensation when the system is single-phase grounded.

[0018] A medium and low voltage distribution network capacitance current online measurement system comprises:

[0019] Grounding transformer, which is connected to the medium and low voltage distribution network;

[0020] The arc extinguishing coil complete set is connected to the grounding transformer, and the arc extinguishing coil complete set includes:

[0021] Arc suppression coil, which connects the grounding transformer,

[0022] A damping resistor, which is connected to the arc extinguishing coil,

[0023] The adjustable voltage device is connected in parallel with the damping resistor to inject voltage to measure the amplitude change of the neutral point voltage U0 in real time and calculate the system capacitance and capacitive current.

[0024] The medium and low voltage distribution network capacitor current online measurement system also includes a control device connected to the adjustable voltage device, and the control device includes a control device detection circuit that detects changes in neutral point voltage or current in real time.

[0025] In the online measurement system for capacitor current in medium and low voltage distribution networks, the adjustable voltage device includes a high-precision adjustable voltage source based on a phase-shifted full-bridge DCDC and an SPWM sine wave inverter.

[0026] Compared with the prior art, the present invention has the following advantages: when the three-phase imbalance of the system is less than 0.2%, the present invention can timely sense the change of the unbalanced voltage value, dynamically track it, avoid the neutral point voltage being too low and causing the online measurement accuracy to decrease, provide an accurate basis for the controller to adjust the gear, and provide accurate compensation after a ground fault occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work. Moreover, the same reference numerals are used to represent the same components throughout the drawings.

[0028] In the attached picture:

[0029] Figure 1 It is a schematic diagram of the principle of an online measurement method for capacitor current in a medium and low voltage distribution network provided by an embodiment of the present disclosure;

[0030] Figure 2 This is an equivalent schematic diagram of a neutral point injection power frequency signal method system provided by an embodiment of the present disclosure;

[0031] Figure 3 It is a schematic diagram of the principle of neutral point injection high-precision AC power supply provided by an embodiment of the present disclosure.

[0032] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0034] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0035] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0036] like Figures 1 to 3 As shown, the online measurement method of the capacitance current of the medium and low voltage distribution network includes the following steps:

[0037] Connect an adjustable voltage device in parallel across the damping resistor of the medium and low voltage distribution network;

[0038] Adjustable voltage device starting injection voltage U im , real-time measurement of the neutral point voltage U0 amplitude change, where the initial injection voltage U im To the injection voltage U im1 , the neutral point voltage U0 is increased to U 01 , the adjustable voltage device injects voltage U again im2 , measure the neutral point voltage U 02 , the neutral point current before and after is I 01 ,I 02 ;

[0039] According to the system phase voltage E a, calculate the system capacitance X C and capacitor current I f for:

[0040] X C =(U 01 -U 02 ) / (I 02 -I 01 )

[0041] I f =E a / X C .

[0042] In the preferred implementation of the method for online measurement of capacitance current in medium and low voltage distribution networks, the system capacitance X is measured and calculated multiple times. C and capacitor current I f , the weighted average is used as the final system capacitance and capacitor current.

[0043] In the preferred implementation of the method for online measurement of capacitance current in medium and low voltage distribution networks, the neutral point voltage U 01 It is 90-100V.

[0044] In a preferred embodiment of the method for online measurement of capacitance current in medium and low voltage distribution networks, the injected voltage U im2 The amplitude is the injected voltage U im1 1.2 times the amplitude.

[0045] In a preferred implementation of the online measurement method for capacitor current in a medium and low voltage distribution network, a dual-segment power frequency voltage signal is injected into the neutral point.

[0046] In a preferred implementation of the online measurement method for capacitor current in a medium and low voltage distribution network, when the arc suppression coil operates normally, the control device detection circuit detects in real time that the neutral point voltage or current changes exceeding the set value and then starts the adjustable voltage device.

[0047] In a preferred implementation of the online measurement method for the capacitive current of a medium and low voltage distribution network, the adjustable voltage device is started when the measurement time meets the time requirement. After the measurement is completed, it is determined whether the arc suppression coil position needs to be adjusted based on the result to ensure reliable compensation when the system is single-phase grounded.

[0048] A medium and low voltage distribution network capacitance current online measurement system comprises:

[0049] Grounding transformer, which is connected to the medium and low voltage distribution network;

[0050] The arc extinguishing coil complete set is connected to the grounding transformer, and the arc extinguishing coil complete set includes:

[0051] Arc suppression coil, which connects the grounding transformer,

[0052] A damping resistor, which is connected to the arc extinguishing coil,

[0053] The adjustable voltage device is connected in parallel with the damping resistor to inject voltage to measure the amplitude change of the neutral point voltage U0 in real time and calculate the system capacitance and capacitive current.

[0054] In a preferred embodiment of the medium and low voltage distribution network capacitor current online measurement system, it also includes a control device connected to the adjustable voltage device, and the control device includes a control device detection circuit that detects changes in neutral point voltage or current in real time.

[0055] In a preferred embodiment of the online measurement system for capacitor current in medium and low voltage distribution networks, the adjustable voltage device includes a high-precision adjustable voltage source based on a phase-shifted full-bridge DCDC and an SPWM sine wave inverter.

[0056] In one embodiment, in an online method for measuring the capacitance current of a medium- and low-voltage distribution network with a well-balanced three-phase voltage, a high-precision adjustable voltage device is connected in parallel at both ends of a damping resistor, and a very low industrial frequency AC power source U is initially injected. im , real-time measurement of the change in the amplitude of the neutral point voltage U0. im to U im1 , U0 is raised to U 01 (Meet 90-100V). The adjustable voltage device injects voltage U again im2 (U im2 The amplitude is 1.2 times U im1 ), measure the neutral point voltage U 02 , the neutral point current before and after is I 01 ,I 02 . System capacitance X C and capacitor current I f for:

[0057] X C =(U 01 -U 02 ) / (I 02 -I 01 )

[0058] I f =E a / X C

[0059] Therefore, the neutral point injection power frequency signal method is not limited by the neutral point voltage of the distribution network itself by injecting a double-segment power frequency voltage signal.

[0060] The high-precision adjustable voltage device uses a high-precision AC power supply based on a phase-shifted full-bridge DCDC and SPWM sine wave inverter. The system principle block diagram is as follows Figure 3 As shown, the device combines a phase-shifted full-bridge DCDC with an SPWM sine wave inverter, realizes high-frequency isolated DCDC voltage regulation control through a phase-shifted full-bridge circuit, and further realizes graded adjustable DCDC output voltage; uses an SPWM sine wave inverter to convert DC into a standard sine wave, and realizes linear adjustment of the sine wave frequency and voltage.

[0061] There are two starting conditions for the high-precision adjustable voltage device: one is that when the arc suppression coil is operating normally, the controller detection circuit detects the change of neutral point voltage or current in real time, and starts when the change exceeds the set value; the other is to manually set the measurement time according to the frequency of the system wiring change, and start when the measurement time meets the time requirement. After the measurement is completed, it is determined whether the arc suppression coil gear needs to be adjusted based on the results to ensure reliable compensation when the system is single-phase grounded.

[0062] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and instructive, rather than restrictive. A person of ordinary skill in the art can also make many forms under the guidance of this specification and without departing from the scope of protection of the claims of the present invention, all of which belong to the protection of the present invention.

Claims

1. A method for online measurement of capacitance current in medium and low voltage distribution networks, characterized in that: The steps include: Connect an adjustable voltage device in parallel across the damping resistor of the medium and low voltage distribution network; Adjustable voltage device starting injection voltage U im , real-time measurement of the neutral point voltage U0 amplitude change, where the initial injection voltage U im To the injected voltage U im1 , the neutral point voltage U0 is increased to U 01 , the adjustable voltage device injects voltage U again im2 , measure the neutral point voltage U 02 , the neutral point current before and after is I 01 ,I 02 ; According to the system phase voltage E a , calculate the system capacitance X C and capacitor current I f for: X C =(U 01 -U 02 ) / (I 02 -I 01 ) I f =E a / X C 。 2. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1 is preferably characterized in that: The system capacitance X is obtained by multiple measurements and calculations. C and capacitor current I f , the weighted average is used as the final system capacitance and capacitor current.

3. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1, characterized in that: Neutral point voltage U 01 It is 90-100V.

4. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1, characterized in that: Injection voltage U im2 The amplitude is the injected voltage U im1 1.2 times the amplitude.

5. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1 is characterized in that: The neutral point is injected with a dual-stage power frequency voltage signal.

6. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1, characterized in that: When the arc suppression coil is operating normally, the control device detection circuit detects in real time that the neutral point voltage or current changes exceeding the set value and then starts the adjustable voltage device.

7. The method for online measurement of capacitance current in medium and low voltage distribution networks according to claim 1, characterized in that: When the measurement time meets the duration requirement, the adjustable voltage device is started. After the measurement is completed, it is determined whether the arc suppression coil position needs to be adjusted based on the result to ensure reliable compensation when the system is single-phase grounded.

8. A medium and low voltage distribution network capacitance current online measurement system, characterized in that: These include, Grounding transformer, which is connected to the medium and low voltage distribution network; The arc extinguishing coil complete set is connected to the grounding transformer, and the arc extinguishing coil complete set includes: Arc suppression coil, which connects the grounding transformer, A damping resistor, which is connected to the arc suppression coil, The adjustable voltage device is connected in parallel with the damping resistor to inject voltage to measure the amplitude change of the neutral point voltage U0 in real time and calculate the system capacitance and capacitive current.

9. The online measurement system for capacitance current of medium and low voltage distribution network according to claim 8, characterized in that: It also includes a control device connected to the adjustable voltage device, and the control device includes a control device detection circuit for real-time detection of changes in neutral point voltage or current.

10. The online measurement system for capacitance current in medium and low voltage distribution networks according to claim 8, characterized in that: The adjustable voltage device comprises a high-precision adjustable voltage source based on a phase-shifted full-bridge DCDC and an SPWM sine wave inverter.

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