CN105738677A - Power network ground capacitance current detection method - Google Patents

Abstract

The invention discloses a power network ground capacitance current detection method, comprising the steps of: installing a current type three-phase four-leg inverter bridge on a three-phase circuit; adjusting a service bridge leg to respectively inject detection current into A, B, C three phases to successively measure a neutral point offset voltage; utilizing a phase voltage, injected current and a neutral point offset voltage phasor to calculate split-phase ground capacitance; and calculating split-phase ground capacitance current according to the split-phase ground capacitance. Based on an original method, the power network ground capacitance current detection method utilizes a power electronic device to respectively add detection current with adjustable amplitudes and angles to the A, B, C three phases, measures the neutral point displacement voltages under the three conditions, and calculates split-phase ground capacitance based on a system phase voltage, thereby respectively calculating system the ground capacitance current of each phase of a system. The method has the characteristics of high accuracy, simple test and great safety, does not interrupt power supply for users, and meets actual use requirements.

Description

A kind of power network capacitive earth current detection method

Technical field

The present invention relates to a kind of power network capacitive earth current detection method, belong to technical field of power systems.

Background technology

High voltage power transmission, because possessing reduction loss, improving the clear superiorities such as economy, is at home and abroad widely applied at present.But the alternation character of three-phase alternating current transmission electric energy makes to form simulated capacitance by electrolyte (air etc.) between circuit or coil and the earth, produce capacitance current in the line, this electric current is elongated and increase along with the rising of electric pressure and circuit, makes the current amplitude at circuit two ends and phase place change therewith.It addition, when ground connection occurs circuit, due to the existence of capacitive earth current, earth current becomes big, it is possible to causes that electric arc not easily extinguishes, causes circuit, device damage, even causes fire.In electrical network, the equipment except transmission line of electricity has direct-to-ground capacitance equally.Therefore, the accurate detection of capacitance current, for safe and stable operation defeated, power distribution network, significant.

The method measuring capacitance current is broadly divided into direct method and indirect method two kinds.Early stage measures capacitance current and is generally adopted direct method, i.e. Single Phase Metal earthing.The method is that by switch, a certain phase of distribution line is carried out artificial ground, then utilizes current transformer directly to measure earth current, and this electric current is capacitance current.The method complicated operation, if an other phase earth fault occurs system in process of the test, will result in line to line fault, affects power supply reliability.Additionally in whole process of the test, personnel and distribution network system can be constituted a threat to safely by this method, thus have certain danger, only use in scientific research.

Widely used is indirect method at present, including the additional capacitance method of neutral point, Biased capacitor method, voltage transformer open delta signal injection method, tuning method, frequency variation method etc..Biased capacitor method is to add a suitable capacitance artificially in a certain phase of system, measures neutral excursion voltage, it is then assumed that A, B, C three-phase ground capacitance is equal, can obtain system capacitive earth current on this basis.Real system three-phase ground capacitance is unbalanced, can there is certain error in aforementioned manners, but scene can use three-phase superposition partially installing capacitor in turn and changes the methods such as capacitance, and after taking arithmetic mean of instantaneous value, its error is acceptable in engineering.The artificial estimation of partially installing capacitor needs that this kind of method uses, owing to the size of partially installing capacitor can directly affect measurement result, therefore chooses the improper result that is likely to result in partially installing capacitor and does not conform to the actual conditions.

Current most of measuring method is all carry out on the basis that hypothesis system three-phase ground capacitance is equal, sometimes can not meet engineering requirements.In order to protect the device can effective action and arrange relevant protection device when ensureing system single-phase earthing, it is necessary to accurately measure single-phase-to-ground current size.

Summary of the invention

The technical problem to be solved in the present invention is: provide the measuring method of a kind of power network capacitive earth current.

For achieving the above object, the present invention provides following technical scheme:

A kind of power network capacitive earth current detection method, comprises the steps:

Three-phase circuit is installed current mode three-phase four-arm inverter bridge；

Adjust work brachium pontis and inject detection electric current to A, B, C three-phase respectively, measure neutral excursion voltage successively；

Phase voltage, injection current and neutral excursion voltage phasor calculation is utilized to divide relatively electric capacity；

By a point relatively capacitance meter point counting relatively capacitance current.

Wherein more preferably, described current mode three-phase four-arm inverter bridge includes first, second, third and fourth power electronics brachium pontis and current source, first, second and third power electronics brachium pontis is connected to bus respectively, and described 4th power electronics brachium pontis ground connection, current source is connected with first, second and third power electronics brachium pontis respectively.

Wherein more preferably, described first power electronics brachium pontis, it is made up of high frequency wholly-controled device S1, S2 and diode D1, D2；

The emitter stage of high frequency wholly-controled device S1 is connected with the colelctor electrode of high frequency wholly-controled device S2, and is connected mutually by inductance L and A by a point of S1 and S2 connecting line；

It is provided with sustained diode 1, D2 between emitter stage and the colelctor electrode of S1, S2；The colelctor electrode of S1 is connected with controllable current source positive pole, and the emitter stage of S2 is connected with the negative pole of controllable current source；

The grid of S1, S2 receives control signal, controls conducting and the closedown of S1, S2, injects detection electric current to A phase.

Wherein more preferably, described calculating divides the step of relatively electric capacity to specifically include:

Relatively electric capacity is divided to be calculated as follows:

$({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_A+i+({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_B+({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_C=0$

Wherein:Represent A, B, C three-phase phase voltage respectively；Represent system neutral offset voltage；I represents each phase injection current；ω represents system angle frequency, ω=2 π f ≈ 314rad/s；C_A、C_B、C_CRepresent A, B, C three-phase line direct-to-ground capacitance respectively；

Bring the neutral excursion voltage of three-phase phase voltage, each phase input current and correspondence thereof into above formula respectively as known quantity, obtain the equivalent formula that three is unknown quantity with direct-to-ground capacitance, form equation group, by calculating, obtain the expression formula of three-phase ground capacitance.

Wherein more preferably, the expression formula of three-phase ground capacitance is as follows:

$\left[\begin{array}{ccc}{C}_A& C_B& C_C\end{array}\right]=-\frac{1}{\mathrm{j\ω}}\left[\begin{array}{ccc}{t}_A& t_B& t_C\end{array}\right]{\left[\begin{array}{ccc}{\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{03}\\ {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{03}\\ {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{03}\end{array}\right]}^{-1}$

Wherein:Represent A, B, C three-phase phase voltage respectively；Represent system neutral offset voltage；I represents each phase injection current；ω represents system angle frequency, ω=2 π f ≈ 314rad/s；C_A、C_B、C_CRepresent A, B, C three-phase line direct-to-ground capacitance respectively.

Wherein more preferably, described point relatively capacitance current time be calculated as follows:

I_C=ω CU

Wherein, U represents that phase voltage, ω represent system angle frequency, ω=2 π f ≈ 314rad/s.

The power network capacitive earth current detection method of the present invention, on former methodical basis, the detection electric current of amplitude and adjustable angle is added respectively on A, B, C three-phase, and measure the neutral point displacement voltage in three kinds of situations, coupling system phase voltage, obtain point relatively electric capacity by calculating, calculate capacitive earth current with this.This kind of method accuracy is high, and test is simple, and safety is good, does not interrupt, to customer power supply, meeting actually used requirement.

Accompanying drawing explanation

Fig. 1 is capacitive earth current testing circuit figure of the present invention；

Fig. 2 is that A phase injects current in resistance property three-phase voltage vector diagram；

Fig. 3 is that A phase injects three-phase voltage vector diagram after current in resistance property.

Detailed description of the invention

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following example are used for illustrating the present invention, but are not limited to the scope of the present invention.

The present invention provides a kind of power network capacitive earth current detection method, specifically includes following steps: install current mode three-phase four-arm inverter bridge on three-phase circuit；Adjust work brachium pontis and detect electric current over the ground to the injection of A, B, C three-phase respectively, measure neutral excursion voltage successively；Phase voltage, injection current and neutral excursion voltage phasor calculation is utilized to divide relatively electric capacity；By a point relatively capacitance meter point counting relatively capacitance current.Below the present invention is launched detailed description.

First, the step installing current mode three-phase four-arm inverter bridge on three-phase circuit is introduced.

As shown in Figure 1, current mode three-phase four-arm inverter bridge includes first, second, third and fourth power electronics brachium pontis and current source, first, second and third power electronics brachium pontis is connected to bus respectively, and described 4th power electronics brachium pontis ground connection, current source is connected with first, second and third power electronics brachium pontis respectively.

First power electronics brachium pontis, is made up of high frequency wholly-controled device S1, S2 and diode D1, D2；Second power electronics brachium pontis, is made up of high frequency wholly-controled device S3, S4 and diode D3, D4；3rd power electronics brachium pontis, is made up of high frequency wholly-controled device S5, S6 and diode D5, D6；4th power electronics brachium pontis, is made up of high frequency wholly-controled device S7, S8 and diode D7, D8.Its medium-high frequency wholly-controled device includes IGBT, IGCT, GTO, MOSFET etc..

Adopt the IGBT of N-channel positive-negative-positive below for high frequency wholly-controled device, introduce three-phase four-arm inverter bridge.

In first power electronics brachium pontis, the emitter stage of IGBTS1 is connected with the colelctor electrode of IGBTS2, and is connected mutually by inductance L and A by a point of S1 and S2 connecting line；It is provided with sustained diode 1, D2 between transmitting and the colelctor electrode of S1, S2, there is protective effect；The colelctor electrode of S1 is connected with controllable current source positive pole, and the emitter stage of S2 is connected with the negative pole of controllable current source；The grid of S1, S2 receives control signal, controls conducting and the closedown of S1, S2, injects detection electric current to A phase.

In second power electronics brachium pontis, the emitter stage of IGBTS3 is connected with the colelctor electrode of IGBTS4, and is connected mutually by inductance L and B by the b point of S3 and S4 connecting line；It is provided with sustained diode 3, D4 between emitter stage and the colelctor electrode of S3, S4, there is protective effect；The colelctor electrode of S3 is connected with controllable current source positive pole, and the emitter stage of S4 is connected with the negative pole of controllable current source；The grid of S3, S4 receives control signal, controls conducting and the closedown of S3, S4, injects detection electric current to B phase.

The structure of the 3rd power electronics brachium pontis and first and second power electronics brachium pontis is identical, repeats no more.

In 4th power electronics brachium pontis, the emitter stage of IGBTS7 is connected with the colelctor electrode of IGBTS8, and by the g point of S7 and S8 connecting line by inductance L grounding；It is provided with sustained diode 7, D8 between emitter stage and the colelctor electrode of S7, S8, there is protective effect；The colelctor electrode of S7 is connected with controllable current source positive pole, and the colelctor electrode of S7 is connected with the negative pole of controllable current source；The grid of S7, S8 receives control signal, controls conducting and the closedown of S7, S8, injects detection electric current to the earth, to constitute single-phase current channel over the ground.

When to arbitrary relatively injection current in A, B, C three-phase, voltage transformer pt gathers A, B, C tri-phase-to-ground voltage, detects change in voltage.

Secondly, introduce and adjust work brachium pontis respectively to A, B, C three-phase line injection detection electric current, measure the step of neutral excursion voltage successively；

The conducting phase of detection electric current can be selected by controlling make-to-break ratio in three-phase inversion brachium pontis and control character and the amplitude of detection electric current.

Detection process is illustrated passing into current in resistance property to A phase below.

First open A phase brachium pontis, close the biphase brachium pontis of B, C.Before adding detection electric current, voltage phasor-diagram is as shown in Figure 2.Inject 5A current in resistance property to A phase, be designated asUtilize voltmeter V to measure neutral excursion voltage at system voltage transformer PT secondary side open delta end, be designated asAfter addition detection electric current shown in voltage phasor Fig. 3.According to said method successively to B, C biphase injection relative current in resistance property of 5A, namelyMeasure the neutral excursion voltage in two kinds of situations respectively, be designated as

Again, the step utilizing phase voltage, injection current and neutral excursion voltage phasor calculation to divide relatively electric capacity is introduced.

According to Thevenin's theorem such as formula (1):

$({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_A+i+({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_B+({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_O)\mathrm{\ω}{C}_C=0---\left(1\right)$

Wherein:Represent A, B, C three-phase phase voltage respectively；Represent system neutral offset voltage；I represents each phase injection current；ω represents system angle frequency, ω=2 π f ≈ 314rad/s；C_A、C_B、C_CRepresent A, B, C three-phase line direct-to-ground capacitance respectively.

By A, B, C three-phase phase voltageEach phase input current i_A、i_B、i_CAnd the neutral point voltage of correspondenceBring formula (1) as known quantity respectively into, obtain three with C_A、C_B、C_CFor the equivalent formula of unknown quantity, as shown in formula (2).

$\left\{\begin{array}{c}({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}{C}_A+t_A+({\stackrel{\·}{U}}_E+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}{C}_B+({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}{C}_C=0\\ ({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}{C}_A+({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}{C}_B+t_B+({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}{C}_C=0\\ ({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}{C}_A+({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}{C}_B+({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}{C}_C+t_C=0\end{array}\right.---\left(2\right)$

Formula (2) is rewritten into matrix form, as shown in formula (3).

$\left[\begin{array}{ccc}{C}_A& C_B& C_C\end{array}\right]\left[\begin{array}{ccc}({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}& ({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}& ({\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}\\ ({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}& ({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}& ({\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}\\ ({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{01})\mathrm{j\ω}& ({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{02})\mathrm{j\ω}& ({\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{03})\mathrm{j\ω}\end{array}\right]+\left[\begin{array}{ccc}{t}_A& t_B& t_C\end{array}\right]=0---\left(3\right)$

Through deriving, three-phase ground capacitance expression formula may finally be obtained, as shown in formula (4).

$\left[\begin{array}{ccc}{C}_A& C_B& C_C\end{array}\right]=-\frac{1}{\mathrm{j\ω}}\left[\begin{array}{ccc}{t}_A& t_B& t_C\end{array}\right]{\left[\begin{array}{ccc}{\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_A+{\stackrel{\·}{U}}_{03}\\ {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_B+{\stackrel{\·}{U}}_{03}\\ {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{01}& {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{02}& {\stackrel{\·}{U}}_C+{\stackrel{\·}{U}}_{03}\end{array}\right]}^{-1}---\left(4\right)$

Finally, introduce by a point relatively capacitance meter point counting relatively capacitance current.

By three-phase ground capacitance value C_A、C_B、C_CBring formula (5) respectively into, the single-phase capacitive earth current of system can be obtained.

I_C=ω CU (5)

Wherein, U represents that phase voltage, ω represent system angle frequency, ω=2 π f ≈ 314rad/s, Power System in China rated frequency f=50Hz.

It addition, system direct-to-ground capacitance is three-phase ground capacitance C_A、C_B、C_CSum.System capacitive earth current value can be obtained after three-phase ground capacitance sum is brought into formula (5).

In sum, power network capacitive earth current detection method provided by the invention, simple to operate, it is convenient to measure, there is higher motility and accuracy, can pass through to regulate input current amplitude and Angulation changes neutral point voltage size, make measurement result more accurately reliable；Can obtaining system by measurement and divide relatively capacitance current, the relay protection scheme for circuit provides reference frame.

Embodiment of above is merely to illustrate the present invention; and it is not limitation of the present invention; those of ordinary skill about technical field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all equivalent technical schemes fall within scope of the invention, and the scope of patent protection of the present invention should be defined by the claims.

Claims (6)

1. a power network capacitive earth current detection method, it is characterised in that comprise the steps:

Three-phase circuit is installed current mode three-phase four-arm inverter bridge；

Adjust work brachium pontis and inject detection electric current to A, B, C three-phase respectively, measure neutral excursion voltage successively；

Phase voltage, injection current and neutral excursion voltage phasor calculation is utilized to divide relatively electric capacity；

By a point relatively capacitance meter point counting relatively capacitance current.

2. capacitive earth current detection method as claimed in claim 1, it is characterized in that, described current mode three-phase four-arm inverter bridge includes first, second, third and fourth power electronics brachium pontis and current source, first, second and third power electronics brachium pontis is connected to bus respectively, described 4th power electronics brachium pontis ground connection, current source is connected with first, second and third power electronics brachium pontis respectively.

3. capacitive earth current detection method as claimed in claim 1, it is characterised in that described first power electronics brachium pontis, is made up of high frequency wholly-controled device S1, S2 and diode D1, D2；

The emitter stage of high frequency wholly-controled device S1 is connected with the colelctor electrode of high frequency wholly-controled device S2, and is connected mutually by inductance L and A by a point of S1 and S2 connecting line；

It is provided with sustained diode 1, D2 between emitter stage and the colelctor electrode of S1, S2；The colelctor electrode of S1 is connected with controllable current source positive pole, and the emitter stage of S2 is connected with the negative pole of controllable current source；

The grid of S1, S2 receives control signal, controls conducting and the closedown of S1, S2, injects detection electric current to A phase.

4. capacitive earth current detection method as claimed in claim 1, it is characterised in that described calculating divides the step of relatively electric capacity to specifically include:

Relatively electric capacity is divided to be calculated as follows:

$({\stackrel{.}{U}}_A+{\stackrel{.}{U}}_0)\mathrm{\ω}{C}_A+\stackrel{.}{I}+({\stackrel{.}{U}}_B+{\stackrel{.}{U}}_0)\mathrm{\ω}{C}_B+({\stackrel{.}{U}}_C+{\stackrel{.}{U}}_0)\mathrm{\ω}{C}_C=0$

Wherein:Represent A, B, C three-phase phase voltage respectively；Represent system neutral offset voltage；Represent each phase injection current；ω represents system angle frequency, ω=2 π f ≈ 314rad/s；C_A、C_B、C_CRepresent A, B, C three-phase line direct-to-ground capacitance respectively；

Bring the neutral point voltage of three-phase phase voltage, each phase input current and correspondence thereof into above formula respectively as known quantity, obtain the equivalent formula that three is unknown quantity with direct-to-ground capacitance, form equation group, by calculating, obtain the expression formula of three-phase ground capacitance.

5. capacitive earth current detection method as claimed in claim 4, it is characterised in that the expression formula of three-phase ground capacitance is as follows:

$\left[\begin{array}{ccc}{C}_A& C_B& C_C\end{array}\right]\text{=-}\frac{1}{\mathrm{j\ω}}\left[\begin{array}{ccc}{\stackrel{.}{I}}_A& {\stackrel{.}{I}}_B& {\stackrel{.}{I}}_C\end{array}\right]{\left[\begin{array}{ccc}{\stackrel{.}{U}}_A+{\stackrel{.}{U}}_{01}& {\stackrel{.}{U}}_A+{\stackrel{.}{U}}_{02}& {\stackrel{.}{U}}_A+{\stackrel{.}{U}}_{03}\\ {\stackrel{.}{U}}_B+{\stackrel{.}{U}}_{01}& {\stackrel{.}{U}}_B+{\stackrel{.}{U}}_{02}& {\stackrel{.}{U}}_B+{\stackrel{.}{U}}_{03}\\ {\stackrel{.}{U}}_C+{\stackrel{.}{U}}_{01}& {\stackrel{.}{U}}_C+{\stackrel{.}{U}}_{02}& {\stackrel{.}{U}}_C+{\stackrel{.}{U}}_{03}\end{array}\right]}^{-1}$

Wherein:Represent A, B, C three-phase phase voltage respectively；Represent system neutral offset voltage；Represent each phase injection current；ω represents system angle frequency, ω=2 π f ≈ 314rad/s；C_A、C_B、C_CRepresent A, B, C three-phase line direct-to-ground capacitance respectively.

6. capacitive earth current detection method as claimed in claim 1, it is characterised in that described point relatively capacitance current be calculated as follows:

I_C=ω CU

Wherein, U represents that phase voltage, ω represent system angle frequency, ω=2 π f ≈ 314rad/s.