CN102608483A - Direction diagnosing system of grounded fault of small current grounded distribution system - Google Patents

Abstract

The invention discloses a grounding fault direction diagnosis system for a small current grounding power distribution system. The system uses a high-voltage live display HS connected to a switch to replace a zero-sequence voltage transformer PT to realize the detection of a capacitive voltage U. For small-current grounded power distribution systems, with the capacitive voltage U as the reference, when a single-phase ground fault occurs on the load side, the zero-sequence current I ₀ leads the capacitive voltage U, and the leading angle θ ₂ =0°～180°; When a single-phase ground fault occurs on the side, the zero-sequence current I ₀ lags behind the capacitive voltage U, and the lag angle θ ₁ =0°～90°. Therefore, by extracting and processing the steady-state component of the feeder ground fault, and further detecting the capacitive voltage U and zero-sequence current I ₀ when the system is faulty, the direction of the single-phase ground fault can be judged. The ground fault direction signal picked up by the ground fault direction diagnosis system of the present invention can notify the controller of the distribution station, and the controller will make corresponding actions, which is beneficial to the protection of the power distribution system.

Description

Diagnosis System of Ground Fault Direction in Small Current Grounded Power Distribution System

technical field

The invention relates to a small current grounding power distribution system, more particularly, a grounding fault direction diagnosis system suitable for power distribution systems with neutral point not grounded, resistance grounded, and arc suppressing coil grounded.

Background technique

There are two types of neutral point grounding methods in power systems: large current grounding and small current grounding.

The large current grounding method is the way that the neutral point is directly grounded or grounded through a small resistance. Its characteristic is that when a ground fault occurs in the system, especially when a single-phase ground fault occurs, the non-fault phase-to-ground voltage does not rise, but the ground phase fault current is relatively large, which will cause great damage to the power system itself and to adjacent communication lines and signal lines. danger and interference, so the faulty part must be removed quickly. The high-current grounding method is mainly used for power transmission and distribution systems of 110KV and above.

The neutral point of my country's 3-66KV medium-voltage power grid is generally ungrounded or grounded through an arc suppression coil. When a single-phase ground fault occurs, the current flowing through the fault point is very small, so it is called a small current grounded power grid. The low-current grounding system has the highest probability of a single-phase ground fault. At this time, the power supply can still ensure the symmetry of the line voltage, and the fault current is small, which does not affect the continuous power supply to the load. Therefore, it is not necessary to trip immediately. The regulations stipulate that it can continue to run for 1~ 2h. However, with the increase of feeder lines, the capacitive current is also increasing. Long-term operation will easily cause the fault to expand into a two-point or multi-point grounding short circuit. Arcing grounding will also cause overvoltage in the entire system, which will damage the equipment and undermine the safe operation of the system. Therefore, the faulty line must be found in time to be removed.

Single-phase grounding faults account for more than 80% of the faults in small current grounding systems, and the magnitude of the steady-state grounding current is small at this time, especially in resonant grounding systems, which adds a lot of difficulty to fault judgment. The detection and reliable identification of single-phase-to-earth faults has not been completely solved.

Contents of the invention

The purpose of the present invention is to propose a ground fault direction diagnosis system for a small current grounded power distribution system. The system extracts the capacitive voltage and zero-sequence current according to the steady-state component of the feeder ground fault, and conducts the detection of the capacitive voltage and zero-sequence current. Analyze and compare, extract the phase relationship between capacitive voltage and zero-sequence current; use high-voltage live display to replace zero-sequence voltage transformer in small current grounding power distribution system, only need to extract the capacitive voltage of high-voltage live display and system zero-sequence The current can determine the direction of the ground fault. The ground fault direction signal picked up by the ground fault direction diagnosis system of the present invention can notify the controller of the distribution station, and the controller will make corresponding actions, which is beneficial to the protection of the power distribution system.

The ground fault direction diagnosis system of a small current grounding power distribution system of the present invention uses a high-voltage live display HS to replace the zero-sequence voltage transformer PT, and the high-voltage live display HS is connected to the power supply side of the three-phase power supply, or connected to the The load side of the three-phase power supply; the high-voltage live display HS includes a first capacitive sensor C7, a second capacitive sensor C8, a third capacitive sensor C9, a first equivalent resistance R4, a second equivalent resistance R5, a third etc. effective resistance R6; the capacitance of the first capacitive sensor C1 is marked as DC ₁ , the capacitance of the second capacitive sensor C2 is marked as DC ₂ , the capacitance of the third capacitive sensor C3 is marked as DC ₃ , and DC ₁ =DC ₂ = DC ₃ ; the resistance value of the first equivalent resistance R4 is marked as DR ₄ , the resistance value of the second equivalent resistance R5 is marked as DR ₅ , the resistance value of the third equivalent resistance R6 is marked as DR ₆ , and DR ₄ =DR ₅ = DR ₆ .

The diagnostic method of the ground fault direction diagnostic system of the small current grounded power distribution system includes the following diagnostic steps:

Diagnosis step 1: collecting the capacitive voltage U on the resistor R0;

Diagnosis step 2: collecting the zero-sequence current I ₀ detected on the zero-sequence current transformer ZCT;

Diagnosis Step 3: The capacitive voltage U is filtered by the first low-pass filter 11 to filter out high-frequency components to obtain a 50 Hz sinusoidal signal DU;

The zero-sequence current _I0 is filtered by the second low-pass filter 21 to filter out high-frequency components to obtain a 50Hz sinusoidal signal _DI0 ;

Diagnosis Step 4: The sinusoidal signal DU is subjected to zero-crossing comparison processing by the first zero-crossing comparator 12 to obtain a 50 Hz square wave signal SU;

The sinusoidal signal DI ₀ is subjected to zero-crossing comparison processing by the second zero-crossing comparator 22 to obtain a 50Hz square wave signal SI ₀ ;

Diagnosis Step 5: The square wave signal SU and the square wave signal SI ₀ are processed by the single-chip microcomputer 13 to perform advanced/lag phase detection processing to obtain the direction of the ground fault.

The advantages of the ground fault direction diagnosis system of the small current ground distribution system of the present invention are:

①Using the high-voltage live display to replace the zero-sequence voltage transformer, only need to extract the capacitive voltage of the high-voltage live display and the system zero-sequence current to determine the direction of the ground fault.

2. the high-voltage live indicator HS designed by the present invention has a plurality of equivalent branches, and the sum of the phase current phasors on the equivalent branches is the capacitive current I, and the capacitive current I is passed through the micro-current transformer MCT and The resistance R0 is converted into a capacitive voltage U. This conversion method can facilitate the diagnosis of single-phase ground fault direction.

③ The present invention can connect the high-voltage live display HS to the power supply side of the three-phase power supply, and can also be connected to the load side of the three-phase power supply, which is conducive to the installation of small current grounding power distribution systems, and is small in size and low in cost.

④Using a single-chip microcomputer for phase detection, the direction of the ground fault can be obtained. This detection method is novel, reliable and accurate.

Description of drawings

Figure 1 is a detection schematic diagram of a traditional small current grounding power distribution system.

Fig. 2 is a structural diagram of a low-current grounding power distribution system in which the high-voltage live display HS is connected to the load side of the three-phase power supply of the present invention.

Fig. 2A is a structural diagram of a low-current grounding power distribution system in which the high-voltage live display HS is connected to the power supply side of the three-phase power supply of the present invention.

Fig. 2B is a structural diagram of the high-voltage charged display HS in the present invention.

Fig. 3 is a schematic diagram of signal detection for ground fault direction diagnosis of the small current grounded power distribution system of the present invention.

Fig. 4 is a flow chart of the ground fault direction diagnosis of the small current grounded power distribution system of the present invention.

Fig. 4A is a phasor diagram detected by the diagnostic method of the present invention when a single-phase ground fault occurs on the power supply side.

Fig. 4B is a phasor diagram detected by the diagnostic method of the present invention when a single-phase ground fault occurs on the load side.

Detailed ways

Refer to Fig. 1, in which the output voltage of circuit A of the three-phase power supply is recorded as V _a , the output voltage of circuit B of the three-phase power supply is recorded as V _b , and the output voltage of circuit C of the three-phase power supply is recorded as V _c ; ZCT is zero Sequence current transformer (the model ZB-LJ-120 current transformer produced by Baoding Zhongbang Electric Co., Ltd. is selected), the zero-sequence current detected by ZCT is recorded as I ₀ ; the load of circuit A of the three-phase power supply is recorded as R ₁ , The load of circuit B of the three-phase power supply is recorded as R ₂ , the load of circuit C of the three-phase power supply is recorded as R ₃ ; the neutral point of the three-phase power supply is grounded through the arc suppression coil L; the distributed capacitance of circuit A on the power supply side to the ground is recorded as C _1. The capacitance of capacitor C ₁ is recorded as AC ₁ , the distributed capacitance of circuit B on the power supply side to ground is recorded as C ₂ , the capacitance of capacitor C ₂ is recorded as AC ₂ , and the distributed capacitance of circuit C to ground on the power supply side is recorded as C _3. The capacitance of capacitor C ₃ is recorded as AC ₃ , and AC ₁ ＝AC ₂ ＝AC ₃ ; the distributed capacitance of circuit A on the load side to ground is recorded as C ₄ , and the capacitance of capacitor C ₄ is recorded as AC ₄ , and the load side The distributed capacitance of circuit B to ground is recorded as C ₅ , the capacitance of capacitor C ₅ is recorded as AC ₅ , the distributed capacitance of circuit C on the load side to ground is recorded as C ₆ , the capacitance of capacitor C ₆ is recorded as AC ₆ , and AC ₄ = AC ₅ = AC ₆ ; PT is a zero-sequence voltage transformer (the model is JDZ-10 voltage transformer produced by China Yongshang Group), and the voltage detected by PT is recorded as V ₀ . As shown in Figure 1, the zero-sequence voltage transformer PT in the traditional small-current grounding power distribution system has the disadvantages of heavy weight, large volume, and high cost. In order to realize the diagnosis of the ground fault direction, the present invention uses a high-voltage live display to replace the zero-sequence voltage Transformer PT.

Referring to Fig. 2 and Fig. 2A, in the present invention, a high-voltage live display HS is used to replace the zero-sequence voltage transformer PT. The high-voltage live display HS can be connected to the power supply side of the three-phase power supply, and can also be connected to the three-phase The load side of the power supply realizes the flexibility of the installation method. Because in the actual system, the high-voltage live display HS is used to display the high-voltage live state on the switch, and it is connected to the grid itself. If the signal is taken out from the high-voltage live display HS to realize the function of the zero-sequence voltage transformer PT, it will not There is additional expenditure, the total cost is greatly reduced, and the volume is also greatly reduced, which has a strong promotion and use value in the actual system.

In the present invention, the specific structure of the high-voltage charged display HS is shown in Figure 2B. The high-voltage charged display HS includes a first capacitive sensor C7, a second capacitive sensor C8, a third capacitive sensor C9, a first equivalent resistance R4, a first capacitive sensor Two equivalent resistance R5, the third equivalent resistance R6; the capacitance of the first capacitive sensor C1 is marked as DC ₁ , the capacitance of the second capacitive sensor C2 is marked as DC ₂ , and the capacitance of the third capacitive sensor C3 is marked as DC ₃ , and DC ₁ =DC ₂ =DC ₃ . The resistance value of the first equivalent resistor R4 is denoted as DR ₄ , the resistance value of the second equivalent resistor R5 is denoted as DR ₅ , and the resistance value of the third equivalent resistor R6 is denoted as DR ₆ , DR ₄ =DR ₅ =DR ₆ .

One end of the first capacitive sensor C7 is connected with the A circuit of the three-phase power supply, the other end of the first capacitive sensor C7 is connected with one end of the first equivalent resistance R4, and the other end of the first equivalent resistance R4 is grounded; the first The capacitive sensor C7 and the first equivalent resistance R4 form a first equivalent branch circuit; the current flowing from the A circuit of the three-phase power supply into the first equivalent branch circuit is denoted as Ia, referred to as the first current Ia for short.

One end of the second capacitive sensor C8 is connected with the B circuit of the three-phase power supply, the other end of the second capacitive sensor C8 is connected with one end of the second equivalent resistance R5, and the other end of the second equivalent resistance R5 is grounded; the second The capacitive sensor C8 and the second equivalent resistance R5 form a second equivalent branch; the current flowing from the B circuit of the three-phase power supply into the second equivalent branch is denoted as Ib, referred to as the second current Ib for short.

One end of the third capacitive sensor C9 is connected to the C circuit of the three-phase power supply, the other end of the third capacitive sensor C9 is connected to one end of the third equivalent resistor R6, and the other end of the third equivalent resistor R6 is grounded. The third capacitive sensor C9 and the third equivalent resistance R6 form a third equivalent branch; the current flowing from the C circuit of the three-phase power supply into the third equivalent branch is denoted as Ic, referred to as the third current Ic for short .

In the present invention, the zero-sequence voltage of the three-phase power supply is denoted as U ₀ , and the phasor sum of the first current Ia, the second current Ib and the third current Ic is denoted as the current I generated by the zero-sequence voltage, also called capacitive Current I, that is, I=Ia+Ib+Ic. The relationship between the capacitive current I and the zero-sequence voltage U ₀ is I=jωDC _n U ₀ , j represents the imaginary number unit, ω represents the angular frequency (value 100πrad/s), and DC _n represents each equivalent The capacitance of the capacitive sensor on the branch, n is the mark of the selected equivalent branch, if it is the first equivalent branch, then the relationship between the capacitive current I and the zero-sequence voltage _U0 is I=jωDC ₁ U ₀ ; similarly, if it is the second equivalent branch, the relationship between the capacitive current I and the zero-sequence voltage U ₀ is I=jωDC ₂ U ₀ ; if it is the third equivalent branch, the capacitance The relationship between the sex current I and the zero-sequence voltage U ₀ is I=jωDC ₃ U ₀ . In the present invention, the zero-sequence voltage _U0 of the small-current grounding power distribution system is obtained by detecting the capacitive current I.

Referring to shown in Fig. 3, in order to realize the detection of capacitive current I, the present invention adopts micro-current transformer MCT (selecting the model that Wuxi Desheng Transformer Co., Ltd. produces is SPT204 micro-current transformer) and resistance R0 connection mode, i.e. The secondary side of the micro-current transformer MCT is connected with a resistor R0, and the primary side of the micro-current transformer MCT is connected in series with the ground terminal of the high-voltage live display HS. The micro current transformer MCT is used to detect the capacitive current I, and the resistor R0 can convert the capacitive current I into a capacitive voltage U.

Referring to Fig. 4, when a single-phase ground fault occurs in the small current grounded power distribution system, the ground fault direction diagnosis system of the small current grounded power distribution system designed by the present invention is used for diagnosis. The specific diagnostic steps are as follows:

Diagnosis step 1: collecting the capacitive voltage U on the resistor R0;

Diagnosis step 2: collecting the zero-sequence current I ₀ detected on the zero-sequence current transformer ZCT;

Diagnosis Step 3: The capacitive voltage U is filtered by the first low-pass filter 11 to filter out high-frequency components to obtain a 50 Hz sinusoidal signal DU;

The zero-sequence current _I0 is filtered by the second low-pass filter 21 to filter out high-frequency components to obtain a 50Hz sinusoidal signal _DI0 ;

Diagnosis Step 4: The sinusoidal signal DU is subjected to zero-crossing comparison processing by the first zero-crossing comparator 12 to obtain a 50 Hz square wave signal SU;

The sinusoidal signal DI ₀ is subjected to zero-crossing comparison processing by the second zero-crossing comparator 22 to obtain a 50Hz square wave signal SI ₀ ;

Diagnosis step 5: the square wave signal SU and the square wave signal SI ₀ are processed by the single-chip microcomputer 13 for advanced/lag phase detection, and the direction of the ground fault is obtained;

Described lead/lag phase detection is meant that the rising edge of square wave signal SU triggers the interrupt service in the single-chip microcomputer 13, detects the level of square wave signal SI ₀ in described interrupt service; If the level of square wave signal SI ₀ is When the level is low, the single-chip microcomputer 13 outputs a single-phase ground fault signal on the power supply side; if the level of the square wave signal SI ₀ is high level, the single-chip microcomputer 13 outputs a single-phase ground fault signal on the load side.

When there is a single-phase grounding fault on the power supply side, its phasor diagram is shown in Figure 4A, in which the zero-sequence current I ₀ lags behind the capacitive voltage U at a lag angle θ ₁ =0°～90°. At this time, for the single chip microcomputer 13 , the level of the square wave signal SI ₀ at the rising edge of the square wave signal SU is low level. Similarly, when there is a single-phase ground fault on the load side, its phasor diagram is shown in Figure 4B, in which the zero-sequence current I ₀ leads the capacitive voltage U by an angle θ ₂ =0°~180°. At this time, for the single chip microcomputer 13 , the level of the square wave signal SI ₀ at the rising edge of the square wave signal SU is high level.

In the present invention, for the small-current grounded power distribution system, with the capacitive voltage U as the reference, when a single-phase ground fault occurs on the load side, the zero-sequence current I ₀ is ahead of the capacitive voltage U, and the leading angle θ ₂ =0° ~180°; when a single-phase ground fault occurs on the power supply side, the zero-sequence current I ₀ lags behind the capacitive voltage U, and the lag angle θ ₁ =0°～90°. Therefore, by extracting and processing the steady-state component of the feeder ground fault, and further detecting the capacitive voltage U and zero-sequence current I ₀ when the system is faulty, the direction of the single-phase ground fault can be judged.

Claims (3)

1. the earthing fault direction diagnostic system of a small current neutral grounding distribution system has adopted high-voltage charge display device HS to substitute zero sequential potential transformer PT; It is characterized in that: said high-voltage charge display device HS includes the first capacitive transducer C7, the second capacitive transducer C8, the 3rd capacitive transducer C9, the first equivalent resistance R4, the second equivalent resistance R5, C grade effect resistance R 6; The electric capacity of the first capacitive transducer C1 is designated as DC ₁, the second capacitive transducer C2 electric capacity be designated as DC ₂, the 3rd capacitive transducer C3 electric capacity be designated as DC ₃, and DC ₁=DC ₂=DC ₃The resistance of the first equivalent resistance R4 is designated as DR ₄, the second equivalent resistance R5 resistance be designated as DR ₅, the C grade resistance of imitating resistance R 6 is designated as DR ₆, DR ₄=DR ₅=DR ₆Said high-voltage charge display device HS is connected the mains side of three-phase supply, perhaps is connected the load side of three-phase supply.

2. the earthing fault direction diagnostic system of small current neutral grounding distribution system according to claim 1; It is characterized in that: the end of the first capacitive transducer C7 is connected with the A road of three-phase supply; The other end of the first capacitive transducer C7 is connected with the end of the first equivalent resistance R4, the other end ground connection of the first equivalent resistance R4; Said first capacitive transducer C7 and the said first equivalent resistance R4 constitute the first equivalent branch road; The electric current that flows into the first equivalent branch road from the A road of three-phase supply is the first electric current I a;

The end of the second capacitive transducer C8 is connected with the B road of three-phase supply, and the other end of the second capacitive transducer C8 is connected with the end of the second equivalent resistance R5, the other end ground connection of the second equivalent resistance R5; Said second capacitive transducer C8 and the said second equivalent resistance R5 constitute the second equivalent branch road; The electric current that flows into the second equivalent branch road from the B road of three-phase supply is second current Ib;

The end of the 3rd capacitive transducer C9 is connected with the C road of three-phase supply, and the other end of the 3rd capacitive transducer C9 is connected with the end that C grade is imitated resistance R 6, and C grade is imitated the other end ground connection of resistance R 6; Said the 3rd capacitive transducer C9 and said C grade are imitated resistance R 6 and are constituted C grade effect branch road; The electric current of imitating branch road from the C road inflow C grade of three-phase supply is the 3rd electric current I c;

The residual voltage of three-phase supply is designated as U ₀, the phasor of the first electric current I a, second current Ib and the 3rd electric current I c and be called capacity current I, i.e. I=Ia+Ib+Ic; Said capacity current I and residual voltage U ₀Relation be I=j ω DC _nU ₀, j representes imaginary unit, ω representes angular frequency (value 100 π rad/s), DC _nThe electric capacity of the capacitive transducer in the expression high-voltage charge display device on each equivalent branch road, n is the sign of the equivalent branch road chosen.

3. according to the diagnostic method of the earthing fault direction diagnostic system of the described small current neutral grounding distribution system of claim 1, it is characterized in that including following diagnosis algorithm:

Diagnosis algorithm one: gather the capacitive voltage U on the resistance R 0;

Diagnosis algorithm two: gather zero sequence current mutual inductor ZCT and go up detected zero-sequence current I ₀

Diagnosis algorithm three: capacitive voltage U carries out Filtering Processing through first low-pass filter 11, and the filtering high fdrequency component obtains the sinusoidal signal DU of 50Hz;

Zero-sequence current I ₀Carry out Filtering Processing through second low-pass filter 21, the filtering high fdrequency component obtains the sinusoidal signal DI of 50Hz ₀

Diagnosis algorithm four: sinusoidal signal DU carries out the zero passage comparison process through first zero-crossing comparator 12, obtains the square-wave signal SU of 50Hz;

Sinusoidal signal DI ₀Carry out the zero passage comparison process through second zero-crossing comparator 22, obtain the square-wave signal SI of 50Hz ₀

Diagnosis algorithm five: square-wave signal SU and square-wave signal SI ₀Carry out the lead-lag phase-detection through single-chip microcomputer 13 and handle, obtain earthing fault direction;

Said lead-lag phase-detection is meant that the rising edge of square-wave signal SU triggers the break in service in the single-chip microcomputer 13, detects square-wave signal SI in said break in service ₀Level; If square-wave signal SI ₀Level when being low level, single-chip microcomputer 13 out-put supply side singlephase earth fault signals then; If square-wave signal SI ₀Level when being high level, single-chip microcomputer 13 output load side singlephase earth fault signals then;

During mains side generation singlephase earth fault, zero-sequence current I ₀Lag behind the drag angle θ of capacitive voltage U ₁=0 °～90 °;

During load side generation singlephase earth fault, zero-sequence current I ₀Be ahead of the lead angle θ of capacitive voltage U ₂=0 °～180 °.

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