CN113659550B - Neutral point through arc suppression coil and medium resistance grounding power network grounding fault protection method - Google Patents
Neutral point through arc suppression coil and medium resistance grounding power network grounding fault protection method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
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Abstract
A neutral point through arc suppression coil and medium resistance grounding power network grounding fault protection method belongs to the field of power system relay protection. If the ratio of the active component of the ground fault current to the zero sequence voltage exceeds a setting value, the ground fault occurs, the feeder is determined to be the ground fault feeder, the value of the active component of the ground fault current of the faulty feeder is calculated, the ratio of the value of the active component of the ground fault current to the value of the active component of the ground fault current is set as the ground fault quantity, 3 ground fault quantity setting values with different magnitudes are respectively set, and when the detected ground fault quantity is larger than the maximum ground fault quantity setting value, the ground fault is taken as a main protection instantaneous action; if the detected ground fault quantity is larger than the setting value of the next-largest ground fault quantity, the next-stage ground fault is used as a near backup protection delay delta t time action; and if the detected ground fault quantity is larger than the setting value of the minimum ground fault quantity, the remote backup protection delay 2 delta t time acts as the ground fault of the lower stage. The method has simple steps and convenient use.
Description
Technical Field
The invention relates to a method for protecting a neutral point through an arc suppression coil and a medium-resistance grounding power grid ground fault, which is suitable for a three-core cable distribution network with the neutral point through the arc suppression coil and the medium-resistance or small-resistance grounding, and belongs to the technical field of relay protection of power systems.
Background
Due to the graceful pursuit of people to urban environments and the requirement of higher power supply reliability, and meanwhile, due to the improvement of the production technology level of power cables and the reduction of the application cost of the cables, the urban 10kV power distribution network increasingly adopts a power cable laying power supply mode. Because of the symmetry of the three-core cable core, and the three-phase copper foil shielding layers are in contact with each other, no induced voltage exists on the copper foil layers when the power grid normally operates, and therefore, both ends of the cable are grounded. Thus, the ground wires of the cable (the copper foil shielding layer and the armor layer of the cable) connect the power substations, the switching stations, the ring websites and the ground poles of the users to form a grounding grid.
The power distribution network has the advantages that the power distribution network is greatly increased in ground fault current due to the fact that a large number of cables are used, and therefore a large number of neutral points are adopted in a ground operation mode of the arc suppression coil, and practice proves that the power distribution network has a great positive effect on safe and reliable operation. However, when the neutral point is grounded to the power grid through the arc suppression coil, the ground fault current is greatly reduced, meanwhile, some difficulties are brought to the ground fault line selection, the ground fault isolation difficulty is increased, and in order to improve the ground fault line selection accuracy, the mode that the arc suppression coil is grounded through the middle resistor (100-132 omega) (or the small resistor (10-15 omega)) is adopted, so that the ground fault line selection (the relay protection transverse selectivity) accuracy is greatly improved. The potential of the neutral point grounding mode is further developed, when the power grid has a grounding fault, the arc suppression coil timely compensates the power grid capacitance current to the ground, the current of the grounding fault point is effectively reduced, the instant grounding fault arc is rapidly extinguished, and the power grid is restored to normal operation; if the ground fault cannot automatically disappear in 3-5 seconds, the permanent ground fault is formed by closing QF in FIG. 1, and the resistor (or small resistor) in the neutral point is integrated between the neutral point and the ground electrode of the power grid for 1 second, during which, the invention effectively realizes the longitudinal selectivity of relay protection of the ground fault of the neutral point arc suppression coil and the medium resistor (or small resistor) ground power grid by measuring the active components of the ground fault current and the ground line current of the power grid and setting a brand-new fault quantity, and the invention effectively and selectively isolates the ground fault.
Disclosure of Invention
Technical problems: aiming at the defects of the prior art, the earth fault protection method for the neutral point through the arc suppression coil and the middle resistor earth power grid is provided, the fault quantity of each section of the longitudinal feeder line of the fault feeder line is effectively pulled through the fault quantity of the ratio of the effective value of the earth fault current, the longitudinal selectivity of the earth fault relay protection of the neutral point through the arc suppression coil and the middle resistor or the small resistor earth power grid is realized, and the relay protection mode not only fully exerts the advantages that the neutral point is automatically extinguished, does not need to be isolated and is beneficial to improving the reliability of power supply through the transient earth fault of the arc suppression coil earth power grid, but also can quickly isolate the permanent earth fault, greatly reduces the isolation range of the earth fault and the searching range of the fault, and also effectively improves the power quality of power supply.
The technical scheme is as follows: in order to achieve the above purpose, the neutral point through arc suppression coil and middle resistance ground power network ground fault protection method of the invention, through the ratio of the active component of the ground fault current to zero sequence voltage as the start signal of ground fault occurrence and route selection judgement, if the ratio of the active component of the ground fault current to zero sequence voltage exceeds the setting value, the ground fault occurs, and the feeder is determined to be the ground fault feeder; then, calculating the active component value of the ground wire current of the fault feeder line, and setting the ratio of the active component value of the ground wire current to the active component value of the ground fault current as the ground fault quantity; setting three ground fault quantity setting values with different sizes respectively, and taking the ground fault quantity as a main protection instantaneous action when the detected ground fault quantity is larger than the maximum ground fault quantity setting value; if the detected ground fault quantity is larger than the setting value of the next-largest ground fault quantity, the next-stage ground fault is used as a near backup protection delay delta t time action; and if the detected ground fault quantity is larger than the setting value of the minimum ground fault quantity, the remote backup protection serving as the lower-stage ground fault is delayed by 2 delta t time to realize selective protection.
The method comprises the following specific steps:
a. synchronously sampling zero sequence voltage and ground fault current and ground line current of each feeder line in a power grid in real time, and calculating the ratio I of active component of the ground fault current of each feeder line to the zero sequence voltage KRe /U 0 And judging: if the zero sequence voltage exceeds the wholeConstant value U 0qd And I KRe /U 0 If the power is more than 3 omega C, judging that the ground fault occurs, and then the feeder is a fault feeder, wherein U 0 Is zero sequence voltage, I KRe The active component of the ground fault current, C is the capacitance of each phase of the feeder line to the ground, and then the following judgment is carried out;
b. calculating the active component value I of the ground wire current of the fault feeder line Reli.j The i is the number of the users from the main transformer substation to the ith grounding electrode, and j is the ground wire where the j grounding fault radiated by the ith grounding electrode is located;
c. setting a fault quantity equal to the active component I of the ground current Reli+x.j And fault current active component I ReK Ratio epsilon of (2) i.i+x ＝I Reli+x.j /I ReK ，x＝0,1,2，x＝0，ε i.i Is the ground fault quantity of the ground fault of the cable section measured by the i-th level ground fault protection, x=1, epsilon i.i+1 Is the ground fault quantity of the ground fault of the next section of cable measured by the i-th level ground fault protection, x=2, epsilon i.i+2 Is the ground fault amount of the ground fault of the lower cable measured by the i-th ground fault protection,
d. setting an action value and an action time of the ground fault protection according to the fault magnitude, and realizing selective protection of the ground fault through the action value and the action time:
(1) minimum fault quantity epsilon when single-phase earth fault occurs at i section farthest end mini.i ＝I minReli.i /I ReK I.e. the furthest single-phase earth fault of the section, the main protection of the earth fault of the section, i.e. epsilon, is set iz1 ≥ε mini.i /K K1 Taking K K1 =1.1, main protection transient action, where ε iz1 Setting value K for i section main protection K1 The reliability coefficient of the main protection;
(2) minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+1 section mini.i+1 ＝I minReli.i+1 /I ReK I.e. single-phase earth fault occurs at the farthest point of the i+1 section, and the near backup protection of the i section to the earth fault of the i+1 section, namely epsilon, is set iz2 ≥ε mini.i+1 /K K2 The near backup protection is delayed by Δt time, where Δt=0.2s, where ε iz2 Setting value K for i section to i+1 section near backup protection K2 For near-backup reliability factor, K K2 ＝1.05；
(3) Minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+2 sections mini.i+2 ＝I minReli.i+2 /I ReK I.e. single-phase earth fault occurs furthest in the i+2 section, and the far backup protection of the i section to the i+2 section earth fault, i.e. epsilon, is set iz3 ≥ε mini.i+2 /K K3 The far backup protection delays 2 Δt time action, where ε iz3 Setting value K for far backup protection of i segment to i+2 segment and beyond K3 For the reliability factor of the far backup protection, K K3 ＝1.05。
As long as a ground fault occurs, it is necessary that the zero sequence voltage of the power grid increases, and thus the zero sequence voltage exceeds the setting value U 0qd Necessarily means that the power grid has a ground fault, and the ratio I of the active component of the zero-sequence current and the zero-sequence voltage of each feeder line KRe /U 0 The actual ground conductance of the feeder is that of the non-fault feeder, the dielectric loss of the cable is about 1% of capacitance reactance to the ground, and the ratio of the dielectric loss to the ground is about the inverse of the sum of the ground resistance of the ground fault point and the ground resistance of the neutral point, and the number is far greater than 3 omega C, so that the feeder is necessarily the fault feeder.
Calculating the active component value I of the ground wire current of the fault feeder line Rel The specific steps of (a) are as follows:
with the ground fault feeder having 3 segments, assume that: the main transformer station arrives at the switching station, the switching station arrives at the looped network station and the looped network station arrives at the 10/0.4kV transformer inlet of the user, and i=1 to n are serial numbers from the grounding electrode of the main transformer station to the grounding electrode of the user; j=1 to m are serial numbers of the ground wires connected to the "i" th ground resistor, and m is the total number of the ground wires connected to the "i" th ground resistor; i eli.j Is the current of the jth ground wire connected to the ith ground electrode; r is R ei.j Is the i-th ground resistance; r is R N The neutral point grounding resistor; x is X N Is arc suppression coilIs a reactance of (2); r is R eli.j Is the ground resistance of the j-th feeder line radiated by the i-th grounding electrode, R' eli.j +R” eli.j ＝R eli.j ；
For a power grid with a neutral point grounded through an arc suppression coil and a medium resistor, if only the active component of the ground fault current is considered to flow in the power grid conductor and the ground wire, the fault current is mainly distributed in the power grid conductor from the fault point to the neutral point, and the current is the active component I of the current flowing through the neutral point NRe The method comprises the steps of carrying out a first treatment on the surface of the Whereas the distribution of the active components of the fault current in the ground, in particular in the ground of the fault feeder, is mainly composed of 2 parts, the resistive current I of the neutral point NRe Ground current distribution under separate action and fault current active component I of fault point K kRE Ground wire current distribution under independent action; zero sequence voltage U 0 The ground wire current distribution and the neutral point arc suppression coil compensation current under the independent action are reactive components of the current, and are not discussed herein;
A. when the active components of the neutral point current act independently, the fault current I of the fault point K kRe Regarded as open circuit, zero sequence voltage U 0 Regarding as a short circuit, ignoring the reactive component of the zero sequence current, the active component I of the neutral point current NRe And fault point current active component I kRe Are equal, i.e. have I NRe ＝-I KRe ＝3I 0Re Moreover, since the lines of the power distribution network are not very long, the middle resistance of the neutral point is far greater than the zero sequence impedance of the lines, and the magnitude of the single-phase grounding fault current mainly depends on the resistance value of the resistance of the neutral point and the impedance of the grounding fault point, so that the power distribution network is K 1 Point or K 2 Point or K 3 Point occurrence of Single-phase ground fault, I NRe And I kRE The value of (I) is almost constant, I NRe After flowing into the grounding grid, the current flows into each grounding electrode along the grounding grid and enters the ground, and the current active components in the ground wire of the fault feeder line are as follows:
the first section main transformer station is connected to the switching station:
the second section switching station is connected between the ring network stations:
the third section loops between the website and the consumer transformer:
definition: r is R cei.j Is I NRel(i-1).j Ground resistance R of injection point ei.j Equivalent resistance of the grounding network of the user, namely the breaking grounding resistance R ei.j Ground wire connected with the power supply grounding net, and the grounding net is observed from the power supply side to the user side, and the grounding resistor R ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R cei.j The method comprises the steps of carrying out a first treatment on the surface of the The resistance can be measured directly to: i.e. to disconnect the ground resistance R ei.j Ground wire connected to ground network, i.e. disconnected I NRel(i-1).j Injection line, measuring ground resistance R ei.j The resistance of the upper disconnection point to the ground E is R cei.j ；R cei.j Calculated by formula (4):
I cNReli.j is neutral point current I NRe The ground current of the jth feeder line radiated by the ith grounding electrode when in the ground; if the longitudinal power supply line exceeds three stages, the calculation can be analogically performed in sequence;
B. fault current active component I of fault point K kRE When acting alone, neutral point current I N Regarded as open circuit, zero sequence voltage U 0 Regarding as a short circuit, the fault current of the fault point K enters the ground through the fault point, returns to the grounding network through each grounding electrode, and returns to the fault point through each ground wire; the fault current only forms a loop and flows in the grounding grid;
if the ground fault occurs in K 1 The current active components from the fault point to the power supply are:
defined herein is: r is R uei.j Is I uReli.j Ground resistance R of injection point ei.j Equivalent resistance of power-supply ground network, i.e. breaking ground resistance R ei.j Ground wire connected with grounding grid of user, and grounding grid is observed from user side to power source side, and grounding electrode resistance R ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R uei.j The resistance can be measured directly to: i.e. to disconnect the ground resistance R ei.j Grounding wire of grounding network connected with user to measure grounding resistance R ei.j The resistance of the upper disconnection point to the ground E is R uei.j ；R uei.j Calculated by the formula (6);
the current from the fault point to the load side is:
the resistance of the grounding electrode of the main transformer is less than or equal to 0.5 omega, and the number of the radiating cables of the main transformer is large, the resistance of the grounding electrode of the switching station is less than or equal to 2 omega, the resistance of the grounding electrode of the ring website and the user is less than 4 omega, and the number of the radiating cables is small, so that the equivalent resistance R of the grounding electrode of the power supply and the user is high uei.j Is far smaller than the resistance R of the grounding electrode of the load cei.j So the current active component I of the fault point to the load side ckReli.j To be far smaller than the current active component I from the fault point to the power supply side kReli.j ；I ckReli.j And I cNReli.j Is in the opposite direction, the active component I of the ground current Reli.j Is the algebraic sum of 2 currents, essentially the difference of 2; obviously, the current active component of the fault point to the load side in the ground is much smaller than the current active component to the power supply side, and therefore, the current active component of the fault point to the load side in the ground is not discussed further below;
if the ground fault occurs in K 2 The current active components between the fault point and the switching station are as follows:
the current active components between the switching station and the power supply end are as follows:
if the ground fault occurs in K 3 The current active components between the fault point and the ring network station are as follows:
the current active components between the ring website and the switching station are as follows:
the current active components between the switching station and the power supply are as follows:
thus K is 1 When the point ground fault occurs, the fault point reaches the ground current active component of the power supply:
I Rel1.j ＝I cNRel1.j +I k1Rel1.j (13)
K 2 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k2Rel1.j (14)
I Rel2.j ＝I cNRel2.j +I k2Rel2.j (15)
K 3 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k3Rel1.j (16)
I Rel2.j ＝I cNRel2.j +I k3Rel2.j (17)
I Rel3.j ＝I cNRel3.j +I k3Rel3.j (18)。
let epsilon be the fault quantity, the subscript I be the serial number from the power supply to the user, k be the fault point, since I NRe ＝-I kRe ＝3I 0Re Thus, k 1 When the point ground fault occurs, the fault amount from the fault point to the power supply is as follows:
k 2 when the point is grounded, the fault quantity from the fault point to the power supply is as follows:
k 3 when the point is grounded, the fault quantity from the fault point to the power supply is as follows:
the beneficial effects are that: the invention aims to provide a selective protection method for a neutral point through an arc suppression coil and a medium-resistance or small-resistance grounding power distribution network grounding fault. When the power grid has a grounding fault, the arc suppression coil timely compensates the current of the capacitance of the power grid to the ground, effectively reduces the current of the grounding fault point, enables the instantaneous grounding fault arc to be rapidly extinguished, and enables the power grid to recover to normal operation; if the ground fault can not automatically disappear in 3-5 seconds, the permanent ground fault is formed by closing QF in FIG. 1, and the resistance in the neutral point is integrated between the neutral point and the ground electrode of the power grid for 1 second in 100-132 omega or 10-15 omega, during which, the invention effectively realizes the longitudinal selectivity of relay protection of the ground fault of the power grid with neutral point arc suppression coils and medium resistance or small resistance by measuring the ground fault current and the active component of the ground current of the power grid and setting a brand new fault quantity and the ratio of the active component of the ground current and the active component of the ground fault current. The relay protection mode not only gives full play to the advantages that the neutral point is automatically extinguished without isolation through the instantaneous grounding fault of the arc suppression coil grounding power grid, and is beneficial to improving the power supply reliability, but also can quickly isolate the permanent grounding fault, greatly reduces the isolation range of the grounding fault and the searching range of the fault, and effectively improves the power quality of the power supply. Moreover, the fault quantity has no dimension independent of the impedance of the grounding fault point and the grounding fault type (single-phase grounding fault or two-phase grounding fault), and the fault isolation performance is more excellent.
The drawings in the specification:
FIG. 1 is a schematic diagram of a simulation model of a cable distribution network;
FIG. 2 is a schematic diagram of a zero sequence circuit of the simplified power supply system of the present invention;
fig. 3 (a), (b), and (c) are schematic diagrams of cable distribution network simulation models after replacing the schematic diagrams by using the replacement theorem of the circuit;
FIG. 4 is a schematic diagram of current signal sampling obtained by the zero sequence current transformers of the feeder and the ground;
fig. 5 is a schematic diagram of sampling current signals obtained by the zero sequence current transformers of the feeder and the ground.
Detailed Description
The invention will be further described with reference to the accompanying drawings, in which:
the implementation of the invention requires a zero sequence current transformer and a current transformer for measuring the ground wire current, wherein the zero sequence current transformers of the feeder wires are arranged on the outer side of a high-voltage cable for movement, the ground wire zero sequence current transformers are arranged on the outer side of the ground wire of the high-voltage cable, the zero sequence current transformers of the feeder wires are arranged on the outer side of the high-voltage cable for movement, and 2 current signal sampling methods obtained by the zero sequence current transformers of the feeder wires and the ground wire zero sequence current transformers are shown in fig. 4 and 5; the 2 current sampling signals are sent to a relay protector for signal conditioning, and then the following calculation and judgment are implemented:
as shown in fig. 1, the selective protection method for the grounding fault of the neutral point through the arc suppression coil and the middle resistor is suitable for the selective protection method for the grounding fault of the neutral point through the arc suppression coil and the middle resistor or the small resistor, the ratio of the active component of the grounding fault current to the zero sequence voltage is used as a starting signal for grounding fault occurrence and line selection judgment, if the ratio of the active component of the grounding fault current to the zero sequence voltage exceeds a setting value, the grounding fault occurs, and the feeder line is determined to be the grounding fault feeder line; then, calculating the active component value of the ground wire current of the fault feeder line, and setting the ratio of the active component value of the ground wire current to the active component value of the ground fault current as the ground fault quantity; setting three ground fault quantity setting values with different sizes respectively, and taking the ground fault quantity as a main protection instantaneous action when the detected ground fault quantity is larger than the maximum ground fault quantity setting value; if the detected ground fault quantity is larger than the setting value of the next-largest ground fault quantity, the next-stage ground fault is used as a near backup protection delay delta t time action; and if the detected ground fault quantity is larger than the setting value of the minimum ground fault quantity, the remote backup protection serving as the lower-stage ground fault is delayed by 2 delta t time to realize selective protection.
As shown in fig. 2, the specific steps of the selective protection method for the neutral point through arc suppression coil and medium resistance grounding power grid grounding fault are as follows:
1) Synchronously sampling zero sequence voltage and ground fault current and ground line current of each feeder line in real time, and calculating the ratio I of active component of the ground fault current of each feeder line to the zero sequence voltage KRe /U 0 And is combined withJudging: if the zero sequence voltage exceeds the setting value U 0qd And I KRe /U 0 If 3 omega C, the ground fault occurs, then the feeder is the faulty feeder, here U 0 Is zero sequence voltage, I KRe Is the active component of the ground fault current and C is the capacitance per phase to ground of the local feeder.
As long as a ground fault occurs, it is necessary that the zero sequence voltage of the power grid increases, and therefore, the zero sequence voltage exceeds the setting value U 0qd Necessarily meaning that a ground fault has occurred in the grid. The ratio I of the active component of the zero sequence current to the zero sequence voltage of each feeder line KRe /U 0 The actual ground conductance of the feeder is the dielectric loss of the cable for the non-fault feeder, which is approximately equal to about 1% of the capacitance reactance of the ground capacitor. And the ratio of the ground resistance to the ground fault feeder is approximately equal to the inverse of the sum of the ground resistance of the ground fault point and the ground resistance of the neutral point, which is much greater than 3 ωc, so that the present feeder must be the fault feeder.
Further, the following determination is made:
2) Calculating the active component value I of the ground wire current of the fault feeder line Rel : with the ground fault feeder having 3 segments, assume that: the zero sequence circuit of the simplified power supply system is shown in figure 1, and the replacement theorem of the circuit is applied according to the theory that the zero sequence current is distributed in the ground wire, and the figure 2 can be replaced by (a), (b) and (c) in figure 3. In fig. 2 and 3 (a), (b) and (c), i=1 to n are numbers from the ground electrode of the main transformer to the user-side ground electrode; j=1 to m are serial numbers of the ground wires connected to the "i" th ground resistor, and m is the total number of the ground wires connected to the "i" th ground resistor; i eli.j Is the current of the jth ground wire connected to the ith ground electrode; r is R ei.j Is the i-th ground resistance; r is R N The neutral point grounding resistor; x is X N Is the reactance of the arc suppression coil; r is R eli.j Is the ground resistance of the j-th feeder line radiated by the i-th grounding electrode, R' eli.j +R” eli.j ＝R eli.j 。
Arc suppression coil for neutral pointAnd a power grid with a grounded intermediate resistor (100-132 omega) (or a small resistor (10-15 omega)), if we only consider that the active component of the ground fault current flows in the power grid conductor and in the ground, the fault current is mainly distributed in the power grid conductor from the fault point to the neutral point, this current is the current active component I flowing through the neutral point NRe The method comprises the steps of carrying out a first treatment on the surface of the Whereas the distribution of the active components of the fault current in the ground, in particular in the ground of the fault feeder, is mainly composed of 2 parts, the resistive current I of the neutral point NRe Ground current distribution under separate action and fault current active component I of fault point K kRE Ground wire current distribution under independent action; zero sequence voltage U 0 The ground current distribution and neutral point choke compensation current under separate action are reactive components of the current and are not discussed here.
A. When the active components of the neutral point current act independently, the fault current I of the fault point K kRe Regarded as open circuit, zero sequence voltage U 0 Regarded as a short circuit, neutral current active component I NRe The distribution in the ground line is shown as light-colored broken-line arrow lines in (a), (b), and (c) in fig. 3. As can be seen from (a), (b) and (c) in FIG. 3, the zero sequence current reactive component is ignored, and the neutral point current active component I NRe And fault point current active component I kRe Are equal, i.e. have I NRe ＝-I KRe ＝3I 0Re Moreover, since the lines of the power distribution network are not very long, the middle resistance (or small resistance 10-15 omega) of the neutral point is far greater than the zero sequence impedance of the lines, and the magnitude of the single-phase earth fault current mainly depends on the resistance value of the resistance of the neutral point and the impedance of the earth fault point, so that the single-phase earth fault current is K 1 Point or K 2 Point or K 3 Point occurrence of Single-phase ground fault, I NRe And I kRE The value of (2) is almost constant. I NRe After flowing into the grounding grid, the current flows into each grounding electrode along the grounding grid and enters the ground, and the current active components in the ground wire of the fault feeder line are as follows:
the first section main transformer station is connected to the switching station:
the second section switching station is connected between the ring network stations:
the third section loops between the website and the consumer transformer:
defined herein is: r is R cei.j Is I NRel(i-1).j Ground resistance R of injection point ei.j Equivalent resistance of the grounding network of the user, namely the breaking grounding resistance R ei.j Ground wire (I) grounded to power supply NRel(i-1).j Injection line), the ground network is observed from the power supply side to the user side, and the ground resistance R is set ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R cei.j . The resistance can be measured directly to: i.e. to disconnect the ground resistance R ei.j Ground wire connected to ground network, i.e. disconnected I NRel(i-1).j Injection line, measuring ground resistance R ei.j The resistance of the upper disconnection point to the ground E is R cei.j ；R cei.j Calculated by formula (4):
I cNReli.j is neutral point current I NRe And the ground current of the jth feeder line radiated by the ith grounding electrode when in the ground. If the longitudinal power supply line exceeds three stages, the calculation can be analogized.
B. Fault current active component I of fault point K kRE When acting alone, neutral point current I N Regarded as open circuit, zero sequence voltage U 0 The fault current at the fault point K is considered as a short circuit, and flows through the fault point to the ground, returns to the ground network via each ground electrode, and returns to the fault point via each ground wire. The fault current only forms a loop and flows in the grounding grid. The distribution in the grounding wire is shown by dark dotted arrow lines in (a), (b) and (c) in fig. 3, wherein (a), (b) and (c) in fig. 3 are K1 fault, K2 fault and K3 fault, respectivelyIs equivalent to the schematic diagram of (a);
if the ground fault occurs in K 1 The current active components from the fault point to the power supply are:
defined herein is: r is R uei.j Is I uReli.j Ground resistance R of injection point ei.j Equivalent resistance of power-supply ground network, i.e. breaking ground resistance R ei.j Ground wire (I) of grounding network connected with user kReli.j Injection line), the grounding grid is observed from the side of the user to the power supply side, and the grounding electrode resistance R is measured ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R uei.j . The resistance can be measured directly to: i.e. to disconnect the ground resistance R ei.j Grounding wire of grounding network connected with user to measure grounding resistance R ei.j The resistance of the upper disconnection point to the ground E is R uei.j ；R uei.j Calculated by formula (6).
The current from the fault point to the load side is:
the resistance of the grounding electrode of the main transformer is less than or equal to 0.5 omega, and the number of the radiating cables of the main transformer is large, the resistance of the grounding electrode of the switching station is less than or equal to 2 omega, the resistance of the grounding electrode of the ring website and the user is less than 4 omega, and the number of the radiating cables is small, so that the equivalent resistance R of the grounding electrode of the power supply and the user is high uei.j Is far smaller than the resistance R of the grounding electrode of the load cei.j Therefore, the current active component I from the fault point to the load side ckReli.j To be far smaller than the current active component I from the fault point to the power supply side kReli.j . It can also be seen from (a), (b), (c) in FIG. 3 that I ckReli.j And I cNReli.j Is in the opposite direction, the active component I of the ground current Reli.j Is the algebraic sum of 2 currents, and is essentially the difference of 2. Obviously, the current active component of the fault point to the load side in the ground is much smaller than the current active component to the power supply side, and therefore, the current active component of the fault point to the load side in the ground will not be discussed further.
If the ground fault occurs in K 2 The current active components between the fault point and the switching station are as follows:
the current active components between the switching station and the power supply end are as follows:
if the ground fault occurs in K 3 The current active components between the fault point and the ring network station are as follows:
the current active components between the ring website and the switching station are as follows:
the current active components between the switching station and the power supply are as follows:thus, K is 1 When the point ground fault occurs, the fault point reaches the ground current active component of the power supply:
I Rel1.j ＝I cNRel1.j +I k1Rel1.j (13)
K 2 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k2Rel1.j (14)
I Rel2.j ＝I cNRel2.j +I k2Rel2.j (15)
K 3 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k3Rel1.j (16)
I Rel2.j ＝I cNRel2.j +I k3Rel2.j (17)
I Rel3.j ＝I cNRel3.j +I k3Rel3.j (18)
3) Setting a fault quantity equal to the active component I of the ground current Reli+x.j And fault current active component I KRe Ratio epsilon of (2) i.i+x ＝I Reli+x.j /I KRe ，x＝0,1,2，x＝0，ε i.i Is the ground fault quantity of the ground fault of the cable section measured by the i-th level ground fault protection, x=1, epsilon i.i+1 Is the ground fault quantity of the ground fault of the next section of cable measured by the i-th level ground fault protection, x=2, epsilon i.i+2 Is the ground fault amount of the ground fault of the lower cable measured by the i-th ground fault protection.
Here, epsilon is the fault amount, the subscript i is the serial number in order from the power source to the user, and k is the fault point. Due to I NRe ＝-I kRe ＝3I 0Re Thus, k 1 When the point ground fault occurs, the fault amount from the fault point to the power supply is as follows:
k 2 when the point is grounded, the fault quantity from the fault point to the power supply is as follows:
k 3 when the point is grounded, the fault quantity from the fault point to the power supply is as follows:
4) And setting the action time of the ground fault protection according to the fault magnitude: (1) minimum fault quantity epsilon when single-phase earth fault occurs at i section farthest end mini.i ＝I minReli.i /I KRe Setting the main protection of the earth fault of the section, namely epsilon iz1 ≥ε mini.i /K K1 Generally take K K1 =1.1, main protection transient action. Here, ε iz1 Is the setting value of i section main protection, K K1 Is the reliability factor of the main protection. (2) Minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+1 section mini.i+1 ＝I minReli.i+1 /I KRe (i.e., single-phase ground fault occurs furthest from the i+1 segment) setting the near backup protection of the i segment against the i+1 segment ground fault, i.e., ε iz2 ≥ε mini.i+1 /K K2 The near backup protection is delayed by Δt time action. Here, ε iz2 Is the setting value of the i section to the i+1 section near backup protection, K K2 Is the reliability coefficient of near backup protection, K K2 =1.05. (3) Minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+2 sections mini.i+2 ＝I minReli.i+2 /I KRe (i.e., single-phase ground fault occurs furthest from the i+2 segment) setting the far backup protection of the i segment against the i+2 segment ground fault, i.e., ε iz3 ≥ε mini.i+2 /K K3 The far backup protection is delayed by 2 Δt time action. Here, ε iz3 Is the setting value of i section to i+2 section long backup protection, K K3 Is the reliability coefficient of the far backup protection, K K3 ＝1.05。
Embodiment 1,
Setting the simplified urban 10kV cable distribution network to explain the setting method: assuming that four stages of grounding poles are longitudinally arranged and are respectively a main transformer station, an switching station and a ring main unit to user transformers, i=4, and the resistances of the grounding poles are respectively: r is R e1.1 ＝0.5Ω、R e2.j ＝2Ω、R e3.j ＝4Ω、R e3.j =4Ω, all 9 feeders of the main transformer are connected to each switching station, all 6 feeders of each switching station are connected to ring network, each ring network station has 2 feeders connected to each user transformer, and all feeders are 240mm 2 The power supply distance of the three-core armored cable is 1km, and the ground wire resistance R of all feeder lines eli,j =0.242 Ω. This can be calculated by the following equation (4): r is R ce1.0 ＝0.0483Ω、R ce2.j ＝0.2389Ω、R ce3.j ＝1.386Ω、R ce4.j =4Ω. Similarly, the values are calculated according to the formula (6): r is R ue1.j ＝0.0537Ω、R ue2.j ＝0.1438Ω、R ue3.j ＝0.3249Ω。
I=1 segment distal most (R', el1.j =0) minimum fault amount measured at the i-segment protection installation when single-phase earth fault occurs:
i+1 distal most end (R') " el2.j =0) minimum fault amount measured at the i-segment protection installation when single-phase earth fault occurs:
i+2 distal-most end of the segment (R') " el3.j =0) minimum fault amount measured at the i-segment protection installation when single-phase earth fault occurs:
thus, the main protection ε between the main substation and the switching station is set 1z1 ≥ε mini.i /K K1 =0.4082, instantaneous actionThe method comprises the steps of carrying out a first treatment on the surface of the Setting near backup protection epsilon 1z2 ≥ε min1.2 /K K2 = 0.3621, delay Δt time action; setting the long-distance backup protection epsilon 1z3 ≥ε min1.3 /K K3 = 0.3374, delay 2 Δt time action.
I=2 segment distal most (R', el2.j =0) minimum fault amount measured at the i-segment protection installation when single-phase earth fault occurs:
i+1 distal most end (R') " el3.j =0) minimum fault amount measured at the i-segment protection installation when single-phase earth fault occurs:
thus, the main protection epsilon between the switching stations and the ring network station is set 2z.1 ≥ε min2.2 /K K1 =0.6909, transient action; setting near backup protection epsilon 2z.2 ≥ε min2.3 /K K2 = 0.6626, delay Δt time action; this section is not far back-up protected.
I=3 segment distal most (R', el3.j =0) minimum fault amount measured at the protection installation when single-phase earth fault occurred:
thus, setting the primary protection ε between the ring site to the consumer 3z.1 ≥ε min3.3 /K K1 = 0.8075, instantaneous action. The section has no near backup and far backup protection.
In this way, if a fault occurs between the ring network station and the primary side of the user transformer, the ground fault protection provided in the main transformer station, the switching station and the ring network station is started, but the fault amount detected by the ring network station is the largest and is necessarily larger than 0.8807, so that the main protection action of the ring network station isolates the fault. If the ring network station fails to isolate the fault, the fault quantity detected by the switching station is necessarily larger than 0.7523, and the switching station delays the backup protection action of the switching station for deltat time to isolate the fault. If the isolation fault of the switching station fails again, the fault quantity detected by the main transformer station is inevitably larger than 0.3587, and the backup protection of the main transformer station is delayed for 2 delta t time to act, so that the fault is isolated. If the ground fault occurs between the switching station and the ring network station, the ground fault protection of the ring network station is not started, and the ground fault protection of the main transformer substation and the switching station is started, but the fault quantity detected by the switching station is maximum and is larger than 0.7970, and the main protection of the switching station acts instantaneously to isolate the ground fault. If the switching station fails to isolate faults, the main transformer station detects that the fault quantity is larger than 0.4048, and the main transformer station acts near the backup protection delay delta t to isolate the grounding faults. If the ground fault occurs between the main transformer substation and the switching substation, only the main transformer substation detects that the fault quantity is larger than 0.5473, the ground fault protection of the switching substation and the ring website is not started, only the main transformer substation ground fault main protection acts instantaneously, and the fault is isolated.
The longitudinal selectivity of the ground fault of the neutral point through the small-resistance ground cable distribution network is realized. The invention can be independently implemented by a microcomputer chip, and can be inserted into a microcomputer relay protection device to realize the function of the protection device.
Claims (4)
1. A neutral point through arc suppression coil and the earth fault protection method of the middle resistance earthing power network is characterized in that: the ratio of the active component of the ground fault current to the zero sequence voltage is used as a starting signal for ground fault occurrence and line selection judgment, if the ratio of the active component of the ground fault current to the zero sequence voltage exceeds a setting value, the ground fault occurs, and the feeder is determined to be the ground fault feeder; then, calculating the active component value of the ground wire current of the fault feeder line, and setting the ratio of the active component value of the ground wire current to the active component value of the ground fault current as the ground fault quantity; setting three ground fault quantity setting values with different sizes respectively, and taking the ground fault quantity as a main protection instantaneous action when the detected ground fault quantity is larger than the maximum ground fault quantity setting value; if the detected ground fault quantity is larger than the setting value of the next-largest ground fault quantity, the next-stage ground fault is used as a near backup protection delay delta t time action; if the detected ground fault quantity is larger than the setting value of the minimum ground fault quantity, the remote backup protection delay 2 delta t time action of the lower-stage ground fault is used for realizing selective protection;
the method comprises the following specific steps:
a. synchronously sampling zero sequence voltage and ground fault current and ground line current of each feeder line in a power grid in real time, and calculating the ratio I of active component of the ground fault current of each feeder line to the zero sequence voltage KRe /U 0 And judging: if the zero sequence voltage exceeds the setting value U 0qd And I KRe /U 0 If the power is more than 3 omega C, judging that the ground fault occurs, and then the feeder is a fault feeder, wherein U 0 Is zero sequence voltage, I KRe The active component of the ground fault current, C is the capacitance of each phase of the feeder line to the ground, and then the following judgment is carried out;
b. calculating the active component value I of the ground wire current of the fault feeder line Reli.j The i is the number of the users from the main transformer substation to the ith grounding electrode, and j is the ground wire where the j grounding fault radiated by the ith grounding electrode is located;
c. setting a fault quantity equal to the active component I of the ground current Reli+x.j And fault current active component I ReK Ratio epsilon of (2) i.i+x ＝I Reli+x.j /I ReK ，x＝0,1,2，x＝0，ε i.i Is the ground fault quantity of the ground fault of the cable section measured by the i-th level ground fault protection, x=1, epsilon i.i+1 Is the ground fault quantity of the ground fault of the next section of cable measured by the i-th level ground fault protection, x=2, epsilon i.i+2 Is the ground fault amount of the ground fault of the lower cable measured by the i-th ground fault protection,
d. setting an action value and an action time of the ground fault protection according to the fault magnitude, and realizing selective protection of the ground fault through the action value and the action time:
(1) minimum fault quantity epsilon when single-phase earth fault occurs at i section farthest end mini.i ＝I minReli.i /I ReK I.e. single phase connection occurs furthest in this sectionGround fault, setting the main protection of the ground fault of the current segment, i.e. epsilon iz1 ≥ε mini.i /K K1 Taking K K1 =1.1, main protection transient action, where ε iz1 Setting value K for i section main protection K1 The reliability coefficient of the main protection;
(2) minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+1 section mini.i+1 ＝I minReli.i+1 /I ReK I.e. single-phase earth fault occurs at the farthest point of the i+1 section, and the near backup protection of the i section to the earth fault of the i+1 section, namely epsilon, is set iz2 ≥ε mini.i+1 /K K2 The near backup protection is delayed for Δt time action, taking Δt=0.2s, where ε iz2 Setting value K for i section to i+1 section near backup protection K2 For near-backup reliability factor, K K2 ＝1.05；
(3) Minimum fault quantity epsilon when single-phase earth fault occurs at the farthest end of i+2 sections mini.i+2 ＝I minReli.i+2 /I ReK I.e. single-phase earth fault occurs furthest in the i+2 section, and the far backup protection of the i section to the i+2 section earth fault, i.e. epsilon, is set iz3 ≥ε mini.i+2 /K K3 The far backup protection delays 2 Δt time action, where ε iz3 Setting value K for far backup protection of i segment to i+2 segment and beyond K3 For the reliability factor of the far backup protection, K K3 ＝1.05。
2. The neutral point through arc suppression coil and medium resistance ground network ground fault protection method according to claim 1, characterized in that: as long as a ground fault occurs, it is necessary that the zero sequence voltage of the power grid increases, and thus the zero sequence voltage exceeds the setting value U 0qd Necessarily means that the power grid has a ground fault, and the ratio I of the active component of the zero-sequence current and the zero-sequence voltage of each feeder line KRe /U 0 The actual ground conductance of a feeder is the dielectric loss of the cable for a non-faulty feeder, which is approximately equal to 1% of the capacitive reactance to ground, and the ground fault feeder, which is approximately equal to the inverse of the sum of the ground resistance of the ground fault point and the ground resistance of the neutral point, which is much greater than 3 omega C,it is therefore necessary that the present feeder is a faulty feeder.
3. The neutral point through arc suppression coil and medium resistance grounding power network grounding fault protection method as claimed in claim 1, characterized by calculating ground current active component value I of faulty feeder line Rel The specific steps of (a) are as follows:
with the ground fault feeder having 3 segments, assume that: the main transformer station arrives at the switching station, the switching station arrives at the looped network station and the looped network station arrives at the 10/0.4kV transformer inlet of the user, and i=1 to n are serial numbers from the grounding electrode of the main transformer station to the grounding electrode of the user; j=1 to m are serial numbers of the ground wires connected to the "i" th ground resistor, and m is the total number of the ground wires connected to the "i" th ground resistor; i eli.j Is the current of the jth ground wire connected to the ith ground electrode; r is R ei.j Is the i-th ground resistance; r is R N The neutral point grounding resistor; x is X N Is the reactance of the arc suppression coil; r is R eli.j Is the ground resistance of the j-th feeder line radiated by the i-th grounding electrode, R' eli.j +R″ eli.j ＝R eli.j ；
For a power grid with a neutral point grounded through an arc suppression coil and a medium resistor, if only the active component of the ground fault current is considered to flow in the power grid conductor and the ground wire, the fault current is mainly distributed in the power grid conductor from the fault point to the neutral point, and the current is the active component I of the current flowing through the neutral point NRe The method comprises the steps of carrying out a first treatment on the surface of the The distribution of the active components of the fault current in the ground of the faulty feeder is mainly composed of 2 parts, the resistive current I of the neutral point NRe Ground current distribution under separate action and fault current active component I of fault point K kRE Ground wire current distribution under independent action; zero sequence voltage U 0 The ground wire current distribution and the neutral point arc suppression coil compensation current under the independent action are reactive components of the current, and are not discussed herein;
A. when the active components of the neutral point current act independently, the fault current I of the fault point K kRe Regarded as open circuit, zero sequence voltage U 0 Regarding as a short circuit, ignoring the reactive component of the zero sequence current, the active component I of the neutral point current NRe With fault point electricityFlow active component I kRe Are equal, i.e. have I NRe ＝-I KRe ＝3I 0Re Moreover, since the lines of the power distribution network are not very long, the middle resistance of the neutral point is far greater than the zero sequence impedance of the lines, and the magnitude of the single-phase grounding fault current mainly depends on the resistance value of the resistance of the neutral point and the impedance of the grounding fault point, so that the power distribution network is K 1 Point or K 2 Point or K 3 Point occurrence of Single-phase ground fault, I NRe And I kRE The value of (I) is almost constant, I NRe After flowing into the grounding grid, the current flows into each grounding electrode along the grounding grid and enters the ground, and the current active components in the ground wire of the fault feeder line are as follows:
the first section main transformer station is connected to the switching station:
the second section switching station is connected between the ring network stations:
the third section loops between the website and the consumer transformer:
definition: r is R cei.j Is I NRel(i-1).j Ground resistance R of injection point ei.j Equivalent resistance of the grounding network of the user, namely the breaking grounding resistance R ei.j Ground wire connected with the power supply grounding net, and the grounding net is observed from the power supply side to the user side, and the grounding resistor R ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R cei.j The method comprises the steps of carrying out a first treatment on the surface of the The resistance is directly measured to obtain: i.e. to disconnect the ground resistance R ei.j Ground wire connected to ground network, i.e. disconnected I NRel(i-1).j Injection line, measuring ground resistance R ei.j The resistance of the upper disconnection point to the ground E is R cei.j The method comprises the steps of carrying out a first treatment on the surface of the Or R is cei.j Calculated by formula (4):
I cNReli.j is neutral point current I NRe The ground current of the jth feeder line radiated by the ith grounding electrode when in the ground; if the longitudinal power supply line exceeds three stages, the calculation can be analogically performed in sequence;
B. fault current active component I of fault point K kRE When acting alone, neutral point current I N Regarded as open circuit, zero sequence voltage U 0 Regarding as a short circuit, the fault current of the fault point K enters the ground through the fault point, returns to the grounding network through each grounding electrode, and returns to the fault point through each ground wire; the fault current only forms a loop and flows in the grounding grid;
if the ground fault occurs in K 1 The current active components from the fault point to the power supply are:
defined herein is: r is R uei.j Is I uReli.j Ground resistance R of injection point ei.j Equivalent resistance of power-supply ground network, i.e. breaking ground resistance R ei.j Ground wire connected with grounding grid of user, and grounding grid is observed from user side to power source side, and grounding electrode resistance R ei.j Considered as an entrance to a single-port network, the equivalent resistance of the single-port network is R uei.j The resistance is measured directly: i.e. to disconnect the ground resistance R ei.j Grounding wire of grounding network connected with user to measure grounding resistance R ei.j The resistance of the upper disconnection point to the ground E is R uei.j The method comprises the steps of carrying out a first treatment on the surface of the Or R is uei.j Calculated by the formula (6);
the current from the fault point to the load side is:
the resistance of the grounding electrode of the main transformer is less than or equal to 0.5 omega, and the number of the radiating cables of the main transformer is large, the resistance of the grounding electrode of the switching station is less than or equal to 2 omega, the resistance of the grounding electrode of the ring website and the user is less than 4 omega, and the number of the radiating cables is small, so that the equivalent resistance R of the grounding electrode of the power supply and the user is high uei.j Is far smaller than the resistance R of the grounding electrode of the load cei.j So the current active component I of the fault point to the load side ckReli.j To be far smaller than the current active component I from the fault point to the power supply side kReli.j ；I ckReli.j And I cNReli.j Is in the opposite direction, the active component I of the ground current Reli.j Is the algebraic sum of 2 currents, essentially the difference of 2; obviously, the current active component of the fault point to the load side in the ground is much smaller than the current active component to the power supply side, and therefore, the current active component of the fault point to the load side in the ground is not discussed further below;
if the ground fault occurs in K 2 The current active components between the fault point and the switching station are as follows:
the current active components between the switching station and the power supply end are as follows:
if the ground fault occurs in K 3 The current active components between the fault point and the ring network station are as follows:
the current active components between the ring website and the switching station are as follows:
the current active components between the switching station and the power supply are as follows:
thus K is 1 When the point ground fault occurs, the fault point reaches the ground current active component of the power supply:
I Rel1.j ＝I cNRel1.j +I k1Rel1.j (13)
K 2 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k2Rel1.j (14)
I Rel2.j ＝I cNRel2.j +I k2Rel2.j (15)
K 3 when the point is grounded, the active components of the ground line current from the fault point to the power supply are as follows in sequence:
I Rel1.j ＝I cNRel1.j +I k3Rel1.j (16)
I Rel2.j ＝I cNRel2.j +I k3Rel2.j (17)
I Rel3.j ＝I cNRel3.j +I k3Rel3.j (18)。
4. the neutral point through arc suppression coil and medium resistance ground network ground fault protection method according to claim 1, characterized in that: epsilon is the fault quantity, the subscript I is the serial number from the power supply to the user, k is the fault point, and I NRe ＝-I kRe ＝3I 0Re Thus, k 1 When the point ground fault occurs, the fault amount from the fault point to the power supply is as follows:
k 2 when the point is grounded, the fault point isThe fault amount of the power supply is as follows:
k 3 when the point is grounded, the fault quantity from the fault point to the power supply is as follows:
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| CN112904232A (en) * | 2021-01-27 | 2021-06-04 | 国网江苏省电力有限公司苏州供电分公司 | Ground fault positioning method and device based on active component of ground wire current |
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| CN112904232A (en) * | 2021-01-27 | 2021-06-04 | 国网江苏省电力有限公司苏州供电分公司 | Ground fault positioning method and device based on active component of ground wire current |
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