CN111130077B - Active power distribution network multi-terminal differential protection method based on amplitude-phase relation - Google Patents

Active power distribution network multi-terminal differential protection method based on amplitude-phase relation Download PDF

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CN111130077B
CN111130077B CN202010095605.9A CN202010095605A CN111130077B CN 111130077 B CN111130077 B CN 111130077B CN 202010095605 A CN202010095605 A CN 202010095605A CN 111130077 B CN111130077 B CN 111130077B
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CN111130077A (en
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吴在军
陈佳铭
桑林卫
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Southeast University
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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
    • H02H7/261—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 involving signal transmission between at least two stations
    • H02H7/263—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 involving signal transmission between at least two stations involving transmissions of measured values
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
    • H02H3/30—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus using pilot wires or other signalling channel
    • H02H3/302—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus using pilot wires or other signalling channel involving phase comparison
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
    • H02H3/30—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus using pilot wires or other signalling channel
    • H02H3/305—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus using pilot wires or other signalling channel involving current comparison
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators

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  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The invention discloses an active power distribution network multi-terminal differential protection method based on amplitude-phase relation, which comprises the following steps: (1) establishing a short-circuit fault characteristic analysis model of three main types of a motor type, a semi-inverter type and an inverter type; (2) analyzing the amplitude-phase relation of three-terminal currents when a multi-terminal line represented by a T-shaped connection line has a fault inside and outside a region according to three types of distributed power supply short-circuit fault models; (3) based on the multi-terminal current amplitude-phase relation, a differential protection scheme is provided, and starting criteria and composite action criteria of multi-terminal current differential protection are set; (4) and the multi-terminal fault information is synchronously transmitted by utilizing a power distribution network multi-terminal information synchronization technology based on optical fiber channel communication. The invention can meet the protection requirement of the multi-terminal power supply network structure and has certain reliability and speed.

Description

Active power distribution network multi-terminal differential protection method based on amplitude-phase relation
Technical Field
The invention relates to the technical field of power distribution network protection, in particular to an active power distribution network multi-terminal differential protection method based on amplitude-phase relation.
Background
The concept of distributed power was generated in the 80's of the 20 th century and refers to the introduction of low capacity power sources near the customer side in power distribution systems. With the maturity of small-scale power generation technologies such as solar energy, wind energy and the like, the demands of small-scale users are met by utilizing scattered resources.
Distributed power generation technology has many benefits, however, traditional power distribution network protection is realized by isolating fault areas through the cooperation of protection equipment according to the radiation characteristics of a power distribution network and following a selectivity principle, so as to reach a minimum power loss range and ensure the reliability of power supply. After the distributed power supply is connected, the unidirectional power flow characteristic of the power distribution network is changed into the bidirectional power flow characteristic, the premise of the traditional protection setting matching does not exist, and how to still achieve the correct matching of protection after the distributed power supply is connected is the research target of distributed power generation protection.
With the continuous development of the distributed power generation technology, the proportion of distributed power sources in a power distribution network is increased. Correspondingly, the topological structure and the trend flow direction of the power distribution network are gradually complicated, the power distribution network is gradually developed into an active power distribution network of a multi-terminal power supply with bidirectional trend from a traditional radial network with unidirectional trend, and T-shaped and multi-terminal distribution lines also gradually appear in the power distribution network. As a mainstream pilot protection strategy, the traditional double-end current differential protection strategy is difficult to adapt to the network structure of multi-end power supply, and has higher risks of normal misoperation and failure operation rejection. Therefore, it is necessary to research an active power distribution network protection strategy for multi-terminal current differential to adapt to the situation.
In order to adapt to the access of a large number of DGs, experts and scholars at home and abroad have already developed a large amount of research work aiming at the protection of related power distribution networks, most of the research is based on single-end or double-end protection, the protection of the distribution network for researching multi-end current is small, and the protection of the multi-end current is mainly researched more in power transmission networks.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an active power distribution network multi-terminal differential protection method based on amplitude-phase relation, which can meet the requirement of increasingly complex power distribution networks and realize reliable action in a protection area and reliable braking of external faults.
In order to solve the technical problem, the invention provides an active power distribution network multi-terminal differential protection method based on amplitude-phase relation, which comprises the following steps:
(1) establishing three main types of distributed power supply short-circuit fault models of a motor type, a semi-inverter type and an inverter type; analyzing the fault characteristics of various distributed power supplies under the fault condition and the influence of the fault characteristics on the amplitude phase of the short-circuit current of the fault point according to the established fault model of the distributed power supplies;
(2) analyzing the amplitude-phase relation of three-terminal currents when a multi-terminal line represented by a T-shaped connection line has a fault inside and outside a region according to the fault characteristics of different types of distributed power supplies; analyzing the amplitude-phase relation between the multi-terminal currents according to different position relations between the fault point and the protected section;
(3) a differential protection scheme based on the multi-terminal current amplitude-phase relation is provided, and starting criteria and composite action criteria of the multi-terminal current differential protection are set; setting a starting criterion and distinguishing a part of external faults, wherein the composite action criterion is the logical sum of two independent criteria;
(4) the method comprises the steps that signal synchronization of a synchronization end and a reference end is achieved by utilizing a power distribution network multi-end information synchronization technology based on optical fiber channel communication; and combining the starting criterion and the composite action criterion to realize the multi-terminal differential protection synchronization of the distribution line.
Preferably, the step (1) is specifically:
(11) equivalence is carried out on the motor type, semi-inverter type and inverter type distributed power supply models:
the motor type DG has inertia, can maintain the electromotive force unchanged when short-circuit fault occurs, and is equivalent to an electric voltage source series end resistor;
the semi-inverter DG is a double-fed induction generator, and when a three-phase short circuit fault occurs, the DG outputs a short circuit current provided for a fault point and comprises a power frequency steady-state component, a power frequency transient component, a rotating speed frequency transient component and a direct current transient component, wherein the rotating speed frequency transient component is ignored and the leakage reactance of a stator and a rotor is ignored;
the inversion type DG can be equivalent to a current source parallel impedance;
(12) carrying out fault characteristic analysis on the motor type, semi-inverter type and inverter type distributed power supply models:
the end resistance of the motor type DG is larger than the equivalent impedance of a system power supply, and at the moment of failure, the short-circuit current of the motor type DG reaches the rated current 6-10 times, but is smaller than the short-circuit current provided by the system; before and after the fault, the phase of the output voltage is approximately equal to the line voltage, and the short-circuit current provided to the short-circuit point is in the same phase with the system short-circuit current;
the equivalent voltage source of the semi-inverter DG does not change before and after the fault, and is similar to the traditional synchronous generator, but the size of the equivalent voltage source is related to factors such as the wind speed of a wind field and the like, so that the equivalent voltage source is difficult to keep constant;
the fault characteristics of the inverter type DG mainly depend on the adopted low voltage ride through strategy; when short circuit occurs, the inverter DG has low-voltage ride through capability and provides reactive support for a distribution network; and determining the maximum short-circuit current amplitude value provided by the inverter type DG to the fault point and the phase difference between the maximum short-circuit current amplitude value and the system short-circuit current according to the overcurrent capacity of the power electronic element of the inverter.
Preferably, the step (2) is specifically:
(21) determining a T-shaped wiring multi-section line as a representative for analyzing a power distribution network powered by a multi-end power supply with bidirectional tide;
(22) dividing the position relation between a fault point and a protected section on the three-terminal line section, wherein the position relation comprises that the fault point is positioned in the protected section, and the upstream and the downstream of the protected section;
(23) determining end current amplitude-phase relation of an active power distribution network section of the multi-end line according to different positions of fault points; and (4) considering the extreme conditions that the DGs in the region are of a motor type, a semi-inverter type and an inverter type DG, making a vector diagram between the three-terminal currents, and obtaining the magnitude-phase relation of the three-terminal currents.
Preferably, the step (3) is specifically:
(31) analyzing the short-circuit current source of each end, comparing the amplitude value, and selecting the larger amplitude value as a starting signal of the multi-end differential protection; the short-circuit currents on the other two sides were normalized:
Figure BDA0002385240610000031
using p1，ρ2To distinguish whether the fault point is located inside the protection zone, wherein IMFor system short-circuit current flowing through side M, IpCircuit provided for P-side through intra-zone DG, INIs the sum of the short-circuit current flowing through the M side and the P side from the N side;
(32) the multi-terminal protection system detects a related signal to start the protection system; based on the fault analysis of the active power distribution network, the current amplitude value close to the end M of the system side in the protected section is used as a protection starting signal:
Figure BDA0002385240610000032
wherein, IMFor system short-circuit current flowing through side M, INThe rated current of the distribution network in normal operation is set, k is a sensitivity coefficient, and the value of k is 1.3-1.5 according to the overcurrent protection characteristic of the three-section protection, so that the protection system can be reliably started;
(33) on the basis of reliable starting of the protection system, the protection system compares the current of the M end with the current of the N end and the current of the P end respectively by using the reference end of the M end to form two independent criteria, namely criterion 1 and criterion 2:
criterion 1:
Figure BDA0002385240610000033
criterion 2:
Figure BDA0002385240610000034
and the logic and the connection of the two independent criteria form a comprehensive action criterion, the comprehensive action criterion is output to a tripping signal, and the circuit breakers at the M, N and P ends are tripped simultaneously.
The invention has the beneficial effects that: (1) the action criterion of the multi-terminal protection provided by the invention comprises a starting criterion and a composite action criterion, wherein the starting criterion not only can be used for starting protection, but also can be used for distinguishing partial faults of fault points positioned at the upstream of a protection area, and has selectivity so as to ensure the rapidity; (2) the action criterion in the provided criteria is the logical AND of the two sub-criteria, so that the reliable action of the zone-inside action and the reliable braking of the zone-outside fault can be ensured; (3) the protection scheme provided by the invention is based on wide-area measurement of the power distribution network, better utilizes the measurement information of the line and the DG, has more flexible setting value, and is suitable for the increasingly complex power distribution network.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Fig. 2 is a schematic diagram of an equivalent circuit of the motor-type distributed power supply model of the invention.
Fig. 3(a) is a schematic diagram of an equivalent circuit of the semi-inverter distributed power supply model according to the present invention.
Fig. 3(b) is a schematic diagram of an equivalent circuit of the semi-inverter distributed power supply model according to the present invention.
Fig. 4 is a schematic diagram of an equivalent circuit of the inverter-type distributed power supply model of the present invention.
Fig. 5 is a schematic diagram of a section upstream of a fault point of an active distribution network of a multi-terminal line of the present invention.
Fig. 6 is a schematic diagram of the vector relationship between the currents in the upstream section of the fault point of the active distribution network of the multi-terminal line.
Detailed Description
As shown in fig. 1, an amplitude-phase relationship-based active power distribution network multi-terminal differential protection method includes the following steps:
(1) establishing a short-circuit fault characteristic analysis model of three main types of a motor type, a semi-inverter type and an inverter type; analyzing the fault characteristics of various distributed power supplies under the fault condition and the influence of the fault characteristics on the amplitude phase of the short-circuit current of the fault point according to the established fault model of the distributed power supplies;
(2) analyzing the amplitude-phase relation of three-terminal currents when a multi-terminal line represented by a T-shaped connection line has a fault inside and outside a region according to the fault characteristics of different types of distributed power supplies; analyzing the amplitude-phase relation between the multi-terminal currents according to different position relations between the fault point and the protected section;
(3) a differential protection scheme based on the multi-terminal current amplitude-phase relation is provided, and starting criteria and composite action criteria of the multi-terminal current differential protection are set; the set starting criterion has the function of distinguishing partial external faults, and the composite action criterion is the logical sum of two independent criteria so as to ensure reliable action and avoid false action;
(4) the multi-terminal information synchronization technology of the power distribution network based on the optical fiber channel communication is utilized to realize the signal synchronization of the synchronization terminal and the reference terminal, and the time delay of the transmission information is adjusted to realize the multi-terminal differential protection synchronization of the distribution line.
The technical scheme of the invention is explained in detail as follows:
step 1: establishing three main types of distributed power supply short-circuit fault models of a motor type, a semi-inverter type and an inverter type, analyzing fault characteristics of various distributed power supplies under a fault condition and influences of the fault characteristics on a fault point short-circuit current amplitude phase, and mainly implementing the following steps:
(1) the motor type, semi-inverter type and inverter type distributed power supply models are equivalent, and equivalent circuits are shown in fig. 2 to 4.
The motor type DG has inertia, can maintain the electromotive force unchanged when short-circuit fault occurs, and can be equivalently used as an electric voltage source EDGSeries end resistance Zdg；
The semi-inverter type DG is a double-fed induction generator, when a three-phase short circuit fault occurs, the DG outputs short circuit current provided for a fault point to be power frequency steady-state component, power frequency transient component, rotating speed frequency transient component and direct current transient component, wherein the rotating speed frequency transient component is ignored, the equivalent circuit diagram 3(a) of the short circuit fault can be obtained by neglecting leakage reactance of a stator and a rotor, and the diagram 3(b) can be obtained by Thevenin equivalent transformation;
the inverter DG is equivalent to a current source IDGParallel impedance ZdgIn which IDGEquivalent amplitude-independent DG output current, IdgEquivalent constrained DG output current, and ZdgEquivalent current splitting under constraint conditions.
(2) Carrying out fault characteristic analysis on the motor type, semi-inverter type and inverter type distributed power supply models:
z of motor type DGdgCompared with the equivalent impedance of a system power supply, the short-circuit current of the power supply is larger than that of the system power supply, and can reach 6-10 times of rated current at the moment of failure but is smaller than the short-circuit current provided by the system; before and after the fault, the phase of the output voltage is approximately equal to the line voltage, and the angle of the phase lag of the short-circuit current provided by the motor type DG to the short-circuit point after the fault is similar to the impedance angle of the distribution line and is in the same phase with the system short-circuit current.
The equivalent voltage source of the semi-inverter DG does not change before and after the fault, and is similar to the traditional synchronous generator, but the size of the equivalent voltage source is related to factors such as the wind speed of a wind field and the like, so that the equivalent voltage source is difficult to keep constant;
the fault characteristics of the inverter type DG mainly depend on the adopted low voltage ride through strategy; when short circuit occurs, the inverter DG has low-voltage ride through capability and provides reactive support for a distribution network; because the overcurrent capacity of power electronic elements of the inverter is limited, the maximum short-circuit current amplitude value provided by the inverter type DG to a fault point is generally restricted to be 1.2-1.5 times of a rated value, and the phase difference between the short-circuit current of the DG and the short-circuit current of a system is-60-70 degrees.
Step 2: analyzing the amplitude-phase relation of three-terminal currents of a multi-terminal line represented by a T-shaped wiring when a fault occurs inside and outside a zone according to different fault characteristics of different types of distributed power supplies, different position relations among fault points and protected zones, and mainly implementing the following steps:
(1) determining a T-shaped wiring multi-section line as a representative for analyzing a power distribution network powered by a multi-end power supply with bidirectional tide;
(2) and dividing the position relation between the fault point and the protected section on the three-terminal line section, wherein the position relation comprises that the fault point is positioned in the protected section and is positioned at the upstream and the downstream of the protected section. Taking the section upstream of the fault point shown in FIG. 5 as an example, the M side flows through the system short-circuit current IMThe P side flows through the short-circuit current I provided by DG in the zonePThe sum I of the short-circuit currents flowing from the M side and the P side on the N sideN。
(3) And determining the end current amplitude-phase relation of the active power distribution network section of the multi-end line according to different positions of fault points. When the fault point is located at the downstream of the protected zone, the in-zone DG is an electric machine type DG, and the I under the extreme condition is consideredP|＝|IMI, when the DG in the region is the inversion type DGMAnd IPThe phase difference is-60 to 70 degrees. At this time, the current phasors at the three terminals M, N and P are shown in FIG. 6, INAnd IMIs between-145 DEG and 150 DEG, INMaximum amplitude of about IM1.7 times of the total weight of the powder. When the fault point is positioned at the upstream of the protected section, considering the extreme condition, the amplitude of the short-circuit current flowing through N is approximately equal to that of the short-circuit current flowing through P, and the phase difference is maximally-70 DEG, IMAnd IPThe absolute value of the phase difference is greater than 75 DEG, and IMAnd INThe absolute value of the phase difference is larger than 145 DEG, IMHas an amplitude of about IN，IP1 of amplitude7 times. When the fault point is located in the protected area, comprehensively considering three types of DGs and IMAnd IPPhase difference of (1)MAnd INThe phase difference is between-60 degrees and 70 degrees, and the amplitudes of the three are equal in consideration of extreme conditions.
And step 3: the differential protection scheme based on the multi-terminal current amplitude-phase relation is provided, the starting criterion and the composite action criterion of the multi-terminal current differential protection are set, and the specific implementation steps are as follows:
(1) and selecting a starting signal of the multi-terminal differential protection. From the analysis of the fault characteristics of the multi-terminal distribution network, it can be found that when the fault and the fault point in the area are located at the downstream of the protected area, the short-circuit current flowing through the end M close to the system power supply side is provided by the system power supply, and when the fault point is located at the upstream of the protected area, the short-circuit current flowing through the end M is the sum of the short-circuit currents provided by all DGs at the downstream. The short-circuit current of the N end is provided by a system power supply only when the fault point is located at the downstream of the protection area, at the moment, the current amplitude is large, and the current amplitude is small because the short-circuit current is provided by a DG at the downstream of the N end under other conditions. The short-circuit current of the P end is only provided by the DG behind the breaker, and the current amplitudes are small. The magnitude of the short-circuit current flowing through the terminal M is a large value in all the possible situations, so the current flowing through the terminal M can be used as a starting signal of the multi-terminal differential protection.
And (3) standardizing the short-circuit current on the other two sides by taking the short-circuit current close to the system side as a reference:
Figure BDA0002385240610000061
using p1，ρ2To distinguish whether the fault point is located inside the protected zone.
(2) And setting a multi-terminal protection starting criterion. The multi-terminal protection system does not detect the amplitude and the phase of current flowing through a circuit breaker at each terminal in real time, but detects a related signal to start the protection system, and based on the fault analysis of the active power distribution network, an article utilizes the current amplitude close to the M terminal at the side of the system in a protected section as a protection starting signal:
Figure BDA0002385240610000062
wherein, IMFor the M side passing through the system short-circuit current, INThe protection system is rated current when a distribution network normally operates, k is a sensitivity coefficient, and the value of k is usually 1.3-1.5 according to the overcurrent protection characteristic of three-section protection so as to realize reliable starting of the protection system;
(3) and setting a multi-terminal protection composite action criterion. On the basis of reliable starting of the protection system, the protection system compares the current of the M end with the current of the N end and the current of the P end respectively by using the reference end of the M end to form two independent criteria, namely criterion 1 and criterion 2:
criterion 1:
Figure BDA0002385240610000071
criterion 2:
Figure BDA0002385240610000072
and the logic and the connection of the two independent criteria form a comprehensive action criterion, the comprehensive action criterion is output to a tripping signal, and the circuit breakers at the M, N and P ends are tripped simultaneously to prevent the misoperation of protection.
R of criterion 11，θ1And R of criterion 22，θ2The method is determined by fault analysis of the active power distribution network, and parameter setting is mainly used for ensuring that a criterion can reliably and quickly act when a fault occurs in a zone and effectively brake when a fault occurs outside the zone, namely, the fault outside the zone which can cause protection misoperation is avoided.
INAnd IMThe phase difference is-60-70 deg. in case of fault in area, the amplitude is equal in extreme case, | I in normal caseNI is less than IML, |; in case of an out-of-range fault, the absolute value of the phase difference between the two is greater than 145 DEG, and in extreme cases, INHas an amplitude of at most about IM1.7 times of that ofNHas a minimum amplitude of about IM0.588 times of the total linear amplitude, the amplitude detection error caused by considering TA is within +/-10%, and the extreme isIn the case where the M side is + 10% and the N side is-10%, then INHas a minimum amplitude of about IM0.588 by 90%/110% — 0.48 times. Therefore, the R of the criterion 1 is taken in summary1，θ10.48 and 145, respectively.
In the same way, IPAnd IMThe phase difference in the case of the fault in the area is also between-60 degrees and 70 degrees, and the amplitude of the phase difference is equal in the extreme case, IPI is less than IML. In case of an out-of-range fault, IPAnd IMIs greater than 75 deg., consider IPIn the extreme case of the inverter type DG, IPHas a minimum amplitude of about IM0.2 times of, and then considering the TA error, IPHas a minimum amplitude of about IM0.16 times of. Therefore, R of criterion 2 is summarized2，θ20.16 and 90, respectively.
In addition, when the fault point is located at the upstream of the protected section, the current flowing through the M side is the sum of all DG currents at the downstream of the M side, and when the DG capacity is small or is limited by a relevant control strategy, the short-circuit current provided to the short-circuit point is small, the amplitude of the short-circuit current may be lower than the threshold value of protection starting, so that protection is not started, but when the fault point is located outside the zone, the protection system may not be started.
And 4, step 4: the method comprises the following steps of utilizing a power distribution network multi-terminal information synchronization technology based on optical fiber channel communication to realize signal synchronization of a synchronization terminal and a reference terminal and realize multi-terminal differential protection synchronization of a distribution line, wherein the method comprises the following specific steps:
(1) and the signal synchronization of the synchronization end and the reference end is realized by utilizing a power distribution network multi-end information synchronization technology based on optical fiber channel communication.
Sampling deviation:
Figure BDA0002385240610000073
channel delay:
Figure BDA0002385240610000081
synchronous end at t1When a synchronous command is sent out, the reference end is at t2At the moment a synchronization command is received, at t3Sending a reference command to a synchronous end at time, wherein the synchronous end is at t4Receiving reference command at the moment, and calculating sampling deviation t according to the reference commandoffsetAnd channel delay tdelay. And the synchronization end adjusts the sampling time by using the sampling deviation to realize the signal synchronization with the reference end.

Claims (3)

1. A multi-terminal differential protection method for an active power distribution network based on amplitude-phase relation is characterized by comprising the following steps:
(1) establishing three main types of distributed power supply short-circuit fault models of a motor type, a semi-inverter type and an inverter type; analyzing the fault characteristics of various distributed power supplies under the fault condition and the influence of the fault characteristics on the amplitude phase of the short-circuit current of the fault point according to the established fault model of the distributed power supplies;
(2) analyzing the amplitude-phase relation of three-terminal currents when a multi-terminal line represented by a T-shaped connection line has a fault inside and outside a region according to the fault characteristics of different types of distributed power supplies; analyzing the amplitude-phase relation between the multi-terminal currents according to different position relations between the fault point and the protected section;
(3) a differential protection scheme based on the multi-terminal current amplitude-phase relation is provided, and starting criteria and composite action criteria of the multi-terminal current differential protection are set; setting a starting criterion and distinguishing a part of external faults, wherein the composite action criterion is the logical sum of two independent criteria; the method specifically comprises the following steps:
(31) analyzing the short-circuit current source of each end, comparing the amplitude value, and selecting the larger amplitude value as a starting signal of the multi-end differential protection; the short-circuit currents on the other two sides were normalized:
Figure FDA0003498044140000011
using p1，ρ2To distinguish whether the fault point is located inside the protection zone, wherein IMFor system short-circuit current flowing through side M, IpCircuits provided for DG in the P-side flow-through area, INIs the sum of the short-circuit current flowing through the M side and the P side from the N side;
(32) the multi-terminal protection system detects a related signal to start the protection system; based on the fault analysis of the active power distribution network, the current amplitude value close to the end M of the system side in the protected section is used as a protection starting signal:
Figure FDA0003498044140000012
wherein, INThe rated current of the distribution network in normal operation is set, k is a sensitivity coefficient, and the value of k is 1.3-1.5 according to the overcurrent protection characteristic of the three-section protection, so that the protection system can be reliably started;
(33) on the basis of reliable starting of the protection system, the protection system compares the current of the M end with the current of the N end and the current of the P end respectively by using the reference end of the M end to form two independent criteria, namely criterion 1 and criterion 2:
criterion 1:
Figure FDA0003498044140000013
criterion 2:
Figure FDA0003498044140000014
the logic and the connection of the two independent criteria form a comprehensive action criterion, the comprehensive action criterion is output to a tripping signal, and the circuit breakers at M, N and P ends are tripped simultaneously;
(4) the method comprises the steps that signal synchronization of a synchronization end and a reference end is achieved by utilizing a power distribution network multi-end information synchronization technology based on optical fiber channel communication; and combining the starting criterion and the composite action criterion to realize the multi-terminal differential protection synchronization of the distribution line.
2. The amplitude-phase relationship-based active power distribution network multi-terminal differential protection method according to claim 1, wherein the step (1) is specifically:
(11) equivalence is carried out on the motor type, semi-inverter type and inverter type distributed power supply models:
the motor type DG has inertia, can maintain the electromotive force unchanged when short-circuit fault occurs, and is equivalent to an electric voltage source series end resistor;
the semi-inverter type DG is a double-fed induction generator, when a three-phase short circuit fault occurs, the DG outputs a short circuit current provided for a fault point, wherein the short circuit current comprises a power frequency steady-state component, a power frequency transient-state component, a rotating speed frequency transient-state component and a direct current transient-state component, the rotating speed frequency transient-state component is ignored and the leakage reactance of a stator and a rotor is ignored;
the inversion type DG can be equivalent to a current source parallel impedance;
(12) carrying out fault characteristic analysis on the motor type, semi-inverter type and inverter type distributed power supply models:
the end resistance of the motor type DG is larger than the equivalent impedance of a system power supply, and at the moment of failure, the short-circuit current of the motor type DG reaches the rated current 6-10 times, but is smaller than the short-circuit current provided by the system; before and after the fault, the phase of the output voltage is approximately equal to the line voltage, and the short-circuit current provided to the short-circuit point is in the same phase with the system short-circuit current;
the equivalent voltage source of the semi-inverter DG does not change before and after the fault, and is similar to the traditional synchronous generator, but the size of the equivalent voltage source is related to factors such as the wind speed of a wind field and the like, so that the equivalent voltage source is difficult to keep constant;
the fault characteristics of the inverter type DG mainly depend on the adopted low voltage ride through strategy; when short circuit occurs, the inverter DG has low-voltage ride through capability and provides reactive support for a distribution network; and determining the maximum short-circuit current amplitude value provided by the inverter type DG to the fault point and the phase difference between the maximum short-circuit current amplitude value and the system short-circuit current according to the overcurrent capacity of the power electronic element of the inverter.
3. The amplitude-phase relationship-based active power distribution network multi-terminal differential protection method according to claim 1, wherein the step (2) is specifically:
(21) determining a T-shaped wiring multi-section line as a representative for analyzing a power distribution network powered by a multi-end power supply with bidirectional tide;
(22) dividing the position relation between a fault point and a protected section on the three-terminal line section, wherein the position relation comprises that the fault point is positioned in the protected section, and the upstream and the downstream of the protected section;
(23) determining end current amplitude-phase relation of an active power distribution network section of the multi-end line according to different positions of fault points; and (4) considering the extreme conditions that the DGs in the region are of a motor type, a semi-inverter type and an inverter type DG, making a vector diagram between the three-terminal currents, and obtaining the magnitude-phase relation of the three-terminal currents.
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