CN106684844B - Power distribution network island identification method - Google Patents

Abstract

The invention discloses a power distribution network island identification method which is mainly suitable for an active power distribution network with a main network adopting a small-resistance grounding mode and a distributed power supply adopting an ungrounded mode, and island detection is carried out by detecting the change of zero-sequence voltage of a grid-connected point, namely a PCC point, of the distributed power supply. No matter whether the voltage amplitude of the PCC point line is within a preset range or not, the method and the device can quickly determine the position of the single-phase ground fault according to the change of the zero sequence voltage of the PCC point and carry out island identification, and the island detection blind area is small.

Description

An island identification method for distribution network

technical field

The invention relates to the technical field of distribution network island detection, in particular to a distribution network island identification method.

Background technique

Islanding means that when the power grid is interrupted due to electrical failures, misoperations, etc., the grid-connected power generation system fails to detect the power outage and disconnects from the grid, and continues to supply power to the grid, so that the grid-connected power generation system and the surrounding loads form an unsatisfactory environment. An isolated power generation system with controlled self-sufficiency. Island operation can be divided into planned island and unplanned island. Planned islands can effectively play the positive role of DG, reduce losses caused by power outages, and improve power supply reliability; unplanned islands may cause casualties, cause serious harm to electrical equipment and users, and threaten the safe and stable operation of the power system. Therefore, it is of great significance to the entire grid-connected system to quickly and effectively detect islands and avoid the occurrence of non-island phenomena.

At present, experts and scholars at home and abroad have done in-depth research on the islanding detection of distributed generation systems, and proposed a variety of islanding detection methods. According to the detection location, these methods can be divided into two categories: remote detection methods on the grid side and local detection methods on the distributed generation side. Remote detection mainly uses radio communication to detect isolated islands, which requires additional equipment, low economic efficiency, and complicated operation. Due to the high input cost, this method has not been widely used in small DGs, and it is suitable for grid-connection of high-power distributed power sources. Local detection is to detect islanding by monitoring the voltage and current signals of the DG terminal, which can be further divided into two types, one is a passive method, that is, by directly measuring the change of DG output power or the change of PCC point voltage or frequency to determine whether it has occurred Islanding; the other is the active approach, where a disturbance is injected into the grid and islanding is detected by the corresponding changes in voltage, frequency, and impedance in the system caused by the disturbance. The passive method is widely used because it does not require additional hardware circuits, is low in cost, and is easy to implement.

Commonly used passive islanding detection techniques mainly include: over/undervoltage detection method (OVP/UVP), over/underfrequency detection method, voltage harmonic detection method, voltage phase mutation detection method, etc. Although the active method has a small detection blind area and high detection accuracy, it introduces disturbances, which cause unnecessary transient responses and degrade the power quality of the distribution network; its control algorithm is complex and difficult to apply in practice; Under different load properties, the detection effect is very different, and even fails in severe cases. Commonly used active islanding detection techniques mainly include: impedance measurement method, reactance insertion method, output power disturbance method, etc.

The over/under voltage island detection method (OVP/UVP) means that when the voltage amplitude of the PCC point is not in the pre-set normal operation area (U ₁ , U ₂ ), the DG will stop the grid-connected operation immediately by sending a control signal, so as to A passive islanding detection method to achieve the purpose of anti-islanding operation. U ₁ and U ₂ are the minimum and maximum voltage amplitudes allowed by the grid-connected power generation technical standard for the system to operate normally. According to the distributed grid-connected power generation system shown in Figure 1, when the grid is operating normally, the circuit breaker QF is closed. At this time, due to the clamping effect of the grid, the voltage at the PCC point will not be abnormal. When the islanding occurs, the circuit breaker QF is disconnected. If the active power supplied by DG is not equal to the active power consumed by the local load, there will be ΔP≠0, and the voltage amplitude of the PCC point will be offset. If this offset is large enough, The occurrence of isolated islands can be detected. This method is simple in principle, easy to implement, the best economy, and has no impact on power quality. It only needs to use the existing detection parameters to judge, without adding any hardware circuit.

However, when the PCC point voltage amplitude deviation is small, that is, the system works within the allowable normal voltage range, the over/undervoltage islanding detection method will fail. Although this method is easy to implement, it contains a considerable detection blind area.

The specific analysis of the detection blind area is as follows: When the DG adopts the constant power control mode, the ratio of the active power P _load consumed by the local load to the active power P provided by the distributed generation device is:

U _PCC indicates the effective value of the PCC point voltage when the DG is normally connected to the grid, and U' _PCC indicates the effective value of the PCC point voltage when the DG is operating in an island.

Under the normal grid-connected operation of the distributed generation system, the active power provided by the grid to the local load can be expressed as:

ΔP＝P _load -P

Before the island effect occurs, the active power mismatch degree of the distributed generation system is:

When the DG is working in the normal allowable voltage range (U ₁ , U ₂ ), the ratio range of the active power provided by the grid and the DG to the local load is:

According to the islanding effect detection time standard of distributed power generation devices stipulated in China, the upper and lower limits of the voltage amplitude of the DG grid-connected system during normal operation are U ₂ = 110% U _n , U ₁ = 85% U _n , which can be obtained by substituting into the formula The island detection dead zone (NDZ) of the over/under voltage method of DG under constant power control mode is:

Similarly, when DG adopts constant current control mode, the range of system active power mismatch before islanding is:

That is, the island detection blind zone of the over/undervoltage method of DG under the constant current control mode is:

To sum up, in the prior art, there is still no effective solution to the problem of detection blind spots in the traditional passive island detection technology.

Contents of the invention

In order to solve the deficiencies of the prior art, the purpose of the present invention is to improve the islanding detection problem when a single-phase grounding fault occurs in a small resistance grounding system containing distributed power sources. Based on the analysis of the traditional passive islanding detection method, a method using fault A detection scheme for judging whether islanding occurs by changing the zero-sequence voltage of the DG grid-connected point (PCC point) before and after the main grid protection when it occurs. The invention takes into account the advantages of simple principle, good economy and no influence on power quality of the passive detection method, and is a supplement to the traditional passive island detection technology.

The invention provides a distribution network island identification method, which is mainly applicable to the active distribution network where the main network adopts a small resistance grounding mode and the distributed power source adopts an ungrounded mode. The change of zero-sequence voltage is used for islanding detection, including:

If the zero-sequence voltage at the PCC point is always zero, then the system is running normally without failure;

If it is detected that the zero-sequence voltage amplitude of the PCC point suddenly changes from 0 to a value greater than or equal to the threshold value U _set3 at a certain moment, a single-phase ground fault occurs in the system at this moment;

After the fault lasts for a period of time, if it is detected that the zero-sequence voltage at the PCC point persists and mutates to a larger value again on the basis of being greater than or equal to the threshold value U _set1 , and the amplitude after the mutation is greater than or equal to the threshold value U _set2 , then At this time, the fault point is located in the isolated island area, and after the fault occurs, the main network protection action of the system forms an isolated island;

If it is detected that the zero-sequence voltage amplitude of the PCC point changes from the previous larger value greater than or equal to U _set3 to a value smaller than the threshold value U _set4 , then the fault point is located outside the island area at this time, and after the fault occurs, the system main Network protection action to remove the fault, wherein, U _set2 >U _set1 >U _set3 >U _set4 .

Further, the active distribution network is equipped with a circuit breaker QF at the outgoing line of each line, and a voltage transformer is installed at the PCC point for detecting the zero-sequence voltage of the PCC point.

Further, in the active distribution network, the main network adopts a small-resistance grounding method, and the DG adopts an ungrounded method. F ₁ and F ₂ represent two fault points at different locations, wherein F ₁ is located between the bus bar of line 1 and the PCC point F ₂ is located on line 2, the distance between the PCC point and the bus is L; the distance between the fault point and the main grid power supply is L ₁ ; the distance between the fault point and the PCC point is L ₂ , and R ₁ is the neutral point pair on the main grid side ground resistance.

Further, when the system is running normally, the circuit breakers QF1 and QF2 do not operate, and the zero-sequence voltage at the PCC point is always zero.

Furthermore, when a single-phase ground fault occurs in the system and the fault point is located in the island area, before the circuit breaker QF1 trips, the zero-sequence voltage amplitude of the PCC point is greater than or equal to U _set1 ; after a period of time, QF1 trips, and the PCC point zero The sequence voltage continues to exist and suddenly changes to a value greater than or equal to U _set2 on the original basis. According to the present invention, it can be determined that an island is formed at this time.

Further, when the fault point is outside the island area, before the circuit breaker QF2 trips, the amplitude of the zero-sequence voltage at the PCC point is greater than or equal to U _set3 ; after a period of time when QF2 trips, the zero-sequence voltage at the PCC point is less than U _set4 , In the range close to zero, according to the present invention, it can be judged that the fault is cut off at this time.

Furthermore, when _a single-phase ground fault occurs at point F1, before the main network protection action is obtained, the ground fault composite sequence network diagram of the distribution network including the rotating DG small resistance grounding method is obtained, and the positive sequence network diagram of the main network side is obtained according to the composite sequence network diagram. , negative sequence, zero sequence impedance, and positive sequence, negative sequence, zero sequence impedance on the DG side, and based on this, calculate the fault point current in the grid-connected state of DG, and obtain the zero sequence voltage at PCC point accordingly. When single-phase grounding occurs In the event of a fault, after the main network protection action, the circuit breaker trips. At this time, the DG forms an island together with the surrounding loads.

Furthermore, when calculating the fault point current in the DG grid-connected state, considering that the DG capacity connected to the distribution network is small, the grid-connected transformer and DG's own impedance are generally large, and the zero-sequence impedance Z' of the DG side _a(0) is a larger value, so:

Among them, Z _a(1) , Z _a(2) and Z _a(0) are the positive sequence, negative sequence and zero sequence impedances of the main grid side respectively, Z' _a(1) , Z' _a(2) , Z ' _a(0) are the positive sequence, negative sequence and zero sequence impedances on the DG side respectively.

Furthermore, when a phase- _A ground fault occurs at point F2 of the system, the zero-sequence voltage of PCC point is still a relatively large value before the main network protection action, and after the main network protection action, line 1 returns to normal operation. In theory, the line does not contain the zero-sequence voltage, considering the influence of the error, the zero-sequence voltage of the PCC point is within a range close to zero at this time.

Further, the distribution network island identification method is complementary to the existing over/undervoltage island detection method. When a single-phase ground fault occurs in the system and the PCC point-to-line voltage amplitude exceeds the preset normal operating range, no matter Whether the fault point is located in the island area or outside the island area, the over/under voltage detection method can quickly detect the island;

When the fault point is located in the island area and the DG capacity and the load capacity in the island area are well matched, and the over/under voltage protection element refuses to operate, because the fault has not been cleared and the zero-sequence voltage at the PCC point continues to exist, the island identification method of the distribution network of the present invention Islanding is accurately detected when over/undervoltage detection fails.

Compared with prior art, the beneficial effect of the present invention is:

Compared with the remote detection method on the power grid side, the present invention does not need to add additional hardware circuits or independent protection relays, has no interference to the power grid, and has no impact on power quality; compared with the active method, the present invention does not need to introduce disturbances, It will not cause unnecessary transient response, and the control principle is simple and easy to implement.

The present invention complements the content of the existing over/undervoltage island detection method. When a single-phase ground fault occurs in the system and the PCC point-to-line voltage amplitude exceeds the preset normal operating range, regardless of whether the fault point is located in the island area or outside the island area, the over/undervoltage detection method can quickly detect the island. However, when the DG capacity in the island area matches well with the load capacity, the voltage change at the PCC point before and after the main grid protection is small, which is not enough to activate the over/under voltage protection element, and the island detection will fail; in addition, in order to prevent the grid voltage from Normal fluctuations cause malfunctions, and the threshold value of over/undervoltage protection cannot be set too low, resulting in a large detection blind zone in the over/undervoltage detection method. When the fault point is located in the island area and the DG capacity in the island area matches well with the load capacity, and the over/under voltage protection element refuses to operate, since the fault has not been cleared and the zero-sequence voltage at the PCC point continues to exist, the present invention can prevent over/under voltage Accurately detect islands when pressure detection fails.

In a word, regardless of whether the PCC point-to-line voltage amplitude is within the preset range or not, the present invention can quickly determine the location of the single-phase ground fault and identify the island according to the change of the zero-sequence voltage at the PCC point, and the islanding detection blind zone is small. The invention is mainly applicable to the active distribution network in which the main network adopts a small resistance grounding mode and the DG adopts an ungrounded mode.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application, and do not constitute improper limitations to the present application.

Figure 1 is a schematic diagram of a distributed grid-connected power generation system;

Figure 2 is a schematic diagram of a grounding fault in a distribution network with a DG small resistance grounding method;

Figure 3 is a composite sequence network diagram of a grounding fault in a distribution network with a rotating DG small resistance grounding method;

Figure 4 is a sequence network diagram of an isolated island;

Fig. 5 is a curve diagram of zero-sequence voltage change at fault PCC point at _{Rf =} 5ΩF1;

Fig. 6 is a curve diagram of the zero sequence voltage variation curve of the PCC point at 2.15-2.4s when _Rf = 5ΩF ₁ fault;

Fig. 7 is a curve diagram of the zero sequence voltage change curve of the PCC point at 7.15-7.4s when R _f = 5ΩF ₁ fault;

Fig. 8 is a curve diagram of zero-sequence voltage change at fault PCC point at _Rf = _5ΩF2 ;

Fig. 9 is a curve diagram of zero-sequence voltage change at PCC point at 2.15-2.4s for a fault at _Rf = _5ΩF2 ;

Fig. 10 is a curve diagram of zero-sequence voltage change at fault PCC point at _{Rf =} 50ΩF1;

Fig. 11 is a curve diagram of the zero sequence voltage variation curve of the PCC point at 2.15-2.4s when _Rf = 50ΩF ₁ fault;

Fig. 12 is the curve diagram of the zero sequence voltage change at the PCC point at 7.15-7.4s of the fault at R _f = 50ΩF ₁ ;

Fig. 13 is a curve diagram of zero-sequence voltage change at fault PCC point at _Rf = _50ΩF2 ;

Fig. 14 is a curve diagram of the zero sequence voltage change at the PCC point at 2.15-2.4s when _Rf = 50ΩF ₂ faults;

Fig. 15 is a curve diagram of the zero-sequence voltage change at the fault PCC point at R _f = 100ΩF ₁ ;

Figure 16 is a curve diagram of the zero sequence voltage change at the PCC point at 2.15-2.4s for _a fault at _Rf = 100ΩF1;

Fig. 17 is a curve diagram of the zero-sequence voltage change at the PCC point at 7.15-7.4s of a fault at R _f = 100ΩF ₁ ;

Fig. 18 is a curve diagram of the zero-sequence voltage change at the fault PCC point at _Rf = _100ΩF2 ;

Fig. 19 is a curve diagram of zero-sequence voltage change at PCC point at 2.15-2.4s for a fault at _Rf = _100ΩF2 ;

Fig. 20 is a curve diagram of the zero-sequence voltage change at the fault PCC point at _{Rf =} 500ΩF1;

Fig. 21 is a curve diagram of zero-sequence voltage change at PCC point at 2.15-2.4s for a fault at R _f = 500ΩF ₁ ;

Fig. 22 is a curve diagram of zero-sequence voltage change at PCC point at 7.15-7.4s of fault at R _{f =} 500ΩF1;

Fig. 23 is a curve diagram of the zero-sequence voltage change at the fault PCC point at _Rf = _500ΩF2 ;

Fig. 24 is a curve diagram of the zero-sequence voltage change at the PCC point at 2.15-2.4s for a fault at _Rf = _500ΩF2 ;

Fig. 25 is a curve diagram of the zero-sequence voltage change at the fault PCC point at _{Rf =} 1000ΩF1;

Figure 26 is a curve diagram of the zero sequence voltage change at the PCC point at 2.15-2.4s for _a fault at _Rf = 1000ΩF1;

Figure 27 is a curve diagram of the zero sequence voltage change at the PCC point at 7.15-7.4s for a fault at R _f = 1000ΩF ₁ ;

Fig. 28 is a curve diagram of zero-sequence voltage change at fault PCC point at _Rf = _1000ΩF2 ;

Fig. 29 is a curve diagram of zero-sequence voltage change at PCC point at 2.15-2.4s of a fault at R _f = 1000ΩF ₂ .

Detailed ways

It should be pointed out that the following detailed description is exemplary and intended to provide further explanation to the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used here is only for describing specific implementations, and is not intended to limit the exemplary implementations according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural, and it should also be understood that when the terms "comprising" and/or "comprising" are used in this specification, they mean There are features, steps, operations, means, components and/or combinations thereof.

As introduced in the background technology, there is an existing over/under voltage island detection method in the prior art. When the DG capacity in the island area matches well with the load capacity, the PCC point voltage changes little before and after the main network protection. If it is not enough to activate the over/under voltage protection element, the islanding detection will fail. In order to solve the above technical problems, this application proposes a distribution network islanding identification method.

In a typical implementation of the present application, a distribution network island identification method is provided. A schematic diagram of an active distribution network with a DG small resistance grounding method using the island detection method of the present invention is shown in Figure 2.

Among them, the main network adopts a small resistance grounding method, and the DG adopts an ungrounded method. F ₁ and F ₂ represent two fault points in different locations, among which F ₁ is located between the busbar of line 1 and the PCC point, and F ₂ is located in line 2. The distance between the PCC point and the bus bar is L; the distance between the fault point and the main network power supply is L ₁ ; the distance between the fault point and the PCC point is L ₂ . R ₁ is the neutral point-to-ground resistance on the main grid side, and the domestic grid is generally 10Ω.

There is a circuit breaker (QF) at the outlet of each line, which is mainly composed of three basic parts, namely contacts, arc extinguishing system and various releases, including overcurrent releases, loss of voltage (undervoltage releases) voltage) release, thermal release, shunt release and free release.

The PCC point is equipped with a voltage transformer for detecting the zero-sequence voltage of the PCC point.

Among them, the voltage transformer for measurement is generally a single-phase double-coil structure, and its primary side voltage is the voltage to be measured. It can be used in single-phase, or two can be connected into a V-V shape for three-phase use. The primary side of the voltage transformer is generally multi-tap to meet the needs of measuring different voltages. The voltage transformer for protective grounding also has a third coil, which is called a three-coil voltage transformer. The third coil of the three phases is connected into an open triangle, and the two terminals of the open triangle are connected with the voltage coil of the grounding protection relay. During normal operation, the three-phase voltage of the power system is symmetrical, and the sum of the three-phase induced electromotive forces on the third coil is zero. When a single-phase ground fault occurs, the neutral point will be displaced, and the zero-sequence voltage will be detected between the terminals of the open triangle, and the relay will be activated to protect the power system. When zero-sequence voltage appears in the coil, zero-sequence magnetic flux will appear in the corresponding iron core. For this reason, this kind of three-phase voltage transformer adopts side yoke type iron core (10KV and below) or adopts three single-phase voltage transformers.

In order to enable those skilled in the art to understand the technical solution of the present application more clearly, the technical solution of the present application will be described in detail below in combination with specific examples and comparative examples.

_A single-phase ground fault occurs at point F1:

Taking the ground fault of phase A at point F ₁ as an example, consider the fault excess resistance R _f . Before the main network protection action, the ground fault composite sequence network of the distribution network including the rotating DG small resistance grounding method is shown in Figure 3. In the figure: Z _S(1) and Z _S(2) are respectively the sum of the positive sequence and negative sequence impedances of the main network power supply and the transformer, Z _S(1) = Z _S(2) ; Z _{S(0) is} the main Zero-sequence impedance of the grid-grounded transformer; Z _T is the impedance of the grid-connected transformer on the DG side; Z _L1(1) and Z _L1(2) are the positive-sequence and negative-sequence impedances of the line from the fault point to the main power supply, respectively, and Z _L1(1) ＝Z _L1(2) ; Z _L2(1) and Z _L2(2) are the positive sequence and negative sequence impedances of the line from the fault point to PCC respectively, Z _L2(1) ＝Z _L2(2) ; Z _L1(0) and Z _L2(0) are the zero-sequence impedance of the line from the fault point to the main power supply and PCC, respectively; Z _DG(1) and Z _DG(2) are the positive-sequence and negative-sequence impedances of the rotating DG, respectively; Positive sequence, negative sequence and zero sequence fault currents on main network side and DG side respectively; It is the positive (negative or zero) sequence current of the fault point, which is equal to the current of the fault point 1/3; the arrow indicates the reference direction of each current; An additional voltage source for the fault point; Z _N is the zero-sequence impedance of the neutral point on the DG side to ground, when DG is not grounded, |Z _N |→∞; is the equivalent capacitance in the island.

The positive sequence, negative sequence and zero sequence impedance Z _a(1) , Z _a(2) and Z _a(0) of the main grid side are respectively:

The positive sequence, negative sequence and zero sequence impedances Z' _a(1) , Z' _a(2) and Z' _a(0) of the DG side are respectively:

Fault point current under DG grid-connected state for:

Considering that the capacity of the DG connected to the distribution network is small, the impedance of the grid-connected transformer and DG is generally large, and the zero-sequence impedance Z' _a(0) of the DG side is a relatively large value, so generally:

At this time, the fault point current:

The zero-sequence current I _a(0) of the main grid side and the DG side, I' _a(0) is not only the zero-sequence current of the lines on each side, but also the zero-sequence current from the neutral point to the ground on each side (the neutral point to the ground current 1/3), which can be expressed as:

At this time, the zero-sequence voltage of PCC point is:

When a single-phase ground fault occurs in the system, after the main network protection action, the circuit breaker QF1 trips, and the composite sequence network of the system is shown in Figure 4. At this point, the DG forms an island together with the surrounding loads.

At this time, the zero-sequence voltage of PCC point is:

A single _- phase ground fault occurs at point F2:

In the same way, it can be analyzed that when the A _- phase ground fault occurs at point F2 of the system, the zero-sequence voltage of PCC point is still a relatively large value before the main network protection action. After the main network protection action, line 1 resumes normal operation. Theoretically, there is no zero-sequence voltage in the line. Considering the influence of errors, the zero-sequence voltage at PCC point is within a range close to zero.

Take excess resistance R _f =5Ω, 50Ω, 100Ω, 500Ω, 1000Ω respectively, L=20km, L ₁ =10km, L ₂ =10km. R conducts ground fault modeling and simulation on the small resistance grounding distribution network with DG, and the zero-sequence voltage curves of PCC points before and after the main network protection of single-phase ground faults at F ₁ and F ₂ are shown in Figure 5-29.

The specific working principle of the system in Figure 2 above is as follows:

When the system is running normally, the circuit breakers QF1 and QF2 do not act, and the zero-sequence voltage at PCC is always zero.

When a single-phase ground fault occurs in the system and the fault point is located in the island area, before the circuit breaker QF1 trips, the zero-sequence voltage amplitude of the PCC point is greater than or equal to U _set1 ; after a period of time, QF1 trips, and the zero-sequence voltage of the PCC point continues It exists and is mutated to a value greater than or equal to _{Use set2} on the original basis. According to the present invention, it can be determined that an island is formed at this time.

When the fault point is outside the island area, before the circuit breaker QF2 trips, the amplitude of the zero-sequence voltage at the PCC point is greater than or equal to U _set3 ; after a period of time when QF2 trips, the zero-sequence voltage at the PCC point is less than U _set4 and close to zero Within the range, according to the present invention, it can be determined that the fault is removed at this time.

To sum up, when a single-phase ground fault occurs in the system and the fault point is located in the island area, the magnitude of the secondary side zero-sequence voltage detected by the voltage transformer at the PCC point before the main network protection action is greater than or equal to the threshold value U _set1 (U _set1 ＝105.7V); islands are formed after the main network protection action, the zero-sequence voltage of the PCC point continues to exist and mutates to a larger value on the original basis, and the amplitude after the mutation is greater than or equal to the threshold value U _set2 (U _set2 = 2559V).

When the fault point is outside the island area, the amplitude of the zero-sequence voltage of the PCC point before the main network protection action is greater than or equal to the threshold value U _set3 (U _set3 = 75.84V); after the main network protection action, the amplitude of the zero-sequence voltage of the PCC point The sudden change is to a value smaller than the threshold value U _set4 (U _set4 =15V), within a range close to zero.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, there may be various modifications and changes in the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Claims (9)

1. a kind of power distribution network isolated island recognition methods, characterized in that be primarily adapted for use in major network using low resistance grounding mode, distribution Power supply uses the active power distribution network of earth-free mode, by the change for detecting distributed generation resource grid entry point, that is, PCC point residual voltage Change to carry out isolated island detection, comprising:

If PCC point residual voltage is always zero, system normal operation does not break down at this time；

If detecting, PCC point residual voltage amplitude is at a time sported by 0 more than or equal to threshold value U_set3Value, then at this When etching system occur singlephase earth fault；

After failure continues for some time, if detecting, PCC point residual voltage continues to exist and is being more than or equal to threshold value U_set1Base Bigger value is sported on plinth again, the amplitude after mutation is more than or equal to threshold value U_set2, then fault point is located at isolated island area at this time In domain, and system major network protection act after the failure occurred, form isolated island；

If detecting, PCC point residual voltage amplitude is more than or equal to U by the larger value before_set3It sports and is less than threshold value U_set4's Value, then fault point is located at outside the isolated island region at this time, and system major network protection act after the failure occurred, cuts off failure, In, U_set2>U_set1>U_set3>U_set4；

The power distribution network isolated island recognition methods is complementary with existing mistake/under-voltage isolated island detection method content, when single-phase connect occurs for system When earth fault and PCC dotted line voltage magnitude exceed preset normal operation range, no matter fault point is located in isolated island region Or outside isolated island region, mistake/under-voltage detection method can quickly detect isolated island；

When fault point is located in isolated island region and DG capacity matches well with load capacity in isolated island region, mistake/under-voltage protection member When part tripping, since failure is not yet removed, PCC point residual voltage persistently exists, and accurately examines in mistake/under-voltage detection method failure Isolated island is measured, DG is distributed generation resource.

2. a kind of power distribution network isolated island recognition methods as described in claim 1, characterized in that the active power distribution network is in every line It is circuit breaker Q F1, QF2 that the outlet on road, which is equipped with circuit breaker Q F, and PCC point is equipped with voltage transformer, for detecting PCC point Residual voltage, circuit breaker Q F1 are located at 1 outlet of route, and circuit breaker Q F2 is located at 2 outlet of route.

3. a kind of power distribution network isolated island recognition methods as claimed in claim 2, characterized in that major network is adopted in the active power distribution network With low resistance grounding mode, DG uses earth-free mode, and route 1, route 2, major network power supply are connected to bus, and PCC point is located at On route 1, F₁, F₂Indicate 2 different location fault points, wherein F₁Between route 1 and PCC point, F₂Positioned at route 2, PCC Point is L at a distance from bus；Fault point F₁Distance to bus is L₁；Fault point F₁Distance to PCC point is L₂, R₁For main net side Neutral point is to ground resistance.

4. a kind of power distribution network isolated island recognition methods as claimed in claim 3, characterized in that when systems are functioning properly, open circuit Device QF1, circuit breaker Q F2 are failure to actuate, and PCC point residual voltage is always zero.

5. a kind of power distribution network isolated island recognition methods as claimed in claim 4, characterized in that when singlephase earth fault occurs for system And fault point, when being located in isolated island region, before circuit breaker Q F1 tripping, PCC point residual voltage amplitude is more than or equal to U_set1；Through QF1 tripping after a period of time, PCC point residual voltage persistently exist and are sported on the basis of the original more than or equal to U_set2's Numerical value can determine that and form isolated island at this time.

6. a kind of power distribution network isolated island recognition methods as claimed in claim 4, characterized in that when fault point is located at outside isolated island region When, before circuit breaker Q F2 tripping, PCC point residual voltage amplitude is more than or equal to U_set3；QF2 tripping after a period of time, PCC point residual voltage is less than U_set4, in the range of close to zero, can determine that and cut off failure at this time.

7. a kind of power distribution network isolated island recognition methods as claimed in claim 4, characterized in that in F₁Singlephase earth fault occurs for point, Before obtaining major network protection act, obtained according to the distribution net work earthing fault compound sequence network figure containing rotary-type DG low resistance grounding mode To the positive sequence of major network side, negative phase-sequence, zero sequence impedance and the positive sequence of the side DG, negative phase-sequence, zero sequence impedance, and DG grid connection state is calculated accordingly Under current in the fault point, and obtain PCC point residual voltage accordingly, when singlephase earth fault occurs, after major network protection act, Circuit breaker Q F1 tripping, at this point, DG is formed together isolated island together with the load of surrounding.

8. a kind of power distribution network isolated island recognition methods as claimed in claim 7, characterized in that the event in the case where calculating DG grid connection state When barrier point electric current, it is contemplated that the DG capacity in access power distribution network is smaller, and grid-connected transformer and DG direct impedance are generally large, and The zero sequence impedance Z ' of the side DG_a(0)For a biggish value, therefore have:

Wherein, Z_a(1)、Z_a(2)、Z_a(0)The respectively positive sequence, negative phase-sequence of major network side, zero sequence impedance, Z '_a(1)、Z’_a(2)、Z’_a(0)Respectively The positive sequence of the side DG, negative phase-sequence, zero sequence impedance.

9. a kind of power distribution network isolated island recognition methods as claimed in claim 3, characterized in that as system F₂Point occurs A phase and is grounded event When barrier, PCC point residual voltage is still a biggish numerical value before major network protection act, and after major network protection act, route 1 restores Normal operating condition does not contain residual voltage theoretically in route, consider that error influences, PCC point residual voltage is at one at this time Close within the scope of zero.