WO2013106985A1

WO2013106985A1 - Method for identifying fault direction without voltage measurement information and directional element thereof

Info

Publication number: WO2013106985A1
Application number: PCT/CN2012/070424
Authority: WO
Inventors: Youyi Li; Bin Su
Original assignee: Abb Research Ltd.
Priority date: 2012-01-16
Filing date: 2012-01-16
Publication date: 2013-07-25
Also published as: CN104054001B; CN104054001A; IN2014CN04230A

Abstract

The present invention discloses a method for identifying the fault direction without voltage measurement information and directional element thereof, which comprises: as to any one of protections, measuring the current value of the local line; calculating the fault component current based on said current value, and further calculating the phase angle of said fault component current; obtaining the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line; comparing the phase angle of fault component current of said local line with that of the other lines; and identifying the fault direction based on the result of the comparison. The proposed methods and directional element without voltage measurement information can be used in both distribution and transmission systems. It shall be noted that the proposed solutions can also be used for any applications which need fault direction without available voltage information.

Description

Method for Identifying Fault Direction without Voltage Measurement Information and Directional Element Thereof

FIELD OF THE INVENTION

The invention relates to the field of electricity transmission or distribution, and more particularly to a method for identifying the fault direction without voltage measurement information and directional element thereof.

BACKGROUND OF THE INVENTION

With more and more DGs (Distributed Generators) connected to the distribution network, the direction of fault currents may be very complex and different to that in traditional distribution system without DG. The traditional over-current (OC) protection relay (also directly named "protection") without direction estimation may mal-trip in some cases, which obviously influences the reliability, stability and security of a power system. Thus, the fault direction or a directional element for identifying the fault direction is very important for P&C (protection and control) systems.

In some conditions, a protection is directly composed of directional elements, for example a directional pilot protection. In other conditions, the directional element is used as an importantly auxiliary component in a protection, for example the directional element for over-current protection.

Usually, the angle between voltage vector and current vector is applied to estimate the fault direction with respect to the sensor's location. Unfortunately, voltage measurement information is not always available for the protection. As to the lines in a distribution network, there is no voltage sensor in many cases. Even for the lines in the transmission network with voltage sensors, the voltage measurement information is not always available either. For example, there is something wrong with the sensors, or the output signals of the sensors are not submitted to the intelligent electric devices (lEDs) due to some reasons. Hence, it's very useful to obtain the fault direction without voltage measurement information so that the protection can operate correctly. There are already some solutions in the prior art which try to provide a directional element without voltage measurement information to identify the fault direction.

In the paper "Fault direction estimation in radial distribution system using phase change in sequence current" (A. KF. Pradhan, etc., IEEE Transactions on Power Delivery, Vol. 22, No. 4, Pages 2065 - 2071 , 2007), a direction detection method for distribution network is proposed without voltage measurement information. Such solution is based on the difference of the current angle between fault and pre-fault current vectors. However, such method in the paper is based on the assumption that the power-flow direction along the line is unchanged before the fault; moreover such direction is already known by the direction element. Taking the intermittent energy of distribution generators (DGs) connected to the network and the change of power-flow directions into consideration, this assumption is not reasonable for many cases, therefore the solution is impractical.

To solve such problem, P. Jena, etc. also published a paper named "Dynamic performance of Phase-Change in Current based Directional Relaying for Transmission Line" in IEEE PES Transactions on Power Delivery in 2009. The method proposed in the paper is an extended application of the method privided by A. K. Pradhan from distribution networks to transmission networks. Similar to the previous method, the method proposed by P. Jena is also based on the assumption that the pre-fault power-flow direction is already known by a direction element. What's more, it needs parameters of the pre-fault voltage and current thereof to calculate the pre-fault power-flow direction. This solution is difficult to be used in practice for system without voltage measurements too. It can not solve the existing issue of identifying the fault direction without voltage measurement information.

In another existing prior art "Research on directional element without voltage in distribution network protection with DG"( Jia Wei, etc. , Power System Protection and Control, Vol. 39, No.2, Pages 94-97, 2011 ), a fault direction detection technology without voltage information is proposed. Such method is based on the comparison of amplitudes of fault component currents of all the lines connected with the same busbar, and does not need any pre-fault voltage or pre-fault power-flow direction. In theory, the method is correct. But it is hard to implement the method when the practical conditions being considered. In fact, it's not reasonable to identify the fault direction by embedding a whole busbar differential protection solution into the method. Furthermore, it needs all measured current information of all lines connected to the same busbar. In this method, once a feeder is added or disconnected to the busbar, the configurations and logic arithmetic of all the lEDs (with this method inside) for the lines connected into the same busbar should be changed. Consequently it's difficult to implementation and further maintenance of this method.

In summary, existed solutions including above mentioned method cannot be essentially used as the practical solution for identifying the fault direction for the conditions that voltage measurements are unavailable.

Due to the above mentioned problems, the present invention is to propose methods for identifying the fault direction without voltage measurement information and directional element thereof. Furthermore, the proposed directional element without voltage measurement information can be used in both distribution and transmission systems. Generally, proposed solutions can be used for any applications which need fault direction but the voltage measurements are unavailable.

SUMMARY OF THE INVENTION

To overcome above mentioned problems, the present invention provides a method for identifying the fault direction without voltage measurement information and directional element thereof.

According to an aspect of the present invention, a method for identifying the fault direction without voltage measurement information is provided, comprising: as to any one of protections, measuring the current value of the local line; calculating the fault component current based on said current value, and further calculating the phase angle of said fault component current; obtaining the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line; comparing the phase angle of fault component current of said local line with that of the other lines; and identifying the fault direction based on the result of the comparison.

According to another aspect of the present invention, a method for identifying the fault direction without voltage measurement information is provided, comprising: as to any one of protection, measuring the current value of the local line; obtaining current values from at least other two lines which are connected to the same busbar with said local line; calculating the fault component currents based on the current values from said local line and the other lines, and further calculating the phase angles of said fault component currents; comparing the phase angle of fault component current of said local line with that of the other lines; and identifying the fault direction based on the result of the comparison.

According to a preferred embodiment of the present invention, the method further comprises: identifying the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of said local line and other lines are similar to each other; identifying the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of said local line is similar to some of the other lines and almost reverse to the others of the other lines; and identifying the fault occurs in the forward direction for the local protection if the phase angle of said local line is almost reverse to all of the other lines.

According to a preferred embodiment of the present invention, the method further comprises: calculating the differences of the phase angles of between said local line and the other lines after getting the phase angles; comparing said differences of the phase angles with a preset threshold; identifying the fault occurs in the reverse direction for the local protection if at least one of said differences of the phase angles is less than a preset threshold; and identifying the fault occurs in the forward direction for the local protection if all differences of the phase angles are much larger than said preset threshold.

According to a preferred embodiment of the present invention, the method further comprises: in the case of the fault in the forward direction for the local protection, calculating each amplitude of the fault component currents on said local line and the other lines respectively; comparing the amplitude of the fault component current on the said local line with that of the fault component currents on the other lines; and determining said amplitude of the fault component current on the said local line is biggest one; otherwise, issuing an alarm or block signal.

According to a preferred embodiment of the present invention, the method is applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation.

According to a preferred embodiment of the present invention, the method can be implemented by the process level, bay level or GOOSE as the communication means in a digital substation.

According to another aspect of the present invention, a directional element for identifying the fault direction without voltage measurement information is provided, comprising: a measuring module, configured to measure the current value of the local line; a calculating module, configured to calculate the fault component current based on said current value, and further calculate the phase angle of said fault component current; a communication module, configured to obtain the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line; a comparing module, configured to compare the phase angle of fault component current of said local line with that of the other lines; and an identifying module, configured to identify the fault direction based on the result of the comparison.

According to another aspect of the present invention, a directional element for identifying the fault direction without voltage measurement information is provided, comprising: a measuring module, configured to measure the current value of the local line; a communication module, configured to obtain current values from at least other two lines which are connected to the same busbar with said local line; a calculating module, configured to calculate the fault component currents based on the current values from said local line and the other lines, and further calculate the phase angles of said fault component currents; a comparing module, configured to compare the phase angle of fault component current of said local line with that of the other lines; and a identifying module, configured to identify the fault direction based on the result of the comparison.

According to a preferred embodiment of the present invention, the identifying module further is configured to: identify the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of said local line and other lines are similar to each other; identify the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of said local line is similar to some of the other lines and almost reverse to the others of the other lines; and identify the fault occurs in the forward direction for the local protection if the phase angle of said local line is almost reverse to all of the other lines.

According to a preferred embodiment of the present invention, the calculating module is further configured to calculate the differences of the phase angles of between said local line and the other lines after getting the phase angles; said comparing module is further configured to compare said differences of the phase angles with a preset threshold; said identifying module is further configured to identify the fault occurs in the reverse direction for the local protection if at least one of said differences of the phase angles is less than a preset threshold; and identify the fault occurs in the forward direction for the local protection if all differences of the phase angles are much larger than said preset threshold.

According to a preferred embodiment of the present invention, in the case of the fault in the forward direction for the local protection, said calculating module is further configured to calculate each amplitude of the fault component currents on said local line and the other lines respectively; said comparing module is further configured to compare the amplitude of the fault component current on the said local line with the amplitudes of the fault component currents on the other lines; and said identifying module is further configured to determine said amplitude of the fault component current on the said local line is biggest one; otherwise, issue an alarm or block signal.

According to a preferred embodiment of the present invention, the directional element is applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation.

According to a preferred embodiment of the present invention, the directional element can use process level, bay level or GOOSE as the communication means in a digital substation.

According to a preferred embodiment of the present invention, the directional element can be used to form directional pilot protection for transmission or distribution network.

Embodiments of the present invention provide methods for identifying the fault direction without voltage measurement information and directional element thereof, which make the protection operated correctly without voltage measurement information in distribution or transmission network based on the right identification of the forward fault direction, especially for the network with multiple power sources or distributed generators.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention will be explained in more details in the following description with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:

Fig.1 illustrates a typical distribution network with a DG;

Fig.2 illustrates an application of the present invention in distribution network with multiple power sources connected to the same busbar;

Fig.3 illustrates another application of the present invention in distribution network with multiple power sources;

Fig.4 illustrates another application of the present invention in distribution network with at least one DG;

Fig.5 illustrates another two applications of the present invention in transmission network in the case that fault direction is necessary while voltage is unavailable; and a directional pilot protection and an unblocking differential protection shown in Fig.5a and Fig. 5b respectively;

Fig.6 illustrates another application of the present invention in distribution network with multiple DGs;

Fig.7 illustrates a diagram of fault component circuit corresponding to the circuit shown in Fig.6;

Fig.8 illustrates the exemplary vector diagram with a fault on line k corresponding to the circuit shown in Fig.7; Fig.9 illustrates a method for identifying the fault direction without voltage measurement information according to an embodiment of the present invention;

Fig.10 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention;

Fig.11 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention;

Fig.12 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention;

Fig.13 illustrates the vectors of fault component currents in the case of a fault on the busbar instead on lines; and

Fig.14 illustrates a directional element for identifying the fault direction without voltage according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in conjunction with the accompanying drawings hereinafter. For the sake of clarity and conciseness, not all the features of actual implementations are described in the specification.

Fig.1 illustrates a typical distribution network with a DG. As shown in Fig.1 , if there is no DG in the network, the power-flow direction is from the left to right; and the over-current protection L₂ will not measure any fault currents in the case of occurrence of fault Fi or F₂. Thus, the over-current protection L₂ won't mal-trip due to occurrence of fault F-i or F₂. Practically, a DG is connected to the network in Fig. 1 , and the situation is much different than that without DG. If the DG is powerful enough, the over-current protection L₂ will measure a large fault current when a fault occurs at Fi or F₂ location. Meanwhile, if there is no directional element in protection L₂, the protection L₂ may mal-trip if the fault current is large enough. It's obvious that directional element is necessary for the protections in distribution network with DG. Considering the situation that there is no voltage measurement information in distribution network normally, voltage will not be applied by the directional element. With the directional element proposed in the present invention, even in the distribution network with DGs, the over-current protection will work very well.

It shall be noted that the proposed method for identifying the fault direction without voltage measurement information and directional element thereof can be used in both distribution and transmission network, especially the networks with multiple power sources connected to the same busbar, the distribution network with multiple power sources, the distribution network with DGs and so on. Regardless of voltage measurement information, Fig.2 illustrates an application of the present invention in distribution network with multiple power sources connected to the same busbar. Fig.3 illustrates another application of the present invention in distribution network with multiple power sources. Fig.4 illustrates another application of the present invention in distribution network with at least one DG. Fig.5 illustrates another two applications of the present invention in transmission network wherein the fault direction is necessary while voltage is unavailable. For instance, the signal of voltage measurement is not submitted to the I ED, and/or the voltage measurement sensor fails for some reasons. In this case, the directional element provided by the present invention can be used as a directional pilot protection or unblocking differential protection shown in Fig.5a and Fig.5b respectively.

For clarity and conciseness, a typical application of the present invention in distribution network with DG will be further described with more details as below.

Fig.6 illustrates another application of the present invention in distribution network with multiple DGs. In Fig.6, the distribution network module has n lines, and each line connects a protection (L-i , L_k L_n) in series. Some DGs are connected to some of the lines individually. And a fault F occurs on the line k.

Fig.7 illustrates a diagram of fault component circuit corresponding to the circuit shown in Fig.6. In Fig.7, the fault component circuit shows the case that a fault occurs on the line K. The fault component currents on each line in the network can be calculated as shown below.

Z₁ // Z₂...//Z_n (n≠k, Sl) (2)

^■χ Δ/,, (3)

Z. + Z„ Z_B ^' _l = Z₁ //Z₂. /Z_B (n≠k, nl) (4)

Wherein, Δ ₅ is the current on the line from power generator to busbar; Z_s , is the equivalent impedance on the line from power generator to busbar; Z_S1 is the equivalent impedance of the parallel lines exce t the line from power generator to busbar and the fault line k, and ;

AI_k is the current on the line / with a fault F; ΑΪ_η is the current on the line n ; Z„ is the equivalent impedance on the line n ; Z_nl is the equivalent impedance of the parallel lines except the line from power generator to busbar and the line n, and — ^ = h +— ; (n≠k, n\) .

7 7 7 7

Normally, the phase angle of all the impedances in equations (1 ) and (3) are similar (about 70°~ 85°), which means the phase angle of fault component current { AI_k ) on the fault line k is quite different (nearly in reverse direction) from all the other fault component currents ( Δ ,Ο^'≠k) ) in healthy lines.

Fig.8 illustrates the exemplary vector diagram with a fault on line k corresponding to the circuit shown in Fig.7.

The present invention is a solution for detecting fault direction without voltage measurement information, wherein the phase angles of fault component currents are different between a fault line and healthy lines. As shown in Fig. 8, it is obvious to the person skilled in art that the phase angle of the fault component current on a fault line is almost reverse to that of all other fault component currents on healthy lines. The one whose phase angle is quite different from the others is regarded as the fault line and its fault direction is regarded as forward direction (fault is at the forward direction to the related protection).

Fig.9 illustrates a method for identifying the fault direction without voltage measurement information according to an embodiment of the present invention.

As shown in Fig.9, the method for identifying the fault direction without voltage measurement information comprises:

Step 902, as to any one of protections, measuring the current value of the local line. That's to say, the protection in each line is configured to measure the local current of its local line.

Step 904, calculating the fault component current based on said current value, and further calculating the phase angle of said fault component current. Each local protection calculates the phase angle of the fault component current on the local line.

Step 906, obtaining the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line. Each local protection communicates with at least other two protections, and obtains the phase angles of fault component currents from such lines connected to the same busbar with its local line.

Step 908, comparing the phase angle of fault component current of said local line with that of the other lines.

Step 910, identifying the fault direction based on the result of the comparison.

The person skilled in art acknowledges that the solutions no longer need voltage measurement information for identifying the fault direction when compared with conventional directional element. Furthermore, the solutions do not need any pre-fault power-flow direction or pre-fault voltages information for identifying the fault direction when compared with the methods proposed by A. K. Pradhan and P.Jena. Thus, the method and direction element thereof are more practical and valuable for identifying the fault direction without voltage measurement information.

In an embodiment of the present invention, each local protection identifies the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of its local line and other lines are similar to each other; also identifies the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of its local line is similar to some of the other lines and almost reverse to the others of the other lines; and identifies the fault occurs in the forward direction for the local protection if the phase angle of its local line is almost reverse to all of the other lines.

For any specific protection, the solution only needs at least three current measurement information (such as the current of local line with the specific protection, and currents of at least two other lines connected to the same busbar) to detect and identify the fault direction of the. While in prior art, especially in Jia Wei's solution, the current measurement information of all lines connected to the same busbar is necessary for identifying the fault direction. Furthermore, the solution in the present invention simplifies the requirements of the hardware, software and communication flow of the system.

Fig.10 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention.

As shown in Fig.10, the method for identifying the fault direction without voltage measurement information comprises: steps 1002-1014; in which steps 1002-1006 are the same or similar to the corresponding steps 902-906 in Fig.9. In order to keep the description brief, the same or similar steps will not be described again.

Step 1008, calculating the differences of the phase angles of between said local line and the other lines after the obtaining step;

Step 1010, comparing said differences of the phase angles with a preset threshold. If at least one of said differences of the phase angles is less than a preset threshold, go to step 1012; otherwise, go to step 1014.

Step 1012, identifying the fault occurs in the reverse direction for the local protection.

Step 1014, identifying the fault occurs in the forward direction for the local protection. If all differences of the phase angles are much larger than said preset threshold, the fault is in the forward direction of the local protection.

For example, a threshold, 40 degree and alike can be preset. If at least one of the differences of the phase angles is less than 40 degree, then the local protection can identify the fault occurs in the reverse direction (that means the fault is not in the forward direction of the local line). So the local protection will not respond to the fault even if the current is larger than the setting in the over-current protection. That's to say, if the difference is less than a specified threshold, we can say such phase angles are similar to each other. Otherwise, if all the differences are larger than the 40 degree, the fault occurs in the forward direction of the local protection. So the protection shall respond to the fault if the current is larger than the setting at the same time. It shall be noted that the person skilled in art can select and adjust the preset threshold according to the specified applications; 40 degree is exemplified as a preset threshold, but not used to limit the threshold.

When a fault occurs on a fault line, the other healthy lines are connected to the same busbar with the fault line. As shown in Fig.8, it's obvious to the skilled person in art that the amplitude of the fault component current on the fault line is different to the ones on all the other healthy lines; furthermore, the amplitude of the fault component current is the largest one among all the fault component currents on the lines connected to the same busbar. Consequently, the amplitude difference can also be used as auxiliary criteria and algorithm to enhance the reliability of the solution.

According to another embodiment of the present invention, in order to double check the accuracy on identifying the fault direction, the present invention provides another method to identify the fault direction without voltage measurement information. After identifying the fault in the forward direction for the local protection in the embodiment as shown in for example Fig.9 or 10, the method further comprises a double check procedure comprising:

Step A01 , calculating each amplitude of the fault component currents on said local line and the other lines respectively. For example, in the case that the fault is in the forward direction, the local protect calculates every amplitude of the fault component currents previously used to identify the fault in the forward direction.

Step A02, comparing the amplitude of the fault component current on the said local line with that of the fault component currents on the other lines.

Step A03, determining the amplitude of the fault component current on its local line is biggest one. Then the fault can be confirmed in the forward direction for the local protection again. Otherwise, there is something wrong with the system, maybe a communication error, measurement mistake or current transformer error and so on; then the local protection issues an alarm or block signal.

It should be noted that the further steps "comparing the amplitudes of all the fault component currents and determining the largest amplitude of the fault component current is from the same fault line where the phase angle of the fault component current represents a nearly reverse direction to the others" are used as an auxiliary means for final confirmation. Such auxiliary means based on the amplitude is benefit to enhance the reliability of the proposed method for identifying the fault direction without voltage measurement information. However, the auxiliary means are not necessary in theory. The person skilled in art appreciates that the steps based on phase angle, for example "identifying one of the phase angles is almost reverse to the others" or "identifying some differences of the phase angles are much larger than said preset threshold" has already determined the corresponding phase angle of fault component current is from the fault line. Without the auxiliary means, the method is also a completed one for identifying the fault direction without voltage measurement information.

Fig.11 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention.

As shown in Fig.11 , the method for identifying the fault direction without voltage measurement information comprises: steps 1102-1110; in which steps 1002, 1108 and 1110 are the same or similar to the corresponding steps 902, 908 and 910 in Fig.9. In order to keep the description brief, the same or similar steps will not be described again.

Step 1104, obtaining current values from at least other two lines which are connected to the same busbar with said local line. After each protection measures the current value on its local line, any local protection can directly measured current values from other lines, for example at least other two lines connected to the same busbar with its local line.

Step 1106, calculating the fault component currents based on the current values from said local line and the other lines, and further calculating the phase angles of said fault component currents.

Fig.12 illustrates a method for identifying the fault direction without voltage measurement information according to another embodiment of the present invention.

As shown in Fig.12, the method for identifying the fault direction without voltage measurement information comprises: steps 1202-1214; in which

Steps1204 and 1206 are the same or similar to the corresponding steps 1104 and 1106 in Fig.11 , and steps 1202, 1208-1214 are the same or similar to the corresponding steps 1002, 1008-1014 in Fig.10. In order to keep the description brief, the same or similar steps will not be described again.

According to another embodiment of the present invention, after identifying the fault in the forward direction for the local protection in the embodiment as shown in for example Fig.11 or 12, the method also comprises a double check procedure comprising:

Step A03, determining the amplitude of the fault component current on its local line is biggest one. Then the fault can be confirmed in the forward direction for the local protection again. Otherwise, there is something wrong, maybe a communication error or measurement mistake and so on; then the local protection issues an alarm or block signal.

According to an embodiment of the present invention, the methods mentioned above are applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation.

According to an embodiment of the present invention, the methods mentioned above can be implemented by the process level, bay level or GOOSE as the communication means in a digital substation. Especially the method directly obtaining current values from at least other two lines is easy to be implemented by digital substation with Standard IEC61850-9-2.

Fig.13 illustrates the vectors of fault component currents in the case of a fault on the busbar instead on the lines.

As shown in Fig.13, when a fault occurring on the busbar, the phase angles of all the lines connected on the same busbar are similar to each other. The characteristics represented in Fig.13 show that the methods provided by the present invention are immune to the fault on busbar. That's to say, the method proposed in the present invention can take advantage of phase angles to correctly identify the fault occurring in fault line and the direction thereof. And the proposed methods don't need any additional process for identifying the fault direction without voltage measurement information in the condition of a fault on busbar. On the contrary, a whole busbar protection is embedded into the directional element to resolve the case of fault on busbar in the existing art proposed by Jia Wei.

As shown in Fig.14, the directional element 1400 comprises a measuring module 1402, a calculating module 1404, a communication module 1406, a comparing module 1408 and an identifying module 1410.

According to a preferred embodiment of the present invention, the measuring module 1402 is configured to measure the current value of the local line; the calculating module 1404 is configured to calculate the fault component current based on said current value and further calculate the phase angle of said fault component current; the communication module 1406 is configured to obtain the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line; the comparing module 1408 is configured to compare the phase angle of fault component current of said local line with that of the other lines; and the identifying module 1410 is configured to identify the fault direction based on the result of the comparison.

The proposed solution in the present invention is much more practical and easier for implementation than existing arts, especially when the amount or status of the lines in the distribution/transmission networks is variable. If more lines are connected into the busbar according to the present invention, all configurations and the embedded arithmetic strategy in the existing protections do not need any modification. While in Jia Wei's solution, the settings and arithmetic strategy of all protections need be changed in this condition.

According to another preferred embodiment of the present invention, the communication module 1406 is configured to obtain current values from at least other two lines which are connected to the same busbar with said local line; the calculating module 1404 is configured to calculate the fault component currents based on the current values from said local line and the other lines, and further calculate the phase angles of said fault component currents.

According to another preferred embodiment of the present invention, the identifying module 1410 further is configured to identify the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of said local line and other lines are similar to each other; identify the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of said local line is similar to some of the other lines and almost reverse to that of the other lines; and identify the fault occurs in the forward direction for the local protection if the phase angle of said local line is almost reverse to that of all the other lines.

According to another preferred embodiment of the present invention, the calculating module 1404 is further configured to calculate the differences of the phase angles of between said local line and the other lines after getting the phase angles; the comparing module 1408 is further configured to compare said differences of the phase angles with a preset threshold; the identifying module 1410 is further configured to identify the fault occurs in the reverse direction for the local protection if at least one of said differences of the phase angles is less than a preset threshold; and identify the fault occurs in the forward direction for the local protection if all differences of the phase angles are much larger than said preset threshold.

According to another preferred embodiment of the present invention, in the case of the fault in the forward direction for the local protection, the calculating module 1404 is further configured to calculate each amplitude of the fault component currents on said local line and the other lines respectively; the comparing module 1408 is further configured to compare the amplitude of the fault component current on the said local line with the amplitudes of the fault component currents on the other lines; and the identifying module 1410 is further configured to determine said amplitude of the fault component current on the said local line is biggest one; otherwise, issue an alarm or block signal.

In the preferred embodiments of the present invention mentioned above, the directional element is applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation. Furthermore, the directional element can use process level, bay level or GOOSE as the communication means in a digital substation.

According to a preferred embodiment of the present invention, said directional element can also be used to form directional pilot protection for transmission or distribution network.

Compared with the existing prior arts, the proposed solution of the present invention is much more practical and easier for implementation. Referring to the description of the exemplary embodiments, those skilled in the art appreciate the advantages of the present invention:

1 , According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, the solutions no longer need voltage measurement information for identifying the fault direction when compared with conventional directional element.

2, According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, the solutions do not need any pre-fault power-flow direction or pre-fault voltages information for identifying the fault direction when compared with the methods proposed by A. K. Pradhan and P.Jena. Thus, the method and direction element thereof are more practical and valuable for identifying the fault direction without voltage measurement information.

3, According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, for any specific protection, the solution only needs at least three current measurement information (such as the current of a line with a protection, and currents of at least two other lines connected to the same busbar) to detect and identify the fault direction of the line with such protect device. While in prior art, especially in Jia Wei's solution, the current measurement information of all lines connected to the same busbar is necessary for identifying the fault direction. Furthermore, the solutions in the present invention simpliyies the requirements of the hardware, software and communication flow of the system.

4, According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, the proposed solutions in the present invention are much more practical and easier for implementation, especially when the amount or status of the lines in distribution/transmission networks are variable. If more lines are connected into the busbar according to the present invention, all configurations and the embedded arithmetic strategy in the existing protections do not need any modification. While in Jia Wei's solution, the settings and arithmetic strategy of all protections need be changed in this condition.

5, According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, no busbar differential relay needs be integrated into the directional element like that in Jia Wei's solution, which also simplifies the implementation of the present invention's solution.

6, According to the methods for identifying the fault direction without voltage measurement information and the directional element thereof provided in the present invention, the current transformer (CT) saturation has less impact on phase than the amplitude of a current normally. That's to say, the solutions provided by the present invention will be more reliable in case of CT saturation than the one disclosed by Jia Wei.

Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no means limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

1 . A method for identifying the fault direction without voltage measurement information, wherein said method comprises: as to any one of protections, measuring the current value of the local line;

calculating the fault component current based on said current value, and further calculating the phase angle of said fault component current;

obtaining the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line;

comparing the phase angle of fault component current of said local line with that of the other lines; and

identifying the fault direction based on the result of the comparison.

2. A method for identifying the fault direction without voltage measurement information, wherein said method comprises: as to any one of protection, measuring the current value of the local line;

obtaining current values from at least other two lines which are connected to the same busbar with said local line;

calculating the fault component currents based on the current values from said local line and the other lines, and further calculating the phase angles of said fault component currents;

identifying the fault direction based on the result of the comparison.

3. The method according to claim 1 or 2, wherein said method further comprises:

identifying the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of said local line and other lines are similar to each other;

identifying the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of said local line is similar to some of the other lines and almost reverse to the others of the other lines; and

identifying the fault occurs in the forward direction for the local protection if the phase angle of said local line is almost reverse to all of the other lines.

4. The method according to claim 1 or 2, wherein said method further comprises:

calculating the differences of the phase angles of between said local line and the other lines after getting the phase angles;

comparing said differences of the phase angles with a preset threshold; identifying the fault occurs in the reverse direction for the local protection if at least one of said differences of the phase angles is less than a preset threshold; and

identifying the fault occurs in the forward direction for the local protection if all differences of the phase angles are much larger than said preset threshold.

5. The method according to any one of above claims, wherein said method further comprises: in the case of the fault in the forward direction for the local protection,

calculating each amplitude of the fault component currents on said local line and the other lines respectively;

comparing the amplitude of the fault component current on the said local line with that of the fault component currents on the other lines; and

determining said amplitude of the fault component current on the said local line is biggest one; otherwise, issuing an alarm or block signal.

6. The method according to any one of above claims, wherein said method is applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation.

7. The method according to any one of above claims, wherein said method can be implemented by the process level, bay level or GOOSE as the communication means in a digital substation.

8. A directional element for identifying the fault direction without voltage measurement information, wherein said directional element comprises:

a measuring module, configured to measure the current value of the local line;

a calculating module, configured to calculate the fault component current based on said current value, and further calculate the phase angle of said fault component current;

a communication module, configured to obtain the phase angles of fault component currents from at least other two lines which are connected to the same busbar with said local line;

a comparing module, configured to compare the phase angle of fault component current of said local line with that of the other lines; and

an identifying module, configured to identify the fault direction based on the result of the comparison.

9. A directional element for identifying the fault direction without voltage measurement information, wherein said directional element comprises:

a measuring module, configured to measure the current value of the local line;

a communication module, configured to obtain current values from at least other two lines which are connected to the same busbar with said local line; a calculating module, configured to calculate the fault component currents based on the current values from said local line and the other lines, and further calculate the phase angles of said fault component currents;

a identifying module, configured to identify the fault direction based on the result of the comparison.

10. The directional element according to claim 8 or 9, wherein said identifying module further is configured to:

identify the fault occurs in the reverse direction for the local protection if the phase angles of fault component currents of said local line and other lines are similar to each other;

identify the fault occurs in the reverse direction for the local protection if the phase angle of the fault component current of said local line is similar to some of the other lines and almost reverse to the others of the other lines; and

identify the fault occurs in the forward direction for the local protection if the phase angle of said local line is almost reverse to all of the other lines.

11 . The directional element according to claim 8 or 9, wherein

said calculating module is further configured to calculate the differences of the phase angles of between said local line and the other lines after getting the phase angles;

said comparing module is further configured to compare said differences of the phase angles with a preset threshold;

said identifying module is further configured to identify the fault occurs in the reverse direction for the local protection if at least one of said differences of the phase angles is less than a preset threshold; and identify the fault occurs in the forward direction for the local protection if all differences of the phase angles are much larger than said preset threshold.

12. The directional element according to any one of above claims, wherein in the case of the fault in the forward direction for the local protection,

said calculating module is further configured to calculate each amplitude of the fault component currents on said local line and the other lines respectively ;

said comparing module is further configured to compare the amplitude of the fault component current on the said local line with the amplitudes of the fault component currents on the other lines; and

said identifying module is further configured to determine said amplitude of the fault component current on the said local line is biggest one; otherwise, issue an alarm or block signal.

13. The directional element according to any one of claims 8-12, wherein said directional element is applied in multiple sources connected to the same busbar, multiple sources connected to the different busbars, a distribution system with distributed generation, a distribution network, a transmission network, a traditional substation and/or a digital substation.

14. The directional element according to any one of claims 8-12, wherein said directional element can use process level, bay level or GOOSE as the communication means in a digital substation.

15. The directional element according to any one of claims 8-12, wherein said directional element can be used to form directional pilot protection for transmission or distribution network.