Detection algorithm for the cross country earth faults in medium voltage network
Umair, Ali (2015)
Umair, Ali
2015
Master's Degree Programme in Electrical Engineering
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
Hyväksymispäivämäärä
2015-01-14
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201501291014
https://urn.fi/URN:NBN:fi:tty-201501291014
Tiivistelmä
The protection of electricity distribution network has been the important topic in terms of reliable and safe power supply for the customers. The field of distribution automation deals with the protection and safety of the electricity distribution network. Recently the topic of centralized protection system has become a hot topic for research and many companies, who are dealing with protection relays, have been working on centralized protection architectures. Traditional protection relays (intelligent electronic device, IED) have the protection blocks for the faults classified as single phase to earth fault, short circuit faults but it is lacking the ability to detect the type of the earth faults termed as cross country earth faults. In cross country earth faults two different phases of the same or different feeder are experiencing the earth fault at different position along the feeder. When the phases are earthed then they are short circuited through the ground. The objective of this thesis is to develop an algorithm to detect the cross country fault using the available protection tools so that the algorithm can be implemented in centralized protection without the need of any new measuring device.
The thesis is divided into two parts. In the literature study part, different types of faults of medium voltage network (e.g. single phase to earth fault, double phase short circuit fault, phase to phase to earth fault and cross country fault), have been discussed along with some of protection techniques for these faults. The details about the IEC61850 standard, the research prototype of centralized protection system of ABB and its protection blocks are also the part of the literature study. The medium voltage network can have neutral isolated or compensated but for this thesis neutral isolated network was the main focus for the research. In the research part, basics of the algorithm for the detection of the cross country fault are explained with the help of the flow charts. The algorithm was tested by different fault scenarios in the PSCAD simulation environment in which three medium voltage (MV) overhead feeders were modelled and also in the real time digital simulator (RTDS) in which two feeders were overhead MV lines while one feeder was MV cable feeder. In each test case, the fault resistances were varied and behavior of the algorithm was observed.
The observations obtained from the testing of algorithm through simulations have proved that algorithm is able to detect the cross country fault and separate the cross country fault from other types of double phase faults. The algorithm is using the protec-tion block signal (i.e. directional earth fault protection block of the IED) for getting triggered. The practical issues relating to its implementation in centralized protection system are highlighted at the end of the thesis. Moreover the algorithm has reduced the time of operation against the cross country fault as compared to the directional earth fault protection block of IED. It was also observed that there are some cases when the fault resistances and the distance between the faults are small then the algorithm detect the cross country fault as the phase to phase to earth fault. For future there is still space for the improvement of the algorithm especially in the cases where the fault is wrongly detected. In addition the algorithm for the compensated neutral network still needs to be developed for the detection of cross country faults.
In the nut shell, it can be said that the new developed algorithm for the detection of the cross country fault covers almost all the cases and it does not need any new measur-ing device for working. It is also using the protection block of IEDs of ABB so it is easy to implement it in centralized protection system as IEDs are basic blocks for this kind of system.
The thesis is divided into two parts. In the literature study part, different types of faults of medium voltage network (e.g. single phase to earth fault, double phase short circuit fault, phase to phase to earth fault and cross country fault), have been discussed along with some of protection techniques for these faults. The details about the IEC61850 standard, the research prototype of centralized protection system of ABB and its protection blocks are also the part of the literature study. The medium voltage network can have neutral isolated or compensated but for this thesis neutral isolated network was the main focus for the research. In the research part, basics of the algorithm for the detection of the cross country fault are explained with the help of the flow charts. The algorithm was tested by different fault scenarios in the PSCAD simulation environment in which three medium voltage (MV) overhead feeders were modelled and also in the real time digital simulator (RTDS) in which two feeders were overhead MV lines while one feeder was MV cable feeder. In each test case, the fault resistances were varied and behavior of the algorithm was observed.
The observations obtained from the testing of algorithm through simulations have proved that algorithm is able to detect the cross country fault and separate the cross country fault from other types of double phase faults. The algorithm is using the protec-tion block signal (i.e. directional earth fault protection block of the IED) for getting triggered. The practical issues relating to its implementation in centralized protection system are highlighted at the end of the thesis. Moreover the algorithm has reduced the time of operation against the cross country fault as compared to the directional earth fault protection block of IED. It was also observed that there are some cases when the fault resistances and the distance between the faults are small then the algorithm detect the cross country fault as the phase to phase to earth fault. For future there is still space for the improvement of the algorithm especially in the cases where the fault is wrongly detected. In addition the algorithm for the compensated neutral network still needs to be developed for the detection of cross country faults.
In the nut shell, it can be said that the new developed algorithm for the detection of the cross country fault covers almost all the cases and it does not need any new measur-ing device for working. It is also using the protection block of IEDs of ABB so it is easy to implement it in centralized protection system as IEDs are basic blocks for this kind of system.