Abstract:
Occurrence of open-circuit faults is common in power transmission and distribution system. Finding exact location of Downed or Broken power line Fault not touching the ground in High voltage and low voltage is one of the most important issues in power system. Till now so many methods to finding location of power line open- circuit fault. In all that methods failed to find exact location because of impedance and reactance of transmission line and some of the methods are too costly to find exact location. By observing all these points, this paper proposes a new method to find exact location of Downed or Broken power line Fault not touching the ground by Hybrid AD Method. The proposed method is economic and easily to find location of fault with simple formula.
Keywords: PLG (Power Line Guardian), High Impedance Faults (HIF’s), Current transformer (CT)
I. Introduction
In Power Transmission and distribution system line faults are common issues. Finding Fault and fault location is a critical issue for both Transmission and distribution system. An efficient fault protection and fault location scheme required to protects the equipment as well as public from hazardous over voltages. Downed conductors or broken power lines not touch the ground are of major concern to electric utilities because they may result in public hazard. Finding fault location of down power lines not touching ground is big problem because finding this type of fault is big concern in power system.
This work was supported in part by the Siemens AG, Germany and Siemens Technology &Services Pvt Ltd, Banaglore.
First Author: Bhanuprasad Nuthalapati, Ph.D, EEE Department, NIT Jamshedpur (Bhanuprasad.n@gmail.com);
Second Author: Umesh Sinha, Ph.D, Guide and Professor in EEE Department, NIT Jamshedpur. (umeshsinha1111@gmail.com)
Downed conductors may not contact a conductive object and, therefore, have good probability of remaining energized. It’s not easy to find fault [1]-[5] and at present this fault comes under open-circuit fault. This paper mainly concentrated on location detection of Downed or Broken power line Fault not touching the ground.
Faults and fault location on transmission lines need be found out as quickly as possible otherwise power systems will face big problem. So many methods using for finding open-circuit fault location. Generally, fault location methods could be classified into traveling-wave technique, knowledge based technique and impedance based technique. Currently travelling wave and impedance based methods used for finding Open –circuit fault location. In Impedance bases method technique, phasor voltage and current can take from both terminals or from single terminal of a transmission line [6]-[14]. The traveling wave fault location method is known as the most accurate method currently in use [15]-[29]. The disadvantage of the traveling wave method is that propagation could be significantly affected by system parameters and network configuration [30]-[31].Travelling waves measured by using Current transformers [32]-[33].
Active Smart Wires (ASW) or Power Line Guardian’s (PLG’s) is a new concept for a low-cost, high reliability method to increase or decrease power flow in a transmission line and as well as observe power line between pole to pole every time [34]-[36].It’s used to find transmission line condition like voltage, current frequency, etc.Harmonics problem in Power system is very low; the cases where they do occur can result in decreasing power system reliability. An understanding of the causes, potential effects and mitigation means for harmonics can help to prevent harmonic. Incidence of harmonic related problems is low, but awareness of harmonic issues can help to increase plant power system reliability [37]-[40].
This paper discusses the Methods for finding open circuit fault location (Sec .II), Power line Guardian (Sec.III), Types of harmonics in power system (Sec.IV) and Hybrid AD Method (Sec V), Simulation Results (Sec .VI), Acknowledgement and Conclusion in Section VII.
II. Methods for finding Open circuit Fault location
Occurrences of High Impedance Faults are common in Power Distribution between Substation to Rural area and within rural area. High Impedance Faults detected based on Fault current measured by Fault Detection devices But an important fault is the Downed or Broken power line Fault not touching the ground cannot be detected when there is not enough faults current to work fault detection devices in Over Head power distribution. At present there are no electrical techniques to detect this fault with 100% Accuracy with less cost. A person touching an energized power line conductor faces real risk, since no detection device known today can react fast enough to prevent injury. The only available solution to this problem today is an alert and informed public [1]-[5]. Finding Downed or broken power line fault not touching ground is very difficult and finding exact location distance of this fault also big problem.
Generally, detection of fault location methods could be classified into traveling wave technique, knowledge based technique and impedance based technique. In below paragraphs explain how these two methods (impedance based technique and traveling wave technique) find location of fault.
In Impedance based method uses the fundamental frequency of voltage and current phasors from installed transducers such as numerical relays and fault recorders. Under this technique, phasor voltage and current could be taken from both terminals or from single terminal of a transmission line. Two-terminal algorithm provides more accurate results compared to single-end algorithm because this two-terminal algorithm is not affected by fault resistance and reactance. Phasor voltage and current data collected from two-ends of a transmission line either by synchronized or unsynchronized. Synchronized data could be collected using GPS, PMU [6]-[9].For the unsynchronized data, users have to first compute the synchronization error and fault location calculated. Since the synchronized method has to use the communication device, it is more expensive than the unsynchronized method. Impedance based method is widely used because of its simplicity and low-cost. After calculating the line impedance per unit length, the fault distance on the line calculated. If fault distance measured by using reactance from one end of the line, it may not give correct fault location because of fault resistance. In case of grounded fault, fault resistance will be high and it will affect the fault location [10]-[13]. This method having some errors they are 1. measuring voltage and current insufficiently. 2. z1 and z0 depend on parameters like size of conductors, distance between conductors etc. If any of these parameters is inaccurately measured [14].
At present the traveling wave fault location method is known as the most accurate method. Fault location on transmission lines using traveling wave was first proposed by Röhrig in 1931 [15]. In this method, when faults occur on transmission lines, a Traveling wave (electrical pulse) originating from the fault propagates along the transmission line on both sides away from the fault point. The time of Traveling wave return indicates the distance to the fault point. This method is suitable for a long and homogenous line.
Under this method, we have single-ended fault location algorithm and double-ended fault location algorithm. In single-ended algorithm, traveling time of the first wave away from the fault point to terminal and the arrival of same wave after reflecting back from fault point is always proportional to fault distance [16]. In single-ended algorithm, fault location is proportional to the first two consecutive transient arrival time. From measurements of the first two consecutive transient arrival times, fault location could be calculated. This algorithm is Consider as incorrect because of differentiating the wave front. Sometimes it is hard to identify the wave front when wave is being lost due to disturbance. In double-ended algorithm, fault location is proportional to the arrival time of waves at each end away from the faults. This method needs communication link to get information from both ends so that the data is at a common time base [17].
This method is expensive and complex compared to single-ended algorithm. This method does not depend on reflections of wave from the fault point to the terminal.
Traveling wave fault locator divided into five different types: A, B, C, D, and E [18]-[29]. Only A, D, and E types of locator will be discussing here .Type-A: Type A locator perform measurements on one end of the line. Below Formula used to find location of fault [17]-[18].
D – Distance to the fault location [m]
T1 – time when first wave generated at fault location arrives at source station [s]
T3 – time when first wave reflected from fault location arrives at source station [s]
V – Wave velocity [m/s]
Type-D: Type D locator measurements on both ends of the line. The waves generated at the fault location run in opposite directions, to substations A and B, and they reach there in few microsecond. For a correct determination of distance, D-type fault locator requires the use of two synchronized devices installed at both ends of the line.
Below Formula used to find location of fault [19]-[20].
T1 – time when the first wave generated at fault location arrives at station A [s]
T2 – time when the first wave generated at fault location arrives at station B [s]
L – Length of line [m]
V – Wave velocity [m/s]
Type-E: Type E locator performs measurements on one end of the transmission line. Type E locator use wave generated by closing circuit breaker on transmission line. The circuit breaker which closes in transmission line could be treated as three separate impulse generators. The time difference between the pulse generated by closing a circuit breaker and a reflected impulse from the fault is use for determines the distance to the fault[21]-[24].
Below Formula used to find location of fault.
D – Distance to fault location [m]
T1 – the time when wave is generated by closing a circuit breaker[s]
T2 – the time when reflected wave reaches a substation [s]
V – Wave velocity [m/s]
The disadvantage of the traveling wave method is that propagation could be significantly affected by system parameters and network configuration [30]. It is also difficult to locate faults near the bus or faults that occurred near zero voltage inception angle [31].At present Current Transformer’s are using for measuring Travelling wave [32]-[33].
III. Power Line Guardians (“PLG”)
One of the important technologies is Power Line Guardian’s (PLG’s). The Fig.1 shows the schematic Diagram of PLG.The PLG’s are mounted directly on the Transmission line. The operating power for PLG is drawn from the conductor and PLG connected in series with the transmission line. The PLG system consists of hardware and software components. Hardware is used for the impedance change on overhead line and software is used for controlling the power flow [34]-[35]. Power line guardian had Current Transformer, Transmission line act as a Primary winding of Current transformer, PLG measure all conditions of Transmission line like Current, voltage, frequency and etc., send observations to Data center [36].
Fig. 1. Schematic Diagram of Power Line Guardians (“PLG”)
IV.Types of harmonics in power system
All periodical non-sinusoidal waveform could be represented as the sum of sine waves whose frequencies are integer multiples of the fundamental frequency, that we call harmonics. Harmonics could be generating by non-linear loads that absorb non-sinusoidal current. The most common loads, both in industrial surroundings and domestic ones, are the following ones Frequency / Variable speed drives, Discharge lamps,Rectifiers ,AC/DC Converters, Arc welding, Induction ovens,UPS,Computers and laptops,etc.Hramonics order are two types, they are even order harmonics( 2nd,4th,6th and 8th ) and odd order harmonics( 3rd,5th and 7th ). The harmonic components of the voltages and currents are integer multiples of the fundamental frequency. For example on 60Hz supply, the 3rd harmonic is 3 x 60Hz (=180Hz); the 5th harmonic is 5 x 60Hz (=300Hz), and so forth. All harmonic currents could be added to the fundamental a waveform known as complex wave [37]-[40].How different harmonics order would behave will explain in below Fig.2 and Fig.3.
Fig.2.Decomposition of a distorted wave form
Fig.3. Order and behavior of harmonics
V. Hybrid AD Method:In above sections explained about travelling wave method for finding open-circuit location, Power line guardian (PLG) for power flow control, Harmonics in Power system (2nd harmonic) . Using Travelling wave method, Power line guardian and 2nd harmonic, we are going to propose new method to find Location of Downed or Broken power line Fault not touching the ground. The proposed method is very simple and less cost and it will give exact location. In this method PLG (Power line guardian) would play big role and using 2nd harmonic travelling wave, we are going to find Location of Downed or Broken power line Fault not touching the ground.PLG having Current transformer and it will measure High frequency ranges (Travelling wave frequency).To find distance of fault please follow below Operation of Hybrid AD Method.
Operation of Hybrid AD method: Please follow below Steps how to detect Location of downed power line conductors fault between two sub stations.
Precondition:
1. First calculate Distance between two sub-stations (distance D)
2. PLG connected between equal distance (at Pont P) (Fig.4) from two sub-stations A and B. Please follow below cases how Hybrid AD method help to detect location of fault.
Figure .4.PLG between two substations
Case 1: Fault occurred between Station A and PLG
Step 1: When Downed or Broken power line Fault not touching the ground occurred (at Point F) (Fig.5) at that point 2nd harmonic first travelling wave generated and travelled towards Station A and Station B (Fig.5).
Step 2: measure 2nd harmonic first forward travelling wave timing between fault point “F” to PLG Point “P”.
Step 3: measure 2nd harmonic first forward travelling wave from fault point “F” to Station B.
Step 4: measure first reflected travelling wave from station B to fault point (at point F).
Step 5: measure first reflected travelling wave from station B to at Point P.
Fig.5.Type AD Method for fault near to station B
D= Total distance between station A and Station B[m]
DX= Fault location distance from Station B[m]
F= Fault point location, P= Power Line Guardian arranged on transmission line
TL =First forward travelling wave time between Fault point (F) and PLG point (P) [s]
TPB = First forward travelling wave time between PLG point (P) and Station B[s]
TR-PB = First reflected travelling wave time between PLG point (P) and Station B[s]
T1 = First forward travelling wave time between Fault point (F) and Station B[s]
PLG= Power Line Guardian, V = wave velocity [m/s], =Total travelling time [s]
, Fault location distance from Station B DX=
Case 2: Fault occurred between Station B and PLG
Step 1: When Downed or Broken power line Fault not touching the ground occurred (at Point F) (Fig.6) at that point 2nd harmonic first travelling wave generated and travelled towards Station A and Station B (Fig.6).
Step 2: measure 2nd harmonic first forward travelling wave timing between fault point “F” to PLG Point “P”
Step 3: measure 2nd harmonic first forward travelling wave from fault point “F” to Station A
Step 4: measure first reflected travelling wave from station A to fault point (at point F)
Step 5: measure first reflected travelling wave from station A to at Point P
Fig.6.Type AD Method for fault near to station A
D= Total distance between station A and Station B[m]
DX= Fault location distance from Station B[m]
F= Fault point location, P= Power Line Guardian arranged on transmission line
TL =First forward travelling wave time between Fault point (F) and PLG point (P) [s]
TPA = First forward travelling wave time between PLG point (P) and Station A [s]
TR-PA = First reflected Travelling wave time between PLG point (P) and Station A[s]
T1 = First forward travelling wave time between Fault point (F) and Station A[s]
PLG= Power Line Guardian, V = wave velocity [m/s], =Total travelling time [s]
, Fault location distance from Station A DX=
VI. Simulation Results
We used PSCAD V4.2 for this simulation results. if we apply in Theoretical calculation to simulation for Case 1, Distance between station A and B is 100 Kilo meters. If Downed or Broken power line Fault not touching the ground occurred at 25 Km from Station A.
Fig. 7. 2nd harmonic wave Generated at fault point.
Fig. 8. First forward Travelling wave travelling towards station B.
Fig .7 & 8. Explains how 2nd harmonic generated at fault point and fault travelling wave travelling towards station B.From Simulation Results,
, Fault location distance from Station B DX= =28.97KM.Final value near to fault location.
VII. Acknowledgment
We would like to thank Siemens AG ,Germany & Siemens Technology and Services Pvt Ltd,India sponsored for my research work & National institute of Technology ,Jamshedpur supported my research work.
VII. Conclusion
In Smart grid, Fault location finding methods using travelling wave concept but all methods measuring travelling wave at end of source or destination .As compare to all that methods, my proposed Hybrid AD Method measure travelling wave at middle of Transmission line length. At present very few methods for finding exact location of Downed power lines Fault without touching ground. As compare to all of that’s methods and process, the proposed solution will give better Solution, economic and with in less time. I hope it will give almost 100% accurate solution for finding exact location Detect Downed power lines Fault without touching ground. This Paper provides solution used for between two substations. Further Research work will be finding exact location of Downed power lines Fault without touching ground between substations to rural area.
LIST OF SYMBOLS
DX: distance to the fault location [m], V: wave velocity [m/s], D: Total distance between station A and Station B[m]
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