Novel Automated Fault Isolation System on Low Voltage Distribution Automation System

Musse Ahmed ECE Department, Faculty of Engineering, IIUM

Kuala Lumpur Malaysia mussemoh@gmail.com

Soo Lian Universiti Teknikal Malaysia Melaka (UTeM), Melaka,

Malaysia ivysoo2004@gmail.com

Abstract-- This novel automated fault isolation system has been developed and integrated into a new customer side distribution system of 415/240V. The distribution system is based on the Tenaga Nasional Berhad (TNB), the Malaysia's power utility company especially the distribution system. Supervisory Control and Data Acquisition (SCADA), Remote Terminal Unit (RTUs) and power line communication (PLC) system have been used and developed for detecting, fault locating, fault isolating, fault segregating and power restoration in terms of hardware and software. Open loop distribution system is the distribution configuration system used as TNB distribution system. It is the first distribution automation system (DAS) based on fault management research work on customer side substation for operating and controlling between the consumer side system and the substation.

Keywords -- New Service Substation, Fault Detection, Fault Isolation, Fault Segregation, Open Loop System and Counter.

I. INTRODUCTION

There have been research works on the fault-location problems in the transmission systems [1]. Techniques published in the reviewed research papers and implemented in the utilities for targeting fault location problems in the distribution systems utilize voltages and currents measured at one or more points of a feeder or feeders. Fault location can be categorized into three parts: 1. techniques which are used for traveling wave variables/parameters [2], [3], [21]. 2. Another technique utilizes harmonic components of higher frequency [4] while measuring currents and voltages variables. The second method focuses on using the fundamental frequency voltages and currents [5] measured at the terminals of the line. The final technique is called the impedance-based method that comprises of computing line impedances that are seen from the line terminals with the consideration of the line distances of the faults location. Impedance-based methods are widely used by the utilities because of their advantages in practical application in the transmission line fault locating solutions. Impedance based solution can be sub-classified into two methods that are based on: one which can be taken the measurement from one terminal of the transmission and the other from which the measurement can be tapped from both sides of the terminals of the transmission line. The impedance based solution that is utilized to compute using a fundamental frequency component is the most commonly used technique

[3]. In summary of the above discussion, the basic approach to calculate the current and voltage as the fault location measurement variables uses the fundamental frequency component [5], harmonics [4], or unsymmetrical component [6]). Recalculation of the voltage and current at each node of the network is also needed for the compensation of the distribution system characteristics [5], [7], and [8]. It is therefore very important to find suitable solution to the problems of fault location in the distribution systems. However, the fact that a distribution feeder has many branches and sub-braches creates complexity of the problem of locating the fault as the trend of calculating the fault location which is based on finding the voltage and current signals produces more than one fault location that affects the accuracy of the fault location. Application of Heuristic and expert system approaches have also been reported in [9] for locating the fault in distribution systems for carrying out more measurements. It is assumed that the measurements of the fault location variables are available at the sending end of the faulty line portion which may be questionable in terms of accuracy as the real measurements are only feasible at the substation and at limited nodes close to the fault position [10], [11] of the distribution networks by the use of remote terminal devices. The application of Artificial Intelligence (AI) techniques have also been reported to the solution of the problem. In AI areas, a fuzzy logic approach has been suggested in [12], and [18] to solve the best possible fault location. A new method has been reported in [22] that method has proposed an algorithm to calculate the fault location based on the differences between the values of pre-faults and during-faults voltages and currents. In this research work, distribution automation system (DAS) technique has been proposed, studied and implemented in step by step manner. The research consists of both newly designed substation hardware and software systems to integrate the two together. However, this paper only focuses on fault management system in order to detect, locate, isolate and operate the faults within the distribution automation system scenario. Through the complete DAS, the fault algorithm has been formulated and implemented. No researches have been done in the service substation side of the downstream distribution systems. This is probably due to the limited degree of damages at the downstream. Faults occur in the substations and distribution substations are more severe and affect wider area compared to faults

2013 UKSim 15th International Conference on Computer Modelling and Simulation

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DOI 10.1109/UKSim.2013.152

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which occur in the service substations. Some minor fault might shut down the whole electricity supply to customers in longer periods. This research is motivated by lack of research work in the customer side substations [23], [24], [25], [26], [27]. The main objective of this research is to develop automated fault isolation system that is capable of detecting, locating, isolating the faults and operating the customer equipment automatically. The fault operation system is integrated to the SCADA system for automating the over distribution system. The steps of implementation of the fault management system will be discussed in sections II, sections III, section IV and section V.

II. SERVICE SUBSTATION PANEL

Fig. 1. Typical TNB Substation

Fig. 1 shows a typical compact substation which is also referred as Ring Main Unit (RMU). A 12KV, 630A, 20KVA RMU is supplying power supply to Low Voltage Feeder Panel. A three-phase, 1000KVA, 11/0.433 kV transformer is used to step down 11kV to 433V before supplying to a Low Voltage Feeder Panel (LVFP). The outgoing supplies are protected by fuses which have to be replaced if faulty occurs. In this research project, fuses have been replaced by circuit breakers which can be manually or automatically controlled for switching operations and are not frequently replaced. This is shown in Fig. 2. The typical panel is using power factor meter,

kilowatt hour meter and three ammeters to provide reading of power factor, kilowatt hour and three phase current values. Instead of using different types of meters to provide the reading, a single power analyzer is used in this research to provide the same readings and is able to send the data to the Remote Terminal Unit as a controller using mod-bus protocol [24].

Fig. 2. New Service Substation

Fig. 3. Developed Flow Chart

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III. DEVELOPED OF FAULT LOCATION METHOD

This research is based on open loop distribution system which means that the loads are connected to two feeders and any section of the feeder can be isolated without interruption. This system operates with any system which has similar physical and operating designs and functions. The time taken for fault system to detect and locate the fault is critical for the system to be faster so that no much is wasted, thus, the overall time and average outage time algorithm is designed to reduce to the time required to locate and detect the fault and do the necessary switching to restore the service. In this research, the switching can be performed either automatically or manually. The developed logic programming is based on the flowchart described in Fig. 3. By using a flowchart, the sequences of operations were determined. Based on the flowchart, there are five major actions which are: the status of ‘power input’, mode state, the status of ‘reset program’, execute ‘start low check’ and execute ‘start high check’.

Fig. 4. Low and High Side Descriptions

Fig. 5. Open Loop Distribution System

First step is to check the power input supply status whether it is turned on or turned off. The power input is referenced from the relay output of Earth Leakage Circuit Breaker (ELCB) with over-current relay protection as one combined relay. Earth leakage relays work with the same manner as the Residual Current Circuit Breaker (RCCB) works and as such, it must be accompanied by a circuit breaker or fuse. So basically it will only break the circuit when there is a leakage current flowing from phase line to the earth. If no faulty condition is detected by ELCB, power input is turned on (Normally Close (NC)). When ELCB detects the fault condition, power input is turned off (Normally Open (NO)). In this case, the ELCB is reset by using a delay timer and power input is turned on automatically. There are two modes of operations, i.e. manual and automatic modes. If automatic mode is selected, when fault occurs, the fault point is isolated automatically by activating the ‘start low check’ and ‘start high check’.

The ‘start low check’ and ‘start high check’ are executed only when the fault point is isolated and the unaffected points are operated as normal condition. Once the fault point is operated as normal, the ‘reset program’ button is pressed. These button resets back the counter to initial values and execute the ‘start low check’ and ‘start high check’ again. ‘Start low check’ checks the low side which is from the left to right while ‘start high check’ checks the high side which is from the right to the left. This is illustrated in Fig. 4. If the manual mode is switched on, when fault occurs, the checking is done manually by the operator, it can also be set to automatic checking by the engineer, operator or whoever is authorized to do so. The developed Graphical User Interface (GUI) provides click buttons to operate and control the switching operations of the loads. The GUI will be discussed in section IV (The developed Graphical User Interface (GUI)). In Fig. 5, if “Load #4” is the fault load, then “Zone #4” and “Zone #5” are switched off to isolate the load from the other loads. “Zone” is referred to a section of the distribution and operated by a relay as switching device. In Fig. 6, the method used in this project has been illustrated. During healthy condition, all loads are switched on. Two counters are used during low side checking which are the Counter Low Trip (CLT) and Counter Low Current (CLC). The CLT is the counter to store the zone which is under fault condition. The CLC will be increased by one on each time zone. Another two counters are used for high side checking which are the Counter High Trip (CHT) and Counter High Current (CHC). When fault occurs, all zones are switched off. The Low Side Checking (LSC) will start to turn on each zone one by one until it reaches to the fault zone. Once the fault zone is reached, trip occurs and all zones are switched off once again. This time, CLC is assigned to CLT to indicate which zones are the fault zones. From the value of CLT, CHT is calculated. The LSC will start to turn on each zone one by one but this time Zone #4 will remain off. The High Side Checking (HSC) will start to turn on Zone #7 and Zone #6 one by one but Zone #5 is remained off. All this process takes in seconds to complete the fault solution. Fig. 7 and Fig. 8 show the flowchart of counter method used in this research project. During LSC, CLT must be greater than the zone number in order for the zone to switch on. During the HSC, the CHT must be less than the zone number in order for the zone to switch on.

A. Fault Location Time Algorithm

In this research, a fast tracking time algorithm has been developed and implemented into the DAS. The following formula has been developed as general case formula which can be applied to any distribution automation system. �� Counter : Start Current Low Current, CLC = 0

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Current High Current, CHC= Total zone, N + 2 �� Counter : End CLC = Total healthy zone during LSC, N1 + 1 LSC= low side checking Current Low Trip, CLT = CLC Current High Trip, CHT = CLT + 1, if CHC < CLT + 1 CHT= CHC, if CHC > CLT + 1 CHT = 0, if CLC = Total zone, N + 1 Timer: Start Delay time, TDTimer: End Total of delay time, Ttotal = Delay time, TD x Total of zone, N.

Fig. 6. Developed Fault Location Method

Figure 7 Flowchart of Counter Method on Low Side Checking

Fig. 8. Developed High Side Checking Counter Method

Fig. 9. Screen Architecture

Figure 10 Log On Dialog Box

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Fig. 11. The Developed Main SCADA Screen

IV. THE DEVELOPED GRAPHICAL USER INTERFACE (GUI)

In Fig. 9, the control screen consists of main screen, customer service substation screen and service substation screen. These screens give flexibility on the operation personnel and also assign authorization privileges to the users so that the only authorized personnel are being able to view, operate and administer the screens of the developed SCADA. The control screen can be divided into three sections which are the footer, header and body section. This is shown in Fig. 11. The header section consists of toolbar and date and time display. Basically the toolbar provides navigation buttons to open other screens and also to exit the whole application. On the left side, the date and time display options provide the current date and time. The traffic light symbol on the top right of the screen indicates the interface between communication and the controller. The header section consists of toolbar and date and time display. Basically the toolbar provides navigation buttons to open other screens and also to exit the whole application. On the left side, the date and time display that provides the current date and time. The traffic light symbol on the top right indicates that the interface is communicating with the controller. The body section consists of symbols of input and output, control button, communication status, values of voltages and currents. The footer section consists of alarm display that is located at the bottom of the screen. Besides that, the alarm display button is selected for filtering the alarm. Selection field is to filter alarm messages by the selection text which is defined by the user. Priority field is to filter alarm messages based on priority level.

Total alarms will indicate the total alarm displayed. By pressing “Ack Top” button, the alarm on top of the alarm list will be acknowledged. Operation personnel can acknowledge all alarms by pressing on “Ack All”. All the alarms displayed will be printed out once the print button is pressed. Operation personnel can press the “beep” button to disable the alarm’s sound.

TABLE 1. SERVICE SUBSTATION VOLTAGE DATA

Fig. 12 shows graph that provides on-line data of voltage and current from the power analyzer. “Cursor” a button at the top of the graph can be dragged to know the value along a certain position of the graph. X-axis and Y-axis can be set to the user preferences. A combo box on the left side of the graph is to change the x-axis and y-axis. Start Date, Start Time and duration are to set the x-axis. By clicking on the “Show Tabular” button, screen shown in Fig. 12 will be displayed. This screen is to display the graph data in a table form. The value is archived from the graph shown in the trending screen. “Reload” button is to update the table based on the graph

Fig. 12. Voltage for Customer Service Substation Panel

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TABLE 2. COMMUNICATION DEVICE SETTING

Device Set ID Com Port Baudrate IP Address

I-7051 0x01 2 9600 -

I-7042 0x02 2 9600 -

I-7044 0x03 2 9600 -

Power Analyzer

0x01 3 9600 -

V. RESULTS AND DISCUSSIONS Table 1 to Table 5 demonstrate the results of voltage output of the service substation, communication setting, connection protocols for the developed system, DAS based currents output values, the captured values of RTU and power analyzer through TCP-IP and overall parameters of the service substation respectively. Figure 13 depicts the developed fault switching operation process. Figure 14 demonstrates the developed SCADA output which is real time data output from the service substation hardware operating in real time mode.

Fig. 13. Fault Switching Process

Fig. 14. SCADA Real Time Output

TABLE 3. LIST OF CAPTURED EVENTS

Analyzer 0x02 3 9600 -

I-7188EG 0x01 TCP/IP - 10.4.26.151

PC - TCP/IP - 10.4.26.128

TABLE 4. PHASE CURRENT OUTPUT FOR DAS VALUES

Power Analyzer Digital Multi-meter Description Phase Current

(Ampere) Phase Current

(Ampere) Main MCCB On 36.06 36.071 MCCB 1 On 26.06 26.069 MCCB 2 On 26.06 26.072 MCCB 3 On 26.06 26.065 MCCB 4 On 26.06 26.067

TABLE 5. ELECTRICAL DISTRIBUTION PARAMETERS

No. Parameter Single

Phase3Phase Location Mode

1 Current (A) 60 100 Main Switch Board (MSB)

Real Time

2 Frequency (Hz) 50 50 Main Switch Board (MSB)

Real Time

3 Voltage (V) 240 415 Main Switch Board (MSB)

Real Time

4 Active Power (kW) 12.96 38.88 Main Switch

Board (MSB) Real Time

5 Reactive Power (KVAR) 6.28 18.83 Main Switch

Board (MSB) Real Time

6 Kilo Volt Ampere (KVA) 14.4 43.2 Main Switch

Board (MSB) Real Time

7 Power Factor 0.9 0.9 Main Switch Board (MSB)

Real Time

VI. CONCLUSIONS

The main contribution of the work in this research project is to develop and design a distribution automation system aimed at the low voltage (LV) distribution system. A new method of fault isolation has been proposed and applied in this research. Results achieved from this research have been presented and discussed. This research helps to optimize staff efficiency by deploying staff to on-site location only when necessary. The operating system described here can reduce the number of outages and segregate the customers affected by the faults from those who are not affected the fault outages. However, customers still experience a short term outage during the low side and high side checking until the appropriate switching functions are activated and the fault location is be to be exactly identified.

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ACKNOWLEDGMENT

The authors would like to thank the Ministry of Science, Technology and Innovation and Universiti Teknikal Malaysia Melaka (UTeM) for providing the necessary funding for this project, project No: 03-01-14-SF0001/L004.

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