Customized Fault Management System for Low Voltage (LV) Distribution Automation System 51
4
x
Customized Fault Management
System for Low Voltage (LV)
Distribution Automation System
M.M Ahmed, W.L Soo, M. A. M. Hanafiah and M. R. A. Ghani
University Technical Malaysia Melaka (UTeM)
Malaysia
1. Introduction
Supply disruption such as overloading will cause interruptions of electricity supply to customers. The
technicians have to manually locate the fault point and this tedious work may last for extended periods
of time. The other reasons are the lack of use of efficient tools for operational planning and advanced
methodology for quick detection of fault, isolation of the faulty section and service restoration.
Currently, fault detection, isolation and service restoration takes a long time causing the interruption of
supply for a longer duration.
An active development phase of information technology has given significant impact to the distribution
network fault management. There is a tendency towards fully automated switching systems with the
introduction of Supervisory Control and Data Acquisition (SCADA) systems. The decision making
feature of the fault management system is depend on SCADA system. SCADA can be used to handle
the tasks which are currently handled by the people and can reduce frequency of periodic visit of
technical personal substantially. SCADA is a process control system that enables a site operator to
monitor and control processes that are distributed among various remote sites. The control functions
are related to switching operations, such as switching a capacitor, or reconfiguring feeders. Once the
fault location has been analyzed, the automatic function for fault isolation and supply restoration is
executed. When the faulty line section is encountered, it is isolated, and the remaining sections are
energized. This function directly impacts the customers as well as the system reliability.
This chapter presents the development of a fault management system for distribution automation
system (DAS) for operating and controlling low voltage (LV) downstream system such as 415 V for
three phase system and 240 V for single phase system. The fault management system is referred as the
fault detection, fault location, fault isolation, electricity restoration and automatic operation and control.
This done because system is equipped with automated equipment to detect earth fault and over-current
faults and identify them accordingly. An embedded controller with Ethernet access is used as remote
terminal unit (RTU) to act as converter for human machine interface (HMI) and to interact with the
digital input and output modules. Supervisory Control and Data Acquisition (SCADA) is integrated
with the RTU for automatic operating and controlling the distribution system. The laboratory results are
compared with the simulation results to verify the results and make the achieved results credible.
2. Substation Model
Fig. 1 shows a typical compact substation which is also referred as Ring Main Unit (RMU).
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52 Fault Detection
RMU can be obtained by arranging a primary loop, which provides power from two
feeders. Any section of the feeder can be isolated without interruption, and primary faults
are reduced in duration to the time required to locate a fault and do the necessary switching
to restore service. 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 Low Voltage Feeder Panel (LVFP).
Fig. 1. Typical Substation
The outgoing loads are protected by fuses which have to be replaced if fault occurs. In this
research project, fuses have been replaced by circuit breaker which can be manually or
automatically controlled for switching operation and are not frequently replaced as shown
in Fig. 1. The typical panel shown in Fig. 1 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 reading and is able to send the
data to the controller using modbus protocol. In this research, the service substation panel
consists of four feeder points and each feeder is connected to customer service substation
panel as shown in Fig.2.
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 53
In Fig. 2, the service substation block diagram consists of power line and control line. The
power line shows the electricity power supply supplied to all the components in service
substation panel. The controller and I/ O modules are supplied with dc power supply.
Relay module received power supply from the digital output module. The control line
shows the communication line between the controller and I/O modules.
Electromechanical relays are interfaces that control one electrical circuit by opening and
closing its contacts in another circuit. An electromechanical relay is a relay with sets of
contacts which are closed by magnetic force that includes magnetic coil and contacts.
Electromechanical relays are limited to switching about 15A but are capable of switching
several different circuits simultaneously.
Current transformers (CTs) are used in power installations for supplying the current to
circuits of indicating instruments such as ammeter and wattmeter and protective relays. CTs
are used so that ammeters and the current coils of other instruments and relays need not be
connected directly to high-current lines. These instruments and relays are insulated from
high currents. CTs also step down the current to a known ratio. The secondary winding is
rated at 5A regardless of the current rating of the primary winding.
MK2200 which is the combination of overcurrent and earth leakage relay is used. The 630A,
50kVA, 415V MCCB is used as the main MCCB. The MCCBs are switched on or off by using
customized solenoids.
Fig. 2. Service Substation System Block Diagram
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54 Fault Detection
In Fig. 3, the customer service substation block diagram also consists of power line and
control line. The power line starts from MCCB1 from the service substation panel. Digital
input/output module is supplied with direct current power supply. The contactor module is
connected to the ac power supply. Relay module received power supply from the digital
input/output module. The control line shows that the digital input/output module is
connected with the controller in the service substation panel.
Relays are connected to contactors to energize or de-energize loads. Contactors typically
have multiple contacts, and those contacts are usually normally-open, so that power to the
load is shut off when the coil is de-energized. The top three contacts switch the respective
phases of the incoming three-phase AC power. The lowest contact is "auxiliary" contact. A
normally-closed relays are connected to this auxiliary contact in series so that when the
relays are opened, contactor coils will automatically de-energize, thereby shutting off power
to the load.
Fig. 3. Customer Service Substation System Block Diagram
3. Relays
In this research work, zero-phase sequence current transformer is connected to the earth
leakage relay as show in Fig. 4. Earth Leakage Circuit Breaker (ELCB) works in the same
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 55
way as the Residual Current Circuit Breaker (RCCB) and as such, must be accompanied by a
circuit breaker (CB) or a fuse. Phase and neutral conductors are passed through a toroidal
transformer, creating a magnetic field proportional to its current. In normal situations, the
vector sum of the currents is zero even with unbalanced three-phase loads. The magnitude
of the zero sequence current increases beyond its normal value when a ground fault is
experienced. If the magnitude of the estimated zero sequence current is more than a
threshold value in earth leakage relay, it is assumed that one or two phases are short
circuited to ground. The short circuit between one phase and earth is probably the most
common type of fault on low voltage electrical installations. This research project is focusing
on earth fault.
Fig. 4. Typical Circuit of ELCB with Current Transformer
A leakage current towards earth on one or more conductors at the downstream of the toroid
causes an imbalance which is detected in the measurement winding and sent to an amplifier
relay. The amplifier relay receives the signal from the ring current transformer and
compares it with the preset threshold value. The relay output is turned on in the case where
the detected value is higher than the preset threshold and lasts for a longer time than the
preset tripping time value. The output remains in the on state until the relay is reset either
manually or electrically. Generally, the relay output is fed to the shunt trip of a protective
device such as CB which isolates the faulted circuit.
In service substation panel, ELCB is replaced by MK2200. Fig. 5 shows the pin assignments
of MK2200. The MK2200 which combined overcurrent and Earth Fault (EF) relay is a digital
microprocessor based relay. MK2200 relay provides three independent Phase Overcurrent
(PO) elements and one non-directional Earth Fault (EF) element. These elements are
connected to the current transformers of the feeders to be protected. PO protection and EF
protection element consists of low-set stage and high-set stage for each PO elements. When
the phase current exceeded the low-set stage or high-set stage, a signal is sent to the user
through pre-assigned contact outputs and display panel.
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56 Fault Detection
MK2200 has six relay outputs of which 4 are user configurables. R1 contact is the dedicated
trip contact and cannot be programmed. Either EF or overcurrent will activate this contact.
The relay output remains in the on state until the relay is reset either manually or
electrically. Generally, the relay output is fed to the shunt trip of a protective device such as
CB which isolates the faulted circuit. Contact R2, R3, R4 and R5 are user configurable
outputs. The sixth output contact internal relay failure (IRF) is also not user programmable.
It is used to signal an internal failure of MK2200.
When the auxiliary power of MK2200 is switched on, the relay starts its operation. If the
MK2200 is functioning normally, the IRF output is energized hence the normally close (NC)
contact of the output will open and the normally open (NO) contact will close.
Fig. 6 shows the typical connection diagram of MK2200 with Current Transformer (CT).
MK2200 works in the same way as the Residual Current Circuit Breaker (RCCB) and as
such, must be accompanied by a Circuit Breaker (CB) or a fuse. Phase and neutral
conductors are passed through a toroidal transformer, creating a magnetic field proportional
to its current. In normal situations, the vector sum of the currents is zero even with
unbalanced three-phase loads.
Fig. 5. Pin Assignment of MK2200
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 57
Fig. 6. MK2200 Typical Connection Diagrams
4. Fault Isolation Methods
The logic of controller is using this flowchart described in Fig. 7. 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 programme',
execute Operation Logic Up-Counter (OLUC) and execute Operation Logic Down Counter
(OLDC).
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58 Fault Detection
Fig. 7. General Flow Chart
First step is to check the power input whether it is turned on or turned off. If no faulty
condition detected by ELCB, power input is turned on. When ELCB detects the fault
condition, power input is turned off. In this case, the ELCB is resetted by using a delay timer
and power input is turned on. There are two modes of operations. If automatic mode is
selected, when fault occurs, the fault point is isolated automatically by activating the OLUC
and OLDC. OLUC and OLDC are executed and only the fault point is isolated and the
unaffected points are operated as normal condition. Once the fault point is operated as
normal, the 'reset programme' button is pressed. This button resets back the counter to
initial value and executes the OLUC and OLDC again.
Fig. 8. OLUC and OLDC Descriptions
The general flow of these algorithms is
described as follows. ALGORITHM: OLUC
Initial: TotalCountOLUC, TotalCountOLDC, NumOfFeeders
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 59
FOR ALL u e NumOfFeeders
IF mode_auto & trip_counter_oluc > u
FeederNo[u
] =Switch
On; IF
FeederNo[u
] = TRUE {
TotalCountOLUC = TotalCountOLUC + 1;
}
}
}
ALGORITHM: OLDC
Initial: TotalCount, NumOfFeeders
FOR ALL u e NumOfFeeders
IF mode_auto & OLUC_done & LastFeederOn & trip_counter_oldc < u
{
FeederNo[u]
=Switch On;
IF
FeederNo[u]
= TRUE {
TotalCountOLDC = TotalCountOLDC + 1;
}
}
}
The TotalCountOLUC and TotalCountOLDC are counters that will store the information of
the fault points. This information was obtained during the second tripped of ELCB. As
illustrated in Fig. 8, OLUC' checks the logic of up-counter which is from left to right while
'OLDC' checks the logic of down-counter which is from right to left. If the manual mode is
switched on, when fault occurs, the checking is done manually by the operator. Fig. 9 shows
the flowchart for OLUC and Fig. 10 shows the flowchart for OLDC. If the manual mode is
switched on, when fault occurs, the checking is done manually by the operator. The
developed GUI provides buttons to control the switching of the loads.
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60 Fault Detection
Fig.9: Flow Chart for OLUC
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 61
Fig. 10. Flow Chart for OLDC
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62 Fault Detection
5. Results and discussions
Both ELCB and MK2200 are fitted with test and reset buttons in order to conduct testing and
commissioning of the relays. 32 bit microprocessor-based power quality analyzer is used to
measure phase voltage and phase current of the incoming power supply to both panels. The
power analyzer is connected using three phase, four-wire input connections for unbalanced
loads. The setup procedures are done by using the keypad. It sends data to the controller
using RS485 network. Table 1, Table 2, Table 3 and Table 4 are the results obtained by the
following procedures described in the tables.
Table 1. Manual Mode Experimental Procedure-1
Table 2. Manual Mode Experimental Procedure-2
By conducting the actual experiments, the appropriate delay timer for controlling the
solenoid operation in service substation and also loads in customer panel are obtained. Fig.
11, Fig. 12, Fig. 13, Fig. 14 and Fig. 15 show graphs build using Excel to show the change of
phase current for customer service substation panel and service substation panel during
fault isolation operation done by the system. The duration time 1 is the time period that
needed by the system to identify which load is the fault load. In this experiment, the Zone 4
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 63
and Zone 5 were chose to be the fault zones. Duration time 2 is the time period that is
needed by the system to isolate the faulted load and restore electricity power supply to the
rest of the healthy loads. Outage time is the duration of time that the customer experienced
electricity power supply disruption. Reset time is the total time needed to restore electricity
power supply to all the loads including the faulted load that already been repaired.
Table 3. Automatic Mode Experimental Procedure-1
Table 4. Automatic Mode Experimental Procedure-2
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64 Fault Detection
Table 5. Automatic Mode Experimental Procedure-2 Continue
Fig. 11. Phase Current Graph for Delay Timer Six Seconds
Table 5 shows the total of restoration time for service substation panel. In the service
substation panel, if the delay timer is set to fast, the solenoid will not be able to switch on or
off the MCCB. The minimum delay timer needs to be set to five seconds for proper
switching operation of the MCCBs by the solenoids. The results in Table 5 can only be
applied using LKE LKS-600S MCCB and LKE LKS-100N MCCB with shunt trip operating
time of five to fifteen minutes.
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 65
Fig. 12 Phase Current Graph for Delay Timer Three Seconds
Panel Duration Time 1 Duration Time 2 Total of time
Service Substation 25 seconds 25 seconds 50 seconds
Table 6. Total Minimum Restoration Time for Service Substation Panel
Fig. 13. Phase Current Graph for Delay Timer One Second
In Fig.15 shows the reset time when the delay timer in customer service substation is set to
one hundred milliseconds. The delay timer was to short and fault was not able to be
triggered manually during the experiment. In this case, duration time 1, duration time 2 and
outage time were not displayed in Table 6. Table 6 shows the details of the duration time 1,
duration time 2, outage time and reset time when the delay timer in customer service
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66 Fault Detection
substation is set to six seconds, three seconds, one seconds, five hundred milliseconds and
one hundred milliseconds.
Fig. 14. Phase Current Graph for Delay Timer Five Hundred Milliseconds
Fig. 15. Phase Current Graph for Delay Timer One Hundred Milliseconds
Table 7 shows the minimum total of restoration time for customer service substation panel
and service substation panel. The ELCB minimum operation time is fifty milliseconds. In
this case, the delay timer has to be set higher than fifty milliseconds. The minimum delay
timer for customer service substation panel is one hundred milliseconds.
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 67
Delay Timer Duration Time 1 Duration Time 2 Outage Time Reset Time
(Second) (Second) (Second) (Second) (Second)
6 24 30 54 42
3 12 15 33 21
1 4 5 15 7
0.5 2 2.5 10.5 3.5
0.1 - - - 0.7
Table 6. Restoration Time for Customer Service Substation Based on Delay Timer
Panel Minimum Restoration Time (Second)
Customer Service Substation 0.7
Service Substation 50
Table 7. Minimum Total of Restoration Time
Experiment Total of Total of Correct Total of Failure Percentage of Failure
Experiment Steps Operation Operation Operation
(%)
Manual 36 34 2 5.56
Mode
Experimental
Procedure-1
Manual 32 36 0 0
Mode
Experimental
Procedure-2
Automatic 27 27 0 0
Mode
Experimental
Procedure-1
Automatic 57 56 1 1.75
Mode
Experimental
Procedure-2
Table 8. Percentage of Failure Operation
The system developed in this research proved to save the time needed to restore back the
electricity supply after fault occurred. The restoration time definitely cannot be achieved by
manually isolation done by technician. The failure percentages of the system for not able to
operate correctly based on the experimental procedures are described in Table 8. The failure
operations were during the manual mode of service substation to switch on Zone 2 and
Zone 3. The reason of this failure is due to loose wiring at the digital output module. One
failure was recorded during automatic mode of customer service substation when fault was
simply triggered at Zone 2. The system was not able to switch on the other healthy loads
during OLDC operation because loose wiring at the second feeder. After the causes of
failures have been fixed, the experiments were continued and no operation failure was
recorded. The percentages of failure operation in Table 8 are contributed by human factors.
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68 Fault Detection
6. Conclusion
In this research, a Customized SCADA is built to provide automatic fault isolation for low
distribution system. The contribution of this research includes developing a complete fault
isolation algorithm based on an open loop distribution system. Service Substation Panel,
Customer Service Substation Panel and Customer Panel have been built to validate the
proposed methodology.
In an open loop distribution system, two feeders are used to provide electricity power
supply to the loads. Any section of the feeder can be isolated without interruption. The
algorithm is written to check the fault point starting from one of the section feeders or
OLUC algorithm and repeated with another section feeder or OLDC algorithm. At the
beginning, this algorithm needs to clarify with which point is the fault point by supplying
the power supply to each load after the fault is detected by the ELCB. When the fault point
is being activated, the ELCB detects the fault and trip mechanism is operated. The algorithm
will find the false point and reset the ELCB to restore the power supply to the loads. This
time, only the un-faulted point will be restored. In Customer Service Substation panel, two
contactors are used to activate one load. Although in Service Substation panel only uses one
feeder, the same algorithms (OLUC and OLDC) are applied to control the switching
operation of MCCBs by using customized solenoid. MCCBs have trip mechanism that is
able to detect faults. MCCBs are different from the loads used in Customer Service
Substation because they don't need to be accompanied by two switching devices to control
their operations.
The HMI is capable to communicate with the I/O devices. An HMI for SCADA is developed
in this research by using an embedded Ethernet controller as the converter to communicate
with the I/ O devices. By integrating the ELCB and MK2200 into the SCADA system, the
SCADA system is capable to respond to the faults by resetting both devices in order for the
algorithm to check the fault point.
Based on the experimental results, the system correctly locates the fault point, isolates the
fault point and reenergizes the un-faulted loads. However, during the fault isolation
operation, the system has to detect the fault point by simply switching on the fault load.
After the system acknowledges the fault point, the appropriate switching functions are
executed. The developed system has a potential in reducing the outage time while
comparing to the manual operation by the technicians and engineers.
From the analysis done, the outage times for both panels to locate fault and restore
electricity power supply to healthy loads are 50.7 seconds. By assuming that it takes 1 hour
for the technician to restore the electricity power supply, thus there is a 98.59%
improvement in the outage time operation. This system will help the utility company to
save money if the outage times are reduced. As described in Table 8, the failure percentage
for the system in detecting the fault and isolating the fault point is none. This means that the
system is reliable.
7. Future Research
The future research work should be aimed at developing of full scale Distribution
Automation system, which can cover from primary substations to consumer level intelligent
automation. Here are few recommendations which will lead new research projects in the
future:
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Customized Fault Management System for Low Voltage (LV) Distribution Automation System 69
a) Automated solutions to the distribution system comprising automation-ready made
building blocks such as a synthesis of state-of-the-art individual components
(distribution switchgear, fault passage indication, RTU, local power supplies, and
communications interfaces), integrated to form complete functional devices. These
devices are assembled into a system to solve the complete control or automation needs
of each distribution network.
b) Data collection of not only the status of CBs and relays but also status of each
component in the panels. This will help to reduce black-out due to equipment
malfunctions.
c) Develop a standard Distribution Automation software such as master distribution
automation software, customer information system (CIS), trouble call management
software (TCMS) and web based monitoring of distribution system.
8. References
Austerlitz, H. (2003). Data Acquisition Technique Using PCs. 2nd ed. California: Academic
Press, 416p. ISBN: 0-12-068377-6
Clarke, G. (2004). Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems,
Massachusetts Newness, 1st ed., 743p. ISBN 07506 7995
Glover, J.D. & Sarma M.S. (2002). Power System Analysis and Design., California: Pacific
Grove, 3rd ed., 527
p. ISBN 0-534-95367-0
Pabla, A.S. (2005). Electric Power Distribution, 2nd ed., New York: McGraw-Hill, 723 p. ISBN
0-07-144783-0
Lee, H.J. & Park, Y.M. (1996). A Restoration Aid Expert System for Distribution Substations.
IEEE Transactions on Power Delivery, Vol. 11, pp.1765 -1769
Hsu, Y.Y & Huang, H.M. (1995). Distribution System Service Restoration using the
Artificial Neural Network Approach and Pattern Recognition Method. IEEE
Proceeding Generation Transmission
Distribution, Vol. 142, No.3, pp.251-256.
Hsiao, Y. T. & Chien, C. Y. (2000). Enhancement of Restoration Service in Distribution
Systems using a Combination Fuzzy-GA Method. IEEE Transactions on Power
Systems, vol. 15, no. 4, November
2000, pp. 1394-1400
Huang C.M (2003). Multiobjective Service Restoration of Distribution Systems Using Fuzzy
Cause-Effect Networks. IEEE Transactions on Power Systems, Vol. 18, No. 2, pp.867
– 874
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70 Fault Detection
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Fault Detection
Edited by Wei Zhang
ISBN 978-953-307-037-7
Hard cover, 504 pages
Publisher InTech
Published online 01, March, 2010
Published in print edition March, 2010
In this book, a number of innovative fault diagnosis algorithms in recently years are introduced. These
methods can detect failures of various types of system effectively, and with a relatively high significance.
How to reference
In order to correctly reference this scholarly work, feel free to copy and paste the following:
M.M Ahmed, W.L Soo, M. A. M. Hanafiah and M. R. A. Ghani (2010). Customized Fault Management System
for Low Voltage (LV) Distribution Automation System, Fault Detection, Wei Zhang (Ed.), ISBN: 978-953-307-
037-7, InTech, Available from: http://www.intechopen.com/books/fault-detection/customized-fault-
management-system-for-low-voltage-lv-distribution-automation-system
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