Automated Electrical Protection System For Domestic Application

1. Automated Electrical Protection System for
Domestic Application
A.Z.H. Abd Azzis, *Nursyarizal Mohd Nor, Taib Ibrahim
* Electrical & Electronic Engineering Department,
Universiti Teknologi PETRONAS,
Bandar Seri Iskandar, 31750 Tronoh,
Perak, Malaysia.
e-mail: nursyarizal_mnor@ petronas.com.my
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Abstract—Power outage is a common problem when there are
electrical faults occurred, which would lead to discontinuity of
electrical supply to domestic building. For domestic consumers,
power continuity is very important since some of the appliances such
as refrigerator, aquarium and alarm system require a continuous
electrical supply. However, fault occurred in the system will trip the
earth leakage circuit breaker (ELCB) and disrupt the supply to all the
appliances. Fault may occur due to short circuit, ground fault or
overloading. Thus, the aim of this paper is to develop an automatic
system for single-phase power system to overcome the problems. The
automatic system is able to detect and isolate the fault in order to
ensure the power continuity in the building.
Keywords— current difference, earth leakage circuit breaker
(ELCB), fault location detection, miniature circuit breaker (MCB),
power recovery, residual current device (RCD)
I. INTRODUCTION
ower reliability and continuity is very important and
critical to a domestic building. There are electrical
equipments and appliances which need to be continuously
turned ON even when the occupants leave the building for a
period of time such as alarm system, refrigerator and aquarium
ventilation system. However, power outage may occur at any
time due to several causes such as strong lightning, short
circuit, grid faults and etc..
Single-phase is very common system used in domestic. The
term of single-phase electric power system is refers to the
distribution of alternating current (AC) electric power using a
system in which all the voltages of the supply is vary in load
demand [1]. Although single-phase system has its own safety
protection, i.e. earth conductor, but this not an hundred percent
reliable all the time. In Malaysia, from year 2005 to 2011,
there are 405 accidents due to electrical fault event, and 191
people are died due to the accidents [2]. Therefore, instead of
giving awareness on electrical safety and hazard to the public,
a proper protection devices also need to be considered as part
of electrical safety.
In domestic premises, there are three common factors that
cause electrical problems at home that might lead to fatality or
equipment failure [3]. The three common factors are faulty
wiring in the house, improper flexible cords, and faulty
appliance. Technically, the causes of the above factors are
current/earth leakage fault and overcurrent fault. Earth leakage
fault is exists when unintended path is established between the
normal current carrying conductors which has contact directly
or indirectly with earth [4]. Overcurrent fault is occur when
the current exceeds the rated current carrying capacity of the
conductor [5] and can be divided into two types: overload and
short circuit.
In this paper, Section II explains the working principle of
ELCB and MCB. Section III gives details on the system
operation. Section IV presents the materials components
selection and simulation circuit setup. Then, Section V and
Section VI analyse about the result of experimental test and
actual test using designed prototype. Section VII is the
conclusion of this paper.
II. WORKING PRINCIPLE
Overcurrent and ground faults are very common faults to be
occurred in single-phase power system. Protection devices
such as MCB and ELCB or RCD are used to protect from
overcurrent and ground faults respectively.
A. Earth Leakage Circuit Breaker (ELCB)
Basically, there are two types of ELCB: voltage operated
and current operated [6]. Voltage operated ELCB operates at a
detected potential of around 50 V to open a main breaker and
isolate the supply from the protected zones [7]. But since it
operates at 50 V, it is not been used in newer domestic wiring
as the 50 V is still considered as safe voltage for alternating
current [8]. For newer domestic wiring, current operated
ELCB is more preferable to be installed in premises due to
reliability. Current-operated ELCB is generally known as
residual current device (RCD). The function is similar, which
protects against earth leakage, though the details and method
of operation are different [6].
The RCD operates by measuring the current balance
between two conductors using a differential current
transformer, as illustrated in Fig. 1. The difference current
flow from the load and to the load is known as residual current
is measured. The current leakage is occurring when the
residual current is not equal to zero and the device will open
the contacts [9]. The RCD in buildings must be installed with
residual current rating of 30 mA for protection against shock
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978-1-4673-5074-7/13/$31.00 ©2013 IEEE
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013
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2. [10]. The RCD will trip if the residual current or the difference
between current flowing in an out exceeds 30 mA.
Fig. 1 Tripping Mechanism of ELCB
B. Miniature Circuit Breaker (MCB)
The MCB is resettable protective device which designed to
isolate a circuit during an overcurrent (both overload and short
circuit) event without using fuse [11]. MCB is choosing for
building protection rather than fuse because of its resettable
capability [12]. MCB typically comprises an electrical contact
mounted on a movable contact carrier which rotates away
from a stationary contact in order to interrupt the current path.
The mechanism of operation includes a movable handle that
extends at the outside of the housing.
The handle has basically three stable positions: on, off, and
tripped. These three positions are to indicate the condition of
the contacts when the handle is viewed. The trip mechanism is
automatically releasable to effect tripping operations and is
manually resettable following tripping operations. The
mechanism will respond to instantaneous high current to open
the contact and therefore interrupt the current flow [12].
III. SYSTEM OPERATION
The automatic system is designed for domestic electrical
system to auto-reset ELCB and auto-detection if any
permanent fault occurred. The system operation is divided
into two parts: power recovery and fault location detection.
A. Power Recovery
Power recovery is a process of turning back the power ON
when electric power encounters unexpected shut down for a
period of time due to tripping or faults. A quick power
recovery is important for equipments or electrical appliances
which require continuous power supply such as refrigerator,
water pump for aquarium, alarm system and others.
Currently, for home electrical system, power recovery is
manually done. In other words, a person has to switch on the
main switch in distribution board to turn the power back on
after tripping occurred. This becomes a problem when the
residents or owner of the house is out for a period of time and
no one is there to turn the power back on.
When fault is occur, ELCB will trip and break the electrical
supply from mains to all feeders (electrical appliances or
loads). An automatic system is needed to switch ON ELCB so
the power supply can be restored. However, if the fault is
permanent, the ELCB will not able to turn ON. Therefore, to
overcome the problem, a system with ability of detecting fault
location need to be developed. Once fault detected and
isolated, ELCB will be switched ON and supply is restored.
B. Fault Location Detection
Domestic electrical fault would normally occur at individual
circuit, either switches or sockets. Electrical fault may occur
due to current leakage or overcurrent condition, such as
overload or high level short circuit, and may occur at any
point in the domestic electric system. Fault location detection
may facilitate the process of power recovery to recover from
unexpected power outage.
To isolate faulty circuit from main line, the location of the
fault must first be identified. This can be done through current
difference between the amount of current travelling into the
load and the current travelling out of the load. Fig. 2 illustrates
a simple domestic electrical wiring diagram, where the current
in live wire (red line) is travelling through ELCB and MCB to
the load. The current then travels out from the load to neutral
bar through neutral wire (black line) and travels back to
ELCB. The amount of current travel in and out is measured
and compared.
Fig. 2 Simple Domestic Electrical Wiring Diagram
The current difference is configured to a 30 mA as the
ELCB trip rating is 30 mA. If the difference exceeds 30 mA,
the system will be able to locate at which MCB is the fault
located. If the difference of any MCBs e.g. MCB 1 exceeds
30 mA, then MCB 1 will be turned OFF and ELCB will reset.
Therefore, the electrical power will be restored since the fault
has been isolated.
IV. COMPONENTS SELECTION AND SIMULATION SETUP
A. Component Selection
There are two main components for this project, the sensor
and microcontroller. The selection of these components is
based on efficiency, cost, size, and the rated values.
1. Current Sensor
It is very important to select an accurate current
sensor in this project. The accuracy of current value
measured by this current sensor will lead to the
accurateness of detecting fault location and fault
isolation from the main line. In general, most home
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013
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3. electrical appliances will draw current up to 20 A.
Therefore, a current sensor with rating at least 25 A and
split core for the ease of clamping is chosen in this
project.
2. Arduino UNO Board
The Arduino UNO board is the main microcontroller
board in this project. All calculations and data
collections will be done through this board. This board
is selected based on its friendly-user characteristic,
with ability of receiving analog input data and able to
produce PWM or digital output. This board is different
from other PICs as it can be powered up by using USB
cable connected directly to the PC.
B. Simulation Circuit Setup
A circuit has been setup as in Fig. 3 with two current
sensors (line and neutral) connected to the input of Arduino
board for simulation purpose. The current sensors function to
capture and deliver the current value to the micropocessor.
The program is successfully developed and downloaded to the
Arduino board. The circuit is designed to simulate and observe
the functionality of the developed system.
Fig. 3 Simulation Circuit Setup
In the simulation, the desired hardware (motor, solenoid and
hand phone) used in real prototype is currently represented by
LED, for testing purpose. The function of each LED is
summarized in Table I. The output of the simulation can be
observed through the LCD display and LED.
TABLE I
LED FUNCTION
LED Number Function
0 Indicate power supply
1 Indicate normal condition
2 Indicate fault condition
3 Represent DCmotor, for ELCB auto-reset
4 Represent DC motor, for triggering MCB off
5 Represent hand phone, for call alert
V. EXPERIMENTAL TEST AND ANALYSIS
Three experiments were conducted to analyze the
functionality of the system developed in normal condition,
during ELCB trip and fault detection.
A. Current Sensor Funtionality Test
A test was conducted to verify the functionality of the
current sensor. The test is conducted with several domestic
devices at 240 VAC that commonly used in human daily life
for example lamp, kettle, iron and rice cooker. The reading is
taken by using current sensor, which can be observed through
the serial display of the microcontroller. According to the
datasheet, accuracy of the current sensor is about ±1 %. The
result of the test is summarized in Table II.
TABLE II
CURRENT SENSOR TEST RESULT
Device
Power
(Watt)
Calculated
Current
(Amp)
Current
Reading
(Amp)
Lamp 70 0.292 0.350
Rice
Cooker 450 1.875 1.887
Iron 1000 4.167 4.204
Kettle 1500 6.250 6.265
From the result in Table II, the reading of the current sensor
is in range of accuracy as in the current sensor’s technical
specifications given by the supplier . The current sensor is
valid to be used as measurement device in this project.
B. Normal Condition
This test is to verify that the system is able to detect normal
condition, at which power is ON (or “1”). When the system
detects a normal condition, LED 1 will light up and the LCD
will display “Normal Condition” as in Fig. 4. Normal
condition means that the circuit is working as usual without
fault, or no fault yet had occurred.
Fig. 4 Normal Condition
C. Auto-Reset ELCB
This section is to test the functionality of automatic ELCB
reset operation. During power outage, at which power is OFF
(or “0”), LED 2 will light up to indicate that the ELCB is
tripped or fault condition is occurred. ELCB will undergo
maximum of three times reset testing. To represent the motor
that will reset the ELCB, LED 3 is set to be ON for 3 seconds
and OFF for 3 seconds as delay. The 3 seconds delay is to
make able for the microprocessor to check if the power is “1”
or “0” and to switch off the motor. If “1”, the system will be
back to normal operation. If “0”, the system will reset ELCB
up to three times. During the reset operation, the LCD will
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013
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4. display “ELCB Tripped, Reset Test: (Test Sequence Number)”.
The result of the test is as in Fig. 5.
Fig. 5 ELCB Reset Sequence
D.MCB Check Operation
Once the ELCB reset operation reaches “Reset Test: 3”, and
the power is still “0”, the system will check each MCB since
MCB is installed at individual circuit. The system will check if
the difference between line current and neutral current exceeds
the limit current, which is 30 mA. When entering the MCB
check operation, LED 3 will turn OFF and LED 4 will turn
ON for 3 seconds while the LCD displays “MCB Checking...”
as in Fig. 6. LED 4 then will turn OFF, and LED 3 will turn
ON again for 3 seconds to reset the ELCB. Assume that once
the LED 4 is OFF, the MCB is in OFF position.
Fig. 6 MCB Check Operation
The program will check, if the power is still “0”, the
system will trigger call alert to inform the user that a fault has
occurred at her/his house. Phone alert is represented by LED
5. LED 5 will turn ON for 4 seconds to trigger call alert and
LCD will display “Unknown Fault; MCB Off” as in Fig. 7
since the cause of fault is unknown.
Fig. 7 Unknown Fault with MCB Off
But if power is “1”, or ON, call alert will also be triggered
but the LCD will display “Fault Detected @; MCB 1” as in
Fig. 8 since the fault is known occurred at MCB 1. For testing
purpose, only one MCB is being used and labelled by “MCB
1”.
Fig. 8 Fault Detected at MCB 1
However, if the difference does not exceeds 30 mA, but the
power is still OFF or “0”, the LCD will display “Unknown
Fault; MCB On” and call alert will be triggered as in Fig. 9.
This is due to unknown fault which cannot be detected by the
MCB. This will keep all the MCBs remain at OFF position.
Fig. 9 Unknown Fault with MCB On
VI. PROTOTYPE DEVELOPMENT AND TEST
The develop system will be implemented in a prototype and
hardware. Fig. 10 shows the overall view of the prototype
designed.
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013
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5. Fig. 10 Overall View of the Prototype
The prototype is designed with one ELCB and two MCBs
to represent the home distribution board. There are two main
boxes in the prototype, the main and external box. The main
box is where the ELCB and MCBs are placed, while the
external box contains batteries, Arduino board, LCD display
and other electronic components.
The ELCB in the prototype will be connected to the 240 V
input voltage for incoming and distributed to the MCBs. The
MCBs are connected to individual socket which will be
connected to any load.
A. Normal Condition
The first test of the prototype is conducted during a normal
condition. It is a condition where everything is working as
usual, no fault during this period. Fig. 11 shows the result of
the test. In this test, both MCBs and ELCB are in ON position
and LCD display will display “Normal Condition”. An
indicator, the green LED, will light up to indicate the system is
in normal condition.
Fig. 11 Normal Condition of the Prototype
B. Prototype Auto-Reset ELCB
The second test is auto-reset ELCB function by using the
prototype designed. The operation and reset sequence is
similar to the simulation test in Section V, part C, but the
LEDs are replaced with a DC motor. The ELCB reset
sequence is shown in Fig. 12. During fault, ELCB will be in
OFF position. After reset operation, ELCB will be in ON
position. The LCD will display the reset sequence to indicate
the number of reset test done.
The system developed for the auto-reset ELCB will check
for power after each reset sequence is completed. For instance,
after ELCB had completed reset test sequence 1, the system
will check for the electrical power supply. If there is no power
supplied, then the system will go for next reset sequence. But
if power is restored after the first or second sequence, then the
system will indicate “Normal Operation”. The triggering
mechanism for the ELCB is controlled by a DC motor.
Fig. 12 Actual Auto-Reset ELCB Test
C. Fault Location Detection Test
Once the auto-reset ELCB operation is at “Reset Test: 3”,
the system will check for fault at MCB. For testing purpose
and real situation demonstration, electrical fault is
intentionally created at MCB 1. Fig. 13 shows the flow of
MCB checking operation. Once the system enters the MCB
checking stage, it will read current value obtained from line
and neutral current sensors and check for the current
difference at MCB 1.
If the difference exceeds 30 mA, MCB 1 is considered as
faulty. Therefore, MCB 1 will be switched off and ELCB will
be reset again. Once the process of switching off and on MCB
and ELCB is completed, the LCD will display “Fault Detected
@ (Fault Location)”. In this test, it displays “Fault Detected
@ MCB 1”, indicating that an electrical fault had occurred at
MCB 1. Then, the system will trigger call alert to notify the
user. Both MCB 1 and MCB 2 are controlled by a DC motor
allocated for each of the MCBs.
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013
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6. Fig. 13 Fault Location Detection Test
D.Unknown Condition Test
There are certain conditions where no fault is detected but
electrical power is still OFF, or the faulted MCB is already
OFF but still there is no supply. For both conditions, two tests
have been conducted.
To test for the first condition, supply is disconnected from
the main box to create no fault situation and with no electrical
power. Result of test is shown in Fig. 14. For the second
condition, supply is disconnected and MCB 1 is intentionally
faulted as in previous test and result shown in Fig. 15.
Fig. 14 Actual Test for Unknown Condition 1
Fig. 15 Actual Test for Unknown Condition 2
VII. CONCLUSION
Automated Electrical Protection System or Auto-EProS can
be considered as a new invention in electrical protection field.
It is an additional feature to the electrical protection system to
enhance the performance of domestic protection system. From
the findings and functionality of the prototype, Auto-EProS
will solve current power problem in domestic electrical
system.
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