This document discusses the design and implementation of a microprocessor-based numerical relay for protection against over/under current and voltage. It emphasizes the need for reliable protection devices in power systems to prevent faults from causing extensive damage, and outlines the operation of the relay using an Arduino Uno microcontroller. Simulations and hardware tests validate the functionality of the relay, which is capable of sensing faults and alerting users through an alarm system.

1. RESEARCHARTICLE
Copyright © 2020 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Computational and Theoretical Nanoscience
Vol. 17, 1–7, 2020
Modelling and Implementation of Microprocessor Based
Numerical Relay for Protection Against Over/Under
Current, Over/Under Voltage
Adeel Saleem1 2 ∗
, Atif Iqbal3
, Kashif Mehmood2 4
,
Muhammad Adnan Samad2 5
, and Muhammad Aftab Hayat6
1
School of Electrical & Electronics Engineering, North China Electric Power University, Beijing 102206, China
2
Department of Electrical Engineering, The University of Lahore, Lahore, Pakistan
3
School of Renewable Energy & Clean Energy, North China Electric Power University, Beijing 102206, China
4
School of Electrical Engineering, Southeast University, Nanjing, China
5
School of Automation, Beijing Institute of Technology, Beijing, China
6
School of Control & Computer Engineering, North China Electric Power University, Beijing 102206, China
This paper includes the design and implementation of Numerical Relay that can protect the equip-
ment against over-voltage, over-current and under voltage. Although, every power system is sub-
jected to faults and these faults can severe damage to the power system. Therefore, it is necessary
to observe and resolve in time to avoid a large damage such as blackouts. For this purpose, there
should be some sensing devices, which give signals to the circuit breakers for preventing of power
system damages. The multipurpose relays have much importance role in power system for sensing
and measuring the amplitude of faults. Numerical relay provides settings of over-current, over-
voltage and under voltage values. Simulations have been carried out using Proteus software along
with tested on hardware with Arduino Uno Microcontroller that proves the working and operation of
numerical relay.
Keywords: Arduino-Uno Board Faults, Microcontroller, Over Voltage, Under Voltage,
Overcurrent, Proteus 8 Professional.
1. INTRODUCTION
The Electrical Power System providing electrical energy
to the consumers is protected by sophisticated protec-
tive systems against faults. Relays, the sensing devices
in protective systems, sense and declare the fault pres-
ence in a system. Thus, relays protect throughout from the
generation, transmission to distribution. There are several
types of relays which can be used for protection tech-
niques: static, digital and electromechanical. Static relay
uses static. It uses medium and large scale integrated. Once
the current and voltage values are stepped down by CT and
PT to a particular level. Rectifier rectifies the output from
a CT or PT [1]. Then this output is fed to comparator or
any logic circuit which have check on the threshold value.
When the value of the current or voltage is out of range, it
energizes the trip signal, which is fed to the circuit breaker.
In electromechanical relays, an electromagnetic interac-
tion is happened for the trip signal but for numerical relays
∗
Author to whom correspondence should be addressed.
only logic implemented in software which uses micropro-
cessor technology. In some cases, the relay is the combi-
nation of static and digital technology [2]. For static relays
measurement is done by the optical, electronic or mag-
netic means which are totally independent of mechanical
motion. Most of the cases the electro-mechanical relays
are the auxiliary relays and static relays shaped as shield-
ing provision for electro-mechanical auxiliary relays [2].
In power system protection field, there have been many
situations where insurance speculations and strategies have
assumed an imperative part. With the progress of the meth-
ods of protection, there are currently numerous applica-
tions for insurance with expanded execution. However,
these systems become complicated and highly composite.
It is therefore expectation that techniques of protection will
make further progress.
As the world progress towards the digital techniques
so power industry power industry had further impact on
development of the power systems protection on equip-
ment and techniques. The low cost, high end performance
J. Comput. Theor. Nanosci. 2020, Vol. 17, No. xx 1546-1955/2020/17/001/007 doi:10.1166/jctn.2020.8809 1

2. RESEARCHARTICLE
Modelling and Implementation of Microprocessor Based Numerical Relay for Protection Saleem et al.
microprocessor has led to their expanding use in digital
relaying techniques. In this thesis, the design and imple-
mentation of microprocessor based numerical relay for
multi-function protection system is done [3]. The project
utilizes knowledge and principle of overcurrent, under
voltage and overvoltage schemes.
The numeric relay in our design employs Arduino Uno
microcontroller. The instrument transformers (CT and PT)
provide stepped down phase current and voltage to micro-
controllers that display values on LCDs. The comparison
of these values is made with pickup values given by user
through keypad, and then decision is made about occur-
rence of the fault. The built-in ADC of Arduino Uno has
been used for running conversion (A/D) and comparison.
Thus, controller indicates fault occurrence by showing the
type of the fault and energizing an alarm [4]. The possible
fault conditions sensed by this design are under voltage,
over voltage and over current faults including time delay.
2. THE FUNDAMENTALS OF POWER
SYSTEM PROTECTION
Electrical energy is produced by the electric power gener-
ation systems, which are basic foundations whose admin-
istration is crucial to the economy of a nation. Electric
power system is a collection of electric components which
are used for the continuous power supply to the consumers
through the transmission. Their main goal is to facilitate
the home and industry with the continuity of power sup-
ply. So, for continuity of reliable electric supply to meet
the demand is a difficult challenge for them. To make it
possible they have to make a strong real time estimation of
the system and coordination with the generating units. In
the result of this is the only way to deliver the electricity
to the load in secure manner. It’s had a worldwide impor-
tance for the power system network security. However, due
to deregulation, power systems are being operated closer
to their nearer load ability [3].
Usually power systems equipment is very expensive,
and in this way a power system represents a very huge
investment. As much as possible the power system must
be utilized within the applicable constrains of reliability
and security of the supply. It is necessary that power sys-
tem should operate in a safe limit for all the times without
knowing that how efficiently a power system is designed.
The occurrence of the faults in the power system can-
not be stopped. So, these faults are the main risk for the
equipment install there and for the employees which are
working over there.
As when the fault occurs so the large surge with a
high current can burn the conductors, transformers or other
machines installed there in just few seconds. Figure 1
shows that a number of components are interconnected in
the power system. So, there should be a very careful pro-
tection to save all these components.
Fig. 1. Block diagram of electrical network.
3. POWER SYSTEM PROTECTION
Protection equipment is a collection of protection devices.
All these components are necessary for the complete
power system protection and reliability of operation of
power system even in case of faults. There are some com-
ponents in power system protection i.e., Relays, Fuses,
CTs, PTs, and Contactors etc. [1, 3].
The specification and necessities of these components
are as follows:
1. Step down the current and voltage by using the current
and voltage transformers in electrical power system to a
save levels for the relays to deal with it.
2. Sensing of the fault by relay and sending a trip signal
to the circuit breakers.
3. Circuit breaker isolates the faulty part from the power
supply part by opening their contacts.
4. Energize batteries are used in case of high power rating
system where energy is required to open terminals in the
system.
5. In some cases, the communication channels are used to
analyze the voltage and current at remote locations of the
line to trip the equipment.
4. ATTRIBUTES OF PROTECTION SYSTEM
An efficient power system protection may have some qual-
ities in it so that if a fault occurs we can sense it properly.
Moreover a protection system should be fast to remove
faults and prevent system from large damage. Following
are the necessary requirements of an efficient protection
system.
1. Speed in power system protection plays a great role.
In automatic protection system the faults from the power
system is isolated in a very much shorter time.
2. Sensitivity is referred as the ability of protection sys-
tem to sense the minimum possible fault in a system and
isolate. The relay or scheme is said to be sensitive if the
primary operating parameter(s) is low.
3. Reliability a power system is said to be reliable when
it is able to meet the power requirements of variable load
over time without any hurdle or discontinuity.
4. Selectivity is referred as the ability of protective system
to identify the fault in exact location and isolate only the
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Saleem et al. Modelling and Implementation of Microprocessor Based Numerical Relay for Protection
Fig. 2. Cyclic development of numerical relay.
faulted part from healthy system. A protective system must
be selective for that purpose.
5. NUMERICAL RELAYS
Numerical relays have great convenience and pre-
cision for the appliances against the conventional
Fig. 3. Block diagram of a microprocessor relay.
electromechanically relays [2]. As one of the factors is the
low capital cost for these numerical relays along with min-
imum maintenance cost. Figures 2 and 3 show the devel-
opment cycle and typical block diagram of numerical relay
respectively.
The Figure 2 is flow chart of numerical relay. It shows
the working strategy of numerical relay. How operations
are performed in a cyclic manner in run times. The
Figure 3 shows the general-purpose block diagram of
numerical relay. Any numerical relay includes the above
mentioned components and working terminology [5].
6. MODELING AND WORKING OF
NUMERICAL RELAY
Numerical Relays which also known as the programmable
relays are totally microprocessor-based relays [6]. The
usage for these particular relays has much importance in
the industries. The microprocessor based relays are capa-
ble for protection against over voltage, over current, ther-
mal overload and various other faults and all this happen
by just few modifications in the program or changing the
plug setting on run time [5]. The working of the numer-
ical relays is based on the data sampling on continuous
basis. It takes the entire signal on run time through analog
to digital converter. Then the numerical relays sense the
faults and make decisions accordingly.
6.1. Overcurrent
Overcurrent occurs if current in excess of the rated cur-
rent of equipment or the ampere capacity of a conductor
flows. It may result from overload, short circuit, or ground
fault [7]. Abrupt rise in current in system is also referred
as overcurrent. Following Figure 4 show the waveform of
overcurrent surges in system.
Above mention figure there is overcurrent surge for a
small interval of time. Short time overcurrent spike is
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Modelling and Implementation of Microprocessor Based Numerical Relay for Protection Saleem et al.
Fig. 4. Overvoltage spike in normal waveform.
referred as surge while abruptly rising of current is referred
as fault or short circuit current. Both can cause severe dam-
age to system or devices. Sometimes large current cause
burning of conductors and insulations and in severe cases
sometimes fire occurs.
6.2. Over Voltage
Overvoltage occurs in response of transients and short
duration spikes of high voltage on the supply. It causes
due to lightening strokes [8].
Also, when some unloaded transmission line is con-
nected in system overvoltage occurs and when full load
transmission line is disconnected in a system overvoltage
may occur. Overvoltage in a system can cause breakage
of insulation, rise in current, and damage of some fragile
components [9]. Figure 5 includes the overvoltage spikes
waveforms and may cause due to lighting strokes.
6.3. Under Voltage
Under Voltage condition occurs when a heavy load is sud-
denly connected to a power supply. The load starts drawing
current; this causes the voltage to temporarily drop [9].
Also when a full load transmission line is connected in
a system then temporary under voltage occurs. Following
Figure 6 show the under voltage in a system waveform.
Fig. 5. Overvoltage spike in normal waveform.
Voltageperunit
–1
0
+1
Time
Fig. 6. Under voltage waveform.
In Figure 6 voltage amplitude is decreasing with time
as a heavy load is connected in a system. Although the
voltage can be set to its original value after some cycles.
No generator or power source is ideal and voltage cannot
be kept constant in a system at all operating conditions.
7. CIRCUIT DIAGRAM AND HARDWARE
METHODOLOGY
In our project, we have tried to design the numeric relay
based on Arduino Uno microcontroller technology with
the provision of Over Current, Over Voltage and Under
Voltage sensing and indication including a definite time
delay. The design is thus a “Discrete time Over-current and
Over/Under voltage relay.” It is a single-phase relay hav-
ing single micro controller, controller monitors the phase
quantities (i.e., current and voltage) thus, makes the trip
decision and displays the results on LCD accordingly. The
project is divided into three main sections as under:
1. Data Acquisition.
2. Data Processing.
3. Auxiliaries.
7.1. Data Acquisition
Data Acquisition Section consists of Instrument Trans-
formers i.e., Current Transformers (C.T) and Potential
Transformers (P.T). The real-time values of high line Volt-
age and Current are stepped down with the help of P.Ts.
and C.Ts. These values are input to a half wave recti-
fier circuit which rectifies these stepped down A.C val-
ues and provides DC voltage values at output terminals
Fig. 7. Connection of arduino with keypad and LCD.
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Saleem et al. Modelling and Implementation of Microprocessor Based Numerical Relay for Protection
Potential Transformer
Fig. 8. Potential transformer.
proportional to the line voltages and currents. This is effec-
tively an Anti-aliasing filter giving smooth and clean signal
at its output. The main part of Data acquisition section
is the built-in ADC (analogue to digital converter) of
Arduino Uno microcontroller which converts analog line
current and voltage signals into digital values, stores them
in respective registers and displays them onto the LCD
connected to the microcontroller.
7.2. Data Processing
The central part of the Numeric Relay consists of
Arduino Uno Microcontroller. A keypad has been inter-
faced to microcontroller that can be used to enter the
pickup/threshold values of current for relay operation. The
values entered by keypad are displayed on a main micro-
controller and read by the controller and compared with
the pre-saved current values. The comparison algorithm
burnt in controller decides whether a fault occurred on the
system, then gives a time delay and waits for the fault
to clear out itself. The micro-controller displays the state-
ment after clearing the fault a buzzer (alarm) has also been
attached to the main micro controller that sounds imme-
diately when the fault occurs. The relay is reset to un-
faulted condition when some personnel attend the fault by
pressing any key from the keypad. The relay is reset too
Current Transformer
Fig. 9. Current transformer.
when fault clears out itself in a pre-set time. This provides
Definite Time characteristics to the relay.
Auxiliaries
1. Arduino Uno.
2. CT and PT.
3. LCD Display.
4. Numeric Keypad.
5. Buzzer/Alarm.
6. Auto Transformer for Variable Voltage Input.
7. USB interface.
8. SIMULATION OF NUMERICAL RELAY
A numerical relay consists of components that includes
LCD for display of voltage and current values, a keypad
for giving the plug setting of voltage and current, a micro-
controller for monitoring all operations and making deci-
sions and a then there are CTs and PTs for stepping down
the voltage and current magnitudes for electronic circuit
feasibility. Following Figure 7 show the block diagram of
overall numerical circuitry that includes the LCD for out-
put display of current and voltages, a keypad for run time
settings of voltage and current.
It is mandatory to simulate each and every component to
ensure the reliability of proper working of numerical relay.
LCD interfacing with controller, keypad interfacing with
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Modelling and Implementation of Microprocessor Based Numerical Relay for Protection Saleem et al.
Fig. 10. Relay tripping circuit.
microcontroller, designing appropriate voltage signal for
microcontroller and scaling current magnitude for micro-
controller are necessary outcomes.
8.1. Designing of Voltage Signal
In numerical relays microprocessor-based circuits monitor
the voltages and currents in run time and take decisions on
the basis of these values and take actions. For this purpose,
first of all the voltage should be measure. Microprocessor
circuits samples the analogue values and read it in digital
values. In a running practical system there are high ratings
of voltages and that cannot be measure directly by elec-
tronic circuits so we need a potential transformer to step
down the high values and then convert in to digital values
for microcontroller processing. Following Figure 8 show
the potential transformer circuit.
The above circuit includes a potential transformer and
the sampling circuitry. Input voltage is scale to a particular
level for some voltage, as the voltage varies output scaled
DC voltage varies accordingly.
8.2. Designing of Current Magnitude Signal
In a practical running circuit, the current values are very
high and cannot be measured directly by some electronic
Fig. 11. Wiring diagram of the project.
circuit. That’s why we use some current transformer that
stepped down the input high current. Then we scale the
stepped down value to a particular level for some running
load current. As the load current varies the output scaled
value varies. Figure 9 shows the current transformer and
scaling value circuitry.
8.3. Relay Tripping Circuit
A relay is connected in series with load so that in case of
any fault we can disconnect the load from supply to avoid
a large damage. The relay is tripped by electronic circuit
when the electronic circuit gives only logic 0 or logic 1
functions. So, we need the following circuit in Figure 10
that can take logic zero or logic 1 function and trips the
relay.
The above circuit includes the whole circuitry that
takes logic input from microcontroller and operates
the relay. The relay needs 12 volts for its operation
while microcontroller logic 1 voltage is only of few
volts. So, to differentiate between these voltage lev-
els we have opto-coupler there. Biasing voltage applied
to relay that will be available only when output of
opto-coupler short circuit accordingly with input small
signal.
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Saleem et al. Modelling and Implementation of Microprocessor Based Numerical Relay for Protection
9. HARDWARE DEMONSTRATION OF
NUMERICAL RELAY
Following Figure 11 includes all the components in a sys-
tem for implementation of numerical relay which includes
the CT’s and PT’s connected with load. All the necessary
components are connecting the microcontroller.
10. CONCLUSION
The built-in ADC (analogue to digital converter) of each
of the Arduino Uno microcontroller which converts analog
line current and voltage signals into digital values, stores
them in respective registers and displays them onto LCD
connected to the microcontrollers. The micro-controller
displays the appropriate fault condition on an LCD includ-
ing the type of fault (i.e., O/C, OV or U.V.). A buzzer
(alarm) has also been attached to the micro-controller that
sounds immediately when the fault occurs. A definite time
delay of 1, 2 or 5 seconds can be introduced between
occurrence of fault and its indication. The relay is reset to
un-faulted condition when fault clears out itself in a pre-
set time. This provides Definite Time characteristics to the
relay.
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Received: 26 May 2019. Accepted: 11 September 2019.
J. Comput. Theor. Nanosci. 17, 1–7, 2020 7