sample of the output voltage is fed to the Arduino. This voltage is ... (6) LCD Display: This displays the supply voltage as well as some information at âswitch onâ ..... library to simplify use of the I2C bus; see the documentation for details. For SPI ...
ARDUINO BASED OVER VOLTAGE RELAY FOR HOME Project Report Submitted to V. R. Siddhartha Engineering College For the award of the degree
Bachelor of Technology In Electrical and Electronics Engineering Under the esteemed guidance of Mr.K.SRIKANTH, M.E
Assistant Professor By
P. SRI VASUDHA VALLI (128W1A02A4) B.SANDHYA (128W1A0264) N.VIJAY (128W1A02A3)
A.SREEKANTH REDDY(128W1A0262)
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING VELAGAPUDI RAMAKRISHNA SIDDHARTHA ENGINEERING COLLEGE (Autonomous) Approved by AICTE-Approved by UGC-NBA Accredited-ISO 9001:2008 Certified Affiliated to JNTU-Kakinada
April - 2016
BONAFIDE CERTIFICATE This is to certify that the project report entitled “Arduino Based Over Voltage Relay for domestic loads” is the bonfide work of P. Sri Vasudha Valli (128W1A02A4), B. Sandhya (128W1A0264), N. Vijay (128W1A02A3), A.Sreekanth Reddy (128W1A0262), out during the VIII Semester, IV/IV B.Tech. The work was duly satisfactory and is in accordance to the partial fulfillment of the award of Bachelor’s Degree
Signature of Guide Mr.K.SRIKANTH M.E
Signature of HOD Dr. P.V.R.L.Narasimham M.Tech, Ph.D
Assistant Professor
Professor and HOD
Department of E.E.E
Department of E.E.E
ACKNOWLEDGEMENT
Applying theoretical knowledge to bring out the desired practical output is just climbing a peak, step by step, sorting out all the potential and crafting them into the requirement. In fact, it was our team work that has got us all through. Though it will not be enough to express our gratitude in words to all those people who helped us, we still like to give thanks to many of them. First of all we take immense pleasure in thanking our head of the department Prof.P.V.R.L.Narasimham for valuing our work all through the semester in regards with our project work. We are always thankful for his generosity in helping his students through their task with success. Great deals appreciated go to our faculty in concern, Assistant Prof.K.Srikanth for his contribution in motivating us all through the semester, sharing his knowledge and his valuable advices towards the completion of our project. His Attitude towards us in crafting the project was enthusiastic and drove us in conceptual Orientation. At last, we owe our true friendship to our fellow students, who had helped us since the inception of our project and also to those who had helped us in finding resources.
‹ Thanking You All ›
P.Vasudha B.Sandhya N.Vijay A.Sreekanth
3
ABSTRACT
The aim of this project is to develop a high voltage tripping mechanism to protect the load from damage. The fluctuation in AC mains supply is frequent in homes and industries. The abnormal over voltages may be caused due to various reasons such as sudden interruption of heavy load, lightening impulses, switching impulses etc. The sensitive electronic devices in these conditions can get easily damaged. It is preferable to have a tripping mechanism to protect the load. Our project aims at protecting the electrical equipment from over voltages using an Arduino. The main purpose of this relay is to isolate the load from over voltage conditions by controlling the relay tripping coil with an Arduino. It detects any voltage greater than 230V AC (pre-set value). If the voltage is greater than the pre-set value, it initiates a trip signal which in turn is given to the circuit breaker. Then the circuit breaker isolates the load from the source. Definite time and inverse time characteristics are being employed for the relay. For definite time characteristics, whatever be the magnitude of the over voltage, the relay operates only after 5 seconds of the fault. For inverse time characteristics, the trip time decreases with increase in magnitude of supply voltage and the relay operates accordingly. During the operation of the relay, if the voltage comes back to the pre-set value (230V AC), then the relay resets. This project can be further extended to over current relay. For all the above process to happen, real time monitoring of the data is required. After getting this data, based upon the programming in the memory (ROM/RAM), the controller takes the decision of the tripping of the system. This device can be used directly as a standalone equipment between the mains supply and the load, or it may be inserted between an existing automatic/manual stabilizer and the load. It has the specialty of tripping 5 loads of different mains at the same time.
4
TABLE OF CONTENTS 1
INTRODUCTION
8
2
OVER VOLTAGE
9
2.1
TYPES OF OVER VOLTAGE
9
2.1.1
EXTERNAL OVER VOLTAGE
9
2.1.2
INTERNAL OVER VOLTAGE
10
2.2
CAUSES OF OVER VOLTAGE
11
2.2.1
INTERNAL OVER VOLTAGE
11
2.2.2
EXTERNAL OVER VOLTAGE
11
3
BLOCK DIAGRAM 3.1
DESCRIPTION OF BLOCK DIAGRAM
14 14
4
CIRCUIT DIAGRAM
17
5
OPERATION
18
6
FLOW CHART
20
6.1
7
DECSRIPTION OF FLOW CHART
21
HARDWARE USED
22
7.1
TRANSFORMER
22
7.2
RECTIFIER
23
7.3
CAPACITOR
25
7.4
VOLTAGE DIVIDER
26
7.5
ARDUINO
27
7.5.1
MORE ABOUT ARDUINO
29
7.5.2
PIN OUT OF ARDUINO
30
7.5.3
COMPLETE ARDUINO
33
7.5.4
AUTOMATIC RESET
35
7.6
LIQUID CRYSTAL DISPLAY
35
5
7.6.1
LCD BACKGROUND
36
7.6.2
LCD PIN OUT
37
7.6.3
INTERFACING LCD WITH ARDUNIO
38
7.7
RELAY
40
7.7.1
TYPES OF RELAY
40
7.8
CURRENT SENSOR
45
7.8.1
INTERFACING CURRENT SENSOR WITH ARDUINO PIN DESCRPTION OF CURRENT SENSOR
46
7.8.2
47
8
CODE
48
9
PROTEUS SIMULINK SOFTWARE
53
10
RESULT
55
11
CONCLUSION
57
12
APPLICATIONS
57
12.1
APPLICATIONS OF OVER CURRENT RELAY 57
12.2
APPLICATIONS OF OVER VOLTAGE RELAY
13
BIBILOGRAPHY
58
59
6
LIST OF FIGURES 2.0
3.0 3.1.1 4.0 6.0 7.1.1 7.1.2 7.2.1 7.2.2 7.3.0 7.4.0 7.5.1 7.5.2 7.5.3 7.6.1 7.6.2 7.6.3 7.7.1 7.7.2 7.7.3
OVER VOLTAGE BLOCK DIAGRAM LIQUID CRYSTAL DISPLAY CIRCUIT DIAGRAM FLOWCHART TRANSFORMER TRANSFORMER EQUIVALENT WITH LOAD RECTIFIER RECTIFIER FILTERED WAVE VOLTAGE DIVIDER ARDUINO PIN DIAGRAM OF ARDUINO COMPLETE DIAGRAM OF ARDUINO LIQUID CRYSTAL DISPLAY PIN OUT OF LCD INTERFACING LCD MODULE OF LCD DEFINITE TIME CHARACTERISTICS INVERSE TIME CHARACTERISTICS RELAY CHARACTERISTICS
7
9 14 16 17 20 22 23
26 27 28 31 33 36 37 39 41 42 43
1. INTRODUCTION Over-voltages occur in a system when the system voltage rises over 110% of the nominal rated voltage. There is always a chance for suffering of an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc. These over voltage stresses may damage insulation of various equipment’s and insulators of the power system. Although, all the over voltage stresses are not strong enough to damage insulation of system, but still these over voltages also to be avoided to ensure the smooth operation of electrical power system. Our project aims at detecting the over voltage and tripping the load from the mains such that the load does not suffer from any damage. The main purpose of this relay is to isolate the load from over voltage conditions by controlling the relay tripping coil with an Arduino. Generally Domestic and small commercial loads are protected for over currents by fuses and MCBs and no protection against over voltages. The present work aims to develop an over voltage and over current relay for Domestic and small commercial electrical installations using ARDUINO at a cheaper cost.
It detects any voltage greater than 230V AC (pre-set
value). If the voltage is greater than the pre-set value, it initiates a trip signal which in turn is given to the circuit breaker. Then the circuit breaker isolates the load from the source. It can also detect and protect appliances from heavy impulse voltages. The present work aims to develop an over voltage and over current relay for Domestic and small commercial electrical installations using ARDUINO at a cheaper cost. The use of Arduino based relay is that the same circuit can be used also as under voltage and over current relay just by changing the coding of the program. Also characteristics like definite time, inverse, very inverse, extremely inverse and many other can be employed.
8
2. OVER VOLTAGE The word over voltage is in use from 1907. According to IEEE standards, Overvoltage is defined as: “Voltage between one phase and ground or between two phases, having a crest value exceeding the corresponding crest of maximum system voltage.” It can also be defined as the voltage in a circuit or part of it is raised above its upper design limit. Also an overvoltage is a voltage pulse or wave which is superimposed on the rated voltage of the network
Figure 2.0
2.1 TYPES OF OVER VOLTAGES
Depending on the duration and the magnitude of the voltage, over voltages are classified into various types as follows:
2.1.1. EXTERNAL OVER VOLTAGES This
type
of
over
voltages
originates
from
atmospheric
disturbances, mainly due to lightning. This takes the form of a surge and has no direct relationship with the operating voltage of the line. It may be due to any of the following causes: 9
a) Direct lightning stroke: A lightening stroke is defined as a direct stroke if it hits either the tower or shield wire or the phase conductor. When the insulator string flashes over by direct hit either to the tower or to the shield wire along the span, it is called back flash. b) Electromagnetically induced over voltages due to lightning discharge taking place near the line are called 'side stroke'. c) Voltages induced due to atmospheric changes along the length of the line d) Electrostatically induced voltages due to presence of charged clouds nearby. e) Electrostatically induced over voltages due to the frictional effects of small particles like dust or dry snow in the atmosphere or due to change in the altitude of the line. 2.1.2 Internal Over voltages: These over voltages are caused by changes in the operating conditions of the power system. These can be divided
into two groups
as below:
1. Switching over voltages or Transient over operation voltages of high frequency: A short-duration highly damped, oscillatory, or non-oscillatory overvoltage, having duration of few milliseconds or less is Transient
overvoltage. This
is carried the network.
is caused when switching
operation
out under normal conditions or when fault occurs in When an unloaded long line is charged, due to Ferranti
Effect the receiving end voltage is increased considerably resulting in over voltage in the system. Similarly when the primary side of the transformers or reactors is switched on, over voltage of transient nature occurs.
10
2. Temporary over voltages: An Oscillatory phase-to-ground or phase-tophase overvoltage that generally exists for long duration (seconds, even minute) and that is un-damped or only weakly damped is Temporary over voltage. Temporary overvoltage usually originate from switching operation or faults (e.g. load rejection, single-phase fault, fault on a high-resistance ground or ungrounded system) or from nonlinearities (Ferro resonance, harmonics), or both. They are characterized by the amplitude, the oscillation frequencies, the total duration or the decrement.
2.2 CAUSES OF OVER VOLTAGES 2.2.1 INTERNAL CAUSES: (I)
Switching surges: A surge, or transient, is a sub cycle overvoltage with a duration of less than a half-cycle of the normal voltage waveform. A surge can be either positive or negative polarity, can be additive or subtractive from the normal voltage waveform, and is often oscillatory and decaying over time. Surges, or transients, are brief overvoltage spikes or disturbances on a power waveform that
can
equipment
damage, within
degrade, any
home,
or
destroy
commercial
electronic building,
industrial, or manufacturing facility. Transients can reach amplitudes of tens of thousands of volts.
Surges
are generally measured in microseconds. Few cases of switching surges are discussed here.
(II)
Insulation failure: Electrical breakdown or dielectric breakdown is a long reduction in the resistance of an 11
electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event (as in an electrostatic discharge), or may lead to a discontinuous arc charge if protective devices fail to interrupt the current in a low power circuit. Under sufficient electrical stress, electrical breakdown can occur within solids, liquids, gases or vacuum. However, the specific breakdown mechanisms are significantly different for each, particularly in different kinds of dielectric medium.
(III)
Arcing ground: Arcing Grounds is a phenomenon which is observed
in
ungrounded
three
phase
systems.
In
ungrounded three phase systems operating in a healthy balanced conditions, capacitances are formed between the conductors
and
ground.
The
voltage
across
these
capacitances is the phase voltage. Now, in the event of a ground fault, the voltage across the faulty conductor becomes zero while the voltages across the healthy conductors
increase
by
a
factor
of
1.732.
The arc caused between the faulty conductor and the ground gets extinguished and restarts many times, this repeated initiation and extinction of the arc across the fault produces severe voltage oscillations of the order of nearly three to four times the nominal voltage. This repeated arcing across the fault due to the capacitances between the conductors and the ground is known as arcing grounds.
2.2.2 EXTERNAL CAUSES: (I)
Lightening: A lightning strike creates over voltages that
propagate along any type of electrical cabling (electrical distribution mains, telephone connections, communication bus, etc.), metallic 12
wiring systems or conducting elements of significant length. The consequences of lightning, i.e. the over voltages created on the installations and equipment, can be appreciable over a radius of 10km.
•
Internal causes do not produce surges of large magnitude.
•
Experience shows that surges due to internal causes hardly increase the system voltage to twice the normal value.
•
Generally, surges due to internal causes are taken care of by providing proper insulation to the equipment in the power system.
•
However, surges due to lightning are very severe may increase the system voltage to several times the normal value.
•
If the equipment in the power system is not protected against lightning surges, these surges may cause considerable damage.
•
In fact, in a power system, the protective devices provided against overvoltages mainly take care of lightning surges.
13
3. BLOCK DIAGRAM OF ARDUINO BASED OVER VOLTAGE RELAY
Figure 3.0
3.1 DESCRIPTION OF BLOCK DIAGRAM: The main purpose of the device is to isolate the load from over voltage conditions by controlling the relay tripping coil using a controller. The controller will compare the supply voltage with the desired pre-set voltage and will operate the tripping coil in the relay if the input voltage falls above the pre-set range of values. If the voltage lies within the desired limits, the load is connected to the power supply. E1lse, the relay isolates the load from the source and prevents damage. (1) AC Input: This is the input supply from the public utility where the device will be energized. It is also supplied directly to the relay contacts in the device which
connects the load to the
supply when the supply is within 200V – 240V range. 14
(2) Step down transformer: It steps down the AC supply into 5v on the secondary side. It is therefore a 230/5 v transformer. Any change in the primary reflects in the secondary of the transformer. So any fluctuations in the input is also reflected as a fluctuation in the output. (3) Rectifier: A center tapped transformer, with four diodes for full wave rectification is used to convert
the ac voltage to a pulsating
dc voltage followed by a filter, comprising of a capacitor to filter out (smooth) the pulsation. After the rectification and smoothening, a sample of the output voltage is fed to the Arduino. This voltage is unregulated and therefore varies as the input mains voltage varies. Since the system is to prevent against over voltage, the transformer was designed and the windings were so selected for the device to be able to sense and withstand input mains voltage up to 600Vac. (4) Arduino: Arduino is an open-source prototyping platform based on easy-to-use hardware and software. Arduino boards are able to read inputs - light on a sensor, a finger on a button, or a Twitter message and turn it into an output - activating a motor, turning on an LED, publishing something online. Arduino is the controller used in this project. It compares the input fluctuations with the preset value. If the fluctuations are within the limit then it makes the pin connected to the relay high. This trips the relay (5) Relay: A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The relay here we use is a single pole relay which, upon being activated by
the Arduino makes under normal 15
mains
supply
voltage and brakes under abnormal mains supply voltage. Its rating is 5vdc, 230v ac, 50 hz. 90millliamps. (6) LCD Display: This displays the supply voltage as well as some information at “switch on” or when the supply voltage is out of range of the desired pre-set range of values. The LCD used is having a 2 x 16 display. The picture of the LCD is shown in Figure.
Figure 3.1.1
16
4. CIRCUIT DIAGRAM
Figure 4.0
17
5. OPERATION
The ac supply at our homes is usually 230 V. Due to the fluctuations in load, it might vary. A tolerance of +2% is accepted. In case of increase in mains above 2%, the load might get damaged. In order to avoid this, we developed over voltage and over current relay. When the supply exceeds the specified limit, the relay operates and isolates the load from the circuit. This rectifier converts the ac supply to dc.
A filter
comprising of a capacitor is connected to smoothen the pulsation. After the rectification and smoothening, a sample of the output voltage is fed to the Arduino. This voltage is unregulated and therefore varies as the input mains voltage varies. As the value of capacitance increases, the ripple content decreases. The capacitor used in this circuit is 460 micro farads. This is followed by a potential divider. The variable of the potential divider is connected to the input of the Arduino. Arduino has five analog input pins and 13 digital output pins. It has an inbuilt analog- digital converter. So, five different loads can be connected at a time. The 13 th pin contains a LED. Arduino takes an input voltage of 5-12 V and gives an output of 5 V or 3.3 V. A preset value with tolerance is given to the Arduino. The Arduino compares the preset value with the analog read value at A0. If it lies within the limit the relay does not operate. If it doesn’t lie within the limits, the Arduino checks if it falls into inverse characteristics or definite characteristics. The operating time for definite characteristics is given as 5 seconds, ie it the relay operates after 5 sec of occurrence of the fault. If it falls into inverse characteristics, the trip time is to be calculated using the formula, T=t/((v/vs)-1) -------------------- eq-5(1) Where T= trip time t=time multiplier setting v=voltage at A0 Vs=source voltage 18
when the trip time reaches to zero, the relay is operated and the circuit is tripped. When operating in the inverse characteristics loop or in the definite characteristics loop if the voltage comes back to the limit, then the relay resets.
19
6. FLOW CHART
Figure 6.0
20
6.1 FLOW CHART DESCRIPTION
Initially we select the type of relay that is whether the relay is to be operated in definite time characteristics or in inverse time characteristics. We put a switch for the selection of the type of relay. If the switch is on then it operates as definite time relay and if the switch is off it operates as inverse time relay. First let us consider the case of definite time relay. As the name indicates, irrespective of the intensity of magnitude of the voltage, the relay operates only after a specified time. Here the specified time is 5 sec. First a range of voltage is set for the definite time characteristics. If the supply voltage magnitude falls in this range, then the relay trips after 5 sec. When the trip time (5 sec) become zero, the relay trips the load. When the relay is operating, if the voltage comes back to reference value or the preset value, then the trip time resets and the relay stops operating. Now let us consider the case of an inverse time relay. Here we have 2 reference voltages vref1 and vref2. We consider two cases whether 1) vref1
