Relays are used industrially in a wide variety of applications. Traditional mechanical re lays are large, slow, noisy devices, but are still widely used in various machines and processes for control purposes. In this paper cross section of a moving electromagnetic relay is A; can be inside the external vertical hole magnetic chamber. Gap between the two is  negligible . R is the resistance in ohms, and the coil  has  N turns. Once a potential source v volt DC and again, AC power is applied to the ends of the coil. Magnetic material can be assumed to be ideal up to saturation flux density of 1.6T. Regardless of efflorescence flux in the air gap. The force exerted on the moving parts is compute d as a function of the air gap y. Ne xt, effect of the dynamic equations is also checked.

 

TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
INTRODUCTION
1.1      BACKGROUND OF THE PROJECT

• AIM OF THE STUDY
• OBJECTIVE OF THE PROJECT
• ADVANTAGES OF THE STUDY
• PROBLEM OF ELECTROMAGNETIC RELAY
• LIMITATION OF ELECTROMAGNETIC RELAY
• APPLICATION OF THE PROJECT

CHAPTER TWO
2.0      LITERATURE REVIEW

• DEFINITION ELECTROMAGNETIC RELAY
• OVERVIEW OF THE STUDY
• HISTORICAL BACKGROUND OF THE STUDY
• TYPES OF AN ELECTROMAGNETIC RELAY
• DIFFERENCE BETWEEN RELAY AND CIRCUIT BREAKER

CHAPTER THREE
METHODOLOGY

• BASIC DESIGN AND OPERATION
• CIRCUIT DIAGRAM
• WORKING PRINCIPLE OF RELAY

CHAPTER FOUR

• ELECTROMAGNETIC RELAY TEST
• RELAYS FAILURES
• TESTING OF SYSTEM OPERATION
• RELAY APPLICATION CONSIDERATIONS

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE
1.0                                                        INTRODUCTION
Relay is an electromagnetic switch which is used to control switching. It is a low-high voltage switch to be precise. Low to High Voltage signifies Low Control Voltage is used to switch contacts of relays which are comparatively at high potential.
The main operation of a relay comes in places where only a low-power signal can be used to control a circuit. It is also used in places where only one signal can be used to control a lot of circuits. The application of relays started during the invention of telephones. They played an important role in switching calls in telephone exchanges. They were also used in long distance telegraphy. They were used to switch the signal coming from one source to another destination. After the invention of computers they were also used to perform Boolean and other logical operations. The high end applications of relays require high power to be driven by electric motors and so on. Such relays are called contactors.
Relay basically has a coil, to be specific switching coil which switches between contacts of relays. It has two or more than two contacts, we will consider relay with two contacts of which one is NO (Normally open) while other is NC(Normally Closed). And a contact termed as COM (Common). Normally Open means if there is no voltage present at the coil of relay the contact will act as open switch with respect to COM. Similarly Normally closed means it will act as short with COM while there is no voltage present at the coil of Relay. Contacts NO & NC are firmly mounted while COM is mounted in a way it can move. A spring is attached to COM for damping. ie: Getting back normal state once coil is de-energized.
In Electromagnetic relays operating current flows through the coil. When this operating current increases, coil energizes the electromagnet. When the operating current becomes large, the magnetic field produced by electromagnet is high such that this magnetic field pulls the armature or plunger making the trip circuit contacts to close.

1.2                                                     AIM OF THE STUDY

The aim of this study is to write on electromagnetic relay, its construction, working principle and application.

1.3                                              OBJECTIVES OF THE STUDY

At then of this work, students involves will be able to understand:

• What an electromagnetic relay is all about
• The working principle of an electromagnetic relay
• Local and industrial application of electromagnetic relay

1.3                                            ADVANTAGES OF THE STUDY

• Electromagnetic relays have fast operation and fast reset
• They can be used for both ac and dc systems for protection of ac and dc equipments
• Electromagnetic relays operating speeds which has the ability to operate in milliseconds are also can be possible
• They have the properties such as simple, robust, compact and most reliable
• These relays are almost instantaneous. Though instantaneous the operating time of the relay varies with the current. With extra arrangements like dashpot, copper rings etc. slow operating times and reset can be possible.

1.4                                PROBLEM OF ELECTROMAGNETIC RELAY

• High burden level instrument transformers are required (CTs and PTs of high burden is required for operating the electromagnetic relays compared to static relays)
• The directional feature is absent in electromagnetic relays
• Requires periodic maintenance and testing unlike static relays
• Relay operation can be affected due to ageing of the components and dust, pollution resulting in spurious trips
• Operation speed for an electromagnetic relays is limited by the mechanical inertia of the component.

1.5                              LIMITATION OF ELECTROMAGNETIC RELAY
  The relay is easily affected by the high voltage surges. Thus, precaution should be taken for avoiding the damages through voltage spikes.
  The working of the relay depends on the electrical components.
  The relay has less overloading capacity.

• The construction of the relay is easily affected by the surrounding interference.

1.6                           APPLICATIONS OF ELECTROMAGNETIC RELAY

There are numerous applications for electromechanical relays. Various types of relays are used in various applications based on different criteria such as rating of contacts, number and type of contacts, the voltage rating of contacts, operating lifetime, coil voltage and current, package, and so on. Relays are frequently being used in power system networks for controlling purpose, automation purpose, and protection purpose.
The typical applications of electromagnetic relays include motor control, automotive applications such as an electrical fuel pump, industrial applications where control of high voltages and currents is intended, controlling large power loads, and so on.

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