Overview

The objective of this project is to design and fabricate an over current protection relay using 8051 based microcontroller. A current feedback circuit is used in this kit. The controller compares the current being consumed with the set current. If the current consumed goes higher than the set current the relay is tripped.  All the information is accordingly displayed on the LCD.

Aim

The Objectives of this project is to design and fabricate over current protection relay using micro controller which can operate on the permissible conditions by setting the over current value.

Project Scope

The scopes of the project are:

• 1. To Convert load current into corresponding voltage value.

The load current (energizing current) will be measured by using current transformer and this output AC current will be then converted converted into corresponding Voltage level.

• 2. To convert the analog voltage into digital form.

The analog voltage level is then given to an ADC which then converts into corresponding digital value.  And then the load current will display on the LCD.

• 3. Trip circuit breaker using microcontroller.

The over current value is set in the controller and when faults (over current) occur, controller will energize the circuit breaker tripping coil which will cause the circuit breaker to trip.

The over current value is set in the controller and when faults (over current) occur, controller will energize the circuit breaker tripping coil which will cause the circuit breaker to trip.

Introduction

Background

Electrical Power System protection is required for protection of both user and the system equipment itself from fault, hence electrical power system is not allowed to operate without any protection devices installed. Power System fault is defined as undesirable condition that occurs in the power system. These undesirable conditions such as short circuit, current leakage, ground short, over current and over voltage.

With the increasing loads, voltages and short-circuit duty in distribution system, over current protection has become more important today. The ability of protection system is demanded not only for economic reason but also consumers just expect ‘reliable’ service. In a Power System Protection, the system engineer would need a device that can monitor current, voltage, frequency and in some case over power in the system. Thus a device called Protective Relay is created to serve the purpose. The protective relay is most often relay coupled with Circuit Breaker such that it can isolate the abnormal condition in the system. In the interest of reliable and effective protection, some designers of power distribution/power controllers select relay as opposed to electro-magnetic circuit breakers as a method of circuit protection.

Overview of Over Current Relay-

This project will attempt to design and fabricate over current protection relay using Atmels AT89S52 micro controller. The micro controller will cause the circuit breaker to trip when the current from load current reaches the set value.

In order to design it first we need to measure the load current using either a current sensor or a current feedback transformer.  In case of over current or short circuit the Over Current Controller will isolate the device in the shortest possible time without harming any other device. We will be using a relay to trip the device if any over current condition occurs.

Block Diagram:

Advantages:

1. Power System fault causes undesirable condition, these undesirable conditions such as short circuit, current leakage, ground short, over current and over voltage.  Over Current Controller avoids such undesirable conditions and protects/isolates the device in the shortest possible time without harming any other device.
2. Prevent secondary accident that result from power system fault.
3. Ensure that the system is operating at optimal efficiency and reduce equipment maintenance and replacement cost

Application:

1. Industries for monitoring current for costly CNC machines.
2. Agricultural Pump for Protections.

Future Scope:

1. GSM can be added for sending SMS to the concerned person in case of any problem.
2. PC interface can be provided so a complete log can be maintained.

Hardware Requirement:

1. Microcontroller 89S52
2. LCD 16x 2 Alphanumeric Displays.
3. ADC: MCP 3201
4. Relay & Relay Driver Circuit.
5. Current Transformer
6. Dual Power Supply.

Software Requirement:

1. Keil Software as Compiler.
2. Proteus for Circuit Designing.
3. Protel for PCB Designing.

Text Books:

1. Muhammad Ali Mazidi –“THE 8051 MICROCONTROLLER AND EMBEDDED SYSTEMS”, Pearson education,
2. Ayala- “INTRODUCTION TO 8051 MICROCONTROLLER”

Website:

1. www.howstuffworks.com
2. www.instructables.com/id/Cellphone-operated-Robot/
3. www.dnatechindia.com
4. www.answers.com

Magazines:

1. Electronics for you
2. Electrikindia