05-01-2013, 03:51 PM
OVER CURRENT PROTECTION RELAY USING PIC MICRO CONTROLLER
OVER CURRENT PROTECTION RELAY USING PIC.pdf (Size: 2.67 MB / Downloads: 143)
Overview of Over Current Relay Project
An "Over Current Relay" is a type of protective relay which operates when
the load current exceeds a preset value. In a typical application the over current relay
is used for over current protection, connected to a current transformer and calibrated
to operate at or above a specific current level.
This project will attempt to design and fabricate over current protection
relay using PIC micro controller. The PIC micro controller will cause the circuit
breaker to trip when the current from load current reaches the setting value in the
PIC micro controller.
In order to design it, first the load current need to measure in order to
monitor it using current sensor including testing the fault (over current) and when
such condition arise, it will isolate in the shortest time possible without harming the
any other electrical devices. It will also including in developing the algorithm for
instantaneous over current relay and IDMT (Inverse Definite Minimum Time) relay
for the circuit breaker to trip. In this project, PIC microcontroller will be used to
control and operate the tripping coil in circuit breaker.
1.3 Objective
The objectives of this project are;
I. To design and fabricate over current protection relay using PIC micro
controller which can operate on the permissible conditions by setting the
over current value.
II. To test unwanted conditions (over current) and when such conditions
arise to isolate the fault condition in the shortest time possible.
III. To investigate IDMT curve characteristic.
Scope of Project
The scopes of the project are;
i. To measure and analyze load current from current sensor.
- The load current (energizing current) will be measured by using
current sensor and converted from analog voltage to digital using
PIC16F877A. Then the load current will display on the LCD.
ii. Trip circuit breaker using PIC microcontroller.
- The over current value is set in the PIC and when faults (over current)
occur, PIC will energize the circuit breaker tripping coil which will cause
the circuit breaker to trip.
iii. Develop algorithm for instantaneous over current relay and IDMT relay.
- The over current setting may be given by definite time or inverse
definite minimum time (IDMT) characteristic. There are four curves for
over current complying with the IEC 255 and are named ‘Normal
Inverse’, ‘Very Inverse’, ‘Extremely Inverse’ and ‘Long Time Inverse’.
This project is to develop the ‘Long time Inverse’ characteristic of
IDMT.
THEORY AND LITERATURE REVIEW
Introduction
This chapter will discuss the study about significant parts of protection
system such as the important of protection system, protection devices, types of
protection system and protection relay. It also includes the PIC Microcontroller
which is ‘the brain’ for this over current protection relay.