MICROCONTROLLER BASED THREE PHASE IMPEDANCE RELAY

fiercebunElectronics - Devices

Nov 2, 2013 (3 years and 9 months ago)

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MICROCONTROLLER BASED THREE PHASE IMPEDANCE RELAY


Objective:


The objective of this project is to design a Microcontroller based impedance relay to
estimate the distance of fault from sub
-
station in transmission lines or feeders.

Theory:


The impedance of

a transmission line will be high during normal condition and will be low
during faulty condition. The impedance measured during fault condition is the impedance of
conductors of feeder or Transmission line. Since the impedance per unit length of the condu
ctor is a
known data, the distance of fault can be estimated from the knowledge of measured impedance. The
impedance can be estimated by measuring the voltage and current.

Functioning:

The Potential Transformers (PT) and Current Transformers (CT) are emplo
yed to sense the
voltage and current of all three phases of the power system. After signal conditioning they are fed to
ADC. The Microcontroller reads the voltages and currents from ADC, from which impedance
values are calculated for all three phases. The
calculated impedance is used to decide the normal
and faulty condition. During faults, the measured impedance and impedance per unit length of
conductors are used to estimate the distance of fault and displayed. This system is also equipped
with a buzzer a
nd LEDs to indicate faults. A solid state relay using TRIAC is also provided to
isolate faulty transmission line. Since the distance at which fault has occurred is displayed, it is
quite flexible to take action from the nearby substation and the service ca
n be restored quickly.

















Hardware:


The hardware of this system includes,



AT 89C52 Microcontroller with 8279
-
keyboard /display interface, display and keyboard.



PTs, CTs with its signal conditioning circuits and 8 bit ADC (ADC0809).



Choi
ce of Display:

Either Seven
-
segment display or LCD display.



Software:


Keil C language for programming 89C52 Microcontroller.

Contactor

3 sets of PT &
conditioning
circuit

3 sets of CT &
conditioning
circuit

R

Y

B

N



8 channel
ADC



89C52

MC

8

TRIAC

3
-
phase
Transmission
line

Buzzer

Keyboard/

Display
interface

Keyboard

Display

LEDs

Block Diagram of Microcontroller based three
-
phase impedance relay