PROTECTIVE RELAY USING 8085 MICROPROCESSOR
The aim of the project is to monitor the voltage, current and frequency of a power system during normal condition and
to protect the system during abnormal (or) faulty condition.
The system is designed to indicate and to sound an alarm or buzzer and turn on the solid-state relay, during over
current, over voltage and over flux conditions of the power system.
FUNCTION OF PROTECTIVE RELAY:
The PT and CT sense the voltage and current of the power system. After signal conditioning they are fed to ADC. The
signal conditioning circuit for voltage signal consists of rectifier and filter. The signal conditioning circuit for current signal
consists of shunt resistance, isolation transformer, rectifier and filter. The 8085 Microprocessor reads the voltage and current
from the ADC. The frequency of the power system is calculated by using the timer of 8085 by estimating the time durations
between the two zero crossings of the sine wave.
During normal conditions, the 8085 Microprocessor calculates the voltage and frequency and displays its values.
During faulty condition the 8085 Microprocessor send a high signal to the output drivers through the port1 to turn ON a buzzer
or a solid-state relay. For low-level fault, buzzer is turned ON, and for high- level fault the relay is turned ON. Also LED
indications are provided as output signals to show the cause of the fault as over voltage or over current or over flux condition.
Refer functional diagram figure1
The hardware of this system includes INTEL 8085 Microprocessor as CPU, INTEL 8279 for driving keyboard and
display. 8 channels ADC, 7 segment LEDs and output drivers. External memories like EPROM and RAM are also present.
CHOICE OF DISPLAY:
In this project a Seven-Segment display is used, which is s connected to INTEL 8279 with cathode/anode Drivers.
Whereas and data lines of LCD are connected to the address and data lines of the system.
Assembly level language (INTEL 8085 Micro controller).
N B Y R
Temperature circuit 2
Freq 7 Drivers
Rectifier Filter Zero crossing PA0
USART Drivers Buffer
Rectifier Filter Relay
Rectifier Filter EPROM
PT 50 pin bus expansion
Rectifier Filter RAM
AC supply IT - Isolation Transformer
PT - Potential Transformer Decoder
Cathode Drivers Keyboard
Fig 3.1 : Block diagram of Protective Relay using 8085 Microprocessor