Microprocessor relays provide many functions that were not available in electromechanical or solid-state designs. Relay logic is very important to understand the microprocessor-based relay. The relay can be ON or OFF, that is, it has two stable states.
Fig: Microprocessor based overcurrent relay
Similarly, the output of a logic function is activated, that is, high or deactivated, that is, low. The three basic logical functions are: AND, OR and NOT functions. All of these functions can be achieved using transistors as well. It is called transistor-transistor logic (ML).
Figure shows the block diagram of the microprocessor-based relay.
The output of the CT line is given to the input receiver block where the signal is processed. Signal processing includes overvoltage protector, rectifier, smoothing filters, auxiliary CT, etc., depending on the requirements. This signal is an analog signal. The A / D converter converts this into a digital signal that is accepted by the microprocessor. The microprocessor is a block of decision making. The received digital signal is compared with the reference to generate the appropriate trigger signal. This is a digital signal that is converted back to analog to operate the trip coil. This is achieved by the D / A converter. The data logger captures the data and sends it to the microprocessor when there is a request from the microprocessor. The information can be displayed with a suitable display device when taking the signal from the microprocessor.
The main advantage of this relay is that it is programmable. The program can handle the online calculations and make the decision accordingly. Another important advantage of the microprocessor-based relay is that a microprocessor unit can perform the retransmission operation of several systems.
Advantages of microprocesser based relay:
Thus various advantages of microprocessor based relay are:
1. Very efficient and reliable.
2. Highly accurate.
3. Very fast in operation.
4. Programmable in nature.
5. A unit can perform retransmission of several systems.
6. economical for large systems.
7. Useful for centrally coordinated backup protection.
Only care that must be taken is that the microprocessor unit must be properly shielded as it gets affected by external interferences and environment Proper care of earthing must also be taken.