What are numerical relays?

Answer 1

As we know numerical relays use DIGITAL SIGNAL PROCESSOR as its computational hardware and based on microprocessor.

WORKING:

Analog input is feed into the anti aliasing filter which is a low pass filter.Output of this filter is feed into the sample and hold circuit , frequency of sampling should be twice of our highest frequency of interest(according to the nyquist criterion).if sampling frequency kept low than aliasing input may occur.

after the sampling, signal are feed into the multiplexer,where all the signal get multiplexed and we have a single signal.this signal is feed into the analog to digital converter.this digital signal is feed into the microprocessor and microprocessor generates control signal according to its input.

for example

if you are using N.R. for over-current protection than you should set a value of current in your program.if the value of current passes through the circuit is greater than the set value..than N.R. enables the circuit breaker and hence our system is protected..

Answer 2

These are microprocessor-based relays in contrast to other relays that are electromechanically controlled. These relays provide great precision and convenience in application in the sophisticated electronic products. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays.