As for protection relays and overcurrent. Why do we have to inform which specific norm to...

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Electrical Engineering

As for protection relays and overcurrent. Why do we have toinform which specific norm to the use of its curve of actuation?

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Operation principle of protective relays The main principleemployed in the operation of the relay is either electromagneticattraction or electromagnetic induction In an electro magneticattraction relay a plunger is drawn into a solenoid or an armatureis attracted to the poles of an electromagnet Such relays can beoperated either by DC direct current or ACalternate currentIn the case of electromagnetic induction relays the principle ofinduction motor is used and the torque is developed byelectromagnetic induction Such relays are operated by the ACquantities onlyExample Buchholz relay is an example of physicoelectricrelayAccording to their functions in the relay protective schemerelays must be divided into main auxiliary or supplementaryand signal relays The main relays are the protective elementswhich respond to any change in the actuating quantity egcurrent voltage power etc The auxiliary relays are those whichare controlled by other relays to perform some auxiliary orsupplementary functions such as introduction of a time delaymultiplying the number of contacts increasing the making orbreaking capacity of the contacts of another relay passing acommand pulse from one relay to another relay acting upon acircuit breaker closing or opening coil energizing a signal or analarm etc Signal relays function to register by flag or targetthe operation of some relay or relay protection and control warningvisible and alarm audible signal devices The choice of signalrelay is governed by the impedance of the associated switch gearthe method of control and the number of alarm indications to See Answer

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