Abstract :
Ultra-high-speed relays will follow faithfully the cyclic changes of alternating currents of commercial frequency in their operating coils. If these relays are polarized, they can be utilized to provide measuring equipment in which the quantity to be measured is converted into impulses whose time duration is a function of that quantity. They can also be utilized to form schemes of protection for transformers, feeders, generators and the busbars of switchgear, employing the principle of phase comparison. This principle is attractive in many ways, and ultra-high-speed relays enable it to be applied with simplicity and fast operation. Restricted zone protective equipment so constructed can be designed to have an overall operating time of the order of 0.015 sec, and the discrimination between an internal and external fault can be obtained in the first half-cycle of fault current. The factors which have to be taken into consideration to overcome difficulties which arise with this principle in the case of complicated faults are discussed in the paper. Experimental equipments have been tried out successfully on system faults on the Central Electricity Board´s system.
