Static Relays Basics:
A Static Relays Basics refers to a relay in which the measurement or comparison of electrical quantities is done in a static network which is designed to give an output signal in the tripping direction when a threshold condition is passed. The output signal operates a tripping device which may be electronic, semiconductor or electromagnetic.
Basis for Static Relay Development:
As a result of the great expansion of electrical transmission and distribution systems during the last thirty years and with the advent of much larger power stations and more highly interconnected systems, the duty imposed upon protective gear has become more and more severe. Since relays now have to perform much more complicated functions many types tend to become very complex mechanically and hence costly and difficult to test and to maintain.
The basis of the so-called static relaying is the use of circuits and components to achieve a variety of functions and operating characteristics which for protection purposes have traditionally been obtained using electromechanical devices. Reliability, always important has been emphasized as short-circuit levels, circuit ratings and complexity of interconnection have increased.
Shorter operating times have become more essential to preserve dynamic stability as the character and loading of systems approach design limits. The satisfaction of these requirements has left little potential for further improvements in conventional electromechanical relays.
Until fifteen years ago, relay design was dominated by the use of electromechanical elements. Such an element of whatever basic characteristics, e.g. square law induction element has a dynamic behavior special to that element and design freedom is consequently restricted by factors such as the conflicting requirements of sensitivity and mechanical robustness.
Experience shows that these more exacting requirements can readily be met using new static relays.
Classification of Static Relays:
Static Relays Basics are classified according to the type of the measuring unit or the comparator as follows: