power systems loss

What are the basic operating principles of relays in protecting electrical equipment? Overcurrent Relays Protection for electrical equipments can be found in many form. Overcurrent relays, perhaps the simplest of the many protective relays, close their contacts when the current flowing in the circuit or equipment reaches a predetermined value. The principle of operation of each of the several types is described below; the variations in their characteristics are illustrated by the curves in Figure 13.3.

IEEE STD C37.91-2000: GUIDE FOR PROTECTIVE RELAY APPLICATIONS TO POWER TRANSFORMER Power Transformers are not only one of the most important piece of electrical device in the power system with respect to its functions but also the most expensive among all other devices found in an electrical substation. Furthermore, once a power transformer is out of service during its operation, the electric utility can not simply replace it in a short period of time not unless one has a spare which is also, mind you, can be very impractical. An electric utility can not afford to loss a power transformer because it would also mean a loss in revenue and for a manufacturer’s perspective is a loss in production. A power transformer, in which I think everybody would agree, is a very complicated form of electrical apparatus. While in operation, it is subjected to a quite number of threats which can be unpredictable, one of which is a fault that can be very damaging. Proper care and maintenance are always