Module 1 :
Fundamentals of Power System Protection
Lecture 1 :
Introduction
1.3
Types of Protection
Protection systems can be classified into apparatus protection and system protection.
1.3.1
Apparatus Protection
Apparatus protection deals with detection of a fault in the apparatus and consequent protection. Apparatus protection can be further classified into following:
Transmission Line Protection and feeder protection
Transformer Protection
Generator Protection
Motor Protection
Busbar Protection
1.3.2
System Protection
System protection deals with detection of proximity of system to unstable operating region and consequent control actions to restore stable operating point and/or prevent damage to equipments. Loss of system stability can lead to partial or complete system blackouts. Under-frequency relays, out-of-step protection, islanding systems, rate of change of frequency relays, reverse power flow relays, voltage surge relays etc are used for system protection. Wide Area Measurement (WAM) systems are also being deployed for system protection. Control actions associated with system protection may be classified into preventive or emergency control actions.
1.3.2.1
Analogy with Functioning of a Human being
A human being is a complex system that performs through various apparatus like legs, hands, eyes, ears, heart, bones, blood vessels etc. The heart is analogous to an electrical generator and stomach to the boiler. The eating process provides raw material to generate calories. The power generated is pumped by heart through a complex network of blood vessels. The primary transmission is through arteries and veins. Furthermore, distribution is through fine capillaries. The system operator is the brain which works on inputs of eyes, ears, skin etc. Diagnosing abnormality in any of these organs and taking remedial measures can be thought of as job of "apparatus protection". However, does this cover the complete gambit of anomalies? Are fever, infection etc, a specific apparatus problem? Why does it cause overall deterioration in functioning of the human being?
The answer lies in the fact that the system which encompasses body has also abstraction like the mind. Overall health is not just an aggregation of apparatus. It is something much more complex. It involves complex process and associated dynamics (biological, chemical, mechanical etc.) and control. Thus, protecting a system is not just apparatus protection but something much more. Since we cannot define this "much more" clearly, it is complex and challenging. Monitoring of system behavior, taking corrective measures to maintain synchronous operation and protecting the power system apparatus from harmful operating states is referred as systemprotection.
