Protection Course over View

Topics: Relay, Transformer, Electric power transmission Pages: 56 (14947 words) Published: March 20, 2013
Fundamental Principles of
Power System Protection

Course Synopsis

Slide 1

Fundamental Principles
Power System Protection

Slide 2

The material in this presentation is for Educational
purposes only.
Practical application of any of the material contained
within must be applied in accordance with legislative
requirements and having due regard to the individual

© Barrie Moor

May 2009

Page 1

Fundamental Principles of
Power System Protection

Course Synopsis

Slide 3

Course Synopsis
Fundamental Concepts of Protection Design
Fault Calculations
Over Current & Earth Fault Protection
VTs & CTs
Fundamentals of Distance Protection
Protection Signalling
Advanced Aspects of Distance Protection
High Impedance Differential Protection
Transformer Biased Differential Protection
Busbar Biased Differential Protection
Feeder Differential Protection
Auto Reclosing
Capacitor Bank Protection

© Barrie Moor

May 2009

Page 2

Fundamentals of Power System Protection1
1.1 Overview of Electrical Energy Systems
They may occupy different angular positions, but all machines rotate at the same electrical speed. This close knitting implies an embedded interaction of generators through the transmission network which is governed by the differential and algebraic equations of the apparatus and interconnects. This aspect is referred to as the system behaviour. This system has to be protected from abnormalities which is the task of protection system.

1.2 Why do we need Protection?
Electrical power system operates at various voltage levels from 415 V to 400 kV or even more. Electrical apparatus used may be enclosed (e.g. motors) or placed in open (e.g. transmission lines). All such equipment undergo abnormalities in their life time due to various reasons. For example, a worn out bearing may cause overloading of a motor. A tree falling or touching an overhead line may cause a fault. A lightning strike (classified as an act of God!) can cause insulation failure. Pollution may result in degradation in performance of insulators which may lead to breakdown. Under frequency or over frequency of a generator may result in mechanical damage to it's turbine requiring tripping of an alternator. Even otherwise, low frequency operation will reduce the life of a turbine and hence it should be avoided. It is necessary to avoid these abnormal operating regions for safety of the equipment. Even more important is safety of the human personnel which may be endangered due to exposure to live parts under fault or abnormal operating conditions. Small current of the order of 50 mA is sufficient to be fatal! Whenever human security is sacrificed or there exists possibility of equipment damage, it is necessary to isolate and deenergize the equipment. Designing electrical equipment from safety perspective is also a crucial design issue which will not be addressed here. To conclude, every electrical equipment has to be monitored to protect it and provide human safety under abnormal operating conditions. This job is assigned to electrical protection systems. It encompasses apparatus protection and system protection. 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...
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