Switchgear and Protection

Preamble:

In order to supply power from generating end to receiving end several equipments are connected in to the system. In order to protect the equipments and components against various operating conditions and over voltages protective devices are required to be installed in the system. Topics specified in this subject deal with various types of protective equipments and their working principle including limitations etc.

Learning objectives:

<!--[if !supportLists]-->· To provide the basic principles and operation of various types of circuit breakers.

<!--[if !supportLists]-->· To study the classification, operation and application of different types of electromagnetic protective relays.

<!--[if !supportLists]-->· To explain protective schemes, for generator and transformers.

<!--[if !supportLists]-->· To impart knowledge of various protective schemes used for feeders and bus bars.

<!--[if !supportLists]-->· To explain the principle and operation of different types of static relays.

<!--[if !supportLists]-->· To study different types of over voltages in a power system and principles of different protective schemes for insulation co–ordination.

UNIT–I:

Circuit Breakers: Miniature Circuit Breaker(MCB)– Elementary principles of arc interruption– Restriking Voltage and Recovery voltages– Restriking phenomenon - RRRV– Average and Max. RRRV– Current chopping and Resistance switching– Introduction to oil circuit breakers– Description and operation of Air Blast– Vacuum and SF6 circuit breakers– CB ratings and specifications– Concept of Auto reclosing.

UNIT–II:

Electromagnetic Protection: Relay connection – Balanced beam type attracted armature relay - induction disc and induction cup relays–Torque equation - Relays classification–Instantaneous– DMT and IDMT types– Applications of relays: Over current and under voltage relays– Directional relays– Differential relays and percentage differential relays– Universal torque equation– Distance relays: Impedance– Reactance– Mho and offset mho relays– Characteristics of distance relays and comparison.

UNIT–III:

Generator Protection: Protection of generators against stator faults– Rotor faults and abnormal conditions– restricted earth fault and inter turn fault protection– Numerical examples.

Transformer Protection: Protection of transformers: Percentage differential protection– Design of CT’s ratio– Buchholz relay protection–Numerical examples.

UNIT–IV:

Feeder and Bus bar Protection: Protection of lines: Over currentProtection schemes – PSM,TMS - Numerical examples - Carrier current and three zone distance relay using impedance relays–Protection of bus bars by using Differential protection.