This document presents information on protective relays. It begins by stating why electrical systems need protection from faults, then defines what a relay is and its purpose of tripping circuit breakers when faults are detected. The operating principles of electromagnetic attraction and induction are described. Types of relays are discussed, including attracted armature, solenoid, induction overcurrent, and induction directional power and overcurrent relays. Examples of each type are shown. The presentation concludes by noting that protective relays are essential for isolating faults and protecting equipment.

1. POWER SYSTEM PROTECTION AND SWITCH GEAR
PRESENTATION ON PROTECTIVE RELAYS
PRESENTED BY:
UTFAL DEBNATH ( ROLL NO-1411030075)
DEBABRATA MAJUMDER(ROLL NO-1411030067)
SUBRATA PAUL(ROLL NO-1411030067)
BE 7th Semester, EE Department
Techno India Agartala
Date of presentation: 07/12/2017

2. CONTENTS
• WHY A SYSTEM NEEDS PROTECTION?
• WHAT IS RELAY?
• OPERATING PRINCIPLES
• TYPES OF RELAYS
• CONCLUSION
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3. WHY A SYSTEM NEEDS PROTECTION?
• There is no fault free system.
• It is neither practical nor economical to make a fault free system.
• Electrical system shall tolerate certain degree of faults.
• Usually faults are caused by breakdown of insulation due to various reasons:
system aging , lightning , etc.
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4. WHAT IS A RELAY?
• Protective relay is a device to trip a circuit breaker when fault is detected.
• Protective relays are electromagnetic devices.
• They need to act quickly to protect circuit, to protect equipment and trip a breaker
within a few thousands of seconds.
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5. OPERATING PRINCIPLES
• They work on the following two main operating principles:
1. Electromagnetic Attraction
2. Electromagnetic Induction
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6. ELECTROMAGNETIC ATTRACTION
• Electromagnetic attraction relays operate by virtue of an armature being attracted
to the poles of an electromagnet being drawn into a solenoid. Such relays may be
actuated by DC or AC quantities.
• Types of electromagnetic attraction relays are:
1. Attracted armature type relay.
2. Solenoid type relay.
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7. ATTRACTEDARMATURETYPE RELAY
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8. SOLENOIDTYPE RELAY
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9. INDUCTIONTYPE RELAY
• Electromagnetic induction relays operate on the principle of induction motor and
are widely used for protective relaying purposes involving ac quantities.
• They are not used with dc quantities owing to the principle of operation.
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10. INDUCTIONTYPE OVERCURRENT RELAY
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11. INDUCTIONTYPE DIRECTIONAL POWER RELAY
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12. INDUCTIONTYPE DIRECTIONAL OVER CURRENT RELAY
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13. CONCLUSION
• Safety is increased.
• Protective relays are essential for keeping faults in the system isolated and keep
equipment from being damaged.
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