22524 Switchgear and Protection Unit 5 Notes PDF

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Protection of Motors, Bus-bar, and Transmission Line

Protection of Motors:

1. Overload Protection:
• Protects the motor from prolonged operation above its rated capacity.
• Typically achieved using thermal overload relays or electronic overload sensors.
2. Short Circuit Protection:
• Protects the motor from direct short circuits.
• Employs HRC fuses or circuit breakers.
3. Single Phasing Protection:
• Protects motors from single phasing, which can result in unbalanced current and overheating.
• Single phasing relays or current unbalance relays are used.
4. Ground Fault Protection:
• Detects leakage current to the ground and trips the motor to prevent damage.
• Ground fault relays are commonly used for this purpose.
5. Under-voltage Protection:
• Disconnects the motor when supply voltage drops below a set level to prevent damage from low voltage operation.
6. Over-temperature Protection:
• Embedded temperature sensors within motor windings detect excessive temperatures and can trip the motor.

Protection of Bus-bars:

1. Busbar Differential Protection:
• Compares the total current entering and leaving the bus-bar.
• If there's a difference, indicating an internal fault, it trips the bus-bar.
2. Overcurrent Protection:
• Protects against overloads or faults beyond the capacity of the bus-bar.
3. Short Circuit Protection:
• Employs circuit breakers to disconnect the bus-bar in case of a direct short circuit.
4. Ground Fault Protection:
• Detects ground faults and trips the affected section of the bus-bar.

Protection of Transmission Lines:

1. Overcurrent Protection:
• Involves the use of relays to detect when the current in a line exceeds a pre-defined safe level.
2. Distance Protection:
• Uses relays that measure impedance to a fault. If the impedance falls below a set value, indicating a fault at a certain distance from the relay, the line is tripped.
3. Carrier Current Protection:
• Utilizes communication channels to send and receive signals. If a fault is detected, the trip signal is sent via the communication channel.
4. Differential Protection:
• Compares the current at both ends of the transmission line. A difference indicates a fault within the line.
5. Earth Fault Protection:
• Specifically designed to detect ground faults in the transmission system.
6. Surge Protection:
• Surge arresters are installed to protect the lines from transient over-voltages, often caused by lightning strikes.

Importance: