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In thermal power plants, generators are vital components that need protection from various fault conditions that could lead to damage or failure. Different protection schemes are implemented to ensure the safety and reliability of the generators. Below are the main types of generator protections used in thermal power plants:
1. Overcurrent Protection (O/C)
- Purpose: Protects the generator from high current that can result from short circuits or faults in the system.
- Operation: It detects when the current exceeds a preset limit and disconnects the generator from the system to prevent damage.
2. Differential Protection (87G)
- Purpose: Provides protection against internal faults, like winding short circuits, which occur within the generator.
- Operation: It compares the current entering the generator to the current leaving it. If there is a difference (due to an internal fault), it trips the generator.
3. Stator Earth Fault Protection
- Purpose: Protects the generator's stator winding against earth faults.
- Operation: This protection scheme detects the presence of earth faults (when one phase gets connected to the ground) and trips the generator to prevent further damage.
4. Rotor Earth Fault Protection
- Purpose: Protects the rotor windings of the generator against earth faults.
- Operation: Similar to stator earth fault protection, this detects any earth faults on the rotor and disconnects the generator if needed.
5. Overvoltage and Undervoltage Protection
- Purpose: Protects the generator from high or low voltage conditions that can cause damage to the windings and insulation.
- Operation: If the voltage rises or falls beyond preset limits, the protection system trips the generator to prevent damage.
6. Overtemperature Protection
- Purpose: Protects the generator from overheating, which can cause damage to insulation and other critical parts.
- Operation: Monitors the temperature of the generator and its components (like bearings, stator, rotor) and disconnects the generator if the temperature exceeds safe levels.
7. Loss of Field Protection
- Purpose: Protects the generator if the excitation system fails, resulting in the loss of magnetic field.
- Operation: In the event of a loss of field (excitation), the generator can start to run unstable and may become damaged. This protection scheme detects that and trips the generator to prevent such damage.
8. Underfrequency Protection
- Purpose: Protects the generator from operating at low frequencies, which may indicate a problem in the power system or abnormal conditions.
- Operation: If the generator’s frequency falls below a set limit (due to load shedding or other issues), the protection system trips the generator to prevent long-term damage.
9. Overspeed Protection
- Purpose: Ensures the generator does not operate beyond its rated speed, which could lead to mechanical damage.
- Operation: If the generator speed exceeds the safe limits, this protection activates and trips the generator.
10. Reverse Power Protection
- Purpose: Prevents the generator from running in reverse (when power flows back into the generator, indicating a system fault).
- Operation: If power flow reverses (e.g., if the grid is unstable or the generator is being driven by external forces), this protection will disconnect the generator from the grid.
11. Bearing Vibration Protection
- Purpose: Protects the generator against excessive vibrations that can cause mechanical damage to the bearings and other moving parts.
- Operation: Vibration sensors monitor the bearing conditions and trip the generator if vibrations exceed safe levels.
12. Main-Tie-Main Protection
- Purpose: Ensures that the generator is isolated from the grid in case of a fault, especially in complex systems with multiple generators.
- Operation: This protection scheme helps isolate the faulted generator by detecting faults and ensuring proper coordination among multiple generators in the system.
13. Grid Frequency and Voltage Protection
- Purpose: Protects the generator from the adverse effects of abnormal grid frequency or voltage.
- Operation: If the grid frequency or voltage falls outside acceptable limits, this protection disconnects the generator to avoid damage from poor grid conditions.
14. Synchronization Check
- Purpose: Ensures that the generator is synchronized with the grid before connecting.
- Operation: This protection checks that the generator’s voltage, frequency, and phase sequence match the grid’s characteristics. If there’s a mismatch, it prevents the generator from being connected to the grid.
By employing these protection schemes, thermal power plants can ensure the safe and reliable operation of generators, minimizing damage from faults and abnormal conditions. Proper coordination and settings of these protections are essential to achieve effective protection while avoiding unnecessary trips during normal operation.
1. Overcurrent Protection (O/C)
- Purpose: Protects the generator from high current that can result from short circuits or faults in the system.- Operation: It detects when the current exceeds a preset limit and disconnects the generator from the system to prevent damage.
2. Differential Protection (87G)
- Purpose: Provides protection against internal faults, like winding short circuits, which occur within the generator.- Operation: It compares the current entering the generator to the current leaving it. If there is a difference (due to an internal fault), it trips the generator.
3. Stator Earth Fault Protection
- Purpose: Protects the generator's stator winding against earth faults.- Operation: This protection scheme detects the presence of earth faults (when one phase gets connected to the ground) and trips the generator to prevent further damage.
4. Rotor Earth Fault Protection
- Purpose: Protects the rotor windings of the generator against earth faults.- Operation: Similar to stator earth fault protection, this detects any earth faults on the rotor and disconnects the generator if needed.
5. Overvoltage and Undervoltage Protection
- Purpose: Protects the generator from high or low voltage conditions that can cause damage to the windings and insulation.- Operation: If the voltage rises or falls beyond preset limits, the protection system trips the generator to prevent damage.
6. Overtemperature Protection
- Purpose: Protects the generator from overheating, which can cause damage to insulation and other critical parts.- Operation: Monitors the temperature of the generator and its components (like bearings, stator, rotor) and disconnects the generator if the temperature exceeds safe levels.
7. Loss of Field Protection
- Purpose: Protects the generator if the excitation system fails, resulting in the loss of magnetic field.- Operation: In the event of a loss of field (excitation), the generator can start to run unstable and may become damaged. This protection scheme detects that and trips the generator to prevent such damage.
8. Underfrequency Protection
- Purpose: Protects the generator from operating at low frequencies, which may indicate a problem in the power system or abnormal conditions.- Operation: If the generator’s frequency falls below a set limit (due to load shedding or other issues), the protection system trips the generator to prevent long-term damage.
9. Overspeed Protection
- Purpose: Ensures the generator does not operate beyond its rated speed, which could lead to mechanical damage.- Operation: If the generator speed exceeds the safe limits, this protection activates and trips the generator.
10. Reverse Power Protection
- Purpose: Prevents the generator from running in reverse (when power flows back into the generator, indicating a system fault).- Operation: If power flow reverses (e.g., if the grid is unstable or the generator is being driven by external forces), this protection will disconnect the generator from the grid.
11. Bearing Vibration Protection
- Purpose: Protects the generator against excessive vibrations that can cause mechanical damage to the bearings and other moving parts.- Operation: Vibration sensors monitor the bearing conditions and trip the generator if vibrations exceed safe levels.
12. Main-Tie-Main Protection
- Purpose: Ensures that the generator is isolated from the grid in case of a fault, especially in complex systems with multiple generators.- Operation: This protection scheme helps isolate the faulted generator by detecting faults and ensuring proper coordination among multiple generators in the system.
13. Grid Frequency and Voltage Protection
- Purpose: Protects the generator from the adverse effects of abnormal grid frequency or voltage.- Operation: If the grid frequency or voltage falls outside acceptable limits, this protection disconnects the generator to avoid damage from poor grid conditions.
14. Synchronization Check
- Purpose: Ensures that the generator is synchronized with the grid before connecting.- Operation: This protection checks that the generator’s voltage, frequency, and phase sequence match the grid’s characteristics. If there’s a mismatch, it prevents the generator from being connected to the grid.
By employing these protection schemes, thermal power plants can ensure the safe and reliable operation of generators, minimizing damage from faults and abnormal conditions. Proper coordination and settings of these protections are essential to achieve effective protection while avoiding unnecessary trips during normal operation.