1 Answer
An impedance-based loss of excitation protection scheme is used to detect and protect synchronous generators (or alternators) in power systems from a situation where the excitation to the generator is lost. This is a critical protection scheme because if a generator loses excitation, it will no longer produce a magnetic field, which can lead to dangerous operating conditions like overheating or even mechanical damage to the generator.
Here’s how it works in simple terms:
1. Understanding Excitation Loss:
- Excitation refers to the DC current supplied to the rotor of a synchronous generator to create a magnetic field.
- If the excitation is lost, the generator will stop producing the magnetic field needed for its operation. This means it will no longer synchronize with the grid and will behave like an asynchronous (induction) machine.
2. Impedance Measurement:
- The key idea is to monitor the impedance (resistance to current flow) of the generator. In a normal condition with excitation, the generator behaves in a certain way electrically.
- When excitation is lost, the impedance characteristics change. The generator will start drawing more current, and the impedance will appear different because of the lack of a magnetic field.
- Typically, the protection system measures the voltage and current at the terminals of the generator.
3. How the Scheme Detects Loss of Excitation:
- The protection relay constantly measures the impedance (Z) based on the ratio of voltage to current (Z = V/I).
- If the excitation is lost, the impedance of the generator will shift significantly from its normal value. This is because, without excitation, the generator's impedance becomes much lower, and the current drawn by the machine increases.
- The protection relay compares the real-time impedance value to predefined threshold values that indicate a loss of excitation.
4. Setting the Protection Threshold:
- The protection system is calibrated with settings based on the normal operating impedance of the generator when it's fully excited. When the impedance drops below a certain threshold (which indicates loss of excitation), the relay will trip the generator to prevent damage.
5. Action Taken:
- If the protection relay detects that the impedance has shifted in such a way that it indicates a loss of excitation, it will trigger a trip signal to disconnect the generator from the grid.
- This action helps to prevent the generator from operating in a dangerous condition, potentially avoiding overheating, mechanical stress, and further damage.
6. Summary:
- The impedance-based loss of excitation protection scheme continuously monitors the impedance of the generator.
- If excitation is lost, the impedance changes, and the protection system detects this and disconnects the generator to avoid damage.
This type of protection is crucial for ensuring the safe operation of synchronous generators, especially in situations where the excitation system might fail or experience issues.
Here’s how it works in simple terms:
1. Understanding Excitation Loss:
- Excitation refers to the DC current supplied to the rotor of a synchronous generator to create a magnetic field.- If the excitation is lost, the generator will stop producing the magnetic field needed for its operation. This means it will no longer synchronize with the grid and will behave like an asynchronous (induction) machine.
2. Impedance Measurement:
- The key idea is to monitor the impedance (resistance to current flow) of the generator. In a normal condition with excitation, the generator behaves in a certain way electrically.- When excitation is lost, the impedance characteristics change. The generator will start drawing more current, and the impedance will appear different because of the lack of a magnetic field.
- Typically, the protection system measures the voltage and current at the terminals of the generator.
3. How the Scheme Detects Loss of Excitation:
- The protection relay constantly measures the impedance (Z) based on the ratio of voltage to current (Z = V/I).- If the excitation is lost, the impedance of the generator will shift significantly from its normal value. This is because, without excitation, the generator's impedance becomes much lower, and the current drawn by the machine increases.
- The protection relay compares the real-time impedance value to predefined threshold values that indicate a loss of excitation.
4. Setting the Protection Threshold:
- The protection system is calibrated with settings based on the normal operating impedance of the generator when it's fully excited. When the impedance drops below a certain threshold (which indicates loss of excitation), the relay will trip the generator to prevent damage.5. Action Taken:
- If the protection relay detects that the impedance has shifted in such a way that it indicates a loss of excitation, it will trigger a trip signal to disconnect the generator from the grid.- This action helps to prevent the generator from operating in a dangerous condition, potentially avoiding overheating, mechanical stress, and further damage.
6. Summary:
- The impedance-based loss of excitation protection scheme continuously monitors the impedance of the generator.- If excitation is lost, the impedance changes, and the protection system detects this and disconnects the generator to avoid damage.
This type of protection is crucial for ensuring the safe operation of synchronous generators, especially in situations where the excitation system might fail or experience issues.