Aux 2 Unit 7 Q3

AVRS stands for Automatic Voltage Regulator System.

It’s a crucial component in power generation systems, primarily responsible for maintaining a stable and consistent output voltage from the generator, even under varying load conditions. It achieves this by controlling the excitation current supplied to the generator’s field windings.

How it Works

In essence, the AVR acts as a feedback control system:

1. Voltage Sensing: It continuously monitors the generator’s output voltage.
2. Comparison: This sensed voltage is compared to a reference voltage (the desired output).
3. Error Signal: Any difference between the sensed and reference voltages creates an error signal.
4. Adjustment: The AVR processes this error signal and adjusts the excitation current supplied to the generator’s field windings.
5. Voltage Correction: Changing the field excitation alters the magnetic field strength, which in turn affects the generated voltage. This allows the AVR to correct any deviations and maintain the desired output voltage.

Why it’s Important

• Voltage Stability: Ensures a constant and reliable voltage supply to connected loads, preventing damage or malfunctions due to voltage fluctuations.
• Load Sharing: In systems with multiple generators running in parallel, AVRs also play a role in load sharing by adjusting the reactive power output of each generator.
• Protection: AVRs can include protective functions to prevent over-excitation and damage to the generator in case of abnormal conditions.

Types of AVRs

There are various types of AVRs, ranging from simple analog circuits to more sophisticated digital controllers. The choice depends on the specific application and the generator’s requirements.

In summary, the AVRS is a vital control system that ensures the stable and reliable operation of a generator by maintaining its output voltage at the desired level.

If an Automatic Voltage Regulator (AVR) produces a low output while the generator is running on its own (not connected in parallel with other generators), the primary effect observed would be low output voltage from the generator.

Let’s break down the consequences and how they might manifest:

1. Under-Voltage at the Load:

• Dimming Lights: If the generator is powering lights, they will appear dimmer than usual.
• Malfunctioning Equipment: Sensitive electronic devices might malfunction or shut down due to inadequate voltage.
• Motors: Motors may struggle to start or run at full power, potentially overheating or stalling.

2. Potential Damage to the Generator:

• Overheating: In some cases, the generator itself might overheat. This is because a low excitation current (caused by the faulty AVR) leads to a weaker magnetic field. To compensate, the generator might draw more current to try and maintain power output, leading to increased heat in the windings.
• Long-term Issues: If the low voltage condition persists, it could cause long-term damage to the generator’s insulation and other components.

3. Other Effects:

• Unstable Voltage: The output voltage might become unstable, fluctuating more than usual.
• Inability to Handle Loads: The generator might struggle to handle even small loads, tripping its breaker or shutting down.

Why This Happens:

• AVR’s Role: The AVR’s job is to maintain a stable output voltage by adjusting the excitation current to the generator’s field windings.
• Low Excitation: If the AVR malfunctions and provides a low output signal, the excitation current is reduced, weakening the magnetic field.
• Weak Magnetic Field: A weaker field leads to lower generated voltage.

Possible Causes of Low AVR Output:

• Faulty AVR: The AVR itself might be defective due to internal component failure, age, or damage.
• Incorrect Settings: The AVR’s settings might be incorrect, causing it to regulate the voltage at a lower level than intended.
• Loss of Sensing: If the AVR’s voltage sensing circuit is faulty or disconnected, it might not be able to accurately measure the output voltage and make appropriate adjustments.
• Other Issues: Problems in the generator’s excitation system or other components can also indirectly affect the AVR’s output.

Action to Take:

• Investigate and Repair: The first step is to investigate the cause of the low AVR output and repair or replace the faulty component.
• Manual Voltage Adjustment: If the problem can’t be immediately fixed, the voltage might be manually adjusted (if the generator allows for it) to a safe level until repairs can be made.
• Load Reduction: Reduce the load on the generator to minimize the risk of overheating until the issue is resolved.

Remember: Operating a generator with a malfunctioning AVR can be dangerous and lead to equipment damage. It’s essential to address the issue promptly to ensure the safe and reliable operation of the generator and connected loads.

If an Automatic Voltage Regulator (AVR) on one generator produces a low output while running in parallel with another generator that has a properly functioning AVR, it will cause an imbalance in the system and can lead to several undesirable effects.

Effects on the Faulty Generator:

1. Low Terminal Voltage: The most immediate effect will be a decrease in the terminal voltage of the generator with the faulty AVR.
2. Increased Reactive Power Demand: The system will attempt to maintain the overall voltage level, and the healthy generator’s AVR will respond by increasing its excitation to compensate for the lower voltage from the faulty generator. This, in turn, means the healthy generator will start supplying more reactive power (kVAr) to the system.
3. Increased Real Power Output: In an attempt to maintain its share of the real power (kW) load, the faulty generator will draw more current. This is because with a lower voltage, it needs to push more current to deliver the same power.
4. Overheating & Potential Damage: This increased current flow in the faulty generator can cause it to overheat, potentially leading to insulation damage and even a complete breakdown if the situation is not addressed promptly.

Effects on the System:

1. Unequal Load Sharing: The load sharing between the two generators will become unbalanced. The healthy generator will be supplying a disproportionately higher share of the reactive power (kVAr), while the faulty generator might be contributing less to the real power (kW) load than intended.
2. Circulating Currents: The difference in terminal voltages between the two generators can lead to the flow of circulating currents between them. While these currents might not be very high initially, they can still cause additional losses and heating in the generators and connecting cables.
3. Potential System Instability: In severe cases, if the voltage difference becomes significant, it can lead to instability in the system, causing voltage fluctuations, power oscillations, and even tripping of protective devices.

Corrective Actions:

1. Identify and Repair: The root cause of the low AVR output on the faulty generator should be identified and repaired as soon as possible. This might involve replacing the AVR, adjusting its settings, or fixing any issues in the excitation system.
2. Manual Adjustment: If immediate repair is not possible, the operator can attempt to manually adjust the excitation of the faulty generator to bring its voltage closer to the desired level, temporarily mitigating the imbalance.
3. Load Reduction or Disconnection: If the situation cannot be rectified quickly, consider reducing the overall load on the system or disconnecting the faulty generator to prevent further damage and instability.

Key Takeaway:

A faulty AVR in one generator of a paralleled system can lead to unequal load sharing, potential overheating, circulating currents, and even system instability. It’s crucial to address such issues promptly to ensure the safe and efficient operation of the power generation system.