AME Unit 11 Q5

A hydraulic governor is a device that utilizes hydraulic fluid pressure to control the speed of an engine or mechanical system.  

1. What are Mechanical-hydraulic governors (Woodward governor types)?

It is essentially a combination of a mechanical governor and a hydraulic system. The mechanical components, like a centrifugal governor, sense the speed and generate a mechanical signal. This signal is then converted into a hydraulic pressure signal, which controls the fuel or power supply to the engine.  

1. Principle of hydraulic governor | Download Scientific Diagram – ResearchGate

How it works:

1. Speed sensing: The mechanical components of the governor, often centrifugal weights, respond to changes in engine speed.   1. Mechanical Governor: Working Principle, Types and Advantages. – Testbook testbook.com
2. Hydraulic conversion: The mechanical movement is converted into hydraulic pressure variations.
3. Control action: The hydraulic pressure controls a valve or actuator that regulates the fuel supply or power output to the engine.

Advantages of Hydraulic Governors:

• Higher power output: Capable of controlling larger engines due to the use of hydraulic power.
• Improved accuracy: Offers precise speed control compared to mechanical governors.
• Faster response time: Hydraulic systems generally have quicker response times.
• Easy maintenance: Hydraulic components are relatively easy to maintain and repair.   1. Understanding and Maintaining Your Hydraulic Systems – Boyd CAT boydcat.com

Applications:

Hydraulic governors are commonly used in:

Industrial machinery

Large diesel engines

Steam turbines   1. Mechanical Governors for Steam Turbines – MSHS www.mshs.com

Hydraulic governors play a critical role in ensuring stable operation when alternators are running in parallel.

The primary function of the governor in this context is to maintain a constant speed of the alternator under varying load conditions. This is essential for:

• Maintaining system frequency: The electrical grid operates at a specific frequency, and all alternators connected to it must maintain this frequency.
• Load sharing: When multiple alternators are in parallel, they must share the load equally. Hydraulic governors help in achieving this by adjusting the power output of each alternator based on the load demand.
• Preventing instability: Unequal load sharing can lead to instability in the power system. Hydraulic governors help to prevent this by ensuring that all alternators operate within acceptable limits.

Specific Considerations:

• Governor characteristics: The governors must have precise speed regulation and quick response times to handle load fluctuations.
• Load sharing: The governors should be designed to cooperate with each other to ensure equal load sharing among the alternators.
• Stability: The governor settings must be carefully adjusted to avoid oscillations and instability in the power system.

In essence, hydraulic governors are indispensable for the reliable and efficient operation of parallel alternators.

Adjustable integral action in hydraulic governors is crucial for achieving optimal performance and stability in parallel alternator systems.

Here’s why:

• Elimination of steady-state error: Integral action helps to eliminate any persistent speed deviation from the setpoint, ensuring that the alternator operates at the correct speed under varying load conditions.
• Improved load sharing: By accurately controlling the speed of each alternator, integral action contributes to better load sharing between parallel units.
• Damping oscillations: Properly tuned integral action can help to dampen oscillations in the power system that might occur due to load changes or disturbances.
• Adaptability: The ability to adjust the integral action allows for fine-tuning the governor’s response to different operating conditions and load characteristics.

By carefully adjusting the integral action, engineers can optimize the governor’s performance to meet the specific requirements of the power system.

Integral action in hydraulic governors is typically implemented using an electromechanical integrator. This component accumulates the error signal (difference between the desired and actual speed) over time. The output of the integrator is then added to the proportional signal to form the total control signal.

Key components involved:

• Error signal: The difference between the desired speed and the actual speed, generated by the governor’s speed sensing element.
• Integrator: An electromechanical device that accumulates the error signal over time.
• Summing junction: Combines the proportional and integral signals to form the total control signal.
• Hydraulic amplifier: Converts the electrical control signal into a hydraulic pressure signal.
• Actuator: Controls the fuel supply or other parameters based on the hydraulic pressure signal.

How it works:

1. Error generation: The governor’s speed sensing element compares the actual speed to the desired speed and generates an error signal.
2. Integral action: The integrator accumulates the error signal over time, producing an integral output.
3. Summation: The integral output is added to the proportional output to form the total control signal.
4. Hydraulic amplification: The total control signal is converted into a hydraulic pressure signal by the amplifier.
5. Actuator control: The hydraulic pressure controls the actuator, adjusting the fuel supply or other parameters to correct the speed error.

By incorporating integral action, the hydraulic governor can effectively eliminate steady-state errors and improve overall system performance.

Achieving a stable 50/50 load share between two generators operating in parallel requires a combination of careful design, precise control, and proper coordination. Here’s a breakdown of the key elements:

1. Governor Characteristics:

• Droop Characteristics: Both generators should have identical droop characteristics. This means that for the same change in frequency, both generators should respond with the same change in output power.
• Governor Gain: The gain of the governors should be properly adjusted to ensure a stable system. Too high a gain can lead to oscillations, while too low a gain might result in poor load sharing.

2. Load Sharing Control:

• Power Sharing Control: Most modern generators use power sharing control systems. These systems measure the power output of each generator and compare it to the desired share. The error signal is then used to adjust the governor setpoint, bringing the generator’s output closer to the desired value.
• Communication: Effective communication between the generators is crucial. Information about load sharing, frequency, and voltage is exchanged between the generators to coordinate their operation.

3. Synchronization:

• Precise Synchronization: The generators must be synchronized in terms of frequency, phase, and voltage before being paralleled. Any mismatch can lead to instability and damage to the equipment.   1. Paralleling & Load Sharing Generator Sets | Article + Video | Read Now www.generatorsource.com

4. Protection Systems:

• Overload Protection: Each generator should have overload protection to prevent damage in case of unexpected load increases.
• Under Frequency Protection: Both generators should have under-frequency protection to prevent system collapse in case of excessive load.

5. Additional Considerations:

• Load Sharing Devices: Some systems use load sharing devices, such as power factor controllers or reactive power controllers, to improve load sharing accuracy.
• Regular Maintenance: Regular maintenance of the governors and control systems is essential for maintaining optimal performance.

By carefully considering these factors and implementing appropriate control strategies, it is possible to achieve a stable 50/50 load share between two generators operating in parallel.

To delve deeper into the intricacies of load sharing between parallel generators, let’s explore a simplified mathematical model.

Basic Assumptions:

• Both generators have identical droop characteristics.
• The load is resistive (for simplicity).
• Neglecting voltage regulation effects.

Model Development:

Let:

• P1 and P2 be the power outputs of generator 1 and 2 respectively.
• f1 and f2 be the frequencies of generator 1 and 2 respectively.
• f0 be the nominal system frequency.
• R be the droop regulation (percentage change in frequency for a full load change).

The droop characteristic can be expressed as:

• P1 = P1_base * (1 – R * (f1 – f0) / f0)
• P2 = P2_base * (1 – R * (f2 – f0) / f0)

Where:

• P1_base and P2_base are the base power ratings of the generators.

For a 50/50 load sharing, we have:

• P1 = P2

Equating the two power equations and simplifying, we get:

• f1 = f2

This indicates that for equal power sharing, both generators must operate at the same frequency.

Impact of Load Changes:

When the load changes, the system frequency tends to deviate from the nominal value. This deviation is sensed by both governors, which adjust the generator outputs accordingly to restore the system frequency to the nominal value. The key to maintaining equal load sharing is the identical droop characteristics of the generators.

Limitations of the Model:

This model provides a basic understanding of load sharing but doesn’t account for several factors that affect real-world systems, such as:

• Voltage regulation
• Reactive power sharing
• Governor dynamics
• Load characteristics (e.g., inductive, capacitive)
• Power system disturbances

To accurately model and analyze complex power systems, more sophisticated models and simulation tools are required.