Automatic Voltage Regulators. What is a generator AVR or Automatic Voltage Regulator?

All modern ship alternators are equipped with voltage regulators. The regulators permit to obtain constant voltage of generators under various amount of load and power factor. Here we shall speak about AVR for brushless alternators.

Block diagram (Fig. 1) shows the regulator principle in an autonomous alternator system. The alternator voltage is fed to the AVR unit via fuses and exciter switch. The reference level of the alternator voltage is set by the voltage adjusting potentiometer. The difference between the actual voltage and reference value is amplified and converted to triggering pulses to the thyristor bridge. A-c voltage is fed from the alternator via supply transformer to the thyristor bridge.

Under normal circumstances, the voltage is kept constant. If speed drops of more than 5% occur, the AVR unit will automatically decrease the voltage proportional to the frequency (U/f-constant).

To obtain correct load sharing between parallel running alternators, the alternator voltage is made current dependent. This is obtained by current transformer and a resistance network inside the AVR unit.

What is a power factor?

Power factor is a measure of how effectively electrical power is being used by a system. It is defined as the ratio of the real power (P), which does the actual work, to the apparent power (S), which is the product of the current and voltage supplied to the circuit. The power factor is a dimensionless number ranging from -1 to 1 and is often expressed as a percentage.

Key Concepts:

Real Power (P):

• Measured in watts (W), real power is the actual power consumed by the electrical equipment to perform useful work, such as turning a motor or lighting a bulb.

Apparent Power (S):

• Measured in volt-amperes (VA), apparent power is the product of the total voltage and current in the circuit. It represents the combination of real power and reactive power.

Reactive Power (Q):

• Measured in reactive volt-amperes (VAR), reactive power is the power that oscillates between the source and the reactive components (inductors and capacitors) in the circuit. It does not perform any useful work but is necessary for the establishment of electric and magnetic fields in these components.

Power Factor (PF): 

• PF = P / S
• It can also be represented as the cosine of the phase angle (ϕ) between the voltage and current waveforms: PF =cos(ϕ)
• Lagging Power Factor: Occurs when the current lags behind the voltage (common in inductive loads).
• Leading Power Factor: Occurs when the current leads the voltage (common in capacitive loads).

Importance of Power Factor:

Efficiency:

• A higher power factor indicates more efficient utilization of electrical power. Lower power factors imply that more current is needed to deliver the same amount of real power, leading to increased losses in the system.

Cost:

• Power companies may charge higher rates for customers with low power factors because it indicates inefficient use of the electrical infrastructure and increased losses in the distribution system.

Capacity:

• Improving the power factor can increase the capacity of the system. It allows more real power to be delivered without increasing the current, thereby reducing the load on the electrical infrastructure.

Voltage Regulation:

• A low power factor can cause significant voltage drops, which can affect the performance of electrical equipment.

Improving Power Factor:

Capacitor Banks:

• Installing capacitors in the system can help to offset the inductive effects of motors and other inductive loads, thus improving the power factor.

Synchronous Condensers:

• These are synchronous motors that can be adjusted to operate with a leading power factor, providing reactive power compensation.

Power Factor Correction Devices:

• These are automatic devices designed to improve the power factor by adding capacitors or inductors as needed.

Power factor is a critical aspect of electrical systems that reflects how efficiently electrical power is used. Managing and improving power factor can lead to significant benefits in terms of efficiency, cost savings, and system performance.

A voltage build-up circuit which uses the alternators residual magnetism provides automatic voltage build-up.

The compounding circuit and a compounding transformer provide the necessary excitation current during short circuit conditions when voltage generator is equal to zero. It is necessary for immediate voltage build-up after elimination of short circuit.

The main unit of regulator is AVR circuit. The AVR circuits consist of the following parts: voltage measuring circuit, amplifier, frequency measuring circuit, synchronizing and triggering circuit, stabilized power supply.

Fig. 1. Automate voltage regulator. Block diagram: 1 — current transformer; 2 — fuses; 3 — excitation switch; 4 — AVR unit: 5 — voltage adjuster; 6 — voltage build-up circuit; 7 — thyristor bridge; 8 — compounding transformer; 9 —rotating diode bridge; 10 — compounding circuit; 11 — supply transformer

All the above mentioned circuits are mounted on a printed board.

Replacing AVR

The alternator voltage is transformed before it is fed to the printed circuit board via terminals. The voltage is rectified and a proportional voltage is fed to an operational amplifier where it is compared to the reference voltage. The difference voltage is amplified and controls, via a triggering circuit, the firing angle of the thyristors and thereby the exciter current.

Automatic Voltage Regulator

In case of alternator voltage change, the regulator generates a signal which changes the firing angle of the thyristors until the desired voltage is obtained. A stabilizing filter ensures stable and alternator voltage.

A Generator Automatic Voltage Regulator (AVR) is an essential component in power generation systems. It is responsible for maintaining a constant voltage level from the generator to the load, ensuring stable and reliable power supply. Here's an overview of how it works and its importance:

Function and Operation:

1. Voltage Regulation:

   • The primary function of an AVR is to regulate the output voltage of a generator by controlling the amount of current supplied to the exciter field, which in turn controls the output voltage of the main generator.
   • When the load on the generator changes, the AVR adjusts the excitation current to maintain a stable output voltage.

2. Feedback Mechanism:

   • The AVR continuously monitors the generator's output voltage through a feedback loop.
   • If the voltage deviates from the desired set point, the AVR adjusts the excitation current to correct the voltage.

3. Protection:

   • An AVR also provides protection against voltage fluctuations and ensures that the generator operates within safe voltage limits.
   • It helps prevent damage to the generator and connected equipment caused by over-voltage or under-voltage conditions.

4. Boost Function:

   • Some AVRs include a boost function to provide additional excitation during transient conditions, such as during the startup of large motors, ensuring the generator can handle sudden increases in load without significant voltage drops.

Components:

1. Sensing Circuit:
   • Detects the output voltage of the generator.
2. Control Circuit:
   • Processes the sensed voltage and compares it with a reference voltage to determine the necessary adjustment.
3. Exciter:
   • Receives the adjusted excitation current from the AVR to control the main generator's output voltage.

Importance:

1. Stability:

   • Ensures stable voltage output, which is crucial for the proper functioning of electrical equipment and appliances.

2. Efficiency:

   • Enhances the efficiency of the generator by optimizing the excitation current.

3. Protection:

   • Protects both the generator and the connected load from voltage irregularities.

4. Performance:

   • Improves the overall performance and reliability of the power generation system.

Applications:

• Industrial Generators:
  • Used in large-scale industrial generators to ensure consistent power supply for critical operations.
• Commercial Generators:
  • Employed in commercial settings to provide stable power for businesses and institutions.
• Residential Generators:
  • Included in residential generators to protect household appliances from voltage fluctuations.

Overall, the AVR is a vital component in any generator system, ensuring the reliable delivery of stable voltage to the end-users.