Mastering Alternator Troubleshooting On Board Ships

Mastering Alternator Troubleshooting On Board Ships

Table of Contents:

1. Introduction
2. Components of a Brushless Alternator 2.1 Stator Body 2.2 Rotor Assembly 2.2.1 Main Rotor 2.2.2 Exciter Rotor
3. Working of a Brushless Alternator
4. Role of the Exciter in Controlling the Output
5. Automatic Voltage Regulator (AVR) Circuit 5.1 Working of the AVR 5.2 Controlling Output Voltage
6. Important Test Procedures 6.1 Electrical Safety Requirements 6.2 Test Equipment 6.3 Battery Test 6.4 Voltage and Phase Testing 6.5 Checking Main Stator and Main Rotor 6.6 Testing Rotating Rectifier Assembly 6.7 Checking Exciter Stator and Exciter Rotor 6.8 Field Flashing
7. Conclusion

Components of a Brushless Alternator

A brushless alternator consists of several components that work together to generate electricity. The two main components are the stator body and the rotor assembly. The stator body houses the main stator and the excitator, while the rotor assembly consists of the main rotor, the exciter rotor, and a bridge rectifier assembly mounted on a plate attached to the rotor.

The stator body plays a crucial role in the alternator as it houses the main stator and the excitator. The main stator is responsible for generating AC output, while the excitator supplies DC magnetizing current to the rotor, which is the field of the main alternator. The rotor assembly, on the other hand, consists of the main rotor and the exciter rotor. When the rotor starts rotating, AC output is generated in the exciter rotor coils, which is then passed through a bridge rectifier and converted to DC before being given to the main rotor.

Working of a Brushless Alternator

The working of a brushless alternator involves the interaction of various components to generate electricity. When the rotor starts rotating, AC output is generated in the exciter rotor coils. This output is then passed through a bridge rectifier assembly, which converts it to DC. The DC output is fed to the main rotor, which, in turn, generates AC current in the stationary main stator coils. This AC current is the final output of the alternator.

Role of the Exciter in Controlling the Output

The exciter in a brushless alternator plays a crucial role in controlling the output. It supplies DC magnetizing current to the rotor, which is the field of the main alternator. By increasing or decreasing the amount of current to the stationary exciter field coils, the output of the main alternator can be varied. This control is essential in maintaining a stable voltage output.

Automatic Voltage Regulator (AVR) Circuit

The automatic voltage regulator (AVR) circuit is a crucial component in a brushless alternator as it controls the exciter current, which, in turn, controls the output voltage. When the output voltage is low, the AVR senses this and increases the excitation current in the exciter stator. This increased excitation current results in an increased output from the exciter rotor, which is then converted to DC and fed to the main rotor. This, in turn, increases the magnetic field strength of the main rotor, resulting in an increase in the output.

Conversely, when the output voltage is high, the AVR decreases the excitation current, thus controlling the output. The AVR continuously monitors the output voltage and adjusts the exciter current accordingly to maintain the desired voltage level.

Important Test Procedures

To ensure the proper functioning of a brushless alternator, it is important to perform regular test procedures. Before conducting any tests, it is crucial to adhere to electrical safety requirements and have the necessary knowledge of using electrical test equipment. Never attempt to work on live equipment if you are not qualified or experienced in this work. It is also recommended to have another competent person present while testing a live generator who can shut down the engine in case of an emergency.

The important test procedures for a brushless alternator include:

1. Battery Test: Remove the AVR connections and insulate the UV and N terminals with tape. Replace the AVR with a 12-volt battery and check the engine speed to ensure it is within 4 percent of the nominal value.

2. Voltage and Phase Testing: Use a multimeter to check the voltage between phases and the voltage between each phase and neutral. The output voltage should be within 10 percent of the nominal value, and the voltage should be balanced across phases within one percent.

3. Checking Main Stator and Main Rotor: If the output voltage is more than 10 percent below the normal value and unbalanced across phases by more than one percent, it indicates a fault in the main stator, main rotor, exciter stator, exciter rotor, or rectifier diodes. Testing the main stator winding and insulation can help identify any faults.

4. Testing Rotating Rectifier Assembly: Disconnect one lead of the main rotor connections from the rectifier assembly and disconnect the connections of the exciter rotor to the rectifier diodes. Using a multimeter in diode test mode, check the diodes in the rotating rectifier assembly for proper functioning. Each plate of the rectifier assembly should carry three diodes, and the diodes should be correctly fitted and tightened.

5. Checking Exciter Stator and Exciter Rotor: Check the resistance and insulation of the exciter stator with a multimeter and a mega tester, respectively. The resistance should be within the specified range, and the insulation value should be higher than one mega ohm to earth. A visual inspection can help identify any burnt or damaged windings in the exciter rotor.

6. Field Flashing: In self-exciting alternators, loss of residual magnetism may occur after a breakdown or long shelf time. Field flashing can be performed by connecting a 12-volt DC battery to the AVR terminals for one second.

By following these test procedures, you can ensure the proper functioning of a brushless alternator and identify any faults or issues that may require further attention.

Conclusion

In conclusion, a brushless alternator is a complex system that consists of various components working together to generate electricity. The stator body and rotor assembly play crucial roles in this process, with the exciter being responsible for controlling the output of the alternator. The automatic voltage regulator circuit ensures the stability of the output voltage by adjusting the exciter current. Performing regular test procedures is essential to identify any faults or issues in the main stator, main rotor, exciter stator, exciter rotor, or rectifier diodes. By following proper testing procedures and ensuring electrical safety, you can maintain the efficiency and reliability of a brushless alternator.

FAQs:

Q: What is the role of the exciter in a brushless alternator? A: The exciter in a brushless alternator supplies DC magnetizing current to the rotor, controlling the output of the main alternator.

Q: How does the automatic voltage regulator circuit work? A: The AVR circuit adjusts the exciter current based on the output voltage, increasing it when the voltage is low and decreasing it when the voltage is high, thereby maintaining a stable voltage output.

Q: What are the important test procedures for a brushless alternator? A: The important test procedures include battery testing, voltage and phase testing, checking the main stator and main rotor, testing the rotating rectifier assembly, checking the exciter stator and exciter rotor, and field flashing.

Q: How can field flashing be performed in a brushless alternator? A: Field flashing can be performed by connecting a 12-volt DC battery to the AVR terminals for one second, ensuring the proper magnetism of the exciter.

Q: Why is it important to perform regular test procedures on a brushless alternator? A: Regular test procedures help identify any faults or issues in the main stator, main rotor, exciter stator, exciter rotor, or rectifier diodes, ensuring the proper functioning and reliability of the alternator.