Generator Rotating Rectifier: Functions, Faults, Causes and Solutions

1.What is the function of a rotating rectifier?

The rotating rectifier is a device that rotates coaxially with the alternator exciter. Its main function is to convert the three-phase AC excitation current output by the alternator exciter armature into DC current through the diodes on the rectifier, which is supplied to the rotor winding as the power source for providing excitation current. It is precisely because of the application of the rotating rectifier that the AC synchronous generator is freed from the constraint of brushes, eliminating the trouble of frequent maintenance and replacement of parts, and making the application of AC synchronous generators more extensive.

2.Symptoms of a faulty generator set rotating rectifier

The rotating rectifier is usually composed of silicon rectifier elements to form a rectifier circuit. If one or more rotating silicon elements in the circuit are damaged, the damaged silicon elements will lose their unidirectional conductivity (conducting in both forward and reverse directions), causing the circuit to be in a short-circuit state. Once the rotating silicon element is short-circuited, the generator will have no output voltage when the unit is running. If the fault is not found and eliminated in time, it will lead to the burnout of the alternator exciter armature winding and force the generator to stop.

3.Causes of rotating rectifier faults in generator sets:

① The silicon rectifier diode of the rotating rectifier is damaged due to overvoltage or overcurrent.

② The silicon rectifier element of the rotating rectifier is installed with excessive torque, resulting in deformation of the tube shell and damage to the internal silicon chip.

③ The load power factor is too low, causing the excitation current to exceed the rated current of the silicon rectifier element for a long time, thereby damaging it.

4.Troubleshooting methods for generator set rotating rectifier:

① Rotating silicon elements should be used according to the current level specified in the drawings. If there are no drawings or data at hand, the excitation current value of the main generator can be used to select the standard specification of silicon elements. At present, the common specifications of rotating rectifiers produced in China are 16A, 25A, 40A, 70A and 200A.

② Reasonably select the voltage level of the rotating silicon element. The reverse peak voltage URN of the rotating silicon element should be 10-15 times the excitation voltage.

③ The torque for tightening the rotating silicon element nut should be appropriate, and a constant torque wrench should be used to tighten the nut. The torque value for tightening the rotating silicon element nut shall be in accordance with the provisions shown in Table 11-4.

④ Take overvoltage protection measures. Overvoltage protection is usually achieved by installing a varistor or a resistance-capacitance absorption circuit on the DC side of the rotating rectifier.

Guangxi Dingbo Generator Set Manufacturing Co.,Ltd. is an early professional manufacturer of generators and diesel generator sets in China. The company has first-class national-level large-scale production and load testing equipment. Provide users with long-term diesel generator set sales, leasing, technical consultation, commissioning, maintenance, training services and generator set trusteeship business. If you would like to get more information welcome to contact us via [email protected].