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What Cause Rotating Rectifier of Generator Set Failure?

Mar. 03, 2020

After using for a certain period of time, the rotating rectifier of diesel generator set maybe break down, which often leads to the failure of normal operation of the whole generator set.


What is the function of rotating rectifier of diesel generator set?

Rotating rectifier is a device which rotates coaxially with AC exciter. Its main function is to convert the three-phase AC excitation current output by the armature of the AC exciter into the DC current through the diode on the rectifier, supply the rotor winding as the power supply for the excitation current. It is because of the application of rotating rectifier that the AC synchronous generator gets rid of the binding of brush, no longer has the trouble of frequent maintenance and replacement of parts, and also makes the application of the AC synchronous generator more extensive.


silent generators

Some rotating rectifiers of AC synchronous generators are installed on the outside of the AC exciter and fixed on the shaft with screws for easy installation and maintenance. Some rotating rectifiers of generators are installed on the inner side of the rear end cover and directly fixed on the bolts protruding from the armature core of the exciter, making the structure more compact. There are two kinds of rotating rectifier circuits: three-phase half wave and three-phase bridge rectifier. If the three-phase bridge rectifier circuit is adopted, in order to facilitate installation, reduce the connection line between the rectifier elements and improve the reliability of the generator operation, the rectifier diodes are of two tube types, positive and negative poles are exactly opposite, which is convenient for wiring.


What is phenomenon when the rotating rectifier failure?

Rotating rectifier is usually composed of silicon rectifier elements. If one or several rotating silicon elements in the circuit are damaged, the damaged silicon element will lose one-way conductivity (both positive and negative conduction), resulting in a short circuit of the circuit. Once the rotating silicon element is short circuited, the generator has no output voltage when the unit is running. If the faults are not found and removed in time, the armature winding of the AC exciter will be burnt out and the generator will be forced to stop.


What causes the rotating rectifier failure?

1.The silicon rectifier diode of rotating rectifier is damaged due to over-voltage or over-current.

2.When the silicon rectifier element of the rotating rectifier is installed, the torsional moment is too large, which leads to the deformation of the tube shell and the damage of the internal silicon wafer.

3.The load power factor is too low, which causes the excitation current to exceed the rated current of silicon rectifying element for a long time and damages it.


How to deal with the problems?

1.Rotating silicon elements shall be provided according to the current level specified in the drawing. If there is no drawing data at hand, the standard silicon element can be relied on according to the excitation current value of the main generator. At present, the common specifications of rotating rectifiers produced in China are 16A, 25A, 40A, 70A and 200A.

2.The voltage level of the rotating silicon element shall be reasonably selected, and the reverse peak voltage urn of the rotating silicon element shall be 10-15 times of the excitation voltage UIN.

3.Tighten the nut of rotating silicon element with proper torque, and tighten the nut with constant torque wrench. The torque value of tightening the rotating silicon element nut shall be in accordance with the provisions shown in the manual which provided by the supplier.

4.Take over-voltage protection measures. Overvoltage protection is usually equipped with varistor or resistance capacitance absorption circuit on DC side of rotating rectifier.


Hope the article is helpful to you. Starlight Power manufacturer also supplies diesel generator set, cover Cummins, Volvo, Perkins, Deutz, Yuchai, Shangchai, Ricardo, Weichai, MTU, Doosan etc. Power range 20kw-3000kw. Welcome to contact us by email sales@dieselgeneratortech.com, we will work with you. 

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