How to Magnetize a Generator

Aug. 23, 2022

If the generator is not magnetized, it can be magnetized with a 12V battery. The specific method is: connect two wires from the + - pole of the battery. Open the protective iron case of the generator control circuit board. Start the generator. Connect the + - pole to F + F - (of the generator control circuit board, and the connection time shall not exceed one second. After the magnetization, check the voltage and frequency. Note that the generator can not be loaded before the magnetization is completed, and then it can be loaded after it is checked to be normal. Another case is to start the generator and it will charge automatically in about ten minutes.


But if generator losses excitation because of faults problems, we should resolve it according to different faults.


What are the cause of generator loss of excitation?


During the normal operation of the generator, the excitation suddenly disappears in whole or in part, which is called the loss of excitation of the generator. The causes of generator loss of excitation can generally be summarized as open circuit or short circuit of excitation circuit, including failure of exciter, excitation transformer or excitation circuit, accidental touching of excitation switch, improper switching of standby excitation, loss of auxiliary power supply of excitation system, open circuit of rotor winding or excitation circuit or serious short circuit of rotor winding, failure of semiconductor excitation system, ignition or burning of rotor slip ring.

 How to Magnetize a Generator

1. Excitation transformer fault trip causes generator loss of excitation


Due to the insulation manufacturing defect of the transformer or the gradual deterioration of the insulation defect during operation, the discharge phenomenon occurs, resulting in the tripping of the excitation transformer protection action and the tripping of the unit due to the loss of excitation protection action. The procedures and standards shall be strictly implemented, and regular tests, implementation and troubleshooting shall be carried out. According to relevant regulations and standards, the implementation of periodic test of insulation discipline shall be carefully carried out.


2. Excitation loss of generator caused by tripping of de excitation switch

The reasons for the trip of the de excitation switch include: (1) the trip command of the de excitation switch is mistakenly sent on the DCS. (2) Tripping command of deexcitation switch is sent out in case of fault of outlet relay. (3) The contact of the trip button of the de excitation switch on the electric vertical panel in the central control room is pulled in to send out the trip command. (4) The local control panel of the excitation room manually separates the de excitation switch. (5) The insulation of the control circuit cable of the de excitation switch drops. (6) The switch body mechanically trips the de excitation switch. (7) The instantaneous grounding of the DC system causes the de excitation switch to trip.


3. Loss of excitation of generator caused by ignition of excitation slip ring


The cause of the accident was that the pressure of the carbon brush compression spring was uneven, resulting in uneven current distribution of some carbon brushes, resulting in excessive current of individual carbon brushes and causing heat. In addition, the carbon brush is dirty, polluting the contact surface of the carbon brush and the slip ring, causing the contact resistance of some carbon brushes and the slip ring to increase and then sparking. In addition, the wear of the positive and negative carbon brushes is uneven, and the wear of the negative electrode is always more serious than that of the positive electrode. The surface roughness of the slip ring is increased due to the serious wear, and the slip ring ring fire is caused due to the failure to control in time.


4. Loss of excitation of generator caused by grounding of DC system


After the positive electrode grounding of the DC system, the long cable has distributed capacitance, and the voltage at both ends of the capacitance cannot change suddenly, which causes the capacitance current of the long cable in the external tripping circuit of the generator deexcitation switch to flow through the intermediate relay at the external tripping outlet, and the relay acts to trip the generator deexcitation switch, resulting in the tripping of the generator deexcitation protection action.


5. Loss of excitation of generator caused by fault of excitation regulation system


The fault of the EGC board of the generator excitation system regulator caused the over-voltage protection action of the rotor of the generator excitation regulator, resulting in the tripping of the loss of excitation protection action.

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