VFD en media tension.

This procedure is to be followed for reforming electrolytic capacitors on Gen IV Perfect Harmony Drives. Reforming is necessary on Gen IV cell capacitors if the cells have not been energised in the last 6 months.

1 Equipment Required:

Variac – (variable auto transformer) variable voltage source.

Rating 0 - 750 Vac - 30Amps. (0 to 415/440 Vac ok if 0 – 750 Vac not available, note this will only partially reform the capacitors).

Safety: All Safety procedures must be followed. Required PPE must be worn.

• Isolation procedure,

• Personal Protective Equipment

2 Reforming Power Cells

Method with power cells in the VFD. This is the preferred procedure when this can be done. This provides a higher level of personal safety protection as well as cooling protection for the power cells.

1. Insure the input interrupting device is open, Locked out and Tagged out. This is the Input Medium Voltage.
2. Connect the variac

1. To power cell C1 or any secondary winding connection.
2. Verify variac input operating voltage and input breaker voltage.
3. Connect the input of the variac to the input breaker of the VFD or other source if required.

1. When applying power and bringing the variac up protect yourself by standing behind the doors of the Cell cabinets with correct PPE on.
2. Turn the variac on and bring up the input cell voltages slowly to 30% of its rating. This is because you are magnetizing the transformer and all the additional cell caps.
3. At 30% input voltage check the voltage across ½ of the 480 Vac circuit and 1/3 of the 690 Vac power cell. If the voltage is balanced then continue increasing the voltage in 10% steps until rated input voltage of the cell is reached.
4. Once full voltage is reached, maintain 100% voltage for 10 minutes.
5. Once this process is complete, decrease voltage source to zero. Let capacitors discharge for ≈ ten minutes. Ensure that the “Safe LED” on the Cell Control Board has gone out.
6. Disconnect variable voltage from cell.

Reforming a Power Cell out of the VFD. This is not the preferred method of reforming power cells. In particular cases this may be required to be done because the VFD cannot be shut down and the power cell has not been installed for a couple of years.

1. (One point of the capacitors is referenced to the chassis of the cell) The power cell must be isolated from earth ground.

2. The power cell must be separated by means of a shielding it behind a wall – protective device.

3. For air cooled and liquid cooled power cells a fan must be directed across the bleeder resistors. This must be done to protect the bleeder resistors.

Failure to do this could result in overheating and failure of the bleeder resistors in the cell.

4. Connect the Variac to the cell 3 phase input

5. Verify variac input operating voltage and input breaker voltage.

6. Connect the input of the variac to the input breaker of the VFD or other source if required.

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