VFD en media tension.

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7. Turn the variac on and bring up the input cell voltage slowly to 30% of its rating. This is because you are magnetizing the transformer and all the additional cell caps.

8. At 30% input voltage checks 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 rate input voltage of the cell is reached.

9. Once full voltage is reached, maintain 100% voltage for 10 minutes.

10. 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.

11. Disconnect variable voltage from cell.

Once the drive has been in continuous service reforming of the drive’s cells should not be necessary. However the spare cell(s) may need to be re-formed if they are not cycled through the drive on a regular basis.

Reason for Forming in Electrolytic Capacitors

- Aluminium Electrolytic Capacitors suffer gradual deterioration of the oxide dielectric during storage. The result is increased leakage current when they are put back in service, until the oxide can re-form itself. If the leakage is too great, the power dissipation may cause venting if full voltage is applied abruptly. The solution is to build up the voltage gradually, limiting the leakage current until the oxide has re-formed.

- The length of storage time after which re-forming is necessary depends on the storage temperature, the manufacturer and the length of time voltage has been applied during the original forming in process.

- Re-forming is never harmful. To be safe, capacitors should be re-formed if the ambient storage temperature is 40 degrees C or higher and/or the cell(s) has not had full voltage applied for 6 months.