SOP OF REFORMING OF DRIVES

BACKGROUND OF DRIVE REFORMING

• Variable Frequency Drives utilize Electrolytic Capacitors for storage of voltage in the inverter section of the drive. These electrolytic capacitors are made up of basically 3 parts. Two conductive plates (usually one being a metal substance similar to aluminum foil and the other being a porous material impregnated with an acidic substance similar to battery acid) that sandwich a layer of insulator material.

• The insulator material is generally made up of an oxide that is created when voltage is applied to the capacitor during manufacturing of the capacitor. Subsequent to this initial power up, every time the capacitor receives a charge it “rebuilds” this layer of oxide. As time elapses and there is no voltage applied to “reform” this layer the layer begins to degrade. This layer “thickness” is the determining factor for the voltage rating of the capacitor. If the layer degrades to a certain point one of two failures will occur.

• The two conducting materials will begin to conduct current at a high rate, and this will cause a boiling of the liquid inside the capacitor. Once this boiling begins the pressure will rise internally and the capacitor will rupture. This failure usually results in a complete destruction of the drive as these capacitors are saturated internally with an acidic mixture.

• The inrush current will arc across the oxide insulator and create a bridge between the plates. This bridge will short the plates and will cause a direct short in the power circuit that can result in other damage to the electronic components. 

REFORMING TIME

• The length of storage time after which reforming is necessary depends on the storage temperature, the manufacture and length of time voltage has been applied during the original forming in process

• To be safe capacitor should be reformed if the ambient storage temperature is 40degree celcius or higher or cell has not had full voltage applied for 12 month.

REFORMING METHOD 1

•Ensure that the converter module is disconnected from all possible power sources (all AC and DC inputs/outputs are disconnected).

•Ensure by measuring that the converter is dead (terminals (U1, V1, W1, UDC+, UDC-, U2, V2 and W2).

•Compose a reforming circuit (see the diagram below) and connect it to the input terminals of the converter module.

•Switch on the AC power supply of the reforming circuit for the time defined in section Reforming time.

•Three-phase or single-phase input, 50 or 60 Hz, without connecting a motor to the output. This voltage should be applied for a period of 1 hour (In six step, 17% of rated voltage in each step for ten minute duration).

•Output current: 0.5…1 A DC and Output voltage during reforming is 1.35…1.45·Ux. Ux denotes the nominal AC voltage of the converter.

•Switch off and disconnect the AC power supply of the reforming circuit.

•Wait for 5 minutes to let the converter DC capacitors discharge.

•Ensure by measuring that the DC terminals of the converter are dead.

•Disconnect the reforming circuit from the converter

•NOTE-: After this energizing process, a wait period of 24 hours before installing or utilizing the drive for motor control is  vital.

REFORMING METHOD 2A

•Ensure that the converter module is disconnected from all possible power sources (all AC and DC inputs/outputs are disconnected).

•Ensure by measuring that the converter is dead (terminals (U1, V1, W1, UDC+, UDC-, U2, V2 and W2).

•Compose a reforming circuit (see the diagram below) and connect it to the DC terminals of the converter module.

•Switch on the AC power supply of the reforming circuit for the time defined in section Reforming time.

•Output current: 0.5…1 A DC and Output voltage during reforming is 1.35…1.45·Ux. Ux denotes the nominal AC voltage of the converter.

•Switch off and disconnect the AC power supply of the reforming circuit.

•Wait for 5 minutes to let the converter DC capacitors discharge.

•Ensure by measuring that the DC terminals of the converter are dead.

•Disconnect the reforming circuit from the converter.

•NOTE-: After this energizing process, a wait period of 24 hours before installing or utilizing the drive for motor control is  vital.

REFORMING METHOD 2B

•Ensure that the converter module is disconnected from all possible power sources (all AC and DC inputs/outputs are disconnected).

•Ensure by measuring that the converter is dead (terminals U1, V1, W1, UDC+, UDC-, U2, V2 and W2).

•Compose a reforming circuit (see the diagram below) and connect it to the DC terminals of the converter module.

•Switch on the reforming circuit for the time defined in section Reforming time.

•Output current: 0.5…1 A DC and Output voltage during reforming is 1.35…1.45·Ux. Ux denotes the nominal AC voltage of the converter.

•Switch off the reforming circuit.

•Wait for 5 minutes to let the converter DC capacitors discharge.

•Ensure by measuring that the DC terminals of the converter are dead.

•Disconnect the reforming circuit from the converter.

•NOTE-: After this energizing process, a wait period of 24 hours before installing or utilizing the drive for motor control is  vital.