Normal operating conditions

The standard contactors 3TF68 ..-.C.. and 3TF69 ..-.C.. for AC operation are fitted with an electronically controlled solenoid operating mechanism with a high interference immunity. The solenoid coil is connected to varistors for protection against overvoltages.

Electromagnetic compatibility

Operation with AC control supply voltage that is particularly subject to strong interference

Contactors 3TF68 ..-.Q.. and 3TF69 ..-.Q.. for AC operation are envisaged for operation in systems with AC control supply voltage that is particularly subject to strong interference. The solenoid systems of these contactors are configured in the DC economy circuit with rectification. The rectifier bridge is connected to varistors for protection against overvoltages.

Such interference can be caused, for example, by the following:

• Periodic overvoltages are injected into the control level of the contactors in the vicinity of operating frequency converters.
• High-energy individual pulses from switching operations and atmospheric discharges are carried over the control cables.

To reduce interference caused by frequency converters, the manufacturer recommends the provision of, for example, input filters, outputs filters, grounding or shielding in the plant.

Other measures that have to be taken for overvoltage damping:

• Contactors supplied via control transformers in accordance with EN 60204 - not supplied directly from the grid
• Use of surge arresters, if applicable.

If operating conditions are such that high levels of interference are created and no measures have been taken to reduce the interference injection into the control voltage level, use of the 3TF68..-.Q and 3TF69..-.Q contactors is especially recommended.