CONTACTORS 


What does a “MIRROR CONTACT function” mean for contact operation?
   

The “mirror contact” principle applies to auxiliary NC (break) contacts of LOVATO Electric contactors, series BG and BF with AC and DC coil control. The meaning of this feature is that the operation travel of power and auxiliary NC contacts are such that, should any main NO (make) contact weld, because of a system failure, auxiliary NC contacts cannot close when the coil
de-energises. The impossibility of auxiliary NC contacts to close is used to identify the fault and prevent further damage.
The auxiliary NC contacts, both built-in and add-on, of the LOVATO Electric contactors, series BG and BF for AC and DC control, fulfill this requirement.

 
  


Why does a surge suppressor need to be fitted on a contactor?
   

A surge suppressor is connected in parallel to A1-A2 contactor coil terminals.
Its function is to eliminate or at least reduce voltage peaks and discharges generated on the auxiliary line when the coil is powered down. The suppression of the peaks prevents eventual disturbances to electronic equipment whenever these are installed on the same auxiliary supply line of the contactors.
There are two types of surge suppressors for AC and DC versions of contactors:
-  VARISTOR
The varistor type surge suppressor can be used for a coil supplied with either AC or DC voltage. Its use does not affect the breaking time of the contactor.
Voltage peak reduction could result to not be so effective. Due to its structural features, the varistor begins to dampen after a certain threshold which cannot be close to the rated voltage value of the coil so a small portion of the peak flows through.
-  DIODE
IThe diode type surge
suppressor can be used with DC voltage coils only.
Its use can cause a
considerable delay of the contactor breaking, up to 2-3 times normal breaking time.
The damping of voltage peaks is exceptional.
   
 


What are the limiting resistors, mounted on the special LOVATO ELECTRIC BFK contactors for power factor correction, used for?

The limiting resistors of the BFK contactors limit current peaks, generated at the capacitor bank connection. Should the capacitors be directly connected that is without resistors, current surges, which can reach 80 times the rated current of the capacitors, could be generated for some milliseconds and cause contact welding of the contactor and inconvenient protection fuse tripping as well as considerably reduce capacitor life. For that reason, the limiting resistors are temporarily connected, during the contactor closing; this contributes to increase the operation reliability of the contactor, avoid damage to the same resistors, and obtain minor wear to all the components of the system.
  
  
   

     
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