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What are the braking techniques of the Schneider Electric variable speed drives and starters & their advantages and disadvantages?

The braking techniques employed by ATS starters and ATV drives are as follows:

  • DC injection in the poles of an asynchronous motor
  • Using a braking resistor to dissipate the excess braking energy according to the Joule effect
  • Rejecting this excess energy onto the electrical network (not discussed in this information)

DC injection braking in the poles of an asynchronous motor

DC injection is used to slow down loads driven by motors powered by starters or drives, but this is also performed by specific braking modules.
 

Advantages:

  • Quicker braking in freewheel mode
  • Economical braking

Disadvantages:

  • Braking time is not controlled; braking in a high-inertia application will be longer than in a low-inertia application. For starters and drives alike, braking times will differ according to the inertia of the application.
  • If customers wish to calibrate the stopping time, this can only be done if the inertia is always the same and if the time is checked by testing, otherwise a drive must be used.

Starters

With a starter, you limit the voltage rise and fall ramp times applied to the motor, rather than the starting and braking times.
 

Specific modules

Square D used to sell products with an EMB part number and Telemecanique used to sell products with an ATP part number. Schneider no longer sells or supports either of these product ranges.
(Square D and Telemecanique are old Schneider brands)
 

Braking with braking resistor

This type of braking is only used by variable frequency drives.
 

Explanation:
The excess energy associated with braking is stored in the drive's DC bus capacitors and increases its voltage. Any excess energy above a specific voltage threshold is discharged into the braking resistor and then dissipated by the Joule effect.
 

Advantages:

  • The braking time can be calibrated, simply by sizing the braking resistor correctly. The braking time will be that of the deceleration parameter DEC in the Settings menu.
  • No product settings

Disadvantages:
  • It is more expensive than DC injection braking, although it is still economical.
  • Braking is not reasonably possible in less than one second.

Selecting the correct resistor

Our ATV71 range of drives includes catalogue references for:

  • standard braking resistors
  • hoisting resistors for high-inertia applications (hoisting, centrifuges, crushers)

Example: For an ATV71 11 kW drive, a 0.2 kW standard resistor and a 9.8 kW hoisting resistor is available.
 

It is also possible to use specially customised resistors, in which case, the following details must be specified to the supplier:

  • The ohm value => This is a characteristic of the drive
  • The dissipative power required (in kW)  => This is a characteristic of the application
  • The degree of protection in relation to the environment: IP00, IP20, IP54
Companies such as AET Technologies or Métal Déployé can manufacture this type of resistor.
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