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

How can we help you today?

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 using a regen braking unit.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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 than 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.

With a soft starter, you limit the voltage rise and fall ramp times applied to the motor, rather than the starting and braking times and the soft start will not offer braking torque for high inertia loads as the voltage to the motor is ramped down. Loads with high resistance to movement will follow the ramp down, like pumps where they are pushing liquids down pipes.

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Specific modules

Square D used to sell products with an EMB part number and Telemecanique used to sell products with an ATP part number. These were a DC injection module for pushing a DC voltage on to the motor winding to make them slow down quickly as a fast stop function, 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, the back generated energy is dissipated through the braking resistor to give better braking torque and stop the drive from tripping on DC bus over voltage.

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 and ATV900 range of drives includes catalogue references for:

standard Duty braking resistors
Medium Duty Braking resistors
hoisting resistors for high-inertia applications (hoisting, centrifuges, crushers), which are Heavy / Severe Duty Braking resistors.

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 (Do NOT use a resistor with a lower ohmic value - it will damage 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 or Cressal in the UK, can manufacture this type of resistor.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

REGEN units.

These again monitor the DC bus voltage and work in a similar way to the use of braking resistors. But in these units if the stored DC bus voltage starts to get too high, the REGEN unit will pass this excess energy back on the the mains power supply as a AC voltage rather than losing the energy as heat as a braking resistor would.

Advantage is that the unit reuses the back generated energy, so saves the energy rather then loses it as heat.
Disadvantage, can be the initial cost of the regen unit against other forms of braking options for the drive.