ABB MicroFlex e190, User Manual, Page: 174 / 210

174 Resistor braking

Braking energy
The braking energy to be dissipated, E, is the difference between the initial energy in
the system (before deceleration begins) and the final energy in the system (after
deceleration has finished). If the system is brought to rest then the final energy is
zero.


The energy of a rotating object is given by the formula:

E
1
2
--- J

2
 
=

where E is energy, J is the moment of inertia, and ω is the angular velocity.


The braking energy, which is the difference between the initial energy and the final
energy, is therefore:

E
1
2
---


J U
2
 


1
2
---


J V
2
 


–
=

1
2
--- J U
2
  
V
2

– =

= ________________ J (joules)

Calculate the braking energy for the motor. If the value is less than the system
braking capacity B
dc
, calculated on page 172 , a brake resistor will not be required.

Braking power and average power
The braking power, P
gen,max
, is the rate at which the braking energy is dissipated.
This rate is defined by the deceleration period, D (see page 172 ). The shorter the
deceleration period, the greater the braking power.

P
gen,max
=
E
D


P
gen,max
= ________________ W (watts)


The brake resistors shown in the table on page 175 can withstand brief overloads, but
the average power dissipation must not exceed the stated continuous power rating.
The average power dissipation is determined by the proportion of the application
cycle time spent braking. The greater the proportion of time spent braking, the greater