bonitron M3575R, Руководство для пользователей

Страница: 27 / 32

User’s Manual
27
7.
A
PPENDICES
7.1.
A
PPLICATION
N
OTES
Resistive load banks are selected based on the application. In order to calculate the
model needed, please use the following guidelines.
Verify the amount of peak power needed for braking.
VFD’s are rated for braking
power as well as peak braking capacity. This information is available in the drive
manual.
7.1.1.
W
ATTAGE
For example: A drive rated for 10 horsepower of output may be rated for
150% braking. This means that there is 15hp of braking required. In this
case the peak power required would be:
746 * .
Braking brake
hp P

Watts hp P
brake
11190 746 * 15
 
7.1.2.
O
HMIC VALUE
The ohmic value of the resistor can usually be determined from the drive
manual under the “minimum ohmic value”. This ohmic value indicates the
rating of the chopper or braking transistor, and may not be directly related to
the horsepower of the drive. In order to calculate the required ohmic value
for the braking load, use the following formula:
brake
DCbus
brake
P
V
R
2
) (

The DC bus voltage for the equation is determined by the level that the drive
begins braking. For 460/480VAC systems, this is typically 750VDC, for
230VAC systems, it is typically 375VDC. Refer to your drive manual for
specifics.
For the above example, the ohmic value would be:
ohms
Watts
VDC
R
brake
3 . 50
11190
) 750 (
2
 
This value must be verified with the drive manual that it is not less than the
“minimum ohmic value” for that drive manual. If so, the braking requirements
may be more than the drive can absorb, and a larger drive or external braking
transistor may be required.
If it is greater, it is possible to select a resistor value lower than the calculated
value.
7.1.3.
D
UTY
C
YCLE
The duty cycle is based on the amount of time the drive is actually braking as
opposed to accelerating, running at constant speed, or idle. For instance, if
a pick and place operation requires 3 seconds to accelerate, traverses for 44
seconds and then decelerates for 3 seconds, the total cycle time is:
The duty cycle for braking is:
sec 50 3 44 3
      
dec run acc cycle
T T T T