GE Industrial Solutions AF-650 GP General Purpose Drive - Manual (Page 12)

5 Application Examples
5.1 Examples
5.1.1 Example 1 - Conveyor Belt
Illustration 6.1 (see next page) shows the relation between the braking power and the acceleration/braking of a conveyor belt. As can be seen, the motor power
during braking is negative, since the torque on the motor shaft is negative. The braking power, i.e. the power to be dissipated to the brake resistor, corresponds
almost to the negative motor power, taking the losses in the motor and the frequency converter into account. The example also shows that the motor power is
time-dependent.
Kinetic energy (E) in conveyor belt + motor:
E = 0.5 × m × v 2 + 0.5 × j × ω2 Ws
m = mass with linear movement [kg]
v = speed of mass with linear movement [m/s]
j = inertia of motor and gear box [kgm 2 ]
ω = motor speed = n × 2
60 rad / s
This formula may also be expressed as follows:
E = 0.50 × m × v 2 + 0.0055 × j × n 2 Ws
However, not all of the energy is to be dissipated to the brake resistor. The friction of the conveyor belt and the power loss of the motor also contribute to the
braking function. Consequently, the formula for energy dissipation (E
b
) to the brake resistor is as follows:
Eb =
(
0.5 × m × v 2 + 0.5 × j × ω 2 − 0.5 × Mf × ω
)
× ηMOTOR Ws
M
f
= Friction torque [Nm]
ŋ
M
= Motor efficiency
When:
ω = n × 2
60
is inserted, the result is as follows:
Eb =
(
0.5 × m × v 2 + 0.0055 × j × n 2 − 0.052 × n × Mf
)
× ηM Ws
AF-650 GP Brake Resistor Design Guide
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