Page 644 - Mechatronics with Experiments

630 MECHATRONICS
Input Output
power Electric motor: power
Power conversion process
Losses converted to heat
Heat transfer to/from environment

Losses

Core losses

Resistive Hysteresis Eddy Friction and
loss loss current windage
loss loss

Heat
transfer

Environment

FIGURE 8.16: Energy losses in electric motors and its effect on the motor temperature.

These losses are in the form of heat. The energy losses can be categorized into three
groups:

2
1. resistance losses (also called copper losses): R ⋅ i ,
2. core losses (hysteresis and eddy current losses),
3. friction and windage losses.

Resistance and core losses are electrical losses, whereas the friction and windage losses are
mechanical losses.
The steady-state operating temperature of the actuator is determined by these losses,
the heat transferred to the surrounding medium through conduction, convection, and radia-
tion type heat transfer mechanisms. The maximum temperature the actuator can operate in
(i.e., before losing its insulation material or magnetic properties) determines the maximum
power capacity of the motor.
The energy balance (Q ) is the difference between the generated heat due to the
net
losses (Q ) and the transferred heat from the actuator to its surrounding environment (Q )
in out
is the energy that must be absorbed by the actuator in the form of temperature rise,

Q net = Q − Q out (8.101)
in
= c ⋅ m ⋅ (T − T ) (8.102)
0
t