CQR-26/56 Fagor Compact Drives and Motors Quick Reference. Ref.1910
ASYNCHRONOUS MOTORS
OPERATING MODES
Next, the motor operating modes are described showing the different
zones in the diagram below (power-torque/speed). The motor
behavior characteristics are different in each of them. For spindle
motors it is crucial to have an ample constant power zone. Three
operating zones are established in order to analyze this characteristic.
The following graph shows each zone and the motor operating mode
in each of them.
OPERATING ZONES
ZONE I. This zone is established from the rest state - null speed (0
rev/min) - to the nominal operation (rated or base speed). The torque
developed by the motor coincides with the rated torque (Mrated) and
is constant in the whole zone. Its value is obtained as the product of
the power generated by the motor (directly proportional to the current
circulating through its rotor up to the rated operation point) times its
corresponding turning speed. The power developed by the motor is
directly proportional to the speed up to the rated operation point
where it reaches the rated power (Prated).
ZONE II. This zone is defined as the constant power zone and covers
from the nominal operating point to where the motor reaches its
maximum available voltage. The torque decreases porportional as the
speed increases. The power remains constant.
ZONE III. This zone begins when the voltage at the motor terminals has
reached the maximum voltage that the drive can provide. The torque
decreases with the square of the speed. The power decreases as the
speed increases.
INFLUENCE OF THE SUPPLY VOLTAGE
The supply voltage of the bus sets the electrical limitation on how the
motor will run.
DEFINITIONS
nmax. Maximum turning speed allowed. The maximum speed nmax
depends on the mechanical design (roller bearings life, short-circuit
ring of the squirrel cage) and electrical design (voltage limiting
characteristics).
n1. Maximum permanent speed. It is the maximum speed allowed
permanently (regardless of the speed duty cycle).
S1. S1 duty cycle (continuous). Operation with constant load enough to
stabilize the temperature of the motor.
S6. S6 duty cycle (intermittent operation). Uninterrupted periodic
service with intermittent load, also called ‘‘continuous cycle with
intermittent load‘‘. It consists of a series of identical cycles that have a
constant load time and another one without load. There is no resting
(stopped) intervals. If no other value is indicated, the duty cycle with
load will be referred to a time period of 10 minutes. Thus, S6-40%
indicates:
tc = 4 minutes with load
tv = 6 minutes without load
Motor limits. For induction motors, the speed and power values are
limited for thermal and mechanical reasons. The maximim current is
only limited by thermal characteristics of the motor windings.
Thermal limit. Heat loss is stored in the motor and dissipated by
cooling systems. The motor temperature depends, among other
things, on the duty cycle with load. This critical motor temperature
must never be exceeded. The characteristics for continuous cycle
S1 and intermittent cycle S6-40% define de outputs allowed for an
ambient temperature of up to 40°C. For this case, the winding
temperature increase is about 100 °C.
Mechanical limit. The mechanical speed limit must never be
exceeded. Exceeding this value may damage the roller bearings,
the short-circuit ring of the rotor, ...
0
POWER
N1
0
ZONE I
TORQUE
Mmax
Pmax
Pn
Mn
ZONE II ZONE III
nbase
Power S6-40%
Power S1
Torque S6-40%
Torque S1
SPEED
nmax
0
POWER
N1
0
ZONE I
Pn
ZONE II ZONE III
nbase
Power S1
SPEED
nmax
Limitation
by current
Limitation
by voltage
Lower voltage
at the drive
Higher voltage
at the drive
T: Duration of the cycle
P: Power of the load
Pp: Lost electrical power
'4
: Temperature increase over ambient
temperature
4
max: Maximum temperature that the motor
may reach without damaging its insulation
'4
TIME
TIME
TIME
T
P
Pp
T
Tmax
tc tv
T: Duration of the cycle
Tc: Time with load
Tv: Time without load
P: Power of the load
Pp: Lost electrical power
'4
: Temperature increase over ambient
temperature
4
max: Maximum temperature that the motor
may reach without damaging its insulation
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