58 • vacon
ASFIFF12 High Speed
Tel. +358 (0)201 2121 • Fax +358 (0)201 212 205
6.3
Parameters of motor thermal protection (ID’s 704 to 708):
General
The motor thermal protection is to protect the motor from overheating. The Vacon drive is capable of
supplying higher than nominal current to the motor. If the load requires this high current there is a
risk that the motor will be thermally overloaded. This is the case especially at low frequencies. At low
frequencies the cooling effect of the motor is reduced as well as its capacity. If the motor is equipped
with an external fan the load reduction at low speeds is small.
The motor thermal protection is based on a calculated model and it uses the output current of the
drive to determine the load on the motor.
The motor thermal protection can be adjusted with parameters. The thermal current I
T
specifies the
load current above which the motor is overloaded. This current limit is a function of the output
frequency.
The thermal stage of the motor can be monitored on the control keypad display. See the product’s
User's Manual.
CAUTION!
The calculated model does not protect the motor if the airflow to the
motor is reduced by blocked air intake grill.
6.4
Parameters of Stall protection (ID’s 709 to 712):
General
The motor stall protection protects the motor from short time overload situations such as one caused
by a stalled shaft. The reaction time of the stall protection can be set shorter than that of motor
thermal protection. The stall state is defined with two parameters,
and
. If the current is higher than the set limit and output frequency is lower than the
set limit, the stall state is true. There is actually no real indication of the shaft rotation. Stall protection
is a type of overcurrent protection.
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