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Vacon Plc

Phone:

+358-(0)201 2121

Fax: +358-(0)201 212 205

Service:

+358-40-8371 150

E-mail: [email protected]

Page 40

Vacon

acon

Multi-purpose Control Application II

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. When the power
of the drive is turned on, the calculated model uses
the heatsink temperature to determine the initial
thermal stage for the motor. The calculated model
assumes that the ambient temperature of the motor
is 40°C.

Motor thermal protection can be adjusted by setting
the parameters. The thermal current I

specifies

the load current above which the motor is overloaded.
This current limit is a function of the output
frequency. The curve for I

is set with parameters

.....

6, 7

.....

7 and 7

.....

9, refer to the figure 6-26. The

parameters have their default values taken from the
motor name plate data.

With the output current at I

the thermal stage will

reach the nominal value (100%). The thermal stage
changes by the square of the current. With output
current at 75% from I

the thermal stage will reach

56% value and with output current at 120% from I

the thermal stage would reach 144% value. The
function will trip the device (refer par. 7

.....

5) if the

thermal stage will reach a value of 105%. The speed
of change in thermal stage is determined with the
time constant parameter 7

.....

8. The bigger the motor

the longer it takes to reach the final temperature.

The thermal stage of the motor can be monitored
through the display. Refer to the table for monitoring
items. (User's Manual, table 7.3-1).

CAUTION!

The calculated model does not protect the motor if the airflow to the

motor is reduced by blocked air intake grill.

7. 5

Motor thermal protection

Operation:

0 = Not in use
1 = Warning
2 = Trip function

Tripping and warning will display the same message code. If tripping is selected the
drive will stop and activate the fault stage.
Deactivating the protection, setting parameter to 0, will reset the thermal stage of
the motor to 0%.

7. 6

Motor thermal protection, break point current

The current can be set between 50.0—150.0% x I

nMotor

This parameter sets the value for thermal current at frequencies above the
break point on the thermal current curve. Refer to the figure 6-26.
The value is set in percentage which refers to the name plate data of the
motor, parameter 1

.....

13, nominal current of the motor, not the drive's nominal output

current.
The motor's nominal current is the current which the motor can withstand in direct
on-line use without being overheated.
If parameter 1

.....

13 is adjusted, this parameter is automatically restored to the default

value.
Setting this parameter (or parameter 1

.....

13) does not affect the maximum output

current of the drive. Parameter 1

.....

7 alone determines the maximum output current

of the drive.