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PROGRAMMING GUIDE
SINUS PENTA
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The graph above shows how trip current It drops depending on the generated speed based on the value set in
parameter C265 .
NOTE
The motor heating can be monitored with measure M026a .
This value is expressed as a percentage of the asymptotic value that can be attained.
When
C274 =Enabled, the thermal protection function is implemented from a PTC sensor: the PTC alarm ( A055 ) trips
when voltage acquired by AIN2 used as a PTC signal input exceeds a preset threshold value when the characteristic
temperature is attained. Alarm A055 can be reset only if temperature decreases by 5% with respect to the trip
temperature.
44.2. Choosing the Characteristic Parameters
Parameter
C266 relates to the instantaneous trip current that the internal thermal protection function will begin to
monitor the current. The default value of 105% is a typical value and it is usually unnecessary to change it.
The motor thermal time is specific to the motor design and it varies between different motor manufacturers.
If the motor thermal time is unknown, the thermal time constant ( C267 ) can be set up as described in the sections below
(IEC Class, Maximum Locked Rotor Time – Basic and Maximum Locked Rotor Time – Enhanced).
The first method is the most simple and gives an approximate result. The other two methods are more complex, but give
more accurate results.
44.2.1. IEC C
LASS
The motor can be protected as defined in the IEC 60947-4-1 standard for the thermal overload relays.
If the protection class is known, in order to set-up the thermal protection for a certain IEC trip class, the value of
C267
can be entered as:
IEC Class C267 [s]
10 360
20 720
30 1080
Table 118: Suggested values for the motor thermal time constant
The standard above defines a 7.2 ratio between LRC and FLC.
The value to be entered in
C267 is then defined from the formula below:
C267 = IEC Class x 36.
If the ratio between LRC and FLC is not 7.2, please refer to the graph in Figure 67.
44.2.2. M
AX IMUM
L
OCKED
R
OT OR
T
IME
– B
ASIC
If the IEC class is not known, then the IEC class can be approximated by the procedure described below.
The following values must be known:
•
Full Load Current (FLC) of the motor
•
Locked Rotor Current (LRC)
•
Maximum Locked Rotor Time (LRT) or Direct On Line (DOL) Start Time
The FLC of the motor can be obtained directly from the nameplate on the motor. The LRC and LRT must be obtained
from the manufacturer or the motor datasheets.
The LRC, also referred to as starting current or motor start-up current, is the current that a motor draws at start-up when
full voltage is applied to the terminals.
LRT is the time a motor can safely maintain LRC from a cold start. This information might also be available as a thermal
withstand curve or a thermal damage curve. If this is the case, then the LRC and LRT must be deduced from the curves.