θ
i
startuptimeof the motor
operatetime when no prior load
= − ×100 10% 00% +
margin
GUID-5B3B714D-8C58-4C5D-910D-A23852BC8B15 V2 EN (Equation 22)
For example, the motor start-up time is 11 seconds, start-up current 6 x rated and Time
constant start is set for 800 seconds. Using the trip curve with no prior load, the operation
time at 6 x rated current is 25 seconds, one motor start-up uses 11/25 ≈ 45 percent of the
thermal capacity of the motor. Therefore, the restart disable level must be set to below 100
percent - 45 percent = 55 percent, for example to 50 percent (100 percent - (45 percent +
margin), where margin is 5 percent).
Setting the thermal alarm level
Tripping due to high overload is avoided by reducing the load of the motor on a prior
alarm.
The value of Alarm thermal value is set to a level which allows the use of the full thermal
capacity of the motor without causing a trip due to a long overload time. Generally, the
prior alarm level is set to a value of 80 to 90 percent of the trip level.
4.1.9.6 Signals
Table 310: 49M Input signals
Name
Type Default Description
I_A SIGNAL 0 Phase A current
I_B SIGNAL 0 Phase B current
I_C SIGNAL 0 Phase C current
I
2
SIGNAL 0 Negative sequence current
BLOCK BOOLEAN 0=False Block signal for activating the blocking mode
START_EMERG BOOLEAN 0=False Signal for indicating the need for emergency start
AMB_TEMP FLOAT32 0 The ambient temperature used in the calculation
Table 311: 49M Output signals
Name
Type Description
TRIP BOOLEAN Trip
ALARM BOOLEAN Thermal Alarm
BLK_RESTART BOOLEAN Thermal overload indicator, to inhibit restart
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 311
Technical Manual
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