ABB 615 series Technical Manual page 308

Section 4
Protection functions
302
In order to accurately calculate the motor thermal condition, different time constants are
used in the above equations. These time constants are employed based on different motor
running conditions, for example starting, normal or stop, and are set through the Time
constant start, Time constant normal and Time constant stop settings. Only one time
constant is valid at a time.
Table 309: Time constant and the respective phase current values
Time constant (tau) in use
Time constant start
Time constant normal
Time constant stop
The Weighting factor p setting determines the ratio of the thermal increase of the two
curves θ and θ .
A B
The thermal level at the power-up of the protection relay is defined by the Initial thermal
Val setting.
The temperature calculation is initiated from the value defined in the Initial thermal Val
setting. This is done if the protection relay is powered up or the function is disabled and
then enabled or reset through the Clear menu.
The calculated temperature of the protected object relative to the operate level, the
TEMP_RL output, is available through the monitored data view. The activation of the
BLOCK input does not affect the calculated temperature.
The thermal level at the beginning of the start-up condition of a motor and at the end of the
start-up condition is available in the monitored data view at the THERMLEV_ST and
THERMLEV_END outputs respectively. The activation of the BLOCK input does not have
any effect on these outputs.
Alarm and tripping logic
The module generates alarm, restart inhibit and tripping signals.
When the thermal level exceeds the set value of the Alarm thermal value setting, the
ALARM output is activated. Sometimes a condition arises when it becomes necessary to
inhibit the restarting of a motor, for example in case of some extreme starting condition
like long starting time. If the thermal content exceeds the set value of the Restart thermal
val setting, the BLK_RESTART output is activated. The time for the next possible motor
start-up is available through the monitored data view from the T_ENARESTART output.
The T_ENARESTART output estimates the time for the BLK_RESTART deactivation
considering as if the motor is stopped.
Phase current
Any current whose value is over 2.5 x I
Any current whose value is over 0.12 x I
currents are below 2.5 x I
r
All the currents whose values are below 0.12 x I
1MAC059074-MB A
r
and all
r
r
615 series ANSI
Technical Manual