1MDU07212-YN Rev. D Section 4
Protection and Control Function
REF601 / REJ601 / REM601 31
Application Manual
4.9.2 Principle of operation
Startup detection
The starting condition of the motor is detected by startup detection. The function
initially recognizes the de-energized condition of the motor when the values of all
three phase currents are less than 0.12xIb for longer than 5s. If any of the phase
currents of the de-energized condition rises to a value equal to or greater than
Istart> within 100ms, the motor start output signal is activated indicating that the
motor startup is in progress. At the same time I
2
t protection is also enabled.
The motor start output remains active until the values of all three phase currents
drops below set value of Istart> and remains below that level for a time period of
500ms to take into consider short voltage dip or interruption into account. If the
current is not reached up to Istart> within 100ms, the occurrence is not considered
to be a normal starting sequence.
In addition during startup condition (i.e. when motor start is active), the start value
settings for I>, I>>, I>>> gets doubled and functions Io> and Io>> gets blocked if
Blocking/doubling feature is enabled. This feature can be enabled or disable by a
setting “Restraint 68M”. The function Io> and Io>> is blocked to avoid mal
operation due to CT saturation during starting.
The start time (t motor start) of the last motor startup is recorded and available as
measurement. Also the maximum startup current is recorded and available as
measurement on LHMI as well as available over communication. Both these
measurement is available in non-volatile memory. The values are updated in
memory each new startup of motor.
Speed switch input
Speed switch is used to indicate whether a motor is accelerating during startup or
not. At motor standstill, the Spd Sw input is active (i.e. the input available from
speed switch), indicating that the rotor is not rotating. When the motor has started,
at certain revolution the deactivation of the Spd Sw by the speed switch indicates
that the rotor is rotating. If the input is not deactivated within the t locked rotor, the
Trip output is activated indicating that the rotor is locked.
If the speed switch is not configured at any binary input this feature is blocked
internally.
Thermal stress I
2
t calculator
This function gets activated during startup detection and calculates the thermal
stress developed in the motor during startup condition. The heat developed during
the starting is equal as the integral of I
2
t. The function integrates the value of I
2
t
and compares it to the limiting value obtained from the product of the square of the
values of the Istartup and t startup settings. When the calculated value of the
thermal stress exceeds this limit, the Trip output is activated.
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