2.24 Motor Starting Time Supervision (ANSI 48)
145
7UM61 Manual
C53000-G1176-C127-3
Figure 2-51
Trip Time Depending on Startup Current
Therefore, if the starting current I actually measured is smaller (or larger) than the
nominal starting current I
StartCurr.
(Parameter
START. CURRENT
) entered at Address
6502, the actual tripping time t
Trip
is prolonged (or shortened) accordingly (see also
Figure 2-51).
Definite Time Over-
current Tripping
Characteristic
(Blocked Rotor
Time)
If the motor starting time exceeds the maximum allowable blocked rotor time t
BlkRT
,
tripping must be executed at least with time t
E
when the rotor is blocked. The device
can detect a blocked rotor condition via a binary input (
“>Rotor locked”
) from an
external rpm-counter. If the current in any of the phases exceeds the already men-
tioned threshold
I MOTOR START
, a motor startup is assumed and in addition to the
above inverse time delay, a current-independent delay time (locked rotor time) is start-
ed. This happens every time the motor is started and is a normal operating condition
that is neither entered in the operational annunciations buffer, nor output to a control
centre, nor entered in a fault record.
The locked rotor delay time (
LOCK ROTOR TIME
) is ANDed with the binary input
“>Rotor locked”
. If the binary input is still activated after the parameterized locked
rotor time has expired, tripping is performed immediately, regardless of whether the
binary input was activated before or during the delay, or after the delay time had
elapsed.
Logic
Motor startup monitoring may be switched on or off using a parameter. It may be
blocked via binary input, i.e. times and pickup indications are reset. the following figure
show the indication logic and fault administration. A pickup does not result in a fault
record. Fault recording is not started until a trip command has been issued.
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