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Necessary
Characteristic
Values
Setting Example:
7UM62 Manual
C53000-G1176-C149-3
RESTART INHIBIT is used to switch the function ON or OFF, or to block only the trip
command (Block Relay).
The user communicates to the protective relay the characteristic motor values
supplied by the manufacturer, which are necessary for calculation of the rotor
temperature. These values include the starting current I
, the maximum permissible startup time T START MAX (address 6603), the
I
Mot.nom
number of permissible restart attempts under cold (n
The starting current is entered at address 6602, expressed as a multiple of the nom-
inal motor current (IStart/IMOTnom). For a correct interpretation of this parameter,
it is important that in Power System Data 1 the apparent power (address 252 SN GEN/
MOTOR) and the rated voltage (address 251 UN GEN/MOTOR) of the motor are cor-
rectly set. The number of warm starts allowed is entered at address 6606 (MAX.WARM
STARTS), and the difference between the number of allowable cold and warm starts
(#COLD-#WARM) is entered at address 6607.
For motors without separate ventilation, the reduced cooling at motor stop can be
accounted for by entering at address 6608 the reduced ventilation, expressed by the
factor Kt at STOP. As soon as the current no longer exceeds the current flow
monitoring setting entered at address 0281 BkrClosed I MIN, a motor standstill is
assumed and the time constant is increased by the set factor.
If no difference between the time constants is to be used (e.g. externally-ventilated
motors), then the factor should be set to Kt at STOP = 1.
The cooling with the motor running is influenced by the extension Kt at RUNNING. This
factor considers that motor running under load and a stopped motor do not cool down
at the same speed. It becomes effective as soon as the current exceeds the value set
at address 0281 BkrClosed I MIN. With Kt at RUNNING = 1 the heating and the
cooling time constant are the same at operating conditions (I > BkrClosed I MIN).
Motor with the following data:
Nominal voltage
Nominal current
Starting current
Starting time at I
START
Permissible number of startups with
cold motor
Permissible number of startups with
warm motor
CT transformation ratio
The ratio between the starting current and the motor nominal current is:
624 A
⁄
I
I
-------------- -
=
Start
Mot.nom
126 A
IStart/IMOTnom
Settings
T START MAX
MAX.WARM STARTS
#COLD-#WARM
Restart Inhibit for Motors (ANSI 66, 49Rotor)
U
= 6600 V
N
I
= 126 A
Mot.nom
I
= 624 A
Start
T
START max
n
= 3
cold
n
= 2
warm
200 A/1 A
≈
4.95 4.9
=
= 4.9
= 8.5 s
= 2
=1
, the nominal motor current
Start
) and (n
) conditions.
cold
warm
= 8.5 s
221
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