2.25 Restart Inhibit for Motors (ANSI 66, 49Rotor)
153
7UM61 Manual
C53000-G1176-C127-3
Required Charac-
teristic Values
The user communicates to the device the characteristic motor values supplied by the
manufacturer, which are necessary for calculation of the rotor temperature. These
values include the startup current Istart, the nominal motor current IMot.nom, the
maximum admissible startup time
T START MAX
(address
6603
), the number of ad-
missible restart attempts under cold (n
cold
) and (n
warm
) conditions.
The starting current is entered at address
IStart/IMOTnom
, expressed as a multiple
of the nominal motor current (
6602
). For a correct interpretation of this parameter, it
is important that in Power System Data 2 the nominal motor current (address
1102
is
correctly set. The number of warm starts allowed is entered at address
6606
(
MAX.WARM STARTS
) and the difference (
6607
) between the number of allowable
cold and warm starts is entered at address
#COLD-#WARM
.
For motors without separate ventilation, the reduced cooling at motor standstill can be
accounted for by entering at address
6608
the reduced ventilation factor
K
τ
at STOP
.
As soon as the current no longer exceeds the setting value entered at address
281
BkrClosed I MIN
, motor standstill is detected and the time constant is increased
by the extension factor configured.
If no difference between the time constants is to be used (e.g. externally-ventilated
motors), then the extension factor
K
τ
at STOP
should be set to
1
.
Cooling with running motor is influenced by the extension factor
K
τ
at RUNNING
. This
factor considers that a 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
281
BkrClosed I MIN
. With
K
τ
at RUNNING
=
1
the heating
and the cooling time constants are the same at operating conditions (I >
BkrClosed
I MIN
).
Setting Example:
Example: Motor with the following data:
Rated voltage
U
N
= 6600 V
Rated current
I
Mot.nom
= 126 A
Startup current
I
Start
= 624 A
Startup Duration for I
STARTUP
T
START max
= 8.5 s
Allowable Starts with Cold Motor n
cold
= 3
Allowable Starts with Warm Motor n
warm
= 2
Current Transformer
200 A / 1 A
The ratio between startup current and motor nominal current is:
The following settings are made:
IStart/IMOTnom
=
4.9
T START MAX
=
8.5 sec
MAX.WARM STARTS
=
2
#COLD-#WARM
=
1
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