-ETHOD OF OPERATION3*
6
#
' #
2ESTART LOCKOUT FOR MOTORS
4HE ROTOR TEMPERATURE OF A MOTOR LIES FAR AWAY FROM
THE CRITICAL TEMPERATURE LIMITS DURING NORMAL OPERA
TION EVEN WITH INCREASED LOAD )N CONTRAST DURING
START
UP OF THE MOTOR THE ROTOR IS THERMALLY ENDAN
GERED RATHER THAN THE STATOR BECAUSE OF ITS SMALLER
TIME CONSTANT IN CONNECTION WITH THE EXCESSIVELY
HIGH START
UP CURRENTS 7HEN THE MOTOR IS STARTED
REPEATEDLY IT IS NOT DESIRABLE THAT THE MOTOR IS DE
ENERGIZED DURING RUN UP SHOULD THE LIMIT TEMPERA
TURE RISE OCCUR DURING THIS RUN
UP PERIOD 4HEREFORE
IT IS ADVISABLE THAT THE MOTOR START IS AVOIDED WHEN
OVERHEATING OF THE ROTOR IS EXPECTED
DURING RUN UP
4HE ROTOR CURRENT CANNOT BE MEASURED DIRECTLY
4HUS THE RESTART LOCKOUT FUNCTION OF 3* APPROXI
MATES THE ROTOR TEMPERATURE RISE FROM THE STATOR CUR
RENTS )T IS ASSUMED THAT THE LIMIT TEMPERATURE OF THE
ROTOR IS REACHED WHEN THE MOTOR IS ENERGIZED WITH
THE RATED START
UP CURRENT SO MUCH TIME AS IT IS PER
MISSIBLE ACCORDING TO THE DATA STATED BY THE MAN
UFACTURER OF THE MOTOR 4HE RELAY CALCULATES FROM THIS
DATA THE THERMAL CHARACTERISTICS WHICH ARE DECISIVE
FOR THERMAL REPLICA OF THE ROTOR 2ESTART OF THE MOTOR IS
LOCKED AS LONG AS THE CALCULATED RESTART LIMIT SEE
&IGURE IS EXCEEDED /NLY WHEN THIS LIMIT IS UN
DERSHOT RESTART IS RELEASED
3WITCH
ON OF THE MOTOR VIA THE INTEGRATED CONTROL
FUNCTIONS IS AVOIDED DURING RESTART LOCKOUT SO THAT
NO MEASURES NEED BE TAKEN LIKE LOGICAL COMBINA
TION OR MARSHALLING OF THE LOCK
OUT COMMAND "UT IF
THE MOTOR CAN BE STARTED FROM EXTERNAL CONTROL COM
MANDS THEN THE LOCK
OUT COMMAND MUST BE MAR
SHALLED TO AN OUTPUT RELAY AND COMBINED WITH THE EX
TERNAL COMMAND SO THAT THE LATTER IS LOCKED
)T IS OF NO CONCERN THAT THE HEAT DISTRIBUTION ON THE RO
TOR CAGE BAR IS MUCH DIFFERENT AND PRODUCES SEVERAL
HOT SPOTS BUT IT IS DECISIVE THAT THE THERMAL REPLICA OF
THE PROTECTION CORRESPONDS TO THE THERMAL STATE OF
THE MOTOR AFTER RUN
UP
&IGURE SHOWS AS AN EXAMPLE THE HEATING
UP
PROGRESS DURING REPEATED START
UP OF A MOTOR AND
THE PROGRESS OF THE CALCULATED THERMAL REPLICA OF THE
PROTECTION
MOTOR ENERGIZED
ST
START
MAX ROTOR TEMPERATURE
,
T
4EMPERATURE AT
UPPER EDGE OF CAGE BAR
LOWER EDGE OF CAGE BAR
THERMAL REPLICA
RESTART LIMIT
4 %15!,
4 %15!, 4 %15!,
ND
START
RD
START
MOTOR ENERGIZED MOTOR ENERGIZED
&IGURE 4EMPERATURE PROGRESS IN THE ROTOR AND THE THERMAL REPLICA DURING REPEATED RUN UP
"ESIDES THE RESTART LOCKOUT AFTER A STATED NUMBER OF
RESTARTS AN ADDITIONAL LOCK
OUT TIME 4 %15!, CAN
BE DEFINED 4HE NUMBER OF PERMISSIBLE RESTARTS AS
STATED BY THE MOTOR MANUFACTURER ASSUMES THAT THE
MOTOR IS NOT RE
ENERGIZED BEFORE IT HAS COME TO
STAND
STILL BECAUSE OF THE DIFFERENT HEAT SPOTS OF THE
ROTOR 4HE MOTOR SHOULD BE RESTARTED ONLY WHEN THE
ROTOR TEMPERATURE HAS COME TO A THERMAL EQUILIBRIUM
AFTER THE TIME 4 %15!, HAS EXPIRED
ONLY FOR MODEL 3*J JJJJ JJJJ
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