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General Inform ation
Star-Delta Starting
of Three-Phase Asynchonous Motors
General
Star-delta starting the most common method reduce the starting current motor.
In order prevent high current peak, least nominal speed
must reached before switching from star delta.e...g. timer set for the starting duration star
connection enough.e.
Exam ple: motor for 400 star-delta starting must designed for 400 «delta» connection.
This starting mode therefore ideal for machines having low starting
torque such as:
- pumps,
- centrifugal compressors,
- wood-working machines, etc. contactor star contactor with .
Utilization
During the initial starting phase («star» connection), the resistive torque
of the driven load must remain, irrespective speed, less than the «star»
motor torque until «star-delta» switching occurs.
5
1SBC101001C0202
.
Transient current generated when switching from star delta connec
tion.
In this type starting, recommended choose motors having high starting torque i. contactor types are used delta and star contactors . This system can used all the squirrel cage motors,
which are normally used delta connection.
Precautions
M otor nominal voltage delta connection must equal that the mains. This prevents short circuit between «star» and «delta». TE5S not recommended.
Maximum duty per the chart side.
(Switching frequency/hour, according acceleration time and load factor). Countdown programmed starting time (normally then begins... The KM1 «line» contactor then
closes and the motor starts.
2nd stage «Star» «Delta» switching When the programmed starting time over, the KM2 «star» contactor opens..
Note:
When . Its usual designation «400 690 motor».
Sequence
Starting three-stage process:
1st stage «Star» connection Press the «On» button the control circuit close the KM2 «star» contactor. contactor delta con
tactor, the use tim including dwelling tim (or transition time) e. much higher than the resistive torque order reach
sufficient high speed when the motor connected star.
Respect the following conditions enables utilization the starter without excessive
overheating the connections nuisance tripping the thermal O/L relay.
The motor must constructed with terminal windings.
Furthermore, open transition, the current interruption may reach ms: shall checked that this duration compatible with the ap
plication i.
An electrical interlock between star and delta mandatory such through auxiliary contacts.
Example:
- Switching frequency sta rts/h r
- Acceleration time "ta" (use curve)
- Maximum load factor %
This corresponds 4-minute operating cycle (15 starts/hr) with seconds acceleration,
2 minutes operation and minutes rest.
3rd stage «Delta» connection transition time (or dwelling time) fixed between opening the «star» contactor and closing of
the «delta» contactor the use TE5S timer.
Star-Delta Starting
Technical Data
When starting:
- inrush current reduced third direct starting current,
- motor torque reduced third even less direct starting torque.. mainly the decreasing rotation speed acceptable during the starting phase
