Page 264 - Motor_protection_and_control_Manual_motor_starters_ contactors

Star-delta starters protected by overload relays

With AF contactors - Open type version in kit form

Application
Star-delta starting is the most common method to reduce the starting current of a motor.
L Y
This system can be used on all the squirrel cage motors, which are normally used in delta connection. In this
type of starting, it is recommended to choose motors having high starting torque i.e. much higher than the
resistive torque in order to reach sufficient high speed when the motor is connected in star.

When starting:
I /In T /Tn
7 – Inrush current is reduced to a third of direct starting
current
6 I (delta) – Motor torque is reduced to a third or even less of direct
1SFC101103V0001 5 Transient current is generated when switching from star to
starting torque.
delta connection.
5 4 During the initial starting phase ("star" connection), the
3 resistive torque of the driven load must remain, irrespective
of speed, less than the "star" motor torque until "star-delta"
2 T∆ (motor) switching occurs.
I (star)
AF16-30-10 + AF16-30-10 + 1 This starting mode is therefore ideal for machines having
AF09-30-10 + BEY16-4 + VEM4 + T (motor) low starting torque such as pumps, centrifugal compres-
TF42 Tr (resistive torque) sors, wood-working machines...
0 20 40 60 80 100
Motor speed (%)
I = current In = nominal current
T = torque Tn = nominal torque

1SFC101104V0001 Precaution
– Motor nominal voltage in delta connection must be equal to that of the mains. Example: a motor for 400 V
star-delta starting must be designed for 400 V in "delta" connection. Its usual designation is "400 V /
690 V motor". The motor must be constructed with 6 terminal windings
– In order to prevent a high current peak, at least 85 % of nominal speed must be reached before switching
from star to delta

Sequence
AF140-30-11 + AF140-30-11 + Starting is a three-stage process:
AF140-30-11 + BEY140-4 + VM19
+ EF146 1st stage: "Star" connection - Press the "On" button on the control circuit to close the KM2 "Star" contactor.
The KM1 "line" contactor then closes and the motor starts. Countdown of programmed starting time (6 to
10 s) then begins.
2nd stage: "Star" to "Delta" switching - when programmed starting time is over, the KM2 "Star" contactor opens.
3rd stage: "Delta" connection - Thanks to AF contactors, a transition time (or dwelling time) of 50 ms is
already integrated between the opening of the "star" contactor and closing of the "delta" contactor.
Conclusion: An on-delay timer without dwelling time (e.g.: CT-ERS.21S or TEF4-ON) is enough to count-
down the programmed starting time (6 to 10 s) during "Star connection". The use of a star-delta timer includ-
ing a dwelling time is not permitted.

Main Technical Data
Standards IEC 60947-4-1 / EN 60947-4-1
Rated operational voltage Ue max. 690 V - 50/60 Hz
Rated insulation voltage Ui
Mounting positions
acc. to IEC 60947-4-1 690 V
acc. to UL / CSA 600 V
Ambient air temperature
Close to the device ≤ 60 °C (TF42: 38 A above ≤ 50 °C)
Degree of protection IP20
1SBC101956S0201
Switching frequency Refer to "Switching frequency diagrams" page

Pos. 1

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