Page 70 - 1SBC104119C0202_MainCatalog_R contactors

Closed transition star-delta starting of three-phase
asynchronous motors
R contactor selection

Application
R contactors can be used for closed transition star-delta starting of three-phase asynchronous motors up to 1300 kW.

Description

This starting method, mainly used for large motor powers, prevents the speed drop during the "star-delta" transition time and maintains the
resulting current peak at a relatively low value.

For this purpose the extra KM4 transition contactor closes first before the KM2 star contactor opens. When the KM4 contactor closes, the motor
windings are automatically delta connected, via resistances, to compensate the lack of current during the transition time. Thus the motor speed
remains basically the same. The final delta connection step is then achieved by the KM3 delta contactor closing which switches-off the coil supply
to the KM4 transition contactor. As in the basic star-delta starting mode, the closed transition star-delta starting mode is restricted to low resistive
torque machines.

It is advisable, especially for big masses of inertia, to observe that the connection is made in acc. to the clockwise or anticlockwise rotation
direction, as indicated in the block diagram shown below, in order to prevent damages due to torque throbs.

5 Equipment sizing
–– KM1 main contactor and KM3 delta contactor: rating = 0.58 x In for both contactors

–– KM2 star contactor: compared with a star contactor that would be used for a basic open transition star-delta starter the present KM2 star

contactor has to be over-rated as it is intended to break the star current (0.34 x In) and the transition current too.

–– KM4 transition contactor: the rating is based on the calculation of the short permissible current duration (Icw).

The value of the current flow is about 1.5 x In and the current flow duration < 100 ms.

A block type contactor in the AF series can be selected for this step.

–– Transition resistances: empiric value, generally as follows, R (Ω) = 0.4 x Ue

In

Watt dissipation values for the transition resistances:

--for 12 cycles/h max. P (W) = Ue2
1200 x R

--for 30 cycles/h max. P (W) = Ue2
500 x R

Block Diagram

L1 L2 L3

13 5 135 135 135

24 6 246 246 246

KM4 KM2 / (Y) KM3 / ( ) KM1 / (L)
R
135
KM1: Line contactor W2 1SBC104041S0201 - Rev. A
KM2: Star contactor V2 246
KM3: Delta contactor U2
KM4: Closed transition contactor W1
R: Transition resistances W2 V1
V2 U1
U2
W1
V1
U1

5/18 | ABB R contactors