Page 144 - Motor_protection_and_control_Manual_motor_starters_ contactors

Star-delta starters protected by thermal overload relays

With AS, ASL 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 I = current I n = nominal current
current 6 T = torque T n = nominal torque
1SBC101207F0014 – Motor torque is reduced to a third or even less of direct 5
I (delta)
4 Transient current is generated when switching from star to
starting torque.
delta connection. 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)
AS09-30-10 + AS09-30-01 switching occurs. I (star)
+ AS09-30-01 + BEY16C-3 + VM3 This starting mode is therefore ideal for machines having 1 T (motor)
+ CT-SDS + CA3-10 + T16 low starting torque such as pumps, centrifugal compres- Tr (resistive torque)
sors, wood-working machines... 0 20 40 60 80 100
Motor speed (%)

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 switch-
ing from star to delta

Sequence
Starting is a three-stage process:
1 stage: "Star" connection - Press the "On" button on the control circuit to close the KM2 "Star" contac-
st
tor. The KM1 "line" contactor then closes and the motor starts. Countdown of programmed starting time
(6 to 10 s) then begins.
nd
2 stage: "Star" to "Delta" switching - when programmed starting time is over, the KM2 "Star" contactor
opens.
3 stage: "Delta" connection - A transition time (or dwelling time) of 50 ms is fixed between opening of the
rd
"star" contactor and closing of the "delta" contactor by the use of CT-SDS timer. This prevent short-circuit
between "star" and "delta".

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 according to IEC 60947-4-1 690 V
Air temperature close to the device ≤ 60 °C
Degree of protection IP20
Switching frequency 70
Switching frequency/hour, according to acceleration
time and load factor. Respect of the following condi- 60
tions enables utilization of the starter without excessive ta = 5 s
overheating of the connections or nuisance tripping of Switching frequency (ops/h) 50
the thermal overload relay.
Mounting positions Example: 40
– Switching frequency = 15 starts/hr ta = 8 s
– Motor starting time "Ta" = 7 s (use 8 s curve) 30 ta = 10 s
– Maximum load factor = 63 %. 20 ta = 12 s
This corresponds to a 4-minute operating cycle (15 ta = 15 s
starts/hr) with 7 seconds acceleration, 2.5 minutes 10 ta = 20 s
operation and 1.5 minutes rest.
0
0 10 20 30 40 50 60 70 80 90 100 1SBC101288S0201
Pos. 1 Duty ratio (%)
Duty ratio in %, Ta: acceleration time

4/24 | ABB