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This circuit represents a Y/∆ starter pack for electric (squirrel-cage) motors.
A Y/∆ starter pack is used for motors which have higher power (kW).
Normally, when a electric motor is started, it's inrush current will be around 6 to 12 × "In" (nominal current). So when a motor has a In of 4 A, the inrush current will be around 24 to 48 A. When a motor has a In of 30 A, this will be around 180 to 360 A!
To reduce inrush current during start up, a Y/∆ starter is used.
When a motor is wired in ∆ circuit, the voltage over the coils (Uco) will be 400 V (L1 & L2, L2 & L3 and L3 & L1 will be connected on a coil).
The current which flows through a coil (Ico), is the total current per phase (Iph) ÷ √3, due to the effect that each phase delivers current to 2 coils.
In the case of this simulation, when the "motor coils" (the 3 lamps) are wired in ∆ circuit, Iph is 30 A, but Ico is 17,3 A.
When starting up in Y, Uco will be the phase-phase voltage, 400 V, ÷ √3, due to the created star connection on the coils.
That means that Uco is 230 V.
As result Ico will again be reduced by √3 (when wired in ∆ Ico is already Iph ÷ √3). This means that Ico will be 30 ÷ 3 (√3 × √3 = 3) = 10 A.
So, instead of 180 to 360 A during startup, the inrush current will be 60 to 120 A (In of 10 A × 6 to 12).
How to use:
Simply close the switch top left.
This will close the mains and the Y contactor.
Look at Uco over 1 coil and Ico through the 2 selected coils, and Iph L1 (middle AC supply).
After a certain time, the "timer" relay becomes active, shuts down the Y contactor and activates the Δ contactor.
Look at Uco, the Ico's and Iph L1 and see the differences.
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