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A star configuration of the windings in a 3-phase transformer or motor is where one end of each winding is connected to form a star or 'Y' pattern and the other ends are each connected to one of the three separate lines of the incoming 3-phase electrical service.
A delta configuration is when each phase winding of a three phase transformer or motor is connected to its two adjacent phase windings to form an arrangement that looks like the Greek letter delta - or triangle - and then each point of the triangle is connected to to one of the three separate lines of the incoming 3-phase electrical service.
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To be able to wire a 3-phase transformer or motor either in star or delta, all 6 ends of the three sets of coils, called "windings", have to be exposed with suitable connection terminals.
The windings are often labelled A1, A2, A3 and B1, B2, B3, where "1", "2" and "3" denote the separate phase windings and "A" and "B" denote the beginning and end of each winding.
Another way of describing it is to say that the separate windings can be labelled:
Winding 1: A1 <---> B1. Winding 2: A2<---> B2, Winding 3: A3 <---> B3.
In star configuration either all the A's or all the B's are connected together and the 3-phase supply (consisting of three separate "phase lines" labelled L1, L2, L3) is connected to the remaining three connectors. For example, if you connect B1 to B2 and B2 to B3 to form the center of the "star" then you must connect supply L1 to A1; supply L2 to A2 and supply L3 to A3.
In delta configuration, connect B1 to A2, B2 to A3, B3 to A1. (If you draw that out as a schematic diagram, it will be a triangle.) Then connect supply L1 to A1; supply L2 to A2 and supply L3 to A3. (Exactly the same as the supply lines were connected before, for the star configuration.)
For more information see the answers to the Related Questions shown below.
What else can I help you with?
What are the parameters on which the timing of star delta starter depends?
The timing should allow the motor to get up to full RPM in the star configuration before switching to delta configuration. Depending on the motor size and inertia loading it will be from 5 to 10 seconds.
How many contactors using in star connection of motor?
two contecter <<>> There are three contactors used in a Star Delta configuration.
How can you wire a 6-pole isolator to disconnect a 6-wire star delta motor away from the mcc and near to the motor?
There is no need to place a 6 pole disconnect to isolate the motor in the field. The motor's leads at the motor's terminal box have to be wired for a delta connection. The star delta contactor in the MCC only has three wires on its output. Six wires do not have to be taken directly to the motor. The voltage is reduced at the start of the circuit when the starter in in the star configuration. From the star configuration it changes to the delta configuration. So as you can see only a three pole isolation switch is needed in the field to isolate the motor from its supply.
What is the starting sequence of a star-delta starter?
This is the schematic for the starter. K1T is a timer. Initially KM1 and KM3 are closed to start the motor. Then KM2 is closed and KM1 is opened to run the motor This is the equivalent ladder logic using relays and timers.
Does a star delta timer rely on the breaking of the retaining contacts on the star contactor side?
The N.C. (timed open) contacts in the star delta timer energize the star contactor's coil when the system is energized. At the same instant the system is energized, the timer starts to time down the required time which lets the motor get up to speed in the star configuration. When the timer reaches the set point time, a second set of N.O. (timed closed) contacts close the delta contactor's coil and open the N.C. timed contacts of star contactor's coil. The motor now runs in the delta configuration. When the system is de energized the timer contact's reset to its de energized state.
