What do you mean by star delta connection?

Answer 1

A star connection is one with 3 hot conductors returning power to a (usually grounded) common return (neutral) conductor. If the three hots are called A, B, and C, and the neutral is called N, then the three phases are connected AN, BN, and CN. If the star connection is balanced, (it must be, for efficient use of power), then the three hots are also equidistant from each other, though with a different voltage, so you could rewire as delta. (A typical 13.2kv system in the US is 13.2kv phase to phase, and 7.6kv phase to ground.) A delta connection is one with three hot conductors returning power to each other. Using the earlier convention, the three phases would be connected AB, BC, and CA. The ground connection is connected to the frame as a safety, but it provides no power. The choice between star and delta is one of design objective. If your load requires three phase power, then it cannot tolerate loss of even one phase. In that case, it would not matter if you chose star or delta, but you must consider the different voltage in each configuration. If your loads, such as in multiple and distinct star connections, do not require three phase power, then loss of one phase only affects one third of the system, but it you wired delta, then loss of that one phase leaves you with only one third of the system operational. If the neutral conductor is not balanced, such as in a quadraplex connection where there are three phases, with the neutral being at the 120/240 split phase point in the middle of one phase, then star connection is not possible. If you wanted star in this case, you would need three Transformers with the primaries wired delta and the secondaries wired star.