Procedure 1 Procedure 2 3. If one of the secondary winding polarities were rever

Question

Procedure 1

Procedure 2
3. If one of the secondary winding polarities were reversed, in Procedure 1 a) Would there be a dead short? b) Would the transformer heat up?__ c) Would the primary voltages become un- balanced?. d) Would the secondary voltages become un- balanced? 4. If one of the secondary winding polarities were reversed in Procedure 4: a) Would there be a dead short? b) Would the transformer heat up? c) Would the primary voltages become un- balanced? d) Would the secondary voltages become un- balanced?

Explanation / Answer

if one phase is reversed, it gets ugly. Suppose Vbc was reversed, so that its angle is not -120 deg, but +60 deg instead. Now the summation around the 3 phasors of unit magnitude with angles of 0, +60, & +120 degrees. so that the sum is a magnitude of 2 with a phase of +60 deg. Due to this unbalce will occure3) a) No dead short circut

a) No Dead short circuit

b)due to flow of high circulating current ,transforme will heats up

c)No unbalance in the primary

d) unbalace will occure in the secondary .

procedure 2:

Connected correctly, the 3 windings have voltages 120 deg apart. Phases have the following voltages - angle Vab=0 deg, angle Vbc=-120 deg, angle Vca=120 deg, all magnitudes are 1.0 per unit. Closing the delta puts these 3 voltages in series where they add together. The 3 phasors are equal in magnitude, displaced 120 deg in phase. Their sum is zero, so that the closed loops results in minimum current, that needed to support triplen harmonic magnetizing current. When a load is connected, current develops in the delta windings. But if one phase is reversed, it gets ugly. Suppose Vbc was reversed, so that its angle is not -120 deg, but +60 deg instead. Now the summation around the delta is 3 phasors of unit magnitude with angles of 0, +60, & +120 degrees. Doing the math shows that the sum is a magnitude of 2 with a phase of +60 deg. So the delta loop is a low impedance closed path with twice the line voltage resulting in enormous circulating current.

a) No Dead short circuit

b)due to flow of high circulating current ,transforme will heats up

c)No unbalance in the primary

d) unbalace will occure in the secondary .

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