# Star/delta connections little help

#### Coefficient

Joined Sep 5, 2012
75
Hello,

Like i always come here for guidance and other things when i am stucked on some confusions

Lately,i am reading up star/delta transformations and there are few things i really want to understand well.

From what i understand so far******The delta-star resistor network can be equivalent to a network of star-delta resistors connection and vice versa through a process of delta-star or star-delta transformation. As such, the electrical performance of the interchangeable delta/star or star-delta resistors networks will be identical*********.

Now,in the attached file lies my questions;

1... in fig 2.......If one of the resistors in a series circuit is shorted, what would happen to the supply current?

2.... in fig 2....If one of the resistors in a parallel circuit is disconnected, what would happen to the supply current?

3... For the circuit in Figure 1, if both E1 and Vab were doubled, what happened to the currents I1, I2 and Iab

4... why the resistors connected in delta can be replaced by the resistors connected in star and vice versa..

few of these questions i have for now,hope to have a good understanding from all responses.

Regards

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#### wayneh

Joined Sep 9, 2010
17,176
1... in fig 2.......If one of the resistors in a series circuit is shorted, what would happen to the supply current?
Forget the numbers, what do you think would happen qualitatively? Could the supply current ever go down as a result of shorting a resistor?

2.... in fig 2....If one of the resistors in a parallel circuit is disconnected, what would happen to the supply current?
Likewise, what do you think would happen qualitatively? Could the supply current ever go up as a result of removing a resistor?

In both cases, the answer comes from Ohm's law. If there was a voltage drop to begin with, changing the resistance up or down will change the current. If there was no voltage drop, then a change will make no difference.

Eventually you need a quantitative answer, and I think if you work out the math to answer your own questions, you'll come to have a much better feel for it.

#### shteii01

Joined Feb 19, 2010
4,644
Smells like homework.

#### rbtmcm

Joined Jun 18, 2016
1
Hello,

Like i always come here for guidance and other things when i am stucked on some confusions

Lately,i am reading up star/delta transformations and there are few things i really want to understand well.

From what i understand so far******The delta-star resistor network can be equivalent to a network of star-delta resistors connection and vice versa through a process of delta-star or star-delta transformation. As such, the electrical performance of the interchangeable delta/star or star-delta resistors networks will be identical*********.

Now,in the attached file lies my questions;

1... in fig 2.......If one of the resistors in a series circuit is shorted, what would happen to the supply current?

2.... in fig 2....If one of the resistors in a parallel circuit is disconnected, what would happen to the supply current?

3... For the circuit in Figure 1, if both E1 and Vab were doubled, what happened to the currents I1, I2 and Iab

4... why the resistors connected in delta can be replaced by the resistors connected in star and vice versa..

few of these questions i have for now,hope to have a good understanding from all responses.

Regards
A star connection can be replaced by an equivalent delta connection, and vice versa. See attachment.
A more intuitive solution would be to apply Thevenins theorem to the circuit shown by you.

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Joined Jul 18, 2013
26,003
If you are looking for information on star delta configuration wave forms etc, I would have though a Google for 3ph Transformer modes of operation would have given you more useful information?
Max.

#### WBahn

Joined Mar 31, 2012
27,486
If you are looking for information on star delta configuration wave forms etc, I would have though a Google for 3ph Transformer modes of operation would have given you more useful information?
Max.
Why do you think that? I don't see anything in the question that even hints at this being related to transformers, let alone three phase AC circuits. Both of his circuits are DC resistive circuits.

Of his four questions, the first three don't seem to need ANY reference to delta or wye connected circuits to answer. As for the fourth, that is directly addressed by the link I recommended.

#### Coefficient

Joined Sep 5, 2012
75
Smells like homework.
This is not a homework.

just trying to learn things........i hope to be like you someday to help others

#### WBahn

Joined Mar 31, 2012
27,486
This is not a homework.

just trying to learn things........i hope to be like you someday to help others
Even if it's not official homework, it's still homeworkish in that you are trying to learn things instead of just trying to solve a specific problem, so the same approaches mostly apply, namely that you need to do most of the work and a lot of the struggling and have others just provide hints, clues, leading questions, and so on to help keep your struggle moving forward.