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Electrical Plant Lab2

Autor:   •  October 11, 2017  •  1,043 Words (5 Pages)  •  596 Views

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We can see from the data that we collected above for the balanced circuit we are getting very accurate results based on the theory that for a star connected circuit the line to line voltages are times the phase voltages. Phase A for example we measured 106.06V and the line to line voltage we got 182.56V. We can see that this is very close to the accurate result of what it should have been of 183.70V, however these errors are small and are acceptable. We also know that the phase voltages are 120° apart from each other, and this can be proven by the phase diagram above, as well as line to line voltages where there is a 30° shift from the respective phase voltage. [pic 5]

For the unbalanced circuit the phase voltage relationship does not change much for each of the 3 phases, and again it can be seen that there is a small margin of error in the line to line voltage.

3-Wire (No Neutral) connection:

For part B of this lab we had to use the same 3-wire connection as A but instead we had to remove the neutral wire connection so as to know have two distinct separate nodes.

Balanced

A

B

C

Line–neutral voltage

100.3V

101.6V

100.9V

Line to line voltages

173.3V

176.7V

173.4V

Phase currents

8.28A

5.37A

5.38A

Neutral current

1.6A

Real power

0.534KW lag

0.543KW lag

0.544KW lag

[pic 6]

Phasor diagram for the phase voltages of a balanced 3 phase circuit.

Unbalanced

A

B

C

Line–neutral voltage

129.7V

130.2V

130.4V

Line to line voltages

175.57V

175.5V

175.6V

Phase currents

2.82A

4.88A

4.80A

Neutral voltage

2.8A

Real power

0.298KW lag

0.440KW lag

0.433KW lag

ANALYSIS:

For part B of this lab we can calculate for the balanced load case the total three phase power using the two wattmeters is:

0.534KW + 0.543KW + 0.544KW = 1.621KW

Comparing this with the sum of the individual phase power from part A we get:

0.532KW + 0.538KW + 0.528KW = 1.598KW

According to these calculations above we can conclude that the total powers of the three individual phases are very similar with only a very slight difference.

For the unbalanced load case we also calculated the total three phase power using the two wattmeter readings:

0.298KW + 0.440KW + 0.433KW = 1.171KW

We can conclude that based on our results we found that the starpoint- neutral voltage in the unbalanced load situation is higher than that in the balanced load situation. The reason behind this is because the system is trying to make up the power that is being lost by the lower power load. It’s doing this by reducing more voltage at the neutral.

Delta Connection Load:

For the final part of this lab we are connecting up a three phase delta connected circuit, again adjusting the variac to 100V and calculating the required measurements.

Balanced

A

B

C

Line to line voltage

Line currents

Phase currents

Real power

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