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Test: Delta Star & Star Delta - Electrical Engineering (EE) MCQ


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20 Questions MCQ Test Network Theory (Electric Circuits) - Test: Delta Star & Star Delta

Test: Delta Star & Star Delta for Electrical Engineering (EE) 2024 is part of Network Theory (Electric Circuits) preparation. The Test: Delta Star & Star Delta questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Delta Star & Star Delta MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Delta Star & Star Delta below.
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Test: Delta Star & Star Delta - Question 1

 The value of the 3 resistances when connected in star connection is_________​

Detailed Solution for Test: Delta Star & Star Delta - Question 1

 Following the delta to star conversion:
R1=10*5/(10+5+3)
R2=10*3/(10+5+3)
R3=5*3/(10+5+3).

Test: Delta Star & Star Delta - Question 2

Which, among the following is the right expression for converting from delta to star?

Detailed Solution for Test: Delta Star & Star Delta - Question 2

After converting to star, each star connected resistance is equal to the product of the resistances it is connected to and the total sum of the resistances. Hence R1=Ra*Rb/(Ra+Rb+Rc), R2=Rb*Rc/(Ra+Rb+Rc), R3=Rc*Ra/(Ra+Rb+Rc).

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Test: Delta Star & Star Delta - Question 3

Find the equivalent star network.

Detailed Solution for Test: Delta Star & Star Delta - Question 3

The 6 ohm and 9 ohm resistances are connected in parallel. Their equivalent resistances are: 6*9/(9+6)=3.6 ohm.
The 3 3.6 ohm resistors are connected in delta. Converting to star:
R1=R2=R3= 3.6*3.6/(3.6+3.6+3.6)=1.2 ohm.

Test: Delta Star & Star Delta - Question 4

Star connection is also known as__________

Detailed Solution for Test: Delta Star & Star Delta - Question 4

The star connection is also known as the Y-connection because its formation is like the letter Y.

Test: Delta Star & Star Delta - Question 5

 Find the current in the circuit.​

Detailed Solution for Test: Delta Star & Star Delta - Question 5

The 3 5 ohm resistors are connected in delta. Changing it to star:
R1=R2=R3= 1.67 ohm.
One of the 1.67 ohm resistors are connected in series with the 2 ohm resistor and another 1.67 ohm resistor is connected in series to the 3 ohm resistor.
The resulting network has a 1.67 ohm resistor connected in series with the parallel connection of the 3.67 and 4.67 resistors.
The equivalent resistance is: 3.725A.
I=2/3.725= 0.54A.

Test: Delta Star & Star Delta - Question 6

If a 6 ohm, 2ohm and 4ohm resistor is connected in delta, find the equivalent star connection.

Detailed Solution for Test: Delta Star & Star Delta - Question 6

Using the delta to star conversion formula:
R1=2*6/(2+6+4)
R2=2*4/(2+6+4)
R3=4*6/(2+6+4).

Test: Delta Star & Star Delta - Question 7

If a 4ohm, 3ohm and 2ohm resistor is connected in delta, find the equivalent star connection.

Detailed Solution for Test: Delta Star & Star Delta - Question 7

Using the delta-star conversion formula:
R1=4*3/(2+3+4)
R2=2*3/(2+3+4)
R3=2*4/(2+3+4).

Test: Delta Star & Star Delta - Question 8

Find the equivalent delta circuit.​

Detailed Solution for Test: Delta Star & Star Delta - Question 8

Using the star to delta conversion:
R1=4.53+6.66+4.53*6.66/1.23
R2=4.53+1.23+4.53*1.23/6.66
R3=1.23+6.66+1.23*6.66/4.56.

Test: Delta Star & Star Delta - Question 9

 Which, among the following is the correct expression for star-delta conversion?

Detailed Solution for Test: Delta Star & Star Delta - Question 9

 After converting to delta, each delta connected resistance is equal to the sum of the two resistance it is connected to+product of the two resistances divided by the remaining resistance. Hence R1=Ra+Rb+Ra*Rb/Rc, R2=Rc+Rb+Rc*Rb/Ra, R3=Ra+Rc+Ra*Rc/Rb.

Test: Delta Star & Star Delta - Question 10

 Find the equivalent resistance between X and Y.​

Detailed Solution for Test: Delta Star & Star Delta - Question 10

The two 2ohm and one 5ohm resistors are connected in delta, changing them to star, we have R1=R3= 5*2/(5+2+2) = 10/9ohm,  R2 = 2*2/(9)ohm
The one 10/9ohm and one 4/9ohm resistors are connected in series to the 10 ohm and 2 ohm respectively.
This network can be further reduced to a network consisting of a 11.11ohm and 2.44ohm resistor connected in parallel and then series with 10/9 whose resultant is intern connected in parallel to the 10 ohm resistor.

Test: Delta Star & Star Delta - Question 11

Delta connection is also known as____________

Detailed Solution for Test: Delta Star & Star Delta - Question 11

Delta connection is also known as mean connection because its structure is like a mesh, that is, a closed loop.

Test: Delta Star & Star Delta - Question 12

 Rab is the resistance between the terminals A and B, Rbc between B and C and Rca between C and A. These 3 resistors are connected in star connection. After transforming to delta, the resistance at A will be?

Detailed Solution for Test: Delta Star & Star Delta - Question 12

After converting to delta, each delta connected resistance is equal to the sum of the two resistances it is connected to+product of the two resistances divided by the remaining resistance. Hence, resistance at A= Ra+Rb+Rc*Rb/Rc.

Test: Delta Star & Star Delta - Question 13

If a 8/9ohm, 4/3ohm and 2/3ohm resistor is connected in star, find its delta equivalent.

Detailed Solution for Test: Delta Star & Star Delta - Question 13

Using the formula for star to delta conversion:
R1=8/9+4/3+(8/9)*(4/3)/(2/3)
R2=8/9+2/3+(8/9)*(2/3)/(4/3)
R3=2/3+4/3+(2/3)*(4/3)/(8/9).

Test: Delta Star & Star Delta - Question 14

Find equivalent resistance between A & B in the circuit:

Detailed Solution for Test: Delta Star & Star Delta - Question 14

Test: Delta Star & Star Delta - Question 15

A balanced, delta-connected load has an impedance of 3∠30° Ω/phase. What will be the impedance of an equivalent star-connected load?

Detailed Solution for Test: Delta Star & Star Delta - Question 15

Concept:

  • In a balanced three-phase system, the relationship between the impedances of delta (Δ) and star (Y) connections is given by ZY = ZΔ / 3.
  • This relationship applies to both magnitude and phase angle.

Given:

  • Delta-connected impedance (ZΔ) = 3∠30° Ω/phase

To find the equivalent star-connected impedance (ZY):

ZY = ZΔ / 3

Substitute the given delta impedance:

ZY = 3∠30° Ω / 3
ZY = 1∠30° Ω

Therefore, the equivalent star-connected load impedance is 1∠30° Ω/phase.

Test: Delta Star & Star Delta - Question 16

Which of the following is correct statement?

I. Star connection also be termed as 'T' connection
II. Delta connection can be termed as 'π'(pie) connection

Detailed Solution for Test: Delta Star & Star Delta - Question 16

Key Points

  • Star Connection:
    • Also known as 'Y' or 'Wye' connection.
    • In this configuration, one end of each of the three coils is connected to a common point, called the neutral.
    • The other ends of the coils are connected to the three-phase lines.
    • Because it resembles the shape of the letter 'Y', it is sometimes referred to as 'T' connection. Hence, statement I is correct.
  • Delta Connection:
    • Also known as 'Δ' connection.
    • In this configuration, the end of each coil is connected to the start of the next coil, forming a closed loop that resembles the shape of the Greek letter 'Δ'.
    • This configuration is sometimes referred to as 'π' (pie) connection because of its looped structure. Hence, statement II is correct.

Additional Information

  • Star (Y) Connection Advantages:
    • Allows for the use of a neutral wire, which can help in balancing the load.
    • Provides two different voltage levels: line-to-line voltage and line-to-neutral voltage, making it versatile for different applications.
    • Commonly used in distribution systems.
  • Delta (Δ) Connection Advantages:
    • Does not require a neutral wire, simplifying the wiring in certain applications.
    • Can handle higher power loads compared to star connection, making it suitable for heavy machinery.
    • Commonly used in transmission systems and for industrial applications.
  • Applications:
    • Star Connection: Ideal for long-distance power transmission and distribution where voltage levels need to be stepped down.
    • Delta Connection: Suitable for short-distance power transmission and industrial applications where high power loads are common.
Test: Delta Star & Star Delta - Question 17

If the resistance in 'Δ' connected resistive network is R1, R2, R3 as shown in the figure,

then what will be the value of resistance 'Rx' in equivalent star network like?

Detailed Solution for Test: Delta Star & Star Delta - Question 17

Key Points

  • In electrical circuits, the transformation between Delta (Δ) and Star (Y) configurations is a common technique to simplify complex resistor networks.
  • The given problem involves converting a Delta network with resistances R1, R2, and R3 into an equivalent Star network with resistances Rx, Ry, and Rz.
  • For the Delta to Star transformation, the resistances in the Star network can be calculated using the following formulas:
    • Rx = (R1 * R3) / (R1 + R2 + R3)
    • Ry = (R1 * R2) / (R1 + R2 + R3)
    • Rz = (R2 * R3) / (R1 + R2 + R3)
  • Therefore, the correct formula for Rx is (R1 * R3) / (R1 + R2 + R3).
  • This transformation is useful in circuit analysis, especially when dealing with complex networks where simplification can make calculations more manageable.

Additional Information

  • Incorrect Options Explained
    • Option Rx = (R1 * R2) / (R1 + R2 + R3):
      • This formula is incorrect for Rx but is actually the formula for Ry in the Star network.
    • Option Rx = RY = RZ:
      • This option is incorrect because the resistances Rx, Ry, and Rz in a Star network are generally not equal unless R1, R2, and R3 are all equal in the Delta network.
    • Option Rx = (R2 * R3) / (R1 + R2 + R3):
      • This formula is incorrect for Rx but is actually the formula for Rz in the Star network.
  • Delta and Star Transformation:
    • The Delta (Δ) configuration is also known as a Pi (π) network, and it is commonly used in three-phase power systems.
    • The Star (Y) configuration is also known as a Tee (T) network and is often used in electrical engineering for simplifying circuit analysis.
    • Understanding these transformations is crucial for analyzing complex circuits in both AC and DC systems.
    • These transformations are not limited to resistors but can also be applied to impedance in AC circuits.
Test: Delta Star & Star Delta - Question 18

Find DELTA equivalent resistance R12, R23, and R31 from the given STAR configuration.

Detailed Solution for Test: Delta Star & Star Delta - Question 18

Concept:

Star-to-delta conversion


Calculation:

Given


= 6 +2 + 4 = 12

= 18 

Test: Delta Star & Star Delta - Question 19

The resistor value in a Y network that is equivalent to a Δ containing three resistors of R Ω each is:

Detailed Solution for Test: Delta Star & Star Delta - Question 19

Delta to Star conversion:

The star equivalent of delta connected resistor is:

If all resistances connected in the delta are 'R', then the star equivalent resistance is:

Test: Delta Star & Star Delta - Question 20

Three resistors, whose values are 20 Ω, 30 Ω, and 50 Ω, are connected in the delta connection. If the delta to star conversion is done, what will be the equivalent resistance used in the star combination?

Detailed Solution for Test: Delta Star & Star Delta - Question 20

Concept:

1) Delta to Star conversion:

2) Star to Delta conversion:

Application:

Let, RA= 20 Ω, RAC = 30 Ω, RBC = 50 Ω
According to the question, by converting the given Delta to star, we get

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