Lecture 1

 

POWER SYSTEM  ANA  A NAL LYSIS

Balanced Three Phase Power System

 

Problem In a balanced three-phase circuit the voltage  is 173.2∠0o V. Determine all the voltages and the currents in a Y-connected load having   = 10∠20o Ω. Assume that the phase sequence is .

Monday, September 28, 2020

Instructor: Muhammad Naeem

2

 

Problem A three-phase line has an impedance of 2 +  4 Ω as shown in figure The line feeds two balanced three-phase loads that are connected in parallel. The first load is Y Y-40 0 Ω per phase connected and has an impedance of 30 + 4 phase.. The sec second ond loa load d is ∆ ∆-connected -connected and has an impedance of 60 − 4 45 5 Ω. The line is energized at the sending end from a three-phase balanced supply of line voltage 207.85 V. Taking the phase voltage  as reference, determine: a)

The current, real power and reactive power drawn from the supply supply..

 b)

The line voltage at the combined loads

c)

The current per phase in each load 

d)

The total real and reactive powers in each load and the line

Monday, September 28, 2020

Instructor: Muhammad Naeem

3

 

Problem A three-phase line has an impedance of 0.4 + 2.7 Ω per phase. The line feeds feeds two balanced three phase loads that are connected connected in parallel. The first load is absorbing 560.1 kVA kVA at 0.707 power factor lagging. The second load absorbs 132 kW at unity power factor factor.. The line-to-line voltage at the load end of the line is 3810.5 V. Determine: a)

The magnitude of the line voltage at the source end of the line

 b)

Total real and reactive power loss in the line

c)

Real power and reactive power supplied at the sending end of the line

Monday, September 28, 2020

Instructor: Muhammad Naeem

4

 

Per Unit System •

Ratio of actual quantity to the base quantity

•

Relative magnitudes

•

 Narrow range

•

Independent of transformer primary or secondary windings

•

Ideal for computations

•

Same unit for all quantities

•

Circuit laws are valid 

•

Factors of 3 and 3 are eliminated 

Monday, September 28, 2020

Instructor: Muhammad Naeem

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