EE4701-ADVANCED EE LAB

POWER SYSTEMS LABEXPERIMENT NO: 2 EE11B049- Vishnu bhargav EE11B008- mrugender lal

OBJECTIVE:To study the various power components and parameters for balanced, unbalanced,

linear and nonlinear loads connected to 3 – phase supply , using MATLAB/SIMULINK software. In this simulation ,we shall study the effect of unbalance and non-linear loads by studying the various power components and parameters.Source Voltages : vsa, vsb , vsc

Source Currents : isa ,isb ,isc

Load Currents : ila,ilb,ilc

Case 1 : Voltages and load currents are balanced.Source voltages - vsa = vsb = vsc = 230 V RMSLoad Impedences : Za = Zb = Zc = 55+j25 Ω Average Real Power :P = 2391 W ; Pa =797.2 W ; Pb = 797 W ; Pc =796.8 WAverage Reactive Power:q = 1087 VARApparent Power :S = 2626.5 VA ; Sa= 875.5 VA ; Sb = 875.5 VA ; Sc = 875.5 VAPower factor :Pf = 0.9103 ; Pfa = 0.9101 ; Pfb = 0.9030 ; Pfc = 0.9105Total Harmonic Distortion:%THDIa = 3.132 e-6 ; %THDIb = 7.175 e-6 ; %THDIc = 7.509 e-6

%THDVa = 7.867 e-6 ; %THDVb = 0 ; %THDVc = 1.196 e-5

Instantaneous Real Power:

Instantaneous Reactive Power:

Oscillating Real Power :

Oscillating Reactive Power :

Case 2 : Voltages are balanced but load currents are unbalanced.Source voltages - vsa = vsb = vsc = 230 V RMSLoad Impedences : Za = 150+j16 Ω ; Zb =50+j47 Ω ; Zc = 75+j16 Ω Average Real Power :P = 1585 W ; Pa =674.7 W ; Pb = 561.4 W ; Pc =348.6 WAverage Reactive Power:q = 709.2 VAR

Apparent Power :S = 1811.2 VA ; Sa= 350.7 VA ; Sb = 770.7 VA ; Sc = 689.8 VAPower factor :Pf = 0.8510 ; Pfa = 0.9781 ; Pfb = 0.7207 ; Pfc = 0.9941Total Harmonic Distortion:%THDIa = 0 ; %THDIb = -6.032 e-6 ; %THDIc = 7.027 e-6

%THDVa = 7.867 e-6 ; %THDVb = 0 ; %THDVc = 1.190 e-5

Instantaneous Real Power:

Instantaneous Reactive Power:

Oscillating Real Power :

Oscillating Reactive Power :

Case 3 : Voltages are unbalanced and load currents are unbalanced.Source voltages - vsa = 230 V ; vsb = 0.8*230 V ; vsc =1.1* 230 V RMSLoad Impedences : Za = 150+j16 Ω ; Zb =50+j47 Ω ; Zc = 75+j16 Ω Average Real Power :P = 1524 W ; Pa =916.4 W ; Pb = 359.3 W ; Pc =349.6 WAverage Reactive Power:

q = 595.8 VARApparent Power :S = 1678.7 VA ; Sa= 350.7 VA ; Sb = 770.7 VA ; Sc = 834.7 VAPower factor :Pf = 0.9081 ; Pfa = 0.9781 ; Pfb = 0.7204 ; Pfc = 0.994Total Harmonic Distortion:%THDIa = 0 ; %THDIb = 6.853 e-6 ; %THDIc = 5.589 e-6

%THDVa = 7.867 e-6 ; %THDVb =1.227 e-6 ; %THDVc = -7.072 e-6

Instantaneous Real Power:

Instantaneous Reactive Power:

Oscillating Real Power :

Oscillating Reactive Power :

Case 4 : Voltages are balanced but load currents are unbalanced and distorted.Source voltages - vsa = vsb = vsc = 230 V RMSLoad Impedences : Za = 150+j16 Ω ; Zb =50+j47 Ω ; Zc = 75+j16 Ω Rectifier Load : R =200 Ω and L=80mHAverage Real Power :P = 3026 W ; Pa =1153 W ; Pb = 1039 W ; Pc =834 WAverage Reactive Power:q = 715.2 VARApparent Power :S = 3210.4 VA ; Sa= 848.4 VA ; Sb = 1183 VA ; Sc = 1179 VAPower factor :Pf = 0.9424 ; Pfa = 0.9781 ; Pfb = 0.770 ; Pfc = 0.9831Total Harmonic Distortion:%THDIa = 17.9 ; %THDIb = 12.73 ; %THDIc = 12.78%THDVa = 7.324 e-6 ; %THDVb = 4.229 e-6 ; %THDVc = 1.295 e-5

Instantaneous Real Power:

Instantaneous Reactive Power:

Oscillating Real Power :

Oscillating Reactive Power :

Case 5 : Voltages are unbalanced but load currents are unbalanced.Source voltages - vsa = vsb = vsc = 230 V RMSLoad Impedences : Za = 150+j16 Ω ; Zb =50+j47 Ω ; Zc = 75+j16 Ω Rectifier Load : R =200 Ω and L=80mH and Feeder Impedences Zsa = Zsb = Zsc = 2+j3.14 ΩAverage Real Power :P = 2556 W ; Pa =1212 W ; Pb = 594.6 W ; Pc =749.4 W

Average Reactive Power:q = 680.1 VARApparent Power :S = 2703.5 VA ; Sa= 769 VA ; Sb = 691.5 VA ; Sc = 1243 VAPower factor :Pf = 0.9456 ; Pfa = 0.9756 ; Pfb = 0.0599 ; Pfc = 0.9746Total Harmonic Distortion:%THDIa = 13.4 ; %THDIb = 12.73; %THDIc = 8.16%THDVa = 5.099 ; %THDVb = 7.058 ; %THDVc = 4.468Instantaneous Real Power:

Instantaneous Reactive Power:

Oscillating Real Power :

Oscillating Reactive Power :

QUESTIONNAIRE:1.Why the voltages and currents are become unbalanced and what are their effects on power system?A. Voltages and currents are unbalanced because of unbalanced or non-linear loads . This causes poor power factor, large neutral current ,more looses in electrical machines and transformers , de-rating of transformers and machines and large reactive power requirement.2.What are the sources of harmonics and how they affect the system?A. Harmonics voltages and currents in an electric power system are a result of non-linear electric loads. One of the major effects of power system harmonics is to increase the current in the system.3.How the neutral current (InN) depends upon the unbalanced load currents?A. The neutral current can be determined by adding the three phase currents together. In an unbalanced system sum of the unbalanced currents is not zero. Hence it results in non zero neutral current.

4.What are the useful and non useful power in electric power system?A. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as Real power. Hence real power is useful power. The portion of power due to

stored energy, which returns to the source in each cycle, is known as Reactive power. Hence reactive power is non useful power.5.How shall you define power factor for distorted voltage and current waveforms given by Eqn.(1) and Eqn.(2)?A.Power factor is defined as the ratio of Average Active Power and Apparent Power.Instantaneous Active power p(t) = vsa* isa + vsb* isb + vsc * isc

Average active power

P = 1T ∫t

t+T

p(t)dt

Apparent PowerS=Sa+Sb+Sc ; Sa = Va*Ia ; Sb= Vb*Ib ; Sc = Vc*Ic

Power factor = PS

6.Why three-phase system is mostly used instead of single-phase system?A. Three phase system is more power efficient than a single phase system.Three phase system gives a smooth power flow unlike the single phase system.Also it is more economical.7.Why is it desired to have balanced and sinusoidal voltages and currents?A.Unbalanced systems create distortion. It increases the neutral currents. It increases the harmonics . Power flow is not smooth. It results inless power factors.Balanced system with sinusoidal voltages and currrents give smooth power flow with more efficiency.8.What is typical power factors of single phase and three phase induction motors?A. The power factor of induction motors varies with load. For single phase it varies typically from around 0.85 or 0.90 at full load to as low as 0.35 at no-load. For 3 phase it varies from 0.84 to 0.91 at full load to 0.7 at no-load.

9.What is typical THD for diode rectifier and which harmonics are dominantly present?A.Typical current THD for diode rectifier is 48.43%. Dominant harmonics are 3,5,7.10.In power systems mostly odd harmonics are present why this is so?What are possible source of even harmonics and why they are considered more problematic than even harmonics?A. Symmetrical waves contain only odd harmonics and un-symmetrical waves contain even and odd harmonics. Most power system elements are

symmetrical. They produce only odd harmonics and have no DC offset. Non -symmetric waves are the sources of even harmonics. Due to this all triplen(3,6,9,12,…) harmonics add with each other in the neutral conductor of a 4-wire Y-connected load. In power systems containing substantial nonlinear loading, the triplen harmonic currents may be of great enough magnitude to cause neutral conductors to overheat. This is very problematic, as other safety concerns prohibit neutral conductors from having overcurrent protection, and thus there is no provision for automatic interruption of these high currents.