× Home MCQ Videos Basic Electrical Circuit Theories Electrical Laws Materials Batteries Illumination Generation Transmission Distribution Switchgear Protection Measurement Control System Utilities Safety Transformer Motor Generator Electrical Drives Electronics Devices Power Electronics Digital Electronics Biomedical Instrumentation

Relationship of Line and Phase Voltages and Currents in a Star Connected System

To derive the relations between line and phase currents and voltages of a star connected system, we have first to draw a balanced star connected system.relation between line and phase voltages and currents of star connected system

Suppose due to load impedance the current lags the applied voltage in each phase of the system by an angle ϕ. As we have considered that the system is perfectly balanced, the magnitude of current and voltage of each phase is the same. Let us say, the magnitude of the voltage across the red phase i.e. magnitude of the voltage between neutral point (N) and red phase terminal (R) is VR. Similarly, the magnitude of the voltage across yellow phase is VY and the magnitude of the voltage across blue phase is VB. In the balanced star system, magnitude of phase voltage in each phase is Vph. ∴ VR = VY = VB = Vph

You may also be interested on
Relationship of Line and Phase Voltages and Currents in a Star Connected System

We know in the star connection, line current is same as phase current. The magnitude of this current is same in all three phases and say it is IL. ∴ IR = IY = IB = IL, Where, IR is line current of R phase, IY is line current of Y phase and IB is line current of B phase. Again, phase current, Iph of each phase is same as line current IL in star connected system. ∴ IR = IY = IB = IL = Iph.

Now, let us say, the voltage across R and Y terminal of the star connected circuit is VRY. The voltage across Y and B terminal of the star connected circuit is VYBBR. From the diagram, it is found that VRY = VR + (− VY) Similarly, VYB = VY + (− VB) And, VBR = VB + (− VR) Now, as angle between VR and VY is 120o(electrical), the angle between VR and – VY is 180o – 120o = 60o(electrical). Thus, for the star-connected system line voltage = √3 × phase voltage. Line current = Phase current As, the angle between voltage and current per phase is φ, the electric power per phase is So the total power of three phase system is


SSYED ZOHAIB HASSAN commented on 10/05/2018
Soo helpful for the beginners and even for the experts as well.
Comments


New Articles
EEG MeasurementElectroencephalography | EEGECG Recording SetupElectrocardiographyECG Lead System
Articles on Phasor Diagram
AC powerVector Algebra Line and Phase Voltage and CurrentVector DiagramThree Phase Circuit
More Articles on Basic Electrical
MaterialFundamentalsQuantum TheoryBasic LawsCurrent VoltageResistorInductorsCapacitorElectromagnetismElectrostaticElectron EmissionMiscellaneousGuest Post
Articles Categories
MCQ Videos Basic Electrical Circuit Theories Electrical Laws Materials Batteries Illumination Generation Transmission Distribution Switchgear Protection Measurement Biomedical Instrumentation Control System Utilities Safety Transformer Motor Generator Electrical Drives Electronics Devices Power Electronics Digital Electronics Guest Post