Phasor Relationship Between Voltage And Current

Relation between phase current and line current in star connection.

Phasor relationship between voltage and current. Current i lags applied voltage e in a purely inductive circuit by 90 phase angle. Once again the current phasor lags behind the voltage phasor as the two waveforms are of the same frequency. At the same time the line current or phase current above 25amps current transformer is used to reduce the current level from high to low typically 1a or 5a. Before drawing the phasor diagram of series rl circuit one should know the relationship between voltage and current in case of resistor and inductor.

Resistor in case of resistor the voltage and the current are in same phase or we can say that the phase angle difference between voltage and current is zero. The new angle between the voltage and the current waveforms gives us their phase difference which as we know is the phase angle of the circuit given the greek symbol phi φ. 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. The phasor diagram is shown below.

Let us derive a relationship between current voltage in a capacitor. Hence in delta connection line voltage is equal to phase voltage. What is line voltage. This means then that the current flowing through the coil will still lag the voltage but by an amount less than 90 o depending upon the values of v r and v l the phasor sum.

Suppose due to load impedance the current lags the applied voltage in each phase of the system by an angle ϕ. The fraction of a period difference between the peaks expressed in degrees is said to be the phase difference. The phasor diagram shows the applied voltage e vector leading above the current i vector by the amount of the phase angle differential due to the relationship between voltage and current in an inductive circuit. Where the phase current will be.

Thus if we differentiate the above relation with respect to time we can get a relationship for current i through the capacitor. The phase difference is 90 degrees it is customary to use the angle by which the voltage leads the current. When capacitors or inductors are involved in an ac circuit the current and voltage do not peak at the same time. In a three phase power system the potential difference between the two phases is called line voltage typically phase to phase.

However as the current waveform is now crossing the horizontal zero axis line at this instant in time we can use the current phasor as our new reference and correctly say that the voltage phasor is leading the current phasor by angle φ. Hence in a 3 phase system of star connections the line current is equal to phase current. The line current will be. Relation between phase current and line current in delta connection.