# Voltage and current relationship in star delta connection Relationship of Line and Phase Voltages and Currents in a Star Connected System. Published on Three Phase Circuit | Star and Delta System We know in the star connection, line current is same as phase current. delta-connecttion-figure Contents: Relation Between Phase Voltage and Line Voltage in Delta Connection; Relation Between Phase Current and Line Current . Three Phase Transformer Star and Delta Configurations . Then the relationship between line and phase voltages and currents in a three-phase system can be Connection, Phase Voltage, Line Voltage, Phase Current, Line Current. Star.

Starting with the top winding and progressing counter-clockwise, our KVL expression looks something like this: Indeed, if we add these three vector quantities together, they do add up to zero. Another way to verify the fact that these three voltage sources can be connected together in a loop without resulting in circulating currents is to open up the loop at one junction point and calculate voltage across the break: Sure enough, there will be zero voltage across the break, telling us that no current will circulate within the triangular loop of windings when that connection is made complete.

Conversely, because each line conductor attaches at a node between two windings, the line current will be the vector sum of the two joining phase currents.

With each load resistance receiving volts from its respective phase winding at the source, the current in each phase of this circuit will be So each line current in this three-phase power system is equal to The answer is no.

With a Y-connected system, a neutral wire was needed in case one of the phase loads were to fail open or be turned offin order to keep the phase voltages at the load from changing.

This is not necessary or even possible!

## Star Connection in a 3 Phase System

With each load phase element directly connected across a respective source phase winding, the phase voltage will be constant regardless of open failures in the load elements. Even with a source winding failure, the line voltage is still V, and load phase voltage is still V. The only difference is extra current in the remaining functional source windings. Compare this fault tolerance with a Y-connected system suffering an open source winding in Figure below.

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

In this case, two load resistances suffer reduced voltage while the third loses supply voltage completely! However, if dual voltages are needed e. The conductors connected to the three points of a three-phase source or load are called lines. The three components comprising a three-phase source or load are called phases. In a balanced three-phase system, there is a very simple relationship between the line and phase quantities, which can be obtained from the phasor quantities or the time-varying expressions of the voltages and the currents. The voltage and current relationships in three-phase ac circuits can be simplified by using the rms values I and V of the quantities.

Voltage and current relationships in three-phase circuits.

### Voltage and Currents in Star- and Delta-Connected Loads | Introduction to AC Circuits | InformIT

Star-Connected Balanced Load Phase current: The VI provides a visual aid to understanding the definitions of phase and line voltages and phase and line currents in the delta- and the star-connected ac systems that contain the loads as well as the ac supplies. In addition, the instantaneous voltage and currents are displayed in the front panel of the VI. Show that the line voltage Vline in the three-phase system is times the phase voltage Vphase, and verify the result by using the VI for a given phase voltage.

Study the concept in question 1 this time for the line currents and the phase currents in the case of a delta-connected three-phase load.

• Delta Connection In a 3 Phase System
• Three-phase Y and Delta Configurations

In question 2, find out the angles in degrees between the phase and the line quantities on the supply side and the load side. Use the single-phase equivalent circuit in each load configuration and calculate the phase currents for given values of the voltage and the load impedance. Three incandescent lamps rated 60 W, V rms are connected in the delta form. What line voltage is needed so that the lamps burn normally at rated conditions? What are the line and phase currents in the circuit? 