LINE VTG

I three phase system, line voltage measures between two lines say L1 and L2 and phase voltage means what voltage drop at load. For example, in three phase start connected load

Line current = Phase/load current

Line voltage = 1.73 X phase/load voltage

380V = 1.73 X 220

Phase voltage = 220V

In three phase delta connected load,

Line Voltage = Phase/load voltage

Line current = 1.73 X phase/load current

Example

30A = 1.73 X 17.73

Phase current = 17.73A

Conclusion: In Star circuit, current is same at every point and in Delta circuit, voltage is same at every point.

There's a good article in Wikipedia on this topic.

Now:

EL(Load) = line voltage of the load
EP(Load) = phase voltage of the load
Ip(load) = phase current of the load
IL(load) = line current to the load
IL(Alt) = line current delivered by the alternator
Ip(Alt) = phase current of the alternator
Ep(Alt) = phase voltage of the alternator
P = Power

415v Ac normally star frm tfr secondary Line voltage RY,YB,RY =415v Phase vol. Rgnd,Ygnd,Bgnd=240v 415/sqrt3 regards Hithu

get back to your university and enroll electrical engineering..

Three-phase, three-wire "Y" connection does not use the neutral wire.

When we measure voltage and current in three-phase systems, we need to be specific as to where we're measuring. Line voltage refers to the amount of voltage measured between any two line conductors in a balanced three-phase system. With the above circuit, the line voltage is roughly 208 volts. Phase voltage refers to the voltage measured across any one component (source winding or load impedance) in a balanced three-phase source or load. For the circuit shown above, the phase voltage is 120 volts. The terms line current and phase current follow the same logic: the former referring to current through any one line conductor, and the latter to current through any one component.

Y-connected sources and loads always have line voltages greater than phase voltages, and line currents equal to phase currents. If the Y-connected source or load is balanced, the line voltage will be equal to the phase voltage times the square root of 3:

However, the "Y" configuration is not the only valid one for connecting three-phase voltage source or load elements together. Another configuration is known as the "Delta," for its geometric resemblance to the Greek letter of the same name (Δ). Take close notice of the polarity for each winding in Figure below.

Three-phase, three-wire Δ connection has no common.

At first glance it seems as though three voltage sources like this would create a short-circuit, electrons flowing around the triangle with nothing but the internal impedance of the windings to hold them back. Due to the phase angles of these three voltage sources, however, this is not the case.

One quick check of this is to use Kirchhoff's Voltage Law to see if the three voltages around the loop add up to zero. If they do, then there will be no voltage available to push current around and around that loop, and consequently there will be no circulating current. Starting with the top winding and progressing counter-clockwise, our KVL expression looks something like this:

Let's see how this works in an example circuit:

With each load resistance receiving 120 volts from its respective phase winding at the source, the current in each phase of this circuit will be 83.33 amps:

So each line current in this three-phase power system is equal to 144.34 amps, which is substantially more than the line currents in the Y-connected system we looked at earlier. One might wonder if we've lost all the advantages of three-phase power here, given the fact that we have such greater conductor currents, necessitating thicker, more costly wire. The answer is no. Although this circuit would require three number 1 gage copper conductors (at 1000 feet of distance between source and load this equates to a little over 750 pounds of copper for the whole system), it is still less than the 1000+ pounds of copper required for a single-phase system delivering the same power (30 kW) at the same voltage (120 volts conductor-to-conductor).

One distinct advantage of a Δ-connected system is its lack of a neutral wire. With a Y-connected system, a neutral wire was needed in case one of the phase loads were to fail open (or be turned off), in order to keep the phase voltages at the load from changing. This is not necessary (or even possible!) in a Δ-connected circuit. 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.

• REVIEW:
• 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.
• Line voltage is the voltage measured between any two lines in a three-phase circuit.
• Phase voltage is the voltage measured across a single component in a three-phase source or load.
• Line current is the current through any one line between a three-phase source and load.
• Phase current is the current through any one component comprising a three-phase source or load.
• In balanced "Y" circuits, line voltage is equal to phase voltage times the square root of 3, while line current is equal to phase current.