What is the difference between three phase three wire and three phase four wire system?

Answer 1

A three-phase, three-wire, system is obtained from a delta-connected source. A three-phase, four-wire, system is obtained from a star-connected source.

A three-phase three-wire system comprises three conductors, called line conductors. The voltages measured between any pair of line conductors is called are called line voltages and, numerically, they are identical to phase voltages.

A three-phase four-wire system comprises three line conductors, and a neutral conductor. The voltages measured between any pair of line conductors are called line voltages and the voltages measured between any line conductor and the neutral conductor are called phase voltages. The value of a line voltage is 1.732 times the value of a phase voltage.

Answer 2

A four wire system is similar to the three wire system. A three wire system is from a delta service transformer coming in. For example if the service is 480, there will be 480 volts between each of the three legs. The delta is minus a ground. In a four wire system, the service coming in is off of a wye transformer. The forth wire is a ground. For example if the service is 480, there will be 480 volts between each of the three hot legs. If you measure between one of the hot legs to the forth wire (ground), it will measure 277 volts. Many times the wye (four wire) system is used in places where higher voltage is needed to run motors (480) and a service higher than 110 is needed to run lighting (277). No transformer is needed to get the 277. It just simplifies wiring.

Answer

A three-phase, four-wire, system comprises three 'hot' conductors which are correctly called 'line conductors' and a 'neutral conductor' (not a 'ground' conductor, as indicated in the original answer). The actual voltages depend on the electricity standards in your country. In Europe, for example, the voltage between any pair of line conductors (called a 'line voltage') is 400 V, while a voltage between any line conductor and the neutral conductor (called a 'phase voltage') is 230 V. The potential of the neutral conductor is approximately that of earth, which by general agreement, is considered to be zero volts.

Answer 3

A three-phase, four-wire, system is an a.c. distribution system supplied from a three-phase distribution transformer or transformer bank having 'star' (or 'wye') connected secondary windings.

This arrangement provides three energised conductors, termed 'line conductors' and a single 'neutral' conductor which is at approximately the same potential as earth (ground).

In UK/Europe, this is the standard connection for low-voltage distribution, supplying 230-V single-phase supplies to residences which are connected between any one of the three line conductors and neutral, and 400/230-V three-phase supplies to offices and factories (400 V between any pair of line conductors, and 230 V between any single line conductor and neutral).

Answer 4

Two-phase is a system that was used before the advantages of three-phase were accepted. A two-phase system supplies two equal voltages 90 degrees apart in phase. This can be used to provide a rotating magentic field for motors, but it does not really provide the transmission efficiency of three-phase, which uses three voltages 120 degrees apart in phase, and has supplanted two-phase almost completely.

Answer 5

It all comes down to the economics.

Here's how it is:

In transmission, loads are always balanced, hence creating its own star point (not needing a neutral to take the out of balance current). This means that there is only need for 3 wires - one for each phase (ABC). Hence not needing to run another wire

In distribution however, the neutral is needed as this is able to take out the out of balance current as no loads are balanced (excluding 3phase motors etc).

By having the forth wire (neutral) allows the connection of single phase houses as electricity needs a circuit to flow.

The transmission side of a transformer (the primary side) is usually delta connected meaning that line and phase voltages are equal whilst line and phase currents vary by root 3.

The distribution side however (the secondary side) is star connected meaning that their phase and line currents are equal whilst their line and phase voltages vary by root 3.

Answer 6

The fourth wire of a wye three phase system is the grounded coil ends which form a neutral (N). The other ends of these coil wires are designated L1, L2 and L3. This allows line to line and line to neutral voltages to be obtained from the same system. Some low voltage wye connections are 120/208, 240/415, 277/480 and 347/600.

Answer 7

A four-wire system has an added conductor - neutral, necessary for supplying single-phase loads where one supply wire is hot and one is at ground potential.

Answer 8

3 wire is 2 hots which are 120 volts each and a ground.

4 wire is 2 hots which are 120 volts each and a ground and a neutral.

Answer 9

In three phase 3-wire system there is no Neutral present while in 3-phase 4-wire system there is presence of neutral.......