3-PHASE POWER SYSTEM

3-Phase power system

3-Phase power system

Three Phase Electric Circuits

Introduction

Most of the generation, transmission, distribution and use of energy power is effected by means of poly phase systems, for economic reasons operational phase systems are the most widespread. Three phase voltage source is constituted by three phase sources of equal RMS but 120 ° out of phase with each other.

The figure below illustrates it.

Figure 1

Discussions

Definitions

Composite or line voltage

It is defined as voltage between two lines of the system (ABC, BCA CAB ).

Phase voltage

It can be given as voltage of each source of stress on the system or impedance each branch.

Line current

The current through the line coming out of the current source or requested by load is called Line current.

Phase current

It is the current through the source or the impedance of each branch.

Triangle System and Star System

The following figure represents each source coil where a three phase generator induces voltages of the three phase system. These three sources can be connected in one of two forms as shown below.

Figure 2

Delta Connection

The connection of the three sources is performed as follows: For this type of connection phase voltages coincide with the line voltages. The phase currents (I AB , I BC I CA ) are different from the line currents (I A , I B, I C ). The following figure illustrates these magnitudes.

Figure 3

It can be shown that this connection to the line current equals the current following phase multiplied by three.

Star connection

The connection of the three sources is performed as follows. For this type of connection line currents (I A , IB, I C ) and phase current (I AB , I BC I CA ) match line voltages (V AB , V BC V CA ) and phase (V AN , V BN, VCN ) are different. The following figure illustrates these magnitudes.

Figure 4

The neutral point N is known and can be seen as the phase voltages are defined on this point. The following figure illustrates the relationship between the phase voltages and line. The two previous figures are equivalent. From these figures one can deduce the relationship between the phase voltages and line between Y and delta connections. Therefore, the systems of phase voltages and line in module differ by root of three and are 30 ° out of phase.

Phase sequence

The order in which the voltages or currents acquire their maximum values is called phase sequence. That means that the sequence ABC presents its voltage VA maximum voltage VB before, and in turn this makes it rather than the voltage VC. This applies to any other sequence and currents. The following figure illustrates the sequence ABC. According to the sequence of phases are defined.

Direct sequence

When compared to a fixed point three voltage vectors rotating counterclockwise pass through the fixed point in the following order: A, B, C. Reverse sequence: when compared to a fixed point three voltage vectors rotating counterclockwise pass through ...