My Final PRoject Tittle is:
DESIGN AND CONSTRUCT OF THREE PHASE CONTROLLED SEMICONVERTER BASED ON MICROCONTROLLER COMPLETED BY PASSIVE FILTER TO PRODUCE LOW HARMONICS (HARDWARE).
It consists of Three Phase Electric Source, Trigger circuit for SCR, Passive Filter.
Now I would tell you about Three Phase Electric sources.
Three Phase Electric Source and Transformers.
A three-phase (3f) system is a combination of three single-phase systems. In a 3f balanced
system, power comes from a 3f AC generator that produces three separate and equal voltages,
each of which is 120° out of phase with the other voltages (Figure 1-3phase).
Three-phase equipment (motors, transformers, etc.) weighs less than single-phase equipment of
the same power rating. They have a wide range of voltages and can be used for single-phase
loads. Three-phase equipment is smaller in size, weighs less, and is more efficient than
Three-phase systems can be connected in two different ways. If the three common ends of each
phase are connected at a common point and the other three ends are connected to a 3f line, it
is called a wye, or Y-, connection (Figure 2-3phase2).
If the three phases are connected in series to form a closed loop, it is called a delta, or D-, connection.
POwer in BAlanced in 3f Loads
Balanced loads, in a 3f system, have identical impedance in each secondary winding (Figure 3-3phase3).
The impedance of each winding in a delta load is shown as ZD (Figure 3a), and the impedence in a wye load is shown as Zy (Figure 3b).
For either the delta or wye connection, the lines A, B, and C supply a 3f system of voltages.
UnBAlanced 3f Loads
An important property of a three-phase balanced system is that the phasor sum of the three line or phase voltages is zero, and the phasor sum of the three line or phase currents is zero. When the three load impedances are not equal to one another, the phasor sums and the neutral current are not zero, and the load is, therefore, unbalanced.
The imbalance occurs when an open or short circuit appears at the load.
If a three-phase system has an unbalanced load and an unbalanced power source, the methods
of fixing the system are complex.
Therefore, we will only consider an unbalanced load with a balanced power source.
Example: A 3f balanced system, as shown in Figure 16a(3phase4), contains a wye load.
The line-to- line voltage is 240V, and the resistance is 40 Ohm in each branch.
In a fault condition, the neutral connection in a wye-connected load will carry more current than the phase under a balanced load. Unbalanced three-phase circuits are indicated by abnormally high currents in one or more of the phases. This may cause damage to equipment if the imbalance is allowed to continue.
Three Phase Transformer Connections
So far, our discussion has dealt with the operation of single-phase transformers.
Three-phase transformer operation is identical except that three single-phase windings are used.
These windings may be connected in wye, delta, or any combination of the two.
In the delta connection, all three phases are connected in series to form a closed loop (Figure
In the wye connection, three common ends of each phase are connected together at a common
terminal (marked “N” for neutral), and the other three ends are connected to a three-phase line
(Figure 4 -trafo2).
Combinations of Delta and Wye Transformer Connections
A three-phase transformer may have three separate but identical single-phase (1f) transformers
or a single 3f unit containing three-phase windings. The transformer windings may be connected
to form a 3f bank in any of four different ways (Figure 5-trafo3).
Figure 5 shows the voltages and currents in terms of applied line voltage (V) and line current (I),
Figure 5 3f Transformer Connections
where the turns ratio (a) is equal to one. Voltage and current ratings of the individual
transformers depend on the connections (Figure 5) and are indicated by Table 1 (TRAFO4)for convenience