3 Phase Power Distribution of Step-Down Transformer

3 power distribution of the step-down transformer∅
The three phase transformer could be formed by three single phase transformers connected to an
individual laminated core (Chunlai & Xiaoku, 2011). They have a separate magnetic circuit,
which are inter-connected so that a uniform distribution of magnetic flux could be produced
(Xinchang & Fengquan, 2010). Hence due to this type of construction they could operate at high
and low voltages and the only exception is the shell type of transformer since they are not inter-
connected. They are cost effective and the three phase winding could be seen in the figure given
below.
Figure 1: Construction of three phase transformer
Group 1:
Star- Delta connection with load 20 ohms:
In this type, the primary side is connected like a star and the secondary type is connected like a
delta (Keping, Daozhuo & Pengfei, 2012). Usually we use different symbols and alphabets to
differentiate the start and delta connections. Normally the primary side could be denoted by the
uppercase letters such as R, Y and B (the phases are differentiated by different colors especially
red, yellow and blue) and the secondary side could be indicated by the lower case alphabets.
Certain technical definitions should be known while dealing with the transformer. The Line
voltage is referred as a voltage between any line and the phase voltage is referred as the voltage
among any line and the neutral point of the transformer (Jing, Xin & Liqiang, et al., 2013). This
phase voltage is equal to 1/√3 times that of the line voltage. This could be represented as,
VP = 1/√3 VL

Every relevant secondary winding will have the same voltage induced in it. Since the secondary
windings are delta connected, the line voltage will be 1/√3 VL.
The Turns ratio could be represented as the ratio between the primary winding NP and the
secondary winding NS. This could be denoted by the following equation
Turns ratio (n) = NP / NS
For the star- delta connection this could be written as,
Turns ratio (n) = VP /√3 VL
If the transformer is provided with the same number of windings in the primary and the
secondary winding of 1:1 ratio then √3:1 is the step-down line voltage ratio. The line voltage will
VL = n VL / √3 and the line current will be IL = √3. IL /n. the transformation ration (K) is defined
as the ratio between the secondary phase voltage and the primary phase voltage (Lin, Yi & Ke, et
al., 2012). Since the primary side is star connected, we could need only few numbers of turns.
This could be used efficiently for the high voltage step-down transformers. The impedance of
each phase could be calculated by Zp = . The connection between primary and
secondary winding and the phasor diagram connection is shown in the figure given below.
Figure 2: Transformer connection – star-delta network

Figure 3: Phasor diagram of star- delta connection
Table 1: Readings taken for star- delta connection at load of 20 ohms
Group 2:
Star-Star connection with the load 10 ohms: