The document discusses one-line diagrams, which are simplified diagrams used in power systems to represent the essential components in a simplified graphical format. A one-line diagram shows the main components of a power system like generators, transmission lines, transformers, and loads using standardized symbols. It represents the paths of power flow through the system from generation to transmission to distribution. The diagram is structured to match the physical layout. Impedance and reactance diagrams are similar but represent electrical elements like generators and lines as impedance/reactance values instead of physical components. An example calculation of voltage drop in a transmission line is provided.

2.  Representation of essentials of a system in a most
simplified form.
 Main components of a power plant
 Generation plant
 Transmission line
 Distribution line
 Industrial, commercial and residential load
 Nowadays all of these are in the form of three phase

3.  A one-line diagram or single-line diagram (SLD) is a
simplified notation for representing a three-phase power
system.
 The one-line diagram has its largest application in power
flow studies.
 Electrical elements such as circuit breakers, transformers,
capacitors, bus bars, and conductors are shown by
standardized schematic symbols.
 Instead of representing each of three phases with a separate
line or terminal, only one conductor is represented.
 It is a form of block diagram graphically depicting the paths
for power flow between entities of the system.
 Elements on the diagram do not represent the physical size
or location of the electrical equipment, but it is a common
convention to organize the diagram with the same left-to-
right, top-to-bottom sequence as the switchgear or other
apparatus represented.

5. Impedance diagram and reactance diagram
 Synchronous generator are replaced by:
 Transformer is replaced by:
 Transmission lines are replaced by:
 In many power system studies synchronous generator
resistance, resistance of transformer windings,
resistance of transmission lines, line charging and
magnetizing circuits of transformer are neglected.
 The impedance diagram then become reactance
diagram

6. Example 8.2
 A three phase synchronous generator delivers 10 MVA at a
voltage of 10.5 kV. The line impedance is 5 ohm. Determine the
voltage drop in the line in per unit and in volts. Use the reference
base as 10 MVA at 11 kV.
 S3φ= 10 MVA
 (Sb)3φ = 12MVA
 Vl=10.5kV
 Vlb= 11kV
 Vpu=(Vl)pu= Vl/Vlb=10.5/11
 Spu=S3φ/(Sb)3φ=10/12
 Ipu=Spu/Vpu=10/12*11/10.5= 0.8730158
 Zb= Vlb
2/ (Sb)3φ =112 /12
 Zpu= ZΩ/Zb=5*12/ 112 =0.4958677

7.  Voltage drop in line per phase:
 ΔVpu= Zpu* Ipu= 0.4958677 *0.8730158=0.4329pu
 ΔVpu=Vactual/Vb
 ΔVactual= ΔVpu*Vb=0.4329*11kV/root(3)=2749.36 V