To get power in our houses and businesses, there are several processes that the power goes though to get generated and carried across miles of power lines. Electricity is generated in a thermal power plant, hydroelectric power plant, and nuclear power plant, etc. This electricity is then supplied to a transmission substation near the generating plant. In the transmission substation the voltage is increased substantially using step up transformers. The voltage is increased to reduce the transmission losses over long distances. This electricity then is supplied to a power substation where it is stepped down using step down transformers and then supplied to a distribution grid. In the distribution grid there are additional transformers and voltage is further reduced for distributing further down the grid. From here the electricity is supplied to step down transformers near residential quarters that step down the voltage to 110/220 Volts as per each country's requirement. The power is produced using a three-phase generator that takes some kind of mechanical energy and generates three-phase power. The three-phase power leaves the generator and enters a transmission substation at the power plant. This substation uses large transformers to convert the generator's voltage (which is at the thousands of volts level) up to extremely high voltages for long-distance transmission on the transmission grid. You can see at the back several three-wire towers leaving the substation. Typical voltages for long distance transmission are in the range of 155,000 to 765,000 volts in order to reduce line losses. A typical maximum transmission distance is about 300 miles (483 km). High-voltage transmission lines are quite obvious when you see them.

The power that comes out of a nuclear power plant is somewhere around 270kv volts and 500 amps. The power will slowly drop over a long distance. This loss can be calculated using certain equations. Power will need to be stepped back up from a substation before it can be sent back out to houses or business. Electric energy is transported across the countryside with high-voltage lines because the line losses are much smaller than with low-voltage lines. Line loss is something every cable has since every cable used today has some sort of resistance over a given distance; in this case the distance is 500 miles. Variables in power loss are; Conductor type, (in this case its aluminum wire), tower configuration, line lengths, power base, voltage base, current base, and admittance base. The power stations are routinely shut down for maintenance of essential equipment and are restarted from a cold start. For this there is a need for “Startup power”. There are “Unit Auxiliary Transformers” where the station power loops back to power these transformers. In the event of the station needing to start from an off position, these transformers are specially designed to give the plant the initial starting power needed to get the generators running and other equipment ready to distribute power. The secondary substations are essentially repeats of the main power plant. The sub stations receive power and lower the voltage through some step-down transformers, clean up the power through a series of filters, raise the voltage through some step-up transformers, and then redistribute the power. Once the power reaches some neighborhood, the power goes through one final transformer to get the power to 110 or 220 depending on the regulations or needs of the customers. Once the power reaches a house or business, the power goes to a breaker box. The power is separated into breakers for the convenience and safety of the homeowners. The breakers allow the homeowners to manage how many devices they have on a circuit as to not try to apply too much current in one place and overload a circuit. This could cause fires or, in extreme cases, mini explosions. Clearly, that would not be good for the homeowner. For all of this to work effectively and efficiently, there are many formulas and equations that go along with all of this information. (see appendix A) There are people who spend weeks and months calculating and recalculating before anything is built to ensure everyone’s safety. If someone were to make the slightest mistake during one of the calculations, something could go seriously wrong during the power-up process, posing a serious threat to those around the equipment. Next time you are driving down the road and see the power lines, or turn on a light, or put in a load of laundry, take a second to think about all of the people, machines, and advanced technology that go into your simple, everyday tasks. Many times we do such things and take for granted the incredible amount of technology around us. Pause for a second and think, someone had to create this…someone had to make this happen.

Appendix A
Formulas to use for general calculations

Distributed Parameters
Resistance

Where:
Rt AC resistance at temperature t per phase per 1 mile in Ohms t Assumed temperature in Celsius degrees
R25 AC resistance of the conductor at 60 Hz and 25°C per 1 mile in Ohms
R50 AC resistance of the conductor at 60 Hz and 50°C per 1 mile in Ohms
R75 AC resistance of the conductor at 60

Inductive Reactance

Where:
XL Inductive reactance in Ohms/meter f Frequency of the system in Hertz
Ded Geometric mean distance between phases in meters
DSL Geometric mean radius between conductors of one phase in meters
The geometric mean distance between phases is defined as:

Where: dab, dbc, dca. Distances between phases a-b, b-c, c-a, respectively in meters
The geometric mean radius between conductors of one phase is defined as:
DSL=GMR For 1 stranded conductor
DSL =(e^ -1/4)r For 1 solid cylindrical conductor For more then 1 conductor bundle
Where:
DSL Geometric mean radius in meters r External radius of conductor in meters
GMR Geometric mean radius given in tables for one stranded conductor dkm Distance between conductors k and m in meters. Note: If k = m, then for one stranded or solid cylindrical conductor. kmd =SLD
Susceptance

Where:
B Susceptance in Siemens/meter f Frequency of the system in Hertz ε Constant permittivity = 8.85418 × 10-12
Deq Geometric mean distance between phases, defined as above
DSC Geometric mean radius between conductors of one phase using external radius in meters
The geometric mean radius between conductors of one phase using external radius is defined as:
DSC=r For 1 conductor For more then 1 conductor bund
Where:
DSC Geometric mean radius in meters r External radius of conductor in meters dkm Distance between conductors k and m in meters. Note: If k = m, then dkm =r.
Conductance
Assumed G = 0
Where:
G Conductance in Siemens/meter
Lumped (Total) Parameters
Resistance, Inductive Reactance, Conductance and Susceptance, using the equivalent π circuit (long line)
Z’=R’+jX’=Zc sinh IL
Y’=G’+jB’=(2/Zc) tanh (YL/2)
Where:
Z’ Total series impedance of line in Ohms
Y’ Total series admittance of line in Siemens
R’ Total series resistance of line in Ohms
X’ Total series inductive reactance of line in Ohms
G’ Total series conductance of line in Siemens
B’ Total series susceptance of line in Siemens
Zc Characteristic impedance in Ohms γ Propagation constant in meters-1 l Line length in meters

The characteristic impedance and propagation constant are:
Zc=√(Z/Y)
Where: z Distributed series impedance in Ohms/meter y Distributed series admittance in Siemens/meter

The distributed series impedance and distributed series admittance are defined as: Z=R+jX Y=G+jB
Where:
R Distributed series resistance in Ohms/meter
X Distributed series inductive reactance in Ohms/meter
G Distributed series conductance in Siemens/meter
B Distributed series susceptance in Siemens/meter

Surge Impedance Loading
The surge impedance loading is defined as the power delivered by a lossless line to a load resistance equal to the surge (or characteristic) impedance Zc, and is given by:

Where:
PSIL Total surge impedance loading in a three-phase line in VA
VN Line-line nominal voltage in Volts
Base Values
Impedance Base φ32)(BllBBSVZ= Where:
ZB Impedance base in Ohms
S(3φ/B) Power base in VA
V(ll\B) Line-line voltage base in Volts
Admittance Base
YB=1/ZB
Where:
BY Admittance base in Siemens
BZ Impedance base in Ohms

Per Unit (PU) Parameters
Resistance, Inductive Reactance, Conductance, Susceptance
RPU = R’/ZB
XPU = X’/ZB
GPU = G’/YB
BPU = B’/YB

Where:
RPU Per unit resistance
R’ Total series resistance in Ohms
XPU Per unit Inductive reactance
X’ Total series inductive reactance in Ohms
XPU Per unit conductance
G’ Total series conductance in Siemens
BPU Per unit susceptance
B’ Total series susceptance in Siemens
ZB Impedance base in Ohms
YB Admittance base in Siemens

MVA To Ampere and Ampere To MVA Limits Conversion
MVA to Ampere Limit Conversion

Where:
LimAmp Limit in Amperes
LimMVA Limit in MVAs
VN Nominal voltage in Volts

Ampere to MVA Limit Conversion

Where:
LimAmp Limit in Amperes
LimMVA Limit in MVAs
VN Nominal voltage in Volts

References
[1] J. D. Glover and M. S. Sarma, Power Systems analysis and design, Brooks/Cole, 3rd edition, 2002.
[2] A. R. Bergen and V. Vittal, Power System Analysis, Prentice Hall, 2nd edition, 2000.
Page
[3] "PowerWorld Transmission Line Parameter Calculator." N.p., n.d. Web.