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Transmission and Distribution Systems Part 1b
Voltage Levels and Equipment in T&D Systems
Now this is part one b of topic one the Structure of Power Systems
and in this part, we will mention
the key equipment used in Power Transmission and Distribution System
and the standard voltage levels used throughout the Transmission and Distribution chain.
Now in part 1a the previous part we talked about
the basic Structures of Power System
and just to give you a glimpse of what's ahead
we're going to talk about in the future videos
the Voltage Levels and Equipment in T&D Systems
Secondary Distribution Infrastructures
and then part two
we'll have several conversations about
the basic Power Transmission Infrastructure, Overhead versus Underground Systems
Transmission Line Models and Representations
and Transmission Line Parameter: Capacitances.
Now continuing on with this part
A worldwide international standard or a set of rules for electrical power systems do not exist.
Now the voltage levels vary from place to place
and different manufacturers of electrical equipment have different standards
and they are a result of different regional situations
and disagreements among engineers and firms
and it has resulted in the formation of different organizational standards like
the IEEE, IEC, NEC, ANSI, UL, NFPA, and so forth.
However what every standard does is that they do group some voltages
in a form of a band with a defined range.
And these bands often do not have sharp boundaries
but they are very useful for defining Voltage Level in the Transmission and Distribution System.
We will follow two most widely used standards in this video
which are the American standard with 60Hz and the European standard with 50Hz frequency of voltage cycles.
Now the voltage levels for which electricity is generated
depends on plant capacity, generator specifications, and type of energy resources.
Traditionally they are at 22kV in the megawatt power plant
and that voltage is then stepped up through a power transformer up to a high voltage or HV band.
The voltage in the HV band can be from 115kV and up to 765kV range
with 500kV, 345kV, 220kV, 115kV and so forth being common levels.
Now transmission lines then carry this voltage towards sub-transmission lines
and any voltage above 800kV is known as ultra high voltage
and it is only used in select places in the world for transmission over very long distances.
Now transmission towers are the most visible component of Power Transmission Systems.
High voltage lines require separation from each other and their surroundings
Transmission towers perform its function by providing structural strength and insulation damping lines oscillations
keeping lines high above the ground, maintaining space among the lines and from other structures
so that their electromotive force effect on the surrounding could be minimized and faults can be prevented.
And we will cover this in more detail in a later video.
Now the Transmission System then steps down in the sub-transmission system.
In the sub-transmission system, the voltage levels are stepped down to 132kV, 66kV, 33kV, and so forth for the European system
and 69kV and 26kV for the American system.
Now the sub-transmission system delivers electricity to further downstream grid station in the network
and to very few heavy industrial consumers that operate their own grid stations.
The voltage levels up to 11kV falls in the range of medium voltage or the MV band
and the sub-transmission system then steps down to the primary distribution systems to distribution substations
and the voltage level here can be 13.2kV or 4kV in the United States of America
and 33KV, 11KV or 6.6KV in Europe.
Now medium voltage are used to deliver power to distribution feeders
which connect medium-sized commercial consumers and clusters of residential colonies.
Now we will continue from substations.
A substation is a part of every generation Transmission and Distribution System
and electrical power flows through several substations before reaching the end-user customer.
It is built wherever change in voltage level is required
a transformer is crucial component of almost every substation which transforms voltage from high levels to low levels or vice versa
and normally substations are categorized as transmission substations, distribution substations, collector substations, and switching substations.
Now we will have more on substations in later videos.
The electricity that comes to our home
is then stepped down from the primary distribution to secondary distribution
with common voltages at 120 Volts or 240 Volt single phase or 400 Volt three phase.
Here consumers are known as secondary consumers or small consumers.
This is the low voltage ban in the range from 70 Volts to 600 Volts.
Now if a living being like a human or an animal comes into contact with voltages higher than this band
then it will cause severe harm and could lead to a death of that living being.
Now low voltage is mostly used in domestic residents to power household appliances.
In the next video, we will discuss the primary transmission infrastructure chiefly the transmission towers.
We hope that you find this content useful and enlightening.
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