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Electricity generation and transmission concept

The purpose of the electric transmission system is the interconnection of the electric energy producing power plants or generating stations with the loads. A three-phase AC system is used for most transmission lines.

The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia.

Electricity generation, transmission and distribution guides
Electricity generation, transmission and distribution guides (photo credit: Matt at Flickr)

The three-phase system has three phase conductors. The system voltage is defined as the RMS voltage between the conductors, also called line-to-line voltage. The voltage between the phase conductor and ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of three.

The generating station produces the electric energy. The generator voltage is usually around 15 to 25 kV. This relatively low voltage is not appropriate for the transmission of energy over long distances. At the generating station a transformer is used to increase the voltage and reduce the current.

In Figure 1 the voltage is increased to 500 kV and an extra-high voltage (EHV) line transmits the generator-produced energy to a distant substation.

Energy generation, transmission and distribution concept
Energy generation, transmission and distribution concept (click to expand)

The voltage is reduced at the 500 kV/220 kV EHV substation to the high voltage level and high voltage lines transmit the energy to high voltage substations located within cities.

At the high voltage substation the voltage is reduced to 69 kV. Sub-transmission lines connect the high voltage substation to many local distribution stations located within cities. Sub-transmission lines are frequently located along major streets.

Electricity distribution concept

The voltage is reduced to 12 kV at the distribution substation. Several distribution lines emanate from each distribution substation as overhead or underground lines. Distribution lines distribute the energy along streets and alleys.

Each line supplies several step-down transformers distributed along the line.

The distribution transformer reduces the voltage to 230/115 V, which supplies houses, shopping centers, and other local loads. The large industrial plants and factories are supplied directly by a subtransmission line or a dedicated distribution line as shown in Figure 1 above.

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1DC Transmission and Distribution star
2Insulator Pollution In Transmission Lines
3Energy Transmission and Distribution Guide
4Guide to High Voltage Direct Current (HVDC) Transmission
5Design and construction of long-distance HV transmission systems
6Transmission And Distribution Electrical Engineering
7De-icing EHV Overhead Transmission Lines by Short circuit Currents
8Guide to Planning of Electric Power Distribution
9Handbook for installation of MV lines in rural electricity systems
10Guide to power distribution systems for electrical engineers star
11Reliability comparison between different 400 kV substation designs New star
12Power grid and centralized substation protection and control star
13Guidelines for HV circuit breaker function and test methods star
14High voltage live work and practices manual star
15Transmission substation work practice manual star
16A case study on SCADA implementation in 220 kV substation star
17Handbook for electrical distribution and transmission fieldworkers star
18Guideline for connecting generating plants to the medium voltage network New
19General specifications for a customer-owned 69 kV outdoor substation New
20Recommended practices for maintenance of LV/MV/HV electrical equipment New
21Energy transmission and distribution over lines and cables in power systems New
22Experience with commissioning & testing complex busbar protection schemes New
23Primary-side protection of distribution substation transformers New
24Interconnecting mini-grids (up to 200 kW) with the central electric grid New
25Lecture notes on high voltage engineering New
26Design and installation of low voltage busbar trunking systems (verified to BS EN 61439-6)
27The basics of high voltage cables for underground energy transmission
28High voltage safety in marine and other electrical installations
29SCADA applications in thermal power plants (TPPs)
30Introduction on HVDC transmission systems and HVDC Submarine Power Cables in the World
31Voltage drop calculations and design of urban distribution feeders
32Fundamentals of High Voltage Circuit Breakers, Switching Stresses and Failure Modes
33Medium Voltage DC Applications And Future Scenarios (That Thomas Edison Has Started…)
34Operations And Maintenance Of Electrical Power And Distribution Systems
35Technical Issues Of Undergrounding High Voltage Transmission Lines
36Experience In Implementation Of Relay-Control House For 230 kV Transmission Substation
37Construction Techniques In Power Transmission, Hydropower and Photovoltaic Projects
38400/220 kV gas insulated (GIS) transmission substation controlled by SCADA
39Experience with IEC 61850 in the refurbishment of 380kV power substation
40Design And Construction Of Electrical Transmission And Distribution Lines
41Implementing Clean Power Plans For Utilities (EPA’s Menu of Options)
42Design of Electrical Power Systems for Nuclear Power Plants (NPP)
43Offshore Wind Park Connection To an HVDC Platform Without Using an AC Collector Platform
44Calculation Of Prospective Short-Circuit Currents On T&D Systems (Practical Guidance)
45Transmission Switching Manual For Grid Operators
46High voltage facts for undergraduate and postgraduate students of electrical engineering
47Class notes on electrical power transmission and distribution (for students, 6th semester)
48Technology of High Voltage DC (HVDC) Networks, Their Applications and Problems
49Class Notes on Power System Control and Operation
50On-shore electrical infrastructure for supplying vessels with electric power in port
51Lecture notes on power system engineering for students (6th and 7th semester B.Tech)
52Design of SCADA for remote control and operation of wind power plants
53The fundamentals of steam power plants
54Design of SCADA for remote control and operation of wind power plants
55Power systems in deep ocean mining up to 3,500 m
56High voltage generation, overvoltages in power grids and insulation coordination
57Design and installation of 12 kV gas-insulated load break switch
58Design project of 500kV HVDC transmission line from Ethiopia to Kenya
59Centralized fault locating system in Vietnam’s power transmission grid
60Basic setting of current differential line protection
60The basics of Gas Insulated Substation (GIS) for students
61Construction of a grid substation for engineers and technical supervisors
61The essentials of high-voltage breakdown and electrical discharges
62Practical training report on 220/66/11 KV substation
63Lecture notes on power station engineering for students

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Page edited by E.C. (Google).


  1. Abhinab Sharma
    Jun 10, 2018

    What is effect of use of shunt capacitor installed in 33 KV side at 132/33 KV grid station ?

  2. Abhinab Sharma
    Jun 10, 2018

    What is function of OLTC ( On load Tap changer) in 132/33 KV power transformer 132 KV side at 132/33 KV grid station? & When to use it ?

  3. Abhinab Sharma
    Jun 10, 2018

    What is reason of low voltage ( 116 KV) supply at 132 KV level at 132/33 KV grid station coming from 220/132 KV grid Station during peak load hours ?

  4. Khaled Yemen
    Dec 30, 2017

    Good books

    Jul 25, 2017

    Sir,please tell how to join practical or video training on electrical engineering like about industrial automation&PLC scada course.or any other like autocad on electrical engineering subjects.
    Please confirm any information about this I want immediately this.

  6. walid mahjoub
    Aug 12, 2016

    good technical manuals

  7. Bhupendra Fumakia
    Aug 11, 2016

    Dear Sir,

    Please let me have PDF version of following

    “Transmission and Distribution Electrical Engineering – Colin Bayliss, Colin R. Bayliss, Brian J. Hardy”

    Best regards.


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