Course EE-1:General overview of Generation, transmission & distribution stages of electricity

fig (1) : generation, transmission and distribution stages

There are three stages of electric power supply (see fig.1) ; generation, transmission and distribution. Each stage must be understood generally to any electrical engineer and here we will give a general overview of these stages as follows:

Generation stage:
Electricity generation is the process of generating electric energy from other forms of energy.

fig (2) : Steam Turbine

Electrical power starts at the power plant, In almost all cases the power plant consists of a spinning electrical generator. A generator is a machine that transforms mechanical energy into electric power.

Something has to spin that generator; it might be a water wheel in a hydroelectric dam, a large diesel engine or a gas turbine. But in most cases the thing spinning the generator is a steam turbine (see fig.2)

The steam might be created by burning coal, oil, natural gas or the fission of nuclear fuel. And some generating stations use renewable energy sources like sun & wind (see fig.3)

fig (3) : some generation stage stations

Sometime, another stages of power generation is provided in transmission and distribution stages (Embedded generation) to meet additional power requirements in some load areas (see fig.4)

 fig (1) : Embedded Generation in transmission and distribution stages

Transmission stage:
Electric-power transmission is the bulk transfer of electrical energy; from generating power plants to substations located near population centers (see fig.5)

fig (1) : transmission stage 

The 3-phase power leaves the generator and enters a transmission substation at the power plant (see fig.6). 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. Typical voltages for long distance transmission are in the 155,000 to 765,000 volt range in order to reduce line losses.

fig (1) : transmission Substation 

Transmission stage may include sub-transmission stages (secondary transmission) to supply intermediate voltage Levels. Sub-transmission stages are used to enable a more practical or economical transition between transmission and distribution systems.

The Distribution stage:

Electricity distribution is the final stage in the delivery of electricity to end users. A distribution system's network carries electricity from the transmission system and delivers it to consumers (see fig.7)

fig (1) : distribution stage

For power to be useful in a home or business it comes off the transmission grid and is stepped down to the distribution grid in a power distribution substation (see fig.8), and this may happen in several phases as follows:

fig (1) : distribution substation

Primary distribution system (HV distribution):
It is that portion of the network between the Sub-transmission substations and secondary distribution system. The primary system consists of step-down transformers and sometimes embedded generation can be used at voltage levels which range from 33 KV to 6.6 KV.


The secondary distribution system (LV distribution):
It is that portion of the network between the primary feeders and utilization equipment. The secondary system consists of step-down transformers and secondary circuits at utilization voltage levels which range from 480V to 120V.

Note :Residential secondary systems are predominantly single-phase, but commercial and industrial systems generally use three-phase power.

EC-1 COURSE: NEC Article 100 - Part Three

again , we will explain more important definitions inclued in NEC code Article 100 which will be used along this Course, toady we will show the term " Bonding" Definition.

Bonding:
It is the connection of two or more conductive objects to one another by means of a conductor such as a wire to provide continuity and conductivity.

the term "Bonding" shouldn't be confused with the term "Grounding" since the two terms has different definitions and applications although some consultants use them interchangeable especially in industrial projects.so, we need to define the term "Grounding" to understand its difference from the term "Bonding" as follows:

Grounding / Earthing:
It is the attachment of a bonded metallic system to earth, typically through ground rods or other suitable grounding electrodes for ensuring zero voltage.

Note: grounding is American standard term is equivalent to earthing which is a British standard term.


Comparison between bonding and grounding is given in the following table:

s/n	Bonding	Grounding
1	Connection between non-live conductive objects	Connection between live or non-live conductive objects to earth
2	Bonding is achieved by using bonding conductors, metallic raceways, connectors, couplings, metallic-sheathed cable with fittings, and other devices approved by the authority having jurisdiction as recognized for this purpose	Grounding is achieved by using a rod or other suitable grounding electrodes.
3	Bonding for grounded system provides the safety during fault current for persons	Grounding provides the safety during fault current for equipments without a need for bonding its enclosure
4	Bonding objects without grounding one of them gives no protection from stray currents but it protect from static charges	Grounding is independent on bonding it gives equipment protection disregard it is bonded to its enclosure or not.

Some definitions related to Bonding:

Bonding Jumper: see fig.1

This is the connection between noncurrent-carrying metallic components of the electrical system that are provided to ensure continuity.

fig(1): Boning Jumper

They may be bare, covered, or insulated conductors, or it may be a mechanical device, such as screws often provided to connect a neutral terminal bar to a service enclosure.


Equipment Bonding Jumper: see fig.2
These are bonding connections made between two portions of the equipment grounding system.

fig (2): Equipment Bonding Jumper

The purpose of the equipment bonding jumper is to provide the low-impedance fault-current path necessary to facilitate the operation of overcurrent protection devices in order to remove dangerous voltage potentials between conductive parts of building components and electrical systems


Main Bonding Jumper: see fig.3

A main bonding jumper provides the Code-required connection between the grounded system conductor and the equipment ground bus at the service equipment for a building or structure.

fig (3): Main Bonding Jumper

The connection between equipment ground and the grounding electrode system in ungrounded services is a “bonding jumper,” but not a “main bonding jumper.”


System Bonding Jumper: see fig.4

The conductor, screw or strap that bonds the equipment bonding conductor (metal parts of a separately derived system) to one of the system conductors or terminal

fig (4): System Bonding Jumper

The system bonding jumper provides the low-impedance fault-current path to the source neutral for fault current.


In the next topic, I will continue explaining other definitions from article 100.

EP-3 Course: Types of Transformers According to Construction

In practical transformer design the manufacturer has the choice between two different basic constructions:

1. Core type Construction.
2. Shell type Construction. 

The one or the other of these Constructions has no influence on operational characteristics or the service reliability of the transformer, but there are essentially differences in the manufacturing process. Each manufacturer chooses the concept that he finds most convenient from a manufacturing point of view and tends to use this concept for the whole production volume.

1- Core-type transformers: see fig.(1) & (2)

The core-type transformer enclose the core i.e. the primary and secondary windings were wound on a separate lamps and around a closed iron ring so that the windings are well visible, but they hide the core limbs, Only the upper and lower youke of the core are visible. The axis of the core type windings is normally vertical.

fig (1): Core-Type Transformers

Core-type (or three limbs) is the most commonly used method of construction, the smaller core means less weight and expense. A wound type of core used in single phase distribution transformers is shown in fig. (3)

fig (2): Core-Type Transformers

fig (3): Wound Core-Type Transformers

2- Shell-Type Transformers: see fig. (4) & (5)

The shell-type transformer is considered the most efficient. Such transformers are used in transmitting commercial power. The core of the shell-type transformer is made of laminated silicon steel sheets placed on top of one another. The coils are wound around the central section of the core; the core of a shell-type encloses the windings and the core hides the major part of the windings. The axis of the shell-type windings can be horizontal or vertical in a shell-type.

fig (4): Shell-Type Transformers

fig (5): Shell-Type Transformers

Since the primary and secondary coils are wound close together around the core, the windings must be highly insulated. A special insulating material is coated on the wires of both coils.
Shell-type (or five limbs) is used for larger transformers because they can be made with a reduced height.


Core-type and shell-type transformers can also be constructed for three-phase transformers as in fig. (6) & (7).

fig (6): 3-Phase Core-Type Transformers

fig (7): 3-Phase Shell-Type Transformers

3- A comparison between the core-type and shell-types Transformers is given in below table as follows:

s/n	Core-type Transformers	Shell-type Transformers
1	enclose the core	Enclose the windings
2	the windings are well visible, but they hide the core limbs	the core hides the major part of the windings
3	The coils are wound around all core lamps	The coils are wound around the central section of the core
4	The axis of the core type windings is normally vertical.	The axis of the shell-type windings can be horizontal or vertical in a shell-type
5	Core-type (or three limbs) is the most commonly used method of construction, the smaller core means less weight and expense	The shell-type transformer is considered the most efficient and used for larger transformers because they can be made with a reduced height.
6	The cylindrical types of coils are used	Generally, multi-layer of disc type or sandwich coils are used
7	The coils can be easily removed for maintenance point of view	Large number of laminations must be removed for  making maintenance for any winding
8	As windings are distributed, the neutral cooling is more effective	As windings are surrounded by the core , there is no neutral cooling
9	It is preferred for low voltage transformers	It is preferred for high voltage transformer
10	It has a single magnetic circuit	It has double magnetic circuits
11	In a single phase type, the core has two limps	In a single phase type, the core has three limps
12	In a three phase type, the core has three limps	In a three phase type, the core has five limps

In the next topic, we will know more about different transformer types according to their applications.

PM-1 Course: The Technical Design Specifications

Definition of Technical Design Specifications : 

The technical design specifications are in practice the contract implementation specifications, i.e. they refer to the characteristics of the means which must be used for implementing the contract, to the way in which the individual activities shall be implemented, to the characteristics (quality, appearance, size etc.) of the results (deliverables) etc.

It is the most traditional kind of specification, it is what most people mean when referring to “Technical Specifications”, having been used historically in public contracting for buildings, highways, and other public works, and represents the kind of thinking in which architects and engineers have been trained.

You can free download an example for the technical design specification by clicking Here 

Who can issue the technical design specifications? 

An expert engineer who is familiar with the technology, products etc. in the market, their availability and the cost for their use can issue this type of specifications.

How the technical design specifications are developed? 

To develop a new Technical Specification, it is recommended to adopt an approach consisting of the following steps: 

1- Specification of the requirements (functional, output, quality etc.) of the intended outputs (work, material, service, construction etc.).

2- Analysis of output requirements and establishment of requirements in inputs (materials, activities, methodologies etc.) for implementation of the outputs.

3- Market” research to identify existing alternative solutions and the possibilities offered by innovative solutions for achievement of the outputs. This includes”:

• Identification of information sources (persons, organizations, documents).
• Communication/ research on the requested data from these sources.

4- Specification of input and output requirements (technical specifications), at a level of detail which allows economic operators to understand what is requested and specify solutions for its achievement. 

5- This activity is performed either “in-house” by the Contracting Authority (and its consultants) or with the participation of the candidate economic operators (through a “consultation” process during which they offer their views). This consultation process is used primarily when the tender procedure applied is the restricted procedure, and the economic operators from which tenders shall be invited have been selected.

6- Checking input and output requirements (derived in the previous step) in terms of: 

• The completeness of their description. 
• Their synergy and cohesion with the other requirements (other technical specifications) of the contract. 
• The clarity of their formulation. 
• The possibility and method of controlling their achievement (during or after the implementation of the contract). 
• The possibility of incorporating them in the method/procedure for evaluation of the tenders submitted by candidate economic operators for the award of the contract. 

You can free download a Checklist for confirming the correct development of a new Technical Specification by clicking Here

Technical Specifications Importance: 

The determination of the Technical Specifications is a crucial task during the development of the tender documents, because the success of the tender procedure in leading to the acquisition of the requested results (supplies or services or constructions) at the right quality, in the available time and within the available budget, depends on it.

For this reason, the Technical Specifications must be determined in such a way as to ensure both of the following two aims:

• The achievement of the desirable characteristics which are requested by them.
• The promotion of the broadest possible competition between the economic operators to tender for the contract (so that the optimum cost is achieved, and the conditions of transparency and equal treatment of candidates are ensured).

Therefore, the Technical Specifications must at the same time ensure that:

• The requirements placed on the Contractor in connection with the required activities and resources, as well as the expected results of the contract, are clear, fully understood without room for misinterpretation, and transparent, so that the economic operators may offer what is actually requested.

• These requirements have the necessary flexibility and allow (render acceptable) other compatible, innovative and economically advantageous (in terms of “best value for money”) solutions, which fulfill the broader requirements of the contract.

• These requirements do not result in discrimination between economic operators, nor to the exclusion of any of them from the tender procedure, but instead offer equal opportunities to all.

Technical specifications Contents: 

The text of a Technical Specification should comprise the following:

Introduction The Introduction presents the purpose of the Technical Specification and the way in which it was composed, as well as any conditions that restrict its application.

Main body The structure of the Technical Specification must be as close as possible to the structure of the other specifications in use in the country.

The contents of a Technical Specification usually include the following:

• The description of its scope. 
• The inputs used (raw materials, methods, labour etc.) and the criteria for their acceptance.
• The characteristics of outputs, which may be either qualitative characteristics or performance/functional characteristics (this is the main section of the Technical Specification) – e.g. printing speed and quality of a printer, strength of a bridge to loads, number of copies per unit of time of a photocopier.
• The quality control requirements (criteria and ways of implementation) for acceptance of the outputs.
• The health & safety conditions/requirements during implementation, and the requirements regarding the protection of the environment.
• The method used to measure the outputs.
• Remarks, Application guidelines :These contain data/information concerning the application of the Technical Specification, reference to other Technical Specifications with which it may combined or with which it inter-works, and description of the relation/interconnection with them, and other clarifications as needed. 

You can free download a Checklist for the approval of the Technical Specifications by clicking Here 

ED-1 Course: Shop Drawings - Part One

Introduction:

The construction/contract drawings and specifications prepared by the consultant show the general design concept of the project and each of the major components and their relationships to each other.

Some of the subcontractors and suppliers must prepare additional drawings, diagrams, schedules, and other data to illustrate the specific way in which their particular company or shop will undertake to furnish, fabricate, assemble, or install their scope of works/products.

These additional drawings are what we called “shop drawings”.

fig (1) Shop Drawing for installation of Diesel Generator

fig (2) installation of Diesel Generator based on fig (1)

Shop Drawings Definition: see fig (1) & (2)

The Means Illustrated Construction Dictionary Third Edition Unabridged defined it as follows:

"Shop Drawings are Drawings created by a contractor, subcontractor, vendor, manufacturer, or other entity that illustrate construction, materials, dimensions, installation, and other pertinent information for the incorporation of an element or item into the construction."

My brief definition for shop drawings is as follows:

Shop drawings are fully detailed and fully dimensioned drawings (disregard for which works they are done).



Shop Drawings importance:

• Shop drawings are submitted for the purpose of illustrating how the contractor proposes to conform to the requirements and design concepts expressed in the construction drawings and specifications. 
• Shop drawings are needed by the fabrication shops for their own use in instructing their own personnel how to carry out the requirements of the contract documents. Fabricators will produce the shop drawings even if they are not asked to submit them for consultant’s approval. 
• Shop drawings are needed to give the consultant the opportunity to review the fabricator’s version of the product, prior to fabrication. Shop drawings facilitate the architect’s and engineer’s approval of the product.
• Shop drawings are needed to ascertain that the contractor understands the architectural and engineering design concepts and to correct any misapprehensions before they are carried out in the shop or field. 

Shop Drawing Procedures:

1. The contractor is obligated by the contract documents to submit shop drawings, product data, and samples for certain parts of the work to the consultant. 
2. The consultant is obligated by the owner- consultant agreement to “review and approve or take other appropriate action upon Contractor’s Shop Drawings submitals. 
3. After reviewing shop drawings by the consultant, they are then sent back to the general contractor, approved, conditionally approved, or disapproved. 
4. The contractor will revise and submit all drawings that are conditionally approved, or disapproved to get final approval from the consultant. 

fig (3): Shop Drawing Stamp

Shop Drawing Stamps: see fig (3)

The consultant usually express their opinion of the shop drawings by use of the rubber stamp which usually has some exculpatory language in fine print plus some options which can be exercised by use of check marks. Often the stamp says something like "Review is for general compliance with Contract Documents. No responsibility is assumed for correctness of dimensions or details."

The various options to be selected include:

• Reviewed.
• Approved.
• Rejected.
• Revise and Resubmit.
• Furnish as Corrected.
• No Exception Taken.
• Make Corrections Noted.
• Submit Specified Item. 

Space is also usually provided for the date of review and action and the shop drawing number.

fig (4): letter of transmittal

Important Notes for Shop Drawings approval:

• The accompanying letter of transmittal (see fig.4) should have additional comments that are needed to explain the reviewer’s action or conditions of approval. 

• In the practical world of construction, all words that do not reject the shop drawings will be interpreted as approving them. 

• The consultant's review is not to be taken as an approval of any safety precautions as these are the contractor's responsibility. The consultant's review is limited to determining if the requirements of the contract documents are being met and that the completed work will be in compliance with the contract documents. 

• The consultant's approval of a shop drawing does not relieve the contractor of responsibility for meeting requirements of the contract documents. 

• It is the contractor's responsibility to assure that all work on the job is in conformance with approved shop drawings 

in the next topic, I will continue explaining some important facts about Shop Drawings. again i promise you to make a special course for Shop Drawings but please, keep following.

Electrical Drawings Details - Group no.(5)

This group will include the following Electrical Drawing Details: 

• Roof penetration detail (conduit system).

• Lightning riser to roof drawing detail.

• Power supply to roof mounted exhaust fan drawing detail.

• Lighting pole base foundation drawing detail.

• Swimming pool lighting fixture drawing detail.

• Automatic gate installation drawing detail.

• Electrical equipment arrangement drawing detail.

• Cable termination at fuse box drawing detail.

• Down conductor drawing detail.

• CCTV one line diagram drawing detail.

• Grounding tap connection # 1 drawing detail.

• Grounding tap connection # 2 drawing detail.

• Galvanized steel pipe grounding drawing detail.

• Roof mounted extract fan grounding drawing detail.

• Swimming pool schematic grounding system drawing detail.

• Bonding connection to water pipe drawing detail.

• Installation of incoming power utility ducts (wall mtd. MDP) drawing detail.

• Recessed mounted luminaries drawing detail.

to Free download the Electrical Drawings Details - Group no.(5), please click Here or Here.

Course LV-1: Sound System Configurations

Sound Systems Are Divided Into (4) Main Systems (According To The Purpose And The Nature Of Use) as follows:

1. Public Broadcasting System
2. Indoor radio system
3. Outdoor broadcasting system
4. Conference Systems

 Now, we will show a brief for each system and a detailed explanation for each one will be posted later.

1- Public Broadcasting System : see fig (1) & (2)

                                           fig (1)                                                            fig (2)

           

Public address system for hotels, commercial buildings, ports, airports, subways, schools provide background music and radio programs. In recent years, public broadcasting system also caters to emergency broadcasts, can be linked with the fire alarm system. The public broadcasting system control functions more. If all call radio broadcasting and electoral functions, work force capabilities and priorities for the right to broadcast functions. Speaker load multiple and scattered, long transmission lines. To reduce transmission line losses, generally 70V or 100V constant voltage with high impedance transmission. Pressure not ask for much, the sound quality to the tone-based alt.

    

2- Indoor radio system: see fig (3)

indoor radio systems are the most widely used system, including various types of theaters, stadiums, dance halls and so on. It is highly specialized, both non-verbal reinforcement, but also for various performances, the use of very high quality requirements, system design should not only consider the problem of electro-acoustic technology, but also issues related to architectural acoustics. The room´s shape and other factors have a greater impact on sound quality.

                            

                                           fig (3)                                                            fig (4)

3- Outdoor broadcasting system: see fig (4)

Broadcasting system is mainly used for outdoor stadiums, railway stations, parks, art squares, musical fountains. Service area is characterized by its large area, space is broad. Large background noise; sound to direct sound transmission main; to Demand high sound pressure level, if high-rise buildings and other reflective objects surrounding the  speaker layout and quite reasonable, sound waves formed by multiple reflections more than 50ms delay will cause double or multiple acoustic sound, in severe cases echo problems affecting the voice clarity and sound image localization. Outdoor sound system is also affected by climatic conditions, wind direction and impact of environmental disturbance.

                              

4- Conference System: see fig (5) & (6)

With domestic and international exchanges increase, in recent years, conference calls, video conferencing and digital conference system (DCN) has developed rapidly. Conferencing systems are widely used for conference centers, hotels, groups and government agencies. Conference system including conference discussion system, voting system, simultaneous interpretation system and TV conference system. Requirements of audio and video (image) system simultaneously, all using the computer control and storage of session data.

                                     fig (5)                                                fig (6)

In the next topic, I will explain the first system; Public Broadcasting System.

Course EE-1:Important Electrical Formulas & Unit Conversion Tables.

1- Important Electrical Formulas:

An important foundation for all electrical design & installations is a thorough knowledge of the laws that govern the operation of electricity. The general laws are few and simple, and you can free download a lot of documents containing these formulas and laws as follows:

Basic and important electrical formulas #1

Basic and important electrical formulas #2
Basic and important electrical formulas #3
Basic and important electrical formulas #4
Basic and important electrical formulas #5
Basic and important electrical formulas #6
Basic and important electrical formulas #7
Basic and important electrical formulas #8




I put (8) nos. different documents containing Basic and important electrical formulas to permit each one of you to choose, print and file the most likely one to you for your use through this course.

You can find detailed information about basic electrical formulas in topic: General Basics of Electricity.



2- Unit Conversion Tables:

With these above formulas sheets, we will need also to put the important unit conversions documents , the Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors

The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, Technical specifications or other published standards, and you can free download a lot of documents containing these unit conversions table as follows:

Unit conversions table #1 

Unit conversions table #2 

Unit conversions table #3 

Unit conversions table #4 

Unit conversions table #5 

Unit conversions table #6 

Please Free download the (6) nos. conversion tables, print and file  the most likely one to you for your use through this course.


There are many programs are designed to do the units conversion automatically, they are very easy and simple use, and you can free download a lot of these programs used for unit conversions as follows:

Unit conversion program #1

Unit conversion program #2

Unit conversion program #3

Unit conversion program #4






Also, you can free download an excel sheet used for unit conversions as follows:

excel sheet for unit conversions


in the next topic , I will show a General overview of Generation, transmission & distribution stages of electricity.

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EE-1: Beginners' Electrical design course