Properties of Sound

In the previous Topic, Fundamentals of Acoustics and Sound Systems, I listed the properties of sound which include:

1. Sound Propagation. 
2. Wavelength and Cycle. 
3. Amplitude and Loudness. 
4. Frequency and Pitch. 
5. Sound Velocity. 
6. Complex Sound waves. 
7. Octaves. 
8. Timbre. 

And today, I will explain these properties for more understanding of the Acoustics field.

1- Sound Propagation

Sound travels radially in all directions from the source, as shown in the fig.1

Fig (1): Sound Propagation 

The behavior of sound propagation is generally affected by three things:

• A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium (see fig.2)

Fig (2): Temperature effect on Sound Waves

• The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported (see fig.3).

Fig (3): Wind effect on Sound Waves

• The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible 

For more information about the factors affecting the sound propagation , please review Topic “ Outdoor Sound System”.

2- Wavelength and Cycle

Cycle: is a single complete vibration which includes one Crest and one Trough.

Crest: The section of the wave that rises above the undisturbed position.

Trough: the section which lies below the undisturbed position.

Wavelength: The wavelength of a Sound wave is the horizontal distance between any two adjacent corresponding locations on the wave train (see fig.4), This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting point.

Wavelength is denoted by “λ” (Greek letter lambda).

fig (4): Wavelength

 

Period : A period (represented by the symbol T) is the amount of time required to complete one full cycle (see fig.5), The period of a sound wave can be mathematically related to several other aspects of wave motion, including wave speed, frequency, and wavelength.

fig (5): Period and Amplitude

3- Amplitude and Loudness

Amplitude: The amplitude of a sound is represented by the height of the wave. When there is a loud sound, the wave is high and the amplitude is large (see fig.5), Conversely, a smaller amplitude represents a softer sound. It represents the intensity of the sound corresponding to the loudness (volume).

The energy of a wave is proportional to the square of its amplitude. Therefore the intensity of a wave is also proportional to the square of its amplitude.

4- Frequency and Pitch 

Frequency: It is calculated as the number of cycles per unit of time. Frequency is denoted by “f”, Units of hertz (Hz). 

Note: The range of human hearing is approximately 20 Hz to 20 kHz (see fig.6)

fig (6): Audible Sound Frequency Range

 

Pitch: It is an ears’ response to sound wave frequencies, it is closely related to frequency, but the two are not equivalent. Pitches are usually quantified as frequencies in cycles per second, or hertz, Low frequency (pitch) is characteristic of bass, an example of high frequency (pitch) is hissing.


5- Sound Velocity

It is the distance travelled during a unit of time by a sound wave propagating through an elastic medium.

Sound travels much faster in denser mediums than less dense mediums. For this reason, sound velocity is very slow (relatively) in air. Typical sound velocities are shown in the table below:

Sound Velocity through various mediums
Medium	Sound Velocity (ft/sec)
Air (70 F)	1,100
Water	4,500
Concrete	10,200
Steel	17,100

In the next Topic, I will continue explaining other Properties of Sound. Please keep following.

Drawing Lines

The line is the fundamental tool of graphic communication. Different line weights (thicknesses) and line types communicate different ideas (see Fig.1). Each line means something, so lines should never be randomly drawn. Because construction drawings are abstract, you should use as few lines as possible to describe an object.

Fig (1): Types of Lines

Lines, whether hand-drawn or plotted, shall be opaque and of uniform width for each type of line. Two widths of lines, thin and thick, with their widths in the proportions of 1:2, shall be used.

The actual width of each type of line shall be governed by the size and style of the drawing; the relative widths of the lines shall approximate those shown in Fig (1).


Types of Lines

fig (2): All Lines Types

1- Center Lines
Center lines shall be composed of long and short dashes, alternately and evenly spaced, with a long dash at each end. Center lines shall cross without voids. (See Fig.1&2)


Very short center lines may be unbroken if there is no confusion with other lines. Center lines shall also be used to indicate the travel of a center. See Fig.2



2- Dimension Lines
Dimension lines shall terminate in arrowheads at each end. They shall be unbroken except where space is required for the dimension (See Fig.1&2).

Another article will be posted giving more information about dimension lines.


3- Leaders Lines
Leaders shall be used to indicate a part or portion to which a number, note, or other reference applies i.e. a connection between the part and the note  (See Fig.1&2), and shall be an unbroken line terminating in an arrowhead, dot, or wavy line. Arrowheads should always terminate at a line; dots should be within the outline of an object.



4- Break Lines
Short breaks shall be indicated by solid freehand lines. For long breaks, full ruled lines with freehand zigzags shall be used. Shafts, rods, tubes, etc., which have a portion of their length broken out, shall have the ends of the break drawn as indicated in (Fig.1&2&3).

Fig (3): Break Lines

Also, a break line is used when the extent of a drawing can’t fit on the size of paper being used for the drawing.



5- Phantom Lines
Phantom lines shall be used to indicate the alternate position of parts of the item delineated, repeated detail, or the relative position of an absent part and shall be composed of alternating one long and two short dashes, evenly spaced, with a long dash at each end. See  (Fig.1&2&4).

Fig (4): Phantom Lines

6- Sectioning Lines
Sectioning lines shall be used to indicate the exposed surfaces of an object in a sectional view. They are generally thin full lines, but may vary with the kind of material shown in section (see fig 1&2)



7- Extension Lines
Extension lines are used to indicate the extension of a surface or to point to a location outside the part outline. They start with a short, visible gap from the outline of the part and are usually perpendicular to their associated dimension lines (see fig 1&2).



8- Hidden Lines
Hidden lines shall consist of short dashes, evenly spaced. These lines are used to show the hidden features of a part or parts below or behind an object. They shall always begin with a dash in contact with the line from which they begin, except when such a dash would form a continuation of a full line. Dashes shall touch at corners, and arcs shall begin with dashes on the tangent points (see fig 1&2). 



9- Stitch Lines
Stitch lines shall be used to indicate the stitching or sewing lines on an article and shall consist of a series of very short dashes, approximately half the length of dash or hidden lines, evenly spaced. Long lines of stitching may be indicated by a series of stitch lines connected by phantom lines (see fig 1).



10- Outlines or Visible Lines
The outline or visible line shall be used for all lines on the drawing representing visible lines on the object (see fig 1&2).



11- Datum Lines
Datum lines shall be used to indicate the position of a datum plane and shall consist of one long dash and two short dashes evenly spaced  (see fig 1).



12- Cutting-Plane/Viewing-Plane Lines
The cutting-plane lines shall be used to indicate a plane or planes in which a section is taken. The viewing-plane lines shall be used to indicate the plane or planes from which a surface or surfaces are viewed. On simple views, the cutting planes shall be indicated as shown in Figure 9 on page 31. View shall be shown in back of the cutting plane (3rd angle).  (see fig 1&2&5).

fig (5): Cutting-Plane/Viewing-Plane Lines

On complex views, or when the cutting planes are bent or offset, the cutting planes shall be indicated as shown in Fig.6

fig (6)

In the next Topic, I will explain the line weights and scale. so, please keep following.

Types of Contracts - Part One

Definition of a Contact:

For implementation of the construction works of a project, an agreement, commonly called a contract, between contracting authority and contractor/supplier should be concluded, the definition of contract will be as follows:

The contract is an agreement between the contracting authority and a contractor /supplier providing contracting services/works and/or goods.

 

It is important that whatever contract is developed it must demonstrate:

• The contracting authority’s intent to contract. 
• A clear offer from the contracting authority and a clear acceptance of the offer by the contractor/supplier. 
• The ability of both contracting authority and supplier to legally contract. 
• A price that the contracting authority agrees to pay the contractor/supplier. 
• A clear agreement between contracting parties about the terms and conditions of the contract which should be precise and definite and there should be no room for ambiguity or misconstruction.

Types of contract:

The nature and content of contracts vary from country to country, however Contract types are likely to vary according to: 

• the degree and timing of the responsibility assumed by the contractor for the costs of performance.
• The amount and nature of the incentive offered to the contractor for achieving or exceeding specified standards or goals. 

Contract types according to pricing arrangement will be divided to two main categories which are:

• Fixed-price contracts.
• Cost-reimbursement contracts.

Note: in the end of this chapter I will include the most common names for contracting contracts.

First: Fixed-price contracts

• A price that is not subject to any adjustments. 
• Places upon the contractor maximum risk and full responsibility for all costs and resulting profit. 
• It provides maximum incentive for the contractor to control costs and perform effectively. 
• Firm Fixed Price contracts are the preferred method of contracting from the government’s perspective. Used when sealed bid is involved. Used for acquiring supplies and services and/or for acquiring commercial items. 

Variations of fixed price contracts

1- Economic price adjustment

•  Revision of prices for specific contingencies. 
• Adjustments based upon increases or decreases from an agreed 
• Upon level in either published or established market prices for specific items. 
• Adjustments based upon actual increases or decreases in the price 
• Adjustments based upon increases or decreases in the specific labor or material cost standards or indexes, such as Bureau of Labor Standards indices. 

2- Incentive Contracts
An FPI (Fixed Price Incentive) contract specifies a target cost, a target profit, a price ceiling and a profit adjustment formula. The FPI contract provides a profit motive for the contractor to perform efficiently from a cost perspective. If the contractor completes the contract while incurring less cost than originally anticipated, the contractor will receive more profit.

• Used when a fixed-firm contract is not appropriate.
• Supplies/services can be acquired at lowers costs, with improved delivery or improved technical performance. 

Cost Plus Contract

A contract agreement wherein the purchaser agrees to pay the cost of all labor and materials plus an amount for contractor overhead and profit (usually as a percentage of the labor and material cost). The contracts may be specified as follows:

1. Cost + Fixed Percentage Contract.
2. Cost + Fixed Fee Contract.
3. Cost + Fixed Fee with Guaranteed Maximum Price Contract.
4. Cost + Fixed Fee with Bonus Contract.
5. Cost + Fixed Fee with Guaranteed Maximum Price and Bonus Contract.
6. Cost + Fixed Fee with Agreement for Sharing Any Cost Savings Contract.

These types of contracts are favored where the scope of the work is indeterminate or highly uncertain and the kinds of labor, material and equipment needed are also uncertain. Under this arrangement complete records of all time and materials spent by the contractor on the work must be maintained.


Cost + Fixed Percentage Contract
Compensation is based on a percentage of the cost.


Cost + Fixed Fee Contract
Compensation is based on a fixed sum independent the final project cost. The customer agrees to reimburse the contractor's actual costs, regardless of amount, and in addition pay a negotiated fee independent of the amount of the actual costs.


Cost + Fixed Fee with Guaranteed Maximum Price Contract
Compensation is based on a fixed sum of money. The total project cost will not exceed an agreed upper limit.


Cost + Fixed Fee with Bonus Contract
Compensation is based on a fixed sum of money. A bonus is given if the project finish below budget, ahead of schedule etc.


Cost + Fixed Fee with Guaranteed Maximum Price and Bonus Contract
Compensation is based on a fixed sum of money. The total project cost will not exceed an agreed upper limit and a bonus is given if the project is finished below budget, ahead of schedule etc.


Cost + Fixed Fee with Agreement for Sharing Any Cost Savings Contract
Compensation is based on a fixed sum of money. Any cost savings are shared with the buyer and the contractor.

In the next Topic, I will continue explaining other types of contracts; Cost-reimbursement contracts.

NEC- Article 110 - Part One

110.1 Scope of Article 100
This article covers the general Requirements for electrical installations. 

110.2 equipment approvals
Conductors and equipment can be installed only if there are approved by AHJ.

NEC Article 110.2

For more understanding of terms “approval”, Please review the following post:

Definitions of identified, listed and approved terms

110.3 equipment installation
Equipment must be installed in accordance with any instructions included in their listing or labeling requirements otherwise it will be a violation of the code.

NEC Article 110.3

For more understanding of terms “listing and labeling”, please review the following post:

Definitions of identified, listed and approved terms

110.4 equipment voltage rating
The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

NEC Article 110.4

110.5 Conductor Material
Where the conductor material is not specified, the material and the sizes given in this Code shall apply to copper conductors. This means that you must pay attention for using appropriate code values which to be applied in case of using Aluminum conductors especially for tables included in chapter 9.



110.6 Conductor size unit
Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils units.

Conductors up to size 4/0 AWG will be sized in AWG.

Conductors larger than 4/0 AWG are sized in circular mils CM or MCM (MCM=1000CM) or Kcmil (Kcmil=MCM=1000CM.

How to calculate the circular mils size of a conductor?

by using the following Equation:

Circular mils CM = D² x10⁶

Where D is conductor diameter in inch.

For converting from mm2 to AWG and vice versa use the below table:

AWG TO MM2 CONVERSION TABLE
AWG	mm2
30	0.05
28	0.08
26	0.14
24	0.25
22	0.34
21	0.38
20	0.50
18	0.75
17	1.0
16	1.5
14	2.5
12	4
10	6
8	10
6	16
4	25
2	35
1	50
1/0	55
2/0	70
3/0	95
4/0	120
300MCM	150
350MCM	185
500MCM	240
600MCM	300
750MCM	400
1000MCM	500

You can also use and download the AWG X mm² Calculator by clicking on the link.

110.9 Interrupting Rating
Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.

You must differentiate between the following terms:

Interrupting Rating(IR): It is the maximum short-circuit current that an overcurrent protective device can safely interrupt under standard test conditions.

Interrupting capacity (IC): is the highest current at rated voltage that a device can interrupt (no fault).

Short circuit current rating (SSCR): The maximum short circuit current that equipment can safely withstand when protected by a specific overcurrent protective device, or for a specified time interval.


Overcurrent protective devices (such as fuses and circuit breakers) should be selected to ensure that the short-circuit current rating of the system components (wire, bus structures, switching, protection and disconnect devices, and distribution equipment) is not exceeded.

in the next topic, we will continue explaining the important code rules in Article 110. please keep following.

Industrial Furnace Transformers

In our course EP-3 for Transformers, I mentioned that Transformers have many different types according to Application, one of these applications was the Power Transformers which have sub-types as follows:

1- Generator step-up transformers.
2- Step-down transformers.
3- System intertie transformers:

• Phase Shifting Transformers.
• HDVC Transformers.

4- Industrial transformers.
5- Traction transformers.


I explained each one of power transformers types in previous topics; just follow the link for each type to land on its topic today i will continue explaining additional types of power transformers which will be the industrial transformers as follows.


Industrial transformers

Industrial Transformers

Transformers play an important role in several industries, especially in metallurgical plants and processes as in primary aluminum, copper, zinc, chlorine, and carbon industries, or for large industrial drives. And while production capacities are growing on a grand scale in order to satisfy worldwide demand, higher voltages and currents need to be supplied by more and more powerful industrial transformers which include the following types:

1. Furnace Transformers.
2. Convertor Transformers.

First: Furnace Transformers

furnace transformer is a transformer where a furnace melts charged material through an electric arc. Transformers of these types are used in steel melting and metallurgical industry.

Types of  Furnace Transformers

Furnace transformers can roughly be divided into two groups:

1. AC Furnaces Transformer.
2. DC Furnaces Transformer.

AC Furnaces Transformer in turn subdivided to:

• Arc Furnace Transformer 
• Reduction Transformer 

1- Arc Furnace Transformer

Arc Furnace Transformer

Technical features:

• Ratings up to 250 MVA.
• Wide Low Secondary voltage from 80 V up to 1,500 V.
• High secondary current.
• Electrode current for steel up to 120 kA depending upon the MVA rating.
• Electrode current for ferroalloy up to 180 Ka depending upon the MVA rating.
• Made both a single and three phase (Arc furnace transformers are normally designed as three phase units).
• Designed as shell type or core type with a few exceptions (core-type construction is common, the shell-type construction is also used because one can get a desired low impedance value by suitably interleaving the primary and secondary windings).

Usage:

Arc furnaces transformers are used in the process of melting scrap metal inside an arc furnace.

Arc Furnace transformer design:

The furnace transformer has to be specially designed to meet the following:

• Withstand frequent short circuits on the secondary side.
• Minimize voltage drop, harmonics and other effects resulting from wide fluctuations and unbalanced conditions for Currents drawn in the arc. 

These effects can be mitigated by supplying furnaces directly from a high voltage transmission line having high capacity (adequate fault level at the supply point) through a furnace transformer.

• Minimizing the Leakage Reactance of the arc furnace transformer since it gets added to the Reactance of the high current connections between the transformer secondary terminals and the electrode tips. 

fig(1): Electric-Arc-Furnace series-Reactor Connection

However, a certain minimum value of reactance is required in the furnace circuit to stabilize arc. In large furnace installations, the low voltage connections usually provide the necessary reactance. For smaller installations, a reactor may have to be added in series with the primary winding to give sufficient reactance value for the stability (see fig.1). These series reactors, which may be housed in the tank of furnace transformer, are usually provided with taps so that the reactance value can be varied for an optimum performance. Hence, depending on the rating of furnace installation and its inherent reactance, the leakage reactance of the furnace transformer has to be judiciously selected to meet the stability and efficiency requirements. Some arrangements must be taken for protecting the secondary winding against the transferred voltages from the high voltage primary winding by the following: 

• Connection of a surge arrester or capacitor between the secondary terminals and ground.
• Placement of electrostatic shield between the primary and secondary windings.

The secondary winding of a furnace transformer is made up of a number of parallel coils arranged vertically and connected by vertical copper bars. The goand-return arrangement is used for input and output connections (placed close to each other) reducing the magnetic field and associated stray losses in the nearby structural parts.

A delta connected secondary winding is preferable since the current to be carried by it is reduced. Many times, both the ends of each phase of the secondary winding are brought out through the terminals and the delta connections are made at the furnace (get automatically formed by the metallic charge in the furnace). This minimizes the inductive voltage drops in the leads and can achieve a better phase balance between the electrode currents. Due to heavy connections, some unbalance may exist which has to be minimized by

Small furnace transformers are naturally cooled with radiators. For large ratings and where there are space restrictions, forced oil cooling with an oil-to-water heat exchanger can be used. The oil pressure is always maintained higher than the water pressure (so that water does not leak into oil if a leakage problem develops).

The LV terminations may be of U shaped copper tubes of certain inside and outside diameters so that they can be water cooled from the inside. These copper tubes can be cooled by oil also.



In the next Topic, I will continue expalining the Furnace transformers types. so, please keep following.

Code of Practice for Energy Efficiency of Electrical Installations

The Code of Practice for Energy Efficiency of Electrical Installations aims to set out the minimum requirements on energy efficiency of electrical installations in buildings. It forms a part of a set of comprehensive Building Energy Codes that addresses energy efficiency requirements on building services installations. Designers are encouraged to adopt a proactive approach to exceed the minimum requirements of this code.

 

Scope:


1- The Code shall apply to all fixed electrical installations, other than those used as emergency systems, for all buildings except those specified in Clause 1.2, 1.3 and 1.4.

2- The following types of buildings are not covered in the Code: 
(a) buildings with a total installed capacity of 100A or less, single or three-phase at nominal low voltage; and
(b) buildings used solely for public utility services such as power stations, electrical sub-stations, water supply pump houses, etc.

3- Buildings designed for special industrial process may be exempted partly or wholly from the Code subject to approval of the Authority

4- Equipment owned by the public utility companies (e.g. HV/LV switchgear, transformers, cables, extract fans, etc.) and installed in consumers' substations will not be covered by the Code

5- In case where the compliance of this Code is in conflict with the safety requirements of the relevant Ordinance, Supply Rules, or Regulations, the requirements of this Code shall be superseded. This Code shall not be used to circumvent any safety, health or environmental requirements.


Contents:


1- SCOPE 


2- DEFINITIONS 


3- GENERAL APPROACH 


4- ENERGY EFFICIENCY REQUIREMENTS FOR POWER DISTRIBUTION IN BUILDINGS
4.1 High Voltage Distribution
4.2 Minimum Transformer Efficiency
4.3 Locations of Distribution Transformers and Main Switchboard
4.4 Main Circuits
4.5 Feeder Circuits
4.6 Sub-main Circuits
4.7 Final Circuits

5- REQUIREMENTS FOR EFFICIENT UTILISATION OF POWER
5.1 Lamps and Lurninaires
5.2 Air Conditioning Installations
5.3 Vertical Transportation
5.4 Motors and Drives
5.5 Power Factor Improvement
5.6 Other Good Practice

6- ENERGY EFFICIENCY REQUIREMENTS FOR POWER QUALITY
6.1 Maximum Total Harmonic Distortion (THD) of Current on LV Circuits
6.2 Balancing of Single-phase Loads

7- REQUIREMENTS FOR METERING AND MONITORING FACILITIES
7.1 Main Circuits
7.2 Sub-main and Feeder Circuits

8- SUBMISSION OF INFORMATION 


SCHEDULE OF FORMS:
FORM EL-l: Electrical Installations Summary

FORM EL-2: Electrical Power Distribution Worksheet

FORM EL-3: Electrical Power Utilization Worksheet

FORM EL-4: Electrical Power Quality Worksheet

FORM EL-5: Electrical Metering & Monitoring Worksheet

APPENDICES:
Appendix A: Explanatory Notes and Sample Calculations

Appendix B: Case Study




To download your copy from Code of practice for Energy Efficiency of Electrical Installations, please click on the link.

Specific Electrical Requirements for Industrial Buildings- Part Two

In the previous Topic “Specific Electrical Requirements for Industrial Buildings- Part One”, I clarified that any designer wants to optimize his design for industrial buildings by completely satisfying the users’ individual needs for these buildings which are: 

1. Workshop and office flexibility.
2. Production facility availability, continuity of service.
3. Time, investment and operating cost control.

And I show that these needs must be satisfied in the following three levels of electrical design for power distribution architecture which are:

1. General distribution.
2. Sub-distribution.
3. Final distribution.

Actually, Each industrial site has its own particular needs and requires a specific type of power distribution architecture based on the following principles:

1. Cost optimization, which is closely, linked to the location of the MV/LV substations, 
2. Availability, which is primarily governed by the higher levels of the architecture, 
3. Flexibility, which is based mainly on the sub-distribution and final distribution design 

These principles can be applied in different types of power distribution architecture, especially in the common three types which are:

1. "Radial branched" power distribution architecture,
2. "Dual-transformer shared" power supply distribution architecture,
3. "Multiple-transformer shared" power distribution architecture.

In the previous Topic as referred above, I explain the first type of power distribution architecture; "Radial branched" and today I will continue explaining the other two types as follows:

"Dual-transformer shared" power supply distribution architecture.

Dual-transformer shared

This power supply distribution architecture meets the needs for increased flexibility and availability for all industrial buildings.

The electrical design levels in this power distribution architecture will be as follows:

1- General distribution Level
It will include two MV/LV substations; both substations will supply the main switchboard (via cables or high power busbar trunking ) with low voltage at the same time, and the main switchboard will supply a high-current busbar trunking.

That is why this power supply distribution architecture is known as a "dual-transformer shared".

2- Sub-distribution Level
In this level, Loads are supplied as follows:

• Large structural loads, such as painting equipment, are supplied directly via cables from the main switchboard on the nearest MV/LV substation. The rating of the high-current busbar trunking consequently relieved of such loads is reduced. 
• High-power machine cubicles will be fed directly via medium or low power busbar trunking. 
• The local sub-distribution board in the office zone is supplied directly via cables from main switchboard. 
• The other power loads are supplied from the high-power busbar trunking.

3- Final distribution Level
In this level, each final load will be supplied as follows:

• The mobile devices connected via their industrial outlets are supplied from multi-functional weatherproof enclosures. 
• The lighting throughout the workshops is distributed via lighting busbar trunking fed from the local sub-distribution board.
• Mobile workstations are supplied via industrial poles. 

Evaluation of "Dual-transformer shared" power distribution architecture:

• This architecture type is optimized more than the “Radial-branched” architecture, as it is designed to provide the process with a distributed power at general and sub-distribution level, making it easier to connect the loads throughout the industrial buildings, irrespective of their location. 
• The design of both the power sub-distribution and the general power distribution can therefore be more independent of the process design. 
• This architecture satisfies the high level of availability required by sensitive loads (servers, programmable controllers, etc.) due to its protected supply which ensures the operation of critical connected equipment in the event of the failure of one of the two MV/LV substations because each load will be supplied simultaneously by both transformers. 
• This architecture (Both the general and sub-distribution) uses mainly factory built components (busbars and sub-distribution boards components) for more standard flexibility, availability, time and cost control requirements which result in the following: 

1. Shorter installation time. 
2. Easy deal with design (specifications, inaccuracies, etc.), installation (worksite, hazards, etc.) and operating (modification, workshop relocation, etc.). 
3. The reliability of the plant is guaranteed 

This power distribution architecture has the following evaluation:

Flexibility	***
Availability	***
Time and Cost Control	***

"Multiple-transformer shared" power distribution architecture

Multiple-transformer shared

This power supply distribution architecture meets the very high flexibility and availability for all industrial buildings

The electrical design levels in this power distribution architecture will be as follows:

1- General distribution Level
It will include many MV/LV substations connected in a low voltage loop by high-power busbar trunking which can connect about four MV/LV substations.

That is why it is known as a "multiple-transformer shared" power distribution architecture.

2- Sub-distribution Level
In this level, Loads are supplied as follows:

• Large structural loads, such as painting equipment are supplied directly via cables from the main switchboard on the nearest substation: the rating of the high-current busbar trunking consequently relieved of such loads is reduced. 
• The high-power machine cubicles, in addition to the roof mounted heat pumps, will be supplied via the medium-power busbar trunking. 
• The local sub-distribution board in the office zone is supplied directly Via cables from main switchboard. 
• The other loads are supplied directly from the low-voltage loop.

3- Final distribution Level
In this level, each final load will be supplied as follows:

• The mobile devices connected via their industrial outlets are supplied from multi-functional weatherproof enclosures. 
• The lighting throughout the building is distributed via lighting busbar trunking. 
• Mobile workstations are supplied via industrial poles. 

Evaluation of Multiple-transformer shared" power distribution architecture

• This architecture is best optimized type, as it is designed to provide the process with a distributed supply at general and sub-distribution Levels and making it easier to connect the loads in all industrial buildings, whatever their location. 
• This architecture satisfies the high level of availability required by sensitive loads (servers, programmable controllers, etc.) due to its protected supply because it ensures that the critical connected equipment continues to operate in the event of MV/LV substation failure for example; if one substation fails, 3/4 of the total power remains available. 
• This type of architecture is particularly justified economically when industrial buildings use reversible heating/air conditioning components (for ex. Roof mounted heat pumps). This equipment in fact requires considerable additional, evenly-distributed power of 100VA/M2. 
• This architecture (Both the general and sub-distribution) uses mainly factory built components (busbars and distribution boards components) for more standard flexibility, availability, time and cost control requirements which result in the following: 

1. Shorter installation time. 
2. Easy deal with design (specifications, inaccuracies, etc.), installation (worksite, hazards, etc.) and operating (modification, workshop relocation, etc.).
3. The reliability of the plant is guaranteed.

This power distribution architecture has the following evaluation:

Flexibility	****
Availability	****
Time and Cost Control	***

Comparison of the three common power distribution architectures with regard of satisfying the user needs will be as follows:

	"Radial branched"	"Dual-transformer shared"	"Multiple-transformer shared"
Flexibility	**	***	****
Availability	**	***	****
Time and Cost Control	**	***	***

Actually, each industrial site has its own particular needs and requires a specific type of power distribution architecture, the selection between these common types of power distribution architecture is usually based on the following points:

1. Type of building use.
2. Level of building installations, equipment and furnishing.
3. Building’s Cost budget.
4. User needs from the building.
5. Regulations of utility companies and local authorities.

You can use the preliminary design checklist for listing the above information and then you will be able to select the right type of power distribution architecture for each case.

For me, I use the advanced preliminary design checklist to do this which has the following advantages:

1- The best professional form for Establishment preliminary design phase
It include all the factors that can influence an electrical design for any project such as Site topology, Service reliability, Load distribution, Environmental impact and etc.

2- Very easy to use
It guides you step by step to design the power distribution architecture for any project.
Besides, it is an excel form; you need only to put marks (√) beside your selection from the multiple choices for each design step.

3- Increase you designs’ credibility and quality
If you get your client’s admiration for the method and arrangements that you use for gathering and analyzing information about his project, of course you add another permanent client and get more good reputation and popularity.

Did you want your copy of advanced preliminary design checklist?! I hear your answer; of course yes. So, let us make a deal; just register as a follower and I will send the advanced preliminary design checklist to you by mail immediately. Is it a fair deal?! I need to know your answer in your comment. 

In the next topic, I will explain the different types of for commercial buildings and their general electrical requirements. So, please keep following.