The Electrical Distribution Architecture – Part Five

In the previous Topics:

I listed the Tasks required for application of Electrical Distribution architecture design process, they were:

  • Assigning of electrical installation characteristics,
  • Assigning of Technological characteristics,
  • Using Architecture assessment criteria,
  • Step (1): Choice of distribution architecture fundamentals,
  • Step (2): choice of architecture details,
  • Step (3): choice of equipment,
  • Recommendations for architecture optimization 

And I began explaining the first task: Assigning of electrical installation characteristics which include the following categories or possible values: 

  1. Activity,
  2. Site topology,
  3. Layout latitude,
  4. Service reliability,
  5. Maintainability,
  6. Installation flexibility,
  7. Power demand,
  8. Load distribution,
  9. Power Interruption Sensitivity,
  10. Disturbance sensitivity,
  11. Disturbance capability of circuits,
  12. Other considerations or constraints.

Today, I will continue explaining other tasks for helping you to use Electrical Distribution architecture design process professionally. 

12- Other considerations or constraints

A- Environment
Sun exposure which can be used to add photovoltaic cells as a power supply in the Electrical Distribution architecture.

B- Specific rules
Please review the following previous topics for more information:

C- Rule of the Energy Distributor 

1- Limits of connection power for LV
Loads up to 250 kVA can be supplied at LV, but power-supply organizations generally propose a HV service at load levels for which their LV networks are marginally adequate. This can be different from country to another depending on their local regulations.

2- Access to MV substation
Substation Plans should indicate clearly the means of access to the proposed substation, with dimensions of possible restrictions, e.g. entrances corridors and ceiling height, together with possible load (weight) bearing limits, and so on, keeping in mind that Some supply authorities or regulations require that the part of the installation operated by the authority is located in a separated room from the part operated by the customer and this will affect the Electrical Distribution architecture.

D- Attachment loads
Loads attached to 2 independent circuits for reasons of redundancy. For example, critical loads which must be have uninterrupted power service, so another power source must be added to the Electrical Distribution architecture like a UPS to ensure power service continuity.

E- Designer experience
The designer experience has a great effect on selecting of the Electrical Distribution architecture and it can be differ from one designer to another in the following points:

  • Consistency with previous designs or partial usage of previous designs.
  • Standardization of sub-assemblies. 
  • Existence of an installed equipment base. 

F- Load power supply constraints
1- Voltage level
The voltage of the local LV network which be used by the LV consumers will affect Electrical Distribution architecture. The LV voltage level will be different from country to another as in fig (1) which indicates the voltage levels used in some countries.

Fig (1): Voltage levels

2- Voltage system
There are different configurations of electrical circuits with different voltage values for single and three phase circuits, fig (2) summarize the common electrical circuit configurations.

 fig (2): configurations of electrical circuits

Please review the following previous topics for more information:

Second Task: Assigning of Technological characteristics

The technological solutions considered concern the various types of MV and LV equipment, as well as Busbar Trunking Systems . 

These characteristics will include the following categories or possible values:
  1. Environment and atmosphere,
  2. Service Index,
  3. Other considerations.

1- Environment and atmosphere

Environmental conditions influence the definition and choice of appropriate installation equipment and the choice of protective measures for the safety of persons.

The environmental conditions are referred to collectively as “external influences”.

Environment and atmosphere
A notion taking account of all of the environmental constraints (average ambient temperature, altitude, humidity, corrosion, dust, impact, etc.) and bringing together protection indexes IP and IK.

Standard: no particular environmental constraints

Enhanced: severe environment, several environmental parameters generate important constraints for the installed equipment

Specific: a typical environment, requiring special enhancements

Classification scheme of external influences

Many national standards concerned with external influences include a classification scheme which is based on, or which closely resembles, that of international standard IEC 60364-5-51.

Each condition of external influence is designated by a code comprising a group of two capital letters and a number as follows:

a- First letter (A, B or C):The first letter relates to the general category of external influence:
  • A = environment 
  • B = utilization 
  • C = construction of buildings 
b- Second letter 
The second letter relates to the nature of the external influence.
c- Number 
The number relates to the class within each external influence. 
d- Additional letter (optional) 
Used only if the effective protection of persons is greater than that indicated by the first IP digit. 

When only the protection of persons is to be specified, the two digits of the IP code are replaced by the X’s. Example: IP XXB.

 the code AC2 signifies: 

A = environment
AC = environment-altitude 
AC2 = environment-altitude > 2,000 m 

List of external influences

Fig (3) below is from IEC 60364-5-51, which should be referred to if further details are required.

fig (3): IEC 60364-5-51- List of external influences

Protection provided for enclosed equipment: codes IP and IK

1- IP code

IP code is the degree of protection provided by an enclosure is indicated in the IP code, recommended in IEC 60529.

Protection is afforded against the following external influences:

  • Penetration by solid bodies,
  • Protection of persons against access to live parts ,
  • Protection against the ingress of dust,
  • Protection against the ingress of liquids.
A brief description of the IP Code elements is given in the following figs (4&5) 

fig (4): IP Code arrangement

fig (5): IP Code Values

Note: the IP code applies to electrical equipment for voltages up to and including 72.5 kV. 

2- IK Code

Standard IEC 62262 defines an IK code that characterizes the aptitude of equipment to resist mechanical impacts on all sides. 

A brief description of the IK Code elements is given in the following fig (6).

Fig (6): IK Code elements

In the next topic, I will continue explaining other Technological characteristics, please keep following. 

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