Electrical installation characteristics

D - MV & LV architecture selection guide

Electrical installation characteristics

These are the main installation characteristics enabling the defining of the fundamentals and details of the electrical distribution architecture. For each of these characteristics, we supply a definition and the different categories or possible values.

Activity

Definition:

Main economic activity carried out on the site.

Indicative list of sectors considered for industrial buildings:

• Manufacturing
• Food & Beverage
• Logistics

Indicative list of sectors considered for tertiary buildings:

• Offices buildings
• Hypermarkets
• Shopping malls

Site topology

Definition:

Architectural characteristic of the building(s), taking account of the number of buildings, number of floors, and of the surface area of each floor.

Different categories:

• Single storey building,
• Multi-storey building,
• Multi-building site,
• High-rise building.

Layout latitude

Definition:

Characteristic taking account of constraints in terms of the layout of the electrical equipment in the building:

• aesthetics,
• accessibility,
• presence of dedicated locations,
• use of technical corridors (per floor),
• use of technical ducts (vertical).
  

Different categories:

•  Low: the position of the electrical equipment is virtually imposed
• Medium: the position of the electrical equipment is partially imposed, to the detriment of the criteria to be satisfied
• High: no constraints. The position of the electrical equipment can be defined to best satisfy the criteria.

Service reliability

Definition:

The ability of a power system to meet its supply function under stated conditions for a specified period of time.

Different categories:

• Minimum: this level of service reliability implies risk of interruptions related to constraints that are geographical (separate network, area distant from power production centers), technical (overhead line, poorly meshed system), or economic (insufficient maintenance, under-dimensioned generation).
• Standard
• Enhanced: this level of service reliability can be obtained by special measures taken to reduce the probability of interruption (underground network, strong meshing, etc.)
  

Maintainability

Definition:

Features input during design to limit the impact of maintenance actions on the operation of the whole or part of the installation.

Different categories:

• Minimum: the installation must be stopped to carry out maintenance operations.
• Standard: maintenance operations can be carried out during installation operations, but with deteriorated performance. These operations must be preferably scheduled during periods of low activity. Example: several transformers with partial redundancy and load shedding.
• Enhanced: special measures are taken to allow maintenance operations without disturbing the installation operations. Example: double-ended configuration.

 

Installation flexibility

Definition:

Possibility of easily moving electricity delivery points within the installation, or to easily increase the power supplied at certain points. Flexibility is a criterion which also appears due to the uncertainty of the building during the pre-project summary stage.

Different categories:

• No flexibility: the position of loads is fixed throughout the lifecycle, due to the high constraints related to the building construction or the high weight of the supplied process. E.g.: smelting works.
• Flexibility of design: the number of delivery points, the power of loads or their location are not precisely known.
• Implementation flexibility: the loads can be installed after the installation is commissioned.
• Operating flexibility: the position of loads will fluctuate, according to process re-organization.

Examples:
    - industrial building: extension, splitting and changing usage
    - office building: splitting

 

Power demand

Definition:

The sum of the apparent load power (in kVA), to which is applied a usage coefficient. This represents the maximum power which can be consumed at a given time for the installation, with the possibility of limited overloads that are of short duration.
Significant power ranges correspond to the transformer power limits most commonly used:

• < 630kVA
• rom 630 to 1250kVA
• from 1250 to 2500kVA
• > 2500kVA

 

Load distribution

Definition:

A characteristic related to the uniformity of load distribution (in kVA / m²) over an area or throughout the building.

Different categories:

• Uniform distribution: the loads are generally of an average or low unit power and spread throughout the surface area or over a large area of the building (uniform density).
  E.g.: lighting, individual workstations

• intermediate distribution: the loads are generally of medium power, placed in groups over the whole building surface area
  E.g.: machines for assembly, conveying, workstations, modular logistics “sites”

• localized loads: the loads are generally high power and localized in several areas of the building (non-uniform density).
  E.g.: HVAC
  

Power Interruption Sensitivity

Definition:

The aptitude of a circuit to accept a power interruption.

Different categories:

• “Sheddable” circuit: possible to shut down at any time for an indefinite duration
• Long interruption acceptable: interruption time > 3 minutes *
• Short interruption acceptable: interruption time < 3 minutes *
• No interruption acceptable.

We can distinguish various levels of severity of an electrical power interruption, according to the possible consequences:

• No notable consequence,
• Loss of production,
• Deterioration of the production facilities or loss of sensitive data,
• Causing mortal danger.

This is expressed in terms of the criticality of supplying of loads or circuits.

• Non-critical:

The load or the circuit can be “shed” at any time. E.g.: sanitary water heating circuit.

• Low criticality:

A power interruption causes temporary discomfort for the occupants of a building, without any financial consequences. Prolonging of the interruption beyond the critical time can cause a loss of production or lower productivity. E.g.: heating, ventilation and air conditioning circuits (HVAC).

• Medium criticality

A power interruption causes a short break in process or service. Prolonging of the interruption beyond a critical time can cause a deterioration of the production facilities or a cost of starting for starting back up.
E.g.: refrigerated units, lifts.

• High criticality

Any power interruption causes mortal danger or unacceptable financial losses.
E.g.: operating theatre, IT department, security department.

* indicative value, supplied by standard EN50160: “Characteristics of the voltage supplied by public distribution networks”.