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.

Sectors of activities

Definition

Among the definitions proposed by IEC60364-8-1 § 3.4, mainly those listed below are part of this chapter.

Residential buildings

• Premises designed and constructed for private habitation

Commercial

• Premises designed and constructed for commercial operations

Industry

• Premises designed and constructed for manufacturing and processing of operations

Infrastructure

• Systems or premises designed and constructed for the transport and utility operation

Site topology

Definition

Architectural characteristic of the building(s), taking into account 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 into account the 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.
  • industrial building: extension, splitting and changing usage
  • office building: splitting

Power demand

Definition

It's the maximum power and apparrent power demands actually required to dimension the installation (see Power loading of an installation for more information):

• < 630kVA
• from 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

Voltage 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.

Disturbance sensitivity

Definition

The ability of a circuit to work correctly in presence of an electrical power disturbance.

A disturbance can lead to varying degrees of malfunctioning. E.g.: stopping working, incorrect working, accelerated ageing, increase of losses, etc

Types of disturbances with an impact on circuit operations:

• overvoltages
• voltage harmonic distorsion,
• voltage drop, voltage dip
• voltage fluctuation,
• voltage imbalance.

Different categories

• low sensitivity: disturbances in supply voltages have very little effect on operations.

E.g.: heating device.

• medium sensitivity: voltage disturbances cause a notable deterioration in operations.

E.g.: motors, lighting.

• high sensitivity: voltage disturbances can cause operation stoppages or even the deterioration of the supplied equipment.

E.g.: IT equipment.

The sensitivity of circuits to disturbances determines the design of shared or dedicated power circuits. Indeed it is better to separate “sensitive” loads from “disturbing” loads. E.g.: separating lighting circuits from motor supply circuits.

This choice also depends on operating features. E.g.: separate power supply of lighting circuits to enable measurement of power consumption.

Disturbance potential of circuits

Definition

The ability of a circuit to disturb the operation of surrounding circuits due to phenomena such as: harmonics, in-rush current, imbalance, High Frequency currents, electromagnetic radiation, etc.

Different categories

• Non disturbing: no specific precaution to take
• moderate or occasional disturbance: separate power supply may be necessary in the presence of medium or high sensitivity circuits. E.g.: lighting circuit generating harmonic currents.
• Very disturbing: a dedicated power circuit or ways of attenuating disturbances are essential for the correct functioning of the installation. E.g.: electrical motor with a strong start-up current, welding equipment with fluctuating current.

Other considerations or constraints

• Specific rules

E.g.: hospitals, high rise buildings, etc.

• Rule of the Energy Distributor

Example: limits of connection power for LV, access to MV substation, etc

• Attachment loads

Loads attached to 2 independent circuits for reasons of redundancy.

• Designer experience

Consistency with previous designs or partial usage of previous designs, standardization of sub-assemblies, existence of an installed equipment base.

• Load power supply constraints

Voltage level (230V, 400V, 690V), voltage system (single-phase, three-phase with or without neutral, etc)

Related technical guides

Power Availability and Reliability Guide

The guide outlines innovative solutions from Schneider Electric™ covering the four main areas of Power Availability and Reliability:

• Digital and power systems reference designs
• How selectivity enhances uptime
• Electrical asset management
• Fault localization, root cause analysis, and power recovery

Download the guide (.pdf)