Technological characteristics

MV & LV architecture selection guide

Technological characteristics

The technological solutions considered concern the various types of MV and LV equipment, as well as Busbar Trunking Systems .
The choice of technological solutions is made following the choice of single-line diagram and according to characteristics given below.

Environment, 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.
Different categories:

• Standard: no particular environmental constraints
• Enhanced: severe environment, several environmental parameters generate important constraints for the installed equipment
• Specific: atypical environment, requiring special enhancements
  

Service Index

The service index (IS) is a value that allows us to characterize an LV switchboard according to user requirements in terms of operation, maintenance, and scalability.
The different index values are indicated in the following table (Fig D4):

	Operation (setting, measurement, locking, padlocking)	Maintenance (cleaning, checking, testing, repaining)	Upgrade (addition, modification, site expansion)z
Level 1	IS = 1 • • Operation may lead to complete stoppage of the switchboard	IS = • 1 • Operation may lead to complete stoppage of the switchboard	IS = • • 1 Operation may lead to complete stoppage of the switchboard
Level 2	IS = 2 • • Operation may lead to stoppage of only the functional unit	IS = • 2 • Operation may lead to stoppage of only the functional unit, with work on connections	IS = • • 2 Operation may lead to stoppage of only the functional unit, with functional units provided for back-up
Level 3	IS = 3 • • Operation may lead to stoppage of the power of the functional unit only	IS = • 3 • Operation may lead to stoppage of only the functional unit, without work on connections	IS = • • 3 Operation may lead to stoppage of only the functional unit, with total freedom in terms of upgrade

There are a limited number of relevant service indices (see Fig. D5)
The types of electrical connections of functional units can be denoted by a three-letter code:

• The first letter denotes the type of electrical connection of the main incoming circuit,
• The second letter denotes the type of electrical connection of the main outgoing circuit,
• The third letter denotes the type of electrical connection of the auxiliary circuits.

The following letters are used:

• F for fixed connections,
• D for disconnectable connections,
• W for withdrawable connections.

Service ratings are related to other mechanical parameters, such as the Protection Index (IP), form of internal separations, the type of connection of functional units or switchgear (Fig. D6):
Technological examples are given in chapter E2.

• Definition of the protection index: see IEC 60529: “Degree of protection given by enclosures (IP code)”,
• Definitions of the form and withdrawability: see IEC 60439-1: “Low-voltage switchgear and controlgear assemblies; part 1: type-tested and partially type-tested assemblies”.

Service rating IS	111	211	212	223	232	233	332	333
Protection Index IP	2XX	2XB		2XB	2XB	2XB	2XB	2XB
Form	1	1	3b 2b 4a	3b	3b	3b	3b	3b
Functional Unit Withdrawability	FFF	FFF	WFW	WFD	WFW	WWW	WWW	WWW
Operation	Switching off the whole switchboard	Individually switching off the functional unit and re-commissioning < 1H
Maintenance	Working time > 1 h with total unavailability			Working time between 1/4 h and 1h, with work on connections	Working time between 1/4 h and 1h, without work on connections
Upgrade	Extention not planned		Possible adding of functional units with stopping the switchboard	Possible adding of functional units without stopping the switchboard	Possible adding of functional units with stopping the switchboard	Possible adding of functional units without stopping the switchboard	Possible adding of functional units with stopping the switchboard	Possible adding of functional units without stopping the switchboard

Other considerations

Other considerations have an impact on the choice of technological solutions:

• Designer experience,
• Consistency with past designs or the partial use of past designs,
• Standardization of sub-assemblies,
• The existence of an installed equipment base,
• Utilities requirements,
• Technical criteria: target power factor, backed-up load power, presence of harmonic generators…

These considerations should be taken into account during the detailed electrical definition phase following the draft design stage.