From Electrical Installation Guide
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.
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
The Service Index (IS), is a tool dedicated to electrical designers in order to specify LV switchboards with reference to user's need rather than to technical aspects. It ensures the effective definition of the switchboards according to IEC61439-1 and 2 criteria for any:
- future evolution,
- operation needs.
IS have been defined by the french standard commitee (AFNOR/UTE) in 2002 under the reference C63-429.
The IS is charactered by 3 numbers from 1 to 3, reflecting respectively:
- level of operation needs,
- level of maintenance request,
- level of evolution request.
The levels are described in Figure D4
|Operation[a] : first number||Maintenance[b]: second number||Evolution[c]: third number|
|Level 1||Full shutdown of the switchboard is accepted||Full shutdown of the switchboard is accepted||Full shutdown of the switchboard is accepted|
|Level 2||Only shut down of the concerned functional unit[d] is accepted||Only shutdown of the concerned functional unit[d] is accepted. But reconnection of the functional unit requests an action on connections||Only shutdown of the concerned functional unit[d] is accepted. Spare functional units are provided|
|Level 3||Only the shutdown of the power of the functional unit [d] is accepted (control circuits are still available)|| Only shutdown of the concerned functional unit [d] is accepted.
Reconnection of the functional unit requests no action on connections
| Only shutdown of the concerned functional unit [d] is accepted.
Evolution does not request pre-equiped spare functional units.
[a] Operation: set of actions on the switchboard, which can be done by non-electrician people.
[b] Maintenance: concerns action of control, diagnostic, servicing, reparation, refurbishment, made by professionals.
[c] Evolution: adaptation of the equipment by addition of devices, increase of power demand.
[d] functional unit: subset of a LV switchboard including all mechanical and electrical parts dedicated to a specific function like : incomer, main feeder, auxiliary, etc.
Fig. D4: Definition of Service Index values
Other considerations have an impact on the choice of technological solutions:
- Previous 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.