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.
1. 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
2. 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 |
Fig. D4: Different index values
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 | Individually switching off the functional unit and re-commissioning < 1/4h | |||||
| 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 | |
Fig. D5: correspondance between service index and other mechanical parameters and relevant service index
3. 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.
