Procedure for the establishment of a new substation
Connection to the MV public distribution network
Procedure for the establishment of a new substation
Large consumers of electricity are invariably supplied at MV.
On LV systems operating at 120/208 V (3-phase 4-wires), a load of 50 kVA might be considered to be “large”, while on a 240/415 V 3-phase system a “large” consumer could have a load in excess of 100 kVA. Both systems of LV distribution are common in many parts of the world.
As a matter of interest, the IEC recommends a “world” standard of 230/400 V for
3-phase 4-wire systems. This is a compromise level and will allow existing systems which operate at 220/380 V and at 240/415 V, or close to these values, to comply with the proposed standard simply by adjusting the off-circuit tapping switches of standard distribution transformers.
The distance over which the energy has to be transmitted is a further factor in considering an MV or LV service. Services to small but isolated rural consumers are obvious examples.
The decision of a MV or LV supply will depend on local circumstances and considerations such as those mentioned above, and will generally be imposed by the utility for the district concerned.
When a decision to supply power at MV has been made, there are two widely-followed methods of proceeding:
1 - The power-supplier constructs a standard substation close to the consumer’s premises, but the MV/LV transformer(s) is (are) located in transformer chamber(s) inside the premises, close to the load centre
2 - The consumer constructs and equips his own substation on his own premises, to which the power supplier makes the MV connection
In method no. 1 the power supplier owns the substation, the cable(s) to the transformer(s), the transformer(s) and the transformer chamber(s), to which he has unrestricted access.
The transformer chamber(s) is (are) constructed by the consumer (to plans and regulations provided by the supplier) and include plinths, oil drains, fire walls and ceilings, ventilation, lighting, and earthing systems, all to be approved by the supply authority.
The tariff structure will cover an agreed part of the expenditure required to provide the service.
Whichever procedure is followed, the same principles apply in the conception and realization of the project. The following notes refer to procedure no. 2.
Preliminary information
Before any negotiations or discussions can be initiated with the supply authorities, the following basic elements must be established:
Maximum anticipated power (kVA) demand
Determination of this parameter is described in Chapter A, and must take into account the possibility of future additional load requirements. Factors to evaluate at this stage are:
- The utilization factor (ku)
- The simultaneity factor (ks)
Layout plans and elevations showing location of proposed substation
Plans should indicate clearly the means of access to the proposed substation, with dimensions of possible restrictions, e.g. entrances corridors and ceiling height, together with possible load (weight) bearing limits, and so on, keeping in mind that:
- The power-supply personnel must have free and unrestricted access to the MV equipment in the substation at all times
- Only qualified and authorized consumer’s personnel are allowed access to the substation
- Some supply authorities or regulations require that the part of the installation operated by the authority is located in a separated room from the part operated by the customer.
Degree of supply continuity required
The consumer must estimate the consequences of a supply failure in terms of its duration:
- Loss of production
- Safety of personnel and equipment
| The consumer must provide certain data to the utility at the earliest stage of the project. |
