What detailed information is available?
In the secure area detailed information is provided for the electricity distribution network from 132kV to the lower voltage busbars of primary substations as follows:
- geographic plans showing the 33kV and 132kV networks. These give the approximate locations of circuits and substations. The 33kV plans are on three sheets and the 132kV plan is on a single sheet
- schematic diagrams for the 33kV and 132kV systems. The 33kV diagrams are on ten sheets and the 132kV diagrams are on three sheets
- circuit data tables listed by substation group giving node references, operating voltage, positive sequence impedance, zero sequence impedance (132kV only), susceptance (132kV only), rating and circuit length. There are tables for 132kV and 33kV circuits and also 11kV or 6.6kV interconnectors where these are normally used to operate 33/11kV or 33/6.6kV (primary) substations in parallel
- transformer tables listed by substation group giving the substation or busbar name on each side of the transformer together with voltage. The vector group, positive sequence impedance, zero sequence reactance (at 132kV substations only), maximum and minimum tapping percentage, rating information, the method of earthing and the Low Voltage earthing impedance. General information relating to reverse power capability is also provided
- loading tables listed by substation group giving substation or busbar name, voltage level, maximum load in previous year in both MW and MVAr. A forecast of future years maximum loads is also provided together with a scaling factor for estimating minimum loads together with typical load duration curves. Substation firm capacities are based on transformer nameplate data and do not take circuit or other potential constraints into account unless specifically stated in the table
- fault level information
- information on connected generation and accepted quotes for generation with a connection voltage at 6.6kV, 11kV, 33kV and 132kV
- interest in demand and generation above 1MVA.
Fault Level tables listed by substation group for both three phase and single phase faults at 6.6/11kV, 33kV and 132kV. These give the substation or busbar name, voltage level, system impedance, existing system fault currents and switchgear ratings. Explanatory notes are also provided at the end of each of the tables.
Other information can be made available for a specific part of the distribution network on request. The categories of information which can be provided and the associated charges can be found on the costs page
Data transfer and system studies
System data will be made available to users or prospective users. For 33kV and 132kV data, this will take the form of an update of the detailed information in this Long term development Statement. For 6.6/11kV it will be in the form of the attached schedule. In each instance the data will be made available on payment of the standard costs. IPSA is predominantly used as a power system analysis tool for the 132kV and 33kV networks, and DINIS for 6.6/11kV networks. When considering connection enquiries or feasibility studies, the following system studies will generally be undertaken for all generator applications:
- loadflow at maximum and minimum loadings. Thermal capacities will be assessed against the appropriate rating of the circuit for the load-factor of the circuit loadings
- voltage profile studies and voltage step changes for credible unplanned outages. Voltage step changes should be limited to 10% for credible outages, pre automatic tap changer corrective tapping
- short circuit studies. The guidance on calculations etc. contained in ER G74 is followed
- Security. Full compliance with ER P2/6 is sought, generation security will be assessed in discussion with the generator and where appropriate in accordance with ER G75/1
- stability. Where it is appropriate, and generally only for any machine over 5MW stability studies should, if necessary be performed for credible outages using machine parameters provided by the user. Where it is necessary to undertake stability studies there will be no additional study charge to the user
- voltage quality studies will not normally be undertaken for generation connection enquires, unless there is some aspect of the machine or its connection that makes such studies appropriate.
The following assumptions are made in undertaking studies:
- maximum and minimum demands are used based on actual system operating conditions, or anticipated operating conditions where these are more appropriate for the study in question
- generally only one contingent outage will be considered. However where there is more than two-circuit security or complex mesh networks, appropriate two-outage contingencies will be considered
- circuit ratings will be used appropriate for the loading cycle anticipated. It will generally be appropriate to use continuous ratings for plant and equipment subject to generator loadings
- appropriate pre-fault operating and running arrangements are made following first circuit outage to cater for subsequent outages
- switchgear make and break duties are assessed at 100% of their nameplate ratings.