| (a) | Transmission/Subtransmission Lines and Cables |
| | Issue: | Conductor and cable size. |
| | Approach: | Determine maximum demand and load cycle. |
| | | Ratings should normally be based on the (n-1) criterion taking into account any cyclic or limited cyclic ratings and fault level ratings. Resize the conductor to the appropriate standard size if necessary, based on meeting reasonably predictable "system normal" maximum demand with the "economic current rating" for the conductor and "first order contingency" loads with the thermal rating of the conductor. Economic current ratings are usually in the range of 25-50% of the thermal rating. |
| (b) | Substations/Zone Substations |
| | Issue: | Transmission/subtransmission voltage bus configuration. |
| | Approach: | Dependent on transmission/subtransmission configuration, should only be necessary to optimise if transmission/subtransmission system is changed. |
| | Issue: | Distribution voltage bus configuration. |
| | Approach: | Standard switch bays to be defined in asset types, optimise to nearest standard rating to match load. |
| | Issue: | Buildings. |
| | Approach: | Optimise if overdesigned for application and/or location. |
| | Issue: | Ancillary equipment. |
| | Approach: | Delete if not required. |
| | Issue: | Fire protection and oil retention facilities. |
| | Approach: | Include unless not required for application and/or location. |
| (c) | Substation/Zone Substation Transformers |
| | Issue: | Transformer rating. |
| | Approach: | Ratings should normally be based on the (n-1) criterion taking into account any cyclic or limited cyclic ratings and fault level ratings. Determine nominal, forced cooled, cyclic and limited cyclic ratings. Check basis of rating. Optimise if ratings excessive for loads e.g. force cooled transformers may be used to achieve emergency ratings rather than having naturally cooled transformers in parallel. Reasonable utilisation factors are of the order of 80%, depending on the nature of the load and its projected growth. |
| | Issue: | Cable or circuit breaker constraints. |
| | Approach: | Derate transformers to cable or circuit breaker ratings if they are a limited on transformer rating. |
| (d) | Medium Voltage Distribution |
| | Issue: | Conductor and cable size. |
| | Approach: | Examine planning and rating rules taking into account "economic ratings", thermal ratings, security requirements, faults and current levels to determine minimum conductor size for each area. |
| (e) | Medium Voltage Switchgear |
| | Issue: | Number of size and type. |
| | Approach: | Determine need for switch in relation to system reliability and system rating standards. Where excessive reduce, delete or modify. |
| (f) | Voltage Control Devices |
| | Issue: | Degree of control. |
| | | Manual and on load tap changes. |
| | | Line regulators, line drop compensation. |
| | | Reactive compensation. |
| | Approach: | Check requirements and optimise as necessary. |
| (g) | Distribution Transformers (pole, kiosk, ground types) |
| | Issue: | Transformer rating. |
| | Approach: | Determine average or typical power utilisation factors based on annual statistics. Nature of load and projected growth should be taken into account. Optimise if ratings excessive for loads. |
| (h) | Low Voltage Reticulation Lines and Cables |
| | Issue: | Where there is undergrounding, whether this is appropriate. |
| | Approach: | Underground reticulation should be taken as appropriate if it is required for commercial, technical, safety or legal reasons and if a prudent commercial operator were to replicate the system, they would use undergrounding. Commercial reasons may include situations where customers are prepared to accept higher tariffs as a consequence of underground reticulation. If underground portions of the system cannot be justified on any of these grounds then the optimisation process should lead to them being replaced by equivalent overhead reticulation. |
| | Issue: | Conductor and cable size. |
| | Approach: | Determine minimum conductor and cable size using standardised approach. |
| | Issue: | Services, meters and load control equipment. |
| | Approach: | Standardise to minimum requirements by part of the system and customer load. |
| (i) | System Control |
| | Issue: | Degree of sophistication of SCADA equipment. |
| | Approach: | Determine whether equipment is appropriate for size and complexity of distribution network. |
| | Issue: | Need for load control system and degree of sophistication. |
| | Approach: | Determine whether equipment is appropriate for size and complexity of distribution network. |