P - Transmission

AECOMPuketoi Wind Farm Technical Report124.5 Hazardous SubstancesThe following electrical equipment makes use of hazardous substances:- Each of the two power transformers will contain approximately 50,000 litres of di-electric insulating oil- The Outdoor Current Transformers (CTs) and Voltage Transformers ( VTs) will contain a minimal amount ofinsulating oil- The 220 kV and 33 kV switchgear will contain Sulfur Hexafluoride (SF 6 ) gas, which is a greenhouse gas.The management and containment of the transformer oil is explained in the next section of this report.The substation layout is depicted in drawings MRP-PKT-4303, MRP-PKT-4305 and MRP-PKT-4306.4.6 Oil Drainage and Interception System4.6.1 DescriptionTo manage potential spills of oil, both transformers will be placed within separate bunded areas designed tocontain the total volume of all transformer oil and stormwater generated from an extreme rainfall event. The totalcatchment area for the bunding is approximately 300m 2 . Each transformer bund will have a sump connected to oilcatch tanks via a gravity fed pipe. The outlet from the catch tanks is connected to an oil plate separator to removeany oil that may be contained in storm water. Any oil separated out can then be removed from site for appropriatedisposal. If there are any issues with high ground water level on site, the catch tanks may require holding downarrangements or ballast to prevent tanks from emerging out of the ground when empty.4.6.2 Oil Volume and Stormwater CriteriaThe following was taken into consideration in the oil plate separator with catch (storage) tank system conceptdesign:- The capacity of the sump tank required for a plate separator system is typically based on a volumeequivalent to the greater of the largest oil filled equipment (50,000 litre of oil in the transformer) OR a 1 in 10year rainfall event of 6 hours duration falling into all of the transformer bunded areas- Based on NIWA high intensity rainfall system data for Makuri, a 1 in 10 year rainfall event of 6 hours durationcorresponds with 72.8mm of rain with a total bunded area of 300m 2 , a volume of approximately 22m 3 wouldbe required for the rainfall event.Therefore, the sump volume required for the plate separator system is 50m 3 (being the volume of oil in onetransformer).4.6.3 OperationFor an oil plate separator system, the oil that is separated goes to a separator waste oil tank which will have ahigh level alarm with SCADA connections to the main control centre. Maintenance personnel will be dispatched tosite for removal of oil. If the separator waste oil tank were to fill completely causing the oil separator to stopprocessing the contents of the storage tank, the system (sump and bunded areas) could hold approximately230m 3 before overflowing the bund walls into the environment. This is more than the volume of oil held inside bothtransformers plus the volume of a 1 in 100 year storm rainfall over 72 hours (308.3mm of rainfall).The separator waste oil tank high level is alarmed to SCADA and 6 hours is considered sufficient time for themaintenance contractor to respond on site.4.6.4 Transformer Bund Area & Wall HeightThe bund surrounding the transformer is to be sufficient to contain 110% of oil volume of the transformer, and besufficiently large around the transformer to include radiators, and allow cubicle doors to be opened. Allowanceshould be made for rainfall should the outlet valve be inadvertently left closed.Assuming a 150m 2 bund area,- 110% of oil volume (55,000 litres) corresponds to a height of 367mm- 1% Annual Expected Precipitation (AEP) corresponds to 218.9mm of rain for 24 hour rainfall27 July 2011