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report of protection - CHAPTER 3 TRANSFORMERS: There are 2...

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CHAPTER 3 TRANSFORMERS: There are 2 transformers used in the outdoor yard which can step down the feeder voltage 34.5Kv to 13.8Kv. This is given to the switchgear and then this 13.8kV is fed to the Substations inside the design site. The number of substations is divided into two cadres for the comparison of cost, reliability, easy construction and many other factors. Accordingly the three divisions are 1) A total of four substations 1 st for building A, 2 nd for building C, 3 rd for building B and 4 th for building D. Finally a total of 4 substations that could step down 13.8Kv to 480/240V. 2) A total of three substations 1 st for building A, 2 nd for building C and 3 rd for building B and D. Finally a total of 3 substations that could step down 13.8Kv to 480/240V. 3) A total of 8 substations one for each building to step down from 13.8kV to 480/240V 3.1 Different types of transformer [3] : There are different designs of transformers as stated below, (i) Overhead or pole mounted (single phase and three phases) – Pole mounted distribution transformers are specially designed for serving the residential overhead distribution loads. They are also suitable for light commercial loads, industrial lighting and diversified power applications. Single Phase: 50 to 833 kVA, Three phase: 30 to 300kVA, 34.5 kV and below 34.5kV and below Figure 3.1: Pole Mounted Transformers [4]
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(ii) Pad Mounted (single phase and three phases) – These types of transformers are designed for underground residential and commercial distribution systems where safety, reliability and aesthetics are especially important. Single Phase: 5 to 50 kVA, Three Phase: 45 to 5000kVA, 34.5kV and below 34.5kV and below Figure 3.2: Pad Mounted Transformers [4] As our design is confined to underground residential and commercial distribution system we prefer using pad mounted transformers. The three phase pad mounted transformers that we recommend are compact power centers for commercial or industrial applications. With proper design selection these can be located near or inside buildings for greater flexibility and savings. iii) For the transformers that are placed at the incoming feeder are of 10/11.2/12/5/14MVA. Therefore normal pad mounted cannot be used for these transformers. For ratings above 5000kVA we use unit substation. This has the capacity to withstand large amount of load and always used in outdoor application. The unit substation is shown as follows
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Figure 3.3: Unit Substation up to 200MVA 3.2 Classification of Transformers [1] Transformers are basically classified into three types a) Liquid immersed b) Dry Type c) Combination of dry and liquid immersed Types of Liquid Immersed i) Mineral oil, ii) Noninflammable or low inflammable liquids Types of dry type i) Ventilated ii) Cast coil iii) Totally enclosed non ventilated iv) Sealed gas filled v) Vacuum pressure impregnated The third type includes combination of liquid vapor and gas filled unit.
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This note was uploaded on 02/16/2011 for the course EE 472 taught by Professor Dr.ilyagrinberg during the Spring '10 term at SUNY Buffalo.

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report of protection - CHAPTER 3 TRANSFORMERS: There are 2...

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