Electrical Machine-I: Three-phase Transformer Lecture Insights
Delve into the world of electrical machines with a focus on three-phase transformers. Explore topics such as Vab Open Delta Connection, balance of secondary three-phase voltage, and the advantages of open delta connections in transformer setups. Understand the impact of removing a transformer in a V-V connection scenario through a detailed example. Discover the significance of power reduction, utilization factor, and load distribution in transformer configurations.
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Presentation Transcript
Subject: Electrical Machine-I This Lecture contains Three-phase Transformer
Vab Open delta (VV) connection = = = o 0 V V Van an o 120 V V bn o 240 V V cn Vbc Vbn Vcn Vca + + = 0 V V V ab bc ca
Vab Open delta Connection + + = 0 V V V ab bc ca = + ( ) V V V ca ab bc Vbc Vca Provide balance secondary three phase voltage
Open delta Connection Vab Ia Van Ia Iba Vcb Vbc Ic Ib Ibc Vbn Ib Vcn Ic Ia lags Vab by (30+ )=>Ia=Ip ( +30) Ic leads Vcb by (30- )=>Ic=Ip ( -30) = + + + + + cos(30 ) cos(30 ) sin(30 ) sin(30 ) S V I = V I jV I jV I p P 2 V I p P + p P p P cos cos30 2 sin cos30 S j V I p P p P = + = 3 cos 3 sin 3 S V I j V I P P V I p P p P
Features Svv= 3VpIp S = 3VlIl=3VpIp Svv/S =0.577 Power reduced in open delta connection significantly Utilization factor= 3VpIp/ 2VpIp=0.866 Transformer is under utilized by 13.3%. Power is unbalanced in both transformer if power factor is not unity. Advantages: If one of the transformer spoiled in three-phase; few load can be till supplied by open delta connection In new villages with lower load three phase connection can be provided using two winding transformer and in future demand additional one transformer can be added to meet future load demand
Example A - 2300/230-V transformer supplies a load of 40kVA. If one transformer is removed , find for the resulting V-V connection (i)KVA load carried by each load (ii)percent of transformer (iii) Total KVA rating of the V-V bank (iv) ratio of the VV bank to - bank transformer rating (v) percent increase in load on each transformer when bank is connected to VV Bank bank Consisting of three 20kVA, rated load carried by each
