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Distribution transformerPrimaryvoltageSecondaryvoltageCapacity(KVA)Construction Impedancerange3-11 380-440 25,40,63 Dry type 3-7%100,150,250 Dry type300,400,500 Oil/dry type630,750,1000 Oil type1250,1600 Oil type2000,2500 Oil type
Star delta connection
Star delta diagram
Star delta voltage current Line voltage on Primary side = √3 X Phase voltage onPrimary side. So Phase voltage on Primary side = Line voltage on Primaryside / √3 Transformation Ration (K) = Secondary Phase Voltage /Primary Phase Voltage Secondary Phase Voltage = K X Primary Phase Voltage. As Secondary in delta connected: Line voltage on Secondary side = Phase voltage onSecondary side. Secondary Phase Voltage = K X Primary Phase Voltage.=K X (Line voltage on Primary side / √3)
Advantages of StarDelta Connection The Y-D connection has no problem with thirdharmonic components fewer numbers of turns are required The neutral available on the primary can beearthed to avoid distortion. Neutral point allows both types of loads(single phase or three phases) to be met Large unbalanced loads can be handledsatisfactory
Disadvantages of star delta The secondary voltage is not in phase with theprimary If secondary of this transformer should beparalleled with secondary of another transformerwithout phase shift, there would be a problemApplication: commonly employed for power supplytransformers. Y connection on the HV side reduces insulationcosts the neutral point on the HV side can begrounded.
Tap changerIt is a device fitted inthe transformer,which is used tovary the voltagetransformationratio. Off load tapchanger Onloadtapchanger(OLTC)
BUSHINGTransformer Bushingsare specially designedelectrical terminals fortaking out windingends (leads) throughthe openings providedon the top cover orwall of the oftransformer tank andconnecting to theincoming andoutgoing lines.
CT =CURRENTTRANSFORMERTypical specification fora 11kV CT System voltage:11 KV Insulation level voltage (ILV) :12/28/75 kV Ratio: 200/1 - 1 - 0.577 A Core 1: 1A, metering, 15VA/class 1, ISF<10 Core 2: 5A, protection, 15VA/5P10 Short time rating:20 kA for 1second
PT=POTENTIALTRANSFORMERTypical specification fora 11 kV VT System voltage: 11 KV Insulation level voltage (ILV) : 12 /28/75 kV Number of phases: Three Vector Group: Star / Star Ratio: 11 kV/ 110 V Burden: 100 VA Accuracy: Class 0.5 Voltage Factor: 1.2 continuous and1.5 for 30 seconds With provision forfuse
Condition ForParallel Operation OfTransformers Same voltage and Turns Ratio (both primary andsecondary voltage rating is same) Same Percentage Impedance and X/R ratio Identical Position of Tap changer Same KVA ratings Same Phase angle shift (vector group are same) Same Frequency rating Same Polarity Same Phase sequence
Oil and winding temperature indicationDescription Setting, degree CFan start 85Fan stop 75Pump start 90Pump stop 80Oil temperature alarm 85Oil temperature trip 95Winding temperaturealarm100Winding temperature trip 110
Transformer protection– Overcurrent & Short circuit (51):The relay used is CDAG 51. Earth Fault (51N): The relay used is CAG 14. TransformerDifferential (87T): The relay used isDTH 31, 11/6.6KV transformers. WTI (49WTX/49WAX): protected against increasein winding temperature. The relay used is VAA 34. OTI (49TX/49AX): protected against increase in oiltemperature. The relay used is VAA 34. Buchholz (63TX/63AX): protected against internal.The relay used is VAA 34.
ACT FAST AND INITIATEFIRST बड़ा सोचो तेजी से सोचो व सबसे पहले सोचो िवचारो पर िकसी का एकािधकार नही होता. ---- धीरभाई अमबानी