3 PHASE TO 5 PHASE TRANSFORMER WHY 5 PHASE OVER 3 PHASE Multiphase machine has a greater fault tolerance compared to its 3 phase counterparts if one phase of the 3 phase machine becomes open circuited so single phasing occurs . It may continue to run, but will require external means for starting and must be massively derated. If one phase of multiphase machine becomes open circuited it will self start and will run with only minimal derating Another reason for multiphase variable speed drive is the possibility of reducing the required rating of the power electronics components for a given output power of the motor, when compared to a 3 phase motor. Utilization of multiphase motor drives also enables improvement in the noise characteristics when compared to three phase motor drives The stator excitation in a multiphase machine produces a field with a lower space-harmonic content, so that the efficiency is higher than in a three-phase machine. Reduction in stator joules loss achieved by increasing the number of phases beyond 3 No of phase - 5 6 9 12 15 18 Stator cu loss - 5.6 6.6 7.9 8.3 8.5 8.8 reduction (%) wrt 3 phase FACTS ABOUT TRANSFORMER It works on the principle of mutual induction It is a shell type of transformer Transformation ratio is unity Phase difference between each phase is 72 degrees CONSTRUCTION & WORKING This is special transformer connection scheme to obtain a balanced five-phase supply with the input as balanced three phases. The fixed voltage and fixed frequency available grid supply can be transformed to the fixed voltage and fixed frequency five-phase output supply. The output, however, may be made variable by inserting the autotransformer at the input side. The input and output supply can be arranged in the following manner: 1) input star, output star; 2) input star, output polygon; 3) input delta, output star; 4) Input delta, output polygon. Transformer Type 1 Parameter primary wdg Voltage Current Turns 240 2.1A 230 secondary wdg1 164 156 secondary secondary wdg 2 wdg3 206 58 196 56 Transformer Type 2 Parameter Voltage Current Turns primary wdg secondary wdg1 secondary wdg 2 240 2.1A 230 240 113 230 108 Transformer Design Calculations Iron Area Iron Area Ai (cm2) = Length x Width x (2.54)2 x stacking factor = 3 x 2 x 2.542 x 0.95 Ai = 36.77 cm2. Operating Flux Density of core = 1.2863 T Volts per Turn V/t = 4.44 x f x Bm x Ai x 10-4 V/t = 4.44 x 50 x 1.2863 x 36.77 x 10-4 V/t = 1.05. Primary Turns Np = Primary Voltage Volts per Turn Np = 240/1.05 Np ~ 230 Turns Secondary Turns Ns1 = Secondary Voltage Volts per Turn Ns1 = 240/1.05 Ns1 ~ 230 Turns Ns2 = Secondary Voltage Volts per Turn Ns2 = 113/1.05 Ns2 ~ 108 Turns Selection of Conductor Material: Electrolytic grade Copper conductor to be used. The operating current density is chosen to be 2.4 A/mm2. Cross Section Area of Conductor: Cross Section Area of Conductor = Operating current Current Density of material = 2.1/2.4 Area of Primary Conductor = 0.833 mm2. SECONDARY TURNS 0.24 (56) b4 (156) 0.68 b3 (156) c2 0.68 c1 a3 0.47 (108) 0.854 (196) c5 a4 c6 c3 0.24 b2 b1 a2 a1 (1) c4 b6 0.854 Voltage 206 58 Turns 196 56 252 turns V 220 36 261 turns 60 -Vx b5 PROTECTION OF TRANSFORMER EARTH FAULT OR LEAKAGE PROTECTION DIFFERENTIAL SYSTEMS COOLING OF TRANSFORMER AIR NATURAL COOLING – FOR SMALLER OUTPUT (5-10 KVA) AIR BLAST COOLING OIL NATURAL COOLING OIL NATURAL AIR FORCED COOLING 0.24 (56) b4 (156) 0.68 b3 (156) c2 0.68 c1 a3 0.47 (108) 0.854 (196) c5 a4 c6 c3 0.24 b2 b1 a2 a1 (1) c4 b6 0.854 Voltage 206 58 Turns 196 56 252 turns V 220 36 261 turns 60 -Vx b5