Transformer Problems c4039

TRANSFORMERS

Problems On Emf Equation 1. A 6600/600V, 50Hz single phase transformer has a maximum flux density of 1.35T in its core. If the net cross sectional area of iron core is 200cm2. Calculate the no. of turns in the primary and secondary windings of the transformer. 2. A single phase transformer has 500 turns on Primary and 1000 turns on secondary . The emf per turn is 0.2V. calculate (i) emf induced in the primary and secondary. (ii) the net cross-sectional area of the core for a maximum flux density of 0.045T. (iii) kVA rating of a transformer if the current in primary at full load is 10A the frequency is 50Hz. 3. A 80 kVA, 3200/400V transformer has 111 turns on secondary. Calculate (i) no. of turns in primary winding, (ii) Secondary current, (iii) cross sectional area of the core, if the max. flux density is 1.2T. 4. The design requirement of a 11000/415V 50Hz, single phase core type transformer are approximately emf/turn 15V, max. flux density 1.5T. find a suitable no. of primary and secondary turns and the net cross sectional area of the core. 5. The core of a 100kVA, 11000/550V, 50Hz, single phase core type transformer has a cross-section of 20cmx20cm. Find (i) the no. of HV and LV turns, (ii) the emf per turn if the max. flux density is not to exceed 1.3T. Assume a stacking factor of 0.9. What will happen if its primary voltage is increased by 10% on no-load. 6. The core of a three phase 50Hz 11000/550V delta /star, 300kVA , core type transformer operates with the flux of 0.05Wb. Find (i) no. of HV and LV turns per phase, (ii) emf per turn, (iii) full load HV and LV phase currents. 7. A single phase transformer has the following data: peak flux density in the core= 1.4T; net core area =0.012m2, current density in conductors= 2.5MA/m2, conductor dia.= 2.0mm, Primary voltage= 230V, 50Hz. Calculate the kVA rating of the transformer and the no. of turns on the primary winding. 8. A 6300/210V, 50Hz single phase transformer has an emf per turn of 9V and max. flux density of 1.2T. Find the no.of HV and LV turns and the net cross sectional area of the core.

Problems On Transformer On No Load 1. A 3300/240VSingle Phase Transformer is supplied at 240V on no lo on LV side. It takes no load current of 2A and the power of 60W. The resistance of the LV winding is 0.8Ω. Find (i) The power factor on no load (ii) Active current (iii) Magnetising current (iv) copper loss in the primary winding(LV winding) (v) Core loss 2. A 1Φ transformer takes an input of 350VA at no load and at rated voltage of 230V. The core loss is 110W. Find (i) The iron loss component of no-load current (ii) Magnetizing component of no load current. 3. A 10kVA 1Φ transformer has a turn ratio of 300/23. The primary is connected to a 1500V 60Hz supply. Find the secondary volts on open circuit and the approximate value of the currents in the two windings on full load. Find also the maximum value of the flux. 4. A 100kVA, 3300/400V 50Hz, 1Φ transformer has 110 turns on the secondary. Calculate the approximate values of the primary and secondary full load currents, the maximum value of flux in the core and the no. of primary turns. 5. The no. of turns on the primary and secondary windings of a 1Φ transformer are 350 and 35 respectively. If the primary is connected to a 2.2kV, 50Hz supply. Determine the secondary voltage on no-load. 6. A 100kVA 2400/240V, 50Hz 1Φ transformer has an exciting current of 0.64A and a core loss of 700W, when its high voltage side is energized at rated voltage and frequency. Determine the two components of the exciting current.

Problems On Transformer On Load 1. A single phase transformer has 1000 turns on the primary and 200 turns on the secondary. The no load current is 3A at a power factor 0.2 lagging when the secondary current is 280A at a power factor of 0.8 lagging. Calculate the primary current and power factor. Assume the voltage drop in the windings to be negligible. 2. A single phase transformer with a ratio of 6600/400V takes a no load current of 0.7A at a power factor of 0.24. If the secondary supplies a current of 120A at 0.8 lagging power factor. Calculate the primary current and power factor.

3. A single phase transformer takes 10A on no load at a pf of 0.1. The turns ratio is 4:1. If a load is supplied by the secondary at 200A and a pf of 0.8. Find the primary current and the power factor. 4. A 2200/200V transformer takes 1A on HT side on no load at a pf of 0.385lagging. Calculate iron losses. If a load of 50A at a power factor of 0.8 lagging is taken from the secondary of the transformer, calculate the actual primary current and its power factor. 5. A 2200/220V, 50Hz 1Φ transformer has exciting current of 0.6A and a core loss of 361W, when its hv side is energized at rated voltage. Calculate the two components of the exciting current. If the transformer supplies a load current of 60A at 0.8pf lag on its lv side then calculate the primary current and its power factor. Ignore the leakage impedance drops. 6. An ideal transformer has three windings: 100 turns on primary winding P, 160 turns on secondary winding and 60 turns on tertiary winding T as shown on fig below. Winding S feeds 10A to resistive load whereas pure capacitance load across winding takes 20A. (a)Calculate the current in the primary winding and its pf in case transformer magnetizing current is neglected. (b) with the polarity markings on P as shown, mark the polarities on windings S and T.

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7. A 400/100 V 1Φ, ideal transformer is connected to a load of 8+6j and its primary is fed from 400V,50Hz source. Calculate the current, power factor and power on both primary and secondary sides. Neglect magnetizing current. 8.