A 25kVA, 1? xformer, 2200V to 220V has a primary resistance of 1? & a secondary resistance of 0.01?. Find the equiv. secondary resistance & the full-load efficiency at 0.8 p.f. if the iron loss of the xformer is 80% of the full-load copper loss.
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Example 2.30: A 500 kVA, 600/400V, single-phase transformer has primary and secondary winding resistances of 0.42 ohm and 0.0011 ohm, respectively. The primary and secondary voltages are 600V and 400V, respectively. The iron loss is 2.9 kW. Calculate the efficiency at half full load at a power factor of 0.8 lagging. Solution: Transformer rating = 500 kVA Primary resistance, R1 = 0.42 ohm Secondary resistance, R2 = 0.0011 ohm Primary voltage, E1 = 600V Secondary voltage, E2 = 400V Iron losses, P = 2.9 kW Fraction of the load, x = 0.5 Load power factor, cosĪø = 0.8 lagging Primary resistance referred to secondary: R' = K * R1 = 30.42 = 0.00154 Total resistance referred to secondary: R = R1 + R' = 0.0011 + 0.00154 = 0.00264 Copper losses at full load: P1R = (1250000 * 0.00264) = 4125W = 4.125 kW Apparent power, S = 100 VA Real power, P = S * cosĪø = 0.5 * 500 * 0.8 = 200 W Efficiency, Ī· = (P / (P + P1R + P2)) * 100 = (200 / (200 + 4.125 + 2.9)) * 100 = 4.47%
Lien L.
6- A 100kVA, 1000/10000V, 50Hz transformer has an iron loss of 1200W. the copper loss with 6A in the high-voltage winding is 500W. calculate the efficiencies at i) 25%; ii) 50% and iii) 100% of normal load for power factors a/1.0 and b/ 0.8, the output terminals voltage being maintained at 10000V. find also the load for maximum efficiency at both power factors. [a/ i) 95.100%; ii) 97.000% iii) 97.470%, 93kVA b/ i) 93.950% ii) 96.270% iii) 96.860% ; 93kVA] 7- A 5kVA, 220/110V, 50Hz 1-phase transformer has Req1 and Xeq1 of 0.968Ī© and 1.963Ī© respectively. Draw kapp regulation diagram referred to the secondary then use the diagram to calculate the voltage regulation down at full-load and power factor: a- 0.3 lag b- 1 c- 0.3 lead 8- A 1-phase transformer, 15 kVA, 660/250V, 50Hz, Req1= 2.7879Ī© and Xeq1 = 5.5757Ī©. the secondary voltage at full load and k power factor 260V. draw the Kapp regulation diagram (referred to secondary) then use the graph to calculate the regulation up at full load and power factor of 0.5 lag and 0.4 lead. Find the value of k. 9- The impedance of two single phase transformers referred to secondary are (0.5+j3) and (0.6+j10)Ī©. Calculate the power supplied by each transformer if the two transformers connected inparallel to supply a load of 100W at power factor lag.
Adi S.
Real transformers are not 100 percent efficient. Write an expression for transformer efficiency in percent using power. A step-down transformer that has an efficiency of 92.5 percent is used to obtain $28.0 \mathrm{V}$ from a $125-\mathrm{V}$ household voltage. The current in the secondary circuit is 25.0 A. What is the current in the primary circuit?
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