Transformers

Problem 616: The low side of a certain welding transformer has 2 turns and delivers 300 A. If the high voltage side has 30 turns, how much current flows through it?

Problem 617: A single-phase transformer is rated 4,160 V primary and 250 V secondary. It has 1,500 turns in the primary and a voltage regulation of 8%. What should be the number of turns in the secondary winding?

Problem 620: A 10 kVA, 2400/240-V single-phase transformer has the following resistances and reactances: \(r_1=3\,\Omega\), \(x_1=15\,\Omega\), \(r_2=0.03\,\Omega\), \(x_2=0.150\,\Omega\). Find the primary voltage required to produce 240 V at the secondary terminals at full load, when the power factor is 0.8 lagging.

Problem 621: A 10-kVA, 2,000/400 V, single-phase distribution transformer has a primary and secondary winding impedances of 5.0 + j10 and 0.2 + j0.45 ohms, respectively. Calculate the voltage across the secondary terminals at full load, 80% power factor lagging, when the primary is supplied with 2,000 volts?

Problem 622: A single-phase transformer rated 75 kVA, 8000 volts primary 240 volts secondary, is given the short circuit test. With the secondary terminals short-circuited, 440 volts (60 Hz) is impressed on the primary, which then draws rated current and 1125 watts. Solve for the percentage impedance of the transformer.

Problem 623: A short circuit test was performed upon a 10-kVA, 2300/230 volt transformer with the following results: \(E_{sc}\) = 137 volts; \(P_{sc}\) = 192 W; \(I_{sc}\) = 4.34 A. Calculate in primary terms the reactance of the transformer.

Problem 624: A single-phase, 25 kVA, 4800/240 volt transformer was given a short circuit tests: With the secondary terminals short-circuited, 93.75 volts was applied on the primary so that the ammeter reads rated current and the wattmeter reads 162.74 watts, all on the primary side. Solve for the percentage resistance of the transformer.

Problem 625: The following data were obtained when a short circuit test was performed upon a 100 kVA, 2400/240 volts distribution transformer: \(E_{sc}\) = 72 volts; \(I_{sc}\) = 41.6 A; \(P_{sc}\) = 1,180 W. All instruments are on the high side during the short circuit test. Calculate the equivalent resistance and reactance of the transformer.

Problem 627: A short circuit test was performed on a 20 kVA, 2000/200 V single-phase transformer. With the secondary winding short circuited, full load current flows in the primary winding with 100 V applied on it. The wattmeter connected in the primary read 300 W. Determine the terminal voltage on full load unity pf.

Problem 628: The following data were obtained when a short circuit test was performed upon a 100 kVA, 2400/240 volts distribution transformer: \(E_{sc}\) = 72 volts; \(I_{sc}\) = 41.6 A; \(P_{sc}\) = 1,180 W. All instruments are on the high side during the short circuit test. Calculate the percent regulation at a power factor of 0.75 lagging.

Problem 629: A 200-kVA transformer with impedance of 5% and the power factor of the load is 85%. The primary voltage is 6,000 volts while the copper loss is 5 kW. Find the percentage regulation.

Problem 630: A 150 kVA, three-phase transformer supplies 100 kVA at 50% lagging power factor. The transformer's winding impedance is 2% resistance and 5% reactance, based on 150 kVA. Determine the voltage regulation of the transformer at this load. Assume 100% voltage.

Problem 631: A short circuit test was performed upon a 10-kVA, 2300/230 volt transformer with the following results: \(E_{sc}\) = 137 volts; \(P_{sc}\) = 192 W; \(I_{sc}\) = 4.34 A. Calculate the percent regulation at a lagging power factor of 0.707.

Problem 632: A 100 kVA, 6600/600 V, 60 Hz single-phase transformer operating at rated condition has the following losses: hysteresis loss = 520 W; eddy current loss = 370 W and copper loss = 2000 W. If this transformer is to be used on a 50 Hz system, determine its new kVA rating. Assume the same total losses and maximum core flux.

Problem 633: When 120 V, 60 Hz is applied to the primary winding of a transformer, the core loss is 240 W. When 50 V, 25 Hz is applied the core loss is 50 W. Determine the core loss when 230 V, 50 Hz is applied to the primary winding.

Problem 634: The eddy current and hysteresis losses of a 4,400-V, 60-Hz single-phase distribution transformer are 280 and 560 watts, respectively. Determine the core loss when the transformer is connected across a 4,600-volt, 50-Hz source.

Problem 635: In a 400 V, 50 c/s transformer, the total iron loss is 2500 W. When the supplied p.d. is 220 V at 25 c/s, the corresponding loss is 850 W. Calculate the eddy current loss at normal frequency and p.d.

Problem 636: When a 220 V, 60 Hz is impressed on a certain transformer at no load, the total core loss is 200 W. When the frequency of the impressed voltage is changed to 25 Hz and the magnitude of the voltage is made such as to maintain the same maximum flux density as before, the core loss falls to 75 W. Calculate the hysteresis losses at 60 Hz.

Problem 637: A 100-kVA, 4160/230 V, 60 Hz single-phase transformer has percentage impedance of 1.75 + j 4.0. Its efficiency when operating at rated conditions at 75% pf lagging is 97%. Determine the efficiency, if the transformer is loaded at rated load and voltage but at 50 Hz. Assume the ratio of eddy current losses to hysteresis losses at 60 Hz to be 2.5.

Problem 638: The full load copper loss of a 75 kVA single-phase transformer is thrice the iron losses. At half load unity pf, the efficiency is 97%. Determine the full load efficiency at 0.8 pf lagging.