Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 5, Problem 7RQ
A 480-volt three-phase load is rated at 34.5 kVA. It is to be supplied with variable three-phase voltage. Because the load is continuous, the transformers ratings are to be increased by 1.25% of the rated load. Three variable autotransformers are used to supply this load. Refer to Table 4-2 and determine the standard size of each transformer that should be used to make this connection.
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The following data were obtained on a 50 kVA 2400/120 V transformer:
Open circuit test, instruments on low voltage side:
Waltmeter reading = 396 Watts
Ammeter reading = 9.65 amperes
Voltmeter reading = 120 Volts
Short circuit test, instruments on high voltage side:
Waltmeter reading = 810 Watts
Ammeter reading = 20.8 amperes
Voltmeter reading = 92 Volts
Find the efficiency when rated kVA is delivered to a load having a power
factor of 0.8 lagging.The following data were obtained on a 50 kVA 2400/120 V transformer :
Open circuit test, instruments on low voltage side:
Waltmeter reading = 396 Watts
Ammeter reading = 9.65 amperes
Voltmeter reading = 120 Volts
Short circuit test, instruments on high voltage side:
Waltmeter reading = 810 Watts
Ammeter reading = 20.8 amperes
Voltmeter reading = 92 Volts
Find the efficiency when rated kVA is delivered to a load having a power
factor of 0.8 lagging.
The arc length voltage characteristic of a DC arc is given by the equation V=24+4L where
'V' is the arc voltage in volts and L' is the length in mm. The static volt-ampere
characteristic of the power source is approximated by a straight line with no load voltage of
80V and the short circuit current of 600A. Then the optimum arc length is
(mm).
A balanced star-connected load of (8 + j6) Q per phase is connected to a Balanced 3- phase 400-V supply. Find the line current, power factor, power
Chapter 5 Solutions
Electrical Transformers and Rotating Machines
Ch. 5 - An AC power source is connected across 325 turns...Ch. 5 - Is the transformer in question 1 a step-up or...Ch. 5 - Prob. 3RQCh. 5 - A load impedance of 52 Ω is connected to the...Ch. 5 - How much current will flow in the primary of the...Ch. 5 - Prob. 6RQCh. 5 - A 480-volt three-phase load is rated at 34.5 kVA....Ch. 5 - If the load in question 7 was supplied by two...Ch. 5 - Prob. 1PCh. 5 - Prob. 2P
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- Two transformers rated at 100 kVA each are connected in an open-delta connection. What is the total output power that can be supplied by this bank?arrow_forwardRefer to the transformer shown in Figure 5-13 to answer the following questions. What is the turns ratio of the winding between points B and E as compared to the winding between points D and E? Figure 5-13 Autotransformer practice problems.arrow_forwardA 10 kVA transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 480 volts. The transformer is connected to a circuit protected by a 100 ampere circuit breaker. The secondary is protected by a 25-ampere fuse. Does the primary require separate overcurrent protection?arrow_forward
- Refer to the transformer shown in Figure 5-13 to answer the following questions. The transformer shown in Figure 5-13 is supplying 325 volt amperes to a load. The primary voltage is 240 volts. What is the primary current? Figure 5-13 Autotransformer practice problems.arrow_forwardName three factors that determine the amount of induced voltage.arrow_forwardQuestion 2 Beli vifth Slack side Motor (imprut) Tight side Beli thickpess\ Centre distance Figure 2 Figure 2 shows an open flat belt drive connected to a motor and a pulley. The motor transmits 20 kw to the connect pulley of 450 mm diameter and is rotating at 850 r/min to a second pulley rotating at 400 r/min. The distance between pulley centres is approximately 2 m. The belt is 6 mm thick and has a density of 970 kg/m. The maximum stress in the belt is not to exceed 2,7 MPa. The coefficient of friction for both pulleys is 0,3. Determine: 2.1. The diameter of the second pulley. 2.2. The length of the belt. 3.3. The width of the belt taking centrifugal tension into account.arrow_forward
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- What is the total current from the voltage source in Figure 6-64 for each switch position? Figure 6-64 15 V + +₁₁ +₁ R₁ 1.0 ΚΩ +₁ R₂ 1.8 ΚΩ www +₁₁ R3 2.2 ΚΩ www R4 2.7 ΚΩarrow_forwardIn a given DC motor, the output power is 45 HP, and the copper losses are 2.005 KW. If the rotational losses is one tenth of the output power, find the converted power and the efficiency of the motor. Select one: O a. None O b. Pcony = 33.57 KW and % efficiency = 89.2 % %3D O C. Pcony = 39 KW and % efficiency = 75.8 % O d. Peony = 36.927 KW and % efficiency = 86.2 %. !! n dunlay I AP-wound armature whicharrow_forwardHow many transformers are needed to make an open-delta connection?arrow_forward
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