Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Chapter 21, Problem 7RQ
To determine
The conductor sizes, overload heater size, fuse size, minimum NEMA and IEC starter sizes, and the upper and lower range of starting current for this motor.
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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
Find the value of the currents I1 and 12.
100 ohm
5V
5V
100 ohm
12
O a. 1=-0.3A, 12=-0.1A
O b. 11=0.3A, 12=0.1A
Oc. 11=0.05A, 12=0.1A
O d. 11=0.1A, 12=0.2A
A 3-phase, 50 Hz, 3000 V motor develops 600 H.P. (447·6 kW), the power factor being 0·75 lagging andthe efficiency 0·93. A bank of capacitors is connected in delta across the supply terminals and powerfactor raised to 0·95 lagging. Each of the capacitance units is built of five similar 600-V capacitors.Determine the capacitance of each capacitor.
Chapter 21 Solutions
Electrical Transformers and Rotating Machines
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- 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.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_forwardA large motor has a full load current rating of 425 amperes. Current transformers with a ratio of 600:5 are used to reduce the current to the overload heaters. What should be the full load current rating of the overload heaters?arrow_forward
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- A shunt generator has a full-load current of 100A at 220V. Stray losses are 1kW and shunt field current is 12 A. The armature resistance including brushes is 0.055 ohms. Calculate the efficiency of the machine.arrow_forwardEx: A single phase 50 KVA transformer has primary voltage of 6600 v and secondary voltage of 254 v and has 32 secondary turns. Calculate the number of primary turns and primary and secondary currents.arrow_forwardExample 7-3. A 460-V, 25-hp. 60-Hz, four-pole, Y-connected induction motor has the following impedances in ohms per phase referred to the stator circuit: - 0.641n X,-1.106 N R2 - 0.332 N X2 = 0.464 XM - 26.3 N The total rotational losses are 1100 W and are assumed to be constant. The core loss is lumped in with the rotational losses. For a rotor slip of 2.2 percent at the rated voltage and rated frequency, find the motor's (a) Speed (b) Stator current (c) Povwer factor (d) Peony and Pout (e) Tiad and Toad Efficiencyarrow_forward
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