Delmar's Standard Textbook Of Electricity
7th Edition
ISBN: 9781337900348
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 34, Problem 2PA
Refer to the preceding Practical Application. When the 30-HP motor is replaced with the 50-HP, will the existing motor starter have to be replaced? If so, what size starter should be selected? A NEMA size 3 starter was used for the 30-HP motor.
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A direct current motor is connected to a 250-volt DC supply. The armature has a current draw of 165 amperes when operating at full load. You have been assigned the task of connecting two resistors in the armature circuit to provide speed control for the motor. When both resistors are connected in the circuit, the armature current is to be limited to 50% of the full-load current draw. When only one resistor is connected in the circuit, the armature current is to be limited to 85% of full-load current. Determine the ohmic value and min-imum power rating of each resistor.
Explain how DOL magnetic starter works step by step with diagram and pictures.
QUESTION 12
The proper way to determine the required over-current protection is to:
determine the FLA based on the nameplate.
Use the standard rule of thumb that the over-current protection shall be 7 to 10x the locked rotor amps.
determine the watts by converting the HP rating on the nameplate to watts.
to determine the FLC by looking up the value in the appropriate table(s) in the NEC as they relate to the horsepower of the motor.
Chapter 34 Solutions
Delmar's Standard Textbook Of Electricity
Ch. 34 - Which NEC table is used to determine the full...Ch. 34 - A 5-HP single-phase motor is connected to 208...Ch. 34 - A 10-HP single-phase motor is connected to 240...Ch. 34 - A 75-HP synchronous motor is connected to a...Ch. 34 - A squirrel-cage induction motor has a nameplate...Ch. 34 - A squirrel-cage motor has a nameplate current...Ch. 34 - A 100-HP three-phase squirrel-cage induction motor...Ch. 34 - A 60-HP synchronous motor is connected to 240...Ch. 34 - Prob. 9RQCh. 34 - Both the motors and the feeder in Question 9 are...
Ch. 34 - A 30-HP squirrel-cage induction motor is connected...Ch. 34 - Refer to the preceding Practical Application. When...Ch. 34 - Refer to the first Practical Application in this...Ch. 34 - A 10-HP single-phase motor is connected to 240...Ch. 34 - A 500-HP synchronous motor is connected to 2300...Ch. 34 - A 30-HP three-phase squirrel-cage induction motor...Ch. 34 - A 75-HP synchronous motor is connected to a...Ch. 34 - Prob. 5PPCh. 34 - A 350-HP squirrel-cage induction motor is...Ch. 34 - Three squirrel-cage motors are connected to a...
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- The armature resistance of 220 V D.C. shunt motor is 0.4 Ω. The full load current is 26 Amp. The ratio of maximum current at starting to full load current is 1.538. Calculate the number of resistance sections and value of each resistance sections to be used in this starter.arrow_forwardDetermine the value of starting resistance of the 7.5 kW, 220 V shunt motor so thatthe current will not exceed 2 times of the motors full load rating. The armature andfield resistance is 0.24 and 101 ohms respectively. The motor efficiency is 95%arrow_forward"A 50 hp, 220 V shunt motor operating at 1200 rpm draws a line current of 94 A when operating at rated conditions. A 1.8 ohm resistor inserted in series with the armature causes the speed to drop to 840 rpm. The respective field circuit resistance and armature circuit resistance are 55 ohm and 0.2 ohm. What will be the new armature current(in Amp)?" 3.15 39.3 90 None is correctarrow_forward
- Figure 24(1.) Compute the efficiency of the motor, if windage and friction losses neglected, for the circuit Q25. i diagram shown Figure 25(i), R 0.750 60A +. R-1250 M 250V Figure 25(i) ii Also calculate armature current. END OF QUESTION PAPER----- Page 4 of 4 Activatarrow_forwardA starting resistor will most likely be needed in a/ an A. line starter.B. reduced-voltage starter.C. full-voltage starter. D. across-the-line starter.arrow_forwardFind the number of resistance sections and the resistance of each section of a starter for a 3.7 kW, 230 V, dC series motor from the following data:-Starting current varies from 1 to 1.5 times full load current Full load efficiency = 85% Motor circuit resistance 1.4 ohm Assume flux increases by 10% as the current rises from 1 to 1.5 times the rated full load current.arrow_forward
- If the starter resistance is 1.9 ohms, what current does the motor take at the instant of starting in a shunt motor rated 25-hp. 230-volt, 600-rpm having armature and a field resistance of 0.275 ohm and 160 ohms, respectively. (Assume a 2-volt brush drop)arrow_forwardQuestion 4 A 55 hp, 440 V, 400 rpm DC shunt motor draws 107 A when operating at rated conditions. The motor has an armature-circuit resistance of 100 m2 and a total field-circuit resistance of 55 2. Draw a schematic of the motor in the space below showing all known quantities (resistances, currents, voltages and load). Show only symbols for unknowns. Determine the following for rated operation What is the motor armature current? (a) 99 A (b) 102 A (c) 107 A (d) 110 A (e) 115 A (i) What is the CEMF developed in the armature? (a) 449.9 V (b) 440.0 V (c) 430.1 V (d) 429.3 V (e) 428.5 V (i) What is the total windings (copper) losses in the motor? (a) 4842.5 W (b) 4500.1 W (c) 3520 0 W (d) 1145 W (e) 980.1 Warrow_forwardInstruction: Design a dc motor reverse and forward circuit using a single switch. Main Components: DC Motor Toggle Switch DC Power Supply/ Battery Additional Components: (Please search the internet for additional components)arrow_forward
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