Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Chapter 2, Problem 7SQ
To determine
Choose the correct option that represents the achievement of an automatic operation for the manual starters.
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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.
A 5-hp 230-volt shunt motor takes 18 amp when operating at full-load. The shunt filed resistance is 115 ohms and the armature resistance is 0.25 ohms. Calculate the value of the starter resistor if the armature current is limited to 1.5 times the rated value of the starting instant. (Assume a 3-volts brush contact).
A 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.
Chapter 2 Solutions
Electric Motor Control
Ch. 2 - If the contacts on a manual starter cannot be...Ch. 2 - If the handle of an installed motor starter is in...Ch. 2 - How may an automatic operation be achieved when a...Ch. 2 - What does the term trip-free mean as it relates to...Ch. 2 - Prob. 5SQCh. 2 - Prob. 6SQCh. 2 - Prob. 7SQCh. 2 - Prob. 8SQCh. 2 - Select the best answer for each of the following....Ch. 2 - Select the best answer for each of the following....
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- Q51 Which NEC table is used to determine the full-load current of a torque motor? Select one: A. NEC TABLE 430.6(B) B. NEC TABLE 430.7(B) C. NEC TABLE 430.24 D. NEC TABLE 430.22arrow_forward6.a. When you're taking a PM motor apart you should exercise special care not to damage theA. end bells.B. commutator.C. permanent magnets.D. brush holders.6.b. A PM field servo motor may be equipped with a resolver that is used toA. excite the armature windings.B. create a voltage that increases with velocity.C. prevent the brushes from sparking.D. feed back position information.arrow_forwardI will be grateful thanks a lot. An automatic starter circuit is to be designed for a shunt motor rated at 20 hp, 240 V, and 75 A. The armature resistance of the motor is 0.12 W, and the shunt field resistance is 40 W. The motor is to start with no more than 250 percent of its rated armature current, and as soon as the current falls to rated value, a starting resistor stage is to be cut out. How many stages of starting resistance are needed, and how big should each one be?arrow_forward
- Mark the correct statements about armature controlled DC motors given below. (You can select multiple statements) 口 A) The armature voltage and the output speed is directly coupled B) The armature voltage and the output torque is directly coupled 口 C) The armature current and the output speed is directly coupled D) The armature current and the output torque is directly coupledarrow_forwardWhat is the necessity of 3point starter? What is starter ?arrow_forwardDraw an electrical diagram for a Star Delta starter with a forward rotation and reverse rotation switch.arrow_forward
- 15/ What is the name of the speed control by varying the field current of the DC motor? a. Flux control method b. None of the above c. Armature control method d. Voltage control methodarrow_forwardQ/ When a series dc motor is operated without a load, which of the following conditions occurs? * Ans 1- The armature draws excessive current 2- The armature speeds out of control 3- The armature will not turn 4-The voltage requirement increasesarrow_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_forward
- When a d-c motor is tested by the electrical input method, the field rheostat is adjusted to giveA. rated speed at full load.B. rated speed at no load.C. maximum speed at minimum load.D. minimum speed at maximum load. Note: I have doubts if it is the letter A or the letter B, can you help me in this question, thanks.arrow_forward22.a. One common type of electronic circuit component that is used to control the voltage and current to aDC motor is theA. silicon-controlled rectifier.B. resistor.C. capacitor.D. diode.22.b. Which one of the following types of motors can be powered with either AC or DC electricity?A. Servo motorB. Pancake motorC. Universal motorD. Shunt-wound motorarrow_forwardSelect suitable three-phase motors for various given application giving details of ratings, starter types and control gear requirements. I. A motor is required for an industrial air-extraction system, and you are asked to give advice on the selection of a suitable motor. The fan speed should be constant between 0 rpm and 2900 rpm, say two speeds. II. III. The maximum torque to nominal torque ratio should be no more than 4.0, the torque rating should be at around 100Nm. The power factor should not be lower than 0.8 for power factor correction reasons. A 100A miniature circuit breaker (MCB) will be used to protect the motor. The enclosure should meet IP55 standard, and the feet are to be bolted to the stator and made of cast iron. From the ABB motors data sheet link attached select a suitable motor, giving the motor type number. A motor is also required for an industrial wood chipper. Justify the selection of both motors by explaining your choice based on the information provided and…arrow_forward
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