Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Chapter 4, Problem 14RQ
To determine
The size of the overload heater that should be used to protect the motor.
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Understanding Motor Controls
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- A three-phase motor nameplate indicates a full load current of 362 amperes. The nameplate indicates that the heaters are to be sized for 125% of motor full load current. Current transformers with a ratio of 600:5 are used to reduce the motor current. Using the chart shown in Figure 4–7B, determine the size of overload heaters needed to protect this motor.arrow_forwardA 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 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
- Name three factors that determine the amount of induced voltage.arrow_forwardTwo 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_forwardWhat is one special problem with dry-type transformers used in unit substations?arrow_forward
- Power-consuming devices are wired in _____(series orparallel).arrow_forwardThe electrical energy consumed by a motor is inversely proportional to its efficiency.arrow_forwardAn air compressor is driven by a 7.5 HP electric motor with a speed of 1750 rpm with A-60 V-belts of length 73.65 in. The pitch diameter of the small pulley is 110mm and the larger pulley is 224mm. Service factor is 1.2. Determine the arc of contact of the (a) smaller pulley and (b) larger pulley in degrees. Express your answer in 3 decimal places.arrow_forward
- What is a special hazard encountered in large industrial transformers used in unit substations?arrow_forwardIf the load in question 7 was supplied by two autotransformers connected in open delta, what would be the minimum standard size transformers that could be used to supply this load?arrow_forwardSketch the following systems: one pipe, two-pipe direct return, and two-pipe reverse return.arrow_forward
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