Horsepower

Anand

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maintenance

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April 15th 2007

ircle

NEWSLETTER FOR MAINTENANCE COMMUNITY Good morning dear colleagues,

Starting this week maintenancecircle will be presenting information on various aspects related to factory and maintenance. It is our conviction that knowledge should be shared and learned. This will help us to be productive and efficient in discharging our responsibilities. We expect our equally passionate colleagues to contribute to this newsletter by sharing their information, experience and more. Welcome aboard! Word for the day: Horsepower (HP)

This is one of the most commonly used technical words in almost every walk of life, definitely in a factory by all people. It indicates measurement of “power” in various senses and measures Rate of doing work. Let us take a look at what horsepower actually means. The term “Horsepower” was invented by James Watt (1736-1819) who is famous for his work on improving performance of steam engines. During his time, horses were used for various activities and Watt determined that a horse could turn an oil mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius. Circumference of a circle = 2π x Radius = 2π x 12’ = 75.4 feet. Therefore, Horse traveled a distance of 75.4 feet per minute. During this travel, James Watt found that horse could pull a weight of 180 pounds.

power =

work forcexdis tan ce (180lbf )(2..4 x 2πx12 ft ) ft.lbf = = = 32,572 min time time 1 min

This figure was rounded off to 33,000 ft (foot)-lbf (pound force) / min (minute) Another information also tells us that James Watt determined that a pony (baby horse) could pull 220 pounds of weight for 100 feet in 1 minute, in a four-hour working shift in coal mines. He then judged that a grown up horse could do 50% more than and hence the figure 33,000 ft-lbf / minute. Put into perspective, an average healthy person can briefly produce 1.2 horse powers and 0.1 horse power continuously. As we can see, horse has been used for centuries as a standard for measuring power of various mechanical and electrical equipments. Today, Kilowatt is widely used as standard SI unit equivalent for Horse Power. Now let us take a look at how to convert the Horse Power into Kilowatt. z

1 feet = 0.3048 meters

z

1 lbf = 9.80665 m/s2 x 1 lb x 0.45359237 kg/lb = 4.44822 kg-m/s2 = 4.44822 N (newtons)

z

1 minute = 60 seconds

ft.lbf 0.3048m 4.4822 N min N .m N .m x x x = 745.6998715 = 746 = 746Watts = 0.746 kilowatts min ft lbf 60 s s s For understanding purpose, if you are told to calculate the work done by a 40HP motor, it can be calculated as below: 40HP = 40 x 0.746 kilowatts = 30 KW = 30000 Nm / second = 300000 Kg-m / second. This means, for example, this motor can pull a 300 kilogram load for 100 meters in 1 second or 3000 kilogram load for 10 meters in 1 second!!! 300000 Kg-m also means “torque or turning moment” the motor can generate. Hence, we can calculate how much load the motor can take in an application. 33,000

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