[How To]Calculate the Power Required for an operation

Good Day viewers..!!

Today i wanna explain you guys how to Calculate the power required for an operation and also how to calculate operating costs for power during an operation, especially in Pharmaceutical industries.

Basically everyone knows the traditional way of calculating the power consumption, but it can't be applied to every case as the Load during the operations will vary everytime, and the one we calculate will give us the power for full load and we will be having many cases like,

1. Motor operating at full loads,
2. Motor operating at empty loads,
3. Motor operating at peak loads,
4. Motor operating at intermittent loads.

So without knowing these all, One cannot calculate the power exactly, and some of you may not know the secret formula of many who are calculating the power by traditional way.

For Calculating the power consumed by a 5hp motor, everyone will go on multiplying 0.746, and reply you with a figure 5 x 0.746, and in addition without asking they will also multiply the returned figure from 5 x 0.746 with 8 or 9, and tell you the amount for that operation to show their talents.

But Actually this Calculation wont give you the exact figure, as this is not an exact calculation as previously i mentioned you that load will vary depending on the operation from time to time,

Even some persons may argue that 1HP = 735.5Watts and some argue as 1HP = 746 Watts,
And Both of them were correct because when we define Horse Power in british units it will be 735.5 Watts and For English Units i.e., S.I. it will be 746Watts.

And before going onto the main calculation part i want you guys to know some basic theory regarding the Motors, that were designated for handling operations. 99.9% of all the motors were provided with VFD ( Variable Frequency Drive) to save the power, and these VFD were provided with a display meter, for displaying the motor running frequency and the Load ( in Amp's), and percentage Load.

VFD - Used for Changing the Frequency

Basically the frequency and the current are not related directly, but whenever the frequency is changed immediately you can observe a variation in Current consumption, 

A 1 hp Motor will Consume 1Amp of current for 100% load.

And coming to Classification of Loads, 

1. Motor Operating at Null Load: It means there is no load over the motor, but in case of empty load also our motor will consume some Amp's as our shaft needs some mechanical torque for its rotation, so for that it will consume some load.

2. Motor Operating at Intermittent Load: It means when there is some resistance to the movement of the shaft of the motor then the current required may vary, so this is what Intermittent Load means.

3. Motor Operating at Full Load: For a Motor operating at full loads it needs complete current i.e., if its a 5hp motor it will consume 5Amp's.

4. Motor Operating at Peak Load: If a Motor operating at peak load means it has crossed the full load i.e., 100% limit and still operating, you may not believe this but its true, because many vendors will provide the motors with a certain service factor, 

And now you may get a doubt that "What is a service factor?" 

A Service Factor is nothing but some additional capacity provided over the full load limit for a Motor to function in Emergency cases, if a Motor of 10HP is having a Service Factor of 1.15 then it will be functional upto 15HP, and if this limit is exceeded then the Motor will be tripped.

So, i think if you can understand the mentioned concept 100%, then you are ready to learn the Calculation, Anyway i'll start this ,

For Calculating the power consumed by a Motor we have to simply use the formula,

P = V x I x Cos(phi)

Here, V - Voltage in Volts, I - Current in Amp's, Cos(phi) - Power Factor,

I think you are much familiar with Voltage and current than the Power Factor, Power Factor is nothing but ration of the Load and Impedance, these terms are much more comfortable for electrical students, so i'll turn off this matter here itself, if not you may loose your interest in reading this. But better to get a sight of the below Formula,

X - Load, R - Resistance, Z - Impedance.

Z = SQRT( (R x R)+(X x X))

We may consider this power factor in between 0.80 to 0.92,

Generally the Voltage supply for Domestic usage will be 240 Volts i.e., Single Phase,
But for industries it will be 440Volts supply (Commercial purpose) i.e., a Three Phase supply, and the whole power need to be multiplied with Square Root of 3 (1.732),

So, Finally for Calculation we have to use the above mentioned Power Formula just like the below mentioned example,

Power Consumption Calculation for a 20HP Motor, current consumed is 16Amp's ( from VFD),

It will be P(Watts) = 440 x 16 x 0.85 x 1.732   For Three Phase,

                              = 240 x 16 x 0.85                For Single Phase,

here the Power Factor Cos(phi) is considered as 0.85,

So for Three Phase commercial purpose it will be P = 10364 Watts = 10.364 K Watts
     For Single Phase Domestic Purpose it will be P = 3264 Watts = 3.264 K Watts.

That's it Cheers, Done

Still have any queries feel free to Ask, We are happie to help,

Comments are most appreciated.

Stay Tuned for more...........!!!!

Also Read:

How to Design a Condenser?  

How to Select a Pump , Motor, Line Sizings ? 

How to Handle an Out Of Specification[OOS] 

Determine the Power Required for an Operation?  

Industrial Distillation Column Design Steps

About The Author

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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a technoholic geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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