# Motor Starting Calculation

## Motor starting case studies

A motor starting case study for any given electrical network can be performed by reduced the network to a smaller equivalent network consisting of a source (generator / grid), the starting motor (largest motor), other large running motor and a lumped load.

This MS Excel based spread sheet is based on this concept and present a small model of electrical network that can be adapted for such motor starting case studies.

This is very helpful especially for quick checks as follows:

1. What is the largest motor size that can be started with a given generator rating
2. What should be the rating of the generator (or nos of generator operated in parallel) for a given load and largest motor size
3. Knowing voltage drop during starting conditions for given motor details and hence deciding the key parameter during design (say max allowable starting current)
4. Deciding the cable size / number of runs etc.

The spread sheet performs an iterative calculation based on pre-start load inputs and starting motor data. Detailed analysis may be performed with the help of available softwares.

## Notes:

1. Motor starting analysis are generally performed for the largest motor connected to a switchboard.
2. For worst case results, motor starting analysis are generally performed considering the weakest source.
3. Considering the above two facts, any given electrical network, where a starting analysis of a motor is required, can be reduced to a simplified network consisting of a source (generator/s or grid), the starting motor (largest motor), the running motor/s (second largest motor/s or motor of same rating as the largest motor under study) and other loads lumped together.
4. Modeling
This spread sheet allows the user to model a given network as follows:

1. Generator/s: The details of one generator shall be entered. If there are more than one generator of identical rating, these can be modeled simply by enter the number of generator in parallel.
2. Grid: The details of grid shall be entered
3. Transformer/s: The details of one transformer shall be entered. If there are more than one transformer of identical rating, these can be modeled simply by enter the number of transformer in parallel.
4. The spread sheet considered either the “Generator/s” or the “Grid” supply for the motor starting analysis. The “source for the motor starting analysis” can be selected by the use via the drop down menu. The selection automatically simulates switching “ON” or “OFF” the respective source breaker.
5. Starting Motor: The details of the largest motor connected to the switchboard shall be entered.
6. Running Motor/s: The details of the second largest running motor/s (or motor of rating same as the starting motor) connected to the switchboard shall be entered. This model can also be utilized by the user to check the voltage drop at the terminals of any remote motor/s.
7. Lumped Load: The details of the remaing load on the switchboard can be modeled as a lumped load. The % motor can be defined which shall be modeled as constant power load while remaining % of load shall be modeled as constant impedance load for the calculation.
8. Error in data entry of the “voltage” input shall be highlighted, if bus voltages are much different from the generator terminal voltage input of transformer voltage ratio inputs.

The excel spreadsheet has 2 sheets as follows:

• Sheet title “Preface” with notes explaining about the calculation spread sheet and the summary about the software and
• Sheet title ” Motor starting calculation” where actual data entry and calculations can be performed

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1. Musse Mohamud Ahmed
Jan 05, 2018

Very good arrangements Guys, thank you very much.

2. bhavin patel
Dec 10, 2016

dear sir
can u please send me a detail example for the above excel sheet

3. Vikram
Jul 05, 2016

Its an awesome workout and very useful.

4. ANIL
Feb 14, 2016

Could not enter value generator voltage 6600 v for solo generator mode

5. FELIX JR.
Feb 14, 2016

THIS IS GOOD EXCEL PROGRAM IN THE CALCULATION OF % VOLTAGE STARTING DIP WHEN A LARGE MOTOR IS TARTED SUDDENLY EVEN WHEN ALREADY THERE’S EXISTING LOADS RUNNING.

6. Boomi
May 13, 2015

Very much informative and I like all spreadsheets
Regards,
Boomi

7. Jason Buda
Apr 21, 2015

The excel spreadsheet downloaded just fine for me… It is very involved and I am looking forward to picking at it to fully understand how to use it. The introduction sheet seems very intuitive! Thanks for sharing!

8. Abdulwahid
Jan 15, 2015

9. Rakesh Dhedhi
Sep 11, 2014

Dear Sir / Ma’am,
First of all thanks for making such beautiful site for electrical world.

Problem:
1. By right click option : It saves html page instead of excel or other file.
2. By box.com : We’re sorry, the server encountered an unexpected error.

I hope admin will rectify this problem asap.
Thanking you in anticipation.

With best Regards,
Rakesh Dhedhi
Electrical Engineer

10. Denis Milton
Aug 27, 2014

Motor Starting Calculation-Rev1.xls

We’re sorry, the server encountered an unexpected error.

11. VICTOR RAUTA
Aug 26, 2014

INTERESTING ENGAGEMENT,
LOVING IT

12. Melvin
Jul 16, 2014

13. Alfredo Labung
Mar 28, 2014

keen to know more about articles, software, guides & lectures of EEP tech refs as well…

14. Nitin
Feb 21, 2014

• Edvard
Feb 21, 2014

15. nandaarief
Nov 19, 2013

thanks a lot, its very helpfull

16. saunak
Sep 23, 2013

This site is really excellent i m very thankfull…it can be change my life electrical engineering….
thank you soo much eep.

17. Ashraf
Jul 25, 2013

18. karthikeyan
Apr 09, 2013

hi guys.. i am fresher to engineering…
i would like to learn how motor starting calculation is done.
please send me some technical articles/books in this regard to y mail id (karthikeyantce50@gmail.com)

19. WillG72
Mar 02, 2013

I cannot download either. I did as you advised about clearing the cache. When I click on ‘Download’, I am taken to a preview page called ‘Box’ and states that I need to login to it. I never heard of this and why do I need to login to some other site?
William

20. munis.munnu
Oct 29, 2012

21. natemp
Jul 03, 2012

The worksheet not producing resuts for the below combination (even though this is not praticle)
Transformer for voltage rating 11/0.2kV
V2 bus voltage 0.2kV

thanks

22. mpsaxena2003
Nov 01, 2011

I have made a vba macro in MS Excel for Transformer Sizing .I want to upload it in this site. How i do it.

23. ajay34
Aug 17, 2011

• Edvard
Aug 17, 2011

Logout and clear the cache in your browser and then login again. It should work. There was some works and improvements on EEP, so try to clear your cache.

BR

• WillG72
Mar 02, 2013