# Motor Starting Calculation Spreadsheet Page Visited: 55
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#### Motor Starting Calculation Excel Spreadsheet

Motor Starting Calculation Excel Spreadsheet 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.
Motor Starting Calculation
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:
5. Motor starting analysis are generally performed for the largest motor
connected to a switchboard.
6. For worst case results, motor starting analysis are generally performed
considering the weakest source.
7. 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.
8. Modeling
This spread sheet allows the user to model a given network as follows:
9. 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.
10. Grid: The details of grid shall be entered
11. 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.
12. 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.
13. Starting Motor: The details of the largest motor connected to the
switchboard shall be entered.
14. 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.
15. Lumped Load: The details of the remains 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.
16. 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. Previous post Fault calculation methods for industrial & commercial power systems Next post Calculator to Determine the Capacitor kVAR

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