Motor Starting Calculation Spreadsheet

0 0

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.