Modeling small LV motors and auxilary loads for Load Flow study.

[rockman7892]

I wanted to hear how others typically model small LV motors (480V) for a load flow study in an industrial plant. Most of these motors I am referring to are typical motors less than 100HP that you would find fed from various MCC's throughout the plant.

For fault analysis we typically lump these motors into a single motor for fault contribution. For load flow can you use the same motor lump in the analysis model or are better results achieved my modeling the individual motors. For the particular project I am working on we are updating customers entire One-Line so we are modeling the individual motors as part of that process but was curious to hear how in cases where this is time consuming if others used the lumped sum approach? By modeling individual motors you can easily turn them off an on to account for demand factors with redundant and standby motors and I guess you could do the same with a lump sum but not including any redundant motors in the sum?

How are the loads from 480V and 208V typically modeled for load flow analysis. I'm thinking these loads can be modeled as fixed kW loads, but coming up with a kW estimate may present a challenge. With 100's of panels in a plant it would be way too much of a cumbersome task to track down individual loads (especially in old plants with no panel schedules) Do others have good techniques or rules of thumb for estimating these panel loads? I guess you could take loading "snapshots" with a clamp on meter or power meter but this loading would surely fluctuate throughout the day so a measurement at any given time may not provide accurate loading.

I appreciate any feedback.

 

[7anoter4]

I was not involved in a large element number flow calculation. However, in my opinion, IEEE 399 IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis
(This Recommended Practice, commonly known as the “Brown Book,”)
ch. 4.9 Models of bus elements.4.9.2 Induction motors, it could be followed for such a study.

 

[waross]

After you arrive at a figure by whetaever means you may use this method as a "Reality Check".
Take a look at the demand meter for the plant.
Estimate your non-motor loads and subtract them from the demand.
Use your demand reading to estimate the maximum HP connected during the demand period.
This will give a good indication of the maximum HP being used;
BUT
The the fault contribution depends on the rated HP not the HP in use.
If your motors tend to be loaded at about 50% of the ratings, then the connected HP will be about double whay this check indicates.
Comparing this result with your other calculation should show a reasonable loading factor.
As I said, not a solution but a quick reality check.


Bill
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"Why not the best?"
Jimmy Carter