Maximum Demand Calculation

http://cr4.globalspec.com/thread/83953/Electrical-Calculations-help

No. For instance, during the times that the intermittent load is actually running, the system must supply 100% of its demand.

You need to determine the maximum concurrent load, plus a reserve for starting the largest motor. The amount of reserve depends on local codes, source of power, etc.

In addition, you may want to allow extra for possible future expansion.

Demand load - Wikipedia, the free encyclopedia

if your continuous demand was 100W and you have a 50kW motor that runs for a few hours now and again you are going to size for a 25kW load. Your assumption doesn't hold water.

The IEE regs give a guide to how to calc max demand. The supply authority will also give you an application form to fill in where you have to detail your electrical loads. The supply authority are particularly interested in inductive kit - motors and transformers etc that can cause brown outs to other people on the circuit.

I have seen this method it is commonly used in petrochemical industries.

Iranian Petroleum Standard for electrical design will help

Since you are happy with the Iranian Petroleum Standard... why bother to ask?

Every installation has to be analyzed independently to determine the demand factor and diversity factor for each type of load (Continuous, intermittent and standby). Also, study the interaction of the different loads to determine worst case scenarios that will give peaks and length of these peaks.

Please check this

Maximum Demand Calculation

I have seen many people follow different methods depending on their local standards and design practices. One of the methodology is as follows:

Working load (WL) is connected load (CL) minus standby load (SL) i.e WL = CL -SL

Maximum demand (MD) = WL x demand factor x diversity factor

demand factor = (maximum KW consumed by motor) / (name plate rating of motor in KW )

Demand factor is normally considered as 0.8 to 0.85 based on the margin kept by the designer over the calculated mechanical power requirement

Diversity factor is selected based on the time of running of intermittent load over a period of time which is integrated for calculating the maximum demand of the plant. Normally the diversity factor is considered as 0.85 to 0.9. This may vary depending on the process adopted for the manufacturing plant.

Guys,

Please see the attached image.

This is what I asked.Please provide your valuable inputs

Please find the large image attached

This is splitting hairs ...

If you look at the intermittent load, it represents ~2% of the continuous loads

Then the maximum intermittent load surge is less than 1.5 kW

The maximum Continuous load element that can produce a starting surge, is 3 kW which come to 3 x 3 = 9 kW

Your total Continuous load is 7.32 kW + (9-3) = 13.32 kW maximum surge. But, if you start the Pump (A or B) at 1st, then you only need ~ 9 kW. Normally, you can expect gensets to take 10% above ratings for short times.

Since you are taking a margin of 20% on 7.32, = 8.8 kW which is rounded to 9 kW

Consider a p.f. of 0.8 as standard, then 9/0.8 = 11.25 kVA ( your average p.f. at best will be 0.83).

I do not recommend to calculate every kVAr and add them to obtain the kVA.

Think of recommending the nearest Genset to supply 11.25 kVA (12 kVA?).

So what are you trying to tell is this right or wrong.?

This method is commonly used in oil industries which uses the most critical and complicated process and systems. The clients some times insist to do the calculation based on the above formula only.

Total running load is calculated based on the mentioned formula only.

That is why i got confused and asked here so that some one will give an idea about this.

There is no absolute right or wrong method as long as the result matches the installation design and usage trend. That is why you only have recommendations and guidance procedures that varies for different fields of applications.

If the installation is already made and there is an existing supply connected (like a utility supply), you can monitor and record the load variation to obtain the worst case scenario and use it.

If not connected to any utility and you need to work out the demand, then use your expert knowledge (if you are a consultant in this field) or use a qualified consultant or just analyse all the responses you got here, for whichever suits you. In the event that you cannot make up your mind about it, revert to the appropriate consultant!

Sorry if you did not get a definitive formula that is absolutely correct for all cases, but this is a statistic and probability issue. Empirical methods are used and some common sense is needed to finish off the result.

Thanks bro...