Maximum Demand (KVA) Calculation Formula

First what is the end objective? One obvious covariant is fuel consumption at the power generator.

The objective is to monitor the KVA value in RTClock and get a predicted KVA (MD) value at the end of the cycle of 30 min.

I should be able to set the value of KVA at which I can control it.

ok,please in design of electrical machine , is maximum demand equal 0.75 of total connected load

Best Regard

Mohammad Arf ALABBADI

Analysis section, Dubai

First what is the end objective? One obvious covariant is fuel consumption at the power generator

XM=KB/2ND

This formulae is interesting, but could you please define the terms? i.e the meaning of those parameters used. Thanks a million.

Regards

Leyonsa

Power consumed is measured as KVA* power factor. In this case max. demand is given in KVA. If max demand sanctioned is 100 KVA, then ,

√3V*I = 100,000 V*A. Hence current , I = 131 amps. In a month there are 30 days, and if one is permitted to use only 100 kva as MD then, assuming each day if he exceeds the line current by 131 amps for One minute at any point of the day, then cumulatively on a 30 day contiunous working he may just be in the border line. The consumer has to restrict the power consumed not to go beyond 131 amps for one minute continously in a day.

You can have an alarm mounted to warn you, if the line current exceeds 131 amps.

Excellent explanation & idea .

Really appreciate your effort to answer this in such a descriptive manner .

Aathi , UAE

KVA CAICULATION

What influence will the PF have on the monitored kVA,

if your equipment still need 86kW to do the work in the

example below ?

Jo

I am not able to understand the formula you have given. For the max demand sanctioned 100kva how does this 3V*I=100,000V*Ais getting converted in to 131amps.Explaining how to calculate the formula in detail would really help me in understanding it.

Thanking you
Inderjeet singh

They probably do the same thing as in the USA. Here they measure the power consumed for 30 minutes and then multiply it by two to get the demand rate -- note that if you integrate the demand over an interval of time you are in essence measuring consumption for that interval.

We also have power companies that have 15 minute demand windows. In that case they measure the usage for each 15 minutes and then multiply by 4 to get the demand rate for that interval. I have not seen a utility company that uses less than a 15 minute "average" for calculating the billing demand.

The demand charge for the month is typically the maximum demand measured during all the demand intervals in the billing period. Normally the demand intervals coincide with the top of the hour. However different utilities do things differently. Some may take the peak usage occuring each week and average teh 4 or 5 values for the past month. Many employ ratchet charges where the lowest possible demand charge is perhaps 80% of the maximum demand for the past 11 months.

Most electric utilities use electronic demand meters that keep track of a facility's energy consumption per demand interval (a demand profile). This is downloaded and stored by the utility for a few years and is usually available on request in a graphic and/or digital printout. A small fee may be required.

My load 10 Minute 2500 KVA forward power and 10 Minute 1000 KVA reverse power and then 10 Minute 500 KVA then what is my Max Demand for integration period 30 Minute?

Sir

We want how to calcaulate maxium demand.

I want to know the formula for rise in maximum demand for motor starting current.Thanks

Can the demand be predicted by the average measured kVA of the first few minutes? So for example, if you had a 5min integration period, it would look something like this :

the formula should be

1/T(∫p(t)dt) for the time duration of the cycle...

If you have a PLC and measure the the current and voltage or better still an instantaneous KW reading then it is relative easy to measure the 30 min demand. I used a Quantum PLC to take the instant value of KW every PLC clock cycle at say 1.0 second and store that value in a series of registers.

Then you can create other registers where the highest instant value is stored for the 30 min cycle with the previous highest being overwritten. Likewise the value of each reading can be added and divided by the number of readings to obtain an average value.

The program I wrote was dealing with values up to 10MW on a large mining machine. Likewise with a suitable Citect HMI the values can be displayed in either bar, circle or numerical output or as I did all 3 types on the one display and time to end of 30min period. It is easy to change the clocking interval to any value that suits your needs.

First of all, the demand is always done in kW or kVAR, not kVA. One is fuel cost, the other is generator reactive capacity. Two different price structures.

Schnieder has this in their demand control software description, formula is near the bottom.

Detailed module operation

Sliding Window Demand calculation

The figure below illustrates how the Sliding Window Demand module calculates the value in the SWinDemand output register. In this case, the Sync input is not linked (hence the Sub Intvl and #SubIntvlssetup registers define the total demand interval).

(see image 1 in link below)

The average demand for each of the six previous subintervals is calculated and these values are averaged across the number of subintervals (specified by the #SubIntvls setup register). In this example, the value in the SWinDemand output register from 2:00 to 2:05 is:

The Sliding Window Demand module allows you to match the power utility’s sliding window demand calculation technique. For sliding window measurements, the Sub Intvl register represents the length of the utility’s demand subinterval, while the #SubIntvl register represents the number of subintervals which make up the total demand interval. For example, with a 6 x 5 minute (30 minutes total) sliding window method, demand is the average power consumption over the last six 5-minute subintervals. This allows you to match virtually any type of sliding window measurement method used by the utilities (i.e. 2 x 15 minutes, 6 x 5 minutes, 1 x 30 minutes).

Alternatively, you can use external synchronization (Sync input linked) to calculate sliding demand values. In this case, a new subinterval begins each time a pulse is received on the Sync input.

Predicted Demand calculation

The Sliding Window Demand module predicts changes in demand based on the following formula:

(See image 2 in link below)

The module automatically calculates the Thermal Average value used in the above formula. The Thermal Average starts at 0 when the Sliding Window Demand module powers up, and gets calculated every second based on the following formula:

The rate at which the Thermal Average responds to demand changes depends directly on the sensitivity of the demand prediction, which is programmed into the Pred Resp setup register. If Pred Resp is set to a higher value, Thermal Average will respond more quickly to changes in the module’s Source input (i.e. the higher the value for Pred Resp, the faster this module will predict).

https://www.productinfo.schneider-electric.com/pm8000/595e26f146e0fb0001f6ffc4/IONReference/English/BookMap_IONReference_0000103690.ditamap/$/IONRef_SlidingWindowDemandModule_0000097940