Present Demand value caclutaion at Sliding Block method in EM7280

[varad]

Hi,

I have installed the EM7280 at customers site for demand controlling application.

Chosen the Auto Demand calculation method for KVA at period of 15 mins. The KVA trend at site is nearly constant, ranges from 9.2 MVA to 9.6 MVA.

As the calculation method is Auto(Sliding Window) we are suspecting that the present demand value should be in the same range as the KVA trend.

But at some instance of time, present demand falls down to 0.9 - 1.2 MVA.

Please help me to understand this so that I would be able to further explain to customer.

[Ramasamy_N]

Hello, 

The present demand value will be calculated and updated at the interval of 15 seconds for auto black in EM7280. If there is any change in power values, there will be change in present demand value also. Please check the power values when the present demand is falling to  0.9 - 1.2 MVA.

Regards, 

Ramasamy N

[varad]

Hi,

Yes its correct about update time for values, but we have checked the power (KVA) is as same ranges 9.0 - 9.5 MVA even though the present Demand shows 0.9 - 1.5 MVA.

[Ramasamy_N]

Hi, 

Ok, if the power values are constant the present demand will be same as last demand for all the interval. one possible cause for drop in the present demand (start from 0VA) will be device power OFF. Is the EM7280 power cycled ?

Regards, 

Ramasamy N

[varad]

Hi Ram,

Device supposed to be continuously on. This fall down occurs frequently so lets check out this possibility.

Is the EM7280 power cycled ? I cant understand what this means? Is it any setting to be done for this?

[Ramasamy_N]

Hi, 

I was asking about, is the  EM7280 powered OFF before the present demand fall down?

If not, please log the power and present demand parameters using any Modbus application (with interval of 5 to 10 seconds) and share the data for further analysis.

Regards, 

Ramasamy N

[varad]

Hi Ram

We have checked the power off with EM 7230 at my lab, The present Demand value does not reset after power off.

Please find attachments from customer about block demand. It seems after every 1 hour the present demand resets.

[Ramasamy_N]

Hi, 

Sorry for the delay in reply, 

Thanks for the details, we are analyzing this issue will keep you posted. 

Regards, 

Ramasamy N

[varad]

Hi

Further more we have observed that this interval demand parameter goes to 0 after every hour. That means at every 33rd minute from hours the demand parameter goes to 0.

Is it the auto reset?