NCEES (version 2018) #122

[iahi_2005]

Hi Guys,

I am looking at the responses,but, none of them make sense, can you all please explain how the average power consumption in interval 2 is 37.5??

 

[Sthabik PE]

Hi Guys,

I am looking at the responses,but, none of them make sense, can you all please explain how the average power consumption in interval 2 is 37.5??

Interval #2 Area; A2 = (25kW x 15min)+ (1/2 x 25kW  x 15min) = 562.5 kW min

Interval #2  time interval; t2: 15 min.

Avg power in interval 2 = A2/t2 = 562.5 kW min / 15 min = 37.5 kW



Does it make sense now?

 

[iahi_2005]

Thanks! it makes sense now!! so you are adding the area of square + area of triangle!

 

[Ahmed S.]

Hi Everyone , I was confused as well but after reading your comments it become easy to understand

Average power ( Pmax+Pmin)/2 

At T=0 , (25+25)/2 = 25

At T=15 , (50+25)/2 = 37.5

At T=30, (75+50)/2 = 62.5

At T=45 , (50+50)/2 = 50 

For the max power , I will quote the best comment above from SSG

In this question the Max demand given at t=0 is 35KW. Understand it like this. Every 15 minute period meter will calculate average KW of this 15minute period and then compare it with earlier data it has preserved- reject the new data if it is less than earlier data or select the new data if it is more than old data. So e.g. at t=15, the Max demand will remain 35KW because average KW between t=0 to t=15 is 25KW, similarly at t=30, the new value is 37.5KW, so it will pick up this value(37.5>35), at t=45, the new value is 62.5KW, again it will pick up new value of Max demand as 62.5KW(62.5>37.5), next at t=60, new data is 50KW so it will reject it and show the max demand as 62.5KW only. Is that the answer?

 

[ahaq]

Hi Everyone , I was confused as well but after reading your comments it become easy to understand

Average power ( Pmax+Pmin)/2

At T=0 , (25+25)/2 = 25

At T=15 , (50+25)/2 = 37.5

At T=30, (75+50)/2 = 62.5

At T=45 , (50+50)/2 = 50

For the max power , I will quote the best comment above from SSG

In this question the Max demand given at t=0 is 35KW. Understand it like this. Every 15 minute period meter will calculate average KW of this 15minute period and then compare it with earlier data it has preserved- reject the new data if it is less than earlier data or select the new data if it is more than old data. So e.g. at t=15, the Max demand will remain 35KW because average KW between t=0 to t=15 is 25KW, similarly at t=30, the new value is 37.5KW, so it will pick up this value(37.5>35), at t=45, the new value is 62.5KW, again it will pick up new value of Max demand as 62.5KW(62.5>37.5), next at t=60, new data is 50KW so it will reject it and show the max demand as 62.5KW only. Is that the answer?

Hi Everyone , I was confused as well but after reading your comments it become easy to understand

Average power ( Pmax+Pmin)/2

At T=0 , (25+25)/2 = 25

At T=15 , (50+25)/2 = 37.5

At T=30, (75+50)/2 = 62.5

At T=45 , (50+50)/2 = 50

For the max power , I will quote the best comment above from SSG

In this question the Max demand given at t=0 is 35KW. Understand it like this. Every 15 minute period meter will calculate average KW of this 15minute period and then compare it with earlier data it has preserved- reject the new data if it is less than earlier data or select the new data if it is more than old data. So e.g. at t=15, the Max demand will remain 35KW because average KW between t=0 to t=15 is 25KW, similarly at t=30, the new value is 37.5KW, so it will pick up this value(37.5>35), at t=45, the new value is 62.5KW, again it will pick up new value of Max demand as 62.5KW(62.5>37.5), next at t=60, new data is 50KW so it will reject it and show the max demand as 62.5KW only. Is that the answer?

How would the maximum power in interval 2 be 37.5 and not 50? Isn't the height of the triangle the maximum power?

 

[ahaq]

Hi Everyone , I was confused as well but after reading your comments it become easy to understand

Average power ( Pmax+Pmin)/2

At T=0 , (25+25)/2 = 25

At T=15 , (50+25)/2 = 37.5

At T=30, (75+50)/2 = 62.5

At T=45 , (50+50)/2 = 50

For the max power , I will quote the best comment above from SSG

In this question the Max demand given at t=0 is 35KW. Understand it like this. Every 15 minute period meter will calculate average KW of this 15minute period and then compare it with earlier data it has preserved- reject the new data if it is less than earlier data or select the new data if it is more than old data. So e.g. at t=15, the Max demand will remain 35KW because average KW between t=0 to t=15 is 25KW, similarly at t=30, the new value is 37.5KW, so it will pick up this value(37.5>35), at t=45, the new value is 62.5KW, again it will pick up new value of Max demand as 62.5KW(62.5>37.5), next at t=60, new data is 50KW so it will reject it and show the max demand as 62.5KW only. Is that the answer?

The values listed under "Average Power Consumption (kW)" refer to the END of the respective time interval. However, the "Max Demand" values refer to the START of the respective time interval. And remembering that in this context, "max demand" refers to maximum average demand measured in any single time interval, NOT the instantaneous maximum value measured.

Max demand at the start of interval #1 = 35 kW (given in the problem statement; we don't necessarily need to know how this number was obtained)

Max demand at the start of interval #2 = 35 kW (during interval #1, the average demand was only 25 kW, so the max demand registered did not change)

Max demand at the start of interval #3 = 37.5 kW (during interval #2, the average demand was 37.5 kW, so the new max demand registered is now 37.5 kW)

Max demand at the start of interval #4 = 62.5 kW (during interval #3, the average demand was 62.5 kW, so the new max demand registered is now 62.5 kW)

Max demand at the start of interval #5 = 62.5 kW (during interval #4, the average demand was 50 kW, so the max demand registered is still 62.5 kW)

Finally, the problem statement asks for the maximum demand registered at t=60 min, which is at the END of interval #4 and the START of interval #5.

"And remembering that in this context, "max demand" refers to maximum average demand measured in any single time interval, NOT the instantaneous maximum value measured." Most important piece of information that had no mention in the question.

 

[akyip]

Hey all. As a friendly FYI, attached is my work on problem 122.

I broke this problem down by each interval (each 15-minute interval):

• For each interval, I listed the maximum demand and the average demand.
• In each interval, the average demand is the area under the graph, within each 15-minute interval. This involved breaking down the shape of the area within each area into separate rectangles and triangles where necessary (this is especially important for the 15-30 min interval and the 30-45 min interval).
• Whenever the average demand in one interval is greater than the maximum demand of the previous interval, that average demand now becomes the new maximum interval. You can see this occurring at the 15-30 min interval and the 30-45 min interval.

Hope this helps!