Calculate Bus Loading According to the Largest Non-Continuous Load - Intergraph Smart Electrical - Help - Hexagon

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When using the bus PDB coincidence factor to calculate bus loading, you can instruct the software to calculate the total normal running and peak loading according to the largest non-continuous load connected to the current bus. This type of calculation is performed after selecting the appropriate preference setting:

  1. In Smart Electrical, select File > Preferences.

  2. On the Preferences dialog, select the Load Summaries and Reports tab.

  3. Select the Calculate according to largest non-continuous load check box.

    Prefs_LoadSumm_Rprt_tab

For the purpose of this calculation, the software checks all the connected loads and looks for the largest non-continuous load, that is, the load that has the highest intermittent, standby, or spare value. The software looks for such a load among all the loads connected downstream to the current bus, including the loads that were rolled up from the downstream buses. Note that the software looks for the largest non-continuous load for each operating mode.

Your settings on the Preferences dialog determine whether to use rated or consumed values when looking for the largest non-continuous load. These settings also determine which largest load to use when rolling loads up from the downstream buses.

After such a load has been identified for the intermittent, standby, or spare operating mode, the software compares its active power value to the sigma of all the connected loads multiplied by the bus coincidence factor. If the active intermittent, spare, or standby power of that individual load is greater than the sigma, the software uses this value to calculate the total active (kw) bus loading. Note that the software uses the reactive power value of the largest non-continuous load to calculate the total bus reactive power loading (kvar). In case there are several loads with the same largest active power value, the software selects among them the load with the largest reactive power value and treats it as the largest non-continuous load. For detailed information about the equations, see the Calculation Based on the Largest Non-Continuous Load section in the Calculating Bus Loading topic.

After such a calculation has been performed, you can see this in the Properties window for the given bus (Calculated According to Largest Load = True). If this property is True, it means that the calculation for this bus has been performed according to the largest non-continuous load. This is not an indication of the preference setting.

When generating an All Feeder Load Summary report, the report heading indicates that the calculation has been made according to the largest non-continuous load and the largest intermittent/spare/standby load is marked accordingly. For details, see Calculations Based on the Largest Non-Continuous Load in the All Feeder Load Summary Report.

To make the calculation, do the following:

  • In Smart Electrical, select Actions > Calculate Bus Loading.

Example 1

The following example shows a three-level network and based on the rated nameplate values. This example is provided as a simple illustration of this calculation mode. In practice, however, the calculations and identification of the largest intermittent load are based on calculated rated or consumed active load values.

Calculate_Bus_Diagrams_Artboard 2

Analysis of PDB 5

PDB

Motor ID

NP Rating (HP)

Load Status (C/I/S)

Coincidence Factor

Resulting Load

Largest Intermittent Load

PDB 5

M15

100

I

0.3

30

PDB 5

M16

200

I

0.3

60

200

PDB 5

M19

200

I

0.3

60

PDB 5

M18

200

I

0.3

60

Sum of Intermittent Loads with Factors

210

PDB 5 Total Intermittent Loading

210

In this example, since the largest intermittent load is 200 hp, which is smaller than the sum of the intermittent loads, the total intermittent loading of PDB 5 equals 210 hp. Note that there are only intermittent loads on this PDB.

Total running load of PDB 5 = PEAK = S (Continuous *1 + Intermittent * 0.3) loads =210hp

Rolling Up PDB 5 and Accounting for it in PDB 4

To calculate the bus loading of PDB 4, the software rolls up the individual loads on PDB 5 as if they were connected directly to PDB 4.

PDB

Motor ID

NP Rating (HP)

Load Status (C/I/S)

Coincidence Factor

Resulting Load

Largest Intermittent Load

PDB 4

Mtr9

500

I

0.3

150

PDB 4

Mtr10

600

I

0.3

180

PDB 4

Mtr11

800

I

0.3

240

800

T1

M15

100

I

0.3

30

T1

M16

200

I

0.3

60

T1

M17

200

I

0.3

60

T1

M18

200

I

0.3

60

Sum of Intermittent Loads with Factors

780

PDB 5 Total Intermittent Loading

800

In this example when calculating the total loading of the intermittent loading of PDB 4 , since the largest intermittent load is 800 hp, which is larger than 780, the result is that the total intermittent loading of PDB4 equals 800 hp. Therefore, when calculating the totals of PDB 4 (all the loads are intermittent only):

Total running load of PDB 4 = PEAK = S (Continuous *1 + LARGEST INTERMITTENT LOAD) loads =800hp

PDB 3

Prior to calculating the loading of PDB 1, which is the highest PDB in this example network, we need to examine how PDB 3 contributes to the calculation.

PDB

Motor ID

NP Rating (HP)

Load Status (C/I/S)

Coincidence Factor

Resulting Load

Largest Intermittent Load

PDB 3

Mtr5

300

I

0.3

90

PDB 3

Mtr7

400

C

1

400

PDB 3

Mtr8

500

I

0.3

150

500

PDB 3

Mtr17

500

C

1

500

Sum of Intermittent Loads with Factors

240

PDB 5 Total Intermittent Loading

500

Because the largest intermittent load is 500 hp, which is larger than 240, the total intermittent loading of PDB 3 equals 500 hp.

In order to calculate the total running and peak load values (there are no standby loads):

Total running load of PDB 3= PEAK = S (Continuous + LARGEST INTERMITTENT LOAD) loads = 900hp + 500hp = 1400hp

PDB 1

In order to calculate the total loading of PDB 1 (the upper bus), the software rolls up the individual loads of all the downstream buses as follows:

PDB

Motor ID

NP Rating (HP)

Load Status (C/I/S)

Coincidence Factor

Resulting Load

Largest Intermittent Load

PDB 1

Mtr1

500

I

0.3

150

PDB 1

Mtr2

500

I

0.3

150

PDB 1

Mtr3

500

C

1

500

PDB 1

Mtr4

1000

C

1

1000

Cable 13

Mtr5

300

I

0.3

90

Cable 13

Mtr7

400

C

1

400

Cable 13

Mtr8

500

I

0.3

150

Cable 13

Mtr17

500

C

1

500

Cable 11

Mtr9

500

I

0.3

150

Cable 11

Mtr10

600

I

0.3

180

Cable 11

Mtr11

800

I

0.3

240

800

Cable 11

M15

100

I

0.3

30

Cable 11

M16

200

I

0.3

60

Cable 11

M17

200

I

0.3

60

Cable 11

M18

200

I

0.3

60

Sum of Intermittent Loads with Factors

1320

PDB 5 Total Intermittent Loading

1320

Because the largest intermittent load is 800 hp, which is smaller than 1320, the total loading intermittent loading of PDB 1 equals 1320 hp.

Total running load of PDB 1= PEAK = S (Continuous + Intermittent load * 0.3) loads = [(Mtr3 + Mtr4 + Mtr17) + (Mtr1 + Mtr2 + Mtr5 + Mtr8 + Mtr9 + Mtr10 + Mtr11 + Mtr15 + Mtr16 + Mtr17 + Mtr18)] = [(1500hp +400hp + 500hp) + (1320hp)] = [240hp + 1320 hp] = 3720hp

Example 2

Calculate_Bus_Diagrams_Artboard 4

When calculating the bus loading based on the largest non-continuous load, the software rolls up the individual loads connected to the downstream buses and selects the largest load for each non-continuous operating mode. In the example shown above, in order to calculate the total of Bus A, all the loads of Bus B are rolled up to Bus A as if they were connected to Bus A.

Then, from M-1, M-2,M-3,M-4,M-6,M-7, M-100,M-200,M-300,M-400,M-500, the software will compare the largest intermittent, standby and spare value as explained above.

The coincidence factor of both bus is: X=1;Y=0.3;Z=0.1

First, the software handles the lower bus (Bus B) and then rolls it upstream.

Bus B Loads

M-1

M-2

M-3

M-4r

M-5

M-6

M-7

Consumed Active Power

100 kw

100 kw

5.5 kw

5.5 kw

20 kw

20 kw

100 kw

Consumed Reactive Power

20 kvar

20 kvar

1 kvar

1 kvar

5 kvar

5 kvar

20 kvar

Operating Mode

C

C

I

I

I

Standby

Standby

Largest Intermittent

X

Largest Standby

X

  • The largest intermittent load on Bus B is M-5.

  • The largest standby load on Bus B is M-7.

  • Total intermittent active load on bus B= 0.3*(5.5kw+5.5kw+20 kw)=9.3 kw

Therefore:

9.3 kw <20 kw (M-5 largest intermittent active load)

Total Running Load of Bus B

The total active running normal load on Bus B:

Total (x*active continuous)+(largest active intermittent) = 100 kw+100 kw+20KW= 220 kw

The total reactive running normal load on Bus B:

Total (x*reactive continuous)+(largest reactive intermittent) = 20 kvar+20kvar+5Kvar=45 kvar

The total apparent running normal load on Bus B:

sqrt (220kw**2+45kvar**2)=224.6kva

Running normal power factor: 220/224.6= 0.98

Total Peak Load of Bus B

Total active standby load:

0.1*20kw+0.1*100kw= 12 kw

12 kw< 100 kw (M-7 largest active standby)

Therefore, the total active peak load on Bus B:

Total (x*active continuous)+(largest active intermittent)+(Largest active standby)= 100 kw+100 kw+20KW +100kw= 320 kw

The reactive power of the largest standby load M-7 is 20 kvar.

Therefore, the total reactive peak load on Bus B:

Total (x*reactive continuous)+(largest reactive intermittent)+(Largest reactive standby) = 40kvar+5kvar+20kvar= 65 kvar

The total peak load on bus B:

Sqrt(320kw**2+65kvar**2)= 326.5 kva

Peak power factor for Bus B:

320/326.5 = 0.98

Bus A Loads

The bus loading calculation for Bus A accounts for the loads rolled up from Bus B.

Bus B loading is stored in both the Incomer of Bus B and in the feeder circuit of Bus A that feeds Bus B, stored in the various properties which can be seen in the Properties window.

Calculate_Bus_Diagrams_Artboard 6

M-100

M-200

M-300

M-400r

M-500

Bus B cnt

Bus B intrm

Bus B standby

Consumed Active Power

100 kw

100 kw

50 kw

100 kw

110 kw

200 kw
(M1=100kw and M2=100kw)

M-3 = 5.5 kw

M-4 = 5.5 kw

M-5 = 20 kw

M-6 = 20 kw

M-7 = 100 kw

Consumed Reactive Power

20 kvar

20 kvar

10 kvar

20 kvar

40 kvar

40 kvar
(M1=20kvar and M2=20kvar)

M-3 = 1 kvar

M-4 = 1 kvar

M-5 = 5 kvar

M-6 = 5 kvar

M-7 = 20 kvar

Operating Mode

C

I

I

Standby

Standby

C

I

Standby

Largest Intermittent

X

Largest Standby

X

  • The largest intermittent load on Bus-A is M-200 with 100kw

  • The largest standby load on Bus-A is M-500 with 110kw

Total intermittent Active load on bus A= 0.3*(100kw+50kw+31kw)= 54.3 kw

Therefore:

54.3 kw < 100 kw (M-200 largest intermittent active load)

The total active running normal load on Bus-A:

Total (x*active continuous)+(largest active intermittent) = (100 kw+200 kw)+100KW= 400kw

The total reactive running normal load on Bus-A:

Total (x*reactive continuous)+(largest reactive intermittent) = (20 kvar+40kvar)+20 kvar= 80kvar

The total running normal load of Bus-A:

sqrt (400**2+80**2)=sqrt(160000+6400)=407.9 kva

Running power factor: 400/407.9= 0.98

Calculating the Total Peak Load on Bus-A

The software calculates the total active standby load and compares it to the largest standby load:

0.1 * 100kw + 0.1 * 110kw + 0.1 * 120 = 33 kw

33 kw < 110 kw (M-500 largest active standby)

Therefore, the total active peak load on Bus-A:

Total {(x*active continuous)+(largest active intermittent)}+(Largest active standby) = 400 kw+110 kw= 510 kw

The reactive power of the largest standby load M-500 is 40kvar.

Therefore, the total reactive peak load on Bus-A:

Total (x*reactive continuous)+(largest reactive intermittent)+(Largest reactive standby) = 80kvar+40kvar = 120 kvar

Total Peak Load on Bus-A:

Sqrt(510kw**2+120kvar**2)= 523.9 kva

Peak power factor: 510/523.9 = 0.97

Calculating PDB Totals

If there are multiple buses in a given PDB, the software behaves as follows:

  • The software does not sum up the buses. Instead, the software shows the total values for each bus.

  • The Multi-Sheet Switchboard Summary report does not sum up the buses on the PDB Summary page. Instead, the report shows one PDB/Bus line for each bus within the PDB.