Calculating bus loading amounts to summing up all the loads that are connected a particular bus. When calculating the total loads connected to a bus, the software calculates the bus totals, stores the individual subtotals in the database as calculated properties and then makes these calculated properties accessible for reporting. During this stage, you can sum them up any way you see appropriate.
In general, the total load of a bus is a variation of the sum of its active and reactive vectors. Smart Electrical calculates these totals for each load by adding up the direct and downstream rolled up loads. Then, Smart Electrical stores these results in the database.
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The software takes into account any existing equipment that is connected in parallel.
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When making calculations, Smart Electrical considers the worst-case scenario in its calculation results and does not take into account any load flow that would be taken into account by a power analysis application such as ETAP. That is, for calculation purposes, Smart Electrical always assumes that the total connected load is supplied from one source only. If there are multiple sources that supply the same connected load, Smart Electrical assumes that each source has the capability to supply the connected load. Smart Electrical, unlike any power analysis application, does not account for multiple sources that share a load. Consequently, in Smart Electrical, the total load for a distribution network can appear artificially high unless the Circuit Mode property is set to either Connected or Disconnected as required on specific circuits.
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For information about calculations made based on the largest non-continuous load, see Calculate Bus Loading According to the Largest Non-Continuous Load.
Bus Values Used in Calculations
Bus Rated Power Values
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Total uncompensated continuous active power
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Total uncompensated continuous reactive power
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Total uncompensated intermittent active power
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Total uncompensated intermittent reactive power
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Total uncompensated standby active power
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Total uncompensated standby reactive power
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Total uncompensated spare active power
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Total uncompensated spare reactive power
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Total compensated continuous active power
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Total compensated continuous reactive power
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Total compensated intermittent active power
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Total compensated intermittent reactive power
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Total compensated standby active power
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Total compensated standby reactive power
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Total compensated spare active power
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Total compensated spare reactive power
Bus Consumed Power Values
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Total uncompensated continuous active power
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Total uncompensated continuous reactive power
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Total uncompensated intermittent active power
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Total uncompensated intermittent reactive power
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Total uncompensated standby active power
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Total uncompensated standby reactive power
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Total uncompensated spare active power
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Total uncompensated spare reactive power
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Total compensated continuous active power
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Total compensated continuous reactive power
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Total compensated intermittent active power
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Total compensated intermittent reactive power
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Total compensated standby active power
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Total compensated standby reactive power
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Total compensated spare active power
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Total compensated spare reactive power
Circuit Load Calculation
Smart Electrical stores downstream load totals in the respective circuit items. The following rules apply to the data that a circuit stores:
Feeder circuits
Hold the values of the total downstream connected load (if there is more than one load connected to a circuit, the circuit stores the total values for all the connected loads).
Incomer circuits
Store the total load of the bus that the incomer circuit is feeding. Note that the incomer circuit values and total bus values should be the same.
Coupler circuit
Stores the values of the load of the coupled bus.
Riser circuits
Store the values of the bus that has the coupler, opposite the riser circuit. That is, each coupler-riser paired circuit stores the values of its counterpart.
Calculating the Total Bus Loading
Smart Electrical calculates the following grand totals of bus loading for each set of the bus rated power values and bus consumed power values:
Rated Power (Compensated and Uncompensated)
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Total running bus active load
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Total running bus reactive load
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Total running bus apparent load
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Running bus power factor
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Total peak bus active load
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Total peak bus reactive load
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Total peak bus apparent load
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Peak bus power factor
Consumed Power (Compensated and Uncompensated)
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Total running bus active load
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Total running bus reactive load
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Total running bus apparent load
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Running bus power factor
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Total peak bus active load
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Total peak bus reactive load
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Total peak bus apparent load
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Peak bus power factor
Bus Run Power Grand Total
The total running load is defined as the sum of the continuous and intermittent loads, compensated or uncompensated, respectively. Active and reactive load values are summarized and stored in separate properties. Rated and consumed values are also stored in separate properties.
Uncompensated Run Power Total
(Prun) = S (Pcontinuous) + S (Pintermittent)
(Qrun) = S (Qcontinuous) + S (Qintermittent)
Compensated Run Power Total Using Individual Load Coincidence Factors
The coincidence factor of each load is taken into account separately.
(Prun) = S (X * Pcontinuous) + S (Y * Pintermittent)
(Qrun) = S (X * Qcontinuous) + S (Y * Qintermittent)
Compensated Run Power Total Using Bus Load Coincidence Factors
The software uses the bus coincidence factors to make the calculation. The coincidence factor of each load has no effect on the calculation.
(Prun) = S (Pcontinuous) * X bus + S (Pintermittent) * Y bus
(Qrun) = S (Qcontinuous) * X bus + S (Qintermittent) * Y bus
Bus Peak Power Grand Total
The total peak load is defined as the sum of the continuous, intermittent, standby, and spare loads - compensated and uncompensated respectively.
Uncompensated Peak Power Total
(Ppeak) = S (Pcontinuous) + S (Pintermittent) + S (Pstandby) + S (Pspare)
(Qpeak) = S (Qcontinuous) + S (Qintermittent) + S (Qstandby) + S (Qspare)
Compensated Peak Power Total Using Individual Load Coincidence Factors
The coincidence factor of each load is taken into account separately.
(Ppeak) = S (X * Pcontinuous) + S (Y * Pintermittent) + S (Z * Pstandby) + S (ZZ * Pspare)
(Qpeak) = S (X * Qcontinuous) + S (Y * Qintermittent) + S (Z * Qstandby) + S (ZZ * Qspare)
Compensated Peak Power Total Using Bus Load Coincidence Factors
The software uses the bus coincidence factors to make the calculation. The coincidence factor of each load has no effect on the calculation.
(Ppeak) = S (Pcontinuous) * XB + S (Pintermittent) * YB + S (Pstandby) * ZB +(Pspare) * ZZB
(Qpeak) = S (Qcontinuous) * XB + S (Qintermittent) * YB + S (Qstandby) * ZB +(Qspare) * ZZB
Calculation Based on the Largest Non-Continuous Load
The following equations are used by the software to calculate the total normal running and peak loading according to the largest non-continuous load connected to the current bus. This calculation is made after selecting this preference option on the Load Summaries and Reports tab of the Preferences dialog.
Selecting Uncompensated values on the Preferences dialog will always result in having the sigma totals larger than any individual load.
The choice of the appropriate equation depends on whether the sigma intermittent active power of a load connected directly or indirectly to the bus multiplied by the bus intermittent coincidence factor is larger or smaller than the largest individual intermittent active power value of a load connected directly or indirectly to the current bus. After the software detects that there is such a load, the software uses its reactive vector to calculate the reactive intermittent load by using it in the calculation instead of the S (Y * Qintermittent) part of the equation.
In this case, the equations used are as follows
Compensated Run Power Total Using Bus Load Coincidence Factors
There is one set of calculated values for the consumed values and another set of
the rated values.
The software uses the bus coincidence factors to make the calculation. The coincidence factor of each load has no effect on the calculation.
(Prun) = S (Pcontinuous) * X bus + Largest (Pintermittent) * Y bus
(Qrun) = S (Qcontinuous) * X bus + Largest (Qintermittent) * Y bus
Bus Peak Power Grand Total Based on the Largest Non-Continuous Load
The total peak load is defined as the sum of the continuous, intermittent, standby, and spare loads - compensated and uncompensated respectively.
Compensated Peak Power Total Using Bus Load Coincidence Factors
There is one set of calculated values for the consumed values and another set of
the rated values.
The software uses the bus coincidence factors to make the calculation. The coincidence factor of each load has no effect on the calculation.
(Ppeak) = S (Pcontinuous) * XB + Largest (Pintermittent) * YB + Largest (Pstandby) * ZB +Largest (Pspare) * ZZB
(Qpeak) = S (Qcontinuous) * XB + Largest (Qintermittent) * YB + Largest (Qstandby) * ZB +Largest (Qspare) * ZZB
In order to identify the largest non-continuous load, the software analyzes the situation
for intermittent, spare, and standby loads separately. For each of these operating
modes, the results of the analysis can be different. Therefore, the largest intermittent,
standby, and spare loads could be different loads.
Calculating Bus Grand Total Apparent Power
The bus grand total apparent power is calculated 2 3 = 8 times (for run and peak, compensated and uncompensated, rated versus consumed power) as a vector sum of grand total of active and reactive power: Note that for this calculation, there is no difference whether the calculation preference was set for the largest non-continuous load or not.
(S) = Ö ((S(P))2 + (S(Q))2)
Where:
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S(P) — active power total
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S(Q) — reactive power total
Calculating Bus Power Factor
The following formula is used to calculate bus power factors (PF):
PF = (P) / (S)
Where:
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(P) — active power total
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(S) — apparent power total
This calculation is also performed eight times: for (run and peak) * (compensated and uncompensated) * (rated and consumed).
Calculating Bus Line Current
The following formula is used to calculate bus line current:
I = (S) / (U * Ö3) in amperes
Where:
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(S) — compensated apparent power
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(U) — bus rated voltage (line voltage)
This calculation is performed only four times. It is made for compensated values only: (run and peak) * (rated and consumed).