The software calculates electrical power requirements for motors based on the load data you enter, which in turn comes from the motor manufacturer. On the Electrical Data Tab (Electrical Motor Common Properties Dialog), the software displays the results of the electrical power requirement calculations.
Calculations for Motors
Input Data
The software requires the following data, which you enter on the Load Data Tab (Electrical Motor Common Properties Dialog):
Motor rated power
Specifies the maximum mechanical power requirement for the motor.
Brake power
Specifies the mechanical power requirement for the motor at the demand point.
Demand factor
The software calculates the demand factor as the ratio of the brake power to the motor rated power. The demand factor represents the operating point of the motor that the software uses for the calculations.
Power factor
The software calculates the power factor at the operating point based on the standard power factor values at 50%, 75%, and 100% of the motor rated power.
Efficiency
The software calculates the efficiency at the operating point based on the standard efficiency values at 50%, 75%, and 100% of the motor rated power.
Power Factor Calculations
The software calculates the power factor and efficiency at the operating point by assuming a linear relation between the standard values at 50%, 75%, and 100% of the motor rated power and interpolating accordingly. For an operating point below 50% of the motor rated power, the software extrapolates using the known slope between the values at 50% and 75% of the motor rated power.
The following values apply to power factor calculations:
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PF50 = power factor @ 50% (number between 0 and 1)
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PF75 = power factor @ 75% (number between 0 and 1)
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PF100 = power factor @ 100% (number between 0 and 1)
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PF@DF = power factor @ demand factor (number between 0 and 1)
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DF = demand factor (number between 0 and 1)
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EF@OP = efficiency @ operating point (number between 0 and 1)
The graph shows how the software uses the user input values to calculate the power factor at a given demand factor.
Based on the graph, the software calculates the power factor for different ranges of the demand factor using the following formulas.
For a demand factor between 75% and 100%:
For a demand factor between 50% and 75%:
For a demand factor below 50%:
The software uses a similar set of formulas to calculate the efficiency.
Locked Rotor Current Calculation by Code Letter
(Applicable for NEC)
Indicating a code letter copies a fixed value from the LockedRotorIndicatingCodeLetters lookup table to the kVA to HP ratio property.
Apparent Power (VA) = 1000 * kVA to HP ratio * Motor Rated Power (hp)
This equation is applicable only when setting the conformity standard to NEC and
the FLA calculation to TABLES.
Calculations for Static Loads
Rated Power
Rated power is the electrical output power of a load as it appears on the load nameplate. The units of measure depend on the type of load.
Absorbed Power
This is the output electrical power at normal operating point.
Demand Factor
This is the ratio of the load power requirement at a specified operating point to the rated power. The demand factor influences the consumed electrical power of the load.
The software calculates the demand factor as the ratio of the absorbed power to the rated power. The demand factor represents the operating point of the load that the software uses for the calculations. Demand factor values can be inserted manually or calculated as the ratio of absorbed power to rated power.
Power Factor
This is the power factor of a static load at rated or operating point. Power factor values can be between zero and one, entered manually.
Efficiency
This is the efficiency of a static load at rated and operating point. Efficiency values can be between zero and one, entered manually.
Equations
The software uses the following equation to calculate absorbed power (or demand factor):
Electrical Power Calculations
The software calculates the rated, particular, and consumed load, that is, the electrical power, using the equations below.
The following equations are used to calculate rated value for all static loads except for capacitors and harmonic filters:
The following equations are used to calculate consumed value for all static loads except for capacitors and harmonic filters:
The following equations are used to calculate consumed values for capacitors and harmonic filters:
Reactive Load (kVAR) = Absorbed Power (kVAR)
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For static loads, the software uses the values of the absorbed and rated electrical power to calculate the electrical quantities.
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For capacitors and harmonic filters, the active load property is disabled and has a null value.
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For heaters, the reactive load property is disabled and has a null value.
Calculation of Full Load Current
The software uses the following formulas to calculate full load current.
Where:
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k=1 for DC and single-phase AC
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k=Ö3 for three-phase AC
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Rated voltage is the line voltage
Calculation of Synchronous Speed
The software calculates the synchronous speed of a motor or a generator according to the following equation:
