Motor Data

Uniquely identifies the equipment item. The program automatically assigns a name, but you can change it, if needed. The name can be up to 16 characters long.

For motors, the program automatically assigns the names M-1, M-2, M-3, and so on.

This is the ID name of the bus to which the equipment is connected. The base kV of the bus is indicated on the right.

Ensure that the To Bus has approximately the same base kV as the motor.

The power type for the motor. Select from:

• NPS (normal power supply—for example, one that has no power backup)
• EPS (emergency power supply—for example, one that uses a generator for backup)
• CPS (critical power supply—for example, one that uses an uninterrupted power source)

Motor horsepower. Motors may be represented individually or as a lumped group. For a grouped motor, enter the total horsepower for the group.

This displays if the unit selected is US.

Motor kilowatts. Motors may be represented individually or as a lumped group. For a grouped motor, enter the total kilowatts for the group.

This is displayed if the unit selected is metric.

Revolutions per minute. Used in output reports and defining equipment for ANSI or IEC standard short circuit calculation multipliers.

By default, ANSI uses 1800 and IEC uses 1500, unless the default equipment settings for motors are set to use a different value.

Selecting this check box changes the motor symbol in the one-line as shown below.

Figure 3: Motor Symbol with Adjustable Frequency Drive

Provides an easy way to enter ANSI Standard impedances and interrupting duty multipliers. Code numbers are chosen according to the motor types, sizes and modeling method. Regardless of the code chosen, ANSI Standard interrupting value multipliers are used.

The codes available in this list change depending on what you have selected in the Type field of the Specifications tab. Using the ANSI Code field is the recommended method to enter motor impedances to assure that the proper interrupting duty impedance multiplier is used for ANSI Standard calculations^1,2,3,4.

See ANSI Code Impedances for more information.

If the Adjustable Frequency Drive check box is selected in the Specifications tab, the following choices are available for the ANSI Code field:

• Non-Regenerative: Motor does not contribute short circuit currents to upstream faults.
• Regenerative: Motor contributes to upstream faults. The impedance multipliers are used as per Conrad St. Pierre’s A Practical Guide to Short –Circuit Calculations.

Note: Grouped motors with an adjustable frequency drive are non-regenerative motors and do not have contribution regardless of the motor type

Reference:
¹ AC High Voltage Circuit Breakers Rated on a Symmetrical Current Basis, ANSI/IEEE Std. C37.010-1979
² Calculation of Fault Current for Application of AC High Voltage Circuit Breakers Rated on a Total Current Basis, ANSI/IEEE St. C37.5-1979
³ Low Voltage Power Circuit Breakers Used in Enclosures, ANSI/IEEE Std. C37.13-1981
⁴ Calculation of Short Circuit Currents with Contributions From Induction Motors, Walter C. Huening Jr., IEEE/IAS Mar/Apr 1982

When this option is selected, IEC short circuit calculations are used. See IEC Impedance and X/R Calculations.

If the motor has an adjustable frequency drive, you can also select the option for a regenerative or non-regenerative drive.

Note: Grouped motors with an adjustable frequency drive are non-regenerative motors and do not have contribution regardless of the motor type

Subtransient reactance in percent on the motor Hp base. Normally this is 16.7% for induction motors.

If you have the locked rotor multiple (LRM) which is the ratio of the lock rotor current to the rated motor current, then you can calculate the impedance in percent using 100 / (LRM).

Provides an easy way to adjust the total motor horsepower used in determining short circuit currents. By changing the percent connected, the actual Hp (total connected value) entered in the Hp field can remain static. This reduces modeling errors and eliminates multiple databases for different contingencies.

For example, an MCC has a group of induction motors (all over 50 HP) that add up to a total load of 600 HP. However, 300 HP is considered backup and is not on-line. In order to keep proper records of the MCC HP, 600 would be entered in the HP field. Since only 300 HP is spinning at any one time and can contribute short circuit current, the connected field is set to 50%.

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1) Calculate the MW per pole-pair by dividing MW by pole-pairs.

• MW is the rated output MW for the motor.
  • Metric: MW = rated kW for motor / 1000.
  • U.S: MW = HP * 0.746 / 1000.
• Pole-pairs = system frequency * 60 / motor sync RPM (from the Specifications tab.)

2) Calculate the X/R ratio of the motor.

• If the motor kV is greater than 1.0 and the MW per pole-pair is greater than or equal to 1.0, then X/R is 10.0.
• If the motor kV is greater than 1.0 and the MW per pole-pair is less than 1.0, then X/R is 6.667.
• If the motor kV is less than or equal to 1.0, the X/R ratio is based on the ANSI calculations.

Impedance is 16.7%.

Impedance and X/R are calculated as follows:

• If motor kV less than or equal to 1.0, then impedance is 20% and the X/R ratio is 2.381.
• If the motor kV is greater than 1.0 and MW per pole-pair is greater than or equal to 1.0, then impedance is 16.7% the X/R ratio is 10.0.
• If the motor kV is greater than 1.0 and the MW per pole pair is less than 1.0, the X/R ratio is 6.667.

Impedance is 16.7% and the X/R ratio is 10.

Provides a list of motor starters. Select the appropriate starter from the following:

• Full Voltage: The motor starts at the rated voltage, without any starting device connected to it.
• Auto-transformer: An auto-transformer is used as a starting device to reduce the starting current. The tap value of the auto-transformer, as a percentage of the rated motor voltage, is entered in the edit field Auto-Xfrmr Tap at the bottom of the dialog box.
• Part-Winding: Part-winding start motors, in which only a part of the winding is used for starting. The entire winding is energized after start up. The Winding Tap must be specified at the bottom of the dialog box.
• Wye-Delta: The starter keeps the motor windings in wye-connection while starting to reduce the starting current. After start up the starter connects the windings in delta configuration.
• Reduced Voltage: The starting voltage during starting is less than the rated voltage. The inrush current for reduced voltage starting, as a multiple of full load amps, must be specified at the bottom of the dialog box.

Full Voltage Starting Parameters

This section specifies the motor current characteristics during starting at the rated motor voltage.

Specifies the starting time and the current or voltage ratio under reduced voltage. Depending upon the motor starter type selected enter one of the following. The starting current will be calculated from this.

• Auto-Xfrmr Tap: The auto-transformer tap ratio as a percentage of rated voltage.
• Winding Tap: Starter winding ratio as a percentage of full motor winding.
• Reduced Inrush Mult: The inrush current at reduced voltage, as a multiple of full load amps.

Motors can be modeled for the power flow solution in several different ways.

• Constant kVA - This is the most common model. It is conservative, and results in slightly lower voltage values than would be measured on an actual system.
• Constant Current - This model is generally not used in motor modeling. It more closely matches an induction motor's characteristics in the reactive component than other models, but is technically incorrect because kW is relatively constant throughout the voltage range for an induction motor.
• Constant Impedance - This model is used for starting induction and synchronous machines, and closely matches motor characteristics during low voltages.
• kW + j Current - This model is a combination of the above models and more closely matches actual motor characteristics within normal operating voltages.

SCADA Model

SCADA data is derived from real time, or metered data, and converted to an ASCII format which can be read into EasyPower. SCADA data is read in as a 100% scaling factor load. The load value is multiplied by the user-defined scaling factor. This provides a way to adjust SCADA loads to form new cases.

SCADA data can be modeled in the power flow solution in several different ways. SCADA load type is set in the ASCII file, but you can change it.

• Constant kVA - This is the most common model. It is conservative, and results in slightly lower voltage values than would be measured on an actual system.
• Constant Current - This model is generally not used in motor modeling. It more closely matches an induction motor's characteristics in the reactive component than other models, but is technically incorrect because kW is relatively constant throughout the voltage range for an induction motor.
• Constant Impedance - This model is used for starting induction and synchronous machines, and closely matches motor characteristics during low voltages.
• kW + j Current - This model is a combination of the above models and more closely matches actual motor characteristics within normal operating voltages.

The default is Linear, indicating the equipment does not produce harmonics. Choosing Harmonic makes the item an harmonic source and makes other fields in this tab available to edit.

Note:
For an adjustable frequency drive (AFD), the Load Type is always Harmonic.
For motors, the Load Type is Harmonic if the With Adjustable Frequency Drive (AFD) check box is selected on the Specifications tab of the motor; otherwise, it is always Linear.

Use to set the fundamental amps. The options are as follows:

• Equipment Rating sets Fundm Amps to the equipment rating of the item described in the Specifications tab. 
• User Specified activates the Fundm Amps field, enabling you to specify a value. 

To use fundamental current calculated by power flow, select Calculated from Power Flow in the Summation Fundamental Voltage area of the Harmonics Options > Control dialog box.

Use the spreadsheet to enter the harmonic spectrum produced by this item. You can enter up to 30 different harmonics in each equipment item. In the spreadsheet, enter the Harmonic Number (such as 5 for the 5^th harmonic), the Harmonic Current in percent of the Fundamental Amps, and the Current Angle. By indicating the current angle, you can simulate transformer phase shift effects on rectifiers so appropriate canceling can take place. The harmonic may be integer or non-integer.

Common harmonic spectra may be entered from the device library. For instructions on how to enter your own spectra information, see Harmonics with Spectrum™. After selecting a particular device library spectrum from the Mfr and Type lists, click Import, and that spectrum is entered into the harmonic spreadsheet.

Select the check box to enter stability information.

Without this, you cannot run a dynamic simulation for the motor.

This setting selects the method by which the motor will be initialized. The two options for this setting are:

• Init Using Rated Power: When initialized using rated power (default), the motor determines the slip necessary to maintain the terminal power conditions (kW) from the power flow case. Motor kVar is determined completely by the induction motor machine equations.
• Init Using Rated Slip: When initialized using rated slip, the motor forces terminal real power conditions (kW) to correspond to the specified rated slip of the motor. Thus, power conditions defined in the power flow case are abandoned to match slip. Motor kVar is determined completely by the induction motor machine equations.

Explanation: There are conditions where a motor parameter derivation has significant errors in rated conditions (such as upwards to 10%) when attempting to match a manufacturer's torque vs. speed curve. This is most likely created by inconsistencies in the supplied data for various reasons. For such conditions, initializing to rated power defined by the power flow causes a new slip to manifest through initialization, which is not equal to the specified rated slip. This then creates a condition where the torque produced by the motor during starting can be significantly greater than the torque vs. speed curve generated in the parameter derivation. For a motor in a borderline start condition (near stalling), the results may show an incorrect successful start (we have seen up to 12% greater torque over the motor's speed range). To correct for this, select "Init Using Rated Slip". This will force the motor to re-create the exact torque vs. speed curve generated in the parameter derivation. Note however that the rated conditions reached after starting will have the error accepted in the parameter derivation.

Motor Starting Load

This section defines the model for load characteristics while the motor is starting.

Lists available starting load models in the library. The choices are:

• Speed Squared: The torque is proportional to the square of the speed.
• Speed Cubed: The torque is proportional to the cube of the speed.
• Torque vs. Speed: User-defined spreadsheet.

Motor Running Load

This section defines the model for load characteristics while the motor is running.