The program in this method runs three load flows: Before Starting, During Starting and After Starting. Voltage dip is defined as:
Voltage Dip = V(Before) - V(During) (Volts) (1)
or Voltage Dip = 100 · ( V(Before) - V(During) ) / V(Before) (%)
A motor is treated as a load in the load flow calculation. For Before Starting condition, the motor load is 0.0; for the After Starting condition the motor load is equal to the motor normal running load and for the During Starting condition the motor load is equal to the motor normal running load times the NEMA factor, which is defined as the ratio of locked rotor motor starting current over the motor normal running current. The following figure shows the input data of NEMA and Lock Rotor Amps.
The motor load can be modeled as constant KVA, constant current or constant Z load. For induction motor starting, it is recommended that the constant Z load type be used. There are also different motor starter types to choose in this method as shown in the following figure (Figure 11).
Figure 11: Motor “Motor Start” dialog box
The following equations are used for motor load calculation:
where, HP is the motor horse power; PF power factor; LRAmps motor locked rotor current. For different motor starters, the motor starting inrush KVA is multiplied by a factor, called tap setting. For example, for an auto-transformer 80% starter, the tap setting (multiplying factor) is 64%. The starting inrush KVA is calculated as follows:
KVA(starting,AutoXfr80%) = 0.64 · KVA(starting,FullVolt) (6)
The following is an example of motor starting output, where the voltage Before, During and After are shown in Volts and voltage dip in %.
System V (PU) V (PU) VDip V (PU)
APPENDIX A: Dynamic Motor Start Tutorial
Motor to be started
Figure 12: Network under study
Figure 12 shows the network topology that will be used for the study. The motor to be started is recognized by the system as bus id 10, and it is clearly marked in the above figure. The motor characteristics are as follows:
Rated Voltage: 4,160 Volts
This tutorial exercise will illustrate, step-by-step, how to perform motor starting analysis using the following methods:
The full voltage method will calculate the worst-case scenario, which can then be compared with the other five Solid-State starting methods. The specific results for rest of the starters can be obtained from Table 1 of this tutorial.
Motor Start Summary Results
The table below summarizes the motor acceleration time and voltage recovery based on starting method.
Table 1: Results comparison between the different motor starting methods.
Starting Method Acceleration
From the above table the user can simulate the motor starting using various starter controller and select the appropriate controller type for his application.
Note:
The series reactance, Series Resistance, Shunt Capacitance, Wye-Delta, Part Winding, and Auto Transformer controllers have speed and Voltage Control function options in addition to the time option. While real controllers may not actually have Speed or Voltage type controls in a motor starting mode, these additional functions are included to help the user determine the correct time at which the motor will reach a particular speed. The user can run the study to determine the time, and then re-run the study with the correct time based on speed and voltage.
A Tutorial No. 1: Full Voltage Start
A.1 Open the pre-built file named “Loadramp.axd”. Once the file has been loaded, proceed to set the motor Bus 10 into the started mode and get the “motor Dynamic Information” dialog box as shown in the following screen picture.
Step 1.
Double-click and set the motor as “To be Started”.
Step2.
Select “Motor Dynamic Information” dialog box button.
Figure 13: Set Starting Motor
A.2 Enter all the relevant data that pertains to the Motor Starting method and the Motor itself. Proceed as indicated in the following screen capture (Figure 14 ~ 16).
Step 2.
Enter an appropriate description and data.
Make sure “Equivalent Circuit” is selected.
Step 1.
On the “General” tab, select the starting motor
Figure 14: General Motor Dynamic Data
Step3.
On “Motor Starter” tab, select “Full Voltage” as the starting method.
Figure 15: Motor Starter Selection
Step 4:
A.3 Enter information in the options dialog and then click “Analyze” button to do the calculation as shown in the following screen pictures (Figure 17 ~ 18).
“Options” and “Analyze”
Figure 17: Motor Starting Tool Bar
Select “Individual Dynamic Motor Start method.
Figure 18: Motor Starting Options
A.4 Select the “Analyze” button to complete the analysis and then select Report Manger to view results.
Report Manager icon.
Result reports
Figure 19: Motor Start Report Manager
Summary text result: Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Full Voltage Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic result:
B Tutorial No. 2: Solid State Voltage Control
B.1 In this tutorial, the same motor used in tutorial No. 1, will be started using a Solid State Voltage controlled starter. The starting process will be ramped up in two time-based steps as follows:
Step 1- Time: 0.0 sec
Voltage: 0.5 PU
Step 2- Time: 3.0 sec
Voltage: 1.0 PU
Step 2:
Enter the required voltage control stages here.
Step 1:
Select “Solid State Voltage Control”, and select “Time (sec.)”
B.2 Select the “Analyze” button to complete the analysis and then select Report Manger to view results. Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Solid State Voltage Control Time (Sec.) : 0.000 3.000
Tap (pu) : 0.500 1.000
Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic Result:
C Tutorial No. 3: Solid State Current Limit
C.1 In this tutorial, the same motor used in tutorial No. 1, will be started using a Solid State Current Limited starter. The starting process will limit the starting current to a maximum value of 3.5 PU, as shown in the following screen picture:
Step 2:
Enter the required current limitation factor here.
Step 1:
Select “Solid State Current Limit”.
C.2 Select the “Analyze” button to complete the analysis and then select Report Manger to view results. Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Solid State Current Limit Current (pu) : 3.50
Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic Result:
D Tutorial No. 4: Solid State Current Ramp
D.1 In this tutorial, the same motor used in tutorial No. 1, will be started using a Solid State Current Ramp controlled starter. The starting process will be ramped up in two points as follows:
Point 1- Time: 0.0 sec
Current: 3.5 PU
Point 2- Time: 3.0 sec
Current: 5.0 PU
Step 2:
Enter the required current ramp stages here.
Step 1:
Select “Solid State Current Ramp”.
D.2 Select the “Analyze” button to complete the analysis and then select Report Manger to view results. Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Solid State Current Ramp Time (Sec.) : 0.00 3.00
Current (pu) : 3.500 5.000
Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic Result:
E Tutorial No. 5: Solid State Voltage Ramp
E.1 In this tutorial, the same motor used in tutorial No. 1, will be started using a Solid State Voltage Ramp controlled starter. The starting process will be ramped up in two points as follows:
Point 1- Time: 0.0 sec
Voltage: 0.6 PU
Point 2- Time: 3.0 sec
Voltage: 0.9 PU
Step 2:
Enter the required voltage ramp stages here.
Step 1:
Select “Solid State Voltage Ramp”.
Summary text result: Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Solid State Voltage Ramp Time (Sec.) : 0.00 3.00
Voltage (pu) : 0.600 0.900
Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic Result:
F Tutorial No. 6: Solid State Torque Ramp
F.1 In this tutorial, the same motor used in tutorial No. 1, will be started using a Solid State Torque Ramp controlled starter. The starting process will be ramped up in two points as follows:
Point 1- Time: 0.0 sec
Torque: 0.7 PU
Point 2- Time: 3.0 sec
Torque: 2.0 PU
Step 2:
Enter the required torque ramp stages here.
Step 1:
Select “Solid State Torque Ramp”.
F.2 Select the “Analyze” button to complete the analysis and then select Report Manger to view results. Motor Magnetization Resistance = 6318.000 Ohms Motor Magnetization Reactance = 54.940 Ohms Motor Rotor Resistance Cage Factor = 0.104 Motor Rotor Reactance Cage Factor = 0.000
Load Name in Library : Loadramp
Motor Start Type at Stage 1: Solid State Torque Ramp Time (Sec.) : 0.00 3.00
Torque (pu) : 0.700 2.000
Switch to Stage 2 at 999.00 seconds Motor Start Type at Stage 2: Full Voltage
Simulation Results
Graphic Result:
APPENDIX B: Simultaneous Multi-Motor Starting Snapshots method Tutorial
G Network under Study
Figure 20: Network under Study (File name: MX339.Axd)
The purpose of this tutorial exercise is to illustrate the steps required to run a Motor Starting Analysis using the Simultaneous Multi-Motor Starting Snapshots method. Additionally, this exercise will be used to verify the validity of EDSA's calculations versus the motor starting analysis example described in IEEE std. 399-1997, pages 244 to 253. The EDSA one line diagram was shown in Figure 20. The impedances provided in the IEEE example are expressed in per-unit on a 100 MVA base. In the tutorial example, a base of 100 MVA has also been used for the purpose of consistency. In addition, the network was modeled as follows:
1. Branches of negligible impedance were added to Load 1, Load 2 and the Motor under study.
2. For the 1000 HP motor, a running power factor of 0.85 and efficiency of 0.88 is assumed. Since it is assumed that 1 kVA = 1HP (Reference IEEE 399-1997 Page 240 Section 9.5.2), then,
EFF*PF = 0.746
In EDSA, PF* EFF = 0.85 * 0.88 = 0.748 and the FLA is equal to:
FLA 1000
4.16 3 138.786 amps then, LRA = 6 x FLA = 832.72 amps
= =
3. The network was modeled as shown in Figure 20 and as defined in IEEE 399-1997, Section 9.6.3, pages 243 to 250. From a Short Circuit point of view, the generator was modeled as an 115kV, 12MVA unit with a 15% transient reactance (refer to page 249, Section 9.6.3 of the standard). These values, translate to a reactance of 1.25 pu on the 100 MVA base. From the Load Flow point of view, the generator has been defined as swing bus.
4. As illustrated in the IEEE std. 399-1997, the driving EMF within the generator (behind the transient reactance) was modeled as an ideal source of 1.0564 Volts pu. This causes the voltage at the physical terminals of the generator to be 1.0 pu, as a result of the voltage drop across the source's short circuit impedance. This tutorial will demonstrate that it is not necessary to resort to this additional modeling effort in order to account for the effect of the source impedance. EDSA Motor Starting includes an option whereby the user can choose to include the source impedance in the motor starting calculations. Once this option is selected, the program will automatically create the driving EMF required for the calculations inside the program. One of the advantages of this feature is that it saves time and avoids confusion by keeping the original single line diagram intact.
G.1 Enter Input Data
G.1.1 Generator Data
After opening the project file (Figure 20), select the Generator bus (Bus 1) and double-click it with the left mouse button. The editor dialog box (Figure 21) comes out.
As can be seen in the generator editor screen capture, the 12 MVA generator was modeled as a source with a reactance of 1.25 pu on the defined basis of 100 MVA and 115 kV. In order to compare the values obtained from this tutorial with those calculated by the IEEE std. 399-1997, an angle of -4.1 degrees was assigned to the generator.
Remember that a fictitious swing bus (bus 99) was used to model the ideal driving EMF of the source in the IEEE std. 399-1997. Since the IEEE std. 399-1997 assigned an angle of 0 degrees to this bus, we must compensate by displacing the angle at our generator terminals by an amount such that it will yield a 0-degree angle on the program's internal swing bus. The angle field is on the Load Flow tab as shown in Figure 22.
Figure 21: Generator Data
G.1.2 Motor Data
Double click the Motor bus (Bus 6) shown in Figure 20, the motor editor comes out. Make sure the “To Be Started”
button under Motor Start tab is on, the Motor Starter Type is Full Voltage, the Motor Load Type is Constant Z and the Tap Setting is 100%, as shown in Figure 23.
Figure 23: Motor Data under Motor Start
Under Short Circuit tab, the Motor Rating is 1000 HP, the Efficiency is 88 %, the Power Factor is 85 %, the Starting PF field type 15 %, the LR Amps (locked rotor amps) field reads 832.72 Amps, as shown in Figure 24.
G.2 Motor Starting Analysis Results
Figure 25: Motor Starting Options
In motor starting options dialog box (Figure 25), select Simultaneous Multi-Motor Starting Snapshots method and for “Include Power Source Z”, select X”, which causes the program to include the 1.25pu source short circuit impedance in the voltage drop calculations.
Select “Analyze” to complete the analysis. The text result will automatically come out if the “Auto Text Report” in Figure 25 is checked, or select the report manager as shown in Figure 26.
Report Manager
Motor Starting Text Report and Summary Report
Figure 26: Report Manager
Motor starting text report and summary report are shown below.
Following is a comparison table between the results obtained with EDSA and the results documented in the IEEE std.399-1997, page 253:
Table 2: Comparison to IEEE Standard
Voltage PU Tot. kW Loss Tot. kVAR Loss BUS ID
IEEE EDSA IEEE EDSA IEEE EDSA
Bus 1 / Main Xfmr Pri 0.929 0.929 Bus 2 / Main Xfmr Sec. 0.865 0.865 Bus 3 / 5MVA Xfmr Sec. 0.835 0.835 Bus 4 / Mtr Strt Bus 0.794 0.794
174 174 3,608 3,608
ERROR 0% 0% 0%
As indicated by the above figures, the EDSA Motor Starting program provides accurate results compared to the IEEE standard.