This document provides an overview of motor acceleration studies and modeling in ETAP 5.0 software. It discusses the importance of motor acceleration studies, different motor types, modeling approaches like circuit models and characteristic curves, and features for simulating starting devices, transformer LTC operations, MOV operations, and more. The goal is to ensure motors can start successfully under voltage drops and evaluate impacts on other loads during starting.

1. ETAP 5.0ETAP 5.0
Copyright 2003 Operation Technology, Inc.
Motor Acceleration

2. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 2
Why to Do MS Studies?
• Ensure that motor will start with voltage drop
• If Tst<Tload at s=1, then motor will not start
• If Tm=Tload at s<sr, motor can not reach rated speed
• Torque varies as (voltage)^2
• Ensure that voltage drop will not disrupt other loads
• Utility bus voltage >95%
• MCC bus voltage >80%
• Generation bus drop <7%
• Ensure motor feeders sized adequately

3. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 3
Motor Types
• Synchronous
• Salient Pole
• Round Rotor
• Induction
• Wound Rotor (slip-ring)
• Squirrel Cage (brushless)

4. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 4
Typical Rotor Construction
• Rotor slots are not parallel to the shaft but
skewed

5. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 5
Wound Rotor

6. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 6
Operation of Induction
Motor
• AC applied to stator winding
• Creates a rotating stator magnetic field in air gap
• Field induces currents (voltages) in rotor
• Rotor currents create rotor magnetic field in air gap
• Torque is produced by interaction of air gap fields

7. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 7
Slip Frequency
• Slip represents the inability of the rotor to
keep up with the stator magnetic field
• Slip frequency
S = (ωs-ωn)/ωs where ωs = 120f/P
ωn = mech speed

8. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 8
Motor Torque Curves

9. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 9
Acceleration Torque

10. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 10
Operating Range
• Motor, Generator, or Brake

11. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 11
Rated Conditions
• Constant Power

12. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 12
Starting Conditions
• Constant Impedance

13. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 13
Voltage Variation
• Torque is proportional to V^2
• Current is proportional to V

14. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 14
Frequency Variation
• As frequency decreases, peak torque shifts toward lower
speed as synchronous speed decreases.
• As frequency decrease, current increases due reduced
impedance.

15. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 15
Number of Poles Variation
• As Pole number increases, peak torque shifts toward lower
speed as synchronous speed decreases.

16. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 16
Rotor Z Variation
• Increasing rotor Z will shift peak torque towards lower
speed.

17. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 17
Modeling of Elements
• Switching motors – Zlr, circuit model, or
characteristic model
• Synch generator - constant voltage behind
X’d
• Utility - constant voltage behind X”d
• Branches – Same as in Load Flow
• Non-switching Load – Same as Load flow
• All elements must be initially energized,
including motors to start

18. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 18
Motor Modeling
1. Operating Motor
– Constant KVA Load
2. Starting Motor
– During Acceleration – Constant Impedance
– Locked-Rotor Impedance
– Circuit Models
Characteristic Curves
After Acceleration – Constant KVA Load

19. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 19
Locked-Rotor Impedance
• ZLR = RLR +j XLR (10 – 25 %)
• PFLR is much lower than operating PD.
Approximate starting PF of typical squirrel
cage induction motor:

20. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 20
Circuit Model I
• Single Cage Rotor
– “Single1” – constant rotor resistance and
reactance

21. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 21
Circuit Model II
• Single Cage Rotor
– “Single2” - deep bar effect, rotor resistance and
reactance vary with speed [Xm is removed]

22. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 22
Circuit Model III
• Double Cage Rotor
– “DB1” – integrated rotor cages

23. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 23
Circuit Model IV
• Double Cage Rotor
– “DB2” – independent rotor cages

24. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 24
Characteristic Model
• Motor Torque, I, and PF as function of Slip
– Static Model

25. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 25
Calculation Methods I
• Static Motor Starting
– Time domain using static model
– Switching motors modeled as Zlr during starting and
constant kVA load after starting
– Run load flow when any change in system
• Dynamic Motor Starting
– Time domain using dynamic model and inertia model
– Dynamic model used for the entire simulation
– Requires motor and load dynamic (characteristic) model

26. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 26
Calculation Methods II

27. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 27
Static versus Dynamic
• Use Static Model When
– Concerned with effect of motor starting on other
loads
– Missing dynamic motor information
• Use Dynamic Model When
– Concerned with actual acceleration time
– Concerned if motor will actually start

28. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 28
MS Simulation Features
• Start/Stop induction/synchronous motors
• Switching on/off static load at specified loading
category
• Simulate MOV opening/closing operations
• Change grid or generator operating category
• Simulate transformer LTC operation
• Simulate global load transition
• Simulate various types of starting devices
• Simulate load ramping after motor acceleration

29. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 29
Automatic Alert
• Starting motor terminal V
• Motor acceleration failure
• Motor thermal damage
• Generator rating
• Generator engine continuous
& peak rating
• Generator exciter peak rating
• Bus voltage
• Starting motor bus
• Grid/generator bus
• HV, MV, and LV bus
• User definable minimum time
span

30. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 30
Starting Devices Types
• Auto-Transformer
• Stator Resistor
• Stator Reactor
• Capacitor at Bus
• Capacitor at Motor
Terminal
• Rotor External Resistor
• Rotor External Reactor
• Y/D Winding
• Partial Wing
• Soft Starter
• Stator Current Limit
– Stator Current Control
– Voltage Control
– Torque Control

31. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 31
Starting Device
• Comparison of starting conditions

32. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 32
Starting Device – AutoXFMR
• Autotransformer

33. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 33
Starting Device – Stator R
• Resistor

34. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 34
Starting Device Stator X
• Reactor

35. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 35
Transformer LTC Modeling
• LTC operations can be simulated in motor
starting studies
• Use global or individual Tit and Tot

36. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 36
MOV Modeling I
• Represented as an impedance load during
operation
– Each stage has own impedance based on I, pf,
Vr
– User specifies duration and load current for each
stage
• Operation type depends on MOV status
– Open status closing operation
– Close status opening operation
• For studies, MOV can only be started once

37. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 37
MOV Modeling II
• Five stages of operation
Opening Closing
Acceleration Acceleration
No load No load
Unseating Travel
Travel Seating
Stall Stall
• Without hammer blow Skip “No Load” period
• With a micro switch Skip “Stall” period
• Operating stage time extended if Vmtr < Vlimit

38. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 38
MOV Closing
• With Hammer Blow- MOV Closing

39. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 39
MOV Opening
• With Hammer Blow- MOV Opening

40. Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration Slide 40
MOV Voltage Limit
• Effect of Voltage Limit Violation