ETAP 5.0 Motor Acceleration
Copyright 2003 Operation Technology, Inc.
Why to Do MS Studies? • Ensure that motor will start with voltage drop • If Tst
• 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
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 2
Motor Types • Synchronous • Salient Pole • Round Rotor
• Induction • Wound Rotor (slip-ring) • Squirrel Cage (brushless)
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 3
Typical Rotor Construction
• Rotor slots are not parallel to the shaft but skewed
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 4
Wound Rotor
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 5
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
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 6
Slip Frequency • Slip represents the inability of the rotor to keep up with the stator magnetic field • Slip frequency S = (ωs-ωn)/ωs
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
where ωs = 120f/P ωn = mech speed
Slide 7
Motor Torque Curves
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 8
Acceleration Torque
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 9
Operating Range • Motor, Generator, or Brake
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 10
Rated Conditions • Constant Power
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 11
Starting Conditions • Constant Impedance
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 12
Voltage Variation • Torque is proportional to V^2 • Current is proportional to V
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 13
Frequency Variation • As frequency decreases, peak torque shifts toward lower speed as synchronous speed decreases. • As frequency decrease, current increases due reduced impedance.
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 14
Number of Poles Variation •
As Pole number increases, peak torque shifts toward lower speed as synchronous speed decreases.
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 15
Rotor Z Variation • Increasing rotor Z will shift peak torque towards lower speed.
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 16
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 Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 17
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 Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 18
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:
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 19
Circuit Model I • Single Cage Rotor – “Single1” – constant rotor resistance and reactance
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 20
Circuit Model II • Single Cage Rotor – “Single2” - deep bar effect, rotor resistance and reactance vary with speed [Xm is removed]
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 21
Circuit Model III • Double Cage Rotor – “DB1” – integrated rotor cages
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 22
Circuit Model IV • Double Cage Rotor – “DB2” – independent rotor cages
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 23
Characteristic Model • Motor Torque, I, and PF as function of Slip – Static Model
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 24
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 Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 25
Calculation Methods II
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 26
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
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 27
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 Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 28
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 Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 29
Starting Devices Types • Auto-Transformer
• Y/D Winding
• Stator Resistor
• Partial Wing
• Stator Reactor
• Soft Starter
• Capacitor at Bus
• Stator Current Limit
• Capacitor at Motor Terminal
– Stator Current Control
• Rotor External Resistor
– Torque Control
– Voltage Control
• Rotor External Reactor Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 30
Starting Device • Comparison of starting conditions
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 31
Starting Device – AutoXFMR • Autotransformer
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 32
Starting Device – Stator R • Resistor
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 33
Starting Device Stator X • Reactor
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 34
Transformer LTC Modeling • LTC operations can be simulated in motor starting studies • Use global or individual Tit and Tot
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 35
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 statusÆclosing operation – Close statusÆopening operation
• For studies, MOV can only be started once Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 36
MOV Modeling II • Five stages of operation Opening
Closing
Acceleration
Acceleration
No load
No load
Unseating
Travel
Travel
Seating
Stall
Stall
• Without hammer blow Æ Skip “No Load” period • With a micro switch Æ Skip “Stall” period • Operating stage time extended if Vmtr < Vlimit
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 37
MOV Closing • With Hammer Blow- MOV Closing
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 38
MOV Opening • With Hammer Blow- MOV Opening
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 39
MOV Voltage Limit • Effect of Voltage Limit Violation
Copyright 2003 Operation Technology, Inc. – Workshop Notes: Motor Acceleration
Slide 40
