09 - Motor Acceleration

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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

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