shorted rotor winding turns detection in salient pole rotor machines
Post on 14-Apr-2016
125 Views
Preview:
DESCRIPTION
TRANSCRIPT
Shorted Rotor Winding Turns Detection in Salient Pole
Rotor Machines
Outline
• Review salient pole rotor winding design• Insulation deterioration processes • Off-line and On-line testing and monitoring• Case studies
2
Off-line vs On-LineOff-line• Machine out of
service• Expensive• No load• Cold winding• No vibration• Testing voltage
source required
On-line• Machine in operation• Inexpensive, saves
time• Normal operation
voltage, temperature and vibrations
• Does not require test voltage source
• Centrifugal force
Synchronous Machines
• Rotor windings provide magnetic field• Windings provide ampere turns to develop
rated generator output within limits of voltage and temperature
• Electrical requirements of insulation minimal• Severe mechanical and thermal requirements• Rotor diameter up to 20 m, weight in hundreds
of tons
Cross section of 2 pole generator
S
N
Cross section of 4 pole generator
SSN
N
Cross section of 12 pole rotor
N
N
N
N
N
N
S
S
S
S
S S
Salient Pole Synchronous Motor Rotor
8
9
Hydro-generator Rotor
Turbo generator salient pole
Typical Laminated Rotor Pole Assembly
11
Rotor Pole
Turn voltages
• Large turbo: 5 to 15 volts per turn• 21,200 kVA 3600 rpm generator: 0.52 volts
per turn• 63000kVA 100 rpm generator 0.16 volts per
turn• 800 HP 1200 rpm motor: 0.098 volts per turn• Turn insulation can be subjected to high
transient voltages
Salient Pole Rotor Windings
• High speed machines are 4-8 poles• Up to 100 poles on large slow hydros• Synchronous motors (salient pole rotors)
have lower starting currents than squirrel cage induction motors
• Three types of winding: wire wound, edge wound and picture frame construction
• Voltages: 125-400 V DC
14
15
Winding Insulation
• Typical materials:- pole piece insulation, wrapped or molded:
nomex, fiberglass/resin laminate- Pole tips and rotor body: collars from high
strength glass/resin, slip planes on long poles
- Pre-wound coils potted after fitting on pole pieces
Multi-Layer Wire Wound Pole
• Mainly for smaller high speed and larger slow speed motors
• Use rectangular magnet wire to create the turns which are wound on to pole
• Turn insulation is usually a polyamide-imide film
• Ground insulation used to separate the turns from the rotor body
• Entire pole dipped in or VPI’d with resin
16
Multi-Layer Wire Wound Pole
17
“Strip-on-Edge” Pole
• For hydro generators and larger motors• Pole winding made from a continuous strip of
copper formed into a “slinky” or use rectangular “picture frames” with brazed connections
• Use strips of NomexTM or epoxy-glass laminates to separate the turns – resin bonded to conductors
• Tape used at the top and bottom few turns to increase creepage distances to pole body
• Sometimes impregnate entire pole with resin, or each pole winding is hot pressed to consolidate it.
18
“Strip-on-Edge” Pole
19
20
Rotor Winding – edge wound
21
Rotor Winding – picture frame
Rotor Winding Insulation Aging Processes
• Thermal• Electrical• Ambient• MechanicalDeterioration processes normally take many years (or even decades)
22
23
Thermal Aging
• Overloading or high cooling air temperatures• Inadequate cooling from poor design,
manufacture or poor maintenance• Use of materials having inadequate thermal
rating• Over-excitation of rotor winding• Shrinkage of bracing materials, looseness• Can result in both turn and ground insulation
failures
24
Thermal Cycling
• Frequent starts and stops or wide variations in load causing:
Relative movement between winding components
Cracking at interfaces due to differential expansion
Distortion of the winding conductors
• Can cause both turn and ground insulation failures
25
Repetitive Voltage Surges
• High transient voltages can be induced on the rotor winding from a static exciter or system surges
• Can cause turn to turn insulation faults
26
Contamination
• Can be in the form of:Moisture in cooling airOil from bearingsConducting dust in atmosphereChemicals in atmosphereA combination of these
• Both turn and ground insulation failures from tracking as well as winding overheating
• Chemicals can degrade winding insulation to cause failure
Strip on Edge Shorted Turns Due to Contamination
27
28
Abrasive Particles
• Abrasive particles such as coal dust, sand, iron ore (grinding) can enter the cooling air flow
• Particles impinge on the rotor winding they wear away the insulation
• Can cause both turn and ground faults
29
Centrifugal Forces• Mechanical failure of the insulation can result
from:
High continuous or cycling centrifugal forces during operation and starts/stops
• These forces can cause rotor winding failures from;
Inadequate intercoil bracing or shrinkage of bracing materials in salient pole and round rotor windings
Shorted Turn from MultilayerWire Wound Pole
30
Detection of Shorted Turns
Off-line• AC pole drop test, IR• RSO testOn-line• Increased bearing vibration• Increased excitation to achieve same MVA• Magnetic airgap flux monitoring
31
Relay Protection
• If fitted, failure of the ground insulation is normally detected by protective relaying that gives an alarm or trips the machine
• Failure of the turn insulation in one or more spots does not cause a trip – but may lead to increased bearing vibration (at once per revolution frequency) and limit the output
• An increasing number of turn shorts over time may indicate a higher risk of ground failure
• Insulation may fail suddenly or gradually due to aging
32
Pole Drop Test
• Apply 120 Vac across field winding and measure voltage drop across each pole
• Measure the 60 Hz inductive impedance of each pole to detect poles with fewer active turns, and thus lower inductance
• Poles with lower than average voltage drop may have shorted turns
• Shorts may disappear when rotor not spinning, and vice versa
33
RSO Test
• Recurrent Surge Oscillation• Low voltage (few volts), high frequency
(kHz range) surge injected into both ends of the rotor winding
• Time domain reflectometry based principle• Identical response indicates no shorted
turns
Magnetic Flux Monitoring to Detect Shorted Turns
• On-line method• Well established to detect shorted turns in
round rotor field windings• TF probe installed on a stator core tooth to
measure the induced voltage from the magnetic flux as each pole passes the probe
35
Total Flux ™ Probe Installation
Kit connection
Personal Computer
RFA II/Flux Trac II/Guard
Power supply 100-240 VAC
TF probe installed on a stator tooth
Flux Probe
Termination Box
Key Phasor
Monitoring shaft rotation
Iris RFA II
InstallationFlux MonitorTF Probe Termination
Box
Sync Sensor
TF Probe
TF Probe DetailMachine
Local USB port for configuration
Installation
Connection One Machine
Up to 4 Machines (Option)
150 m max.
Remote Communication• RJ45 port• Ethernet (LAN)• Off-the-shelf
converters allowed
• RotorFluxPro SW included– Memory data
downloading– Data displaying
LAN
RFA Pro Software
Signal Analysis
• High resolution magnitude and time A/D conversion
• Measure flux from each pole• Algorithms developed to reduce the
influence of rotor or stator asymmetry, air gap variations, etc
• If have a sensor to detect a specific location on the shaft (“key phasor”), then can identify the pole number
43
-Compare pole to average of all poles-Compare pole to its left and right neighbor-Compare pole to poles of same polarity
Three algorithms
Salient pole flux signal
Change of Flux Pattern with Load change
Compare to average
Compare to adjacent
Use of two algorithms 1Compare to average Compare to adjacent
Air gap comparison
Use of two algorithms 2Compare to average Compare to adjacent
Shorted pole graph
Shorted pole identification
Non-circular rotor shape
Square rotor!
Four Pole Motor Result
Conclusions
-In general, disagreements between pole drop test and on-line flux tests are possible due to lack of centrifugal forces in pole drop test
- Rotor winding insulation is very reliableHowever it does age due to thermal, mechanical and contamination stresses
-Shorted turns can cause high bearing vibration and may limit reactive power output
top related