Electrical Condition monitoring part 1

1. © 2010 Eaton Corporation. All rights reserved.
Condition On-Line Monitoring
Technologies
Joel Benzing
Marketing Manager
Eaton Corporation

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Goals Obtainable by User
Reliability increases
• How?
• Receive alerts to problems before fault occurs
Safety increases
• How? Same as above

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Benefits of Using
Predictive Diagnostics
• Avoid unplanned outages
• Lower maintenance costs
• Defer capital expenses by extending asset life
• Enables better decision-making

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Market Drivers
• Aging Infrastructure
• Rising Cost to Replacement Equipment
• Longer Lead Times for New Equipment
• Increased Pressure to Operate 24/7

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Key Enablers of Today’s Technology
Continuous Testing
• Eliminates missing a problem between periodic
tests
• 4-8 measurements per day for accurate trending
On-Line Testing
• Eliminates inaccuracies with off-line tests
• Reduces cost of mobilizing people and equipment

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Introduction to Partial Discharge Technology

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• PD is a localized electrical discharge in an
insulation system that does not completely bridge
the electrodes
Spark
Phase to Phase or
Phase to Ground
Key Enablers of Today’s Technology

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• Includes Wide Variety of Discharge Phenomena
- Internal Discharges in voids and cavities
within solid or liquid materials
- Surface discharges along interfaces of
different materials
- Corona – visible discharges on highly stressed
electrodes in gaseous insulation (commonly applied to
any type of partial discharges)
- Sparking to a conducting components under floating
potential
What is Partial Discharge?

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Partial Discharge

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Partial Discharge

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Phase to Phase Discharges on Ring Bus
49 MVA Generator
Partial Discharge

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Switchgear
Bus Damage
Partial Discharge

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Switchgear
Surface Tracking
On Shutter
Partial Discharge

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38 kV Bus Duct
Partial Discharge

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Switchgear - 38 kV
<<<< PT
Standoff >>>
Partial Discharge

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PD Measurement Technology

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How is PD Measured?
• PD is a very fast electrical spark (nS).
• PD creates phenomena that can be measured:
• Electromagnetic pulse
• Light emission
• Ultrasound wave
• Electro-Chemical reactions (Ozone)
• Any of above are used for PD detection
• Electrical PD sensing is most common
• Electrical PD sensing allows to quantify
phenomenon

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PD Electrical Measurement
PD Pulse
5 nsec - rise time
20 nsec - decay time
The spectrum seen by measuring instrument
20 MHz
Spectrum
PD Pulse

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Equipment Operation PD Limits

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-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
15 Degree Windows
Partial Discharge Pulses
Negative
Polarity
- Positive
Polarity
+
Cycle 1
Cycle 2
To N samples
PD Stops a 90 degrees PD Stops at 270 degrees
PulseMagnitude
PD Measurement Matrix

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Signal Attenuation & Noise
• Signal Attenuation
• Especially True in Rotating Equipment and large
Transformers
• Is higher for higher frequency
• Noise
• Does exist. The higher frequency – the lower noise
floor, but higher the attenuation
• Right Frequency band
• Compromise between Attenuation and Noise

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Signal Attenuation & Noise
• Traditional Factory Testing uses a lower
frequency band. (25 kHz - 800 kHz) (Classical
Band)
• Shielded rooms
• Little to No Noise
• In Field Environment Noise exists!
• Devices Must Move to a Higher Frequency Band to
eliminate Noise
• The Less Shift from the “Classical Band” the Better
• The lower the Frequency Band, the more coverage
by each individual sensor.

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Signal Attenuation & Noise
350 MHz
PD Instrument Response to the Same PD Event at Different Distances and Instrument Low
Frequency Cut-off Point
Distance to PD Source 0
0.2
0.4
0.6
0.8
1
25 kHz
1 MHz
20 MHz
30 MHz
500 kHz
Sensor Location
Coupling Capacitors
PD Pulse
Keep the frequency band of measuring
circuit as Low as possible!
NOISEFloor

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Basic Sensors
Coupling
Capacitor
RTD
Module
Radio Frequency
Current
Transformer

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27 kV
5 kV 7 kV 15 kV
38 kV
Coupling Capacitors
Traditional PD
Sensor – 80pf
Applications:
• Motors,
generators,
switchgear, dry
type transformers,
bus ducts.
• Any MV
equipment with
enough space to
mount and wire.

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Radio Frequency Current Transformer
Applications:
• Motors and small generators –
Feeder shield grounds, Surge
Capacitors grounds, frame ground.
• Substations – Feeder shield
grounds.
• Transformers – Feeder shield
grounds, tank ground.
Used wherever PD signals can be intercepted on
their way to ground

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Coupling Capacitor vs RFCT
PROS CONS
CC •Noise immune
•Has 60 Hz signal
component
•High frequency – can't see far
•Connected directly to HV
RFCT •Low frequency - Wide zone
of sensitivity
•Doesn’t interfere with HV
•Vulnerable to ground network
noise
•Has no 60Hz reference signal
component

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Insulation Degradation

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Main Purpose of Insulation
• Electrically Isolate HV from ground and other
conductors
• Conduct heat from the conductors (rotating
machines, transformers)
• Provide mechanical support to the conductors

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Electrical Stresses
• Operating Voltage Primarily Ages main insulation
• Very slow degradation mechanism by itself.
• PD may speed up insulation degradation. Especially true in
Cables, SWG.
• PD is absolutely critical contributor to insulation failures in
HV equipment. Bushings, transformers, SF6 equipment,
Cables.
• Transients can create new PD defects that will not
extinguish after being created.

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Thermal Stresses
• Steady state thermal stress – relatively slow
degradation
• Load Cycling
• Different Materials have different expansion
characteristics
• Loss of Bonding between conductors and insulation and
between insulation layers
• Creates voids then PD
• Causes strand and turn shorts
• Can cause rapid failure in Rotating Machines

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Thermal Stresses
• One of the Most Common aging mechanisms
• Operational Losses
• Load Losses
• Circulating Eddy Currents
• Poor Cooling Design
• Every 100C increase in Temperature
decreases remaining life by 50%

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Environmental Stresses
• Endwinding Pollution
• Create tracking across spacers between coils of different phases
• Degrades winding mechanical supports
• Will degrade surface insulation
• Pollution and moisture creates surface tracking in SWG –
likely main contributor to insulation failures.
• Improper ventilation and heating speeds problem
• Typically Long Term aging process (months to years)
• May be very fast in 27kV apparatus and above in humid
climate

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Principal Failure Modes of Insulation
• Flashover due to developed surface tracking and
cracks (RM, SWG, Bus ducts)
• Accessory insulation failure (CTs, PTs in SWG,
Cables and terminations, Bus supports)
• Turn to turn shorts (RM)
• Phase to ground and phase to phase shorts due to
reduction of ground wall insulation (RM)
• Enwinding discharges and tracking (RM)

35. © 2010 Eaton Corporation. All rights reserved.
Rotating Machines

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Motor/Generator Winding Construction
Iron
Groundwall
Insulation
Turn
Insulation
Strand
Insulation
Conductor
Wedge
Packing
Semiconductor
material
Cross Section of a Multi - Turn Stator Coil
RTD

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37© 2010 Eaton Corporation. All rights reserved.
Strand/Turn Insulation
• Strand Insulation:
• Lowers Eddy current losses (Sees about 2V)
• Strand to Strand fault does not usually cause immediate
winding failure.
• Turn-to-Turn Insulation:
• Prevents circulating currents. Holds conductors mechanically.
(Sees about 200V)
• Turn to turn fault can cause failure very quickly due to
insulation overheating.

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38© 2010 Eaton Corporation. All rights reserved.
Groundwall Insulation
• Phase-to-Phase/ Phase-to-Ground Insulation:
• is typically made of varnished cambric, epoxy impregnated woven
glass, sheet-form mica, or polymerized plastic sheet. It electrically
isolates and mechanically separates coils that are connected in
different phase circuits and from the grounded magnetic core of the
machine.
Sees the most mechanical and thermal stresses

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Core Iron

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Coil
Connections
Knuckle
Stress Relief
Grading (paint
or tape)
Slot Area – Semiconductor Coating
(paint or tape)
End
Arm

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Non Connection End

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Lead End

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Semicon Grading – Silicon Carbide
Mixture

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One Coil In slot

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Partially Wound Machine

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Finished winding

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Mechanical Stresses
• Vibration
• Forces increase with the (operating current)2
• Insulation Abrasion
• Winding Settling
• Loose Wedges
• End Arm Support
Cause Slot Discharges
• Endwinding – strand and turn cracks
• Can be relatively quick to failure

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Motor
Slot Discharges
Close up >>>
15,000 HP - 13.8 kV
Partial Discharge

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Environmental Stresses
• Endwinding Pollution
• Tracking across blocking and is phase to phase
• Degrades winding mechanical supports
• Will degrade surface insulation
• Typically Long Term aging process

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Partial Discharge
<<< Corona
Corona (Close up) >>>
6.9 kV - 17,000 HP

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Principal Failure Modes
• Turn to turn shorts
• Reduction of groundwall Insulation
• Endwinding discharges and tracking

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52© 2010 Eaton Corporation. All rights reserved.
Corona
12,000 hp, 13.8 kV
Partial Discharge

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Partial Discharge

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PD Monitoring System Overview:
Rotating Machinery
Coupling Capacitors RFCT
Predictive Relay/Monitor PD Sensors
+
RTD Module
NEMA 4X

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Typical Rotating Machine Application

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Motor Installation

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•Use existing support beams or add support beams.
•Install using brackets or without.
•Ensure good ground connections
Coupling Capacitor Installation

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RTD Module:
Using RTD’s as a PD Sensor
• Motor stator winding RTDs
• RTD/Wire becomes RF antenna
• Passive device
• No affect on the operation of the
RTD or connected protective relay
and/or temperature monitor
• RTD is normally at ground
potential
Iron
Groundwall
Insulation
Turn
Insulation
Strand
Insulation
Conductor
Wedge
Packing
Semiconductor
material
Cross Section of a Multi - Turn Stator Coil
RTD

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RTD Module Installation

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Sensing Range
RTDs increase sensing range
AC Coupling
Capacitor
8 kV
0 kV
Voltage Profile
RTD

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Motor PD
Software - Trending Screen

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Motor PD
Software - Correlation Charts

63. © 2010 Eaton Corporation. All rights reserved.
Switchgear

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Switchgear - What is failing?
• Main Bus Insulation
• Bus Supports & Windows
• Breaker Insulation
• Insulating Barriers
• Standoffs
• Cable Terminations
• Cables of diff phases touching one another or ground
• Current Transformers
• Potential Transformers

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Results of Partial Discharges
5kV Circuit Breaker Bushing
Surface Tracking
15kV Switchgear
Voids between bus sleeves

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Results of Partial Discharges
Switchgear Primary Stab
Surface Tracking
Current Transformer
Corona Damage

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Results of Partial Discharges

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Results of Partial Discharges
25 kV Cable Terminations

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Partial Discharge Tracking

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PD Monitoring System Overview:
Switchgear
Coupling Capacitors RFCT
Predictive Relay/Monitor PD Sensors
+
NEMA 4X

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• Three coupling capacitor sets in several cubicles along a
line-up.
• Rule of thumb – one set in every third section
• RFCT on feeder shield grounds – one per three phases
• Auxiliary sensors for Temperature and Humidity
Combination of CC and RFCT sensors allows for reliable monitoring
of PD activity and for identifying the origin of PD (internal and external)
relative to the monitored equipment.
Actual sensors configuration should take into account optimum
coverage of the equipment. Some applications may require additional
monitors for additional channels.
Switchgear Sensor Selection

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Switchgear Sensor Location
• Two types of installation:
• On load side of a breaker – allows for installation
without taking the switchgear off-line
• On Main Bus – requires the bus outages or factory
installation.
• Main bus application can require fewer
sensors.

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Coupling capacitors on load side of a breaker
Switchgear Sensor Location

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Coupling capacitors on main
bus in transition section
Coupling capacitors on main
bus in end section
Switchgear Sensor Location

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Coupling capacitors in disconnect switch
Switchgear Sensor Location

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Commonly one sensor per three phases
on cable shields ground wire.
Switchgear RFCT Installation

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Typical Switchgear Application
Sensor Selection Guideline
• RFCT – One for every cable-set (in or out)
• Coupling Capacitors – One set for every 3 structures
RFCT
Coupling Capacitors
LEGEND
Load Cables or Bus
Switchgear Cable Compartment
L1 L2 L3
52
MV Power Circuit Breaker
Cable Shields
Breaker Cubicle 1 Breaker Cubicle 2 Breaker Cubicle 3 Breaker Cubicle 4 Breaker Cubicle 5 Breaker Cubicle 6

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RFCT RFCT
RFCT
Bus section #1.
Sensor set include 4 sets of coupling capcitors and 3
RFCTs
Switchgear Sensor Location

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Possible PD locations in switchgear
• Bus supports/windows
• Potential transformers
• Current transformers (usually bar type)
• Standoff insulators
• Cable terminations
• Rubber cables in contact with other phases or ground
• Corona rings
• External sources (switchyard, connected rotating
machines)
• Contamination (including humidity)

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81© 2010 Eaton Corporation. All rights reserved.
PD in Switchgear
• PD in SWG is frequently unstable. Caution
should be taken making a conclusion on a
few measurements
• Alert trigger in SWG is always high pulse
count >100ppc regardless to magnitude
• High magnitude and low pulse repetition PD
(<10ppc) is not necessary an alert trigger, if
not trending upward
• A PD alarm is an alert for data analysis but
not for equipment shutdown

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82© 2010 Eaton Corporation. All rights reserved.
PD in Switchgear
• Ways to locate PD while the equipment is on
line:
• Human senses: smell – visual – listen
• Equipment schematic modification: pull out –
disconnect probable source
• Always confirm a result of modification with an
instrument
• You must know an equipment design, history
and probable problem source
• If you have seen PD – it does exist. This is not
black magic. It does exist even if you can’t find
visual signs

82. © 2010 Eaton Corporation. All rights reserved.
Case Study

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Case Study:
13.8kV Switchgear PD Discovery
Note:
Qmax is useful,
but sometimes can
be misleading
because it ignores
pulse repetition rate
Actual Alarm Event Occurred Here

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85© 2010 Eaton Corporation. All rights reserved.
Case Study:
13.8kV Switchgear PD Discovery
Note:
Pulse Count (pulses per
cycle or pulses per
second) is useful,
but cannot be used to
set alarm levels.
Sometimes it can be
misleading because it
ignores pulse magnitude
Actual Alarm Event Occurred Here

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86© 2010 Eaton Corporation. All rights reserved.
Case Study:
13.8kV Switchgear PD Discovery
Note:
PDI (partial discharge
intensity) reduces
confusion by combining
magnitude and pulse
repetition rate into one
unit of measure
Actual Alarm Event Occurred Here

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Case Study:
13.8kV Switchgear PD Discovery
Alarm
Sensor with PD:
Phase C Coupling Capacitor
located in structure #1

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Case Study 1:
intermittent PD activity
Alarms level on PDI has been exceeded in only two channels
connected to IPDS sensors on main incoming bus
Significant correlation to Humidity on B and C phase
Set Point

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Case Study:
13.8kV Switchgear PD Discovery
Diagnostics Information:
• Positive Pulse Predominance
(PD occurring between Insulation & Ground)
• Phase B & C Conductors contributing

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Case Study:
13.8kV Switchgear PD Discovery
15kV Bus at Large Petrochemical Refinery in Houston, TX
Moisture

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91© 2010 Eaton Corporation. All rights reserved.
Case Study:
Discovery - bus duct from transformer!
Water leakage into
outdoor bus-duct, sun
heating and fast
evaporation when hot,
increasing conductivity
of fiberglass support
and surface
conductivity of epoxy
bushings, air gaps
between bushings and
fiberglass

91. © 2010 Eaton Corporation. All rights reserved.
Thank you!