Monitoring Technologies
Motors
Generators
Switchgear
Cables
Transformers
Focus on Major Failure
Focus on Major Failure
Monitoring Technologies
Fixed Mounting
Partial Discharge Monitoring
Monitoring Technologies
Portable Partial Discharge
Monitoring
Monitoring Technologies
Sensor
Monitoring Technologies
Communication Network
What is Partial Discharge?
PD is a leading indicator of
insulation breakdown.
 The higher the voltage the more
destructive the activity.
 Phenomena that only occurs at
higher AC voltages (> 2,000 V).
Prefer 3 kV and higher.

Definition - PD
Spark
A Localized Electrical Discharge in an Insulation
System that does not completely bridge the
Electrodes.
Phase to Phase
Phase to Ground
What Is PD
HV
CA
CT
Cv
What is PD

TT

T
T
PD Pulse Characteristics

Generates a High frequency Pulse
 Rise
Time 1 nS to tens of nS
 Pulse width 1 nS to few hundred nS
 Frequency Range 0 – 10’s of GHz
 Usually measured in pC or mV

TT

T
T
PD Quantities

PD Magnitude (mV or pC)
 Size

or the volume of the defect
Pulse Count (PPS)
 Number

PD Intensity/Power (mW)


or Growth of defects
Destructive Power of the PD events
PD Signature
 Phase
of the Defect
 Type of Defect
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

Insulation Aging Mechanisms




Electrical with PD – SWG, Bus, Transformer,
Cable. Slow in rotating equipment.
Thermal - Rotating machines, Transformers,
Cables
Mechanical - Rotating machines, Transformers
Environmental - Primarily SWG, Buses, Dry
transformers. Applies to rotating and cables.
Motor/Generator Winding Construction
Iron
Wedge
Conductor
Packing
RTD
Semiconductor
material
Groundwall
Insulation
Strand
Insulation
Turn
Insulation
Cross Section of a Multi - Turn Stator Coil
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.

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
Core Iron
Coil
Knuckle
Connections
End
Arm
Stress Relief
Grading (paint or
tape)
Slot Area – Semiconductor Coating (paint or
tape)
Non Connection End
Lead End
Semicon Grading – Silicon Carbide
Mixture
One Coil In slot
Partially Wound Machine
Finished winding
How PD Is Measured
180 - 270
Positive Polarity
Negative Polarity
0 – 90
1st Cycle
2nd Cycle
How PD is Measured
Phase Resolved Data
• Phase to Ground
• Phase to Phase
• PD Signature
Which are the most common stator winding problems?

Poor impregnation of coils (voids)
Overheating of coils (delamination)


Looseness of windings (slot discharge)
Deterioration of semiconductive or grading
coatings (slot or endwinding discharge)

Contamination of windings (tracking)
Results of Partial Discharges
6.9 kV - 17,000 HP
<<< Corona
Corona (Close up) >>>
Results of Partial Discharges
Slot Discharges
Close up >>>
Results of Partial Discharges
Slot Exit
PD Examples?
4 yr Old Machine - Spacing
Endwinding Damage
Results of Partial Discharges
Phase to Phase
Discharges on Ring Bus
49 MVA Generator
Bar damage due to vibration
13.8 kV, 100MW hydro generator
Why Monitor PD?
The stator winding is one of the most frequent reasons
for machine failure!
Delamination
Endwinding vibration cracks
Insufficient spacing
Endwinding contamination
Contamination and spacing
Phase Resolved Data –
Fingerprint Analysis
• Phase to Ground
• Phase to Phase
• PD Signature
Fingerprint Analysis
Partial Discharge between
insulation and HV
(delamination from copper)
Pulse magnitudes on positive
half wave is higher than on
negative.
(Negative Preference)
Fingerprint Analysis
Balance of Polarity Pulses: Internal
Insulation Delamination
Fingerprint Analysis
Partial Discharge between
insulation and ground (Probably
Slot Discharge)
Pulse magnitudes on negative half
wave is higher than on positive.
(Positive Preference)
Negative Temp
Coefficient
Positive Temp
Coefficient
Partial Discharge
Most of You have heard a lot about Partial
Discharge
 Many Myths
 Two Main Issues

 Signal
Attenuation
 Noise Rejection
Signal Attenuation

The higher the Measurement Band, the
less coverage of the winding
Higher
Frequency
Providers
350
100
M
MH
H zz
40
20
1
0.5
0.025
0
5
10
15
20
25
30
35
40
45
50
% Relative Coverage
55
60
65
70
75
80
85
90
95
100
Sensitivity To PD Pulses
Type Of Sensor
 

 

 
 
 
 
 
This illustrates that the
capacitors have do limited
coverage!
 
 
 
 
 
1)
2)
3)
4)
5)
6)
Traces 1, 2, 3 Coupling Capacitor
Traces 4, 5, 6 – RFCT on surge cap
ground
CCA:
CCB:
CCC:
SCA:
SCB:
SCC:
2 Volt
2 Volt
2 Volt
2 Volt
2 Volt
2 Volt
500 ns
500 ns
500 ns
500 ns
500 ns
500 ns
Defect is at Third coil
Signal To Noise Ratio

How to improve SNR
 Increase
Signal Level
 Reduce Noise Level
 Combination
PD Frequency Spectrum
EDI Range of Operation
• Frequency:
• Pulse width:
1 – 20 MHz
< 600 ns
Summary Of Signal Attenuation
Coupling capacitors at the line terminals
can only cover a limited portion of the
winding
 If the complete circuit associated with the
measurement of PD is taken into
consideration with the coupling capacitors,
the signals are several times more in the 1
- 20 MHz bandwidth than > 40 MHz

Noise
Difficult to mathematically model
 It is a function of installation/location
 Discuss Noise Cancellation techniques
instead and Case Studies

Noise Cancellation
Frequency
 Pulse Width

<

600 nS
Gating
 Not
looking at certain phase areas of the
patterns
Time (Synchronous – Noise from static exciter)
 Event

Noise Cancellation

Designated Noise Channels
 Sensors
installed at noise sources and all
pulses ignored that occur at the same time as
the noise channel

Magnitude Comparison
 Comparing
magnitudes of all pulses
simultaneously from multiple channels
Only count the highest magnitude Pulse
 Ignore all others

Noise Cancellation

Pulse Polarity (To determine direction)
 Uses two types of
 One Capacitive
 One Inductive
Sensors
RFCT
D
One + and
One - Pulse
Noise Cancellation

Pulse Polarity (To determine direction)
 Uses two types of
 One Capacitive
 One Inductive
Sensors
RFCT
Two + Pulses
D
Noise Cancellation
Time of arrival
 Compares Time of Pulses to reach
instrument

Pulse Polarity

Pulse Polarity (To determine direction)
 Uses


two types of Sensors
One Capacitive
One Inductive (RFCT or GS)
Noise Cancellation


Time of arrival
Compares Time of Pulses to reach instrument
Dt
Noise Cancellation


Time of arrival
Compares Time of Pulses to reach instrument
Dt
Noise Cancellation

Software Filters
 Applying
custom designed signal processing
algorithms to determine signal versus noise.
 Have been done successfully for many types
of noise
Replacement Monitor
Before
After
Summary – Noise Cancellation

Advanced Noise Cancellation techniques
are critical.
 Allows
to make in field measurement at lower
frequencies where signals are much higher
 Required to provide an excellent SNR while
allowing more coverage by each individual
sensor
Use of Multiple Sensors

Since each sensor has its own limited
“Zone of Sensitivity” it makes sense to use
as many sensors as reasonably possible.
 More

information = Better Diagnostics
One Option
 Use
RTDs that are already embedded in the
winding as a PD sensor
How it Works

Use the existing RTDs already embedded
in the winding as a PD sensor
RTD and wiring acts as an antenna
 Used in conjunction with traditional sensors
 Transducer installed in series with existing
wiring




Passive device
Must be installed at the machine
Will not affect the operation of the RTD or
connected monitoring or protection devices
RTD Module
Zone of Sensitivity
8 kV
Voltage Profile
Turbine
0 kV
AC
RTD
Coupling
Capacitor
Motor
Zone of Sensitivity
8 kV
Voltage Profile
0 kV
RTD
AC
Coupling
Capacitor
• Provide more information
• In order for you to make a better decision
Signal Attenuation

The higher the Measurement Band, the
less coverage of the winding
Higher
Frequency
Providers
350
10 – 15%
100
M
MH
H zz
40
20
60 – 80 %
1
0.5
0.025
0
5
10
15
20
25
30
35
40
45
50
% Relative Coverage
55
60
65
70
75
80
85
90
95
100
Use of RTDs PD SENSOR
Use of RTDs provides more
information for better decisions
What Sensors Do We Need?
Data taken from sensor at line terminals.
Motor 1
Good
Motor 2
Moderate
Motor 3
Moderate
Data taken from RTD-sensors.
Motor 1
Motor 2
Poor
Moderate
Motor 3
Moderate
Case Study

TT

T
TT
T

T
T

T
T

T
T

1)
2)
3)
4)
T
T


T
T

TT
1)
2)
3)
4)


T
T

T
T

TT
TT
SHA: 100 mVolt 500 ns
RTD1: 100 mVolt 500 ns
RTD3: 100 mVolt 500 ns
RTD5: 100 mVolt 500 ns
T
T



TTT
TTT


T
T
SHA: 1 Volt 500 ns
RTD1: 1 Volt 500 ns
RTD3: 1 Volt 500 ns
RTD5: 1 Volt 500 ns
1)
T
T
2)


T
3)
T
4)
T
T

TT

TT
TT

 1) SHA: 1 Volt 500 ns
Shows
how sensors at
1)
SHA:
5 Volt
500 ns
1)2)
SHA:
mVolt
500
RTD1: 100
1 Volt
500
ns ns
2)
RTD1:
Volt
500
2)3)
RTD1:
RTD3: 5100
1
Volt
mVolt
500ns
500
nsline
ns terminals and
3)
RTD3:
5
Volt
500
ns
RTD5: 100
1 Volt
500 500
ns ns
3)4)RTD3:
mVolt
RTDs
can complement
4)
RTD5:
5
Volt
500
ns
4) RTD5: 100 mVolt 500 ns
SHA: 5 Volt 500 ns
RTD1: 5 Volt 500 ns
RTD3: 5 Volt 500 ns
RTD5: 5 Volt 500 ns
each other
Case Study – 16,000 HP
Response of 6 RTDs
Origin is near RTD5 (Highest magnitude)
Case Study, 12,000 HP 13.8 kV
Before
After Recon
Before
After Recon
Case Study, 12,000 HP 13.8 kV
Comparison of RTD to SSC
300 MW Turbine Generator
RTD Right Under SSC
Similar Patterns
Similar Pulse Shape
RTD slightly more sensitive
Capacitors and RTDs
Complementary
Little PD at capacitors, but significant at RTDs
Capacitors and RTDs
Complementary
Little PD on RTDs, but significant at Capacitors
What Does This Tell Us?

Limited sensors offers limited information
 Line
Couplers are not sensitive to internal PD
 RTD
sensors are not sensitive to PD near Line
terminals


For the best analysis, use all the valid
information you can get
Our Recommendation is to use BOTH
Line Couplers and RTDs!!!
Can PD occur on 3.3 and 4 kV
Motors?

There are varied opinions on the value of
performing PD measurements
 Range
from no value to
 Some value (Not much notice)
Magnitudes are lower
 PD Activity is not as destructive
 Function of Sensitivity

Can PD Occur at 4,160?
4,160Volt - 5,000HP - Synchronous
New 4,160 Volt Motor
Two measurements – One Year Apart
11/16/2002 & 11/18/2003
Can PD Occur at 3,300?
3,300 Volt, 5,000HP - VFD Application
Case Study - Design
Deficiency?
13.8 kV motor
Many rather large air gaps between bus rings. Can
be phase to phase and phase to neutral, depending
on layout of the ring buses
Case Study - 49 MVA Generators
Spikes more frequent and
increase trend
Before Repair
After Repair
Small Change in Magnitude
Large Decrease in PPC
Power Factor Tip-up
Power Factor Tip Up for TG1
0.7
0.66
0.6
Phase
A
0.57
% Power Factor
0.5
0.50
0.44
0.4
0.39
Phase
B
0.35
0.3
0.2
Phase
C
0.1
0
2
4
5
6
7
8
KV Applied
Showed no Indication of Pending Problem
PD Sites not excited at Phase to Ground Voltage
Case Study - 49 MVA
Generators
A & C Phase Connection Ring
Need more space
Case Study – 6.6 kV Motor
Phase Resolved Data
Rotating Machine Monitor - RMM
 Up to 90 PD
channels
 Cables
 Switchgear
 Motors
 Generators
 Bus Duct
Main CPU and I/O module
7 – 100 Ω RTD inputs
5 LEDs
1 - Form C
3 – Form 1 Relays Outputs
Connector for Display
1 - TCP
Six – 4-20 ma
Inputs
1 - Local USB
1 Humidity Input
4 – Vibration Inputs
One – 4-20 ma Output
2 – RS485 Ports
3 – Voltage Inputs
3 Current Inputs
PDM
LEDs – Local Status
Display Connector
15 PD Inputs
USB
RMM




Stores 2 years of data
Standalone
ModBus Serial and ModBus TCP Communications
Alarms on
Magnitudes
 PDI
 Trend



Watch Feature
Current Signature analysis of Induction Machines

Indication of broken Rotor Bars