PD Sensors & Applications
Transformers
Karl Haubner – HV Applications Engineer - Asia Pacific
khaubner@doble.com
+61 417178026
1
Backround: PD Monitoring of Power Transformers
Causes for PD generation
contamination, manufacturing issues,
incorrect design
aging due to electrical, thermal and
mechanical stresses in operation
[1]
General complete information about a PD
activity
its intensity
(might be apparent charge q)
PD –Yes/No?
its type
PD – If yes, where?
(voids, etc.; failure identification)
its location
especially in transformers the
PD location is of great
(appraise the severity of the fault)
importance
2
Electrical PD diagnostic techniques
PD measuring circuits according to IEC 60270
often applied in on-site/online PD investigations
frequently used circuit in
test laboratories
[König, 1993]
a) coupling device in series with the coupling capacitor
b) measurement at a bushing tap
Components:
AC voltage source U, optional blocking impedance Z, coupling capacitor CK,
measuring impedance Zm, a measuring instrument M and generalized test object Ca.
3
Electrical detection of partial discharge
Offline In accordance with IEC 60270
Signals can be measured via Coupling
capacitors bushings tap, via the neutral HF-CT,
specific sensors etc.
Acceptable max level ranges
300 pC at 1.3 Um
500 pC at 1.5 Um
continuous PD lower than 100 pC at 1.1 Um
Many utilities specify much lower (e.g <50pC
limits)
4
5
Field Test of Large Power Transformers (I)
using the Digital PD Measuring System LDS-6
6
Electrical PD diagnostic techniques
PD Measuring Impedance for Bushing Tap Installation
Decoupling of PD signals from the bushing tap
in a wide frequency range up to 30 MHz
Lower cut-off frequency < 60 kHz
Additional voltage signal for phase-resolved
500 kV Transformer Bushing
measurements
Superimposed PD and test voltage signal
Very fast and safe over-voltage protection
TNC-socket for signal output
Dimensions: diameter 125 mm, length 120 mm;
Weight: 2 kg
Special feature for continuous PD monitoring (IP 68)
7
PD Guard
Enclosure:
- IP65 for all industrial surroundings
- Weight: 6 kg
- Dimensions: 330 x 280 x 110 mm
- Power Supply: 100 V to 240 VAC, 50/60Hz, < 25 W
Interfaces:
- TCP/IP Interface 10 Mbps / 100 Mbps
- Trigger Source: Phase, Internal Mains, External
- Extern Trigger Input Connector
- 4 channel PD Input on TNC Connectors
- 1 Gating channel for suppression of external
noises
- For PD Sensors: Capacitive, Inductive, Bushing
Tap (Transformers)
Applications:
Signal Processing:
- FPGA based digital signal processing
- Pre-configured digital filters (low & high cutoff)
- Embedded RTOS-computer
- PD signal resolution: 12 bit bipolar
- Accuracy at 50/60 Hz: 0.3 degree
- Pulse repetition frequency: 50 kHz
- PD Signal and low frequency sync. signal on same
signal path (only one cable needed)
- Rotating Machines & Generators
- Transformers
- GIS
- Cables
Software Interfaces:
- ActiveX Control
- DCOM-Interface
(Distributed Component Object Model)
8
Advanced tools for PD monitoring – Electromagnetic
PD Tests
Cone-shaped drain valve UHF-sensors
for the decoupling of electromagnetic PD signals
from the inner of an oil-paper-insulated transformer
PD-signals in the UHF frequency range
(e.g. 300 MHz – 1 GHz)
sensors support „Performance/Sensitivity Check“
(high-frequency test impulses can be injected via
Cone-shaped active UHF-sensor
(DN 50/80 oil gate-valve)
additionally integrated electrode)
sensor head is grounded (for lower frequencies)
sensor application at oil drain valves
View from inside the transformer
9
Advanced tools for PD monitoring – Electromagnetic
PD Tests
Cone-shaped drain valve UHF-sensors
10
Advanced tools for PD monitoring – Electromagn. PD
Tests
Example for a single-port performance check
Functional check of the whole measuring path
including sensors and partial discharge (PD)
output path
input path
acquisition system through injection of highfrequency test impulses
Cone-shaped active UHF-sensor
(DN 50/80 oil gate-valve)
grounded probe
Performance Check
normalized amplitude
1,0
0,8
UHF PD
spectra for
grounded and
ungrounded
sensor head
0,6
0,4
0,2
0,0
0,00
0,25
0,50
0,75
1,00
„single-port“ solutions are possible
the Performance Check „controls“ e.g. the effect of a
contact to grounded elements within the oil valve.
Phase-resolved
view in UHF PD
device LDS-6/UHF
1,25
frequency / GHz
11
Advanced tools for PD monitoring – Electromagn. PD
Tests
Case study A - test laboratory UHF PD measurement of a 450 MVA autotransformer
UHF PD pulse
recorded at
max. 70 pC
electr. PD
level
amplitude (mV)
4
2
0
-2
-4
-1000
0
1000
2000
3000
time (ns)
2.5
2.0
amplitude (Vs)
top view of the 3-phase
400kV transformer, with
position of the gate-valve
UHF-sensor
corresponding
UHF PD
spectrum up
to 1 GHz
1.5
1.0
0.5
0.0
0.00
0.25
0.50
0.75
1.00
frequency (GHz)
Application benefit:
customer wanted to assure that sporadic electrically recorded strong PD is external to transformer
clear UHF signals during moderate PD activity and no UHF signals during activity which was visible
as noise in the electrical PD measurement
12
Advanced tools for PD monitoring – Acoustic PD location
Alternatives of arrival time based positioning
triangulation
1. Mixed-acoustic methods:
sensor 3
sensor 2
sensor 3
electro-acoustic
PD
sensor 2
sensor 1
(test laboratory or on-site/off-line)
electromagnetic- acoustic
sensor 1
(test laboratory or on-site, off-line or on-line)
s1
all-acoustic
2
s1
2
s
S1
Input parameters:
sensor coordinates,
sound velocity, meas.
time difference
(test laboratory or onsite, off-line or on-line
with reduced sensitivity)
2
s1
(x − xs2 )2 + ( y − ys2 )2 + (z − zs2 )2 = (vs ⋅TS 2 )2
(x − xs3 )2 + ( y − ys3 )2 + (z − zs3 )2 = (vs ⋅TS3 )2
unknowns x, y, z
2. All-acoustic methods:
t
(x − x ) + (y − y ) + (z − z ) = (v ⋅T )
2
Observation equations:
electrical PD
S3 (xs3, ys3, zs3 )
S
(xs4 , ys44, zs4 )
Si
(xsi , ysi , zsi )
Di
D3
D2
D4
PD
(x, y, z)
S2
(xs2 , ys2 , zs2 )
D1
S1 (xs1, ys1, zs1)
schematic view of a transformer
tank with acoustic sensors
13
LDA-6 SYSTEM SETUP – COMBINED ELECTRICAL AND ACOUSTIC PD MEASUREMENT
PD1, TV1
PD2, TV2
PD3, TV3
AE1
PDM SYSTEM LDS-6
AE2
AE3
Z
Y
X
EXTERNAL / ELECTRICAL
TRIGGER
PCI BUS
d
i
g
i
t
a
l
AE - PDM SYSTEM LDA-6
AE1, … ,
Acoustic PD Detection (I)
AE8
14
‘Location Results’ – GPS Bancroft Algorithm (EL Triggering)
Averaged evaluation / pulse averaging (left) and cluster of several evaluated
AE trigger events (right)
LDA-6 Localization Results
15
High Voltage Testing, Monitoring and Diagnostics is our business
PD Sensors & Applications
Switchgear
16
In MV switchgear often high humidity leading
to surface tracking, material defects and
incorrect assembly are responsible for PD
activity
Examples of earth fault air insulated S/G
18
Tests to determine insulation condition
Partial Discharge Test Trolley for off- line testing. (new setup ¼ of size
shown)
19
20
Case Study Surface Tracking 2006
Switchboard was tested off-line and PD
was detected. Location was using
acoustic detector
TEV MicroTev did not indicate problem
Ultrasonic detection very sensitive for
this kind of defect
21
The PD Surveyor™ - Examples of Use
On-Line PD Testing – Now a Field Reality
Example 1: 11kV GIS Switchgear
The TEV LEDs (middle line) show a ‘Red 1’ TEV PD Level
in the SF6 busbar section, which equates to 44dB.
The action here was to use the high level OSM-LongshotTM
PD Diagnostic Test Unit to test and locate the site of the PD
activity which was confirmed to be in the busbar section. The
PD activity measured across the 50Hz Power Cycle is
shown opposite on the screen of the OSM-LongshotTM test
unit
Case Study - PD in CT bus-bar
Suspect
Section
Normal
Section
(Schneider-Yorkshire YS6)
DC Step voltage
test (Ileakage @
30kV) μA
Dielectric
Dissipation
Factor
Insulation
Resistance
@ 5kV
GΩ
PD (pC)
@ 12.7
PD (pC)
@ 15.3
L1
<0.2
0.0083
>1000
<10
<10
L2
5
0.0137
260
510
600
L3
<0.2
0.0089
>1000
<10
<10
L1
<0.2
0.0088
>1000
<10
<10
L2
<0.2
0.0085
>1000
<10
<10
L3
<0.2
0.0091
>1000
<10
<10
23
Case Study
Significant deterioration of a 30 year old 11 kV
switchboard
DCStep
Insulation
voltage
Dielectric
PD
∅
Resistance
Rear test (Ileakage Dissipation @5kV (pC)
Factor
@6.3
Busbar @20kV)
MΩ
μA
PD(pC)
@ 7.6
PD
Inception&
Extinction
L1
6.8
0.0442
93100
<20
<20
>7.6kV
L2
7.4
45200
<20
<20
>7.6kV
L3
50
0.0575
0.0838*
17700
1500
1800+
2.4kVinc
2.5kVext
alsohighDDF
tip-up
24
Case Study
Significant deterioration of a 30 year old 11 kV
switchboard
25
26
UHF – PD-Sensors for GIS
Detector
Detector
Conductor
Conductor
Cage
Cage
- UHF-Window Sensor
- Internal UHFSensors
Field grading electrodes
27
GIS UHF Spectrum
28
Examples– Field Application
29
Examples of readings
• Phase resolved plot:
Background noise/no flaws:
Partial discharge:
Examples of readings
• Particles:
Continuous Mode:
Partical Mode:
PD Sensors & Applications
Cables
32
Diagnostic testing of medium voltage cable systems
Examples for defective sites which can cause PD in PILC cables
dry area
lead corrosion with water penetration
Field strength increased
Carbonised traces accompanied by PDs
Paper layers
Several meters
33
Examples of typical PD types in Polymeric insulated cables
Water tree
with Electrical
tree
cracks
Detachment
s
Cavities
Semicon Layer
Protrusion
Abb. 1 : Mögliche TE- Stellen in VPE- Kabeln
Vented- tree an der äußeren Leitschicht mit einer
Länge von 2,38 mm mit aufgesetztem Electrical
tree.
Quelle: ABB Energiekabel GmbH
34
3
Most frequent PD sources in cable
accessories
Terminations
Joints
Possible PD fault locations
35
Diagnostic testing of medium voltage cable systems How to localise
defective sites
PD decoupling
PD pulses (~ up to 1/1000 of a 1.5 V battery)
1.
~
Available voltage sources:
- operating frequency [50 Hz]
2.
Defective site(s)
Several km
Data recording
and
evaluating unit
1. direct pulse
-*attenuated oscillation [30-90 Hz]
2. direct impulse
-*variable frequency [25-80 Hz]
3. Round trip pulse
- VLF [0,1 Hz]
- pulse voltages
*used by us
36
Diagnostics on Distribution Cables
S
Compact-PD
Cable test van
with rear and
interior view
OWTS M 28
and 60 portable
Stand alone units
37
Site HV supplies
Getting the volts on site
is the big issue.
38
38
S
39
On-Line PD Sensors
Permanent
Joints/Terminations with built in capacitive couplers (very rare mostly at
HV/EHV)
Temporary/Permanent
High Frequency Current Transformer (HFCT)
Rogowski Coils (not as sensitive as HFCT)
40
On-Line
Testing
– NowPD
a Field
Reality
Main
2 x PD
Types
of On-line
Sensors
High Frequency CT
Generally useful sensor used primarily to
detect Cable PD’s by attaching the splitcore sensor around the earth strap or core
of the HV cable. Can also be used to test
other types of high voltage plant.
‘TEV’ type probe
Generally useful sensor – magnetically
attached and used to detect ‘local’
discharges in all types of metalclad hv plant
On-line PD detection using HFCT
PD conductor current = i+
PD earth current = i-
i+
i+
iOK
i(insulated gland)
iOK
i+
i(insulated gland)
iOK
i+ + i- = 0
i+
i(insulated gland)
iNo Signal
i-
(plumbed gland)
42
Earth Strap Arrangements with Insulated
Glands
= Suitable for On-Line Cable PD Testing
Insulated
Gland
33kV cable box
11kV cable box with high frequency
current transformer (HFCT)
43
On-Line PD Test Method
44
Longshot Data Capture Method
Whole periods captured synchronously
Threshold level for number of pulses per cycle
Noise waveforms can be used for ‘gating’ external pulsed interference
Period divided up into slots, and peak detected for each slot
This is the way the PDGOLD software works using an oscilloscope front end in peak
detector mode i.e.
PD data f or Channel 1
PD pulses
26
24
PD Magnitude (mV)
22
20
18
16
14
Pulse threshold level for
Counting PD pulses
12
10
8
Background
6
4
2
‘noise level’
0
0
50
100
150
200
Phase (Degrees)
250
300
350
45
Typical Cable PD Pulse Shape
The PD magnitude in
picoCoulombs (pC) is
the area under the PD
pulse.
Segment view
Volts (mV)
25
20
15
10
5
0
-5
-10
-15
-20
-25
2
3
4
Time uSec
5
6
This can be calculated
from the output
voltage of the HFCT
using the HFCT’s
transfer impedance,
ZTR
Qapp
Rise time
Pulse Width
Fall time
1
=
Z TR
pulseend
∫V
out
pulsestart
dt
46
On-line Cable PD Mapping (Location) –
with Portable Transponder and
PDMAP© Software
Results in:
•
Detection of the location of Critical
Sites, Defective Cable Accessories or
Sections of Cables
•
Detailed data from which repair and/or
replace decisions on defective cable
joints, terminations and cable sections
can be made.
PD Map of Circuit
Stuart St - Queens Park (tee Eastlands)
9,000
All
8,000
Identification of Circuits Chosen for
Continuous, Long Term Monitoring
7,000
All Phases PD
•
6,000
5,000
4,000
3,000
2,000
1,000
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
Location (% along cable)
PD Pulse propagation
Direct Pulse
Reflected
Pulse
PD event
Measurement End
Direct pulse
ΔT = Time difference between
Reflected pulse
ΔT
Remote End
direct and reflected pulses.
L = Return time for cable
L
L
ΔT
48
Formula for PD Location
Direct pulse
ΔT = Time difference between
Reflected pulse
direct and reflected pulses.
L = Return time for cable
ΔT
L
L
ΔT
⎛ ⎛ ΔT ⎞ ⎞
PD% = ⎜⎜1 − ⎜
⎟ ⎟⎟100
⎝ ⎝ L ⎠⎠
49
Case Study: On-line PD Cable Mapping
Results on 33KV Cable
PD MapMixed
of CircuitPaper/Polymer/EPR
Stuart St - Queens Park (tee–Eastlands)
33kV
2677m long
9,000
All
8,000
PD Levels = 6,200pC and 9,100pC
All Phases PD
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
Location (% along cable)
The accuracy of the On-Line PD location in this case
was 0.4% (10m) and 0.7% (18m) of the cable length
Test set-up for on-site-pd-measurement
on 380- kV-joint
380 kV XLPE-cable
PD device
Detector
1,2,3
A
B
DCS
C
D
DCS
51
Setup and signals of directional coupling for
detection of PD from joints
1
2
direct. coupling
C D
direct. coupling
A B
impulse source / -No.
joint / 1
left cable / 2
right cable / 3
3
signal at coupling output
A
–
X
–
B
X
–
X
C
X
X
–
D
–
–
X
52
Test set-up for on-site-pd-measurement
on 380- kV-joint
53
PD UHF Sensors
Inductive Decoupling Sensor
for grounded terminations
Capacitive Decoupling Sensor
for ungrounded terminations
54 / 4054
PD UHF Sensors
55