SUBSTATION SURVEILLANCE
USING RADIO FREQUENCY
INTERFERENCE (RFI)
MEASUREMENTS
Eduardo Pabuna
WESTCO ELECTRICAL
Eduardo.pabuna@westco-phil.com
Agenda
• Introduction.
• Partial Discharge – a precursor to failure.
• Radio Frequency Interference (RFI)
detection - understanding what we are
measuring.
• Complimentary EMI detection techniques
using different sensors
• Case studies
• Conclusions
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Key Drivers
 A successful substation asset management strategy depends
heavily on predictive maintenance assessments conducted
periodically:
 Surveillance based techniques to identify potential sites of
insulation degradation
 Followed by more investigative and invasive quantitative
techniques
 Adds value to the maintenance work, selectively identifying
and replacing those items of plant that have deteriorated
significantly.
 Identifies HV apparatus that presents a potentially safety
hazard to staff and public.
 Cost effective and non expert use.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
External discharges

Surface discharges caused by
pollution on the insulator surfaces.

Leakage currents on insulator
surfaces.

Insulator damage.

Corona.

Loose connections
Internal discharges
 Voids in the insulation.
 Poor conductor-insulation
interfaces.
 Metal irregularities/contaminants
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
PDS100 – PD Surveyor
PD Detection by RFI/EMI
Partial Discharge (1)
• PD occurs when insulation defects exist which produce
distorted and enhanced electric field stress.
• Causes of PD in insulation system:





Voids in epoxy resins, polymers, paper
Bubbles in liquids/oils
Metal depositions/irregularities/contaminants
Electrodes and insulation surfaces
Poor terminations/loose joints
• Environmental stresses can act to accelerate the
deterioration of the insulation system in HV apparatus.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Partial Discharge (2)
Can also arise through:
Poor design and manufacture
Damage of equipment
Poor installation processes/workmanship
General “ageing” or deterioration of materials
Lightening strikes, transients, overloading
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Partial Discharge (3)
•
•
PD is a symptom of
degradation
Once present – it
dominates as it’s own
“inherent” stress
degradation mechanism
poor preparation
poor
preparation
erosion traces
• Precursor to complete
insulation failure and
breakdown
poor preparation
Cable Termination Area
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Detection of partial discharges
Detection is based on the energy exchanges that take place during the discharge
Dielectric
losses
Heat
Light
Electromagnetic
Chemical changes,
Radiation
gases
Impulse current
pulses
Sound/
noise
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI Emissions
IEC60270 measurements
– Quantify “apparent charge” involved in PD event
– Integration of current pulse
– Requires physical connection to measure current
pulse
RFI measurements
– Radiated signals depends on the dynamics of
charge motion
– Signals generated when charge is accelerated, e.g.
• Charge oscillation
• Charge movement
– PD current pulse comprises moving charges thus
radiation will ensue
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI Case in UK, 1984:
Experience of a transformer fire that followed a bushing failure:
 During 6 months before this failure neighbors were complaining
about Radio & TV interference, foretelling what was coming.
 Since then, RFI surveys are routine.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Understanding What We Are Measuring
Partial discharge pulse
RFI emission frequency
spectrum
 PD current pulse comprises moving charges thus radiation
will ensue
 It emits an impulsive electromagnetic wave that travels in
the surrounding media.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Understanding What We Are Measuring
Detecting and measuring a partial discharge event is
analogous to listening for the strike of the hammer on
the bell – at distance what we hear are the resonant
harmonics.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI propagation
discharge
source
Amplitude of
higher
frequency
emissions drop
of quicker with
distance
Source of
discharge may
be located to an
area or specific
item of
equipment
Discharge pulse propagation
 Radio frequency, or RF signals, weaken as they travel
through free space because of divergence or dispersal,
much the same way light travels away from a light bulb.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
How?
• RFI from PD source
radiates intermittently
• PDS100 scans
VHF/UHF in steps of 6
MHz for 1-1000 ms
(set by user)
• Captures RF energy
by amplitude
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Scanning for RFI emissions
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
How?
1. Establish baseline outside
substation or switch room
2. Walk from point to point inside
substation in service
3. Look for changes in amplitude of
the RF-activity
4. If indications of PD – approach
the apparatus and see if the
activity increases
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Typical RFI spectrum without discharge source
(frequency sweep mode)
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Compare Background signal with signal next to
source
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Frequency Range Contributions
1) Corona in air around sharp metal will be dominant up to 10
MHz but will go as high as ~250 MHz
1) Surface discharge on dirty porcelains will dominate from
10 to 250 MHz. Heavily influenced by time of year, rain
washing etc.
3) PD will extend RFI up to 1GHz on the PDS100 (but actually
can go much higher).
The higher the frequency the greater the attenuation
Localization of PD requires the using the attenuation to your
advantage!
The closer you get to the source of PD the more sensitive
(elevated) the higher frequencies
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Fault Characterization
Measured impulse events from an
arcing discharge source
(time resolved mode)
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 1
Survey of Switchyard revealed high
RFI in vicinity of Isolator
The time resolved plot
shows a typical arcing
type discharge
Deviations from Background (Black) becoming larger when approaching
the isolator
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 1
Survey of Switchyard revealed
high RFI in vicinity of Isolator
•
•
•
It was recommended to pay particular attention to the isolator and
to look for floating metal parts.
Several Cu braids and springs were found to be burned off and
just lying in the centre pole enclosure of the isolator. In addition
the insulators on the load end (CSBP) were replaced due to
glazing damage of the surface due to a previous flashover.
A repeat test after repair of the isolator showed no significant
deviation from background for all HV plant in this switchyard.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 2
11KV switchboard
During a routine Survey some RFI activity
was found in front of only one 11kV
switchgear panel.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
400/275/22kV 800MVA Transformer
• RFI scans
performed
on places
indicated by
red dots
L11
L12
Radiator
L13
L3
L4
400 kV
L2
275 kV
L5
L1
Tapchanger
L7
L10
L9
L6
L8
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
400/275/22kV 800MVA Transformer
The PD scans at location L3 and the baseline is shown .
The PD measurements showed increases in amplitudes
when compared with the baseline measurement
indicating evidence of discharge activity.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
400/275/22kV 800MVA Transformer
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
400/275/22kV 800MVA Transformer
•
RFI scan at
L8 (TDM at
arrow
790MHz)
•
Time domain mode at
780MHz – Pos. L8
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
400/275/22kV 800MVA Transformer
• Clear signs of severe PD
• The transformer failed 2 weeks after this
survey
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
132kV CT
•
Strong RFI emissions were detected in the range of 750 to 900 MHz
indicating significant PD activity in the oil dielectric.
•
Further interrogation of RF signals were done in time domain mode at
different PD frequencies.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4
132kV CT
Time Resolved Mode
showing
correlation with
system voltage
DGA results confirm
internal PD
C & TD Test data of CT’s insulation
measured Tan Delta at 3.0%.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case 5 – 300 kV - Surge Arrester
RFI measurement was carried out
during routine substation survey.
• Very high amplitudes at the
highest frequencies indicated
serious PD.
• Other arresters in the same
switchyard followed the baseline.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Other decoupling options TEV
Joint
Metal Cladding
HV Busbar
EM Wave
EM Wave
PD
TEV Probe
EM Wave
PDS 100
Far-Field
Propagation
Photo showing the
deployment of a TEV
probe
Graphic Showing Transient Earth Voltage
Detection of Partial Discharge Activity.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Other Sensors: High Frequency CT’s
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
UHF Transformer Sensors
UHF Plate Sensors
(Mounted in Hatch)
UHF Drain Valve
Sensors
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Use of Complementary EMI Couplers
Frequency plot of injected pulse
Using a UHF coupler on a GIS
Substation.
Time resolved trace @ 810 MHz
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Example of a Detected GIS Defect
Frequency trace for a
floating particle
UHF signal @ 2.5 GSs-1
Time resolved trace @ 871 MHz;
-repetition rate 1 s-1
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Summary
• Impulsive broadband emissions are a
characteristic of insulation defects in HV
substations.
• The PDS100 instrument platform is
specifically designed for substation
surveillance and can greatly assist in early
stage recognition and reporting of PD.
• RFI offers a routine non-invasive and costeffective surveillance technique.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Thank You!
QUESTION?
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS