SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS. Eduardo Pabuna WESTCO ELECTRICAL

SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS Eduardo Pabuna WESTCO ELECTRICAL [email protected] Agenda...
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SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS Eduardo Pabuna WESTCO ELECTRICAL [email protected]

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

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