SWER Broken Conductor Detector R&D Project – Progress Update · 2019-08-20 · Document Control and Non-Disclosure Notice 18.07.19 SWER Broken Conductor Detector R&D Project - Final

SWER Broken Conductor Fault Detector R&D Project

Report SummaryStage 1- Final Report for Department of Environment, Land, Water and Planning (DELWP)

18.07.19

Document Control and Non-Disclosure Notice

18.07.19 SWER Broken Conductor Detector R&D Project - Final Report

The information in this document has been provided for the Department of Environment, Land, Water and Planning (DELWP) to summarise the work undertaken in the SWER Broken Conductor Fault Detector R&D project.

Victorian government funding (via DELWP) has been directed into the development of bushfire mitigation technology for the benefit of the Victorian community. United Energy (UE) provides consent for this document to be published by DELWP in the interests of transparency.

The information contained in this report is provided in good faith. No representation, warranty or undertaking, expressed or implied is or will be made or given and no responsibility or liability is or will be accepted by United Energy and Victoria University or by any of its directors, employees or advisors in relation to the accuracy or completeness of this document or any other written or oral information made available in connection with this project by United Energy and Victoria University. The contents of this document have not been independently verified.

This document is not to be reproduced, disseminated, copied, disclosed, modified, distributed and or published by any other entity other than DELWP without the written consent United Energy. All Intellectual Property (IP) gained from this project remains the property of United Energy.

Revision Description Authors Approver1.0 For DELWP website release Cagil Ozansoy (VU) & David Wilkinson (UE) Dave Denny (UE)

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Project Team


Victoria University and United Energy would like to acknowledge the important contribution to the success of this project by the following people and organisations:

Name Organisation Name OrganisationDr Cagil Ozansoy Victoria University Mr. David Wilkinson United Energy

Dr Mohd Noor Islam Victoria University Mr. Dave Denny United Energy

Professor Mike Faulkner Victoria University Mr. Thusara Perera United Energy

Mr Douglas Gomes Victoria University Mr. Robert Doyle United Energy

Mr. Mahamudul Hasan Victoria University Mr. Stephen Watt Zinfra

Mr. Miroslav Radev Victoria University

The project team acknowledges in-kind contributions by Energy Safe Victoria (ESV).

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Executive Summary


Single Wire Earth Return (SWER) distribution systems are commonly used in Australia, New Zealand and some other parts of the world for the electrification of rural areas. A single wire (or electrical conductor) is used to supply electrical power with the return current flowing through the ground. SWER networks consist of thin and typically long conductors under high tension. Under certain fault conditions the SWER conductor is prone to breaking, e.g. when a tree falls over the powerline on a windy day. This is likely to result in the broken SWER conductor falling to the ground or into vegetation and creating a phase to earth short circuit fault. These faults have a high risk of starting a bushfire.

SWER networks are typically installed in rural areas with more than 28,000km installed in Extreme and High Bushfire Risk Areas (HBRA) across Victoria. The “SWER Broken Conductor Fault Detector R&D Project” aims to develop a communications-assisted scheme to detect broken conductors on SWER powerlines. The proposed scheme relies on continuous transmission of test signals from one end of the line and listening to these test signals at a receiver placed at each SWER automatic circuit recloser (ACR). If the signal is lost, then the ACR will be instantaneously tripped, interrupting the electricity supply prior to it having an opportunity to start a bushfire.

The following key tasks were undertaken as part of stage one of this project:

Literature Review: This task explored powerline carrier (PLC) application in power networks. Modeling of a power system network as a communication channel was studied. Communication interference (electrical noise), signal attenuation and distortion, and different PLC standards were examined. Different digital transmission and modulation schemes were reviewed.

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Executive Summary


SWER Background Noise Analysis: This task focused on development of a hardware set-up for recording background electrical noise levels over a SWER communication channel. The developed hardware was connected to the network and noise recordings were taken for both High Frequency (HF) and Low Frequency (LF) channels in continuous and sweep modes. Data was analysed to identify levels and potential sources of noise.

Network Coupling Design: This task focused on network data collection and design of a number of coupling methods. Different matching circuits were built and signal strengths/attenuation measured.

Injection and Modulation Analysis: This task compared different injection coupling methods. Injection tests were undertaken on three separate days. These include offline (isolated network) and online (HV connected) injection tests.

Prototype Development: This task focused on the development of a prototype fault detector inclusive of a transmitter and a receiver. An experimental LV injection test setup was successfully constructed in the Victoria University (VU) laboratory and used to evaluate the developed system under different configurations.

Key Conclusion:

A PLC based SWER broken conductor protection system is feasible. The optimum operating frequency range was identified with sections of the spectrum providing adequate noise floor to achieve a high signal-to-noise ratio. Further development is recommended.

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Project Background: What is SWER?

18.07.19 SWER Broken Conductor Detector R&D Project - Final Report 6

A SWER network is a low cost solution for the supply of small amounts of electrical power in sparsely populated rural areas. It is used widely throughout regional Australia in all states and is used in New Zealand. The design is low cost because it uses just a single electrical conductor (typically zinc or aluminium coated steel) unlike other designs that use two or three wires. The single conductor may stretch for tens or even hundreds of kilometres (supported by poles), with distribution transformers tapped off to provide the low voltage (LV) supply to customers along its length. The distinguishing feature is that the ground (or earth) becomes the return path for the current.

For two and three wire systems any substantial current flow to earth is abnormal and can be detected as a fault allowing protection systems to operate to disconnect the electricity supply. But for the SWER network the normal load current is designed to flow to earth so this method cannot be used to detect faults.

SWER protection is therefore generally less sensitive at detecting faults than the protection on two and three wire systems.



The SWER design simplicity offers some advantages. With a single wire there is no possibility that multiple electrical conductors can clash together under the influence of wind to create a fault. There are fewer electrical assets and less that can go wrong. Fault currents are lower and less energy is released when a short circuit fault occurs. As a result SWER powerlines are generally more reliable than two and three wire systems and more reliable systems start fewer electrical fires.

However SWER networks consist of thin and typically long conductors under high tension and the conductor is prone to breaking if hit by a falling structure, such as a tree. Although good design standards, workmanship and general asset management including asset inspection and replacement programs can reduce the risk, the steel conductor is still prone to failure.

Some SWER conductors fall to the ground and start fires. Some have resulted in catastrophic bushfires such as those in Victoria on Black Saturday in 2009.

On days of greatest bushfire risk the wind speeds are high increasing the risk of electrical conductor failure. Furthermore vegetation and soil is typically very dry. A broken SWER conductor resting on the ground or vegetation may only cause a few amperes of current to flow (with high impedance fault path under dry conditions) and existing protection may be slow or may not operate at all. But sufficient current could still flow to result in fire. It is often a challenge to detect such high impedance phase to earth faults. The fault current is similar to the normal load current.



• SWER = Single Wire Earth Return

Current supplied by a single wire

Current returns in the ground

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Remote-controlled Automatic Circuit

Recloser

Typically 300kVA22/12.7 kV

Isolation Transformer

ACR Control and Communications

Cubicle

22 kV

.7 kV

12.7kV/240 VLocal Power Transformer

. . . . . . . . . . . . . . .. . . . . . . . . . . . . . Earth return path

. . . . . . . . . . . . . . .. . . . . . . . . . . . . . Earth return path

. . . . . . . . . . . . . . . . . .


Project Background: Project Genesis and Drivers


On Black Saturday, 7th February 2009, a SWER conductor failure started a catastrophic bushfire in Kilmore East. It was this event which is the driver behind the need to develop new technology to reduce the risk of SWER powerlines starting bushfires.

While new SWER ACRs have been deployed with special total fire ban (TFB) operating modes, overhead lines have been replaced by underground cables and new covered conductor (insulated overhead) lines have been built in extreme risk areas, the majority of SWER powerlines use a bare overhead conductor and there is a risk of a SWER conductor falling to the ground and starting a bushfire.

United Energy has proposed and initiated the development of broken conductor fault detection technology for the benefit of the Victorian and Australian community.

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Project Background: Aims and Objectives


Even if the development of the SWER broken conductor fault detector is successful, and it is widely adopted, it will not prevent all SWER powerline faults from starting bushfires. It may not even prevent the majority. Not all faults and fires that are started from SWER powerlines result in the break of a conductor. However the technology is expected to provide an additional control to reduce risk that is affordable and when combined with other technologies such as low set instantaneous overcurrent protection and disabling of reclose will reduce risk to a level that is comparable to multi-phase REFCL protected lines. If R&D continues it is also possible the technology could be improved via low cost firmware updates (no new hardware) to add fault signature detection algorithms that may expand upon the type of faults that can be detected.

The overall objective of stage one of this project was to assess the feasibility of a PLC communications based SWER protection scheme in the detection of conductor breakage in SWER networks. The specific aims in stage one were:

• The measurement and recording of background electrical noise over the PLC frequency range of interest. This background noise has potential to interfere with the ability of the receiver to detect the PLC signals transmitted.

• Analysis of background electrical noise to determine the optimum frequency bands over which to operate, the required transmitter power levels and the modulation and signal encoding methods to use.

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Project Background: Aims and Objectives


• Detailed desktop review of PLC communication technologies and their use in protection applications.

• Tests to evaluate different techniques in regards to different transmission frequencies, modulation methods, error correction techniques, communication time delays, signal to noise ratios, impact of intermittent interference and high power signal jammers.

• Design and analysis of three different transmitter network coupling methods.

• Investigation into electromagnetic compliance issues both in regards to compliance with regulations and the impact the transmitted signals have on the operation of other equipment.

• Evaluation of the need for line traps.

• Development of a prototype fault detector ready for deployment on a real SWER network with multiple transmitters and a single receiver.

• Material to support the continuation of R&D for stage two including cost-benefit analysis as required to prepare a business case.

• To partner with a Victorian based University to support local innovation and foster academic / industry collaboration. (Victoria University was selected following a competitive selection process.)

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Project Background: PLC-Based SWER Protection


The concept relies on detecting broken conductors by placing PLC transmitters at certain positions at the end of SWER lines with a receiver at each ACR. If the signal is lost, then the ACR is instantaneously tripped.

Remote-controlled Automatic Circuit

RecloserIsolation

Transformer

ACR Control and Communications

Cubicle

22 kV

12.7 kV

Coupling Capacitor

2Coupling Device

3PLC Receiver

1Line Trap


Coupling Capacitor

Coupling Device

PLC Transmitter

Project Background: Myers Road SWER Network – test site


The “Myers Road” SWER network is located in Balnarring, Victoria. The network is a relatively small SWER network with a total network length of 10.2 km.

The Myers Road SWER network serves 28 customers all supplied power through the 12.7 kV SWER network.

Data logging and tests were undertaken at the “Myers Road” isolation transformer (ISO). Note the ISO isolates the SWER network from the 22kV multi-phase network, changing the voltage from 22kV to the SWER voltage (12.7 kV).

SWER Network

“Myers Road” SWER network in Balnarring.

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Project Background: Myers Road SWER Network


The SWER ACR is located on a second pole approximately 22 meters away from the pole where the test set up was located. The data logging test equipment was located in an enclosure placed 3 meters high on Pole #1.

Isolation TransformerSWER conductor

SWER ACR

Test Set Up

Pole #1

Pole #2

“Myers Road” SWER ISO and ACR.

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Project Background: Noise Logging


Key elements of the background noise logging included the: 1.1 nF coupling capacitor, a coupler termination box, a custom designed and built Capacitive Voltage Divider (CVD), a low-noise filter, two Digitisers and the Gen 3i logger.

The objective was to develop a logging concept that enabled voltage background-noise data collection and analysis to be carried out for the communication channel.

The two CVD channels were recorded individually. This enabled background noise levels of the SWER network to be measured in two channels: the 10 kHz to 500 kHz High Frequency (HF) channel and the 0 Hz to 50 kHz Low-Frequency (LF) Channel

HF ChannelDigitiser TransmitterSampling @ 5 MS/s

Low-Pass Bessel IIR AA Filter < 500 kHz

Receiver Noise Analysis Concept DesignTarget Bandwidth = 10 kHz to 500 kHz | 0 Hz to 50 kHz

F/O

Second-stage over-voltage protection

BNC

GNDCTB1APower

Diagnostix Systems Coupler Termination Box

12.7 kV

12.7 kV

Gen 3i Logger

TNC

F/O

Suitable Conductor

MCC124 Coupling Capacitor 1.1nF

BNCBNC

BNC

BNC

BNC

RG58 Coaxial

LF ChannelDigitiser TransmitterSampling @ 5 MS/s

Low-Pass Bessel IIR AA Filter < 50 kHz

11 m

0.5m

0.5m

RG58 Coaxial

RG58 Coaxial

RG58 Coaxial

1m

5m

RG58 Coaxial

1m

RG58 Coaxial

Input

OSC

LP

HP

HF Digitiser

LF Digitiser

CVD

Low-Noise Pre-Amplifier/Filter

“Myers Road” SWER network noise analysis concept.

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Project Background: Transmitter Setup


The transmitter set-up was connected at the “French No: 3 Bittern” SWER distribution substation. The pole is located next to a farmhouse and an enclosure was erected 3 meters high on the pole enabling the placement of all relevant injection hardware.

The direct distance between the transmitter and receiver is approximately 3.6 km.

A coupling capacitor was mounted on the pole enabling the injection of HF signals directly onto the 12.7 kV conductor through the coupling capacitor.

SWER ConductorSWER

Transformer

Transmitter

Enclosure

Coupling Capacitor

“French No: 3 Bittern” SWER Distribution Transformer Pole.

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Project Background: Transmitter Setup


Three different injection options were designed and tested. These include the coupling capacitor, MV earth, and SWER Transformer Low Voltage Winding injection approaches.

The SWER substation LVW circuit included the matching circuit, a low-pass filter, and the arbitrary signal generator, and it was connected directly to a 240V general purpose outlet (GPO) located within the enclosure. The MV Earth injection circuit included a Toroidal Transformer.

80 Amps Fuse

SWER conductor

MV Earth LV Earth

A

N

Coupling Circuit

FilterSignal Generator

RG58

RG58

RG58

PLC FilterCustomer

Load

Coupling Circuit Filter Signal

Generator

RG58RG58

4 Amps Fuse

GPO

Electrical Plug12.7 kV

Toroidal CT

Coupling Circuit

Filter

Signal Generator

RG58

CTB1A

RG58

RG58

RG58

RG58

MV Earth Injection and Coupling Circuit

SWER TR Low Voltage Winding Injection and Coupling Circuit

Coupling Capacitor Injection and Coupling Circuit

Injection Set-Up at “French No: 3 Bittern” SWER Distribution Substation

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Project Deliverables – Literature review


There are limited published applications of real world distribution PLC protection applications. Published academic papers focus on abstract concepts.

Selection of the optimum frequency range for PLC signal transmission is critical. Background noise/signal analysis over the communication channel should be performed before the selection of the appropriate frequency. There is a need to balance between signal attenuation, signal to noise ratio (SNR) and compliance with regulations.

The type of modulation and error correction will have significant impact on the signal-to-noise ratio and accurate transfer of any key information.

No mandatory standard for the Electromagnetic Compatibility (EMC) for HV distribution systems exists. The CENELEC Standard EN 50065 (for LV PLC installations) has been used as a guide.

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Project Deliverables – Noise Measurements


Communication over powerlines is degraded by external electrical noise, and the signal to noise ratio (SNR) plays a key role in the reliability of a PLC scheme.

Specialised electrical circuits were custom designed and built to record noise with the network in energised and de-energized states.

The test equipment was located in an enclosure placed 3 meters high on Pole #1 at the “Myers Road” SWER ISO.

The noise recordings were analysed to understand the impact on the ability to successfully communicate using PLC signals.


SWER conductor

SWER ACR

Test Set Up

Pole #1

Pole #2

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Project Deliverables – Noise Measurements


Based on the investigation of the SWER communication channel background noise levels, a PLC application is feasible.

In the frequency range of interest, sections of the spectrum have sufficiently low noise to permit reliable communication.

The noise floor levels are sufficiently low enough to achieve a high signal-to-noise ratio even for received signals as low as -60 dB.

This would ensure a minimum signal-to-noise ratio of 10 dB, which is sufficient for the reliable operation and decision making in a receiver.


SWER conductor

SWER ACR

Test Set Up

Pole #1

Pole #2

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Project Deliverables – Coupling Circuits


Three injection coupling methods were modelled including the Coupling Capacitor (CC), Low Voltage Winding (LVW), and Medium Voltage Earth (MVE).

Coupling Capacitor (CC)

Injection Circuit

Medium Voltage Earth (MVE)

Injection CircuitLow-Voltage Winding (LVW)

Injection Circuit

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Project Deliverables – Injection Tests


Signal strength received for the three signal injection methods were compared over a range of frequencies. The LV line injection method performed the best and is a low cost option. The SWER distribution transformer LV winding coupling has been selected as the signal injection method for the prototype fault detector.

80 Amps Fuse

SWER conductor

MV Earth LV Earth

A

N

Coupling Circuit

FilterSignal Generator

RG58

RG58

RG58

PLC FilterCustomer

Load

Coupling Circuit Filter Signal

Generator

RG58RG58

4 Amps Fuse

GPO

Electrical Plug12.7 kV

Toroidal CT

Coupling Circuit

Filter

Signal Generator

RG58

CTB1A

RG58

RG58

RG58

RG58

MV Earth Injection and Coupling Circuit

SWER TR Low Voltage Winding Injection and Coupling Circuit

Coupling Capacitor Injection and Coupling Circuit

A

Injection Set-Up at “French No: 3 Bittern” SWER Distribution Transformer.

SWER Conductor

SWER Transformer

Transmitter Enclosure

Coupling Capacitor

Pole #1

“French No: 3 Bittern SWER Distribution Transformer Pole.

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Project Deliverables – Injection Tests


A summary of test days and tested injection methods are provided below.

On the 7th of August 2018, successful injection was achieved when the Isolation Transformer was isolated from the 22 kV three-phase network. The failure of a Low-Pass (LP) filter in the injection set up prevented successful injection during the online injection periods. This necessitated the online tests to be repeated on the 17th of August 2018, when the coupling capacitor based injections were successfully retested for the connected Myers Road SWER network.

On the 14th of December, all three-injection methods were tested under the same weather and network conditions in the 22 kV grid connected network. These include the Coupling Capacitor (CC), Medium Voltage Earth (MVE), SWER Transformer Low Voltage Winding (LVW) injection methods.

SWER Transformer LVW based injection was observed to be superior to the other two methods in terms of both received signal strengths and peak correlation levels. This is a key advantage in the direction towards cost-effective implementation of the proposed scheme without requiring the use of expensive coupling capacitors or CTs.

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Test Date Method Mode Comments

7th of August 2018 Coupling Capacitor Online & Offline Successful injection during offline periods

17th of August 2018 Coupling Capacitor Online Successful injection

14th of December 2018 Coupling Capacitor, Medium Voltage Earth, SWER

Transformer LV Winding

Online Successful injection


Project Deliverables – Prototype Development

The PLC prototype consists of a transmitter and a receiver. A combination of Digital Signal Processor (DSP), ARM microcontroller and Field Programmable Gate Array (FPGA) have been used in developing the prototype.

Transmitter Prototype. Receiver Prototype.

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Project Deliverables – Prototype Development

An experimental LV injection test setup has been successfully constructed in the VU laboratory. The experimental setup was used to test the developed system under different configurations including

(i) noiseless modulated signal transmission, (ii) recordings of the “Myers Road” SWER network background noise and (iii) recording of a transmission test on the network including the PLC modulated signal and background noise.

Results show that the autocorrelation function implemented in the Receiver can successfully identify the transmitted signal even in cases of strong real background noise.

Laboratory experimental setup.

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Stage 1 Project Findings

Various digital modulation, error correction techniques, and suitable communication protocols were reviewed as part of the literature review. Different PLC transmitter & receiver coupling techniques were analysed.

Background network voltage noise recordings were successfully gathered over a six-day period, dominated by phase-to-ground voltages. This includes ten-second continuous mode recordings taken every 15-minutes for a period of five days and trigger based sweep mode recordings for three days.

Peak-to-peak periodic pulses were observed at the HF channel associated with Variable Frequency Drive (VFD) equipped electro-mechanical systems.

A noise floor of -70 dB was observed in the designated bandwidth, ideal for signal transmission requiring -60 dB received signal level for a practical SNR of +10 dB.

The direct path between a transmitter (TX) and receiver (RX) was observed to be most critical in signal attenuation with the lengths of adjoining spurs having minimal impact.

In injection tests, the LVW coupling based injection produced signal strengths and peak correlation levels superior to the other two methods. This is expected to aid in the development of a cost-effective solution as SWER transformers are readily available and connected on the network.

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Conclusion

A collaborative R&D project between UE, DELWP and VU has enabled a prototype SWER broken conductor fault detector to be developed that can rapidly detect the break in a SWER powerline and de-energise the powerline before the fault has an opportunity to start a bushfire.

Simulations and testing undertaken in the laboratory have demonstrated that the prototype is expected to perform well on a real SWER network, however the technology remains immature and the prototype is yet to be installed and tested on a real SWER network.

Further development is proposed to install the prototype protection system on real SWER networks to monitor and improve upon the design. Challenges remain including the impact of communication interference, PLC signal losses associated with transitions from overhead and underground cable, spur fusing and others however solutions may also be available.

If testing on real networks is successful and the technical challenges can be overcome, the final stage will be to develop a mature robust, reliable and cost effective commercial product.

The ultimate objective is to develop technology that can be widely deployed to reduce the number of bushfires started from SWER powerline in Victoria and beyond.

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Documents

SWER Broken Conductor Detector R&D Project – Progress Update · 2019-08-20 · Document Control and Non-Disclosure Notice 18.07.19 SWER Broken Conductor Detector R&D Project - Final