Case study: Achieving accurate time synchronisation testing without access to GPS clear sky

CASE STUDY
ACCURATELY TESTING TIME
SYNCHRONISATION WITHOUT
DIRECT ACCESS TO GPS
SIGNALS IN THE SKY

PAGE 01
SUMMARY
This case study describes a challenge faced during a major
Australian Underground Rail New Build Project that involves the
installation of high voltage transmission shunts and reclosers,
which requires thorough end-to-end testing, including the
simulation of protection relays on both ends of a high voltage
cable.
The testing process requires accurate synchronisation, which is
typically achieved through GPS devices. However, working
underground at a depth of 30 metres presents a challenge as GPS
signals are inaccessible.
The solution involved the use of Albedo Telecom's xGenius
synchronisation tester, which features a Rubidium oscillator that
can maintain stratum 1 accuracy for up to 32 hours with less than a
1 microsec deviation. The xGenius was used to synchronise the
Omicron testing equipment using a PTP trigger source, which
allowed the testing process to continue without inaccuracies or
interruptions. This ensured that the project met the required safety
and quality standards, giving the client confidence in the reliability
of the high voltage transmission equipment they had installed.

PAGE 02
THE CHALLENGE
A major Australian Underground Rail New Build Project involves the
installation of high voltage transmission shunts and reclosers,
which is a critical and complex task. This requires thorough end-toend
testing, which involves simulating protection relays on both
ends of a High Voltage cable. These cables can span distances
ranging from a few hundred metres to hundreds of kilometres,
making it important to ensure synchronisation and accuracy during
testing.
To achieve accurate testing, synchronisation of injection on both
sides of the cable is critical. This is achieved through the use of GPS
devices that are connected on both sides, and the start of the test
is triggered by a next minute countdown.
To aid with the testing process, our client was using their existing
Omicron equipment. This helped them to check the timing between
different parts of the equipment, enabling them to identify and
address any issues that may arise.
However, there is a challenge when working 30 metres
underground. Typically, GPS signals are used to clock synchronise
the Omicron equipment and ensure accurate timing during testing.
Without access to GPS signals, they need to find an alternative way
to maintain synchronisation during testing.

PAGE 03
THE SOLUTION
The Albedo xGenius played a key role in overcoming the
synchronisation challenge encountered during testing. This
handheld transmission and synchronisation tester features a
Rubidium oscillator that, when disciplined to lock to GPS accuracy,
was able to maintain stratum 1 accuracy for up to 32 hours with less
than a 1 microsec deviation. The output PPS signal was used to
synchronise the Omicron equipment across all the sites involved in
the project.
The Omicron equipment offered an option of using a PTP (Precision
Time Protocol) trigger source, which was necessary in this
underground setting where GPS signals were inaccessible. This
option enabled the testing process to continue without
interruptions or inaccuracies.
Once the xGenius was synchronised and set to holdover mode, it
was connected to the Omicron testing equipment to provide the
next minute trigger option, ensuring that the timing between
different parts of the high voltage transmission equipment was
accurately tested and certified for faults. This ensured that the
project met the required safety and quality standards, giving our
client confidence in the reliability of the high voltage transmission
equipment they had installed.

PAGE 04
THE RESULTS
The use of the xGenius with built-in Rubidium clock disciplined
with GPS/GNSS has enabled our client to achieve accurate and
reliable testing of high voltage transmission equipment in a
challenging underground environment. Without access to GPS
signals, the xGenius provided the critical clock synchronisation
required for testing, allowing our client to commission the site 30+
metres underground and hand over the site results within three
weeks. By using this solution, our client was able to save a
significant amount of time in the testing process, without the need
for additional civil works to allow a sky mount ground antenna.
Overall, the success of this project demonstrates the importance of
innovative solutions in overcoming complex challenges and
achieving efficient results.
Albedo Telecom is a manufacturer of Network Clocks, Test and
Measurement Testers and WAN Emulators that are used by Utilities,
Telcos, Railways, Defence, Aerospace and R&D centres. Their
innovative solutions are used to install, troubleshoot and maintain
telecom infrastructures supporting critical voice, video and data
applications.

PAGE 05
CONTACT US
At CoverTel, our commitment is to provide our clients with topnotch
solutions that not only meet but surpass their expectations.
This project's success showcases the value of our team's knowledge
and expertise in delivering innovative solutions to overcome
complex testing challenges and achieve efficient results. By
partnering with Albedo Telecom, we are equipped to tackle all your
synchronisation challenges, including those in the most
challenging environments.
Contact us today to discuss your requirements for innovative and
efficient solutions that will exceed your expectations.
114 Bakehouse Road
Kensington, Victoria
Australia 3031
1800 268 378
www.covertel.com.au