A laboratory setup of a power transmission line system scaled model ...

A laboratory setup of a power transmission line system scaled model
for testing and validation of sensor network applications
Philip W. T. Pong, Carson K. S. Hung, Ronald C. L. Li, Simon C. F. Tam, W. K. Lee, Kenneth K. K.
Wong, K. S. Lui
Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
Abstract—A laboratory setup of a scaled model of sensor
network system and power transmission system has been
developed at the Smart Grid and High Power System
Laboratory of the University of Hong Kong. The sensor network
consists of accelerometers, infrared sensor, strain gauge, and
magnetic sensors, which provide accurate readings to monitor
the status and position of the power transmission line, the tilt of
power tower, and power quality of the power transmission
system. A LabVIEW program was developed to provide the
user interface for the monitoring system which can visualize the
power transmission line infrastructure, process the sensors’
data to display on the screen in real time, and synchronize GPS
sensors data.
Index Terms— Laboratory setup, Power transmission system,
Sensor network system, LabVIEW
I. INTRODUCTION
Monitoring a power transmission line system with a more
effective and accurate method in real time becomes more and
more important in nowadays. The system covers in our entire
city or country, and any problems may seriously affect our
lives. For example, US and Canada occurred a very large
scale power failure in 2003 which led to large economic loss
and influenced the lives of people. The power transmission
line may also be a sabotage target. In Colombia, terrorists had
attacked on the electricity infrastructure, and it is very
difficult to avoid and predict which power node or
transmission infrastructure is damaged. In the snowstorm in
China in 2008, ice and snow aggregated on transmission lines
and overloaded the power towers to led tower collapse.
However, China did not have adequate technology to monitor
the entire system, and they relied on manual field inspection
of damaged cables. It is very time consuming and inefficient.
Hence, an effective and accuracy sensor network for
monitoring the power transmission line system in real time is
necessary.
Nowadays, Smart Grid System is starting to become
popular in the world. A lot of countries’ government policy,
such as Australia, Korea and China started to investigate the
system feasibility in their country or planning development in
the future. Moreover, in the Smart Grid System, renewable
energy resources are often far away from the load centres.
Long-distance power transmission lines are necessary to
efficiently transmit the renewable energy to the load centers.
Sensors are needed to monitor the effective operation of the
transmission system. To save energy, reduce cost and
increase reliability of power transmission, better sensors and
communication are required.
This paper presents an advancement of a sensor network to
provide a more effective and accurate real time monitoring
system, and scaled model of the power transmission line
system is presented in this paper. The monitoring system
included sensors which are needed to monitor the power
status to ensure constant power supply, assert for different
power demand in different time period to reduce or increase
the demand, and monitor the power tower and power
transmission line status. A LabVIEW program was developed
for the monitoring system which can visualize the power
transmission line infrastructure, and process the sensors’ data
to display on the screen for classify the problems in real time.
In addition, the optical fiber is used for network
communication, since they can support fast data transmission
and are robust to noise. GPS is used for sensor network time
synchronization.
The rest of this paper is organized as follows. In section II,
the details of application for each sensor in the monitoring
system are discussed. The whole laboratory setup including
the scaled power transmission line model, sensor network
with the monitoring system, and the LabVIEW interface are
shown in section III. Section IV discusses the strengths and
weaknesses of the setup. Finally, the conclusion and future
works are included the section V.
II. APPLICATION OF THE SENSORS
The purposes of developing the smart grid sensor network
are (1) Real-time monitoring to enhance situational
awareness, and keep check the power status to ensure
constant power supply due to merging of the non-renewable
energy and renewable energy and power failure.
Furthermore, the network monitors the different power
demands due to different usage in different time period. (2)
Anticipation to check for potential problems, assess trouble
signs and estimate possible disturbances. (3) Locate the
accurate position of abnormal power towers or transmission
line in a large power supply network. (4) Self-healing based
on sensor data and identifies corrective actions.
The sensor network includes different type of sensors to
monitor the power transmission line system. Four type of
sensors are used in the monitoring system - Accelerometer,
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infrared sensor, Strain Gauge and Magnetic sensor- and their
applications are presented as following.
A. Accelerometer
Accelerometer is applied to monitor the power
transmission line tilting and the power tower vibration and
tilting. A common problem in the power transmission system
is the overhead transmission line sagging problem. When too
much current is flowing, the cable heats up and sags. The
cable may touch trees and lead to short circuit. Hence, the
accelerometer can keep check of the tilting angle of the power
transmission line to avoid this problem. Moreover, the power
tower may not bear the weight of the transmission line if the
ice or snow placed on the transmission line, and the power
tower may be deformed due the weight of the transmission
line, so the accelerometer is needed to monitor the power
tower vibration and tilting.
Fig. 1 Accelerometer
B. Infra red sensor
The temperature is monitored by the infrared sensor, since
the temperature of the transmission line is increased when the
current flow is increased, which increases the length of the
transmission line. The extension can be calculated by the
temperature variation and the characteristic of the material, so
the monitoring system can output the warning if the
transmission line length exceeds the length limit. Hence, the
problem can be avoided. If the temperature is too high, it may
damage the transmission line, so the operator can reduce the
load of that transmission line, and use the others for the
transmission. The infrared sensor is used to detect the
temperature, and has the advantage of fast response and high
accuracy without physical contact. It is used to monitor
overheat conditions.
C. Strain Gauge
The strain gauge is applied to keep check of the length of
the transmission line. For the overhead transmission line
sagging problem, accurate length with the tilting angle is
necessary to avoid this problem. The strain gauge can output
the accurate length extension calculated from the weight or
force applied to the transmission line.
Fig. 3 Strain Gauge
D. Magnetic sensor
The magnetic sensor is a very important sensor in the
monitoring system, since it monitors a few parameters at the
same time, including the power transmission line position and
tilting, current flow, magnitude and frequency. A common
problem in the power transmission system is the overhead
cable gallop problem. In adverse weather conditions with
strong wind, the cable swings which can lead to contact with
another phase line or mechanical failure. Therefore, the
position of the transmission line is needed to be monitored.
Based on the characteristic of the transmission line, the
current passing through the transmission line will generate a
magnetic field, and the field is detected by the sensor, and the
readings are passed back to the system for analysis. This data
can be used to find out the power transmission line position
and tilting, current flow, magnitude and frequency.
Fig. 4 Magnetic sensor
III. LABORATORY SETUP
Fig. 2 Infra red sensor
The mission of the smart grid sensor network is monitoring
the operation of the power delivery network system. For each
power tower or power station, the sensors are installed, which
connects to a Collect Data Station, for collect the data of the
status of power tower and power transmission line, and
sending back the monitoring data to Power System Control
Centre, which to be a Monitoring Station, for monitoring a
number of power tower or power station. Due to low cost and
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easy installation of the sensors, enormous number of sensors
can be deployed over a huge geographic area. Fig. 5 shows
the Power System Control Centre monitoring the status of
power tower and power transmission line.
power delivery system. Four accelerometers are setup in the
model, two are installed vertically for each power tower
vibration and tilting, and the other two are setup horizontally
on the cable near to the power tower for monitoring the tilting
angle of the cable. Two strain gauges are also setup on the
cable in the same way as the accelerometers to keep check of
the extension. The infrared sensor targets on the cable near to
the tower, since the cable stays at a more stable position for
monitoring the temperature. Two magnetic sensors are placed
at the left and right of the cable for detecting the magnetic
field to calculate the accurate position of the cable, and
monitoring the current status, such as, flow, magnitude and
frequency. The data of the sensors send to the DAQ card
(analog-digital interface card) for data conversion, and then
send to Collect Data Station for data processing.
Fig. 5 Sensor network with Power System Control Centre
For the sensor network system, the sensors receive the
monitoring data. The data is passed through the analog-digital
interface card for data processing in the Collect Data Station,
and the data will be converting to optical signal. After the data
processing, the status of power tower and power transmission
line are sent back to the Monitoring Station by the optical
fiber interface, and the networking is from a Hybrid
Topology. Fig.6 is shown the data flow from the sensors to
optical fiber.
Fig. 7 Schematic diagram of the sensor network
Fig. 8 shows the laboratory setup dimension. The power
transmission line is 3m in length. Strain gauge is located 0.1m
from to the power tower on the power transmission line, and
the accelerometer, on the power transmission line, is 0.2m
from to the power tower. The accelerometer is 0.25m from
the ground. Infrared sensor is 0.15m horizontally from the
power line. The magnetic sensors under the power
transmission line are 0.35m away from the line, and the
distance between the sensors is 0.6m, and 1.5m to the power
tower.
Fig. 6 Sensors’ data flow
The laboratory setup is developed at the Smart Grid and
High Power System Laboratory at the University of Hong
Kong. The whole setup includes three parts, (1) Power Tower
and Power Transmission Line, (2) Sensor Network with the
Collect Data Station, and (3) User Interface by LabVIEW
with Monitoring Station. The whole system is a scaled down
model. Fig. 7 illustrates the schematic diagram of the sensor
network with the power tower and power transmission line.
In the model, two power towers and a power cable to form a
Fig. 8 Laboratory setup dimension
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Fig. 9 illustrates the physical layout of the model of the
schematic diagram of the sensor network with the power
tower and power transmission line.
Fig. 9 Setup in the laboratory
Fig. 11 Accelerometer in the setup
A current generator is supplies a constant AC current with
a sine wave form, and the current range is within 10 to 2000A
with a small voltage.
Fig. 12 Accelerometer sensing axis
For the strain gauge, four oVishay Micro-Measurements
125AC strain gauges form a full-bridge circuit (Wheatstone
bridge), which can provide all-round and accurate length
extension when placed on the power transmission line. Eight
strain gauges were installed in the model.
Fig. 10 Power supply for the transmission line
The accelerometer is Freescale Semiconductor three axis
micro-machined surface mount accelerometer (MMA7360L).
It has x, y and z axis motion detection, so it works like as a
motion sensor to monitor the motion and the tilting angle of
the power transmission line. Moreover, it has free fall
detection, which is useful for detection of damaged or
destroyed power transmission lines or power towers. It can
detect the tilting angle within 90 degrees, and the sensitivity
is +/-1.5g or +/-6g.
Fig. 13 Strain gauge in the setup
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The infrared sensor is the Micro-Epsilon thermometer
CTlaser (CTL-SF75-C2) and is used to monitor the
temperature of the power transmission line. The detector
temperature range is within -40°C to 975°C, and it has a fast
response time of 120ms. The infrared sensors should not be
directed upwards while targeting the transmission line,
because sunlight may affect detection, so the targeting should
be done in a horizontal or downwards orientation.
Fig. 17 Magnetic sensors in the setup
Fig. 14 Intra red sensor
The monitoring data from sensors is passed to the DAQ
card (analog-digital interface card), which is the National
Instruments NI USB 6211 M series multifunction DAQ card.
The DAQ card has 16 analog input pins with +/-10V voltage
range (16bits) which are enough for receiving the data from
the sensors. The card accepts 250kS/s, a high rate for data
sampling. The USB interface is convenient to connect to the
Collect Data Station for data processing.
Fig. 18 DAQ card
Fig. 15 Intra red sensor head in the setup
For the magnetic sensor, the Honeywell HMC2003
three-axis magnetic sensor hybrid is selected for this
laboratory setup. It can monitor x, y and z axis magnetic field
at the same time, and it has a linear detection dynamic range
of +/-2gauss with high resolution 40 micro-gauss. Moreover,
an offset can be set to reduce the external magnetic field. The
sensors are placed under the power transmission line, in the
bottom left and bottom right positions.
The Collect Data Station converts the monitoring data to
optical signal, which passes through the optical fibre to the
Monitoring Station for analysis and display in the LabVIEW
user interface; therefore, the Collect Data Station and
Monitoring Station also have to include the optical interface
card. For this card, OLYCOM OM910-FE/S25 is selected for
the setup, due to its capability to operate at 100Mbps and to
provide a network throughput of 200Mbps in full-duplex
mode, and fast response of optical fiber reconnection.
Moreover, it can operate over a long distance. The FC/PC
connector, single-mode optical fiber is connected between the
Collect Data Station and Monitoring Station.
Fig. 16 Magnetic sensor
Fig. 19 Optical interface card
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The Monitoring Station is a LabVIEW User Interface, base
on the operation of the sensor network system, all the sensors
also have their duty, and their data can provide the numeral
and visual result on the interface.
Fig. 20 illustrates the LabVIEW User Interface. The top
left diagram is the position of the power transmission line,
and it is generated using data from the magnetic sensors. In te
normal case, they should form a triangle as in the setup. If the
power transmission line is moved, the varied magnetic field is
received by the magnetic sensors, and the field strength of x
and z vector component change (vector y is zero due to
parallel with the current flow). Therefore, the angle and the
distance between the magnetic sensors and the power
transmission line are detected and displayed visually. The
bottom left is the magnetic field waveform which is generated
by the magnetic sensors. The centre-top window monitors the
tilting of the power towers, and this visual information is
generated by the vertical accelerometer’s x and z axis on the
power tower. The centre-bottom window shows the power
transmission line position and tilting status, and this visual
information is generated by the accelerometer’s x and z axis
readings on the transmission line and the magnetic sensors.
The top right is the numerical results, including power
towers’ tilting, power transmission line’s tilting, magnetic
field strength, positioning. Extension is found out by the
strain gauge, temperature is found out by the infrared sensor,
and the current magnitude is found out by the magnetic
sensor. Moreover, there are some warning indicators, and
they are lighted up according limiting values. Finally, the
bottom right monitors the frequency, and it is generated by
the magnetic sensor.
Fig. 21 Sensor node interface
To achieve real-time monitoring of the smart grid system
status, the idea of GPS is added in this sensor network, which
can synchronize the reading of the sensors with the accurate
time. A GPS receiver can communicate with several satellites
at a time to evaluate its geographical locations and get the
Coordinated Universal Time. Hence, the GPS receivers are
installed in each Collect Data Station, and the Collect Data
Station can convert and transfer the GPS information to
Monitoring Station for synchronization of all the readings
from different Collect Data Stations.
The Holux GR-213U GPS receiver is installed in our
laboratory setup. It can parallel satellite tracking with twenty
channels for fast acquisition (1 sec for hot start) and
reacquisition (0.1 sec average), and 1 micro-second
synchronize GPS time, and the position accuracy is within 2.2
meters.
Fig. 20 LaVIEW user interface
The Monitoring Station not only monitors the status of the
power transmission line and tower of the smart grid system,
but also monitors the networking of the sensor node. If there
are any problems between the Collect Data Station and
Monitoring Station, such as broken optical fiber or
disconnected optical interface card in the sensor network, it is
easy to debug in the interface.
Fig. 22 GPS receiver
The information of the GPS receiver can also been seen in
the LabVIEW User Interface at the Monitoring Station. In
this interface, the application of Google Maps is added for
getting a picture of that position. The time and position
information can display in the interface. Fig. 23 illustrates the
LabVIEW User Interface of GPS section.
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transmission system model. In the future, a solar system to act
as the sensors’ voltage supply can be added. Moreover, the
power transmission line will be improved to a three phase
system, and the magnetic sensors will accurately detect the
position of the power lines separately.
Fig. 23 GPS interface
IV. DISCUSSION
In this sensor network monitoring system, the status of the
smart grid system is monitored by different types of the
sensors, and the accurate readings of the sensors are
displayed in numeral and visual result on the interface,
including power transmission line position and power tower
tilting, which be easily understood visually. Moreover, the
power quality can also be monitored in the system. Therefore,
it is a user friendly and convenient system to apply on the
smart grid system. The cost for this sensor network
monitoring system is low, requiring around $8000 Hong
Kong dollars for the sensors setup.
However, the sensors require different voltage input
supply, and extra power supply and batteries are needed in the
setup. Hence, a solar system and backup power supply form
the power transmission system will be developed in the
future. Moreover, the sensors’ installation positions in the
real power transmission system have to be considered. For
instance, the magnetic sensor cannot be installed at a place
where other magnetic sources affect the operation of the
sensors.
V. CONCLUSION
Recently, a lot of country and city are paying attention to
the energy and environment problems; hence, renewable
energy is more and more important in our life. The smart grid
system can potentially be used in the world. The monitoring
of the system is necessary to maintain the power quality,
increase the reliability, efficiency when combining the
renewable energy to the power transmission system and to
manage of the output energy to decentralize the power
generation. The laboratory setup presented in this paper is a
model of a sensor network system which includes
Accelerometer, Intra red sensor, Strain gauge, and Magnetic
sensor to monitor the power transmission system. A
LabVIEW user interface for display the numeral and visual
result for users to keep check of the status of the system. The
application of the system has been demonstrated on the power
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