Abstract—
Monitoring of electric power systems in real time for
reliability, aging status, and presence of incipient faults requires
distributed and centralized processing of large amounts of data
from distributed sensor networks. To solve this task, cohesive
multidisciplinary efforts are needed from such fields as sensing,
signal processing, control, communications, optimization theory,
and, more recently, robotics. This review paper focuses on one
trend of power system monitoring, namely, mobile monitoring.
The developments in robotic maintenance for power systems
indicate significant potential of this technological approach.
Authors discuss integration of several important relevant sensor
technologies that are used to monitor power systems, including
acoustic sensing, fringing electric field sensing, and infrared
sensing.
Index Terms—Automated maintenance, distribution power systems,
mobile sensing, real-time monitoring, sensor arrays.
I. INTRODUCTION
ECONOMICALLY effective maintenance and monitoring
of power systems to ensure high quality and reliability
of electric power supplied to customers is becoming one of
the most significant tasks of today’s power industry. As with
any preventive maintenance technology, the efforts spent on the
status monitoring are justified by the reduction of the fault occurrence
and elimination of consequent losses due to disruption
of electric power, damage to equipment, and emergency equipment
replacement costs.
In the past few years, there have been several significant developments
on monitoring technologies for distribution power
cables. This review describes technical results relevant to mobile
sensing of distributed systems, especially for maintenance
tasks.
II. BACKGROUND
It is a well-recognized fact in surveillance and monitoring
fields that measurement of parameters of a distributed system
has inherently higher resolution and accuracy when it is accomplished
with a scanning device as opposed to a wide-angle
global system. Experimentally, this has been confirmed in numerous
cable testing studies (e.g., [1]). This principle remains
in force for almost all sensing techniques: it is possible to monitor
a distributed system with a global device; for example, using
terminal characteristics or propagating waves, but this approach
Manuscript received November 28, 2001. This work was supported in part by
National Science Foundation CAREER Award 0093716 and in part by the Electrical
Energy Industrial Consortium and Advanced Power Technologies (APT)
Center at the University of Washington. The APT Center is supported by RTE,
AREVA, PJM, CESI, LG Industrial Systems, and Mitsubishi Electric Corp.
The authors are with the Sensors, Energy, and Automation Laboratory
(SEAL), Department of Electrical Engineering, University of Washington,
Seattle, WA 98195 USA (e-mail: mamishev[at]ee.washington.edu).
Digital Object Identifier 10.1109/TPWRD.2004.829918
does not match the resolution of equivalent sensors placed in the
direct vicinity of system components.
In addition to sensitivity improvement and subsequent
system reliability enhancement, the use of robotic platforms
for power system maintenance has many other advantages.
Replacing human workers for dangerous and highly specialized
operations, such as live maintenance of high-voltage transmission
lines, has been a long-standing effort in the power
community. Other needs of robotics in power systems include
operation in hazardous environments, such as radioactive
locations in nuclear plants, access to tight spaces, such as
cable viaducts and cooling pipes, and precise positioning of
measurement equipment. Therefore, one may expect that the
mobile sensing will play an increasingly important role in the
monitoring of power systems.
Numerous worldwide projects attacked this challenging
application from different angles. In 1989, two manipulator
systems differing in operating method were developed by Tokyo
Electric Power Company to traverse and monitor fiber-optic
overhead ground transmission wires (OPGW) above 66-kV
power transmission lines [2]. It was shown that the systems are
fully capable of performing distribution line construction work
using stereoscopic TV camera system. Several other teleoperated
robots have been developed for live-line maintenance in
Japan [3], [4], Canada [5], Spain [6], and other locations.
An autonomous mobile robot was developed to inspect the
power transmission lines in 1991 [7]. The robot can maneuver
over obstructions created by subsidiary equipment on the
ground wire. It is equipped with an arc-shaped arm that acts
as a guide rail and allows it to negotiate transmission towers.
At the same time, a basic synthesis concept of an inspection
robot was described for electric power cables of railways [8].
Since the feeder cables are extremely long and have many
irregular points, a multicar structure with joint connections and
biological control architecture was adopted; thus, the robot
could run on the cable smoothly with sufficient speed and deal
with the shape irregularities.
III. TECHNOLOGICAL NEEDS
Hardly any successful robot applications have been reported
for underground distribution cables. Numerous problems have
to be solved for this kind of a robot, such as space confinement,
size and weight restrictions, wireless design requirements, and
adverse environmental conditions. Miniaturization has been one
of the most difficult problems.With the continuing development
of MEMS, microelectronics, and communication technologies,
this problem is on the verge of being solved. Successful applications
of microbots were demonstrated in other fields (e.g., [9]).
Fig. 1 shows a conceptual design of a mobile platform, a modular
system with a separate unit providing autonomy of opera-
0885-8977/04$20.00 © 2004 IEEE
JIANG AND MAMISHEV: ROBOTIC MONITORING OF POWER SYSTEMS 913
Fig. 1. Miniature robotic platform for monitoring of transmission and
distribution power cables. (a) Internal platform. (b) External platform.
tion and reconfigurable sensing arrays in a master/slave arrangement.
Generally speaking, the mobile monitoring of power systems
involves the following issues.
1) Sensor fusion: Monitoring the condition of cables
requires incorporation of sophisticated property-monitoring
sensors in addition to positioning, tactile, and
other sensors aimed to support the autonomy of robot
movement.
2) Motion pattern: Inspection robots used in power systems
can be subdivided into external and internal ones (see
Fig. 1). External robots travel over the outer surface of
electrical components and may possess a high degree of
autonomy [8], whereas internal units use inner spaces of
ducts and pipes and are often implemented as track-following
devices with a predetermined route, and a limited
set of operations [10]. The level of autonomy depends on
the task. For example, routine inspection and maintenance
require a high degree of autonomy for economical reasons.
3) Power supply: Since the cable network is a global distributed
system, it is very limiting for the inspecting robot
to draw a power cord behind itself. Ideally, the power
supply has to be wireless. It is desirable that the platform
harvest energy from energized cables. Inductive coupling
for a wireless power supply could be a desired method.
It has been investigated for vehicles [11], batteries [12],
microsystems [13], and numerous consumer applications.
Although a low-frequency coupling is less efficient than a
microwave mode [14], direct proximity to the power cable
will make it a viable choice. Of course, the platform requires
an independent backup power source as well.
4) Control strategy: It includes object tracking, collision
avoidance, and prevention of electrical short circuits. The
control system receives initiating commands from the
operator for the global tasks, and small tasks are often
preprogrammed. The most important requirements are
the following.
a) The control should be robust because of complicated
motion requirement and the irregular surface
of the cable connections.
b) It should include an optimum algorithm used to locate
the sensor array with respect to the inspected
system, a path planning algorithm used to track the
whole or part of the network with the shortest path,
and control sequences adaptively switching sensor
operation from a fast superficial inspection mode
to a slow detailed inspection mode.
c) The robot requires considerable computational
resources to be adaptive and flexible. This fact is
highly problematic because of the limited size of
the robot, especially for underground applications.
Accordingly, this strongly argues for the use of
communication and offboard intelligence. This
also involves allocation between local and remote
signal processing.
5) Communication: The communication module exchanges
data between the master computer and the mobile robot,
including data originating from different streams on both
sides of the communication page link and different priorities
associated with it. A multiplexing problem that concerns
the allocation between local and remote computation capacity
has to be solved too [15].
6) Positioning system: It should work like the Global Positioning
System (GPS), used to estimate the location of the
robot. Therefore, effective maintenance and rescue tasks
for cable systems, even for the robot itself, can be carried
out. In most applications, two basic position estimations
are employed: relative and absolute positioning. Relative
positioning can provide rough location estimate, the absolute
one can compensate the errors introduced
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