ABSTRACT
The present day scenario of growing demand for electrical power claims a
lot of work t be done in the field of reliability of the power systems.diagnosis and
clearing of a fault in power system generally calls for an expert who is specialized in
that particular domain.the scenario continues even if the same faults occur again. The
use of a system that simulates the expert’s reasoning is obviously a helpful tool for
such situations.
It is in this direction that the paper makes an attempt to develop an expert
system for fault diagonisis to improve power system realiability.the system is capable of
dealing with faults in general power system equipment. It is developed with the data
obtained from experts in different domains and is capable of handling faults on D.C
motors, transformers , induction motors and synchronous motors etc.
INTRODUCTION
Expert System
“an expert system is a computer program that represents and reason s with
knowledge of a specialized subject with a view to solving problems directly or giving
advice”.
Advantages of Expert System
Expert system works by storing expertise of a domain expert. Then a user can
interact with the system and let it solve a problem using the same logic generally used
by the expert. Usually the expert systems is faster and more accurate than a human ,
and does not get tired or bored. A very strong benefit of Expert Systems is being able to
widely distribute the knowledge of a single expert , or being able to accumulate in one
place the knowledge of several widely represented experts.
Some situations when ES should be considered
Only one expert is available , but is needed in multiple locations.
Expertise is divided among several experts.
Expertise is required is a harsh environment.
An expert is retiring.
Expert systems are especially helpful when a task is performed only occasionally and
the expert has to relearn the procedure each time it is performed . one can use expert
systems are especially helpful when a task is performed only occasionally and the expert
has to relearn the procedure each time it is performed. One can use Expert systems to
standardize operations . another use for expert system is as job aid for experts. This
will allow them to perform more accurately, more consistently, and faster , freeing up
time for the expert to be more creative in performing the task. This is especially helpful
when dealing with tedious, repetitious tsks. Thus an expert system is needed to
completely fulfill a function that normally requires a human expertise or it may play the
role of an assistant to a human decision maker. An expert system can be distinguished
from a more conventional application program in that:
It simulates human reasoning about a problem domain, rather than
simulate the domain it self.
It performs reasoning over representations of human knowledge, in addition
to doing numerical calculations or data retrieval.
It solves problems by heuristic or approximate methods, which unlike
algorithmic solutions are not guaranteed to succeed.
Traditional program is termed as procedure oriented programming where as for an
expert system term it as object – oriented programming
INFERENCE ENGINE:
It provides the system control.it applies the expert domain knowledge to what
is known about the present situation to determine new information about the
domain.this process will lead to the solution of the problem.the inference engine also
enables the expert system’s interface to data sources and to the user.the method use to
reproduce part of an expert’s reasoning process is called chaining.there are two
methods presently available,namely,forward chaining and backward chaining.
Input interference : this allows the expertise to be entered into the knowledge base by
the expert or a knowledge engineer.
User interface: this allows a user to consult the expert system.
Working memory: the working memory contains the information that the system has
received about a problem at hand. In addition, any information the expert system
derives about the problem is also stored in working memory.
APPLICATION TO FAULT DIAGNOSIS:
The expert systems to be used for fault diagnosis calls for a very deep
knowledge base.the knowledge base is formed by the knowledge engineer by collecting
knowledge form the expert’s and representing it using the expert system shell.the expert
in the particular domain should have extreme expertise in his field and preferably
should be an ‘operation engineer’.
The knowledge base designed for this application of fault diagnosis deals
with the symptoms, causes and remedies of various faults frequently occurring in power
system equipment. The data was collected form the MES of Vishakapatnam section.
The expert system developed is very user friendly. It starts with a menu
displaying the equipment to be selected, followed by options of probable symptoms and
the system ends giving a remedy or solution for the occurred fault.
VP EXPERT SYSTEM
Paper back software VP Expert is primarily a rule base expert system
building tool but it offers several additional features and costs less than $100. its
dominant control mechanism is backward chaining; how ever the program can do
limited forward chaining through the use of a special command. VP Expert offers a
standard IF-THEN rule structure and can handle situation –involving uncertainity very
effectively. More ever,VP Expert also supports limited induction feature that can
generate rule for data. But unlike true induction tools, even when this features is used in
VP Expert the end result is that the program still performs its reasoning from a
standard IF-THEN set.
It has an effective lay out, incorporates plenty of graphics and is well
written. VP Expert takes a straight forward “EDITOR” approach to knowledge entry.
The rules can be typed in directly and even when induction is used the editor is still the
primary means for finishing or refining the expert system. VP Expert also supports
other methods for visualization of the reasoning process. TRACE feature when onvoked
will save the search patron that led to particular result during a consultation. It handles
certainity or “confidence factors” in variety of ways. It also offers a high level graphic
feature for tracing system logic. A typical module of the expert system developed for the
present cause using VP Expert is presented here. This is for induction motor.
MOTOR FAILS TO START DUE TO?
BURNT FUSE, WORN BEARINGS, OVER LOADING,
OPEN PHASE, SHT COIL, LOOS BARS, WRONG CONN:
When clicked on for BURNT FUSE the user interface gives the remedy as follows:
EXAMINE THE FUSES AND REPLACE IF NECESSARY
When clicked WORN BEARINGS the user interface gives the remedy as follows.
CHECK THE BEARINGS. REPLACE THE BEARINGS.
SUPPLY SHOULD BE CHECKED.
The detailed knowledge base has been created for some of the power system equipment
and the package is found to work satisfactorily.
CONCLUSIONS:
If through knowledge is gathered in the domain of work, the expert system
is one of the best and most powerful tools in fault diagnosis and can be used by a person
who is new to the domain environment. the knowledge base is developed for a few
power system equipments using the expertise of a person completely familiar eith them.
The expert system will now be a useful tool to an operator / engineer who is unfamiliar
with the equipment. With the symptoms manually observed in the system, the person
can take the help of the expert system to diagnosis the fault and also have an idea about
the remedy.
This is an attempt towards fault diagnosis of power system equipment and can
be extended to other power system components like relays, circuit breakers, isolaters,
insulators etc to make it commercially viable. With the detailed statistics available over
past breakdowns and faults, the expert system can help in identifying the equipment
which is most vulnerable to faults. This analysis would help to move in the direction of
“total preventive maintanence” by enabling the decisions regarding the periodicity and
extent of maintance of various equipment.
