IJET-V3I2P17

International Journal of Engineering and Techniques - Volume 3 Issue 2, March-April 2017
ISSN: 2395-1303 http://www.ijetjournal.org Page 97
Power System Reliability improvement by proper
application of Problem Solving Tool
K.V.Imayavaramban1
R.Karhikeyan2
1
PG Scholar , 2
Assistant Professor ,
Department of EEE, SCSVMV University, Enathur, Kancheepuram -631 561
Introduction
The Article titled “Power System
reliability improvement in industrial
power distribution system” aimed at
reducing Power Distribution System
Network and Equipments failure .
Electrical fault is the deviation of voltage
and current from normal values or states.
Under normal operating condition,
Power system equipment or lines carry
normal voltage and currents which
results in safe operation of the system.
but the when the fault occurs, it causes
excessively high current to flow which
causes damage to equipment and
devices. Fault detection and analysis is
necessary to select or design suitable
power system network equipments like
switch gears, protective relays, cables
etc. On the other hand usage of power
electronics devices , non linear loads etc
are increasing day by day for the need
of process capability improvement,
process automation and process
optimization .Increased usage of Power
Electronics devices is also degrading
the power quality which leads to the
failure of Power System equipments .
The Power supply is the main source for
operating the industry and hence any
interruption in the power system
equipments leads to unplanned
production stoppage, increased cost of
maintenance, Energy Loss , product
scrape, increased maintenance man hour
etc.
Hence a systematic approach and review
of failure analysis and Problem Solving
is required for implementing necessary
corrective action and to improve the
reliability of Power system equipments.
RESEARCH ARTICLE OPEN ACCESS
Abstract:
This Paper is aimed at analyzing the few important Power System equipment failures generally
occurring in the Industrial Power Distribution system. Many such general problems if not resolved it may
lead to huge production stoppage and unforeseen equipment damages. We can improve the reliability of
Power system by simply applying the problem solving tool for every case study and finding out the root cause
of the problem, validation of root cause and elimination by corrective measures. This problem solving
approach to be practiced by every day to improve the power system reliability. This paper will throw the light
and will be a guide for the Practicing Electrical Engineers to find out the solution for every problem which
they come across in their day to day maintenance activity.

Objective
The Objective of this Paper is to analyse
the various common failures generally
occurring in the industrial power
Distribution system network equipments
and providing necessary solution to
eliminate the root cause of the failure
and to improve the Power System
reliability in a typical industry. A few
general case study of problem with
power system equipment failure and
necessary corrective action carried out
to improve the power system reliability
has been discussed in this paper and the
following relevant guide lines and
relevant tools is also kept in
consideration and applied suitably while
carrying out improvement plan.
• Standard practices in the
Selection, Installation and
maintenance of Power
Distribution system equipments.
• Adhering to regulatory guidelines
• Adhering to fire and safety
standards
• Adhering to usage of PPE as per
risk category
• Practicing improvement
techniques like
FMEA,PDCA,KAIZEN,Problem
solving techniques like Why
Why Analysis etc
• Principles of Energy
Management System ,
Environment Management system
and quality management system
Power System Reliability
Improvement - Case Study#1
Conventional single phase power
distribution system
Fig.1 Single Phase Power Distribution System
The scheme in Fig.1 shows the
traditional way of Power distribution
scheme for Single phase equipments in
industry or in domestic application. In
this scheme when ever incoming neutral
connection is cut or disconnected due to
loose connection, Over voltages appear
across single phase equipments when
the load is unbalanced. Hence the
complete circuit elements and
equipments gets damaged. Neutral
disconnection /loose is general recurring
problem in the domestic service
connection and as well as in industry.
But if we fail to detect and isolate the
supply, there will be a severe damage to
the equipments
Hence when ever the incoming neutral
failures occur, equipments will get damage

due to the over voltage appearing across
the equipment when the load is not balanced
in the three phases.
Problem Statement: In the Three Phase to
Single Phase power Distribution board, All
the Single Phase Devices connected in the
distribution circuit failed during incoming
neutral failure.
Root Cause Analysis
Why did single phase equipment fails in
the Three phase to Single phase PDB
during Incoming Neutral link failure?
Ans: Because of Over voltage appeared in
the Single Phase equipments.
Why did over voltage appear in the Single
Phase equipment when the three Phase
voltage is within the limits?
Ans: Because of incoming neutral failure in
the three phases to Single Phase power
distribution board, Over voltage appears in
the circuit due to unbalanced loading.
Why can’t we prevent the Unbalanced
loading ?
Ans: We can only balance the connected
load in the circuit but the loading varies
depends upon utilization/operation.
Why can’t we prevent the Failure of
Incoming neutral continuity?
Ans: During Preventive maintenance, The
tightness is ensured, But man is with errors,
Hence the possibility neutral loose
connection could not be eliminated?
Why can’t we detect and isolate the
circuit when over voltage appears in the
Single Phase distribution circuit?
Ans : By installing suitable Power
frequency over voltage protection device
across the single phase sub incomer, We can
prevent the damages caused during
incoming failure
Voltage Triangles of Un balanced loading
system when neutral is cut
Fig.2 Voltage triangles of Unbalanced loading system when
neutral is disconnected
Root Cause validation
After installing Power frequency over
voltage protection device in Single Phase
Power Distribution Board, Equipment
damages eliminated due to over voltage
incase of incoming neutral failure
Power System Reliability Improvement -
Case Study-2
Existing System
In the Existing system, when there is LG
fault in the down stream, the near by breaker
did not clear the fault but instead the next
upstream breaker tripped. Hence unintended
power outage to other equipments instead of
the respective faulted zone.
LV Power Distribution Scheme

Fig.3 LV Power Distribution Scheme
In the LV distribution scheme shown in fig
3, all the three breakers are having
OL+SC+Earth fault protection. There is
clear discrimination with respect to
symmetrical short circuit but when there is
unsymmetrical fault like LG fault, The fault
was cleared by 1200 Amps ACB instead
nearest Up stream breaker like 100 A or
400A CB. The earth fault current setting is
20 Amps at 100 Amps CB, 80 amps at 400
A CB and 400 Amps at 1200 Amps ACB.
Under this condition when there is LG fault
below the 100 Amps MCCB, The fault was
cleared by super upstream CB. Hence there
is unintended power outage to other
equipments other than faulted equipments.
The actual fault current recorded during this
incident is 4.3 KA.
Problem Statement: Unintended power
outage to other equipments other than the
faulted equipments in the LV distribution
system when there is L-G fault.
Problem Solving approach:
Why did the power outage happen other
than the faulted equipment?
Ans: Because the LG fault current is higher
than the Ground fault setting of the all the
breaker from downstream to upstream
breaker. (Note: 1200 A is highest permitted
setting in the 3200 Amps ACB as per IEC
standard but the LG fault current is in the
order of several KA).
Why can’t we have intelligence in the
Breaker to establish the communication
to isolate the faulted Zone alone?
Ans: Yes, If the breaker is intelligent, we
can establish Zone Selective Interlock
through the communication system.
Root Cause validation
Zone Selective Interlock implemented in the
MV Distribution. After implementation of
Zone Selective Interlock, there is no power
outage to other than the faulted Zone.
Power System reliability
Improvement – Case Study-3
Introduction
In Industrial LV power distribution system
cable termination failures are very common
in nature and it is frequently occurring at
various pats of the plant. Though the
corrections are carried out the technician
level, it is important to analyse the route
cause and carry out the corrective and
preventive action to prevent recurrent of
such failures. Hence by implementing the
corrective action for cable termination
failure, the power system reliability will be
improved to a great extent. The image of
Breaker Not tripped

temperature rise at the faulty cable
termination and improved termination is
explained in this case study.
Thermal Image of faulty cable
termination
Fig.4 :Thermal Image of faulty cable
termination
In the above figure 5 , R Phase cable
termination is defective and it is not in
intact. Hence there is abnormal temperature
rise in the R Phase cable termination when
compare to other two phase. If we continue
to operate at this condition, R phase cable
socket will fail with in the short period of
time. This will lead to unintended equipment
stoppage. The correction required will
consume labor, materials, Some times if
there is extra length cable, we need to
prepare additional joint to extend the
connection. This additional joint is another
problem prone area. Hence the more no of
joints will have more termination issue.
Hence by applying proper corrective action
for such type of failure, will help to improve
the power system reliability.
Problem Statement:
Abnormal temperature rise in the end
termination Power cable which leads to
cable termination failure / fire and affects
the power system reliability
Y-Phase - 66 C (deg centigrade).
R-Phase - 105 C ( deg centigrade).
Problem Solving Approach
Why did the temperature at End
termination one phase is higher than the
other when each phase carries same
magnitude of current?
Ans : Because the temperature rise depends
up on ( I2
Rt ), Hence when I and t is same,
The Resistance should be varying
Why the resistance at One termination is
different from other ?
Ans: Because of the difference in the
effectiveness of crimping.
Why the effectiveness of crimping varies
from one termination to other
termination?
Ans : Because of the difference in quality
of Workmanship, cable socket surface, Area
of jointing contact preparation, Improper
contact during crimping leads to vary
jointing resistance.
Why can’t the jointing resistance be
checked immediately after crimping ?
Ans : Yes, the Jointing resistance can be
checked after crimping by conducting Mili
volt drop test and verify that the voltage is
drop is <than 10 milli volt across the
jointing to avoid abnormal temperature
Thermal Image after rectification cable
termination

Fig.5Thermal Image after rectification
cable termination
This fig 5 shows the thermal image after
rectification cable termination fault.
The temperate of all the three phases are at
equal temperature and no abnormality. If we
continue to operate at this condition , the
termination failures are remote and hence
the power system reliability will be
improved
Root Cause Validation : After
retermination , Milli volt drop test
conducted and it was < than 10 milli volt at
the jointing, After putting in to service
thermal imaging carried out after 6 hours of
operation. No abnormal temperature rise
was found and it is monitored periodically
during periodical condition monitoring .
Hence the corrective action and evaluation
carried out after corrective action is
effective. and the temperature is
Conclusion:
Based on the failure analysis, It is noted that
most of the failures are relating to human
error in the selection and installation and
maintenance of Power system equipments.
Solutions are available for all technical
problems. Hence by application of problem
solving tool for each and every problem, we
can eliminate the root cause of problem and
improve the Power system reliability day by
day and it is a continuous improvement
journey for all practicing engineers
References
1. IS: 1255-1983 Code practice for
installation and maintenance of
power cables upto 33 KV
2. Article on “Reliability of LT Joints
in distributions Network” by Shri
S.P.Joglekar, Ms.Shweta K
3. Article on “On Zone Selective
Interlock System “ by Shneider
Electric, France
4. Article on Over voltage protection
in LV Distribution System by Eaton,
Legrend
5. Article on “Zone Selective System in
LV Distribution system : by L&T

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