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International Journal of Engineering Science Invention
ISSN (Online): 2319 – 6734, ISSN (Print): 2319 – 6726
www.ijesi.org
Volume 1 Issue 1 ‖‖ December. 2012 ‖‖ PP.13-17
www.ijesi.org 13 | P a g e
Failure Events Analysis of Uninterruptible Power
Supply (UPS) In Nigeria
Mohammed Adamu Biraol1
, Musa Momoh2
, Ismaila Garba Saidu3
1
(Physics department, faculty of science, Usmanu Danfodio University Sokoto- Nigeria)
2
(Physics department, faculty of science, Usmanu Danfodio University Sokoto- Nigeria)
3
(Physics unit, Sokoto State polytechnic, Sokoto- Nigeria)
ABSTRACT: This paper discusses the failure events trend analysis of uninterruptible power supply (UPS)
system taking the Sokoto state experience as a case study. We identified and considered the manner and effects
of failure events using empirical method to evaluate the quantities meantime to repair (MTTR) and mean time to
detect (MTTD). The data obtained were analyzed using the method of weighted average to compute failure
events probabilities. The results of this research show that UPS systems in Sokoto state, failed largely as a
result of a significantly poor electrical supply, over utilization and excessive high temperature.
Keywords: Failure events, Maintainability, MTTR, MTTD, Weighted average
I. INTRODUCTION
Nigeria ostensibly since the early 1980s has accepted information technology (IT) as a veritable
resource in the country’s quest for development technologically, economically and socially. The level of the
development of electrical supply system of a nation is one of the factors which determine the socio-economic
development of any country [1]. Sokoto state is characterized by energy crises such as voltage fluctuation and
transient disturbances in the distribution network of the power supply so that a short term power supply system
like UPS becomes inevitable to meet the demand of the constant power demanding equipments like computer
system and peripherals which constitutes major component of IT. It is therefore obvious that every UPS will
eventually fail which consequently effects the computers and peripheral(s) [1, 2]. The distribution of end users
cuts across private establishments, government agencies, educational institutions, recreational centers and the
home. The pervasive use of the UPS system in the Nigeria has led to a number of issues, one of which motivated
the authors into this research work. Worthy to be mentioned among the issues are: indiscriminate importation of
UPS system into the country, after-sales support service availability, equipment quality assurance and
maintainability, to mention a few. Equipment maintainability is the central point in this paper
1.1 Problem Definition
According to [5], maintainability is a statistical expression of the quantity mean time to repair (MTTR)
that is required in viability analysis. Viability is a concept used in the architecture and engineering of digital
UPS measure of a system’s capability–performance and reliability. In practice and in theory, a system that
cannot fail is unachievable. So therefore, it is obvious that every UPS can and will eventual fail [1]. Hence, it
remains to consider the manner and effect of those failures and the cost of minimizing them. In this paper, we
identified the various manner failure occurred in UPS over five year period and the effects of those failures on
MTTR.
The justification of this study will be its application as an information system base to:
 Government regulatory bodies responsible for policy formulation and monitoring as it affects imported
good standardization such as standard organization of Nigeria (SON), customs and exercise department etc.
 Federal office of statistics and Federal Ministry of Trade and Industries.
 Universities and research institutions.
II. LOCATION OF STUDY
The empirical data used for analysis were gathered from the equipment maintenance centre Usmanu
Danfodio University Sokoto. In addition to the empirical data, interviews were also organized with selected UPS
servicemen in Sokoto metropolis.
2.1 Sample Used in the Study

Failure Events Analysis Of Uninterruptible Power Supply (Ups) In Nigeria
S/No MODEL YEAR OF
MANUFACTURE
(YM) YR
YEAR OF 1ST
FAILURE
(YFF) YR
MTTF=
(YM–YFF)
YR
DIAGNOSIS REMARKS
1 BK650MI 2005 2007 2 Bad o/p
Transfer
Repaired
2 BK650MI 2007 2009 2 Blown MOV Repaired
3 BK650MKI 2005 2006 1 Blown FET Repaired
4 BK650MI 2005 2006 1 Blown FET Repaired
17 BK650MI 2006 2009 3 Bad o/p
ransformer
Repaired
18 BK650MI 2005 2008 3 Bad battery Repaired
19 BK650MI 2005 2008 3 Not charging Repaired
21 BK650MI 2005 2006 1 Blown board Repaired
32 BK650MI 2007 2008 1 Blown Board Repaired
35 BK650MI 2006 2007 1 Bad o/p
transfer
Repaired
36 BK650MI 2005 2006 1 Bad Battery Repaired
42 BK650MI 2005 2007 2 Bad o/p
transform
Repaired
47 BK650MI 2008 2009 1 Blown board Repaired

Sample were drawn from various users ranging from individuals (staff and students), corporate
(faculties, departments and units). We also noted, from interviews conducted with users as preliminary step to
troubleshooting procedure that, large number of users deploy UPS as back-up for computer systems largely for
word processing and very minimal number for data-base management activities.
2.2 Types of Samples: The type of samples belongs to the circuitry of the BK650MI UPS. A faulty
UPS requires a high level manpower skill to diagnose its electronic circuitry and to effective repair it [2]. Failure
rate analysis of 60 BK650 BK650MI UPS is given in the table below
Sample were drawn from various users ranging from individuals (staff and students), corporate (faculties,
departments and unit). We also noted, from interviews conducted with users as preliminary step to
troubleshooting procedure that, large number of users deploy UPS as back-up for computer system largely for
word processing and very minimal number for data-base management activities.
2.2 Tools and Troubleshooting Method
In the process of troubleshooting faulty equipment, a viva session is always arranged between the users
and a serviceman. The importance of a viva session is:
 To establish the use to which the equipment being put.
 To picture the working conditions the equipment must have been subjected to and
 How and when the fault was noticed on the equipment.
Also, the main tool used for diagnosis is the multimeter (digital and analogue). The multimeter is used
to test electrical components, both passive and active, for short, open-circuited situations and leaky functions
[4]. Semi conductor components catalogue is also used to check out the characteristic of active components.
2.3 Mathematical Modeling
MTTR can be viewed as the measure of the expected time required to remove those events that have
been accepted to constitute a failure in a device. On the other hand, MTTR may not be easily evaluated as the
quantity mean time between failures (MTBF) which measures the expected time between conjunctions of events
that are accepted to constitute the failure [5]. However, the time required to repair a malfunctioning device
consists of the time to follow a sequence of many steps to a logical conclusion whose duration is uncertain.
Therefore, there are steps required to accomplish compound measure of MTTR.
 Detecting that the failure has occurred
 Isolating the malfunctioning element
 Removing the malfunctioning element
 Obtaining a replacement by either repair or form a stock of spare elements
 Inserting the working element
 Verifying that the replacement works.
There is an imaginary stopwatch required to measure MTTR. The stopwatch is started only at the point
of failure detection. But, the quantity Mean Time To Detect (MTTD) should be determined first before
determining the result of MTTR. We can sufficiently model the number of trials until a successful repair as a
geometrical random variable given the probability of successful repair [5, 6].
Moreso, the probability that a device is UP called the availability of the device. The availability of a device is
given by
Prob (UP) =
𝑀𝑇𝐵𝐹
𝑀𝑇𝐵𝐹+𝑀𝑇𝑇𝑅
----------------------(1)
While the probability that the device is down given by
56 BK650MI 2006 2007 1 Blown MOV Re[paired

Prob (down) = 1 – prob (UP) =
𝑀𝑇𝑇𝑅
𝑀𝑇𝐵𝐹+𝑀𝑇𝑇𝑅
-----------------------(2)
MTBF and MTTR should reflect the preventive maintenance policy put in place for the system. This is
recommended because a device is down during maintenance period as well [6]. To achieve a good
maintainability, a low MTTR value is desirable.
III. OBSERVATIONS
The period under review is five years (2005 – 2010). In the course of this investigation, we observed
causes of faults. These faults are mainly electrical in nature. These faults are more difficult to diagnose and
repair, so therefore contributing to large values of the MTTD and MTTR.
The following are the fundamental causes of electrical faults in UPS system from the user’s perspective:
1. Over-usage (OU): this is a situation whereby the user was found to have subjected the equipment to a
continuous working condition beyond the limit of the equipment under an unfavorable condition-high
temperature [1].
2. Under-usage (UU): a situation found to be common with beginners. The equipment was perhaps used
for a while, thereafter packaged and keep in store or long period under unfavorable weather condition such as
excessive humidity [1,2,3].
3. Old-age (OA): a situation where in the equipment fails to function as a result of aged electrical
components such as electrolytic capacitors with leaky di-electric, leaky diode function, weakened resistors and
partial contacts [4]
4. Poor-power supply (PPS): Power supply refers to the quality of electricity available to the users to
power their UPS. A poor state is synonymous to a situation of erratic and unstabilised electricity supply. The
following conditions of electricity supply have been classified as poor [1, 3]:
a. Brown-out: Brown-out is a condition of lower than normal power line voltage being supplied by
local utility or generating equipment. This condition may be short term (minutes to hours) or long term (½ day
or more). A power line voltage reduction of 8 – 12% is usually considered a brown-out.
b. voltage upsurge beyond 20%
c. power fluctuation
5. User-negligence (UN): User carelessness is another factor responsible for equipment failure. Newly
acquired UPS systems have been reported faulty as a result of poor usage or handling. Very often we have found
out the following:
A. Power supply mis-matching (110/220 volts).
B. exposure to unfavorable weather conditions such as excessive humidity, temperature, pressure
and dust.
C. Over current drainage
3.1 Maintainability Analysis
From empirical analysis carried out on equipment manufactured over the years (2005-2010). We have
been able to estimate MTTR values ranging from 1 hour to 2 hours which have assumed an MTBF value of
10,000 hours that is equivalent to one year of span usually specified for hardware original equipment
manufacturer [7].
The media value MTTR (2005-2010) =
1+2
2
From equation (2) above
PrDOWN (2005-2010) =
1.5
10000+1.5
Approx value = 1/10000
3.2 Data Analysis
We have adopted the method of weighted average in computing probability in this analysis. Arrival
rate of equipment and frequency of faults occurrence were obtained from the repair centre log book.

Table2: Fault analysis for 60 BK650MI UPS
S/NO PARTS NO. OF
OCCURENCE
 OF
OCCURENCE
1 Blown Metal Oxide varistor (MOV) 23 38.33
2 Blown FET (Field Effects Transistor) 18 30.00
3 Blown Board 4 6.67
4 Bad Output Transformer 3 5.00
5 Bad Battery 6 10.00
6 Charging Problem 6 10.00
TOTAL 60 100
The result shows that Blown MOV and Blown FET accounts for the major faults that are associated
with UPS in Sokoto state. Anti surge suppressor and stabilizer will serve as a measure against these problems.
IV. CONCLUSION AND RECOMMENDATIONS
For the system at hand, taken over five years, demonstrates and established the motivation for this
study. Our motivation being a significant noticeable inverse relationship between the quality of service of UPS
in terms of viability. Furthermore it is not overstatement that the same period under review, experienced a very
high demand for UPS to support the constant demand of power by IT equipment, while quality of service was
being jeopardized for cheap and huge quantity by importers. From the user’s perspective, users suffered huge
capital losses as a result of poor maintainability and availability of these UPS system.
The following steps are recommended for the viability and reliability of the UPS system in Nigeria
A .Provision of parallel configuration in the design so as to reduce the rate of failure of the components
in the system
B. The design of UPS system that will consider the environmental as well as stress factors in Nigeria
REFERENCES
[1]. Adamu, M.B, “Mathematical modeling for reliability assessment of Uninterruptible Power Supply (UPS) in Sokoto-Nigeria”
M.SC Thesis, Usmanu Danfodio University, Physics department, 2012.
[2]. Oluwatope O.A. (2006). “Failure Events Trends Analysis of Computer Systems in Nigeria” NSE Technical Transaction Vol. 41,
No. 2 April – June, 2006.
[3]. Akinsanmi. O. “Assessing the Reliability of UPS system for medical operations in zaria, kaduna state” the information manager.
Vol. 5, 2005. PP 1-11, Department of Library and Information Science. Ahmadu Bello University, Zaria.
[4]. Taylor P.F.U (1989) Reliability Assessment and Design of Micro Computers for Administrative Purposes in Developing
Countries PhD. Thesis. ABU Zaria
[5]. Alberto Leon-Garcia (1994). “Probability and Random Processes for Engineering”Addison-Wesley Edition Chapters 1, 2,3and 6.
[6]. Oyebisi T.O. (1999), “On reliability Maintenance Management of Electronic Equipment in the tropics”. Technical Elsevier
Science Ltd. October 1999.

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