1. DEVELOPMENT OF THE KNOWLEDGE BASE FOR OPERATION AND MAINTENANCE THE EQUIPMENT WITH POLYMERIC INSULATION
Kemo Sokolija, Professor, Faculty of Electrical Engineering University of Sarajevo Bosnia & Herzegovina
Amra Omeragic, Head of Investment Planning, Elektroprenos B&H, Bosnia & Herzegovina

2. CONTENT
INTRODUCTION
MODIFICATION OF OUR “TECHNICAL SPECIFICATION FOR CPIs” BASED ON OURS AND THE OTHER’S EXPERIENCES
ELABORATION OF THE PRELIMINARY POLLUTION MAP
CONDITION MONITORING OF CPIs INSTALLED IN TEST STATIONS
DATA BASE FOR OBSERVATION OF CPI’s BEHAVIOUR
ESTIMATION OF LONG-TERM PERFORMANCES OF CPIs
PERSONAL EDUCATION
CONCLUSIONS

3. INTRODUCTION

4. IMMORTAL NEW APPROACH TO OLD APPROACH TO
INSULATORS USED FOR TLs AND SWITCHGEARS ARE NOT
IMMORTAL
EVEN THEN ARE PRODUCED USING '‘DEAD'' MATERIALS
BAD QUALITY
BAD CHOICE
EL.TENSIONS
INSULATORS WITH MATERIALS WHICH ARE NOT
CHEMICAL INERT – POLYMERS
CAN BE MORE SUBJECT TO AGEING
CLIMATIC IMPACT
AIR POLLUTION
INSULATORS ARE LIVE ELEMENTS OF EES 
HAVE OWN WORKING LIFETIME DEPENDING
FROM A FEW INFLUENCE FACTORS
NEW APPROACH TO
OLD APPROACH TO
CHOICE
(material, design, ...)
HANDLING
OBSERVATION
DURING
OPERATION
MAINTENANCE
BUYING (more cheaper)
INSTALL AND CAN
CONSIDER THAT THEY
WILL BE IN FUNCTION
'‘FOR EVER''

5. INSULATORS HAVE THEIR LIFE TIME
WHEN WE MAKE A CHOICE FOR A SPECIFIC APPLICATION
WE MUST TAKE INTO ACCOUNT
LONG LIFE CYCLE COSTS:
PURCHASE
MAINTENANCE
OUTAGE (NON-DELIVERED POWER)
HOWEVER, EVEN TODAY,
FOLLOWING ON OLD APPROACH WAKE,
THERE ARE PLANTY OF THEM SEEING
NOTHING MORE
THAN BARE PURCHASE COSTS !?
ENGINEERS MUST LONG FOR THE
OPTIMUM
TO INCLUDE
TOTAL OPERATING AMBIENT
REQUIRED PERFORMANCES
EXPECTED LONG LIFE CYCLES COSTS

6. WHY CP INSULATION ? ONE OF THE STARTING POINTS OF THE NEW APPROACH ARE
LONG LIFE CYCLE COSTS
EXPECTED LIFE TIME MUST BE PUT
INTO THE FOCUS
POLYMERIC INSULATION SUBJECT TO AGEING
UNCERTAINTY REGARDING EXPECTED LIFE TIME
THE MAIN LIMITING FACTOR IN EXTENSIVE
APPLICATION OF CPIs

7. IT IS A QUESTION OF PREJUDICE !!!
WHY ?
THE AGEING PROBLEM IS NOT DISTINCTIVE TRAIT
OF CPIs
CONVENTIONAL INSULATORS ARE ALSO SUBJECTED TO
AGEING
IF NOT PORCELAIN PARTS, METAL PARTS WILL DEFINITLY AGE
BEING “KILLED” ONE IS SUPOSED TO BE OUT OF FUNCTION
EARTHQUAKES, HURRICANES
IF ENVIRONMENTAL CONDITIONS CHANGE
DRAMATICALY THEY WILL BE
“RUN OVER BY TIME”

8. FROM THE OTHER SIDE LOWER PURCHASE COSTS LOWER WEIGHT
LOWER MAINTENANCE COSTS
TO USE CPIs IS SOMETIMES
MORE ECONOMICALY EFFICIENT
EVEN MORE THEIR REAL LIFE TIME IS
TWO, FIVE OR THEN TIMES
SHORTER THEN THAT OF THEIR CONVENTIONAL PATERNS

9. ALTHOUGH PORCELAIN STILL HOLDS THE MAJORITY
CONSUPTION IN HV INSULATORS,
CONSERVATIVE POWER INDUSTRY CHANGES
UNDER FOLLOWING ADVANTAGES OF CPIs:
LIGHT WEIGHT  MORE ECONOMIC DESIGN OF THE TOWERS OR ENABLING TO UPGRADE THE VOLTAGE OF EXISTING SYSTEM;
MUCH BETTER PERFORMANCE IN PRESENCE OF HEAVY POLLUTION, SPECIALLY SILICON RUBBER;
HIGHER MECHANICAL STRENGH TO WEIGHT RATIO  LONGER SPANS OF TOWERS;
CAN WITHSTAND SEVERE GUNSHOT DAMAGE WITHOUT IMMEDIATE FAILURE;
REDUCTION IN MAINTENANCE COSTS IN HEAVILY POLLUTED CONDITIONS;
REDUCTION IN THE PURCHASE PRICE, TRANSPORTATION AND INSTALLATION COSTS

10. THE MAJOR DISADVANTAGES CPIs ARE:
LIMITED LONG-TERM SERVICE EXPERIENCE
UNCERTAIN LIFETIME
DIFFICULTIES IN DEFECTING FAULTY INSULATORS AS WELL AS MONITORING IN SERVICE
BESIDES
MANUFACTURERS MARKED CPIs AS A PRODUCT
WHICH DID NOT NEEDED TO BE HANDLED CAREFULLY
CPIs WERE USED AS TOOLS BEEING DESTROYED
BY UNPROPER HANDLING

11. ALTHOUGH NATURAL WEATHERING HAS BEEN SHOWN
TO CAUSE CPIs AGEING, THERE IS A GREAT EXPERIENCE SHOWING:
THE LIFETIME OF CPIs HAS BEEN MORE
RELATED TO DESIGN WEAKNESSES AND
POUR QUALITY CONTROL DURING MANUFACTURING.
GREAT EFFORTS HAVE BEEN MADE
IN ORDER TO OBTAIN AN OPTIMAL MIX OF
GOOD PROPERTIES OF THE MATERIALS USED FOR CPIs
AND TO RESOLVE DIFFERENT DESIGN PROBLEMS
HOWEVER, WE MUST SAY:
NOT ALL PRODUCTS WE COULD FING TODAY ON THE
MARKET HAVE REACHED REQUIRED
QUALITY LEVEL EVEN THEY HAVE PASSED
REQUIRED STANDARD TESTS.

12. HOW TO MAKE DIFFERENCE BETWEEN GOOD AND A BAD PRODUCT ?
IF ONE WISH TO LEARN SWIMING HE/SHE MUST
GO INTO THE WATER !!!
THE ONLY SURE METHOD OF DISTINGUISHING
GOOD FROM BAD IS TO ACCES THEIR
BEHAVIORING IN REAL SERVICE CONDITIONS.
THAT WAS THE IDEA WHICH OUR UTILITY
(TODAY “ELEKTROPRIJENOS BiH”),
IN COLABORATION WITH UNIVERSITY OF SARAJEVO,
ENDEAVOR TO REALISE DURING LAST YEARS.
WE DID NOT PROCEEDED IN A WAY:
AFTER BEING INSTALL CPIs ARE LEFT TO THEIR DESTINATION
HOPEING THEY WILL BEHAVE A GOOD BEHAVIOUR IN SERVICE
OUR AIM WAS AND REMAIND THE SAME:
TAKE CARE OF INSTALLED CPIs
AND TAKING INTO ACCOUNT COLLECTED
KNOWLEDGE
IMPROVE OUR BEHAVIOUR IN THIS TECHNOLOGY

13. THE STUDY WORK PRESENTED HERE IS RESULT
OF OUR NEED TO SINTHETISE
OUR’S AND THE EXPERIENCES OF OTHER UTILITIES
IN ORDER TO FORM A BASE FOR THE
NEW KNOWLEDGE DEVELOPMENT
..... AND TO TRACE THE WAYS LEADING TOWARDS THE DEFINED TARGET
THE RESULTS OF THIS STUDY WORK ARE:
SINTHESIS OF PREVIOUS EXPERIENCES
PRELIMINARY POLLUTION MAP OF THE REGION
ANALYSIS OF THE RESULTS OF PREVIOUS MONITORING OF CPIs
THE PROPOSAL OF THE ORGANISATION OF DATA BASE ON CPIs BEHAVIOUR IN SERVICE
SPECIFICATION OF THE PROCEDURES FOR CPIS MONITORING
PROGRAM OF STAFF TRAINING

14. WHAT WAS THE AIMS OF THIS STUDY WORK?
TO DEFINE LONG-TERM PROGRAM WHICH WILL ENABLE THAT
JP ELEKTROPRIVREDA BiH
DEVELOP THE KNOWLEDGE BASE NEEDED FOR A NEW APPROACH THAT
 CHOICE (materials, design, production process)
 HANDLING in all phases before putting into operation
 OBSERVATION DURING EXPLOITATION
OF EQUIPMENT WITH POLYMERIC INSULATION BE ESTABLISHED ON
K N O W L E D G E

15. “TECHNICAL SPECIFICATION FOR COMPOSITE INSULATORS” BASED ON OURS AND
MODIFICATION OF OUR
“TECHNICAL SPECIFICATION
FOR COMPOSITE INSULATORS”
BASED ON OURS AND
THE OTHER’S EXPERIENCES

16.  On the base of worldwide experiences and studying of papers regarding one of the most important failure mechanism on CPI – brittle fracture– it is made possible to us that suggest following modifications in document ''Technical specification for composite insulators'':
(a) Explicite define that only CPIs with silicone rubber housing can be installed in the network.
(b) Explicite define that minimal thickness of rubber on the sheat has to be 3,0 mm.
(c) Beside formulation «it is prefered insulator with ECR core», explicite define that CPIs with ECR core can be installed in the network only.
(d) Exclude possibility of insulator choice with underribes on sheds.
(e) Exclude following «it is prefered insulator design where the metal fittings are not covered by housing material».
(f) Regarding moulding line parallel to insulator axis, stay on decision that is prefered design where the one does not exist. But, it does not mean that the insulators, which had moulding line parallel to insulator axis and producer was removed it in finish phase, are «handicaped». Because of that formulation of this point should be: «Insulator designs on which does not exist noticeable tracks of moulding line parallel to insulator axis are prefered.».

17. PRELIMINARY POLLUTION
ELABORATION OF THE
PRELIMINARY POLLUTION
MAP

18. Environment conditions
Table 3.1. gives the categories of input data and their parameters to be
considered resolving the problem of insulators choice
Table 3.1. Categories of input data and parameters
System requirements
Environment conditions
Insulator parameters
Application
Level and type of pollution
Type
Withstand voltages
Fog, dew, rain…
Material
Reliability, availability, maintenance
Wind
Profile
Costs
Temperature, humidity
Leakage distance
Installing position, distances,…
Heigh above sea level
Diameter
Vandalism
Earthquakes
Flashover distance
Thunderstorms

19. The Fig gives three possible approachs used for choice of insulators for specific application on specific site, on the base of three categories of input data.
 Since, insulators performances are determined by the means of complex dynamic interaction between environment conditions and insulators parameters, approach A should be used whenever possible; that can not be correctly done using existing laboratory tests
– Approach B.
ENVIRONMENT CONDITIONS
SYSTEM’S REQUIREMENTS
INSULATOR PARAMETERS
EXISTING EXPERIENCE IN EXPLOITATION AND/OR RESULTS OF NEW INVESTIGATIONS IN REAL EXPLOITATION CONDITIONS
ESTABLISHMENT OF POLLUTION LEVEL
RESULTS OF EXISTING AND/OR NEW INVESTIGATIONS IN LABORATORY’S CONDITIONS
 Approach C makes possible these interactions to be taken into account using empirically determined corection factors.
Although it is simply and cheap, this approach has restrictions which could have negative impact on system requirements: reliability, availability, maintenance.
MSCD
CORRECTION FACTORS
CHOICE AND DIMENSIONING
LEGEND:
approach A
approach B
approach C
MSCD – minimal specific creepage distance
Fig Three approachs to the choice and the dimensioning

20. We could not make the proper choice of insulators for our lines and substations because we have not had a document unambiguously prescribing to which IEC zone (pollution level) allocate location of interest.
Our engineers used the approach based on its subjective judgement and imprecisely defined pollution levels in IEC documents.
So we decided to establish a preliminary pollution map.

21. 3.1. Procedure used for the preparation of the preliminary
pollution map
Into the topographic map of the theritory we inserted all our lines and substations, as well as the all existing pollution sources.
Using the definitions of the pollution levels according IEC documents, we assigned the corresponding pollution levels and adequate minimal creepage distance for all the facilities of the company.
Special attention was dedicated to our specific climate conditions (fog, drizzle, rain); impact of the great cities is specially treated.
The topographic configuration of the ground is also taken into consideration, as well as the impact of the main roads and wind directions.
The proper care is also taken regarding the future capital projects to be realised (highway, industry).

22. Before we have established the preliminary pollution map our utility usualy prescribed MCD of 20 mm/kV, sometimes also 16 mm/kV in its tenders.
The results obtained analising pollution sources and other relevant issues during the preparation of the preliminary pollution map showed that in some substations 110 kV we must applied 31 mm/kV, as well as at many parts of our power lines; the same we have found regarding the existing substations and power lines where we need 25 mm/kV.
To establish the real state it is necessary to prepare a “real pollution map” on the base of measuring of ESDD and NSDD. The list of the 18 locations where we need to install measuring equipment is also the result of our considerations during the preparation of the preliminary map.

23. OF CPIs INSTALLED IN TEST STATIONS
4. CONDITION MONITORING
OF CPIs INSTALLED IN TEST STATIONS

24. 4.1. Visual inspection
 Today, this technique is the most applicable. Technicians being in charge of the visual inspection have to possess a great experience regarding design, materials and behaviour of CPIs, and be well familiar with diferent types of deteriorations, damages and faults which could be happened on this type of insulators.
 Tipical signs of deterioration (acceptable ageing) of CPIs are:
– appearance of chalking on insulator surface;
– change of insulator surface color;
– appearance of microcrack on insulator surface;
– appearance of corrosion on metal fittings;
– light surface erosion of sheds or sheat of insulator;
– small peeling between some components;
– small splitting of material on sheds or sheat of insulator.

25.  As the result of progressiv ageing and/or environment impact, or wrong handling with CPIs, damages, which have a negative impact on performances and life time of insulators, can be appear:
– direct exposure of FGR to environment conditions;
– branching off different insulator parts which could cause important decreasing of creepage distance or thickness of housing on sheat;
– surface erosion which caused important material removing on insulator sheat;
– branching off of sealing from the metal fittings;
– destroying of metal fittings caused by electric arc over insulator surface;
– punctures of sheds or sheat of insulator;
– cutting/cracks of housing which cause important reduction of creepage distance or thickness of the housing on sheat;
– tracking – forming of conductive paths on insulator surface;
– damages caused by animals.

26. Insulator type (producer)
4.2 Results of visual inspections in JP Elektroprivreda BiH
 In order to systematicly monitor behaviour of different type of insulators (design, material, producer) which are installed in transmission network, according to CIS Program (Composite Insulator Status Program), addopted by STRI, the three test stations are formed where the insulators of different producers are installed – Table 4.1.
Table 4.1. CPIs installed on three test stations
Test station (TS)
Insulator type (producer)
Housing material
Pollution level
(IEC 60815)
Year of installation
Kakanj – TS 1
E1, SE1, S2, S3, S5, S6
E1 – EPDM*)
SE1 – SIL ALLOY
S1 – S6 – SIR
III
E1, SE1, S2 – 1998.
S3 – S6 – 2002.
Hadzici – TS 2
E1, SE1, S2, S3, S5
– '' – II
S3, S4, S5 – 2000.
Pratace – TS 3
E1, SE1, S6 I
E1, SE1, S6 – 1998.
(*) EPDM – etilen propilen dien monomer
SE1 – silicone alloy
SIR – silicone rubber

27. The main data cocerning those insulators are given in the Table 4.2.
Table 4.2. The main data of the insulators installed in the test stations
Insulators given in Table 4.1. E1
SE1 S2
Housing material
EPDM
Silicone alloy
Silicone rubber
Date of installation
November 1998.
Position
horizontal
Max. System voltage (kV)
123
Nominal system voltage (kV)
110
Corona rings NO
Arcing horns
Flashover distance (mm)
879
930
887
Creepage distance (mm)
2700
2320
2717
Specific creepage distance (mm/kV)
21,95
18,86
22,09
Alternating sheds
YES
Number of sheds 16 15 24 – 19
Diameter of sheds (mm)
105 90 94
129
Diameter of sheat (mm) 26 25 20
Distance between sheds (mm) 55 39 40

28.  The complete review of the results of our observations of different types of CPIs which are installed in the test stations in the period 1999–2009 is not presented here because of its extensiveness.The results have been sent to STRI (in the framework of CIS Program). It is important to note that the same tipes of the insulators are installed (type E1 and SE1 in huge number) in transmission network of BiH.
 According to the results of observation it is concluded that there is not any insulator on test station which has had changes that could be characterised as a damage. Also, there is not any insulator which sustained a failure.
 Regarding the hydrophobicity of insulator surface, it was obviously confirmed the fact that only insulators based on sillicone rubber were keeping their hydrophobicity even after long time exposure to atmospheric impacts. Insulators with EPDM housing, during the time have lost this characteristic (Fig. 4.1.(a)) and has not been able to recovery it, as it was the case for silicone insulators -Fig.4.1.(c).

29. (a)
(b)
(c)
Fig Hydrophobicity of insulators surface after four years of operation (test station Hadzici):
(a) insulator E1;
(b) insulator SE1;
(c) insulator S2

30.  However, it could be interesting to discuss the observations of the insulators with the housing made using so cold silicone alloy.
It is very reasonable question why they in their formulations use silicione at all when those insulators immediately (after one year of operation-Fig 4.1. (b)) loose their very modest starting hydrophobicity.
 These observations can not, of course, refer at once to conclusion that insulators with silicone alloy are more inferior product, because neither the hidrophobicity is the only one important factor of housing material, nor the material is the only one stipulate factor which determine performances of CPIs.
 However,existence or non-existence of the hydrophobicity itself as a first defense line has definitely one very important reflection on the process of housing deterioration caused by surface discharges.

31. (b) color changing on insulator E1
In that sense, behaviour of insulator type E1, specially SE1 is very indicative. As it is shown on picture 4.2. and 4.3., after four years of operation in real environment conditions, those insulators have a serious changes on housing. However, those changes are still signs of acceptable ageing.
On such behaviour of insulators type E1 and type SE1, their design has an important impact. Since that test stations are located on areas which belong to the III pollution level (Kakanj), and II pollution level (Hadzici), it can be concluded that creepage distances of insulators 18,86 mm/kV (insulator SE1) and 21,95 mm/kV (insulator E1) are not adequate. Insulator SE1 is not corectly dimensioned for both locations, and insulator E1 for location Kakanj.
(a)
(b)
Fig Appearance of deterioration on insulators after four years of operation (Kakanj (a) and Hadzici (b))
(a) color changing on insulator SE1;
(b) color changing on insulator E1

32. a) changes of surface on insulator SE1;
(b)
Fig Deterioration on insulators after four years of exploitation:
a) changes of surface on insulator SE1;
b) changes of surface on insulator E1

33. 4.3 Application of special equipment for visual inspection
 There is a logical question: “What is the activity of discharges on the surface of a insulator which could be considered as allowed?”
 The answer is: “No sort of discharges which are in contact with the insulator housing or with sealing between metal parts and housing.”
 It is aside the question to replace immediately or not the insulator in the case of unacceptable discharges registrated. This question is not jet answered!
 Until such correlation does not exist IR – thermography could be considered as a complementary technique for visual inspection of CPIs.
 So we use this technique extensively.

34.  Since the human eye, as well as standard night vision cameras, are not sensitive on the part of spectrum where the main part energy of unacceptable discharges is located ( nm) and since the glass used in standard lenses do not transmit this part of the spectrum, we have not been able to detect those partial discharges visually until few years ago when special cameras equipped with quartz’s lenses were developed.
 These instruments can be very efficient for detection of discharges in dry conditions, when any visual corona discharges should not be on insulator’s surface. Drawback of night vision technique is the fact that discharges which we want to detect on this way – discharges on insulator surface caused by leakage current – have a specific and sporadic nature; they do not happen only during the night.
 Thanks to techological progress, after only a few years, from the situation when we could not see anything what is happening on insulator surface, today we are in position that can see everything during the day light. The special instruments, which it make possible, are developed and have world wide application today.
 Following the experiencies of other utilities we will be very ready to use this inspection technique very soon.

35. 5. DATA BASE FOR OBSERVATION OF
CPI’s BEHAVIOUR

36. General survey of the data base
 Data base Izolatori (Fig.5.1.) represents a program package developed whith the purpose of monitoring, registration and strage of all information regarding the changes noticed during the CPIs inspection on the lines and substations of Elektroprivreda BiH.
 Data base includs:
the characterisctics of all types of CPIs installed;
the time and the places of CPIs instalation;
information regarding conditions and behaviour of CPIs during the inpections;
information regarding regisrated damages/faults .
Fig Starting “window” of application

37.  The application is realised as related data base in ACCESS 2000 (Access 9) for WINDOWS 98/2000/XP, what mean that it can be installed and used on PCs where the WINDOWS 98/2000/XP and MS Access 2000/2003 (XP) are installed.
 In technical appearance, the system is outlined as back end – front end data base. Term back end – front end mean that program has two files at least. In one file (back end) there are only tables with data, till in the other file (front end) there are other objects for work and control of data base, as forms, reports, moduls in program language Visual Basic
 System can be implemented as:
- centralized or
- distributed.

38. 6. ESTIMATION OF LONG – TERM
PERFORMANCES
OF CPIs

39.  When the CPIs are new, they have extraordinary electrical characteristics. Observations made on CPIs after their long term operation under working conditions show that, depending of chosen housing material and specific design, CPIs can be deteriored or damaged.
 So the information regarding CPIs ageing are very important for electric utilities in order to keep required system relaibility.
 Those informations can be obtained using visual inspections and other diagnostic procedures in operation, as well as conducting laboratory tests on insulators removed from lines.
 The laboratory tests should be chosen in the way that they can describe basic insulators’ characteristics (electrical and mechanical).

40. The Table 6.1. showes testing procedures steps, which are necessary strictly follow to ensure a reprodicibility and repeatibility of examinations and to make possible comparation of basic insulators characteristics. On that way the results of surface characteristics measurements can be compared with results of laboratory testings of electrical characteristics and with results of visual inspections.
Table 6.1. Steps of testing procedures
Test No.
Test type
Standard 1.
Visual inspection 2.
2.1.
2.2.
2.3.
2.4.
2.5.
2.6.
Surface insulator’s characteristics
Hydrophobicity classification
Zinc galvanization on fittings
Pollution level (ESDD and NSDD)
Surface changes on polymer
Hardness of polymer housing material
Roughness of insulator surface
STRI Guide 92/1
IEC –1
IEC 60507
IR spectroscopy
ISO 868
ISO 4287 3.
3.1.
3.2.
3.3.
Electrical characteristics of insulator
Atmospheric withstand voltage test - dry
Industrial withstand voltage test 50 Hz - wet
Voltage test of corona beginning
IEC 60060–1 4.
4.1.
4.2.
Internal insulator integrity
Test of housing material peeling
Test of sealing for interface housing/fitting
CT–AR
IEC 61109 5.
5.1.
5.2.
Mechanical characteristics of insulators
Routine test and verification of SML
Test of extreme durability on strain

41. 7. PERSONAL EDUCATION

42. Our utility has organised the program of education of the human resources in charge of selection, inspection, comissioning, stocking and installing of CPIs.
For that purpose we have prepared a special handbook.
The program is being realised using different forms: courses, workshops and practical
training.
 The following aspects are treated in he framework of the education program:
selection of design and material;
comissioning in the factory, stock, transport and handling, installation;
visual inspection: identification of detorations, damages and failures;
causes of detorations and damages;
using of special instruments and methods for CPIs monitoring and diagnostics.

43. 8. CONCLUSIONS

44. CONCLUSIONS
 After almost four decades of research, development and continuous improvements in production of CPIs, it is clearly that this product expirienced its full ripeness.
 Design, materials and technology of production reached the levels which could be able to ensure a product of high quality.
 At the same time, polymer housing has almost comletely changed porcelain housing for MV surge arresters, and it is more and more used in production of other equipment.
 Basic shortages in application of CPIs are connected to insufficient experiences of their long term performances. These factors are consequence of weaking their electrical, probably also mechanical performances during the time.
 JP Elektroprivreda BiH has made decision to take such approach to CPIs which means to take care about installed CPIs, and to improve its own relation to this technology on the base of acquired experiences.