Reliability-Centered Maintenance of

Distribution System Equipment

prof. Ing. Stanislav Rusek, CSc.doc. Ing. Radomír Go o, Ph.D.doc. Ing. Vladimír Král, Ph.D.andothers

Introduction

Relation reliability vs. maintenance

1

2

3

Impact of maintenance downtimes on reliability

Intensity of breakdowns P (yr -1)

Mean time of breakdowns P (h)

Intensity of maintenance U (yr -1)

Mean time of maintenance U (h)

4

Model of ageing

I II III time

periodof early

breakdownsperiod of standard operation

period of operation

beyondservice life

5

Distribution function of period unto breakdown

t . . . . breakdown time (hrs)t0 . . . . guaranteed period without breakdowns [hrs]

. . . . characteristics of wear and tear< 1 indicates period of early breakdowns= 1 indicates incidental breakdowns> 1 indicates wear and tear breakdowns

. . . . characteristic service life (hrs)

0

1tt

etF

6

Goal: to maintain reliability with minimum costs

by carrying out coordinated maintenance, i.e.when such maintenance is carried out on severalelements which are in series from the point ofview of reliability (e.g. separate devices at theoutlet from a switching station), it is then carriedout usually in a single maintenance downtimewhat means that no addition of intensity ofmaintenance occurs.

by implementing the principle of reliability-centered maintenance.

7

History of maintenance

Until the 50-ties of 20th centurySimple equipment usually amply dimensionedNot very high level of mechanisationCorrective maintenance“Operation until a breakdown”

time t

Technical condition

S (%)

100 %

t1 t2 t3 t4

t1, t2, ... const., S1 = S2 = ... = 0

8

History of maintenanceIn the 50-ties through 70-ties of 20th

centuryPeriod after the World War TwoDevelopment of industry, more complicated equipmentFirst concept of Preventive (periodical) maintenance

t1 = t2 =... = const., S1,S2,... const.

time t

Technical condition

S (%)

100 %

t1 t2 t3 t4

9

History of maintenance

In the 80-ties of 20th centuryDevelopment of measuring / metering / diagnostic methodsSubordination of maintenance to actual needs of equipment –“maintenance according to the condition”

t1, t2, ... const., S1 = S2 = ... = const.

time t

Technical condition

S (%)

100 %

t1 t2 t3 t4

mainte-nance

10

History of maintenanceIn the 90-ties of 20th century

Effort for the highest possible efficiency of maintenanceUsually taking into account so called “equipment importance”Oncoming of reliability-centered maintenance

t1, t2, ... const., S1,S2,... const.

time t

Technical condition

S (%)

100 %

t1 t2 t3 t4

RCM

Reliability-Centered Maintenance

2

11

12

Reliability Centered Maintenance [RCM]

The goal of reliability-centered maintenance is tocreate such a maintenance strategy, so that theoverall operating costs are minimised whilepreserving required rates of reliability, safety andenvironment-friendly attitude in the equipment tobe operated.

13

RCM Procedure

1. Determine all the equipment which is subject to maintenance andwhich therefore takes part in the RCM process.

2. Determine the function of such equipment.

3. Define resulting model of equipment ageing.

4. Determine the importance of such equipment.

5. Identify equipment breakdowns and related consequences

6. Set up the equations of overall operating costs related to suchequipment and find the most convenient form of maintenance.

14

Breakdown consequencesSafety consequences – personal injury, equipment destruction, firebreaking out, endangering of public

Environmental consequences – pollution of atmosphere or watercourses, soil contamination, e.g. through an oil leakage during atransformer breakdown, radioactivity leakage during a nuclear powerstation breakdown

Operating consequences – direct economic losses due to any reductionof power generation / distribution and due to repair costs

Non-operating consequences – related to direct repair costs

Hidden consequences – due to breakdowns which are not evident on thefirst sight and can cause multiple breakdowns, such as malfunctions orsafety equipment failures

15

General chart of RCM procedure

Logika

RCM

Program

údržby

za ízení

emíst ní

Zm na konstrukce nebo

ení

Preventivní údržba

Prediktivní údržba

Opravná údržba

Vým na

Analýza p vodních in

Stanovení rizik

Výpadky zákazník

intenzita a trvání

Náklady na výpadekzákazníka

Aktuální výkon komponentu a

trendy

Lidskézdroje

Koordinace se zákaznickým

asovým plánem

Regulace:Vládní

Bezpe nostníŽivotního prost edí

Výpadky zákazníkvodní p inyAnalýzy

Za ízení:PohotovostSpolehlivost

Údržba:Historie, praxe,Dokumentace

Efektivnost

Údržbové náklady

Zautomatizovaný systém správyúdržby

Regulation: Governmental

Safety Environment

Customer outages Original reasons

Analyses

Equipment: Readiness Reliability

Maintenance: History, experience

Documentation Efficiency

Maintenance costs

Logic of RCM

Risk determination

Relocation

Design or metering

modification

Preventive maintenance

Predictive maintenance

Repairing

maintenance

Replacement

Analysis of original

reasons

Coordination with customer time

scheduleHuman

resources

Equipment

maintenance

program

Computerized system of

maintenance administration

Customer outages: intensity and

duration

Customer outage costs

Actual performance of

resp. component and trends

16

Criteria for selection of elements for RCM

1. Criteria which reflect the importance of individualelements for respective distribution systemoperator.

2. Criteria of this group should reflect“completeness” and sufficient quantity of inputdata for the implementation of RCM system.

3. “Third group” of criteria should take into accountthe returnability, i.e. the fact that the existingsystem of maintenance of certain elements willnot be possibly modified.

17

Equipment importanceBy importance, it is understood the significance of respective equipment from the pointof view of impact of its outage on the system operation – such importance dependsdirectlyon the costs of such outage.

The importance of equipment therefore does not depend on the reliability of equipmentitself but on its position in the system.

TR 22/0,4 kV TR 22/0,4 kV

Importance

lower higher

[Big consumers] -industrial plantsSmall consumers -

households

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Possible approaches to the application of RCM

Optimisation of maintenance cycle Determination of order of elements for maintenance

Number of specific type elements is high. Number of elements of specific type is low.

Generally, respective specific type element is less important.

Respective specific type element is highly important.

It is impossible to estimate the cost of a specific type element.

It is necessary to set a limit from which it would be reasonable to start a maintenance process (not only economic parameters should be then taken into consideration).

When analysing an event (failure, outage), it is impossible to find out a specific element [responsible for such event]

When analysing an event (failure, outage), it is possible to find out a specific element…

Monitoring of equipment (also online) is recommendable, with the aim to determine the condition and importance of respective equipment elements.

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Determination of elements for the application of RCM

Optimization of the maintenance cycleDistribution Transformer Substation (DTS) HV/LVOverhead HV line (except of circuit breaker elements)

Determination of optimum order of elements formaintenance

transformers 110 kV/HVoutlet fields 110 kVlines 110 kVcircuit breaker elements in overhead HV lines

Optimisation of maintenance cycle

Costs

3

20

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Cost equation

Equation of overall operation costs should becomposed for each equipment system and itslocal minimum should be found

NU . . .Equipment maintenance costs (CZK . yr -1)

NO . . . Repair costs (CZK . yr -1)

NV . . .Outage costs (CZK . yr -1)

ND . . .Other costs (CZK . yr -1)

)rok(K -1DVOUC NNNNN CZK . yr -1

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Example of cost equation

VOUC NNNN

UUU NN . 1 PKOO NN . 1

U

P

P e - 1 . PK

PNV N . P . T . PKVN

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Application of the methodology to DTS

Graf závislosti náklad - 2002 (DTS s údržbovými prostoji)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

0 0,05 0,1 0,15 0,2 0,25

Intenzita údržby

Nák

lady

[K]

Celk. nákl.

Nákl.údrž.

Nákl. výp.

Nákl. na údržb. prostoj

Nákl. opr.

Optimum maintenance intensity in this case is 0.105 yr -1.

Cos

ts [C

ZK]

Maintenance intensity

Diagram of cost dependence - 2002

(DTS with maintenance downtimes)

Total costsMaintenance costs

Calculation costs

Maintenance downtime costs

Repair costs

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Division into groups according to their importance (or weight)

Methodology according to the structure of customers

Methodology according to the credits of DTSs

It is possible to divide DTSs only into three groups

Number of groups can be determined “arbitrarily”

There is no need to specify any boundaries between groups

Specification of boundary credit values is required

DTS with a Big Consumer (or at least Small Commercial Consumer) has always a higher priority, no matter how many other customers (Small Household Consumers) are in a group

The importance of any DTS depends on the number of customers and their weight (Big Consumer : Small Commercial Consumer : Small Household Consumer = 50:5:1)

The type of DTS is not taken into consideration

It is taken into consideration whether respective DTS is a “kiosk” type DTS or not

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Division of DTSs according to their credits

Credit expresses the importance [of a DTS]

NMOO Number of Small Household Consumers connected to a DTS

NMOP Number of Small Commercial Consumers connected to a DTS

NVO Number of Big Consumers connected to a DTS

kMOO coefficient of Small Household Consumers; value = 1

kMOP coefficient of Small Commercial Consumers; value = 5

kVO coefficient of Big Consumers; value = 50

Ttype parameter of a DTS; value = 2 for kiosk & building types, 1 for other types

P loadon a DTS (kW)

kP weight coefficient of the load; for the time being: value = 0

PVOVOMOPMOPMOOMOO kPTkNkNkNKredit )(

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Graphical division of DTSs into groups

1989

4966

1333

0

765

184

3368

43257

71607

34278

349788

408507

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Po et DTS Sou et VO Sou et MOP Sou et MOO

A

B

C

Number of DTSs Sum of BigCons Sum of SmCommCons Sum of SmHousCons

Metering Type

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Optimisation of maintenance cycle for DTS

Maintenance intensity

Cos

ts [C

ZK]

Determination of optimum order of elements for

maintenanceCondition vs. importance

4

28

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Basic methodology principle

Determine the condition and importance of each element

Equipment importance

Equi

pmen

t rea

dine

ss

(Tec

hnic

al c

ondi

tion)

Equipment No.1 Equipment No.3

Equipment No.2

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Basic methodology principle

Maintenance plan setup

Tech

nica

l con

ditio

n

Equipment importance

Equipment No.1

Equipment No.2

Equipment No.3

Equipment No.4

Put out of operation

immediatelyMaintenance required as

soon as possible

Include into Plan of Maintenance for the next year

Inspection and diagnostics

required

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Application to high-voltage/power circuit breakers [110 kV]

Identify each element, its technical condition and importanceIdentification dataPower station

Field / outletPutting in operation [year]

Type of circuit breaker

Quenching mediumCircuit breaker serial No.

Produced in [year]

Drive typeDrive model

Drive serial No.Drive produced in [year]

Importance of circuit breakerPlace of installation

Type of line

Possibility to back up

Importance of power consumption area

Power transmitted per year

Technical condition of circuit breakerDate of last intervention

Tightness of quenching chamber

Date of last major overhaul of the compressor (drive)

Hours of compressor operation after major overhaul

Number of circuit breaking cycles after major overhaul

Date of last diagnostic tests

Evaluation of last diagnostic tests

Date of [last] evaluation of technical condition

Climatic conditions

Number of circuit breaking cycles [actual]

Hours of compressor operation [actual]

Condition of metal parts (corrosion, coating)

Condition of earthing parts

Condition of insulators

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Application to transformers 110 kV / HV

IdentificationTransformer node point

AbbreviationDesignationYear of productionSerial No.Number of operating hours in the period under considerationSn [MVA]cos

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Technical condition criteriaClimatic conditionsTime from last ordinary [minor] maintenance or repairType of machineAge of machineAge of tapping switchAge of transformer bushingVessel condition (corrosion, coating)LeakageCondition of control box and its electrical equipmentCablingNumber of switch-over eventsAverage hourly load (value not available)Evaluation of diagnostic tests

Application to transformers 110 kV / HV

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Criteria of importanceTransmitted power per yearPossibility of backup (transformer, HV line)Importance of connected HV lines

Application to transformers 110 kV / HV

RCM Software

Database exploitation

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Block diagram

Sou adniceza ízení

Optimální údržbový cyklus

ProgramRCMKritéria

ležitost

TIS FIS

Regulace

Criteria

Regulation

Importance

RCM Program

Equipment coordinates

Optimum maintenance cycle

37

DTS

Maintenance intensity 1/yr

Cos

ts [C

ZK]

Optimum value

Maintenance Repairs Outage Maintenance downtime Sanctions Total

Costs of

38

Overhead line 22 kV

Maintenance intensity 1/yr

Cos

ts [C

ZK]

Costs of

Maintenance Repairs Outage Maintenance downtime Sanctions Total

Optimum value

39

Circuit breakers 110 kV ELF

Equipment importance (%)

Tech

nica

l con

ditio

n (%

)

Overview

40

Transformers 110 kV/HVTe

chni

cal c

ondi

tion

(%)

Equipment importance (%)

Overview

Summary and conclusion

Current situation

6

41

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Summary and conclusionPeriodical application of RCM for planning of routine maintenance of distribution transformer stations (DTS)Application of RCM according to the situation for planning of general maintenance of 110 kV circuit breakersCompleted application of RCM to 110 kV/HV transformersCompleted application of RCM to 110 kV lines

Currently, verification [of the method] is in progress based on data provided by EZ Distribuce.

Thank you for your attention …

Any questions?

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Radomír Go oVŠB – Technical University OstravaDepartment of Power Engineeringradomir.gono@vsb.czPhone (+420) 597 325 913