Francis V. Mapile, P.E.E.
SUBSTATION MAINTENANCE
1. INTRODUCTION PHILIPPINE DISTRIBUTION CODE (PDC) CHAPTER 7. DISTRIBUTION OPERATIONS
Article
7.5. Distribution Maintenance Program
requires
the Distribution Utilities (DU) to prepare Distribution Maintenance Program based on forecasted Demand, User’s provisional Maintenance Program, and requests for maintenance schedule: 3-year Maintenance Program Annual Maintenance Program Monthly Maintenance Program
SERVICE LIFE
Electrical Equipment – designed for certain economic service life
Equipment Life – dependent on operating environment, maintenance program, quality of the original manufacture and installation
Beyond Service Life Period – they are not expected to render their services according to its expectations with desired efficiency
GENERAL CAUSES OF EQUIPMENT FAILURE MUCH EARLIER THAN EXPECTED ECONOMIC LIFE SPAN? Poor quality of raw material Workmanship and manufacturing techniques Frequent electrical, mechanical, and thermal stresses during the operation
FINANCIAL CONSTRAINTS
Replacement of failed power equipment either before or after their economic life
WHAT AN ELECTRICAL ENGINEER IS EXPECTED TO DO?
Explore new approaches/techniques Monitoring Diagnosis Life
Assessment and Condition Evaluation Possibility of extending the life existing assets (i.e., circuit breakers, transformers, etc.)
Minimize service life cost Ensure reliability of power supply at a minimal cost
WHAT IS THE MAIN GOAL?
To reach a COST EFFETIVE SOLUTION using available resources
ASSET MANAGEMENT MECHANISM
ASSET MANAGEMENT MECHANISM OPERATE EFFICIENTLY High Performance
•SAIFI, SAIDI •Power Quality •Power Availability •Reduced loss, etc.
REASONABLE RETURN Low Cost
•Investment •O&M •Stocking, etc.
ASSET MANAGEMENT Balancing cost, risk, and performance in the context of asset full life cycle
MAINTENANCE MANAGEMENT Assessment of the internal condition of the equipment while in service before catastrophic failure can take place Types of Maintenance
Breakdown
Maintenance Time or Calendar Based Maintenance Condition Based Maintenance Reliability Centered Maintenance
MAINTENANCE WORK CLASSIFICATION
Planned Maintenance Preventive
Maintenance Conditioned Based Maintenance Statutory Maintenance
Unplanned Maintenance Routine
and Breakdown Maintenance Incident Maintenance
PLANNED MAINTENANCE
Preventive Maintenance The
action performed to prevent failure by providing systematic inspection and monitoring to detect and prevent incipient deterioration or failure and includes testing to confirm correct operation.
Conditioned Based Maintenance Corrective
maintenance work performed as a result of significant deterioration or failure, to restore an asset to its required condition standard. The work maybe programmed as a result of condition assessment or as random additions to the program based on priority
PLANNED MAINTENANCE
Statutory Maintenance Both
preventive service maintenance and condition based maintenance may contain elements of statutory maintenance which is defined as actions performed to provide the minimum level of maintenance to meet legal and other mandatory requirements contained under ERC/DMC regulations and Code of Practice
UNPLANNED MAINTENANCE
Routine and Breakdown Maintenance Unplanned
and reactive maintenance actions performed to restore an asset to operational condition, as a result of an unforeseen failure.
Incident Maintenance Unplanned
maintenance actions to restore an asset to an operational or safe condition as a result of property damage resulting from storms, fire, forced entry, vandal damage.
MAINTENANCE MANAGEMENT
CALENDAR BASED MAINTENANCE (Traditional)
CONDITION BASED MAINTENANCE •MONITOR •DIAGNOSE •ASSESS
OPTIMIZE THE MAINTENANCE EFFORT
Development of various state-of-the art on-and –off line non-intrusive test
Ensuring maximum availability and reliability of the system
WHY “CONDITION BASED” ? Too many assets “ageing” Age by itself is not a good indicator of future performance Able to fully justify decisions in terms of proven engineering principles Able to make sound asset management by understanding asset condition
CONDITION BASED MAINTENANCE Define asset current condition and use this to estimate future condition and performance A sound engineering basis for evaluating risks and benefits of potential investments strategies
Need Consequences Condition
and future performances
DEFINE ASSET CONDITION (HEALTH INDEX) HI or the condition index link the performance to the Probability of Failure (HI vs PoF) Calibrate HI/PoF against historic fault rates Priority ranking of work Relatively simple but not a substitute for engineering expertise and judgement instead an additional aid to engineers
HEALTH INDEX MECHANISM
A means to define proximity to EOL by combining varied and relatively complex information as a SINGLE number Define
significant condition criteria Coded numerically Apply weights Rank/calibrate
HEALTH INDEX RANKING CONDITION 10 BAD
REMAINING LIFE (Years)
At EOL (less than 5 yrs)
POOR
5-10 yrs
FAIR
10-20 yrs
GOOD
More than 20 yrs 0
PROBABILITY of FAILURE
High
Medium
Low
Very Low
DIAGNOSTIC TECHNIQUES FOR CONDITION MONITORING OF TRANSFORMER
TRANSFORMER DESIGN AND CONSTRUCTION
TRANSFORMER DESIGN AND CONSTRUCTION TYPES OF TRANSFORMER CORE
TYPE
OIL-IMMERSED TYPE DRY TYPE
SHELL
TYPE
CORE TYPE
SHELL TYPE
TYPICAL WINDING CONNECTIONS DELTA–DELTA STAR–DELTA STAR–STAR DELTA–DELTA ZIG-ZAG TERTIARY WINDINGS DOUBLE SECONDARY SCOTT (T-T) CONNECTION AUTO-TRANSFORMER
COIL WINDINGS
Three fundamental requirements Electrical Mechanical Thermal
ANSI C.57/IEC 60076
TRANSFORMER CORE
Silicone steel Grain Oriented Electrical Steel Amorphous metal
INSULATION
Interlayer of high quality epoxy coated kraft paper Corrugated pressboards are placed within the coil for cooling Thickness in accordance with the voltage.
TRANSFORMER TANK
Hermetically sealed Corrugated fins Cable box
TAP CHANGERS
On-Load Tap Changer
Off-Circuit Tap Changer
AUXILIARIES
Pressure Relief Device Gas and Oil Relays (Buchholz) Temp Gauge Fan Controls Conservator Tank Radiators etc
DIAGNOSTIC TECHNIQUES FOR CONDITION MONITORING OF TRANSFORMER
TRANSFORMER INSULATING OIL AND PAPER DIAGNOSTICS
OIL QUALITY TEST
PHYSICAL PROPERTIES
CHEMICAL PROPERTIES
ELECTRICAL PROPERTIES
OIL QUALITY
PHYSICAL PROPERTIES
Visual appearance Colour Flash Point Viscosity Density Pour Point IFT Particle Count
CHEMICAL PROPERTIES
Moisture content Acidity Corrosive Sulphur Oxidation stability Sludge Sediment
ELECTRICAL PROPERTIES
DBV PF
INSULATION IN THE TRANSFORMER
OIL
Provides overall insulation to the transformer Act as coolant Provides a means to monitor insulation condition and operation of the transformer
PAPER
Provides insulation to conductor in the windings Stress relief
TRANSFORMER STRESSES
Primary Stress
Electrical Mechanical Thermal
Secondary Stress
Ageing rate due to primary stress Test done
Continuous Cyclic Intermittent
DETERIORATION OF THE INSULATION CONDITION
REVERSIBLE CONDITION
Oil insulation condition can be reversed through the filtration Can reduced the effect of aging Can prolong serviceability of the oil insulation
IRREVERSIBLE CONDITION
Paper insulation degradation Transformer life is determined by the life of its paper insulation
INSULATION DEGRADATION
3-Most common degradation factor of insulation
Degradation by-products
Thermal Presence of Oxygen Presence of Water and Acid
CO CO2 H2O Organic Acids 5H2F (Furaldehyde)
OIL SAMPLING
Follow procedure ASTM D923 & D3613 (IEC 60475 & IEC 60567)
Factors in taking oil samples
Sample container Sampling technique Weather condition Sample storage and transport
IEEE C.57.106 LIMITS-OIL QUALITY TEST Colour IFT Neut. No. Dielectric Strength
Water Content
0.5 > 25MN/m for <69KV <0.2 mg KOH/gm >20kv for <69kv for 1mm gap <27ppm for <69kv @ 50deg C
DISSOLVED-GAS-IN-OIL ANALYSIS IEEE LIMIT Hydrogen (H2) Carbon Monoxide (CO) Methane (CH4) Carbon Dioxide (CO2) Ethylene (C2H4) Ethane (C2HO) Acetylene (C2H2)
100ppm 350 120 250 50 65 35
DIAGNOSTIC TECHNIQUES FOR CONDITION MONITORING OF TRANSFORMER
TRANSFORMER BASIC ON-SITE & OFFLINE DIAGNOSTIC TESTING
BASIC ELECTRICAL TEST
Insulation Resistance Test Polarization
Index (P.I.) – to detect moisture content
Winding Resistance Test To
detect open or short circuit or poor electrical connections
Turn Ratio Test To
detect shorted turns, open circuit
CATEGORY OF ON-SITE TESTS
DESTRUCTIVE
“Go/No Go” Tests
NON-DESTRUCTIVE
ON-SITE TESTS Pre-energization After maintenance After network alteration
Diagnostics Condition Monitoring Tests
POLARIZATION INDEX
INTERPRETATION
P.I. = R10/R1=I1/I10 Note: Voltage Constant
Insulation
60/30 sec Ratio
10/1 min Ratio
Condition
Dielectric
P.I.
Where: R10 - megohm insulation resistance @10 mins R1 - megohm insulation resistance @ 1 min I1 - insulation current @ 1 min I10 - insulation current @ 10 min
Absorption Ratio
Dangerous
less than 1
less than 1
Poor
less than 1.1
less than 1.5
Questionable
1.1 to 1.25
1.5 to 2
Fair
1.25 to 1.4
2 to 3
Good
1.4 to 1.6
3 to 4
Excellent
Above 1.4
Above 4
C0NDITON BASED MAINTENANCE (CBM)
Power Transformer Switchgears MV Cable Feeders LV Cable Feeders LV Equipment LV OH Line Feeders MV OH Line Feeders DC Battery Banks Etc...
Master List of all eqpt Prioritize Group accdng to voltage rating, type, manufacturer, age, etc Technical manuals, manufacturer Maintenance history Assess size of staff Identify task that can be outsourced
THANK YOU !
Engr. Francis V. Mapile, P.E.E. Member, Board of Electrical Engineering Professional Regulation Commission Member, Technical Committee Wholesale Electricity Spot Market Philippine Electricity Market Corp.
