• Home
  • Courses
  • Machines
    • Transformer
    • AC Motors
      • Induction Motor
      • Synchronous Motor
    • DC Motor
    • DC Generator
  • Power System
    • Circuit Breaker
    • Switchgear
    • Substation
    • Control System
    • Measurement
  • Electronics
  • Blog
  • Contact
    • Contact Us
    • Privacy Policy
Have any question?
[email protected]
Login
StudyElectrical.Com
  • Home
  • Courses
  • Machines
    • Transformer
    • AC Motors
      • Induction Motor
      • Synchronous Motor
    • DC Motor
    • DC Generator
  • Power System
    • Circuit Breaker
    • Switchgear
    • Substation
    • Control System
    • Measurement
  • Electronics
  • Blog
  • Contact
    • Contact Us
    • Privacy Policy

    Power System

    Condition Monitoring for Transformers

    • Categories Power System, Transformer
    condition-monitoring-transformer

    Condition monitoring for transformers is the process of monitoring a parameter of conditions in transformer (moisture, temperature, etc.), in order to identify a significant change which is indicative of a developing fault.

    Power transformers are critical and costly assets in the electric power system beginning with the grid, transmission, and down to the plant. They are one of the most important electric apparatus for providing reliable energy flow. 

    As an asset class, transformers constitute one of the largest investments in a utility’s system or in an industrial complex. For this reason, transformer condition assessment and management is a high priority.

    Each entity is unique and the investment levels in asset condition and assessment management vary according to the risk level and investment return models.  

    The transformers are stratified according to the criticality of individual transformers and in this approach, the most critical transformers receive the highest investment of condition assessment and management tools and less critical and non-critical transformers receives the decreased level of asset allocations.

    The performance expectation of a transformer is:

    • Transfer of voltage level
    • Supply of required loads and
    • Accommodating voltages fluctuations to a specified range 

    Need for Condition Monitoring

    • Expensive capital equipment
    • Not easy to repair or replace
    • Advanced computer-aided design practices.
    • Transformers operation.
    • Condition Monitoring imperative.
    • A corrective/preventive action can be initiated

    Table of Contents

    • Types of Condition Monitoring
      • Working Condition Monitoring of Transformer
      • Frequency of Inspection and Maintenance
      • Typical Condition Monitoring Schedule of Transformer
      • Related Articles

    Types of Condition Monitoring

    The condition monitoring of transformer may be classified as:

    1. Working condition monitoring
    2. Emergency condition monitoring

    The first is to watch all the parameters and take corrective actions to keep them within specified limits, whereas the second is to bring out the equipment from the working system by sharp monitoring of the type of emergency occurs.

    Working Condition Monitoring of Transformer

    The working conditions of transformers in the substation are classified as “ATTENDED” but those in distribution are classified as “UNATTENDED”. Hence, condition monitoring differs and classified as follows: 

    • Continuous monitoring (hourly monitoring) for transformers in the substation
    • Random monitoring in case of distribution transformers

    The objective of transformer maintenance is to safeguard against breakdowns by detecting potential causes and eliminating them. Therefore, periodic transformer maintenance will ensure many years of trouble-free operation. 

    Transformer maintenance schedules should determine according to the critical or noncritical nature of the transformer and the load that is connected to it.

    A transformer that has been operating satisfactorily for many years may, because of neglection, suddenly fail without warning or any outward sign of distress thereby causing expensive repairs or replacement and loss of production.

    The term maintenance as applied to transformers consists of:

    1. keeping all peripheral parts clean and protected from dust, dirt, and corrosion
    2. testing the winding insulation, core, insulating and cooling liquid to check its suitability to onward use
    3. inspecting and testing the protective and indicating devices for its healthiness
    4. inspecting the transformer internally for any abnormalities
    5. inspecting the auxiliary equipment such as fan, coolers, lightning arrestors and grounds, etc. for soundness

    Although a transformer with its associated equipment does not have as many moving parts as most of electrical pieces of equipment, the same rules still apply.

    These basic rules are:

    1. current-carrying components must operate in a moisture-free insulating liquid or area
    2. the installation must be kept clean from dirt, rust or corrosion
    3. all moving parts must be kept well-lubricated
    4. all enclosures containing insulating and cooling liquids as well as weatherproof enclosures that protect the equipment from the weather must be kept tight 

    Frequency of Inspection and Maintenance

    Frequency on Inspection of a transformer depends upon:

    • Size
    • Type
    • Existing practice
    • Prevailing atmospheric conditions

    Frequency of inspection and maintenance greatly depend upon size and type of the transformer and also on the prevailing atmospheric condition at site and by existing practice and experiences.

    Normally the large power transformers supplying critical load should receive more frequent inspection and maintenance rather than small transformers delivering lighting loads or less critical circuits. 

    For a particular transformer, a maintenance schedule can be fixed in consultation with supplier. Once a schedule has been established it should be closely followed and various events shall be recorded.

    A general guideline of transformer maintenance is laid down and shall be modified to suit the actual equipment under use. Before starting any maintenance work safety regulations enforced must be strictly observed.

    Typical Condition Monitoring Schedule of Transformer

    The typical condition monitoring schedule of a transformer is given below.

    SI.
    No.
    Inspection Frequency
    Items to be Inspected
    Inspection Notes
    Action Required if Inspection shows Unsatisfactory Conditions
     
    1
     
    Hourly
     
    1) Ambient Temp.
    2) Winding Temp.
    3) Oil temperature.
     
    4) Load(amperes)
    5) Voltage
     
    6) Free delivery of water in case of water-cooled transformer
     
    7) Check for full flow indication by oil flow indicator
     
    Check that temperature rise is reasonable
     








    Check against rated figures
     



    Check for oil traces in the water at outlet
     
     
    Ensure that a sufficient quantity of oil flow
     
    Shut down the transformer and investigate if either is persistently higher than normal
     
     
     
     
    Isolate heat exchanger and put the stand by in the circuit. Rectify leak in the faulty heat exchanger
     
    2
     
    Daily
     
    1) Oil level in transformer
     
     
    2) Oil level in bushings
     
     
    3) Leakage of water into the cooler
     
    4) Relief vent diaphragm
     
    5) Dehydrating breather
     
     
     
    6) Oil level in OLTC conservator
     
     
    7) Pressure relief diaphragm of OLTC DS chamber
     
     
    Check against transformer oil temperature
         
                     –
     
     
    Check that air passages are free.
     
    Check the colour of the active agent
     
    Low/Increasing/Overflowing
     
     
     
    Check for damage
     
    If low, top up with dry oil, examine transformer for leaks
     
    If low bring it to correct oil level
     
    Replace if cracked or broken
     
    Replace if cracked or broken
     
    If silica gel is pink, change by spare charge. The old charges may be reactivated for reuse.
     
    Replenish oil if low. If increasing  or overflowing check for oil leakage from the main tank to OLTC DS chamber
     
    Replace by new one
     
    3
     
    Quarterly
     
    1 ) Bushing
     
     
     
    2) Oil in the transformer
     
     
     
    3) Cooler fan bearings, motors, and operating mechanism
     
     
     
     
    4) OLTC
     
     
    5) Indoor transformers
     
    Examine for cracks and dirt deposits
     
    Check for dielectric strength and water content
     
     
    Lubricate bearings. Check gearbox.
    Examine contacts.
    Check manual control and interlocks
     
     
    Check oil in OLTC driving mechanisms
     
    Check ventilation
     
     
    Clean or replace
     
     
    Take suitable action to restore the quality of oil
     
     
    Replace burnt or worn contacts or other parts
     
     
     
     
     
    Filter or replace
     
    4
     
    Half Yearly
     
    Oil cooler
     
     
    Test for pressure
     
     
    5
     
    Yearly (or earlier if, the transformer can be conveniently be taken out for checking)
     
    1)Oil in the transformer
     
     
    2)Oil filled bushings
     
     
    3)Gasket joints
     
     
    4)Cable boxes
     
     
     
     
    5)Surge diverter and gaps
     
     
    6) Relays, alarms, their circuits, etc.
     
     
     
    7)Earth resistance
     
     
    8)Winding
     
    Check for acidity and sludge. DGA
     
     
    Check for tan delta and Capacitance
     
     
    Check for sealing arrangements for filling holes. Examine compound for cracks
     
    Examine for cracks and dirt deposits
     
     
     
     
     
     
    Examine relay and alarm contacts, their operation, fuses etc. Check relay accuracy, etc.
     
     
     
     
     
    Tan δ and Capacitance

    Related Articles

    • Differences between Power Transformer and Distribution Transformer
      Power Transformer and Distribution Transformer

      The power transformer and distribution transformer are an important part of an electrical power distribution…

    • Construction of High Voltage Current Transformer
      Basic Types of Current Transformers

      Current Transformers (CT’s) are instrument transformers that are used to supply a reduced value of…

    • dc motor voltage and power equations
      Voltage and Power Equations of DC Motor | Condition of Maximum Power

      In this post, we will look at the voltage and power equation of a dc motor and…

    • Open Delta Connection in Transformer
      Open Delta (V-V) Connection of Transformers

      Open Delta Connection is a method of transformer connection used to transform three-phase power using…

    • Effects of Voltage and Frequency Variation on Transformers
      Effects of Voltage and Frequency Variation on Transformers

      The effects of voltage and frequency variation on the transformer is discussed in this article.…

    • core-type-transformer
      Core Type and Shell Type Transformers

      Depending on the type of construction used, the transformers are classified into two categories. Core type…

    • Share:
    author avatar
    Electrical Engineer

    Previous post

    Circuit Breakers - Objective Questions - Part 2
    June 9, 2014

    Next post

    Transformer Oil - Tests and Purification Methods
    June 10, 2014

    You may also like

    Transformer testing at factory
    Percentage Reactance in Power System (Transformer, Generator or Reactor)
    16 January, 2023
    transformer-winding
    Transformer Windings: Types and Design
    22 November, 2022
    Load Curve and Load Duration Curve
    Load Duration Curve in Power Station
    29 September, 2022

      5 Comments

    1. Sajid Ali
      December 11, 2019
      Reply

      I request more information about the condition monitoring tests on transformers, specifically Recovery voltage measurement. how to perform the test and what is the pass criteria?

      Thanks

      • Tesla Edison
        admin
        December 18, 2019
        Reply

        We will add it soon. Thank you

        • vicky
          February 17, 2023
          Reply

          welcome

    2. Millie Hue
      September 21, 2022
      Reply

      Thanks for helping me understand that the most important electric apparatus to provide reliable energy flow are the power transformers. With that in mind, a community or city must be using the best option or equipment for their company or area to give the best services to the people living in the vicinity. Also, I think picking the best quality option will ensure safety for anyone working near the unit to maintain or monitor it.

    Leave A Reply Cancel reply

    Your email address will not be published. Required fields are marked *

    Search Here

    From Blog

    Effects of Voltage and Frequency Variation on Transformers
    Effects of Voltage and Frequency Variation on Transformers
    12Aug2014
    Types of analog instruments
    Three Types of Analog Instruments
    28Aug2017
    multimeter
    Digital Multimeter: Working and Application
    08Jul2022
    electrical-Interview-Questions
    Objective Questions on Single Phase Motors | Part 3
    10Dec2013

    Categories

    • Alternator
    • Arduino
    • Basic Electrical
    • Battery
    • Books
    • Cables
    • Capacitor
    • Career
    • Circuit Breaker
    • Control System
    • DC Generator
    • DC Generator MCQ
    • DC Generator Solved Problems
    • DC Motor
    • DC Motor MCQ
    • Drives
    • Electric Vehicles
    • Electrical Circuits
    • Electrical Machines
    • Electrical Relays
    • Electrical Safety
    • Electronics
    • Embedded System
    • Exams
    • Generation
    • Guest Post
    • HVDC
    • Instrumentation
    • Interview Questions
    • Locomotives
    • MCQ
    • Measurement
    • Microcontroller
    • Objective Questions
    • PCB
    • PLC
    • Power System
    • Problems and Solution
    • Projects
    • Resistor
    • Signals and Systems
    • Single Phase Motors
    • Substation
    • Switchgear
    • Synchronous Motor
    • Three Phase Induction Motor
    • Transformer
    • Transmission Line
    • Uncategorized

    Copyright © 2021 Study Electrical, Inc.

    © StudyElectrical.Com 2021

    Login with your site account

    Lost your password?