Hands-On Transformer Testing and Maintenance

Course Description

This Hands-On course will teach you how to prioritize your transformer maintenance strategy, stretch your maintenance budget and at the same time maximize the life and condition of your electrical transformer.

As an owner of transformers you are faced with the challenge of how to minimize downtime and maximize life expectancy of your valuable asset. With budget restraints, knowing how to prioritize your transformer testing and maintenance expenditures is crucial. This transformer testing and maintenance course will review what traditional and new maintenance testing procedures should be utilized by transformer owners. We will also look at the latest developments in transformer design, construction, testing, diagnostics, oil sampling techniques, interpretation of results and transformer asset planning.

Today's capital spending on new and replacement transformers is at its lowest level in decades. To make matters worse, the load on each transformer (or its utilization) continues to grow. Increased equipment utilization, deferred capital expenditures and reduced maintenance expenses are all challenges facing todays transformer owner.

Many electric utilities and large industrial, commercial and institutional owners of medium and large power transformers are beginning to develop their own "Life Cycle Transformer Management" programs.

Our transformer testing and maintenance course will deal with many of the technical and economic issues dealing with a) The Screening Process to prioritize the transformer fleet b) Transformer Condition Assessment of individual transformers, and c) Life Cycle Decisions retire, refurbish, replace, relocate.

Students will learn safe and proper maintenance and testing procedures on power transformers. The course covers transformers used in commercial and industrial power distribution systems, including oil and dry-type units. Larger power transformers used in utility applications are also covered.

Students Will Learn

1. Understand the basics of transformer asset management.
2. Understand transformer life cycle and maintenance planning
3. Learn sulphur in transformer oil solutions
4. Learn how to resolve moisture in transformer oil
5. Understand turns ratios and calculate terminal voltage and current.
6. Learn about proposed Federal and State transformer regulations
7. Understand transformer operation, aging and failure
8. Understand transformer standards
9. Understand transformer factory testing and quality assurance
10. Understand the electrical testing methods performed on transformers such as insulation resistance testing, excitation and power factor testing.
11. Understand transformer on-line monitoring techniques
12. Understand the various tests performed on insulating oil.

Target Audience

Anyone working with, supporting, maintaining, and testing Electrical Transformers.

Prerequisites

A Basic understanding of Electricity and Electrical Transformers and components.

Course Outline

Module I. Transformer Design and Construction
Students will be introduced to the different types of single- and three-phase transformer construction, various types of core material, windings layout, connection, tap changers, voltage classifications and transformer applications, with an emphasis on explaining recent innovations in transformer design.

Transformer Core

Transformer core
Core form and shell form
Core loss
Exciting current
Noise level
Structure

Transformer Windings

Winding conductors - ASTA
Load loss
Impedance and voltage drop
Winding insulation
Cooling structure
Short circuit withstand capability
Core and coil assembly

Transformer Insulation

Oil paper insulation system
Two functions of insulation fluid
Various insulation fluids
Factors affecting quality
Factors accelerating degradation
Paper and pressboard insulation
Two functions of solid insulation
Factors affecting quality
Factors accelerating aging
Aging cycle

Transformer Tank

Main tank
Main tank components
Seals, gaskets and valves, bushings

Oil Preservation Systems

Air cell systems
Breathing systems
Auto-recharging dehydrating breather
Oil cooling systems

Transformer Bushings

Voltage class
Current ratings
Top and bottom terminal connections
Mounting flange
Test and voltage taps
Air side dimensions
Oil side dimensions
CT pocket length
Oil reservoir
Many styles and types in use

Tap Changers

LTC
DETC (OCTC)
ULTC
Headboard links

Components and Accessories

Top oil temperature monitoring
Devices/Indicators
Winding temperature monitoring
Liquid level Gauges/Indicators
Pressure and vacuum Gauges/Indicators
Pressure relief device
Gas Detection Relays
Alarm and trip functions are equipped and preset

Module II. Transformer Operation and Appplication

Transformer Applications and Types

Dry type
Liquid filled
Industrial vs public distribution
Potential transformers (PTs)
Current transformers (CTs)
Control and power supply transformers
Auto transformers

Transformer Operation and Theory

Load vs no load
Transformer losses
Hysteresis losses
Eddy current losses
Copper losses
Stray losses
Relationship between primary and secondary values
Transformer polarity
Single phase transformer connections
Transformer impedance
Transformer ratings
Optimum transformer rating

Transformer Cooling

Transformer cooling techniques and devices

Three-Phase Theory/Transformer Types

Transformer configuration
Three phase transformer connections
Delta connection
Wye 'star' (Y) connection
Voltage and current in various combinations
Transformer terminal markings and identifications

Resistive Loads

Inductive loads
Capacitive loads

Three-Phase Ratio's

Parallel operation of 3 phase transformers
Phase angle shift
Phase rotation
Grounding transformers
Auto transformers
Regulators
Phase shifters
Three-phase ratios

Transformer De-Rating

Harmonics
K-factor

Transformer Failures

Misapplication
Vibration
High operating temperature
Lightning or line surges
Overloading
Care of control equipment
Lack of cleanliness
Care of idle or spare equipment
Improper lubrication
Careless or negligent operation

Module III. Transformer Field Diagnostic Testing and Maintenance Techniques

WINDING RESISTANCE

Testing techniques
Voltmeter – Ammeter method
Bridge technique
Micro ohmmeter

TRANSFORMER RATIO/POLARITY

Testing Techniques
Inductive kick (DC method) polarity
Alternative voltage (AC method) polarity
Turn ratio test set
Double voltage meters

EXCITATION CURRENT MEASUREMENT

Hysteresis
Eddy currents
Copper losses

SHORT CIRCUIT IMPEDANCE MEASUREMENT

Testing techniques
Voltmeter – Ammeter method

SWEEP FREQUENCY RESPONSE ANALYSIS

Testing techniques
Problems detected
Shifted winding/core
Deformed windings
Loose windings

INSULATION RESISTANCE

Testing techniques
Megger
Polarization index test (PI)
- Can detect the following problems
  Insulation dryness
  
  Insulation contamination
  
  Sensitive to temperature
INSULATION CAPACITANCE AND POWER FACTOR
- Testing techniques
- Capacitance bridge method – DF
- AC Dielectric loss method - PF
PARTIAL DISCHARGE MEASUREMENT
- Can detect the following problems
  Insulation defects
  
  Insulation contamination
  
  Air bubbles trapped in insulation
  
  Localized high electrical stress
  
  PD is the "cancer" of insulation system
  
  PD detector
  
  RIV
TRANSFORMER CORE TESTING
- Problems
- Insulation resistance
- More grounding points
- Megger
- Separate external core ground lead from 250 resistor
- Measure core
INSULATING OIL
- Sulphur in transformer oil solutions
- Resolving moisture in transformer oil
- Proposed federal PCB transformer regulations
- Transformer on-line oil monitoring techniques
- Various tests performed on insulating oil
- Properties and parameters of insulating
- Why oil sample?
- Dielectric breakdown
- Water content
- Power factor
- DGA "key" fault gasses
- Benchmarks
- Rating system
BUSHING VISUAL CHECK
- Oil Level
- Leaking
- Chipped porcelain
- Fractured flange
- Poor gaskets
- Peeled painting
- Terminal connection
- Corrosion
TAP CHANGERS
- DETC
- Contact resistance increase
- Loose contact pressure
- Misalignment
- Electrical and mechanical centers
- LTC
- Contact continuity
- Arcing switch and tap selector
- Drive mechanism operation
- Motor
- Timing
- Oil compartment
- Protection and control
TRANSFORMER TANK
- Visual check
- Oil leaking
- Poor gaskets
- Peeled painting
- Rust/corrosion
- Temperature hot spot
COMPONENTS AND ACCESSORIES
- Visual check and function test
- Cooling system – radiators, fans or pumps
- Gauges and indicators – oil level, pressure and temperature
- Pressure relief device
- Gas relay
- Air breather
- Inert air system
- Oil filters
INFRARED TEMPERATURE MEASUREMENT

Delivery Method

Instructor-Led with numerous Hands-On Labs and Exercises.

Equipment Requirements
(This apply's to our hands-on courses only)

BTS always provides equipment to have a very successful Hands-On course. BTS also encourages all attendees to bring their own equipment to the course. This will provide attendees the opportunity to incorporate their own gear into the labs and gain valuable training using their specific equipment.

Course Length

2 Days