New Version Available
This study guide is out of date, click here to see the latest release.
This study guide is out of date, click here to see the latest release.
- Inspection and maintenance - Identify type and record nameplate data. Inspect pumps, fans, auxiliary control components, connections, tank, nitrogen apparatus, gauges and levels, grounding, shipping braces, gaskets, bushings, insulators, barriers, and other accessible components.
- 3 Routine Inspections and Checks for Liquid Filled Transformers The following inspections should be made on a routine basis. The extent and frequency of maintenance should be based not only on the size or voltage level but also on the relative importance of the transformer in the system.
- Transformer Testing — Are You Missing the Test Point? [PDF] Transformer testing whether internal or external is paramount in providing the maximum life expectancy of our equipment whether new or one from our aging fleet.
- Dry-Type Power Transformers: Understanding Transformer Isolation and Noise [PDF] One of the more overlooked aspects of dry-type transformer installations is the removal of shipping bolts and/or shipping blocking material attached to the unit.
- 8 Important Checks To Do Before Powering Up The Dry-Type Transformer The transformer should be powered up only after checking the following 8 items.
- Condition Monitoring of Transformers - Detecting early signs of deterioration It is possible to provide transformers with measuring devices to detect early signs of degradation in various components and provide warning to the operator in order to avoid a lengthy and expensive outage due to failure.
- Erection Procedures for Power Transformers Transformers should be inspected for internal or external damage, particularly if they have been dropped or tipped over.
- Understanding the Mechanical Effect of Magnetic Forces in Transformers During normal operation, transformer internal structures and windings are subjected to mechanical forces due to the magnetic forces.
- Do Not Energize Oil-Filled Transformer Without Performing These 15 Tests and Checks! The following tests and checks should be performed at a minimum to ensure that the transformer is ready to be energized. Do not energize the transformer without performing these tests and checks.
- Connections and ratings - Determine the correct ratings, winding connections and taps for specific application. Have knowledge of scott-t, zig-zag, open delta, broken-delta, wye, and other configurations and phase relationship considerations.
- Three-Phase Transformer Winding Connections The primary and secondary windings of a three-phase transformer can be connected in different configuration to meet just about any voltage requirement.
- Three Phase Transformer Connections If we take three single-phase transformers and connect their primary windings to each other and their secondary windings to each other in a fixed configuration, we can use the transformers on a three-phase supply.
- What is an Open Delta Transformer? An open delta transformer is a special arrangement which uses only two windings.
- The Scott T Question This connection was initially developed and is a practical solution for the conversion of three phase primary to a two phase secondary. On the three phase side a neutral point is available for grounding or for loading. On the two phase side the windings may be connected to give three or four wire supply.
- Understanding Transformer Vector Diagrams Three phase transformer consists of three sets of primary windings, one for each phase, and three sets of secondary windings wound on the same iron core. Separate single-phase transformers can be used and externally interconnected to yield the same results as a 3-phase unit.
- Selecting, sizing transformers for commercial buildings This article presents several useful design concepts for selecting and sizing transformers in the design of electrical systems for commercial buildings.
- Easy way to calculate transformer fault current This quick calculation can help you determine the fault current on the secondary of a transformer for the purpose of selecting the correct overcurrent protective devices that can interrupt the available fault current.
- Full Load Current Ratings of Self-Cooled Three-Phase Transformers FLA reference table for transformers 208V to 34.4kV
- Power transformers - general - Perform standard field test procedures for a power transformer. Understand methods of treatment of fluid insulation to improve characteristics. Perform electrical and functional tests of insulating, auxiliary, and control components.
- Important Standards
- IEEE C57.19.03 Standard Requirements, Terminology, and Test Code for Bushings for DC Applications
- Transformer Maintenance and Testing
- Transformer Diagnostics and Condition Assessment The following is a summary of testing and diagnostic techniques, and tools used to assess the condition of transformers.
- High-voltage bushing maintenance techniques To prevent electrical catastrophes and optimize HV bushing service life, the following preventive maintenance and testing procedures should be performed at regular intervals.
- Medium Voltage Transformer Testing [PDF] The types of tests and the procedures for conducting them are published in IEEE Standard C57.12.90 for liquid-filled transformers and IEEE Standard C57.12.91 for dry-type transformers.
- Testing Procedures for HV Voltage Transformers General overview of HV transformer tests and checks.
- Ratio Testing
- Introduction to Transformer Turns Ratio Testing The transformer turns ratio test is used to determine the number of turns in one winding of a transformer in relation to the number of turns in the other windings of the same phase of the transformer.
- Transformer Turns Ratio (TTR) Explained Transformers efficiently transfer electrical energy from one circuit to another by means of magnetic induction. Each phase of a transformer is composed of two separate coil windings wound on a common core.
- Transformer Turn Ratio Testing A direct relationship exists between the number of turns and the voltage ratio of the primary to the secondary.
- Power Transformer Turns Ratio Test The turns ratio test is an AC low voltage test which determines the ratio of the high voltage winding to all other windings at no-load. The turns ratio test is performed on all taps of every winding.
- Measurement of Transformer Voltage Ratio and Checking of Phase Displacement The aim of measurement is: Confirming the no-load voltage ratio given in the customer order specifications, determining the conditions of both the windings and the connections and examining the problems (if any).
- Polarity
- Transformer Polarity Test Procedures You can easily test for transformer polarity by using a reduced voltage source to excite the primary winding.
- Identifying The Primary And Secondary Phasor Polarities Of Transformers Polarity testing identifies the transformer primary and secondary phasor polarities. It is a must for poly phase connections.
- Winding Resistance
- Transformer Winding Resistance Testing Explained Winding resistance measurements are an important diagnostic tool for assessing possible damage to transformers resulting from poor design, assembly, handling, unfavorable environments, overloading or poor maintenance.
- A Guide to Transformer Winding Resistance Measurements [PDF] Measuring a transformer's winding (DC) resistance from one external terminal to another can reveal a great deal of information about a transformer.
- Power Factor
- Capacitance and Dissipation Factor Testing on Power Transformers The capacitance and dissipation factor test is an AC low voltage maintenance test and is very similar to the power factor test.
- Application guide for power factor testing of power & distribution transformers Power factor testing is an effective method to detect and help isolate conditions such as moisture, carbonization, contamination in bushings, windings and liquid insulation. In addition to power factor testing, transformer excitation current measurements will help detect winding and core problems.
- Power Factor Testing Dry-Type Transformers The additional costs associated with performing insulation power factor testing on these smaller units are difficult to justify. However, larger dry-type transformers — especially ones that provide critical power — should be given a power factor test to ensure continued serviceability.
- Additional Reading
- Large Power Transformer Condition Assessment and Life Extension [PDF] Large power transformers are the backbone of the power grid.
- High Resistance Grounding: Is It More Than Just a Big Heater? [PDF] The purpose of a transformer neutral grounding resistor is to control the amount of current flow into a ground fault in the event of insulation failure of one of the normally energized conductors to ground.
- Measurement of Transformer No-Load Loss And Current The no-load loss and current measurements of a transformer are made while one of the windings (usually the HV winding) is kept open and the other winding is supplied at the rated voltage and frequency.
- Primary Current Injection Through-fault Testing Power Transformers Proper testing of large power transformers and their protective relaying circuits following installation or replacement is vital to their proper and continued long-term operation as well as that of the adjacent electric power system.
- Important Standards
- Instrument transformers - general - Perform current and voltage transformer polarity, ratio, burden and saturation, and dielectric tests. Analyze the test results.
- 6 electrical tests for Current Transformers explained It is essential to inspect and calibrate current transformers and their connected instruments at regular intervals. There are 6 electrical tests that should be performed on CT's to ensure accuracy and optimal service reliability.
- Back to the Basics: Current Transformer Testing [PDF] The purpose of this article is to help a test-set operator understand the tests he performs, reinforce a test technique, or add it to his repertoire.
- Current Transformers - A Forgotten Piece of the Relay System [PDF] If instrument transformers are not up to speed, those wonderfully engineered protective relays are about as much use as bus bar.
- Current Transformer Grounding [PDF] This Powell Technical Brief investigates the preferred ground location of typical CT circuits such as transformer and bus differential relays.
- Phase-Matching Considerations with Open-Delta PTs [PDF] Whenever a power system is supplied by multiple sources, such as a main-tie-main configuration, special consideration should be given as to how the sources are phased or matched to each other.
- Inspection and Test procedures for Instrument Transformers Follow these inspections and tests when testing instrument transformers.
- Identifying The Primary And Secondary Phasor Polarities Of Transformer — Polarity Test This is needed for identifying the primary and secondary phasor polarities. It is a must for poly phase connections. Both a.c. and d.c methods can be used for detecting the polarities of the induced emfs.
Getting Started