Without Transformers, There is No Electricity

Flick on the kitchen light, turn on the coffee maker and one of the burners on the stove; nothing to it, you do it without a thought.

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By Elsa Cantu

Flick on the kitchen light, turn on the coffee maker and one of the burners on the stove; nothing to it, you do it without a thought. You don't think about the electricity that lights the bulb, perks the coffee, and heats the burner. You turn on the television to get the early news. You take a hot shower. Again you don't think about the electricity or what it is that ensures the correct voltage flowing from the wall outlet to your television or the hot water heater.

So how does all of this work?

Power plants generate huge amounts of electrical energy used to power your house, your business, your town or city. Usually that's as far as most folks look in trying to answer how it all works. But to be useful, those huge amounts of electrical energy must first be transported, usually long distances to your cities or towns, homes or businesses, where you flick on the light or turn on the coffee maker.

But if electrical energy at the power plant were just transmitted directly through those large overhead cables that cross the landscape, then as the energy traveled over distance it would be used up in the effort, much like the air in a balloon that is let loose.

We're back to the question of how this works.

The resolution can be found in the transformer.

Transformers at the generating power plant are used to step up the voltage to the level required to transport electrical energy over long distances. They are found again at substations along the way where the depleted power is given another step up boost for the next leg of the journey. When the electrical energy finally reaches its destination, transformers are again used, but now to step down the voltage again and again until it is useable in your home or business. Transformers then are the vital link between electrical source and application.

Megger's DET4TC

But what happens when transformers anywhere along that line start to fail? There are thousands of aging transformers in today's aging power grids and these represent potential loss of revenue and high repair costs to utilities.

In light of the above it is obvious that better monitoring and testing is vital.

Transformer Testing

Given the importance of transformers in high voltage power transmission it is obvious that transformers must perform at peak or near peak capacity night and day.

Several tests can be run to ensure transformers are at near peak condition. Megger offers many different types of transformer tests and tools to keep these transformers running and businesses functioning.

Types of Transformer Tests and the Tools:

  • d.c. insulation resistance testing for assessing the condition of vital and vulnerable components. Voltages from 5 kV and 10kV voltage can be used for non-destructive testing. Diagnostic testers with high output and if needed high noise rejection like the S1-554 are ideal.
  • To check the integrity of the windings as well as the tap-changer's operation a TTR test set is used. Megger supplies TTR test sets in various forms, the most popular series tests all 3 phases at once. The TTR300 series unique testing procedures and storage capability makes set up and testing faster, allowing accurate measurement of turns ratio, phase deviation and excitation current.
  • Winding resistance is another key indicator of the state of the transformer windings and the associated tap-changer. The MTO210 can measure the primary and secondary windings simultaneously offering a fully automated winding resistance measurement.

By applying a balancing current to attenuate the circulating current induced when the test current is applied to the primary a tenfold improvement in reading time is achieved. Once finished the unit automatically demagnetizes the transformer.

  • Bond testing is also important, checking the continuity of the connections to a transformer is vital, whether it is ensuring that the resistance of the connection of the earth strap or the viability of the connections to the network. DLRO10 is a lightweight and tough micro-ohmmeter.
  • Sweep frequency response analysis (FRA) is a powerful tool for gauging the health of a transformer. Provided an initial fingerprint scan is done while the while the transformer is functioning in a satisfactory manner it is enough to give a good reference.

This trace needs to be retained along with the connection conditions of the transformer for future comparison.

Following an incident, doing a new scan is the quickest and simplest method of ascertaining the health of the whole transformer.

  • Earth systems for transformers require attention too. To design the system a survey is normally done using a high resolution earth tester like the DET2/2, which with its superior noise rejection allows the measurement of the low earth values required on such installations.

Megger's DLRO10

FRAX101 is a small and rugged FRA instrument

  • Guaranteed repeatability using reliable cable practice and high-performance instrumentation
  • Industry's highest dynamic range and accuracy
  • Fulfils all international standards for SFRA measurements
  • Wireless communication and battery operated
  • Advanced analysis and decision support built in to the software

The DET2/2 can also be used with advantage to assess the condition of the earth system.

Megger's FRAX101

DET4TC can be used with a clamp to test parts of the earth system without disconnection.

  • Tan ō or power factor testing is a useful tool for monitoring the deterioration or contamination of the bushing which are subjected to considerable electrical and mechanical stress in the lifetime of a transformer. Capacitance and tan ō are recorded as the voltage is increased. Because one monitors these parameters against time, the Delta3000 with Power DB on-board is the ideal instrument.
  • Frequency domain spectroscopy (FDS), also known as dielectric frequency response, is a technique for looking deep into the interior of a transformer by measuring the capacitance and tan ō between the transformer windings at multiple frequencies. IDAX300 brings this technique to field testing identifying problems due to moisture content in the transformer insulation, in particular the cellulose based material that significantly accelerates aging of transformers.
  • Moisture in the oil can be assessed using the Karl-Fischer technique of coulometric titration. The KF series of instruments have automated this process to give a simple readout.
  • Monitoring the insulation properties of the oil in a transformer is one of the easier tests to perform and is common in transformer maintenance. Testers such as the OTS range of oil test sets can identify degradation of the insulation properties due to oxidation, acids, sludge gas and water absorption.

Megger's IDAX300

These tests and these tools are designed to warn utilities of potential problems or failures. Periodic testing can not only head off problems, it can also extend the life of these transformers and allow utilities to schedule eventual replacement. Transformers are the life of our massive electrical grids and regular maintenance and testing keeps life in those transformers.

About the Author:
Elsa Cantu is the Marketing Manager for Megger in the United States and is based out of Dallas, Texas.

Save on Insurance—Test Your Transformers

Businesses that suffer a power transformer failure on their site could face bills running into hundreds of thousands of dollars. Hopefully this unfortunate event will be covered by insurance.

Most insurance companies however will want evidence of a maintenance regime to show that this expensive asset has had care and attention throughout its working life to minimize the risk of failure. If test and maintenance reports are not available there is a risk that the insurance company could seek to minimize its liability.

A new power transformer of the type used in on-site substations can cost from a few thousand dollars to over $1 million, and it's not unusual for the delivery time to be many months. Add the downtime from a failure and the cost of alternative temporary supplies, and the total loss suffered by a business, as the result of a transformer failure can be enormous.

As a result, it's no real surprise that insurers are taking care that every aspect of their policy agreement has been satisfied before they pay out on such large claims. And the policy small print invariably puts the onus on the transformer owner to take all practicable steps to keep it in good condition—which essentially means regular testing and maintenance.

Many business owners assume that the power transformers on their sites are the responsibility of the utility company that supplies them with power. While this is usually the case, there are many instances where the transformer is the responsibility of the company that owns or rents the site.

"We strongly recommend that any company with a power transformer on site should check whether or not they are responsible for it," says a Loss Prevention Consultant. "If they are, they should at least consider setting up a regular testing program. Not only will this help to keep their insurers happy, it will also minimize the risk of the major disruption to business that invariably follows a transformer failure."

To assist with testing and preventative maintenance, Megger offers an extensive range of transformer test equipment.

This includes insulation diagnostic analyzers using dielectric frequency response to accurately measure the moisture content in transformer insulation, and sweep frequency response analyzers that can detect electromechanical changes inside transformers. Also offered by Megger are turns ratio test sets, transformer oil analyzers, and transformer ohmmeters.

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