Title: Recommended Practices for Applying an Effective Test Protocol to Power Transformers

9:30AM - 10:15AM
Presenter: Charles Sweetser, OMICRON electronics Corp. USA

The primary goal when performing diagnostic tests on power transformers is to ensure safe operation and accomplish life extension. Often, influences outside of our control compromise the results. Understanding and controlling these influences will increase the effectiveness and ROI of diagnostic testing. We will investigate the best practices regarding test procedure, test preparation, and the analysis of the results.

The following standard electrical field tests will be included in the discussion:

Power Factor; Exciting Current; Turns/Voltage Ratio; Leakage Reactance; DC Winding Resistance; Sweep Frequency Response Analysis (SFRA)

Issues such temperature, test environment, user error, test connections, and lead placement will be investigated for each test. The audience will be provided with an understanding, application, and analysis of these best practices, supported by specially selected case studies validating the value that these diagnostic tests bring to testing, and finally assessing, power transformers.

Title: Transformer Turns Ratio Test: Some Unknown Facts

10:30AM - 11:15AM
Presenter: Dinesh Chhajer and Daniel Carreno Perez, Megger

Transformer Turns Ratio (TTR) is one of the most common test performed to assess the condition of a transformer's windings and core. It is performed as part of acceptance and maintenance test procedure to determine any problems due to poor design, assembly, handling, overloading, fault conditions or poor maintenance. The results can be compared against nameplate ratings to determine any possible insulation deterioration, shorted turns or any other winding or core abnormalities.

TTR is such a simple and easy test to perform that often operators take it for granted without fully understanding the principle and basis of the test, such that when measurements are not as expected it becomes a challenge to diagnose the issue and resolve the problem. This paper will focus on some of the unknown facts associated with the TTR test, going over in detail on the effect of applied test voltage, comparison of energizing from primary vs. secondary side, different vector configurations, differences between nameplate ratio, voltage ratio and turns ratio, source of ratio and phase angle errors, comparison between per phase testing and true three phase testing, testing special applications such as zig-zag transformers and voltage regulators, extreme tap ratios being out of tolerance for On Load Tap Changers, and TTR test correlation with other electrical tests. The paper will also provide field test results and case examples to better explain the above-mentioned facts.

Title: Utilizing Primary Injection for Transformer Differential Protection Commissioning

11:30AM - 12:15PM
Presenter: Alan Andrew Holt, Premier Power Maintenance Corporation

NETA companies continually seek to create added value for our customers whose needs and demands are ever changing. The recent increase of transmission substation projects have created many opportunities for providing increased value as well as many opportunities for failure involving intricate systems. Given two knowns:

  1. The transformer is typically the most expensive component of the substation.
  2. One very common protection mis-operation after substation commissioning is failure of the transformer differential protection scheme.

It is imperative we ensure the transformer protection scheme is fully functional.

This presentation will demonstrate the need to go beyond simple individual component commissioning to include entire system functionality tests. The project includes: 1) research of various projects involving primary injection testing of substation transformer differential protection, 2) development of a best practice method, and 3) implementation of the actual plan.

Title: Relay Testing for Real World Conditions

2:15PM - 3:00PM
Presenter: John Lane, Doble Engineering Company

While relay element testing is a good acceptance test that the relay functions as designed, system faults rarely present themselves in such a clean manner. A fault may have inrush current, severe dc offset. The current transformer may not replicate itself accurately due to high fault current or remnant flux. These conditions may cause the relay to misoperate. Comtrade files from actual events captured from event recorders are extremely useful in testing and verifying a relay will operate under a actual conditions. Comtrade files can played back through a relay test set. This is very useful after a misoperation to verify modified relay settings are correct and do not misoperate. These comtrade files can be modified to add harmonics or high dc offset to test different system conditions. We will look at how to use comtrade files to functional test and commission not only a relay but a system.

Title: Beyond the Knee Point: A Practical Guide to CT Saturation

3:15PM - 4:00PM
Presenter: Brad Heilman, Schweitzer Engineering Laboratories, inc.

Current transformer (CT) saturation, while a fairly common occurrence in protection systems, is not often clearly understood by protective relay engineers. This paper forgoes the usual physics equations to describe how CTs saturate in a simple and intuitive way. We then describe the CT equivalent circuit and how it results in the familiar CT excitation graph. We explain the differences between saturation due to large symmetrical ac current components and saturation due to smaller, but long-lasting, exponentially decaying dc components in the fault current. We also explain how remanence accumulates in the core of a CT. ANSI ratings of CTs are explained, and we show how to analyze the performance of CTs using simple tools. Finally, we explain how CT saturation can affect the operation of various protection elements and show how to spot and analyze CT saturation in protective relay event reports. Real-world event reports are presented where relay operation was compromised due to incorrect secondary current values from saturated CTs.

Title: Travel Measurement and Analysis of Medium Voltage Vacuum Circuit Breakers

4:15PM - 5:00PM
Presenter: Volney Naranjo and Robert Foster, Megger; Albert Livshitz, CE Power Engineered Services, LLC

Medium voltage vacuum circuit breakers (MV VCB) have been used for well over 40 years and are subjected to maintenance, overhaul and testing procedures loosely defined by OEMs. Travel measurements and analysis are paramount for the comprehensive evaluation and diagnostic of the MV VCB. It provides the tool to determine parameters such as the stroke, speed, contact pressure (wipe), overtravel, rebound, etc.

Travel measurements on high and medium voltage circuit breakers with tulip and finger/wedge type contacts that have a relatively long contact travel are a well-developed technique and commonly practiced in the field. Different types of transducers are available, their usefulness is proven, and mounting accessories are available from different manufacturers to facilitate their use.
MV VCBs have butt type contacts with a much shorter stroke and a small gap between contacts when open. Any deviation from the required gap and travel parameters affects the reliability of the vacuum interrupters and breaker performance. But, due to the lack of knowledge or information, and difficulties of connecting a transducer, travel measurements are often neglected.

This paper will present the results from testing several MV VCB from various OEMs using different transducers to determine the viability of usage and provide recommendations for the most suitable transducer to achieve the reliable results and best practices. Several mounting options will be tested to show the effects of and convenience of each with the goal to identify the most common transducers and accessories to have in order to test a variety of MV VCBs. This is a continuation of a paper presented during PowerTest2018 by CE/Power - Albert Livshitz