Monday

PROTECTIVE RELAYS TRACK

Title: Testing High Magnitude Faults on a Transmission Line Using COMTRADE Records: A Case Study

2/27/17
9:30AM - 10:15AM
Presenter: Mohit Sharma, Chinmay Desai, and Vijay Sundaram, Megger
Description:

Abstract - Modern testing techniques are reliable for testing most protective relays but some cases such as generator out-of-step and high magnitude line faults cannot be accurately tested with conventional methods. Another limitation of these methods is that the transient conditions that lead to CT saturation at the time of fault are ignored. The introduction of COMTRADE, a standard data format for data recording, has paved the way for users to test these special functions and cases. The complex protection schemes can also be validated by playing back an actual fault scenario.

This paper discusses the use of COMTRADE records to test an actual three phase fault that occurred on a 400 kV transmission line. The fault current magnitude was more than 30 times the nominal value. The modern testing practices recommend the use of multiple shots or pulse ramping to carry out relay testing. However, this does not take into account the whole power system’s condition at the time of the fault. As a result, the accuracy is compromised. With higher magnitudes of fault current, the error is quite significant. This paper provides a solution for testing such high amplitude fault scenarios using a practical case study. In addition, this paper describes in detail the advantages of using COMTRADE based testing over other conventional methods.

PROTECTIVE RELAYS TRACK

Title: Influence of Non-Linear Loads on Generator Differential Protection

2/27/17
11:30AM - 12:15PM
Presenter: Vijay Sundaramand Dhanabal Mani, Megger
Description:

Abstract - The primary function of generator differential protection scheme is to protect the generator from any internal faults. Any time delay in isolating the faulty circuit could result in permanent damage to the generators. A typical generator differential protection scheme (87G) does not consider the harmonic content of the system. Due to the proliferation of non-linear loads, the effect of harmonic content has to be considered when designing a differential protection scheme. The increase in harmonic content can lead to unwanted operation of the differential protection.

State-of-the-art protection relays are capable of monitoring the waveforms and isolate the circuit in the event of high harmonic content. This paper focuses on the effects of connecting heavy non-linear loads to the power system located near generators. The susceptibility of generator differential protection scheme to external load condition is explained using a practical case-study.

The case-study involves a rectifier transformer in a zinc plant located in South Asia. Due to multiple operations of 87G in the nearby generating stations, an investigation was carried out. The investigation led to the determination that the harmonic distortion in the waveform caused asymmetric CT saturation in the 87G circuit. This paper discusses the factors affecting a differential protection scheme. Also, the paper will thoroughly explain the root cause of unwanted relay operation using real life case-study.

PROTECTIVE RELAYS TRACK

Title: Understanding Basic High Speed Tripping and Communications (Basics of Tone and Carrier Schemes)

2/27/17
2:15PM - 3:00PM
Presenter: Jay Garnett, Doble Engineering Company
Description:

Abstract - One of the most important functions of protecting a bulk transmission line is the high speed tripping of that line in the event of a fault. In order to cause the least amount of disruption to the power gird, the fault must be identified and trip the line off as fast as possible. This is to minimize the effect to other lines as well as power generation supplying those lines.

High speed communication is used to send signals to the other end of the line at a remote station to either trip the breaker at the other end or to stop it from tripping. Communication signals are transmitted over several ways to allow the relays at both ends of the line to evaluation what is happening during the fault and trip the breaker accordingly.

This paper will cover the basics of phase and ground zone protection as well as other protection and how it interfaces with the high speed communication equipment. It will also go over the basics or how those communication devices send the signals to the other end of the transmission line.

PROTECTIVE RELAYS TRACK

Title: End-To-End Testing Methods Compared

2/27/17
3:15PM - 4:00PM
Presenter: Christopher Pritchard and Will Knapek, OMICRON electronics Corp. USA
Description:

Abstract - For many years now we see the increasing number of communication assisted protection schemes. While it is mandatory to test these protection schemes for compliance, the NERC misoperation study 2013 also underlined the importance of testing not only for relay failures but also for communication failures and design errors.

End-to-end or distributed testing is already a well-accepted method for line protection testing. The same technique for testing line protection can also be applied for bus protection or distribution schemes. While most technicians are implementing a certain method of distributed testing, there are many different methods available that can save a significant amount of time. Opposed to other papers on this topic, this paper tries to give a broad overview of the different methods of conducting a distributed test, which will provide technicians with a guide to choose the right tool for their next job. Each method will be characterized by the way the test inputs are defined, the test cases are executed and the results are assessed. Additionally we will give tips for each method, what to consider when preparing a distributed test, how systematical order of tests can reduce error and how to troubleshoot failing tests in the field.

An in depth discussion will be dedicated on testing distributed logic. Additionally to the complexity of running a setup with multiple test sets, this use case adds special requirements. Test cases for logic usually involve a sequence of system events. Each event causes the real power system to transition into another state. Logic schemes expect and rely on this transition to work properly. A simple example is a reclosing logic that shall be tested; if the 52a status and current do not disappear, the relay will fall back to its breaker failure logic. The conclusion is that all test sets have to output a consistent system state for each test case. The paper will show a method that has been applied several times successfully in the field to test distributed logic.

PROTECTIVE RELAYS TRACK

Title: Man-Made Faults – Line Protection Operation for an Unintended Phase Cross-Connect Condition

2/27/17
4:15PM - 5:00PM
Presenter: Ryan McDaniel and Jon Larson, Schweitzer Engineering Laboratories, Inc.
Description:

Abstract - For a temporary operating condition, a utility installed a new switch to tie together two subtransmission lines. During the installation, operating personnel inadvertently crossed two phases. When the operators closed the line switch, it created an unusual fault, cross-connecting two phases between the sources and causing the line protection to operate on one end of the line. Another relay protecting a line connected to a common bus also tripped for this condition. The elements that operated in these microprocessor-based relays were compensator phase distance elements. Compensator phase distance relays have evolved from the electromechanical relays of the 1950s to protection elements included in today’s microprocessor-based relays. In this paper, we discuss the theory of operation of compensator phase distance relays and some of their applications. We then explain why the compensator phase distance elements operated for this phase cross-connect condition by analyzing the event reports from the relays involved. We use symmetrical components to demonstrate how to analyze the phase cross-connect condition and analyze the responses to this condition by a negative-sequence voltage-polarized directional element and a positive-sequence polarized mho element. Finally, we discuss methods for making a compensator phase distance element secure for similar phase cross-connect conditions.

Here is Ron Widup, Conference Chair,
with PowerTest 2017 details!