Donald G. Dunn

Recent problems experienced with motor and generator windings

In many respects, large motors and generators in petrochemical plants have become a commodity product with intense competition amongst manufacturers from around the world to secure orders. This has resulted in pressure on machine designers to reduce manufacturing costs. Some of the methods employed to accomplish this include: • Reducing the conductor cross section • Reducing the insulation thickness • Reducing the amount of steel core material • Developing manufacturing methods that result in less time to manufacture. Each of these methods tends to increase the operating temperature of the windings or put additional voltage stress on the electrical insulation. Many design and processing innovations have been successfully implemented. However, there are both anecdotal and statistical data that indicates that there are more problems with machines made in the past 10 years, as compared to machines made previously. Engineering firms and end-users perhaps need to provide comprehensive, yet reasonable, purchase specifications that allow all manufacturers to compete on a level playing field. This paper is mainly concerned with stator windings rated greater than 6 kV, and rotors of various sized machines.

CT saturation calculations - are they applicable in the modern world? Part 1, the question

Previously, ANSI/IEEE relay current transformer (CT) sizing criteria were based on traditional symmetrical calculations that are usually discussed by technical articles and manufacturers guidelines. In 1996, IEEE Standard C37.110-1996 introduced (1+X/R) offset multiplying, current asymmetry, and current distortion factors, officially changing the CT sizing guideline. A critical concern is the performance of fast protective schemes (instantaneous or differential elements) during severe saturation of low-ratio CTs. Will the instantaneous element operate before the upstream breaker relay trips? Will the differential element misoperate for out-of-zone faults? The use of electromagnetic and analog relay technology does not assure selectivity. Modern microprocessor relays introduce additional uncertainty into the design/verification process with different sampling techniques and proprietary sensing/recognition/trip algorithms. This paper discusses the application of standard CT accuracy classes with modern ANSI/IEEE CT calculation methodology. This paper is the first of a two-part series; Part II provides analytical waveform analysis discussions to illustrate the concepts conveyed in Part I

Motor and Generator Windings

In many respects, Large Motors and generators in petrochemical plants have become a commodity product with intense competition to secure orders among manufacturers from around the world. This has resulted in pressure on machine designers to reduce manufacturing costs. Many design and processing innovations have been successfully implemented. However, there are both anecdotal and statistical data that indicate that there are more problems with machines made in the past ten years when compared with machines made earlier. Engineering firms and end users perhaps need to provide comprehensive, yet reasonable, purchase specifications that allow all manufacturers to compete on a level-playing field. Stator windings rated greater than 6 kV and rotors of various-sized machines are the main topics of discussion.

CT Saturation Calculations - Are they Applicable in the Modern World? - Part II, Proposed Responsibilities

Part I expressed concerns about using IEEE Standard C37.110-1996 (1+X/R) criteria for sizing current transformers (CTs) for feeder short-circuit conditions [1]. Part II introduces an overview of relay filter algorithms, and proposes responsibilities of the IEEE Power System Relay Committee (PSRC), operating company and engineering company electrical power engineers, CT manufacturers, switchgear manufacturers, and relay manufacturers to guarantee CT/relay system performance. International Electrotechnical Commission (IEC) responsibilities are also included.

CT saturation calculations - are they applicable in the modern world? - Part III, low-ratio, high-current CT/microprocessor relay comparisons at a high-current testing laboratory

Part III is an extension of the Part II testing effort, but with relay manufacturers providing, commissioning, and configuring the relays for the high-current test laboratory activities. Part III provides high-current testing laboratory results for multiple 50 kA and 63 kA tests involving several typical low-ratio switchgear CTpsilas (with typical burdens) and microprocessor feeder relay instantaneous 50 elements. Saturated low-ratio CT graphical waveform plots obtained from a series of tests are analyzed. Microprocessor relay 50 element true rms and bipolar peak detector relay filter algorithm types are considered. Discussions also include power system concerns resulting from delayed microprocessor relay instantaneous 50 element operation, i.e., arc flash PPE recommendations, relay coordination selectivity, equipment. Comments about electro-mechanical instantaneous relays are included.

Is My UPS Distribution System Coordinated

This paper reviews typical uninterruptible power supply (UPS) distribution systems for the petroleum and chemical industries, focusing on the selectivity of interrupting devices during short-circuit conditions. When selectivity is not achieved, alternative solutions are proposed. Distribution-system-selectivity comparisons are performed for standard circuit-breaker panelboards, fuse panelboards, and custom panelboards utilizing hydraulic magnetic circuit breakers. When remote panels are implemented, application considerations should include oversizing feeder cables or using step-up/step-down transformers. To determine the ride through response of operating plant individual UPS loads, the voltage-depression time during UPS distribution-system-fault clearing is compared with the load ride through capability. General guidelines are provided for improved UPS distribution-system performance

Common Questions on Partial Discharge Testing: A Review of Recent Developments in IEEE and IEC Standards for Offline and Online Testing of Motor and Generator Stator Windings

Partial discharges (PDs) are small electrical sparks that occur in voids within electrical insulation or on the surface of motor and generator stator winding coils. Offline and online PD testing have become widely used tools for in-factory quality acceptance and baseline performance evaluations of new groundwall insulation in stator windings rated 6 kV and above. Many petrochemical plants and refineries perform online PD tests to periodically assess the condition of the statorwinding insulation on machines during operation. The IEEE and the International Electrotechnical Commission (IEC) have created standards that are called recommended practices or technical specifications (TSs) to address offline and online PD measurement using electrical diagnostic equipment and optical measurement of surface PDs. The standards explain testing objectives and principles, discuss commonly used methods for measuring PDs, and provide guidance for data interpretation.

Seeking global harmony in standards

This article discusses the relevance of standards in a global marketplace. In addition, it outlines the methods used by the IEEE and the International Electrotechnical Commission (IEC) standards process as well as the rules for standards development, including the procedures required to bring a standard to publication. A comparison of the IEEE and IEC standards processes and their impact on industry is made in this article.

A user's guide to factory testing of large motors: What should your witness expect?

Witness testing is a fact of life. There is nothing like close proximity to increase awareness of a machine in both the customer and the factory organizations.

Implementing an Electrical Network Monitoring and Control System on a Grassroots Refinery Project—Part I

This paper shares the authors experiences with implementing an Electrical Network Monitoring and Control System (ENMCS) on a grassroots 400,000 bpd refinery project with approximately 250 MW of peak load. The scope of the ENMCS spans from the 380 kV primary substation to the 480 V switchgear. The project is expected to proceed into the detail design phase this year. This is a two-part paper. Part I will discuss the primary objectives of the ENMCS and the intended benefits to the refinery. The technical bases considered for selection of the ENMCS architecture and protocol will be presented along with the historical background. Engineering management aspects of ENMCS implementation will be discussed. This paper is expected to be of interest to many within the petrochemical community as it is one of the first implementations of IEC 61850, Communication Networks and Systems for Power Utility Automation, on such a large grassroots scale. The intent is to publish Part II after the ENMCS is commissioned and will present the lessons learned and suggested improvements.