Roy E. Cosse

Fundamentals of Turbine/Generator Speed Control: A Graphical Approach for Islanding Applications

To promote a better understanding of industrial turbine/generator speed control, the fundamentals of droop and isochronous turbine/generator control are discussed via graphical examples for typical industrial islanding applications with bus-connected generators. A mathematical analysis of several examples illustrates the validity of a practical graphical approximation approach. By comprehending these fundamental concepts, industrial application engineers can more thoroughly investigate advanced governor control topics, such as isochronous load sharing with communication lines between governors, manual operator control of multiple generators, and load sharing via automatic power-management systems.

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.

Is selectivity achieved in critical low-voltage UPS and standby generator power circuits?

This paper reviews typical critical low-voltage UPS (uninterruptible power supply) systems and standby generator power circuits used in the petrochemical industry to determine if selectivity is achieved between protective devices during short-circuit conditions. Alternate system configurations are proposed when selectivity is not achieved. Generator excitation systems and UPS support during fault conditions is discussed.

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.

Gas turbine generator governor speed/voltage control for non-complex, islanding operating systems — “Which control strategy should I use?”

Papers [1] and [2] focused on governor fundamental speed control basics; the focus of this paper is a fundamental understanding of Automatic Voltage Regulator [3] basics for voltage control and MVAR load sharing. Discussions focus on non-complex, islanding applications for upstream oil and gas and downstream petrochemical facilities, such as, large motor starting, gas turbine step load capability after mechanical tripping of an online generator, load shedding to preserve continued system operation, and electrical protection philosophy basics to maintain system stability.

Symmetrical, Total, and Peak-Oh My: Is Current All I Use to Select My Circuit Breaker?

ANSI/IEEE Medium-voltage circuit breaker ratings have changed in recent years, causing a great deal of confusion over how to properly select a breaker for short-circuit duty. This paper reviews basics of an asymmetrical short-circuit current waveform. It illustrates the effect of the X/R ratio and how the relationship between the dc component and the circuit breaker contact parting time determines the interrupting time of the short-circuit current. Five examples are discussed. The first set examines basic power distribution system applications that illustrate the potential issues of mixing older MVA rated switchgear with new circuit breakers rated using the voltage range factor K=1. The second set examines the complexities that occur when a generator with significant X/R ratio is directly supplying distribution switchgear. Examination of these different conditions is intended to aid equipment users in specifying the correct circuit breaker by identifying the critical factors and conditions affecting the performance of the circuit breaker.

Ground fault protection for MV bus connected generators

In contrast with utility generators, the generators found in industrial facilities often form an integral part of the plant grounding system. This creates particular issues related to the provision of effective protection of these machines for ground faults. This paper reviews current grounding practices within industrial plants. It discusses the generator ground fault phenomenon and the resulting damage. Several configurations of directly connecting multiple generators at the medium voltage level are described, methods for ground fault protection are discussed and typical application examples are reviewed.