G. J. Cokkinides

Multifunctional synchronized measurement network [power systems]

In 1992, the New York Power Authority (USA) and the other Empire State Electric Energy Research Corporation member electric utilities initiated the deployment of a network of power system synchronized measurement units using phasor measurement technology on the New York State high-voltage transmission system. This article defines the current and future status of the measurement network, featuring its harmonics measurement and disturbance monitoring.

Distributed state estimation based on the supercalibrator concept - laboratory implementation

The supercalibrator concept was introduced based on a statistical estimation process that fits the GPS- synchronized measurements and all other available standard data into a three-phase, breaker-oriented, instrumentation inclusive model. In this approach, the asymmetries, unbalances and the instrumentation errors are taken into account in the state estimation procedure.The laboratory setup considered in this paper is the scaled down model of a three substation power system.

On stability of implicit numerical methods in nonlinear dynamical systems simulation

This paper examines the numerical stability properties of numerical integration techniques. The paper focuses on trapezoidal integration method and the algebraic companion form. For linear systems, both methods are absolutely numerically stable. For nonlinear systems, several conditions for numerical stability are presented.

Comparison of implicit and explicit integration techniques on the non-ideal transformer example

This paper presents a comparison of implicit and explicit methods for system simulation. Emphasis is placed on nonlinear systems. The results of the paper illustrate that implicit methods are more robust than explicit methods.

Dynamic state estimation-based protection of power transformers

Power transformers are expensive and critical power system components. Reliable and secure protection schemes for transformers are extremely important. While transformer protection has evolved to a high degree of sophistication they cannot ensure 100% reliable and secure protection. A new transformer protection scheme based on dynamic state estimation is proposed. The dynamic transformer state is continuously estimated from measurements and the protective decision is based on the transformer state only (operating condition or health status). This scheme requires very few and simple settings, such as maximum permissible hot spot temperature. The protection algorithm is object-oriented. Specifically, the transformer model is expressed in a standard format, named the algebraic quadratic companion form (AQCF) and the dynamic state estimation operates directly on this object model. The method has been demonstrated in the laboratory. The paper describes the laboratory hardware. An example transformer protection is presented for a 115/25 kV three-phase transformer. Results verify the advantages of this scheme over traditional methods.

A laboratory setup for relay and GPS-synchronized equipment transient testing

This paper presents a laboratory setup for transient testing of relays and GPS-synchronized devices. The setup relies on a unique, realistic scaled model of a small three substation system, along with its metering equipment. Lumped models of transmission lines are included that realistically represent the mutual couplings between the phases and asymmetries. Two phase shifters provide loading controllability of the scaled model as well as controlling system imbalances. The inherent accuracy of all the modeled power system elements, including generators, transmission lines, and instrumentation channels allows the transient testing of PMUs and relays with a level of accuracy equal to commercially available GPS clocks (1 mus). The system is designed to be a research tool for a variety of activities and studies including (a) development and validation of distributed state estimators (based on the SuperCalibrator concept), (b) protective relaying and PMU testing, and (c) validation of interoperability among IEDs. The overall laboratory setup provides a multivendor environment.

Harmonic monitoring system via synchronized measurements

The New York Power Authority (NYPA), and the other Empire State Electric Energy Research Corporation (ESEERCO) member utilities, initiated deployment of a high voltage transmission harmonic measurement system (HMS) in 1992. The HMS consists of hardware and software, which determine the harmonic state of a transmission system, in real time, and stores the acquired data in a historical harmonic database. The HMS hardware consists of GPS synchronized digital event recorders linked to on-site computers, and a master station computer. The present installation includes instrumentation for a total of 150 measurements of which 138 are three phase quantities (voltages or currents) resulting in 46 phasors. The system performs synchronized waveform data acquisition every 15 minutes. The captured data are processed at the on-site computers to correct for error from the nonideal characteristics of the instrumentation, and to compute the harmonics. The computed harmonics (magnitude and phase) are transmitted to the master station computer where the system wide harmonic flow is constructed, using a harmonic state estimation technique. This paper describes the HMS hardware and software as well as HMS applications.

Comparison of grounding system designs using copper or Copperweld® ground conductors

This paper presents a commentary, computational procedures for design of grounding systems using copper or Copperweld® ground conductors and comparison of these designs. The methodology is based on the IEEE Std 80. Safety and integrity of the grounding system can be achieved by proper selection of ground conductor sizes and installation procedures. The paper examines the technical performance of Copperweld® ground conductor systems and provides a number of example designs. It is concluded that the performance of ground systems designed with copper conductors or with comparable Copperweld® conductors is similar. The use of Copperweld® conductors, is a viable technical solution with the additional benefit of being a good deterrent against theft.

Voltage-load dynamics: Modeling and control

This paper discusses voltage recovery phenomena following typical faults in a power system considering the existence of dynamic loads, consisting mainly of induction motors. A three-phase, physically based power system model is utilized, allowing inclusion of system asymmetries and imbalances. The proposed modeling and simulation is based on a quadratic power system model and on a numerical integration technique that assumes quadratic variation of the state within an integration step. Numerical experiments are presented for the purpose of quantifying the phenomena and identifying the major parameters affecting these phenomena.