Armando Guzmán

Synchrophasor-Based Real-Time Voltage Stability Index

This paper presents a new online voltage stability index (VSI) that predicts the power system steady-state voltage stability limit. Starting with deriving a method to predict three types of maximum transferable power (real power, reactive power, and apparent power) of a single-source power system, a new VSI based on the calculated load margins is devised. In order to apply the VSI to large power systems, a method is developed to simplify the large network behind a load bus into a single source and a single transmission line using time-synchronized phasor measurements and network parameters. The simplified system model, to which the devised VSI can be applied, preserves power flow and voltage information of the particular load bus under study. The proposed VSI combined with the network simplification method provides the voltage stability margin of each individual load bus in an informative format and identifies the load bus that is the most vulnerable to voltage collapse. Test results from applying the VSI on two test systems validate its applicability for online applications

A Current-Based Solution for Transformer Differential Protection. Part I: Problem Statement

This paper analyzes the problem of transformer differential protection. First, we review the concept of transformer differential protection. We then analyze magnetizing inrush, overexcitation, and current transformer (CT) saturation phenomena as possible causes of relay misoperation. Finally, we summarize the existing methods for discriminating internal faults from inrush and overexcitation conditions. In Part II of the paper we propose a new approach for transformer differential protection and describe the relay that is based on this approach.

Anti-islanding today, successful islanding in the future

Distributed generation (DG) is gaining popularity in the United States and across the world. The Florida Public Service Commission recently passed rules encouraging the use of renewable resources. Integrating DG with the utility network poses challenges for anti-islanding schemes. These schemes detect islanding conditions and trip the DG. Fig. 1 shows a typical network configuration for DG installations. Failure to trip islanded generators can lead to problems such as threats to personnel safety, out-of-phase reclosing, and degradation of power quality. This paper discusses a wide-area measurement-based islanding detection scheme (IDS_WA) that uses time-synchronized measurements to calculate the slip frequency and acceleration between two systems to detect islanded conditions. The proposed scheme has significant advantages compared to traditional anti-islanding schemes, specifically when the power mismatch is minimal. Local-area measurement-based schemes (IDS_LA) complement the IDS_WA. The paper also discusses the use of a real-time digital simulator to model DG along with the rest of the system to validate the proposed anti-islanding scheme. The paper shows the performance of the scheme for different system configurations and load flow conditions. The paper presents a successful islanding scheme that monitors the system power exchange, takes remedial actions when islanding occurs, and maintains quality of service in the islanded system.

A Current-Based Solution for Transformer Differential Protection Part II: Relay Description and Evaluation

This paper describes a new approach for transformer differential protection that ensures security for extemal faults, inrush, and overexcitation conditions and provides dependability for internal faults. This approach combines harmonic restraint and blocking methods with a wave shape recognition technique. We compare in the paper the behavior of some traditional transformer protection methods to that of the new method for real cases of magnetizing inrush conditions.

Local- and Wide-Area Network Protection Systems Improve Power System Reliability

Increasing demands on electricity supply, with the need for system economic optimization and power system growth limitations, have a significant impact on power system reliability. When the system operates in extreme conditions, load shedding, generation shedding, or system islanding must occur to prevent total system collapse. Typical causes of system collapse are voltage instability or transient angle instability. New monitoring, protection, and communications technologies allow us to implement economical local- and wide-area protection systems that minimize risk of wide-area system disruptions or total system collapse. This paper presents solutions that use programmable logic capabilities, faster communications, and synchronized phasor measurements available in meters and protective relays to prevent system disruptions

Locating faults by the traveling waves they launch

Faults on overhead transmission lines cause transients that travel at the speed of light and propagate along the power line as traveling waves (TWs). This paper provides an overview of TWs and TW fault locators. It explains the physics, reviews the theory of TWs, explains the foundations of various types of TW fault locators, and provides an in-depth discussion on a number of TW fault locating implementation challenges. Finally, it discusses integration of TW fault locating in microprocessor-based relays and presents Bonneville Power Administrations (BPAs) field experience using these relays.

Improvements in transformer protection and control

This paper describes protection elements that detect transformer faults quickly and avoid unnecessary transformer disconnections. The paper introduces a differential element that combines the security and dependability of harmonic restraint with the speed of harmonic blocking to optimize relay performance. An additional negative-sequence differential element improves sensitivity for internal turn-to-turn faults under heavy load conditions. External fault detection supervision adds security to this negative-sequence differential element during external faults with CT saturation. The paper also describes a dynamically configurable overcurrent element that improves protection coordination for different operating conditions but does not require settings group changes. In addition, the paper discusses an underload tap changer control system that uses time-synchronized phasor measurements to minimize loop currents and losses in parallel transformer applications.

Reliable busbar protection with advanced zone selection

Modern digital relays use innovative algorithms to fulfill busbar protection requirements of fast operating times for all busbar faults, security for external faults with heavy current-transformer (CT) saturation, and minimum delay for evolving faults. This paper describes a reliable protection system that includes busbar protection and advanced zone selection; the protection system is suitable for the protection of multiple busbar arrangements. The protection system consists of several protection principles and measuring techniques using instantaneous and phasor quantities in a unique combination to achieve reliable busbar protection with minimum CT performance requirements.

Protective Relay Synchrophasor Measurements During Fault Conditions

This paper describes details of the signal processing techniques that a protective relay uses to provide both synchronized phasor measurements and line distance protection. The paper also presents a comprehensive system model of normal and faulted power system operating conditions. Finally, the paper provides power system model test results that demonstrate the ability of the described protective relay to provide synchrophasor measurements during both normal and faulted conditions

Dynamic simulations help improve generator protection

This paper describes a digital simulation study of a set of two 160 MW generating units operating in the Juan de Dios Batiz Paredes thermal power station, in Topolobampo, Sinaloa, Mexico. This plant belongs to Comision Federal de Electricidad, the national Mexican utility. We first discuss the factors that limit the active and reactive power delivered by a generating unit, such as thermal and voltage limits, power-system imposed limits, and the minimum excitation limiter. We then describe generator protection functions related to the capability curve. Later, we propose a P-Q plane-based scheme that provides generator loss-of-field protection and capability-curve violation alarming. Finally, we present the simulation results of loss-of-field and loss-of-synchronism conditions of one of the two generating units for several cases, including different initial load conditions, different loss-of-field modes, and different numbers of units on line.