Edmund O. Schweitzer

Synchrophasor-based power system protection and control applications

Synchrophasor data consist of analog and digital values with an associated precise time stamp. With precise time, these quantities are collected from various locations, time-aligned, and then processed as a coherent data set. Synchrophasors have generally been used for visualization and post-event analysis. However, new technologies allow synchrophasors to be processed in real time. Synchrophasor systems are now being used for realtime wide-area protection and control. This paper examines several ways synchrophasors are being used: · Voltage stability detection and correction · Load/generator shedding · Islanding control · Intermittent generation source control and grid interconnection Each application includes a discussion of how synchrophasors provided a unique solution and benefit over traditional solutions. Application performance, speed, data requirements, and equipment are also reviewed. We also discuss a future time-synchronized control solution.

Predicting the optimum routine test interval for protective relays

This paper discusses the goals of routine maintenance testing for protective relays. The paper advances a Markov probability model that predicts the optimum test interval for protective relays with and without self-testing capabilities. The model uses known system transition rates and relay failure rates. The probability model shows that the optimum test interval for a relay with self-tests is quite long. >

Real-Time Power System Control Using Synchrophasors

To date, synchronized phasor measurements have been used mainly for power system model validation, postevent analysis, real-time display, and other similar activities. However, synchrophasors have a greater potential than monitoring and visualization. Synchrophasors will increasingly contribute to the reliable and economical operation of power systems as real-time control and protection schemes become broadly used. Synchronous phasor measurements are now available in relays and meters; however, a practical means of processing the data in real time had been lacking. This paper describes a synchronous vector processor and several practical applications, including automated diagnostics, remedial action schemes, direct state measurement, and stability assessment.

Real-world synchrophasor solutions

Synchrophasors are no longer an academic curiosity. Today synchrophasors are providing solutions that otherwise would have been too expensive or too complicated to implement with traditional approaches. This paper examines ten synchrophasor applications being applied to monitor, visualize, and control electric power systems. 1. Voltage and current phasing verification 2. Substation voltage measurement refinement 3. SCADA verification and backup 4. Communications channel analysis 5. Wide-area frequency monitoring 6. Improved state estimation 7. Wide-area disturbance recording 8. Distributed generation control 9. Synchrophasor-assisted black start 10. Synchrophasor-based protection Included with each application is a description of the required equipment, communications channels, and data rates.

A new method for protection zone selection in microprocessor-based bus relays

Use of graph theory simplifies representation of complex bus arrangements in power system stations. This paper presents a new method, based upon graph theory, for selecting bus protection zones in microprocessor-based relays. We use a typical bus arrangement to illustrate the graphical representation of station arrangements, graph operations, and associated matrix operations. We also describe an implementation of the zone selection method and use two examples to demonstrate the advantages of the method. Using the status of switching devices in the station, the zone selection method provides the relay with real-time bus arrangement information. The bus relay uses this information to assign input currents to a differential protection zone and to select which breakers to trip for a bus fault or breaker failure.

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.

A fresh look at limits to the sensitivity of line protection

This paper considers the sensitivity of essential line protection elements: ground distance and ground directional overcurrent elements applied as time-coordinated functions or in pilot-assisted protection schemes and line current differential schemes. Factors discussed include fault resistance, line unbalance and charging currents, impact of in-line reactors, system short-circuit capacity, load encroachment and swings, sequential tripping and weak feed terminals, steady-state and transient errors of instrument transformers, impact of current transformers (CTs) in dual-breaker line terminals, and single-pole-open conditions. Protection element design improvements and application principles enhancing sensitivity are included.

Line protection: Redundancy, reliability, and affordability

In this paper, we apply fault tree analysis to compare the dependability and security of line protection schemes with different degrees of redundancy. We also compare the scheme costs. For each scheme, we use a basic protection scheme as the reference. We then evaluate schemes with double redundancy and two-out-of-three voting schemes. We also evaluate the effect of comprehensive commissioning testing, hidden failures, and common-mode failures, as well as using relays from the same or different manufacturers in redundant schemes.

Speed of line protection - can we break free of phasor limitations?

Todays relays are predominantly based on phasors, and as such, they incur a delay associated with the full-cycle observation window required for accurate phasor estimation. Considerable improvement in speed is possible by using information in the transients of voltages and currents. We review a number of protection techniques, including directional elements, direct tripping underreaching elements, and differential elements that significantly speed up line protection.