W.A. Mittelstadt

Model validation for the August 10, 1996 WSCC system outage

A major power outage occurred in Western North America on August 10, 1996. In this paper, the authors describe the simulation of this disturbance using a transient stability program. Initially, the sequence of events was simulated using the standard WSCC dynamic database, and the simulations did not agree with the disturbance recordings. Several model additions and data modifications were made before the simulations approximated the disturbance recordings. These model changes are discussed in the paper.

Electromechanical Mode Online Estimation Using Regularized Robust RLS Methods

This paper proposes a regularized robust recursive least squares (R3LS) method for online estimation of power-system electromechanical modes based on synchronized phasor measurement unit (PMU) data. The proposed method utilizes an autoregressive moving average exogenous (ARMAX) model to account for typical measurement data, which includes low-level pseudo-random probing, ambient, and ringdown data. A robust objective function is utilized to reduce the negative influence from nontypical data, which include outliers and missing data. A dynamic regularization method is introduced to help include a priori knowledge about the system and reduce the influence of under-determined problems. Based on a 17-machine simulation model, it is shown through the Monte Carlo method that the proposed R3LS method can estimate and track electromechanical modes by effectively using combined typical and nontypical measurement data.

Use of the WECC WAMS in Wide-Area Probing Tests for Validation of System Performance and Modeling

During 2005 and 2006, the western electricity coordinating council (WECC) performed three major tests of western system dynamics. These tests used a wide-area measurement system (WAMS) based primarily on phasor measurement units (PMUs) to determine response to events including the insertion of the 1400-MW Chief Joseph braking resistor, probing signals, and ambient events. Test security was reinforced through real-time analysis of wide-area effects, and high-quality data provided dynamic profiles for interarea modes across the entire western interconnection. The tests established that low-level optimized pseudo-random plusmn20 -MW probing with the pacific DC intertie (PDCI) roughly doubles the apparent noise that is natural to the power system, providing sharp dynamic information with negligible interference to system operations. Such probing is an effective alternative to use of the 1400-MW Chief Joseph dynamic brake, and it is under consideration as a standard means for assessing dynamic security.

Operating Experience with Modulation of the Pacific HVDC Intertie

Implementation and operating experience with a control system which modulates power on the Pacific HVDC Intertie to damp oscillations on the parallel Pacific AC Intertie is described. This system significantly improves the damping of the Western interconnected power system, which has had a long history of periods of negatively damped oscillations. The successful operation of dc modulation was a key factor in permitting an increase in the rating of the Pacific AC Intertie from 2100 MW to 2500 MW. This uprating results in large economic and energy conservation benefits.

Small-signal modulation of the Pacific HVDC intertie

Recent undamped oscillations in the Western U.S. power system have indicated the need to improve system damping. The development of a control algorithm for small-signal modulation of the Pacific HVDC Intertie is described. The control signal which would be applied to the current regulator at the sending end of the dc intertie is based on rate of change of ac-intertie power. Results from simulation studies are presented which show that modulation will produce considerable damping.

An EMTP study of SSR mitigation using the thyristor controlled series capacitor

This paper presents an EMTP (Electro-Magnetic Transient Program) simulation study of the subsynchronous resonance (SSR) mitigation effect of thyristor controlled series VAr compensation (TCSC) operated in the vernier mode, based on a simplified model of the North-Western American Power System (NWAPS). The study shows that TCSC vernier operation provides significant mitigation of SSR in some cases. An analysis of the equivalent TCSC impedance with respect to different frequencies is used to supplement these studies. >

A study of TCSC optimal damping control parameters for different operating conditions

This paper illustrates the use of a cost function or performance measure to carry out a sensitivity analysis on the Slatt Thyristor Controlled Series Capacitor (TCSC). The sensitivity analysis performed revealed that a choice of controller parameters for optimal system damping are dependent upon the system loading level and configuration. This result suggests that by tuning the control parameters of the TCSC controller for the various system conditions encountered on the power system a significant improvement in system damping may be obtained.

Modulation and SSR tests performed on the BPA 500 kV thyristor controlled series capacitor unit at Slatt substation

Field experience is reported for a thyristor controlled series capacitor (TCSC) recently commissioned at BPAs Slatt substation. Subsynchronous resonance tests show that TCSC interactions with shaft dynamics of PGEs Boardman steam generator are well understood and are effectively avoided by normal TCSC valve firing logic. Modulation tests, performed with the Boardman plant offline, show that the TCSC can be a powerful and responsive actuator for swing damping. Security considerations did not permit lightly damped operation of the controlled plant. Close analysis indicates that the TCSC damping contribution, though small, was measurable. The best estimate is that damping for the McNary mode is 7.33% and 8.55%, for the TCSC damper loop open and closed respectively. TCSC testing and monitoring is facilitated by an advanced interactive measurement network representing BPAs approach to the information requirements of major control systems.

Hopf bifurcations in a SMIB power system with SSR

This paper presents a Hopf bifurcation analysis for a single-machine infinite-bus (SMIB) power system experiencing subsynchronous resonance (SSR) by applying a Hopf bifurcation theorem combined with numerically solution of the Monodromy matrices. A Hopf bifurcation in the power system is predicted, together with stable periodic orbits.

Probing Signal Design for Power System Identification

This paper investigates the design of effective input signals for low-level probing of power systems. In 2005, 2006, and 2008 the Western Electricity Coordinating Council (WECC) conducted four large-scale system-wide tests of the western interconnected power system where probing signals were injected by modulating the control signal at the Celilo end of the Pacific DC intertie. A major objective of these tests is the accurate estimation of the inter-area electromechanical modes. A key aspect of any such test is the design of an effective probing signal that leads to measured outputs rich in information about the modes. This paper specifically studies low-level probing signal design for power-system identification. The paper describes the design methodology and the advantages of this new probing signal which was successfully applied during these tests. This probing input is a multi-sine signal with its frequency content focused in the range of the inter-area modes. The period of the signal is over 2 min providing high-frequency resolution. Up to 15 cycles of the signal are injected resulting in a processing gain of 15. The resulting system response is studied in the time and frequency domains. Because of the new probing signal characteristics, these results show significant improvement in the output SNR compared to previous tests.