Léonard Bolduc

GIC observations and studies in the Hydro-Québec power system

Abstract On March 13, 1989, at 7 h 45 UT, Hydro-Quebec experienced a complete black-out of its system due to a severe geomagnetic storm. Consequently, service was interrupted for many hours and overvoltages resulting from line openings cost 6.5 M

Study of the acceptable DC current limit in core-form power transformers

in material damages alone among a total of 13.2 M

Development of a DC current-blocking device for transformer neutrals

. In 1991, geomagnetically induced currents (GIC) produced some effects and damages on the Radisson–Sandy Pond HVDC link. On March 24, at 21 h 55 UT, GIC larger than 110 A were measured in one of two transformers in parallel (presumably, giving a total of 220 A) at Radisson substation which led to the loss of the HVDC link. The same thing happened on October 28, but this time with material damages to equipment. From these events, short-term studies led to the upgrading of operational processes, modifications of opening thresholds of Static Var Compensators and modifications of some filters at Radisson. Also an agreement was concluded with Geological Survey of Canada (GSC) for sending a warning alert to the Network Control Centre (CCR) before any anticipated severe geomagnetic storms. Among more long-term studies, in collaboration with GSC, we have installed 5 acquisition substations along a 250-km long copper telephone line in Abitibi, a site typical of Hydro-Quebec facilities, and from 1992 to 1994 measured ground voltages and magnetic fields every 10 s . The highest ground voltage measured at Louvicourt substation was ∼1.70 V/km for 20 s . Asymmetry measurement of line voltages, based on techniques developed at IREQ in the 1980s, have been upgraded, the number of installations has been increased (from 4 to 8) and functions like harmonic measurement have been added. Voltage asymmetries over a fixed threshold produce an alarm at the CCR, which reacts by taking security measures in network operation. During March 1989 and 1991 events, voltage asymmetry grew to 9.6% and 15.5%, respectively, at the Arnaud substation. A major change, for needs of network stability during short circuit or other contingencies, has been the installation of series compensation in 1996 into the Hydro-Quebec 735-kV network. Since capacitors block DC current, the observed asymmetry has remained about 20% of that observed before. So, now, we are confident that our network would survive the anticipated worst case GIC.

Saturation time of transformers under dc excitation

The temperature rise in power transformers subjected to a DC source of excitation was measured on core-form single-phase 735 kV autotransformers rated 370 MVA and 550 MVA. The measurements were compared to the temperature rise values obtained on the same transformers operating in overexcitation at 1.95 T. The results show that the tie plates of this particular type of transformer are the components most susceptible to rapid temperature rise. Smaller-scale tests on 100 kVA transformers were performed to take a specific look at these tie plates under the effect of a temperature increase. Finite-element simulations combined with analytical studies of temperature rise were performed in an attempt to determine a tolerable DC current limit based on permissible temperature standards.

A study of geoelectromagnetic disturbances in Quebec. II. Detailed analysis of a large event

In the early 1990s, Hydro-Que/spl acute/bec undertook a joint project with GE to develop and commission a dc current-blocking series capacitor for the transmission lines forming part of its main power system in the area surrounding the grounding electrode of the Radisson HVdc substation. The aim of this project was to minimize the harmful effects of dc current flowing through the main network during the ground-return operating mode of the Radisson-Sandy Pond multiterminal HVdc link. With a view to having available technology applicable anywhere in the network, TransE/spl acute/nergie and IREQ, two divisions of Hydro-Que/spl acute/bec, later took part in the development of a dc current-blocking device that could be installed in transformer neutrals. This work was undertaken not only with immediate needs in mind but also to solve specific problems that could appear sporadically at different network locations. Tests on a prototype of the new blocking device were performed in the High Power Laboratory at IREQ, followed by tests on the preproduction unit, in accordance with the specified requirements. The neutral dc current-blocking device (NCBD) was then installed at a regional substation for a one-year operating period to verify its immunity under normal network events and switching conditions. During this period, no disruption to the smooth operation of the substation or protection of the ac system occurred. The NCBD operated correctly and suffered no fault or unsolicited operation.

Capacitive divider substation

Abstract This paper studies the saturation time of transformers under the effect of a dc voltage bias. An approximation formula developed in an earlier project has been honed and validated. Comparison with EMTP simulation results allowing the stages of development of the saturation process over time to be reproduced bears witness to the capability of this formula. Different cases studied in order to describe the saturation phenomenon by dc excitation, show how the formula is applied and point out its limitations. It is stressed that the saturation time on the power system can be very long (in the order of 1 min or more), when the dc voltage applied to the magnetizing inductance is very low. The presence of low-resistance windings connected in delta can substantially increase the transformer saturation time. The flow of dc current is not necessarily an indication that a transformer has reached saturation.

No-load losses in transformer under overexcitation/inrush-current conditions: tests and a new model

For pt. I see ibid., vol.13, p.1251-6 (1998). As part of investigations of geomagnetically induced currents in the Hydro-Quebec power system, the geoelectromagnetic field was recorded at five sites in western Quebec in 1992 to 1994. A description of the measurements and some general results are presented in an accompanying paper. This paper concentrates on an analysis of a disturbance on February 21, 1994, that produced one of the largest electric fields recorded. The magnetic recordings are used to determine the intensity, location, and orientation of the auroral electrojet that is the cause of the disturbance. By tracking these parameters we show that dB/dt is due to both the changing intensity of the electrojet and due to movement of the electrojet. The resulting electric fields are found to be anti-parallel (parallel) to the electrojet when the magnetic field is increasing (decreasing).

IVACE: A self-regulating variable Reactor

The development of a passive damper-filter has made it possible to achieve a stable capacitive-coupling substation (SCC). This paper presents the underlying theory and analyzes the impact of the SCC on a power network system. The related nuisance phenomena (overvoltage, ferroresonance) are described together with the solutions applied. Test results are presented as proof that the nuisance phenomena have been satisfactorily eliminated: overvoltage is adequately limited at the worst node by protecting the equipment and ferroresonance never lasts more than two cycles. Lastly, the paper describes Hydro-Quebecs first such capacitive-coupling substation installed at Riviere Ste-Anne (Quebec).

Mitigation of Ferroresonance Induced by Single-Phase Opening of a Three-Phase Transformer Feeder

Tests were conducted on several transformers rated at 100 kVA or less and on a power transformer rated 370 MVA in an effort to characterize the no-load losses and magnetizing resistance for transformers subjected to overexcitation and inrush current. Analysis of the results revealed that the magnetizing resistance changes as a function of the peak magnetization flux or the amplitude of the magnetic field. A new model of the instantaneous magnetizing resistance (IMR) as a function of the instantaneous flux has been developed and its dynamic use in the Electromagnetic Transients Program (EMTP) allows the form of the hysteresis cycle and the mean losses in overexcitation to be reproduced with a high degree of accuracy. The same model also accounts for losses due to the harmonics superimposed on the fundamental. The results showed that the IMR calculated under inrush current conditions is higher than that in overexcitation conditions.

Study of the apparent load loss unbalance in three-phase transformers

Inductance Variable Auto-Controle/spl acute/e a/spl grave/ Entrefers (IVACE) is a self-regulating variable reactor consisting essentially of passive components: magnetic cores with air gaps, four windings, and a diode bridge rectifier. Originally designed for use as a static var compensator, it is now used by Hydro-Que/spl acute/bec near its 735-kV transmission lines as a new voltage regulator for the overhead-ground-wire supply system for the utilitys microwave stations in remote areas.