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Bulletin S.R.A.C l a n December r u o J u a t décembre n e m e l p p u 1991 S / l a n r u o J Royal Astronomical Society of Canada e h t o t t n Volume 1 e m e l p p u Number 6 S BULLa SociétéL Royale d'AEstronomie dTu Canada IN Auroræ and the Power AURORA CURRENT To SUN System EASTWARD WESTWARD Joe Yurchesyn Senior Project Engineer 100,000 V Nova Scotia Power Corporation Halifax Centre North Pole On March 13th 1989, almost all of Québec’s power system was knocked out for about five hours, with some customers in the dark for close OUTGOING INCOMING to two days. The subsequent Québec Hydro CURRENT CURRENT press report, blaming the previous night’s au- rora, was met with a certain degree of scepti- cism by the general public. Believe it or not, our DIRECTION OF ROTATION modern power system is at risk from aurorae. The impact of geomagnetic storms on man- MAGNETOTAIL made systems has been chronicled for almost 150 years. It began with spontaneous electric Figure 1. currents being observed on telegraphs in 1846. The first occurrence of a geomagnetic storm The explanation begins with the Sun. A flow solar wind distorts the magnetic field of the Earth affecting a power system was on March 24th, of charged particles, called the solar wind, is and stretches it out as a long cylindrical shaped 1940, in New York City. continuously streaming away from the Sun. This structure pointing away from the Sun called the magnetotail. In so doing, the positive and nega- tive charged particles of the solar wind are AURORA CURRENT separated, with each type going to opposite MAGNETIC FIELD EFFECT sides of the magnetotail. Since opposite charges attract, these particles want to become "un- NORMAL POSITION EARTH'S MAGNETIC separated”. One path that they can follow to FIELD LINE OF MAG. FIELD LINE accomplish this is down the magnetic filed lines (ie. one of...) of the Earth to the upper atmosphere, and through two curved parallel paths to the oppo- site side of the Earth (and the magnetotail) and AURORA CURRENT then back up to outer space. See figure 1. The MAGNETIC FIELD high altitude part of this current causes the ~ 100 km aurora; the lowest part interaction (altitude ~100 km) affects the power system. EARTH MAGNETIC FIELD LINE DISPLACED BY AURORA Every electrical current has a magnetic field CURRENT MAGNETIC FIELD associated with it. The magnetic field of the auroral current interacts with, and distorts, the Earth’s magnetic field. See figure 2. The move- ment of the Earth’s magnetic field lines induces NORTH LOOKING EAST (at night...) Figure 2. (continued on page 2) R.A.S.C. BULLETIN S.R.A.C. - December/décembre 1991 - Page 1 Prices are per issue At the National Council meeting on May 17th, the Canadian advertisers must pay 7% G.S.T. extra following rates and conditions for advertisements Advertiser is to supply black and white copy two in the BULLETIN were approved. months prior to month of publication along with payment in full to the Society c/o the BULLETIN editor. BULLETIN Number of Insertions One copy of each issue of the BULLETIN contain- is a publication of the Royal Astronomical Society Width Height Size 1 to 3 4+ ing the ad will be mailed to the advertiser. of Canada and is distributed together with the 7.5 " 10.0 " 1 page $750 $600 The BULLETIN is mailed bi-monthly, along with the Society’s Journal. It contains articles on curreni Journal to about 4,000 members and subscribers 90% of 7.5 " 5.0 " 1/2 page $480 $375 activities of the Royal Astronomical Society of whom are in Canada. 5.0 " 7.5 " 1/2 page $480 $375 Canada and its Centres across Canada, as well as Classified ads will be charged at the rate of $1 per word 5.0 " 5.0 " 1/3 page $350 $250 articles from members and non-members which with a minimum charge of $20, subject to the same terms 2.5 " 5.0 " 1/6 page $250 $175 as above. are of general interest to members of the Society. Manuscripts (in English or French) should be sub- field. It will not work with DC electricity. Trans- of harmonic voltages. Harmonic voltages are mitted to the Editor at the address below. Inquiries formers normally carry two types of AC current: multiples of 60Hz (e.g. 120Hz, 180Hz, 240 Hz). about the Society should be directed to its National load current, and magnetizing current. The Harmonic voltages can cause misoperation of Office at 136 Dupont Street, Toronto, Ontario, Canada M5R 1V2. magnetizing current is very small (1% of load) relays in protection schemes resulting in errone- and maintains the internal magnetic field neces- ous tripping of healthy equipment. Editor: Patrick M. Kelly sary for the transformer to work. DC current is Harmonic voltages also greatly affect today’s Mailing Address: 2 Arvida Avenue, Halifax, Nova magnetizing current only, and for economic most modern high-tech power system device, Scotia, Canada B3R 1K6 reasons transformers are not designed for the the Static Var Compensator or SVC. SVC’s are E-mail Address: [email protected] FAX: (902) 423-6672 flow of DC current. Even a small DC current can very complicated control devices which raise cause a dramatic increase in the flow of AC and lower the system voltage at high speed to Editorial Staff: Diane Brooks, Harlan Creighton magnetizing current, perhaps more than the damp out oscillations in the power system. In so Rédacteur pour les Centres francais: Marc Gélinas, load current, and possibly more than the coils doing, SVC’s generate their own harmonic 11 Pierre-Ricard, N-D-lle-Perrôt, Québec, Canada are capable of carrying. The immediate result to voltages which are removed by filters. The nor- J7V 8M6 the transformer is the overheating of the internal mal level of system harmonics plus those pro- Printing: University of Toronto Press coils. Also, more magnetic flux is created than duced by the SVC determines the rating of the This publication is printed on recycled paper con- the core is capable of holding. This causes core filters. Abnormally high levels of system har- htaining 50% pre-consumer recycled paper and at heating plus the excess flux spills into places not monics will overload the filters, causing the SVC least 5% post-consumer de-inked fiber. normally designed to carry it, such as the steel to “trip off” when it is needed most. A trip at the Deadline for the February issue is Dec 15th. containment tank. This can cause sufficient wrong time can initiate a total system collapse, heating to blister the tank’s paint. A prolonged just what happened to Québec Hydro. Auroræ and the Power System flow of even a small amount of DC current can If SVC’s have such problems, then one is destroy a transformer. tempted to ask “Why are they used?”, and “Why (continued from page 1) In addition to problems caused for transform- are they so heavily depended upon?”. Well, ers, another problem is created in the power strangely enough, the answer lies not in engi- a voltage in the ground as if the ground was a system. For complicated reasons, the increase neering, but in economics. It is an example wire in a generator. This voltage is about 5 V/km. in magnetizing current flow causes the creation These voltages are direct current (DC), as op- (continued on page 7) posed to the alternating current (AC) delivered to your home. Long transmission lines are electrically (and ORIGIN OF GROUND INDUCED CURRENTS physically) connected to ground through trans- NORMAL POSITION formers. See figure 3 on page 2. The auroral OF MAG. FIELD LINE DIRECTION OF AURORA CURRENT FLOW induced ground voltage causes the ground at each transformer to have a different voltage. lt is as if a giant battery was connected between the DISPLACED MAG. FIELD LINE transformers. The transformer has a high resist- ance to the normal AC power frequency, but a very low resistance to this DC voltage. The GROUND INDUCED CURRENT / 3 result is a significant flow of DC current into the GIC GIC transformers. The magnitude of this current is IINDUCED GROUND VOLTAGE proportional to the resistance of the ground beneath the transformers. Québec Hydro’s trans- EARTH CURRENT formers, situated on the high resistance bed- WEST LOOKING NORTH rock of the Canadian Shield, are particularly susceptible to this type of current flow. RESISTANCE OF ELECT. EQUIP. Transformers have coils of wire wrapped RESISTANCE OF BEDROCK around an iron core which holds the magnetic R.A.S.C. BULLETIN S.R.A.C. - December/décembre 1991 - Page 2 The weather, while not perfect, was reason- 36 inch telescope to yourself for an hour? Much Alberta Star Party 1991 able. Afternoon thundershowers cleared off in later, John Dobson comes out to see what we’re Glen Hawley the evenings, only annoying us slightly with looking at. Someone at the eyepiece describes Calgary Centre some dewing problems. A large group of sun- NGC 6888, the Crescent Nebula, as a big egg. spots was slowly creeping out of sight around John scurries (and I mean scurries) up the The 1991 Alberta Star Party was a joint effort the limb of the Sun, but enough of them re- ladder to see for himself. After a moment, he of the Lethbridge Astronomy Club, and the Cal- mained to make a worthwhile view through solar announces definitively, “This is no hen’s egg - gary and Edmonton Centres of the Royal Astro- filters during the day.
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