United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-42: Failure of Electrical Power Equipment Due to Solar Magnetic Disturbances

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                                June 19, 1990


Information Notice No. 90-42:  FAILURE OF ELECTRICAL POWER EQUIPMENT DUE 
                                   TO SOLAR MAGNETIC DISTURBANCES


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is intended to alert addressees to possible failure 
modes of electrical power equipment in nuclear power plants and the 
connected transmission systems due to solar magnetic disturbances.  The 
events described herein may be precursors to station blackout or partial 
loss of offsite power sequences.  It is expected that recipients will review 
the information for applicability to their facilities and consider actions, 
as appropriate, to avoid similar problems.  However, suggestions contained 
in this information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances:

On March 13, 1989, an exceptionally strong geomagnetic storm caused major 
damage to electrical power equipment in Canada, Scandinavia, and the United 
States.  The greatest damage occurred in Canada, where the Hydro-Quebec 
extra high voltage (EHV) transmission system experienced seven static 
compensator trips, causing system instability and tripping of lines carrying 
power to Montreal from hydroelectric generating facilities at James Bay.  
Automatic load-shedding was not able to offset the loss, and within a few 
seconds, frequency and voltage excursions occurred throughout the rest of 
the system resulting in total blackout of the Hydro-Quebec system.

In the United States, a voltage fluctuation of up to 4 percent was recorded 
on the EHV systems in Pennsylvania, New Jersey, and Maryland.  In the 
Allegheny Power System, this storm caused 10 of the 24 transmission class 
capacitor installations to trip and eight EHV autotransformers to heat.

Specific events occurred at the Three Mile Island Unit 1, Hope Creek Unit 1, 
and Salem Unit 1 nuclear power plants.  At Three Mile Island 1, the licensee 
observed tripping of capacitor banks in the 500-kilovolt substation.  At 
Hope Creek 1, the licensee observed swings in reactive electrical power and 
six operations of the main generator negative sequence alarm, indicating 



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                                                            IN 90-42
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electrical faults or power imbalances that could damage equipment.  At Salem 
1, the licensee observed swings in reactive electrical power and, in a 
subsequent inspection of the generator step-up transformer, the licensee 
observed severe overheating, melted low-voltage service connections in 
phases A and C, and insulation discoloration in phase B.  

On September 19, 1989, at the Salem Unit 2 nuclear power plant, a second 
solar storm damaged the generator step-up transformer. 

Discussion:

Solar flares and other solar phenomena radiate waves of ions, electrons, and 
protons called the solar wind.  The solar wind interacts with the earth's 
ionosphere and magnetic field in a complex manner to produce auroral 
currents near the earth.  The auroral currents induce an earth-surface 
potential (ESP) that establishes geomagnetically induced currents (GICs) in 
electrical power distribution systems through the neutral grounding points 
of wye-connected transformers at the ends of high-voltage transmission 
lines.

The GICs are quasi-direct currents, compared to the usual alternating 
current frequency of 60 hertz.  Measured values of GICs in transformer 
neutral grounding points have exceeded 100 amperes.  Such currents can 
distort current transformer responses and undesirably trip protective 
relays.  Further, GIC can cause magnetic saturation of transformer cores.  
Depending on the extent of saturation, these GICs may initiate excessive 
reactive, eddy, and harmonic currents.  Excessive reactive current can 
overheat transformers and produce excessive voltage drops in a transmission 
system.  Core saturation with harmonic currents can cause localized heating 
in transformer steel members, winding conductors, and leads.  Excessive 
harmonic currents in transmission lines can cause system voltage 
distortions, which can overload capacitors in the transmission system and 
trip their protective devices, causing further voltage degradations.

In general, solar magnetic disturbances follow an 11-year cycle.  In the 
present cycle, these disturbances exhibited minimum activity in September 
1986 and are expected to peak in 1990-91 and in 1993-94.  Some researchers 
in the field of solar activity expect this present cycle to be the strongest 
yet recorded.  If these predictions are accurate, these peaks may produce 
equipment damage, loss of electrical power, and problems with voltage 
control in transmission systems connected to nuclear power plants. 

Several organizations are actively studying the effects of solar magnetic 
disturbances and ways to mitigate these effects.  In particular, the 
Institute of Electrical and Electronics Engineers (IEEE) has established a 
working group that convened a group of experts to discuss these phenomena in 
July 1989 ("Effects of Solar-Geomagnetic Disturbances on Power Systems,"  
Special Panel Session Report, IEEE/PES Summer Meeting, July 12, 1989, Long 
Beach, California).  A copy of this report is available in the NRC Public 
Document Room, 2120 L Street, N.W., Washington, DC. 
.

                                                            IN 90-42
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This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please call one 
of the technical contacts listed below or the appropriate NRR project 
manager.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation


Technical Contacts:  Vern Hodge, NRR
                     (301) 492-1861

                     Subinoy Mazumdar, AEOD
                     (301) 492-4308

Attachment:  List of Recently Issued NRC Information Notices 
.ENDEND
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