Global Geomagnetic Storm Induced Failure of 400 Mega-HVAC Transformers is Avoidable by Redundant HVAC Transformer Arrays
- or -
A Current and Voltage Division Method to Reduce Mega-HVAC Transformer Failures by Redundant Transformer Arrays




Abstract

During severe solar storms HVAC transformers used by utilities of dimensional size similar to a medium sized house are subject to catastrophic failure. As these transformers have very long commissioning and repair schedules their failure poses a catastrophic risk. Large parts of grids that depend on their existence of these AC transformers can be rendered non-functioning when the mega transformers fail. This catastrophe can be avoided by using simple voltage division and current division principals implemented in the form of redundant arrays of smaller HVAC transformers.


Electric power is modern society's cornerstone technology on which virtually all other infrastructures and services depend. Yet HVAC power grids are particularly vulnerable to space weather events.

Ground currents induced during geomagnetic storms can create excess currents in the electrical grid. These excess unregulated currents have the power to melt the copper windings of electrically stressed transformers at the core of many mains power distribution systems.

Sprawling power lines in essence act like VLF antennas. The grid's distribution network picks up the induced currents created by the solar storm and absorbs them [at full energy] into the power grid.

Mechanisms
A time-varying magnetic field external to the Earth induces electric currents in the conducting ground.

These currents create a secondary (internal) magnetic field.

As a consequence of Faraday "Law of Induction" electric fields aligned along the surface of the Earth are induced in association with the time variations of the magnetic field. The surface electric field causes electrical currents that are known as Geomagnetically Induced Currents (GICs) to flow into any conducting structure.

This GIC induced electric field (typically measured in V/km) acts as a voltage source across networks.

Examples of Geomagnetically Induced Current conducting networks are

GICs are often described as being 'quasi Direct Current' (DC) although the variation frequency of GIC is governed by the local time variations of the Earth's electric field. Geomagnetically Induced Currents in the systems that conduct them are more like DC bias currents.  For GICs to be a hazard to technology, the current flows have to be of a magnitude and frequency that makes electrical equipment susceptible to either immediate or cumulative damage.

The size of the GIC in any network is governed by the electrical properties and the topology of the network. The largest (magnetospheric) ionospheric current variations, resulting in the largest external magnetic field variations typically occur during geomagnetic storms. Geomagnetic storms by their nature create the largest GICs.

Significant temporal variation in GICs is known to range from from a few seconds to about an hour.

Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s.

GICs of tens to hundreds of Amperes have been recorded outside the Polar regions. GICs have also been recorded at mid-latitudes during major geomagnetic storms with nearly the same magnitude as the GICs in Polar regions. However, GICs are not a problem exclusive to the mid-latitudes or the Arctic.

There is still a substantial GIC risk to low latitude areas (the tropics). When a geomagnetic storm commences suddenly -- a high, short-period rate of change of the Earth's magnetic field will occur on the dayside of the Earth. This sudden induction event will induce high current GICs into the tropic regions. These events are typically short lived, but pose a threat to the power supply systems in the tropics.

The problem
According to a study by Metatech corporation, a geomagnetic storm with a strength comparative to that of 1921 would result in at least 130 million people without electrical power and 350 broken HVAC transformers. The overall cost of restoring the grid to its original functionality and the economic damage caused by the disruption would be around 2 Trillion Dollars (2 000 000 000 000 USD).

Power distribution grids are not designed to absorb large scale geomagnetically induced currents as part of their normal day to day operation.

Modern electric power transmission systems consist of generating plants interconnected by electrical circuits that operate at fixed transmission voltages controlled at substations. The grid voltages employed are largely dependent on the path length between these substations. Typically 200kV to 700kV system voltages are common.

There is a trend towards higher voltages and lower line resistances to reduce transmission losses over longer and longer path lengths. Low line resistances produce a situation favourable to the flow of GICs.

Power transformers typically have a magnetic circuit that is disrupted by the quasi-DC GIC: the field produced by the GIC offsets the operating point of the magnetic circuit and the transformer may go into half-cycle saturation. This produces harmonics to the AC waveform, localized heating and leads to high reactive power demands, inefficient power transmission and possible failure or abnormal operation of protective devices.

Balancing the electrical network in such situations requires significant additional reactive power capacity.

The magnitude of GIC that will cause significant problems to transformers varies with transformer type. Modern industry practice is to specify GIC tolerance levels on new transformers.

There are some partial solutions for coping with geomagnetically induced currents, typically involving grounding the electrical grid at
It must be noted that most electrical utilities often fail to fully implement these recommendations.

GIC risk can, to some extent, be reduced by capacitor blocking systems, maintenance schedule changes, additional on-demand generating capacity, and ultimately the policy of load shedding.

These options are expensive and sometimes impractical.

The continued growth of high voltage power networks results in a higher risk for all users. This is partly due to the increase in the interconnectedness at higher voltages; connections in terms of power transmission to grids in the auroral zone, and grids operating closer to capacity than in the past.

To understand the flow of GICs in power grids and to advise on GIC risk analysis of the quasi-DC properties of the grid is necessary. This analysis must be coupled with a geophysical model of the Earth that provides the driving surface electric field, determined by combining time-varying ionospheric source fields and a conductivity model of the Earth.

This kind of analysis has been performed for North America, the UK and in Northern Europe. The complexity of power grids, the source ionospheric current systems and the 3D ground conductivity make an accurate analysis difficult but not computationally impractical. By being able to analyze major storms and their consequences it is possible to build a picture of the weak spots in a transmission system and run hypothetical event scenarios.

The perils of interconnection
From the 1990s into the present day US utilities have joined grids together to allow long-distance transmission of low-cost power to areas of sudden demand. Canada is also part of this North American electrical grid network, a fact often lost in the technical literature. Canada is even more susceptible to  coupled Winter storm + Geomagnetic storm conditions. In Canada, substantial loss of life is possible due to a grid failure's direct effects. In the US the secondary effects of grid failure will lead to larger per capita loss of life than Canada via primary effects.

As it were : on a hot summer day in California, for instance, people in Los Angeles might be running their air conditioners on power routed from Oregon. This may make short term economic sense -- but not necessarily geomagnetic sense. Grid interconnectedness makes the power distribution network susceptible to wide-ranging "cascade failures."

The problem

These power grid failure problems are totally 'man made' and are 'design induced problems' with several different and notable causes

Tentative recommendations for making power grids survive severe solar storms

General system recommendations and practices

Specific system recommendations and practices, typical transformer redundancy mode of 7

Operation modes

Redundant Transformer Array State Machine Operating Modes

Operation Modes (Notes)

Why the above recommendations will work, or the electrical engineering laws we know so well

Recommendations for Australia, Canada & New Zealand

Recommendations for the European Union

US HVAC distribution network, regions of possible
        failure


Definitions

Technical references

Physics
Specific Solar Storm Events
Electrical Engineering
Circuit Analysis
Power Grid Issues
Power Outage Issues




map of suspect US grid HVAC transformers




Created by
Original Idea
Created
Last Modified Version
Revision State


Max Power
15 May 2006
24 October 2009
22 May 2014 (readability, content)
0.87a
Revisable