can we calculate, measure, predict the gics? how will the gics affect transformers? how will the...
TRANSCRIPT
GICs AND THEIR EFFECTS ON ELECTRIC GRIDSSEREN meeting, Edinburgh, March 2014
CT GauntUniversity of Cape Town
Assuming we know a CME is on its way: … what about the power network?
Can we calculate, measure, predict the GICs?
How will the GICs affect transformers?
How will the power network respond?
What could we have done to reduce damage?
What can we do next?
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Simplified GIC+ failure model
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Transformer real time risk estimate
Weather forecast
Historical line failure probability
Historical trfmr failure probability
Real time & alt. network topologies
LT network reliability probability analysis
Real-time trfmr condition, temp & measured load
Line load flows
Damage cost modelValue-at-risk
estimate
Planning decisions
Long term economic model
Customer interruption cost model
Capacitor & protection risk model
Switching mitigation options
Alt. network topologies
Line real time risk estimate
Operational failure probability analysis
Real time GIC measurement
Component failure model
Credibility test
Utility outage cost model
Real time GIC calc
System Operating Procedure
Two questions
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What are the characteristics of a GMD?
What will be the driving voltage of the GICs in the electricity network – the E field?
Where? – Varies with G. latitude
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How big?
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Projected 1-in-100-year E-field in Quebec: 10-50 V/km (10 sec data)
Experience of E-fields: 5-15 V/km
Order of magnitude reduction of E-field (1min) at mid-latitudes.
How big – at mid-latitudes?
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Expect past events (Quebec and Halloween storms) to have produced E-fields of 0.3-0.4 V/km at mid-latitudes (1 min data).
Consistent with measured GICs in S Africa.
Therefore – expect extreme event in Southern Africa to generate 3-4 V/km (1 min), and have effects similar to Quebec storm in North America?
Engineering problems
GIC in transformers: distorts magnetic flux, generates harmonics, increases ‘reactive power’, causes overheating, degrades insulation.
Power system failure: stability under non-active power variation.
Transformer condition monitoring: dissolved gas analysis and interpretation.
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Sa
S Qa
Q
QA P=SA
Mitigation options
Do nothing - High risk. Series caps in all lines – High cost; increases
transmission capacity, but risk of SSR. Replace all transformers and reactors with ‘robust’
designs – Unrealistic: time and cost Change earthing (grounding) of all transformers
and reactors – Protection, operations and cost impact.
Implement a temporary network configuration approach – Limited effect in extreme events.
Economic and social problems
What is the cost of an interruption?
What is the effect on society of a serious dislocation of power supplies?
Who or what provides the ‘cover’ for the damage of an extreme event?
Is a utility responsible for ‘externalities’?
Are costs of mitigation allowable under electricity regulation?
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Back to the GICs
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TSU
HMO
HBK
KMH
HER
TSU
KMHHBK
Measuring more
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Calculated from B-field
Measured 1-min values
NamPower 02 Oct 13
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Calculation, measurement, prediction
Calculation: Four Intermagnet observatories allow B-fields to be calculated with SECS.
Transformer neutral measurements: collaboration with Eskom and NamPower.
Additional MT and magnetometer measurements, but earth resistance mostly unknown.
ISSUES Data base standards, hosting, access. Adding value by analysis. Almost no operational prediction.
(in Southern Africa)
Characteristic disturbance models
How does the fringe of the auroral zone change? Network modelling taking into account the time
response of transformers to the change of ‘dc’ shows possibility of resonance … Is there a characteristic frequency of CMEs equivalent to wavelength 1 – 4 min?
Is there a characteristic direction or ‘turbulence’ of induced E-fields?
How accurate is the E-field modelling for distances of 50-300 km?
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What remains?
Examine GICs in context of risk.
Reduce uncertainty within models of GIC: ◦GMD prediction – onset, magnitude and end of
event ◦equivalent earth surface resistance model, ◦ transformer and system response under unusual
conditions.
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