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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