ieee pes/ias joint chapter meeting geomagnetic disturbance ... · 7/22/2015 · 3 – phase, 3 –...

IEEE PES/IAS Joint Chapter July Technical Presentation MeetingBasics of solar phenomena & How transformers react and handle events

July 22, 2015

Copyright © ABB Inc. 2015All rights reserved. Any reproduction – in whole or in part –is forbidden without ABB’s prior written consent. 1

Topic and abstractGeomagnetic disturbances

Events associated with GMD have been known and studied in power systems since the 1960’s.

Early events pre dating the AC power have been recorded to the 1850’s.

This technical meeting of the joint Maine Chapter of the IEEE PES/IAS will educate attendees on:

Basics of solar phenomena

How transformers are impacted and react to GMD events

GMD impact on the power system

Impacts of GMD in Maine

Mitigation technologies

IEEE PES/IAS Joint Chapter MeetingGeomagnetic disturbance impact on transformers and the power grid

Craig L Stiegemeier; Transformer Remanufacturing & Engineering Services; July 22, 2015

© ABB Group


July 22, 2015


Geomagnetic disturbance impact on transformers and the power gridTopics reviewed

Geomagnetic disturbances (GMD) and mechanism of generation of geomagnetically induced currents (GIC)

Effects of GIC on power transformers

Recent significant GMD events

Effects of GIC on power systems

Developing a plan

Evaluating the GIC capability of a power transformer

Fleet assessment of GIC susceptibility

Grid resiliency / mitigation

© ABB Group July 22, 2015 | Slide 3

Mechanism Of Generation Of GIC – GeomagneticallyInduced Currents



July 22, 2015


Geomagnetic disturbance (GMD)

Strong solar flare activities => Sends plasma beams to earth

Changes the magnetic field of Earth => GMD

By NASA


Source: NASA

Solar cycle by sun Sunspot count

Occurs on an average of 11 year cycle (prediction is still difficult)

Reported: Worst recorded in 1859, called “Carrington Event”

Reports of strong GMD in 1921



July 22, 2015


Detection/prediction of solar storms


© ABB Inc. 2015 - Slide 8

Movies should be screened in the grey area as featured here, size proportion 4:3. No titles should be used.


July 22, 2015


Mechanism of generation of GIC

Change of earth’s magnetic field => Voltage in transmission circuits

Transmission line / Power transformers / Ground

Fraction of a volt to several volts / km

Ground currents flow into neutrals of power transformers

Magnitude of GIC in a transmission circuit is a function of:

Magnitude & orientation of GMD, location on earth, proximity to large bodies of water, resistance of the soil, and direction / height / length of the transmission line

Highest for > 500 kV Transmission

K – Scale


GIC Effects on Power Transformers Factors that determine the magnitude of GIC

Affected location on Earth is dependent on location & timing of the sun activity

A significant Sun-spot activity may, or may not, mean high GIC in a particular location on Earth

Magnitude of GIC is a function of location on earth, resistance of the soil, direction, height, and length of the transmission lines

500 kV and 765 kV transmission lines travelling long distances are the most susceptible to higher levels of GIC

Based on above, only specific power grids or parts of a power grid would be susceptible to high levels of GIC



July 22, 2015


History of recent significant GMD events

March 13, 1989: Highest recorded GIC level in recent history for North America

Short duration peaks of 80 – 100 Amperes / phase in GSU’s at PSE&G’s Salem Generating station


Effect of DC on Power Transformers



July 22, 2015


DC flux density shift in transformer cores

Flux Density vs Phase angle (20 Ampd DC)

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

-90 -60 -30 0 30 60 90 120 150 180 210 240 270 300 330 360

Phase Angle, Degrees

Flu

x D

ensity,

Tes

la

Bm, AC

Bm, (AC+DC)

DC flux = N I DC / R


Time I

B

Time

DC Shift

AC + DC

ImAC+DC

AC

ImAC

Non – linearity of the core material

limits core from fully saturating

DC causes part – cycle saturation of the core



July 22, 2015


% Exciting Current - 1 phase transformer - 20 Amps DC

0%

5%

10%

15%

20%

25%

30%

35%

40%

-90 -60 -30 0 30 60 90 120 150 180 210 240 270

Degrees

Ex

citi

ng

cu

rren

t, %

of

Lo

ad

Cu

ure

nt

High – Peak pulse

One per Cycle

Small mean – width

1/8th – 1/12th of Cycle

RMS = 15 – 20 % of peak

Magnetizing current pulse caused by DC/ GIC


% Imag of 1 – phase Transformer under effect of DC

Per Phase Currents



July 22, 2015


VAR consumption vs. magnitude of GIC

0

2

4

6

8

10

12

14

16

18

0 25 50 75 100 125 150 175 200

% F

unda

men

tal M

VAR

GIC, Amps/Phase

Fundamental Inductive MVAR Drawn by Transformer vs GIC


Utilities should use this data to plan their VAR resources during GMD events

VAR consumption vs. magnitude of GIC (2)


0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250 300 350 400

% M

VA R

atin

g

GIC, Amps/Phase



July 22, 2015


0%

1%

2%

3%

4%

5%

6%

60 120 180 240 300 360 420 480 540 600 660

% H

arm

on

ic A

mp

litu

de

(% o

f R

ated

Lo

ad C

urr

ent)

Harmonic Frequency, Hz

Harmonic Spectrum of Magnetizing Current under different levels of GICs

Idc = 25 Amps/Phase

Idc = 50 Amps/Phase

Current harmonics associated with DC / GIC


Utilities use this data to optimize protection during GMD events

GIC Effects on Power TransformersDC flux path in different core types

Core / Shell Form, 1 phase

Core Form, 3 phase, 3 limbCore Form, 3 phase, 5 limb

Shell Form, 3 phase, conventional

Shell Form, 3 phase, 7 limb

3 – Phase, 3 – Limb cores require much higher magnitudes of DC to saturate

compared to all other core types

Other core types are basically equivalent, other design factors are more relevant© ABB Group July 22, 2015 | Slide 20


July 22, 2015


Transformer core types – core form

3-phase, 3 limb

3-phase, 5 limb


Transformer core types – core form


1-phase, 3 limb

1-phase, 4 limb


July 22, 2015


GIC Effects on Power Transformers Modelling of transformer cores with DC

3 – phase, 3 – limb Cores: DC return flux through air & tank

All other Core – Types: DC flux flows within core

T a n k

C o n s i d e re d D C F l u x

F c c 1F c c 2

F c w t o p

F c w b o t

F a F w

F c b 1 F c b 2

C o r e

F c

F t b

F t c

Ls

LhLFw

BwHw

FsBsHs

Fy = FsBy = BsHy = Hs

FmBmHm

outerloop

innerloop

only 1/2considered

Due to Symmetry only1/2 of the core is considered

Lm

I+

I-

I+

I-

3 – phase, 3 – limb core 1 – phase, 4 – limb core

Considered AC + DC flux


Effect of DC/GIC on core loss and core noise

Increase in core loss / noise level is significant even at low levels of DC

Noise increases in level and also in frequency content

Typically, 120 / 240 / 360 / 480 Hz => Much higher > 480 Hz

GIC (A/Phase)

Core Loss Increase

Core Noise level Increase

(dB)

15 29.0% 29.6

20 31.5% 31.2

30 35.3% 33.7

40 38.1% 35.4

50 40.4% 36.9

100 48.2% 41.6

200 56.9% 46.7



July 22, 2015


A high magnitude pulse of magnetizing current

High magnitude of leakage flux, rich in harmonics

Higher I2 R and eddy current losses in windings & structural parts

Increase is low because of low RMS value

Some of the core flux flows outside the core

Causing higher windings, tie – plates, and tank losses

Core saturation => significant change in leakage flux pattern

=> High winding circulating currents in some designs

Thermal effects of DC


Winding Hot Spot Temperature vs Time, 1-Phase Transformer

108

110

112

114

116

118

120

122

124

0 5 10 15 20 25 30Time, Minutes

Wd

g H

ot

Sp

ot

Tem

pt,

Deg

ree

C

Idc = 50 Amps

Idc = 30 Amps

Idc = 20 Amps

Effect of DC on winding hot–spot temperature



July 22, 2015


Effect Of GIC On Power Transformers


-40

-30

-20

-10

0

10

20

30

40

50

GIC

, Am

psA

DC

Low / moderate magnitudes of GIC sustained for several hours;

interrupted by short – duration / high –peak pulses

7 hr signature of GIC

Signature / profile of GIC



July 22, 2015


Winding Hot Spot Temperature vs Time, 1-Phase Transformer

108

110

112

114

116

118

120

122

124

0 5 10 15 20 25 30Time, Minutes

Wdg H

ot S

pot Tem

pt, D

egre

e C

Idc = 50 Amps

Idc = 30 Amps

Idc = 20 Amps

Effect of GIC on winding hot spot temperature

Actual temperature rise is much lower for the short duration of high GIC peaks

For a 2 – minute duration: Rise is 3, 4, and 6 C for GIC of 20, 30, and 50 Amps


GIC Effects on Power Transformers Injection of 75 Amps DC into 370 MVA and 550 MVA, 735 kV, 1 phase transformers, by IREQ



July 22, 2015


• Temperature rises in structural parts & tank are moderate even after applying 75 A DC (75 times the Excitation Current) for an hour

• No damage resulted in either transformer

GIC Effects on Power TransformersInjection of 75 Amps DC into 370 MVA and 550 MVA, 735 kV, 1 phase transformers, by IREQ


GIC Effects on Power TransformersCharacteristics of GIC

A base current of several Amps or 10s of Amps

High magnitudes of peak GIC of short duration (1-2 minutes)

Fig 4.8 in Meta-R-319 Report by J. Kappenman



July 22, 2015


GIC Effects on Power TransformersPer phase GIC wave-form used for thermal calculations

400 Amps 400 AmpsIdc

20 Amps 20 Amps 20 Amps

(0,0)30 2 30 2 30 Time, Minutes


GIC Effects on Power TransformersWinding hot spot rise due to GIC in a single-phase transformer

Winding Hot Spot Temperature vs Time

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70 80

Time, Minutes

Win

din

g H

ot

Sp

ot

Tem

pt,

Deg

ree C

1° C rise due to 20 Amps

35° C rise in the 2-minute duration of the GIC pulse

Drops back to original temperature in 4 minutes

Duration of Temperature pulse is too short to cause winding damage

Temperatures & durations << allowed by IEEE for emergency overload

Same is true for structural parts of the transformer



July 22, 2015


GIC Effects on Power TransformersMeasured Temperature rises in windings & structural parts due to DC

1 – phase at HQ, 75 Amps DC for 20 minutes

3 – phase, 5 limb at FINGRID using 50, 100, 150, 200 Amps DC for intervals of 30 minutes each

Tokyo Elec., Toshiba, Hitachi, and Mitsubishi, tested large models of core form and Shell form transformers with DC equivalent to 400 – 600 Amps / phase for full size transformers for 30 – 120 minutes.

Measured from 30° – 110° C temp rises in mainly structural parts

No damage observed in windings or major insulation

Again, because of its short duration, GIC would cause much lower temperature rises and no insulation damage / loss of life


History of Recent Significant GMD Events



July 22, 2015


History of recent significant GMD events March 13, 1989

Base GIC of 20 Amps / phase interrupted by short duration pulses of 80 Amps / phase in GSU’s at PSE&G’s Salem and Hope Creek generating stations

Significant overheating of series LV connection of an old shell-form transformer caused by high circulating currents

Transformer taken out of service a week later because of significant gassing

Less overheating of others of same design transformers in the area with continued operation

Some gassing / tank paint discoloration of a number of transformers in northeast of USA

An 8 hr. blackout of the HQ system

Due to tripping of Capacitor banks / SVC’s; causing system instability

High VAR demand initiated response


History of recent significant GMD events2003-2004

Sweden / Oct. 31, 2003

Report of very strong GMD storm; 3 phase / 5 limb / 400 kV transformers were subjected to 330 Amps GIC in the neutral

20 min. black out / system instability caused by tripping of 130 kV line

Low level gassing in the transformers; indicating Minor overheating

S. Africa: Nov.’03 – June ‘04

A few transformers had significant winding damage

Moderate levels of GIC

Coincided with winding failures caused by Copper Sulphide



July 22, 2015


Evaluation of Susceptibility of A Fleet of Power Transformers to Effects Of GIC


Evaluation of total susceptibility of transformersto effects of GIC

To determine which transformers:

Are susceptible to damaging overheating

Are susceptible to core saturation and only moderate overheating

Have low level of susceptibility to either effects of GIC

Are not susceptible to effects of GIC

Total susceptibility to effects of GIC is determined by:

Transformer design – based susceptibility

GIC level – based susceptibility



July 22, 2015


Results of GIC susceptibility study on large power transformer fleet > 500 kV


Orange: Susceptible to both core saturation and possible damaging winding and/or structural parts overheating

Yellow: Susceptible to core saturation and only moderate overheatingGreen: Low susceptibility to both core saturation and overheating

Blue: Not susceptible to core saturation or overheating

Benefit of fleet GIC susceptibility evaluation

Allows utilities to focus their mitigation / studies efforts

For transformers identified to be susceptible to core saturation

Utilities could request manufacturers to provide data on the additional VAR consumption and current harmonics as a function of the level of GIC the transformer would be exposed to

For transformers identified to be susceptible to possible damaging overheating

Utilities could request manufacturers to provide data on the thermal Capability of these transformers



July 22, 2015


Evaluation of GIC Capability of Transformer Designs


Approach / Definition

Combinations of load current and GIC current for which the hot spot temperatures of neither the Windings nor structural parts would exceed certain temperature limits

To limit loss of life of solid insulation

Avoid formation of gas bubbles

45



July 22, 2015


Approach / Temperature Limits46

For low / moderate level Base GIC, the hot – spot temperature limits

recommended by IEEE / IEC loading Guides to be used for long duration

overloading of transformers, are used

Windings: 140 ºC Structural parts: 160 ºC (IEC & IEEE)

For high – peak, short – duration GIC pulses, the hot – spot temperature limits

recommended by IEEE / IEC Loading Guides to be used for short – duration

Emergency overloading of transformers (< 30 minutes), are used

Windings: 160 ºC Structural parts: 180 ºC (IEC)

Windings: 180 ºC Structural parts: 200 ºC (IEEE)


GIC capability of a large 1 – phase transformer



July 22, 2015


Transformer designs susceptible to damaging windings overheating are those where core saturation changes the leakage flux pattern

This change in the flux pattern results in very high levels of winding circulating currents

The PSE&G Salem transformer is an example of one of these designs

GIC fleet assessment studies help utilities identify transformers that require magnetic & thermal evaluations; reducing risk of blackouts and possible thermal issues in some old design transformers

For many technical reasons, DC testing of power transformers in the factory is of little benefit and little relevance to actual operating conditions and is also unnecessary

Also, DC testing of transformers on the power Grid for partial verification of some calculations may be okay, but the cost is very high and the test would be performed at no load

GIC impact on power transformersSummary


Because of the nature of GIC signature, the majority of large power transformers would not fail thermally, even under high GIC levels

Therefore, months / years of blackouts (as predicted by some,) is not realistic

The effect of the increased VAR consumption & current harmonics on the power system, and its components, is the most significant consequence of GIC

This is even more true for high levels of GIC

It is important to evaluate this effect

GIC impact on power transformersSummary



July 22, 2015


Grid GIC studiesTopics

Simplified analysis

VAR consumption due to GIC and effects

Voltage and reactive power control

Transformer saturation and harmonics effects

FERC required GIC studies


Simplified analysis

Increased transformer VAR can be expressed as:

Q = I2 X

Voltage drop along a line:

∆V = I Xline

Power transfer:

PMax =V1 V2 Sin(δ12) / Xline

As Q , I , ∆V , V1 and / or V2 and Pmax

Thus, stability may become a concern



July 22, 2015


VAR consumption vs. magnitude of GIC

0

2

4

6

8

10

12

14

16

18

0 25 50 75 100 125 150 175 200

% F

unda

men

tal M

VAR

GIC, Amps/Phase

Fundamental Inductive MVAR Drawn by Transformer vs GIC



Examples of voltage instability caused by imbalanced VAR support

New York Power Pool September 22, 1970

French system December 19, 1978

Florida system December 28,1982

Northern Belgium August 4, 1982

Swedish system December 27, 1983

Southern Florida 1985

Japanese system July 23, 1987

Western France 1987

Hydro Quebec blackout (GIC) March 13, 1989

Southern Finland August 1992

Western Systems Coordinating Council (WSCC) Region 1996



July 22, 2015


Reactive Power in the News(New York Times, Sept. 26, 2003)

“Experts now think that on Aug. 14, northern Ohio had a

severe shortage of reactive power, which ultimately caused the power plant and transmission line failures that set the

blackout in motion.

Demand for reactive power was unusually highbecause of a large volume of long-distancetransmissions streaming through Ohio to areas,including Canada, than needed to import powerto meet local demand. But the supply ofreactive power was low because some plantswere out of service and, possibly, becauseother plants were not producing enough of it.”

NERC - Minutes Board of Trustees (February 23, 2012)

I.9 Conclusions

“The most likely worst‐case system impacts resulting from a low probability GMD event and corresponding

GIC flow in the bulk power system is voltage instability caused by a significant loss of reactive power support simultaneous to a dramatic increase in reactive power

demand.

The lack of sufficient reactive power support was a primary contributor of the 1989 Hydro

Québec GMD induced blackout.

During the geomagnetic disturbance, seven static SVC’s tripped off‐line within 59 seconds of each other, leading to voltage collapse of the system 25 seconds

later.”

Voltage instability Examples


Voltage and reactive power control

Requires the coordination work of transmission and distribution disciplines. Typical needs are to:

Forecast the reactive demand and required reserve margin.

Plan, engineer, and install the required type and location of reactive support.

Maintain reactive devices for proper compensation.

Recommend the proper load shedding scheme, if necessary.

Provide and maintain monitors to ensure accurate data.



July 22, 2015


Typical voltage control devices

Shunt capacitors

Series capacitors

Shunt reactors

Synchronous condensers

SVC (static var compensator )

STATCOM (Static Synchronous Compensators)


0%

1%

2%

3%

4%

5%

6%

60 120 180 240 300 360 420 480 540 600 660

% H

arm

on

ic A

mp

litu

de

(% o

f R

ated

Lo

ad C

urr

ent)

Harmonic Frequency, Hz

Harmonic Spectrum of Magnetizing Current under different levels of GICs

Idc = 25 Amps/Phase

Idc = 50 Amps/Phase

Current harmonics associated with DC / GIC



July 22, 2015


Magnetizing current harmonics vs. magnitude of GIC

Amplitude of harmonics in % of Rated Current

0

1

2

3

4

5

6

7

8

9

5 10 15 20 25 30 35 40 45 50

GIC - Amps/Phase

% A

mplitu

de

of H

arm

onic

sFirst Harmonic Second Harmonic

Third Harmonic Fourth Harmonic

Fifth Harmonic Sixth Harmonic

Seventh Harmonic Eighth Harmonic

Nineth Harmonic Tenth Harmonic

Eleventh Harmonic

Utilities use this data to study effect on their power system equipment


Possible harmonics effects on power systems

Possible amplification of harmonic levels resulting from series or parallel resonances. Might damage equipment.

Increase equipment losses and thus the thermal stress.

Interfere with protective relays;

Capacitor bank and SVC tripping may occur.

The 2nd order harmonic could cause transformer differential relay miss- operation.

The 3rd order harmonic may cause some line differential relay miss- operation.

Generator overheating and tripping may occur.

Interference with metering devices, control and communication circuits, and with sensitive electronic equipment.

Increase in equipment noise and vibration.



July 22, 2015


March 13, 1989 blackout of the Hydro‐Québec (HQ) system initiated

from tripping of seven

SVC’s.

The tripping occurred due to GIC saturation of transformers which

caused large components of 2nd, 3rd

and 4th harmonics in voltages and currents at the SVC locations.

October 30, 2003 Sweden blackout was initiated by GIC saturation of large power transformers which resulted in

large amount of harmonics.

The 3rd harmonics content caused tripping of a 130 kV line which

cascaded into the blackout.

Harmonics effectsExamples


FERC REQUIREDGIC STUDIES AND ANALYSIS



July 22, 2015


FERC Order 779

In May 2013, FERC issued Order 779 which directs NERC to submit reliability standards that address the impact of GMD on the reliable operation of the bulk-power system

Stage 1 – operating procedures

Stage 2 – detailed assessments (planning studies)

Standards project 2013-03 (GMD mitigation) began in June 2013


TPL – 007 summary

Requires a GMD Vulnerability Assessment of the system

for its ability to withstand a benchmark GMD event without

causing a wide area blackout, voltage collapse, or damage

to transformers, once every five years. Applicability:

Planning Coordinators, Transmission Planners

Requires a Transformer thermal impact assessment to

ensure that all high-side, wye grounded transformers

connected at 200kV or higher will not overheat based on

the Benchmark GMD Event. Applicability: Generator

Owners, Transmission Owners



July 22, 2015


Screening criterion, recommended by NERC, for Thermal Assessment of Power Transformers

Originally > 15 Amps / phase for reference GMD storm

Upon technical input from 5 major transformer manufacturers, it

was recently changed to > 75 Amps / phase


GIC effects



July 22, 2015


Studies needed for GIC concerns

Geo-electric field determination

DC system modeling

GIC calculation

Calculation of transformer reactive power absorption and harmonics

Planning type studies with added reactive power absorption, considering contingencies.

Conduct harmonics studies and determine the effects

Identify limit violations and system issues

Conduct thermal assessment of a portion of transformer fleet

Determine mitigations and study their effects


Available means of mitigation

Alerting

Monitoring / measurements

Simulations and evaluation of risk

Increasing robustness of network

Increasing robustness of protection

Proper operating procedures during a storm

Installation of appropriate GIC blocking devices if needed and feasible



July 22, 2015


Geomagnetic disturbance impact on transformers and the power gridSummary

The specific transformer design influences the impact of GMD/GIC events on a given transformer

Only a small number of transformers are vulnerable to significant overheating when subjected to high levels of GIC

All types of transformers place demands on the grid in terms of magnetizing current and reactive power demand, as well as the generation of harmonics

The most significant impact of GIC is its effect on the stability of the power grid


ieee pes/ias joint chapter meeting geomagnetic disturbance ... · 7/22/2015 · 3 – phase, 3 –...

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