effect of geomagnetically induced currents on … of geomagnetically induced currents on protection...

Effect of Geomagnetically Induced Currents on Protection Systems

Sture Lindahl2004-01-23

Industrial Electrical Engineering and [email protected]

Sture Lindahl, LTH/IEA 2

Effect of GIC on Protective RelaysActivity of the Sun

Propagation of the Solar Wind

Magnetospheric Processes

Ionospheric Processes

Earth Surface Potential

Geomagnetically Induced Currents

Saturation of Power Transformers

Performance of Protective Relays


Solar Flare Effects


Geomagnetically Induced Currents

GICGIC

Earth Surface Potential Gradient-+

GIC

Electrojet

GIC


Conclusions

• The risk is that protective relays operate unwantedly during a geomagnetic storm and causes a severe power system disturbance or even a nationwide blackout

• A less obvious risk is that the current transformers operates so far into saturation that the secondary current is too low for proper operation of the protection equipment at internal faults during geomagnetic storms.


Protective Relays at Risk

• The most important class of relays is the non-directional low set residual overcurrent relays commonly applied on– shunt capacitors,– power transformers,– shunt reactors, and– transmission lines


Shunt Capacitors

• International operational experience shows very clearly that low-set residual overcurrent relays for shunt capacitors with directly earthed neutral point are very vulnerable.

• So far, protective relays for shunt capacitors is Sweden have not maloperated during geomagnetic storms.

• It is recommended that the setting and the harmonic restraint of the (1) residual overcurrent and(2) neutral-point overcurrent relay are reviewed and tested.


Power Transformers

• Security of transformer protection• There are some protective relays for power

transformers that should be reviewed and tested. The candidates are:– (1) the low-set residual overcurrent relay,– (2) the low-set neutral-point overcurrent relay, and– (3) the restricted earth-fault relay.

• The same holds true for similar protective relays applied on directly earthed shunt reactors.


Power Transformers

• Dependability of transformer protection• Are the power transformers sufficiently

protected in case of GIC?• Power transformers and shunt reactors

are in general equipped with mechanical and thermal fault detectors.

• These fault detectors operate independently of the instrument transformers and may keep up the dependability


Transformer Damage


400- 220- and 130-kV Power Lines

• Operational experience shows that the low-set residual overcurrent relays are vulnerable to GICs.

• In 1986, all such relays on the 400- and 220-kV network were replaced by modern dependent time overcurrent relays with logarithmic characteristic and second harmonic restraint.

• There are, however, a number of residual over-current relays applied on power lines that have inadequate performance.


Residual Overcurrent Relays

• Future low-set residual overcurrent relays should preferably just measure the fundamental frequency component of the current.

• How to justify that the dependent time residual overcurrent relay must operate at 150 Hz? (SNDR-requirement)

• It should also be possible to restrain the relay not only from the second harmonic but also from other harmonics.


GIC Disturbance 2003-11-20

• 400-kV Hemsjö-Karlshamnsverket with the HVDC converter for SwePo Link

• 400 MW import from Poland interrupted• The residual overcurrent dependent

time relay operated unexpectedly.



Recordings Hemsjö 2003-11-20

0

50

100

150

200

0 500 1000 1500 2000 2500 3000

Time [ms]

Cu

rren

t [A

]

RMS(Ires) RMS(3I0)



Recordings Hemsjö 2003-11-20, Harm(3I0)

0.006 0.004

0.144

0.0050.004

0.120

0.0050.002

0.004

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

Fund 2nd 3rd 4th 5th 6th 7th 8th 9th

Rel

ativ

e M

agn

itu

de



Recordings Hemsjö 2003-11-20, Harm(Ires)

0.013

0.002

0.140

0.003 0.003

0.134

0.003 0.0030.004

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1


Rel

ativ

e M

agn

itu

de



Recordings Hemsjö 2003-11-20 (3i0)

-1000

-500

0

500

1000

260 280 300 320 340 360

Time [ms]

Cu

rren

t [A

]



Recordings Hemsjö 2003-11-20, ires

-1000

-500

0

500

1000

260 280 300 320 340 360

Time [ms]

Cu

rren

t [A

]



Recordings Hemsjö 2003-11-20, Harm(Ures)

0.0010.001

0.021

0.001 0.001

0.059

0.002

0.0040.003

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1


Rel

ativ

e M

agn

itu

de



Recordings Hemsjö 2003-11-20, ures

-400

-200

0

200

400

260 280 300 320 340 360

Time [ms]

Vo

ltag

e [k

V]



• The relay operation is caused by the 3rd

and 6th harmonic current and not by the fundamental frequency current

• The stabilising 2nd harmonic in the residual current is very low

• SNDR has requested that the residual current dependent time relay must operate for the 3rd harmonic


Three-Phase System Model (Ch 5)

AC Source

DC Source

Transformer Load ShuntCapacitor


Magnetising Inductance

Relative Incremental Magnetising Inductance

-0.5

0.0

0.5

1.0

1.5

-20 -10 0 10 20

(Magnetising Current)/Is

Mag

net

isin

g In

du

ctan

ce

Saturated Region Saturated Region

Non-Saturated Region


Magnetising Inductance

Incremental Magnetising Reactance

0

25

50

75

100

125

-10 -5 0 5 10

Relative Magnetising Current

Mag

net

isin

g R

eact

ance

ms= 6 ms= 10 ms= 14


Analytical or Dynamic Simulation

RMS-Value of Magnetising Current

0

100

200

300

400

500

0 50 100 150 200 250

(DC Current)/Is

(RM

S-V

alu

e)/Is



Peak-Value of Magnetising Current

0

100

200

300

400

500

0 50 100 150 200 250

(DC Current)/Is

(Pea

k-V

alu

e)/Is



Fundamental Frequency Current

0

100

200

300

400

500

0 50 100 150 200 250

(DC Current)/Is

(Fu

nd

amen

tal)

/Is



Second Harmonic Current

-40

-20

0

20

40

60

0 50 100 150 200 250

(DC Current)/Is

(Sec

on

d H

arm

on

ic)/

Is



Third Harmonic Current

-40

-20

0

20

40

60

0 50 100 150 200 250

(DC Current)/Is

(Th

ird

Har

mo

nic

)/Is



• Both methods give similar results• Saturating power transformers cause a

reduction of the busbar voltage• Saturating power transformers cause

both even and odd harmonics (k=1 to 9)• Higher order harmonics not accurate• The analytical method gives upper limit


Busbar Voltages (Ch 7)

Busbar Voltage

400

405

410

415

420

0 10 20 30 40 50 60

(Direct Current per Phase)/Is

Vo

ltag

e [k

V]


Busbar Voltages

Total Harmonic Distortion

0

1

2

3

4

5

0 10 20 30 40 50 60


TH

D [

%]


Busbar Voltages

Magnitude and Phase Angle of Second Harmonic

0.00

0.01

0.02

0.03

0.04

0.0 6.0 11.9 17.8 23.8 29.7 35.6 41.6 47.5 53.5 59.4


Mag

nit

ud

e V

2/V

1

-180

-90

0

90

180

An

gle

[d

egre

es]

Magnitude Phase Angle


Busbar Voltages

Magnitude and Phase Angle of Third Harmonic

0.00

0.01

0.02

0.03

0.04

0.0 6.0 11.9 17.8 23.8 29.7 35.6 41.6 47.5 53.5 59.4


Mag

nit

ud

e V

3/V

1

-180

-90

0

90

180

An

gle

[d

egre

es]



Busbar Voltages

• Saturating transformers cause harmonic distortion of the busbar voltages

• Busbar voltage drops by about 3%• Total harmonic distortion is about 3%• Individual harmonics is lower than 3%



Recordings Hemsjö 2003-11-20, Harm(Ures)

0.0010.001

0.021

0.001 0.001

0.059

0.002

0.0040.003

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1


Rel

ativ

e M

agn

itu

de


Earthed Shunt Capacitors (Ch 9)

Phase Currents at 200 Mvar (Idc/Is=5.94)

-600

-400

-200

0

200

400

600

0 20 40 60 80 100

Time [ms]

Cu

rren

t [A

]

Phase a Phase b Phase c


Earthed Shunt Capacitors

Total Harmonic Distortion of the Phase Currents

0

5

10

15

20

0 10 20 30 40 50 60


TH

D [

%]




0.00

0.05

0.10

0.15

0.20

0.0 6.0 11.9 17.8 23.8 29.7 35.6 41.6 47.5 53.5 59.4


Mag

nit

ud

e I3

/I1

-180

-90

0

90

180

An

gle

[d

egre

es]




Magnitude and Phase Angle of 6th Harmonic

0.00

0.05

0.10

0.15

0.20

0.0 6.0 11.9 17.8 23.8 29.7 35.6 41.6 47.5 53.5 59.4


Mag

nit

ud

e I6

/I1

-180

-90

0

90

180

An

gle

[d

egre

es]




RMS-value of Residual Current

0.0

0.1

0.2

0.3

0.4

0.5

0 10 20 30 40 50 60


(Res

idu

al C

urr

ent)

/In



Magnitude and Phase Angle of Second Harmonic

0.00

0.01

0.02

0.03

0.04

0.0 5.9 11.9 17.8 23.7 29.7 35.6 41.5 47.5 53.4 59.3


I2/In

-180

-90

0

90

180

An

gle

[d

egre

es]





0.0

0.1

0.2

0.3

0.4

0.0 5.9 11.9 17.8 23.7 29.7 35.6 41.5 47.5 53.4 59.3


I3/In

-180

-90

0

90

180

An

gle

[d

egre

es]




Magnitude and Phase Angle of 6th Harmonic

0.0

0.1

0.2

0.3

0.4

0.0 5.9 11.9 17.8 23.7 29.7 35.6 41.5 47.5 53.4 59.3


I6/In

-180

-90

0

90

180

An

gle

[d

egre

es]




• The fundamental frequency phase current decreases because of the busbar voltage

• The total harmonic distortion in the phase current is higher than 10%

• The 3rd harmonic of the phase current is higher than 6% of the phase current while the 6th harmonic is higher than 10%

• The RMS value of the residual current is about 40% while the 6th harmonic is higher than 20%.


Current Transformers (Ch 12)

pi′pi

:pn snI I :1

si

sΨ

Lλ wR bL

bRse


Instrument Transformers (Ch 10)

• How to determine the B-H characteristic from the V-I characteristic?


Experimental Data

Magnetising Curve

10

100

1000

10000

0.1 1.0 10.0 100.0 1000.0

I [mA]

U [

V]

U [V]


Instrument Transformers

RMS Characteristics of a Saturating CT

0.0

0.5

1.0

1.5

2.0

0 2 4 6 8 10 12

Current [pu]

Vo

ltag

e [p

u]

Sinusoidal Current Sinusoidal Voltage


Instrument Transformers

• It seems reasonable to use the RMS value of the magnetising current at the knee point and use that value to determine when the magnetising inductance drops from the non-saturated value to the saturated value


Current Transformers

Harmonic Content of Secondary Current

0

500

1000

1500

2000

2500

100 200 500 1000 1500 2500

Magnitude of Direct Current, IDC [A]

Am

plit

ud

e [A

]

Fundamental 2nd 3rd 4th 5th 6th


Future Work

• Requirements on the dependent time residual overcurrent relay for power lines and power transformers

• Protection for earthed shunt capacitors• How to protect power transformers

against GIC?

effect of geomagnetically induced currents on … of geomagnetically induced currents on protection...

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