03_Technical_Background.pdf

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Energy Sector – E T HP AR © Siemens AG 2010

SurgeSurge arrester arrester

TechnicalTechnical backgroundbackgroundEnergy Sector E T HP AR



Page 2

© Siemens AG 2010

March 10 Energy Sector / E T HP AR

Basics

Recommended Installation-Points

generally at transitions overhead line - cable

generally at the entrance of overhead lines into a station usually in the HV-bushing area of transformers

in isolated cases additionally at GIS or busbar

usually in parallel to shunt reactors

usually in parallel to reactors within HV filter circuits

overheadline

G

tower portal Surgearrester

cable GIS

trans-former

GIS cable generator



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© Siemens AG 2010


Basics

Fundamentals of Insulation Coordination

Time duration of (over-)voltage

Possible voltages without arresters

Voltages limited by arresters

Withstand voltage of equipment

Lightning overvoltages

(Microseconds)Switching overvoltages

(Milliseconds)

Temporary overvoltages

(Seconds)

Highest system voltage

(Continuously)

M a g n i t u d e o f ( o v e r - ) v o l t a g e

/ p . u

.

1

2

3

4

0

5



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© Siemens AG 2010


Continuous operating voltage (Uc/MCOV)

Rated voltage (Ur )

Rated frequency

Short circuit current

Line discharge class (LD-Class)

Nominal discharge current (In) (8/20 µs)

Protection level (= residual voltage at In)

Additional: residual voltages for different

current shapes and amplitudes

Basics

Characteristic Values (1): Main Data



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© Siemens AG 2010


Long duration current impulse withstand capability(amplitude, time)

Energy absorption capability (in kJ/kV of Ur or Uc)

High current impulse capability (4/10 µs)

Temporary overvoltage (TOV) capability (1 s, 10 s, 100 s)

Creepage distance

Dielectric withstand values of the housing

Permissible mechanical headloads (static, dynamic)

Basics

Characteristic Values (2): Additional Data



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© Siemens AG 2010


MO ResistorsManufacturing Process (1)

Delivery of raw materials

Release of raw materials

Weighing

Milling/Mixing

≈90% ZnO

≈ 10% additives

1...5 tons



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© Siemens AG 2010


Granulating(Spray drying)

Release of granulate

Pressing

Check of:• V-I-Characteristics• Power loss• Long duration current capability




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© Siemens AG 2010


I3.5 V

100 μA

MicrovaristorZincoxide grain

10 ... 50 μm

Decarbonizing

δ ≈1200 °CVolume reduction ≈40%

Sintering




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© Siemens AG 2010


Coating with glass paste

Metallization

Electrical tests

Grinding

Sample tests:• V-I-Characteristics• Long duration current capability• Accelerated aging• High current impulse

Routine tests:• Residual voltage (U10kA)• Power loss at Uc (P0)• Long duration current test




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© Siemens AG 2010


Marking

Visual inspectionand packing

2

SIEMENS

18230

P 64 13.21 LE70SR133

Long duration currenttest (2 ms) passed

Manufacturer's name

Type

Lot number

Power loss (10-2 W)

Residual voltage (kV)and classification

To:PTD H 4Berlin

1PP70572X14230L0007




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© Siemens AG 2010


Basics

Voltage-Current-Characteristic

Example: Us = 420 kV

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

10-4

10-2

102 10

41

Nominal discharge current = 10 kA

P e a k v a l u e o f v o l t a g e / k V

Peak value of current / A

Peak value of phase-to-earth voltage: √2·Us /√3 = 343 kV

Leakage current ≈ 100 µA

10-kA residual voltage = lightning impulse protective level = 806 kV

F a c t o r

2 . 4

8 orders of magnitude



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© Siemens AG 2010


0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

0.1 1 10 100 1000

t / s

k T O V

( = p .

u . o f U r )

preheating to 60 °C and max. prior energy

preheating to 40 °C and no prior energy

BasicsPower-frequency versus Time (u/t-) Characteristic



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© Siemens AG 2010


General

0

200

400

600

800

1000

1200

1400

1600

1800

0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6

U/Umittel

H [ m m ]

H= 1200 mm

H= 1465 mm

H= 1805 mm

⇒ Grading rings necessary forarrester heights > 1.5 m ... 2 m

BasicsVoltage Distribution along Arrester Stack (1)



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© Siemens AG 2010


Arrester Ur = 224 kV, Voltage Distribution, Equivalent Circuit

U/Umean

H e i g h t [ m m ]

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

0,7 0,8 0,9 1 1,1 1,2 1,3

BasicsVoltage Distribution along Arrester Stack (2)



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© Siemens AG 2010


Lightning Strikes

Direct Strike into Overhead Line Conductors

Direct lightning strikes to the line conductor can only develop within the blue area.

Example: he = 50 m ⇒ I ≈ 17 kA

CIGRÉ electro-geometrical model

The maximum possible discharge currentcan be estimated by the followingequation:

I in kAhe in m

0.65

8

hI e=



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© Siemens AG 2010


Lightning Strikes

Propagation on a Transmission Line1 2 3 4 5 6 7

1st insulator: flashover (Example: flashover voltage ≈1500 ... 2000 kV for Um = 420 kV)

Lightning stroke: two travelling waves of û = ½ ·Z · î (Example: û = ½ · 350 Ω · 20 kA = 3.5 MV)

Travelling wave: 1st peak = flashover voltage,

2nd peak depending on earthing resistance

2nd insulator: flashover if 2nd peak > flashover voltage

Travelling wave: 1st and 2nd peak = flashover voltage,3rd peak dep. on earthing resistance

Remaining surge passes the following insulators

1

2

3

4

5

6 7



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© Siemens AG 2010


LI currents in the substation usually below 10 kA

No direct lightning strikes of discharge currents higher than ≈ 20 kAon shielded transmission lines (all other strikes will hit the shield wireor directly the ground)

Currents limited by flashover voltage of line insulatorsand surge impedance of the line:

î = ûflashover /Z

Examples:

Um = 123 kV, ûflashover ≈ 600 kV, Z = 450 Ω î = 1.3 kA

Um = 420 kV, ûflashover ≈ 2,000 kV, Z = 350 Ω î = 5.7 kA

Lightning Strikes

Lightning Impulse Current Stress of Station Arresters



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© Siemens AG 2010


Protection Characteristics

Protection Level

4 m

T r av elling w av e ef f ec t s

3 . 5

m

2 . 5

m

Inductivity of

current path

≈1 µH/m(here: L = 10 µH)

Currentsabove In

Voltage at terminalsof equipment to be

protected higher thanprotection level of arrester

Recommendation:

Protection level ≤ BIL/1.4



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© Siemens AG 2010



Protective Zone (1)Due to travelling wave effects on the line the protection of the equipmentby an arrester can be guaranteed only for short distances betweenarrester and equipment.

Simplified estimation of the protective zone *):xs protective zone [m]

BIL basic insulation level [kV]

Ures protection level of the arrester [kV]

s front steepness of the overvoltage [kV/µs](in the range of 1000 kV/µs)

vtw propagation speed of travelling wave:- 300 m/µs (overhead line) (equals "c")- 200 m/µs (cable)

(BIL / 1,15) - Ures

2·s· v

tw

xs =

Example 1: Distribution network, Um = 24 kV, insulated neutral, arrester of Ur = 30 kV:

(125 / 1,15) - 80

2·1000· 300 m = 4.3 mxs =

Example 2: Transmission network, Um = 420 kV, effectively earthed, arrester of Ur = 336 kV:

(1425 / 1,15) - 806

2·1000 · 300 m = 65 mxs =

*) For more detailed information see IEC 60099-5, IEC 60071-1 and IEC 60071-2



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© Siemens AG 2010


Assumptions:• overvoltage surge as a voltage ramp

1000 kV/μs (1 kV/ns)• arrester limits voltage to 80 kV at its terminals

a) Distance arrester - transformer:1,5 m (propagation time 5 ns)

b) Distance arrester - transformer:3 m (propagation time 10 ns)

0

10

20

30

40

50

60

7080

90

100

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

t [ns]

u [ k V ]

Voltage at arrester

Voltage at transformer

0

10

20

30

40

50

60

7080

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120

t [ns]

u [ k V ]

Voltage at arrester

Voltage at transformer


Protective Zone (2)



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© Siemens AG 2010



Protective Zone (3)

Switchgear and cable

Transformer

In case of doubt: verification of protection effect by calculation

Example 1600 kV

tower no. 2 13 gantry

200 kA

30 kA

G

G

150 m

OHL / cable

600 m

OHL / cable

0

100

200

300

400

500

600

700

800

900

1000

switchgear cabletransformer

kV

10 µs 20 µs 30 µs

BBBIIILLL / / /SSS

BBBIIILLL / / /SSS



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© Siemens AG 2010


Specific inductance of surge current path ≈ 1 µH/m

Case 1: Porcelain housed arrester Um = 420 kV

Ur = 360 kV

u10kA, 8/20 µs = 864 kV

u10kA, 1/2 µs = 916 kV

Length of surge current path ≈ 10 m

⇒ Inductance of surge current path ≈ 10 µHSteepness of surge current impulse ≈ 10 kA/µs

3 . 5 m

4 m

2 . 5 m

Additional inductive voltage drop ≈ 100 kV


Increase of Protection Voltage by Inductive Voltage Drops (1)



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© Siemens AG 2010


Case 2: Metal enclosed GIS arrester Um = 420 kV

2 . 5 m

Ur = 360 kVu10kA, 8/20 µs = 864 kV

u10kA, 1/2 µs = 916 kV

Length of surge current path ≈ 2.5 mSpecific inductance of surge current path ≈ 0.3 µH/m

⇒ Inductance of surge current path ≈ 0.75 µH

Steepness of surge current impulse ≈ 10 kA/µs

⇒ Additional inductive voltage drop ≈ 7.5 kV


Increase of Protection Voltage by Inductive Voltage Drops (2)



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© Siemens AG 2010


Energy Absorption Capability

Characteristic Values

Two aims:

Mechanical integrity of the MO blocks

Thermal stability

Line discharge class (acc. to IEC 60099-4)

Long duration current withstand capability (acc. to IEC 60099-4)

Thermal energy absorption capability (not defined in IEC 60099-4)

Impulse energy absorption capability (not defined in IEC 60099-4)

Main Parameters:



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© Siemens AG 2010


Energy Absorption CapabilityLine Discharge Class (IEC 60099-4, Cl. 7.4.2)

Arrester classification

Linedischarge

class

Surgeimpedance of

the line Z

(Ω)

Virtualduration

of peak T

(μs)

Chargingvoltage U L

(kV d.c.)

10 000 A

10 000 A

10 000 A

20 000 A

20 000 A

1

2

3

4

5

4.9 U r

2.4 U r

1.3 U r

0.8 U r

0.5 U r

2 000

2 000

2 400

2 800

3 200

3.2 U r

3.2 U r

2.8 U r

2.6 U r

2.4 U r

Example:

A MO arrester with resistors of 4 kJ/kV (2 · 2 kJ/kV) energyabsorption capability may be

specified as a Class 2 arrester if Ures/Ur = 2, but as a Class 3arrester if Ures/Ur = 2.4



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© Siemens AG 2010



Energy Ratings acc. to IEC Line Discharge Classes

LDclass

Siemenstype

MO dia.mm

Ures /Ur E/Ur kJ/kVUr

(per impulse)

E/Ur kJ/kVUr

(total)

E/Uc kJ/kVUc

(per impulse)

E/Uc kJ/kVUc

(total) 1 3Exx xxx-1..1 48 2.01 1 2 1.25 2.5

2 3Exx xxx-1..2 48 2.13 1.9 3.8 2.38 4.75

3 3Exx xxx-2..3 58 1.91 3 6 3.75 7.5

4 3Exx xxx-3..4 70 1.94 4.4 8.8 5.5 11.0

5 3Exx xxx-4..5 78 1.86 6.5 13 8.13 16.26

5 3Exx xxx-5..5 100 1.87 6.5 13 8.13 16.26

Note: U r /U c = 1.25

Energy per impulse (6 groups of 3 imp.)

Total energy injected by 2 impulses + thermal recovery



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© Siemens AG 2010



Energy Ratings of Siemens Arresters

LDclass

Siemenstype

MO dia.mm

E/Ur

kJ/kVUr

(single impulse)

E/Ur

kJ/kVUr

(thermal)

E/Uc

kJ/kVUc

(single impulse)

E/Uc

kJ/kVUc

(thermal)

1 3Exx xxx-1..1 48 2,5 3,5 3,125 4,375

2 3Exx xxx-1..2 48 2,6 5,0 3,25 6,25

3 3Exx xxx-2..3 58 4,0 8,0 5,0 10,0

4 3Exx xxx-3..4 70 5,6 10,0 7,0 12,5

5 3Exx xxx-4..5 78 7,8 13,0 9,75 16,25

5 3Exx xxx-5..5 100 11,5 18,0 14,375 22,5

Note: U r /U c = 1,25

Injected by long duration current 4 ms

Injected by 2 impulses during operating duty test



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© Siemens AG 2010


Um

kV1 p.u. =

kVk û

kVC'

µF/kml

kmCµF

EkJ

min. MCOVkV

E/MCOVkJ/kV

72.5 59.2 2.6 153.9 0.0075 240 1.8 21.32 44 0.49

123 100.4 2.6 261.0 0.0075 240 1.8 61.31 75 0.82

145 118.4 2.6 307.8 0.0075 240 1.8 85.27 88 0.97

170 138.8 2.6 360.9 0.0087 280 2.436 158.54 103 1.54

245 200.0 2.6 520.0 0.0087 280 2.436 329.35 149 2.21

550 449.1 2.0 898.2 0.011 320 3.52 1,419.90 333 4.26

Acc. to IEEE/ANSI C62.11 - 1999 (Transmission Line Discharge Test 8.10.2.1):

E = 1/2 * C * U2

Energy per imulse (3 groups of 6 imp. + 2 imp. + thermal recovery)


Energy Ratings acc. to IEEE Transmission Line Discharge Test



Page 29

© Siemens AG 2010


Energy Absorption Capability of MO Arresters

Transmission Line Discharge Test (ANSI/IEEE Std. C62.11-1999)

Cool downto ambienttemperature

3 groups of 6transmission line discharges

2 transmissionline discharges

Preheat to60 °C

1 minuteapart

recovery voltage for 30 minutes

max. 5minutes

Test evaluation (pass criteria):• Thermal recovery has been demonstrated• Discharge voltage has not changed more than ±10%• No physical damage is evident

Timemax. 10minutes



Page 30

© Siemens AG 2010


For further information:www.siemens.com/arrester

Thank you for your time!

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