Metal Oxide Surge Arresters Prof. Dr.-Ing. Volker Hinrichsen Darmstadt University of Technology High Voltage Laboratories
[email protected]
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-1-
Contents • Arrester application in general • considerations on protective characteristics • Arrester design (station arresters) • porcelain housed • polymer housed • Configuring arresters • electrical data • mechanical data
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-2-
Development of Surge Arresters over the past 25 years Internally gapped SiC arresters with porcelain housings 1980
MO arresters without gaps with porcelain housings Æ "state of the art" latest by 1990 MO arresters without gaps with polymeric housings (mv; distribution class)
1990
MO arresters without gaps with polymeric housings (hv; station class)
Technology
2000
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-3-
Development of Surge Arresters over the past 25 years Failure Failure rates rates of of MO MO arresters: arresters: Distribution: Distribution: 0.1 0.1 %/a %/a ... ... 11 %/a %/a (with (with geographical geographical variations) variations) High-voltage: High-voltage: virtually virtually zero zero
1980
1990
2000 2003
Today's situation …
Expected Expected life life time time of of MO MO arresters: arresters: >> 30 30 years? years? (no (no indication indication for for any any severe severe degradation degradation of of MO MO material material so so far) far)
Fachgebiet Hochspannungstechnik
Market Market share share of of polymer polymer housed housed MO MO arresters: arresters: Distribution: Distribution: 80 80 % %… … >> 90 90 % % Reasons: Reasons: -- partly partly poor poor performance performance of of porcelain porcelain housed housed types types -- benefits benefits of of polymeric polymeric designs: designs: sealing, sealing, handling, handling, overload overload performance performance -- cost/price! cost/price! High-voltage: ≈ 30 %, with increasing tendency Reasons: - hv users more conservative - higher requirements - cost/price! Overvoltage Protection and Insulation Coordination / Chapter 5 b
-4-
Typical Arrester Application: Transformer Protection Us = 420 kV
Siemens / VEAG
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-5-
Special Arrester Application: Protection of an SC Capacitor Bank Us = 550 kV
Siemens / Hydro Québec Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-6-
Special Arrester Application: Line Arresters Us = 245 kV
Us = 800 kV
ABB / AEP
Siemens / REN Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-7-
Special Arrester Application: HVDC Valve Protection Arresters UDC = 600 kV
UDC = 600 kV Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-8-
Arrester Application Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
-9-
Fundamentals of Insulation Coordination 5
Magnitude of (over-)voltage / p.u.
Possible voltages without arresters 4
Withstand voltage of equipment 3
2
1
Voltages limited by arresters 0
Lightning overvoltages (Microseconds)
Switching overvoltages (Milliseconds)
Temporary overvoltages Highest voltage of equipment (Seconds) (Continuously)
Time duration of (over-)voltage
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 10 -
Voltage-Current Characteristic of an MO Arrester (Us = 420 kV) α≤5
α≤5
I = k·Uα with α values up to 50
1200 1100 10-kA residual voltage = lightning impulse protection level = 823 kV
900 800 700 600 500 400
Factor 2.4
Peak value of voltage / kV
1000
Peak value of rated voltage: √2·Ur = √2·336 kV = 475 kV
Peak value of continuous operating voltage: √2·Uc = √2·268 kV = 379 kV
300
Peak value of line-to-earth voltage: √2·Us /√3 = √2·242 kV = 343 kV
200 100
Leakage current îres ≈ 100 µA
Nominal discharge current In = 10 kA
0 -4
10
-2
10
1
10 2
10
Peak value of current / A
8 decades of magnitude Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 11 -
4
Voltage-Current Characteristic of an MO Arrester (Us = 420 kV) 400
1,00
300
0,75
200
0,50
100
0,25
0
0,00
-100
-0,25 Current
-200
at at U U == U Ucc: Itotal ≈ 1 mA total ≈ 1 mA
Current / mA
Simplified circuit diagram
Voltage / kV .
Voltage
-0,50
-300
-0,75
-400
-1,00 0
5
10
15
20
Time / ms
900
C
18 Voltage
800
16
700
14
Voltage / kV
600
12 Current
500
10
400
8
300
6
200
4
100
2
0
0
-100
at î = Inn: ûû ≈≈ 825 kV
Current / kA
R = f(u)
-2 0
5
10
15
20
25
30
35
Time / µs
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 12 -
Voltage-Current Characteristic of an MO Arrester Voltage
R = f(u)
C
Voltage, Current
Simplified circuit diagram
“Resistive component“
Total leakage current Time
at U = Ucc: ≈ 1 mA Itotal total Icapacitive ≈ 1 mA capacitive ≈ 10 µA … 100 µA îresistive resistive ≈ 10 µA … 100 µA Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 13 -
MO Resistors Ø 70 mm
Ø 100 mm Ø 58 mm
Ø 48 mm
Ø 78 mm
Ø 41 mm
Ø 32 mm
Example: EPCOS
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 14 -
U-I- vs. E-J-Characteristics U-I-characteristics U-I-characteristics for for different different MO MO resistors resistors
common common E-J-characteristics E-J-characteristics
J
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 15 -
LI Protection Characteristics 2 Tra veling wav
e effects
4
m
1
Doubling of voltage due to full reflection at "open" end of line
Currents exceeding In
•• Voltage Voltageat atarrester arresterterminal terminal might mightbe behigher higherthan thanthe theLI LI protection protectionlevel level •• Voltage Voltageat atterminals terminalsof of equipment equipmentto tobe beprotected protectedare are higher higherthan thanvoltage voltageat atthe the arrester arresterterminal terminal
2.5 m
Inductivity of current path ≈1 µH/m (here: L = 10 µH)
3.5 m
3
!!!!!
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 16 -
Protective Distance – Model Calculation 1 (Um = 420 kV) Overvoltage surge of s = 800 kV/ µ s
Arrester u pl = 800 kV = const. x=0 Fachgebiet Hochspannungstechnik
Transformer LIW = 1425 kV ℓ?= = 300 m x=ℓ
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 17 -
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 00 µs µs
2000 1600
1600
uArr (x = 0)
kV 1200
1200 800
800 400
400
0 0
-400
0
0,5
1
1,5
2 µs
2,5
1600
-800
uTr (x = ℓ)
kV
-1200
x=0
xx == 0: = 0 kV 0: u uArr Arr = 0 kV
x=ℓ
1200 800 400
xx == ℓ: = 0 kV ℓ: u uTr Tr = 0 kV 0 0 Fachgebiet Hochspannungstechnik
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 18 -
2 µs
2,5
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 0,5 0,5 µs µs
2000 1600
1600
uArr (x = 0)
kV 1200
1200 800
800 400
400
u1v
0 0
-400
0
0,5
1
1,5
2 µs
2,5
1600
-800
uTr (x = ℓ)
kV
-1200
x=0
x=ℓ
xx == 0: = u 1v == 400 0: u uArr 400 kV kV Arr = u1v
1200 800 400
xx == ℓ: = u 1v == 00 kV ℓ: u uTr kV Tr = u1v 0 0 Fachgebiet Hochspannungstechnik
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 19 -
2 µs
2,5
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 11 µs µs
2000 1600
1600
uArr (x = 0)
kV 1200
1200 800
800
u1v
400
400
0 0
-400
0
0,5
1
1,5
2 µs
2,5
1600
-800
uTr (x = ℓ)
kV
-1200
x=0
x=ℓ
xx == 0: = u 1v == 800 0: u uArr 800 kV kV Arr = u1v
1200 800 400
xx == ℓ: = u 1v == 00 kV ℓ: u uTr kV Tr = u1v 0 0 Fachgebiet Hochspannungstechnik
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 20 -
2 µs
2,5
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 1,5 1,5 µs µs
2000 1600
1600
uArr (x = 0)
kV 1200
1200
u1v
800 400
800 400
u1r
0
u2v
0
-400
0
0,5
1
1,5
2 µs
2,5
1600
-800
uTr (x = ℓ)
kV
-1200
x=0
x=ℓ
xx == 0: = u 1v ++ uu2v = 0: u uArr Arr = u1v 2v =
1200
Increase at double steepness!
800
(1200 (1200 –– 400) 400) kV kV == 800 800 kV kV 400
xx == ℓ: = u 1v ++ uu1r1r == ℓ: u uTr Tr = u1v
(400 (400 ++ 400) 400) kV kV == 800 800 kV kV Fachgebiet Hochspannungstechnik
0 0
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 21 -
2 µs
2,5
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 22 µs µs
2000 1600
1600
uArr (x = 0)
kV 1200
u1v
1200
800
800
u1r
400
400
0 0
-400
0
u2v
-800
1,5
2 µs
2,5
uTr (x = ℓ)
kV
x=ℓ
xx == 0: = u 1v ++ uu2v = 0: u uArr Arr = u1v 2v =
1
1600
-1200
x=0
0,5
1200 800
(1600 (1600 –– 800) 800) kV kV == 800 800 kV kV 400
xx == ℓ: = u 1v ++ uu1r1r == ℓ: u uTr Tr = u1v
(800 (800 ++ 800) 800) kV kV == 1600 1600 kV kV Fachgebiet Hochspannungstechnik
0 0
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 22 -
2 µs
2,5
Protective Distance – Model Calculation 1 (Um = 420 kV) tt == 2,5 2,5 µs µs
2000 1600
u1v
1600
uArr (x = 0)
kV 1200
1200 800
u1r
800 400
400
0
u3v
-400 -800
0
u2r
0
1
1,5
2 µs
2,5
1600
u2v
uTr (x = ℓ)
kV
-1200
x=0
0,5
x=ℓ
xx == 0: = u 1v ++ uu1r1r ++ uu2v + u 3v == 0: u uArr Arr = u1v 2v + u3v
1200 800
(2000 (2000 ++ 400 400 –– 1200 1200 –– 400) 400) kV kV == 800 800 kV kV 400
xx == ℓ: = u 1v ++ uu1r1r ++ uu2v + u 2r == ℓ: u uTr Tr = u1v 2v + u2r
(1200 (1200 ++ 1200 1200 –– 400 400 –– 400) 400) kV kV == 1600 1600 kV kV Fachgebiet Hochspannungstechnik
0 0
0,5
1
1,5
Overvoltage Protection and Insulation Coordination / Chapter 5
- 23 -
2 µs
2,5
Protective Distance – Model Calculation 2 (Um = 24 kV) Assumptions: • overvoltage surge as a voltage ramp 1 000 kV/µs (1 kV/ns) • arrester limits voltage to 80 kV at its terminals
100
100 Voltage at transformer
80
80
70
70
60
60
Voltage at arrester
50
Voltage at transformer
90
40
u [kV]
u [kV]
90
40
30
30
20
20
10
10
0
Voltage at arrester
50
0 0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
0
10
20
30
40
50
t [ns]
a) Distance arrester - transformer: 1.5 m (propagation time 5 ns)
Fachgebiet Hochspannungstechnik
60
70
80
90 100 110 120
t [ns]
b) Distance arrester - transformer: 3 m (propagation time 10 ns)
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 24 -
Protective Distance – Estimation (Rule of Thumb) Due to traveling wave effects on the line the protection of the equipment by an arrester can be guaranteed only for short distances between arrester and equipment. Simplified estimation of the protective distance *):
xs =
(LIWV / 1.15) - Upl · vtw 2·s
xs LIWV Upl s vtw
*) For more detailed information see IEC 60099-5, IEC 60071-1 and IEC 60071-2
protective distance [m] standard rated lightning impulse withstand voltage [kV] LI protection level of the arrester [kV] front steepness of the overvoltage [kV/µs] (in the range of 1000 kV/µs) propagation speed of traveling wave: - 300 m/µs (overhead line) (equals "c0") - (150 ... 200) m/µs (cable)
Example 1: Distribution network, Um = 24 kV, insulated neutral, arrester of Ur = 30 kV: xs =
(125 / 1.15) - 80 2·1000
· 300 =
4.3 m
!!!
Example 2: Transmission network, Um = 420 kV, effectively earthed, arrester of Ur = 336 kV: xs =
(1425 / 1.15) - 823 2·1000
Fachgebiet Hochspannungstechnik
· 300 =
62.4 m !!!
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 25 -
Representative Overvoltage (acc. to IEC 60071-2) A L U rp = U pl + n ( Lsp + Lt )
Lt =
adopted return rate 1/a shielding failure rate + back flashover rate 1/a ⋅ m
Lsp ... span length in m L ... distances a1 + a2 + a3 + a4 in m n ... number of connected lines A ... factor describing the lightning performance of the OHL in kV (see next slide)
Note: Note: nn should should reasonably reasonably be be set set to to nn == 11 (if (if only only one one line line is is connected) connected) or or nn == 22 (if (if two two or or more more lines lines are are connected). connected). Assuming Assuming nn >> 22 could could yield yield too too optimistic optimistic results results that that are are not not valid valid in in aa real real failure failure scenario scenario (e.g. (e.g. possible possible loss loss of of lines). lines). Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 26 -
Representative Overvoltage (acc. to IEC 60071-2) Factor A describing the lightning performance of an OHL
[IEC 60071-2]
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 27 -
Representative Overvoltage (acc. to IEC 60071-2) Example: Us = 420 kV • • • • • • •
Upl = 825 kV; A = 11000 kV (four conductor bundle) L = 30 m Lsp = 400 m ≥ 2 lines connected; Shielding failure rate (typ. for Germany; one OHGW): 2.5 per 100 km and year = 2.5·10-5 (a·m)-1 Adopted return rate: 1·10-3 a-1
1 ⋅ 10−3 Lt = = 40 m 2.5 ⋅ 10−5 A L 11000 kV 30 m U rp = U pl + = 825 kV + ⋅ = 1200 kV n Lsp + Lt 2 (400+40) m Note Note 1: 1: These These equations equations yield yield representative representative overvoltages, overvoltages, which which are are not not implicitly implicitly the the real real overvoltages! overvoltages! Fachgebiet Hochspannungstechnik
Note Note 2: 2: No No effect effect of of the the lightning lightning overvoltage overvoltage amplitude! amplitude!
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 28 -
Increase of Protection Voltage by Inductive Voltage Drops Example: outdoor arrester Us = 420 kV 4
Ur = 336 kV
m
u10kA, 8/20 µs = 823 kV (= Upl)
3,5 m
u10kA, 1/2 µs = 872 kV Specific inductance of surge current path ≈ 1 µH/m Length of surge current path ≈ 10 m
2,5 m
⇒ Inductance of surge current path ≈ 10 µH
Fachgebiet Hochspannungstechnik
Steepness of surge current impulse ≈ 10 kA/µs ⇒ Additional inductive voltage drop ≈ 100 kV
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 29 -
Arrester Design Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 30 -
Examples of High-Voltage Arresters
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 31 -
Grading Rings – Corona Rings Corona rings
• Beginning with a height of about 1.5 m to 2 m arresters need grading rings for control of voltage distribution along the arrester axis. • Corona rings serve to reduce RIV, usually applied in system voltages of 550 kV and higher.
Grading rings
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 32 -
Examples of Medium-Voltage Arresters
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 33 -
Design of a Porcelain Housed High-Voltage Arrester O-ring Pressure relief vent Sulfur cement bonding Pressure relief diaphragm
MO column
Compression spring Supporting rod (FRP) Fixing plate (FRP) Porcelain housing Aluminum flange
Example: Siemens
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 34 -
Basic Designs of Polymer Housed High-Voltage Arresters
Porcelain/Type A MO column
Type B1a Gas
Solid/semi-solid material Fachgebiet Hochspannungstechnik
Type B1b
Type B2
FRP supporting structure Outer housing
Metal end fittings
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 35 -
Type A "Tube Design" Type Type A AÆ Æ "tube design" •• "conventional" "conventional" approach approach (like (like porcelain porcelain type) type) •• gas gas volume volume included included •• separate separate sealing sealing system system •• pressure pressure relief relief vents vents •• outer outer housing: housing: silicone silicone rubber rubber (SR) (SR) (all (all types: types: HTV, RTV, LR/LSR)
Porcelain/Type A MO column
Gas
Solid/semi-solid material Fachgebiet Hochspannungstechnik
FRP supporting structure Outer housing
Metal end fittings
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 36 -
Type A "Tube Design" Top cover plate Flange with venting outlet Sealing ring Pressure relief membrane Compression spring MO resistor column Composite hollow core insulator (FRP tube/ rubber sheds)
Example: Siemens Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 37 -
Type A "Tube Design" Ü Nearly any desired mechanical strength and energy absorption capability (separate housing, multi-column possible)
Ü Safest possible short-circuit performance (closed tube) Ü Single unit arrester up to Um = 300 kV (control of radial fields) Þ Most expensive design Þ Internal partial discharges possible (depending on design) Þ Separate sealing system – risk of sealing deficiencies Æ The Type A arrester is the typical "special feature" arrester. Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 38 -
Basic designs of polymer housed high-voltage arresters Type B • no (intentional) gas volume included Type B1 Æ "wrapped design" Type B1a Æ "wrapped design" • FRP material directly wrapped onto MO stack • outer housing slipped over or molded on (SR, EPDM, EPDM/SR blends …) Type B1a MO column
Gas
Solid/semi-solid material Fachgebiet Hochspannungstechnik
FRP supporting structure Outer housing
Metal end fittings
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 39 -
Type B1a "Wrapped Design" Implementation example 1: • Fiber glass rovings soaked in uncured epoxy resin or pre-impregnated ribbons are wound crosswise around the MO stack. • They do not fully overlap and form rhombic "windows". • Best compromise between mechanical strength and short-circuit performance must be found. MO column
FRP wrap
main orientation of glass fibers Fachgebiet Hochspannungstechnik
Example: Ohio Brass
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 40 -
Type B1a "Wrapped Design" Implementation example 2: • Full overlapping of the ribbons or pre-impregnated FRP mats with appropriate (crosswise) orientation of the glass fibers • Forms a closed tube (good for mechanical strength, bad for short-circuit performance) • Slots as pre-determined weakened breaking areas
MO column
FRP wrap
main orientation of glass fibers Fachgebiet Hochspannungstechnik
Example: Ohio Brass
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 41 -
Type B1a "Wrapped Design" Implementation example 3: • Pre-impregnated FRP mats with axial orientation of the glass fibers • Forms a closed tube, which however easily tears open by the arc in case of short-circuit
MO column
FRP wrap
main orientation of glass fibers Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 42 -
Basic designs of polymer housed high-voltage arresters Type B • no (intentional) gas volume included Type B1 Æ "wrapped design" Type Type B1b B1b Æ Æ "wrapped design" •• FRP FRP material material with distance to to MO MO stack stack •• gap gap filled filled by by other other material material (solid/semi-solid) (solid/semi-solid) •• outer outer housing housing slipped slipped over over or or molded molded on on (SR, (SR, EPDM, EPDM, EPDM/SR EPDM/SR blends blends …) Type B1b MO column
Gas
Solid/semi-solid material Fachgebiet Hochspannungstechnik
FRP supporting structure Outer housing
Metal end fittings
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 43 -
Type B1 "Wrapped Design" Ü Most economical design; lowest market prices Ü Short-circuit performance better than for porcelain Ü Lightweight; easy to handle Þ Limited mechanical strength (diameter of housing, wall thickness) Þ Big differences in performance (e.g. with regard to moisture ingress, short-circuit performance) depending on design variants and implementation
Þ Multi-unit arresters even for lower system voltages (radial fields) Æ The Type B1 arrester is the typical "low cost" arrester. Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 44 -
Basic designs of polymer housed high-voltage arresters Type B • no (intentional) gas volume included Type Type B2 B2 Æ Æ "cage "cage design" design" •• FRP FRP rods rods or or loops loops form form an an open open cage around around the the MO MO stack stack •• outer outer housing housing directly directly molded molded onto onto the the MO MO stack stack (silicone (silicone rubber) rubber)
Type B2 MO column
Gas
Solid/semi-solid material Fachgebiet Hochspannungstechnik
FRP supporting structure Outer housing
Metal end fittings
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 45 -
Type B2 "Cage Design" 1st sub-variant Loops
Example: ABB Switzerland Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 46 -
Type B2 "Cage Design" 1st sub-variant Loops
Example: ABB Switzerland Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 47 -
Type B2 "Cage Design" 2nd sub-variant Loops + bondage
Example: ABB Sweden
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 48 -
Type B2 "Cage Design" 3rd sub-variant Rods
Example: Siemens
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 49 -
Type B2 "Cage Design" 3rd sub-variant Rods
Example: Siemens Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 50 -
Type B2 "Cage Design" Ü Ü Ü Ü
Economical design; low market prices Short-circuit performance better than for porcelain Mechanical strength usually higher than for B1 design Lightweight; easy to handle
Þ Limited mechanical strength (diameter; mechanical strength of MO blocks) Þ Multi-unit arresters even for lower system voltages (radial fields) ÆThe Type B2 arrester is a higher performance "low cost" arrester. Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 51 -
Configuring Arresters Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 52 -
System Highest voltage of the system Us
electrical
Grounding Temporary overvoltages (TOV)
Arrester
Environment
Min. MCOV, Uc,min → rated voltage Ur1 Rated voltage Ur MCOV, Uc Rated voltage Ur2
Lightning current stress
Nominal discharge current
Energy (line discharge, switching overvoltages)
Line discharge class
LIWV, safety margin, distance (protection zone)
LI protection level, SI protection level
Density of lightning strikes, magnitude of lightning strikes
mechanical
Active part specified
Length of housing, number of units, flashover distance (withstand voltages)
Short-circuit current
Mechanical stress (short-circuit current, tensile loads)
Height of erection
Creepage, sheds
Pollution
Diameter, material, length of units (number of units)
Seismic stress
Housing Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 53 -
Choice of Continuous Operating and Rated Voltage System
(phase-to-phase)
1 3
System
(phase-to-earth)
Arrester
TOV (1 s) TOV (10 s)
Highest system voltage
1-s-voltage
Nominal system voltage
Rated voltage Cont. operating voltage ≥+5%
Note: Nominal system voltage of no interest for configuring an arrester! Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 54 -
1.25
Choice of Continuous Operating and Rated Voltage Ur1 = 1.25 · Uc,min = 1.25 · (1.05 · Um/√3) UTOV
1,3
Ur2 = _______ = f(tTOV) kTOV
Power-frequency vs. time (U-t-) characteristics
1,25 1,2
k t ov = U /U r
1,15 1,1 1,05 1 0,95 0,9 0,85 0,8 0,1
1
10
100
1000
t /s
Urr is the higher value of Ur1 and Ur2 , rounded up to a multiple of three r1 r2 Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 55 -
Calculation Example 1 (Um = 550 kV) Um = 550 kV
U10sec = 1.4 · Um/√3 = 445 kV
LIWV = 1550 kV
LD-class = 5
Rated Voltage: Uc, min = 1.05 · Um/√3 = 333 kV Ur1 = 1.25 · Uc, min = 416 kV UTOV
445
Ur2 = _______ = _______ = 414 kV kTOV 1.075 ⇒ Ur, min = 417 kV
Fachgebiet Hochspannungstechnik
Ur, typ = 420 kV
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 56 -
Calculation Example 2 (Um = 24 kV; isolated neutral) Um = 24 kV
U10sec…1h = Um = 24 kV
LIWV = 125 kV
LD-class = ---
Rated Voltage: Uc, min = Um = 24 kV Ur1 = 1.25 · Uc, min = 30 kV UTOV
19.4
Ur2 = _______ = _______ = 18.1 kV kTOV 1.075 ⇒ Ur, min = 30 kV
Fachgebiet Hochspannungstechnik
Ur, typ = 30 kV
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 57 -
System Highest voltage of the system Us
electrical
Grounding Temporary overvoltages (TOV)
Arrester
Environment
Min. MCOV, Uc,min → rated voltage Ur1 Rated voltage Ur MCOV, Uc Rated voltage Ur2
Lightning current stress
Nominal discharge current
Energy (line discharge, switching overvoltages)
Line discharge class
LIWV, safety margin, distance (protection zone)
LI protection level, SI protection level
Density of lightning strikes, magnitude of lightning strikes
mechanical
Active part specified
Length of housing, number of units, flashover distance (withstand voltages)
Short-circuit current
Mechanical stress (short-circuit current, tensile loads)
Height of erection
Creepage, sheds
Pollution
Diameter, material, length of units (number of units)
Seismic stress
Housing Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 58 -
Direct Lightning Strokes to Overhead Line Conductors The nominal discharge current In is a coordination current on which the protective characteristics and thus insulation coordination are based. Question: What is a reasonable value for In? To answer this question: what are the highest possible currents of a lightning stroke directly into the overhead line conductor?
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 59 -
Direct Lightning Strokes to Overhead Line Conductors CIGRÉ electro-geometrical model
• rc and rg are the maximum striking distances of a return stroke to the stepped leader. • The higher the stroke current, the higher rc and rg. • Im is the maximum current at and above which no strokes will terminate on the phase conductor:
h+ y ⎡ ⎤ ⎢ ⎥ 2 Im ≈ ⎢ 7.1 ⋅ (1 − sin α ) ⎥ ⎢ ⎥ ⎣ ⎦ Examples:
α = shielding angle
h = 60 m, y = 45 m, α = 30 °
Strokes Strokes between between A A and and B BÆ Æ phase phase conductor conductor Strokes Strokes between between B B and and C CÆ Æ ground ground wire wire Strokes Strokes beyond beyond A AÆ Æ ground ground Fachgebiet Hochspannungstechnik
1 0.75
⇒ Im ≈ 36 kA
h = 30 m, y = 25 m, α = 15 °
⇒ Im ≈ 9 kA
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 60 -
Lightning Stroke and Surge Propagation on a Transmission Line 1
2
1 Lightning stroke: two traveling waves of û = ½ ·Z · î (Example: û = ½ · 350 Ω · 20 kA = 3.5 MV) 2 1st insulator: flashover Example: • 100 % flashover voltage (negative polarity*)): ud100 ≈ 2100 kV for Um = 420 kV • max. current of propagating wave: î = 2100 kV / 350 Ω = 6 kA
Surge currents are limited to values below 10 kA! *) More than 90 % of lightning flashes to ground are negative cloud-to-ground flashes! Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 61 -
Lightning Impulse Current Stress of Station Arresters Usually, Usually, no no direct direct lightning lightning strokes strokes of of discharge discharge currents currents higher higher than than ≈≈ 20 20 kA kA on on shielded shielded transmission transmission lines lines (all (all other other strokes strokes will will hit hit the the shield shield wire wire or or directly directly the the ground) ground) Currents Currents limited limited by by flashover flashover voltage voltage of of line line insulators insulators and and surge surge impedance impedance of of the the line: line:
î = ûflashover /Z flashover Examples: Examples: U ≈ 600 kV, Z = 450 Ω Umm == 123 123 kV, kV, ûûflashover flashover ≈ 600 kV, Z = 450 Ω
î = 1.3 kA
U ≈ 2 100 kV, Z = 350 Ω Umm == 420 420 kV, kV, ûûflashover flashover ≈ 2 100 kV, Z = 350 Ω
î = 66 kA kA
LI LIcurrents currentsin inthe thesubstation substationusually usuallybelow below10 10kA kA Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 62 -
System Highest voltage of the system Us
electrical
Grounding Temporary overvoltages (TOV)
Arrester
Environment
Min. MCOV, Uc,min → rated voltage Ur1 Rated voltage Ur MCOV, Uc Rated voltage Ur2
Lightning current stress
Nominal discharge current
Energy (line discharge, switching overvoltages)
Line discharge class
LIWV, safety margin, distance (protection zone)
LI protection level, SI protection level
Density of lightning strikes, magnitude of lightning strikes
mechanical
Active part specified
Length of housing, number of units, flashover distance (withstand voltages)
Short-circuit current
Mechanical stress (short-circuit current, tensile loads)
Height of erection
Creepage, sheds
Pollution
Diameter, material, length of units (number of units)
Seismic stress
Housing Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 63 -
Energy Requirements
Two aims: 1) 1) Mechanical Mechanical integrity integrity of of the the MO MO blocks blocks 2) 2) Thermal Thermal stability stability
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 64 -
Energy Requirements
Single impulse energy absorption capability • Energetic overloading (puncture or thermo-mechanical cracking of one or more MO-resistors)
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 65 -
Energy Requirements Thermal energy absorption capability
Electrical power losses
Heat dissipation, electrical power losses
Limit of thermal stability (unstable operating point)
Heat dissipation Normal operation (stable operating point)
Temperature
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 66 -
"Thermal" and "Impulse" Energy Values "Thermal" 1)
"Impulse"
2 long duration current impulses, 1 minute apart
1 long duration current impulse
Ur for 10 seconds
Uc for 30 minutes
Time
Time
Preheat to 60 ºC max. 100 ms
Energy input by two long duration current impulses 1 minute apart (each impulse 50% of the injected energy); thermal stability required 1)
Energy input by one long duration current impulse t ≥ 4 ms; thermal stability not critical
Note: If no thermal stability has to be guaranteed after energy injection (i.e. arrester de-energized afterwards) higher energy values are allowed.
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 67 -
Thermally Equivalent Prorated Section for Operating Duty Test Current supply Gripping Hard tissue
Gripping
Cork
Test sample Porcelain
Temperature measurement
Current supply
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 68 -
Choice of Line Discharge Class acc. to IEC 60099-5 IEC 60099-5, 1996-02 Surge Arresters - Part 5: Selection and application recommendations Table 1: L D c la s s
a p p ro x . U m kV
a p p r o x . lin e le n g th km
a p p ro x . Z Ohm
1
≤ 245
300
450
a p p r o x . o v e r v o lta g e fa c to r p .u . *) 3 ,0
2
≤ 300
300
400
2 ,6
3
≤ 420
360
350
2 ,6
4
≤ 550
420
325
2 ,4
5
≤ 800
480
300
2 ,4
*)
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
1 p.u. =√2 x Um/ √3
- 69 -
Line Discharge Class (IEC 60099-4) – Problem of Definition W · (U – U res)) ·· 1/Z W == U Ures 1/Z ·· TT res · (ULL – Ures
Arrester classification
Line discharge class
Surge impedance of the line Z (Ω)
Virtual duration of peak T (µs)
Charging voltage UL (kV d.c.)
10 000 A
1
4,9 Ur
2 000
3,2 Ur
10 000 A
2
2,4 Ur
2 000
3,2 Ur
10 000 A
3
1,3 Ur
2 400
2,8 Ur
20 000 A
4
0,8 Ur
2 800
2,6 Ur
20 000 A
5
0,5 Ur
3 200
2,4 Ur
Example: Example: A A MO MO arrester arrester with with resistors resistors of of 44 kJ/kV kJ/kV (2·2 (2·2 kJ/kV) kJ/kV) energy energy absorption absorption capability capability may may be be specified /U = 2, specified as as aa Class Class 22 arrester arrester ifif U Ures res/Urr = 2, but /U = 2.4. but as as aa Class Class 33 arrester arrester ifif U Ures res/Urr = 2.4. A /U = 2 needs A Class Class 33 arrester arrester of of U Ures res/Urr = 2 needs resistors resistors of of 66 kJ/kV kJ/kV (2·3 (2·3 kJ/kV). kJ/kV).
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 70 -
System Highest voltage of the system Us
electrical
Grounding Temporary overvoltages (TOV)
Arrester
Environment
Min. MCOV, Uc,min → rated voltage Ur1 Rated voltage Ur MCOV, Uc Rated voltage Ur2
Lightning current stress
Nominal discharge current
Energy (line discharge, switching overvoltages)
Line discharge class
LIWV, safety margin, distance (protection zone)
LI protection level, SI protection level
Density of lightning strikes, magnitude of lightning strikes
mechanical
Active part specified
Length of housing, number of units, flashover distance (withstand voltages)
Short-circuit current
Mechanical stress (short-circuit current, tensile loads)
Height of erection
Creepage, sheds
Pollution
Diameter, material, length of units (number of units)
Seismic stress
Housing Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 71 -
LI protection level from U-I-Characteristics U-I-characteristics U-I-characteristics for for different different MO MO resistors resistors
U Uplpl == (2.8 (2.8 ... ... 3.4)·U 3.4)·Ucc
ûr ûc
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 72 -
Calculation Examples 1 + 2 (Um = 550 kV and 24 kV) 1) Um = 550 kV
U10sec = 1.4 · Um/√3 = 445 kV
Rated Voltage:
LIWV = 1550 kV
LD-class = 5
Ur, typ = 420 kV
Protection Level:
1550 kV
U10kA = 420 kV · 2.3 *) = 966 kV <
__________
1550 kV (
= 1107 kV )
__________
1.4
1.4
;
*) Typical value for LD class 5, but manufacturer dependant
2) Um = 24 kV
U10sec…1h = Um = 24 kV
LIWV = 125 kV
LD-class = ---
Rated Voltage: Ur, typ = 30 kV Protection Level: 125 kV U10kA = 30 kV · 2.67 *) = 80 kV <
_________
1.4
125 kV (
_________
= 89 kV )
1.4
*) Typical value for 5-kA distribution arrester, but manufacturer dependant Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 73 -
;
Typical Values of Protection Level Us
Neutral earthing
Standard lightning Lightning impulse impulse withstand protective level upl voltage LIWV kV kV kV 24 Resonant earthed 125 80 123 Resonant earthed 550 370 145 Solidly earthed 650 295 245 Solidly earthed 950 485 420 Solidly earthed 1425 825 550 Solidly earthed 1550 960
As a rule of thumb, a factor LIWV/upl ≥ 1.4 offers sufficient protection against lightning overvoltage:
upl pl ≤
Factor LIWV/upl
1.56 1.49 2.2 1.96 1.73 1.61
LIWV ________ ________
1.4
The voltage at the terminals of the equipment to be protected must not reach values above LIWV/1.15 (Ks = 1.15 = safety factor for non-self restoring insulation, acc. to IEC 60071-2) For more detailed information see IEC 60099-5, IEC 60071-1 and IEC 60071-2 Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 74 -
Protection Level and Stability against Power-Frequency Stress 600
Example: Um = 245 kV, neutral effectively earthed Ur = 224 kV u10kA=538 kV
500
u [kV]
400
Ur = 198 kV u10kA= 475 kV
300 200 1.4 times line-to-earth-voltage 100 Line-to-earth-voltage 0 0,0001
0,001
0,01
0,1
1
10
100
1000
10000
i [A]
100000
Lower LI protection level Æ higher specific power-frequency stress Protection level should be set to reasonable (not necessarily the lowest) values!
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 75 -
System Highest voltage of the system Us
electrical
Grounding Temporary overvoltages (TOV)
Arrester
Environment
Min. MCOV, Uc,min → rated voltage Ur1 Rated voltage Ur MCOV, Uc Rated voltage Ur2
Lightning current stress
Nominal discharge current
Energy (line discharge, switching overvoltages)
Line discharge class
LIWV, safety margin, distance (protection zone)
LI protection level, SI protection level
Density of lightning strikes, magnitude of lightning strikes
mechanical
Active part specified
Length of housing, number of units, flashover distance (withstand voltages)
Short-circuit current
Mechanical stress (short-circuit current, tensile loads)
Height of erection
Creepage, sheds
Pollution
Diameter, material, length of units (number of units)
Seismic stress
Housing Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 76 -
Housing Requirements • Mechanical strength • static and dynamic loads by connected conductors • strength against seismic events • Dielectric strength • Short-circuit performance • Performance under polluted conditions • shed profile • creepage distance • flashover distance • partial heating of active parts • internal partial discharges • hydrophobicity (incl. dynamics of hydrophobicity) Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 77 -
Mechanical Strength of Housing Minimum recommended strength if there are no further requirements (given by conductor loads ÅÆ wind, vibration, short-circuit current forces): System voltage Um
Fmin static
Fmin dynamic min. breaking value
(kV)
(N / lbf)
(N / lbf)
(N / lbf)
≤ 420
400 / 90
1000 / 225
1200 / 270
550
600 / 135
1500 / 337
1800 / 405
800
800 / 180
2000 / 450
2400 / 540
(Table valid for porcelain housed arresters)
• Ratio Fdyn / Fstat = 2.5 for porcelain housings • Ratio Fdyn / Fstat for polymer housings not yet definitely established
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 78 -
Pressure Relief of a Porcelain Housed Arrester Unit
1) Puncture and flashover of individual MO resistor(s) Fachgebiet Hochspannungstechnik
2) Internal arc along the full length of the unit
3) Opening of pressure relief devices and venting of the unit
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 79 -
Pressure Relief of a Cage Design Polymer Housed Arrester Unit
Fachgebiet Hochspannungstechnik
1.
Arrester has failed and gas begins to be expelled through the housing.
2.
The gas streams trigger an external flashover and the internal arc is commutated to the outside
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 80 -
Pressure Relief Test according to IEC 60099-4 Ed. 2 (inf.) Test with high current (rated short-circuit current): 5
10
16
20
31.5
40
50
63
80 kA
Test with low current: 600 A ± 200 A
(additionally: tests with ≈50% and ≈ 25% of rated short-circuit current)
Basic idea: Ød
• Explosion not allowed • Thermal breaking allowed (definition: all parts within the circular enclosure)
Arrester unit H Circular enclosure
• Short housings • Large gas volume • Fast opening pressure relief devices
h >= 0,4 m
• High mechanical strength (porcelain quality, thickness) • Favorable short circuit current loop
Ø D = (d + 2H) >= 1,8 m
Problems: - how to initiate the failure - pass criteria Fachgebiet Hochspannungstechnik
Factors that improve pressure relief performance:
see 37/317/CDV
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 81 -
Influence of the Short Circuit Current Loop i
i
i
i
i i
Porcelain Polymer (with gas volume included) Polymer (without gas volume included)
Fachgebiet Hochspannungstechnik
i
i
worst case
most favorable case
neutral case
favorable case
most favorable case
worst case
most favorable cases
Overvoltage Protection and Insulation Coordination / Chapter 5 b
worst case
- 82 -
Examples for Successful Pressure Relief Tests with High Current Test with 63 kA/0,2 s on porcelain housed arrester
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 83 -
Examples for Successful Pressure Relief Tests at High Current Test with 63 kA/0,2 s on polymer housed high-voltage arrester (FRP hollow insulator)
Before test Fachgebiet Hochspannungstechnik
After test
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 84 -
Examples for Successful Pressure Relief Tests at High Current Test with 63 kA/0,2 s on polymer housed high-voltage arrester (cage design)
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 85 -
Examples for Successful Pressure Relief Tests at High Current Test with 20 kA/0,2 s on polymer housed distribution arrester (cage design)
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 86 -
Short-Circuit Performance – Wrap-Up • In general, polymer housed arresters tend to offer a "safer" short-circuit performance. • But not all polymer housed arresters are intrinsically "safe". • Design differences must still be regarded.
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 87 -
Performance under Pollution Conditions Measures against: 1 • Long creepage distance • Optimized shed profile 2
3
2
Radial filed stress: - risk of "internal" partial discharges, degradation of the MO resistors and deterioration of the supporting structure or - risk of puncture in case of the housing directly applied to the MO column Risk of partial heating of the active parts (see Annex F of IEC 60099-4)
Fachgebiet Hochspannungstechnik
1 Risk of external flashover
• Few number of units (best: single-unit arrester)
3 In case of gas volume included: • large distance MO column - housing • no sharp edges at the MO column • MO blocks with stable aging characteristics • internal gas volume free of oxygen • high tracking resistance of supporting structure • use of desiccants In case of no gas volume included: • sufficient thickness of housing • optimized shed profile • high tracking resistance of materials
General: General:High Highrated ratedand andcontinuous continuousoperating operatingvoltage voltage rather than low protection level if possible (leads rather than low protection level if possible (leadstoto moderate moderateelectrical electricalstress stressunder undercontinuous continuousoperating operating conditions and improves long term stability) conditions and improves long term stability) Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 88 -
Performance under Pollution Conditions – Radial Field Stress MO column Gas or solid
Conductive layer
Uaxial, int
Solid
Uradial
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 89 -
Summary - Characteristic Values (1): Main Data • Continuous operating voltage (Uc/MCOV) • Rated voltage (Ur) • Rated frequency • Rated short-circuit current (Is) • Line discharge class (LD-Class) • Nominal discharge current (In) (8/20 µs) • LI protection level (Upl) (= residual voltage at In) Additional: residual voltages for different current shapes and amplitudes Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 90 -
Summary - Characteristic Values (2): Additional Data • 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) (for distribution arresters) • Temporary overvoltage (TOV) capability (1 s, 10 s, 100 s) • Creepage distance • Dielectric withstand values of the housing • Permissible mechanical headloads (static, dynamic)
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 91 -
Metal Oxide Surge Arresters
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 92 -
Voltage and Temperature Distribution of MO Arresters 1800 1600 1400
H [mm]
1200 1000 800
H= 1200 mm H= 1465 mm
600
H= 1805 mm
400 200 0 0,7
0,8
0,9
1
1,1
1,2
1,3
1,4
1,5
U/Umitte l U/U mean
⇒ Grading rings necessary for arrester heights > 1.5 m ... 2 m
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 93 -
1,6
Arrester Ur = 224 kV, Voltage Distribution, Equivalent Circuit 2200 2000 1800 1600
Height [mm]
1400 1200 1000 800 600 400 200 0 0,7
0,8
0,9
1
1,1
1,2
1,3
U/Umean
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 94 -
Specified Currents for Residual Voltage Tests on MO Arresters Double exponential current impulses: definition by T1/T2 and î T1 T2 î
Front time [µs] Time to half value [µs] Amplitude [kA] from IEC 60060-1
FS UL
T1 = 1.25 · T
Fachgebiet Hochspannungstechnik
L
R PO
C
Typical test circuit
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 95 -
Specified Currents for Residual Voltage Tests on MO Arresters • Switching current impulse: (30…100)/(2·T1) µs, î <= 2 kA • Lightning current impulse: 8/20 µs, î <= 40 kA (nominal discharge current In usually 5, 10 or 20 kA) • High current impulse: 4/10 µs, î <= 100 kA (typical values 65 and 100 kA) • Steep current impulse: 1/<20 µs, î <= 20 kA
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 96 -
Specified Currents for Energy Tests on MO Arresters Long duration current impulse: î <= 2 kA Td
Virtual duration of the peak
Tt
Virtual total duration
Standard values of Td: 500, 1000, 2000, 2400, 2800, 3200 µs from IEC 60060-1 Ln UL
L1 C1
Cn
Typical test circuit
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 97 -
FS PO
Accelerated Aging Procedure Accelerated Aging Test:
• Part of Operating Duty Test acc. to IEC 60099-4 • Quality assurance for running MO production
Test Conditions:
• ϑ = 115 ºC, U = 1,05 ·Uc, t = 1000 h (6 weeks) • "actual surrounding medium": Air, N2, SF6, (CO2, N2H2) Accelerated Aging Test acc. to IEC 99-4 2 1,8 Normal Behaviour
1,6
Aging Resistor
1,4 P /P o
1,2 1 0,8 0,6 0,4 0,2 0 0
5
10
15
20
25
30
35
40
sqrt (t) [sqrt (h)]
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 98 -
Accelerated Aging Tests
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 99 -
Switching Surge Operating Duty Test (IEC 60099-4) 2 long duration current impulses, 1 minute apart
Conditioning 4 groups of 5 impulses at In 8/20 µs, superimposed on 1,2 x Uc
2 high current impulses 100 kA, 4/10 µs
1 minute apart
Ur for 10 seconds
Uc for 30 minutes
Time
Preheat to 60 °C
Cool down to ambient temperature
Time interval not specified
max. 100 ms
Test evaluation (pass criteria): • Decrease of temperature, power loss, resistive component of the leakage current • No significant change of residual voltage (max. 5%) • No puncture, flashover or cracking of MO blocks Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 100 -
High Current Impulse Operating Duty Test (IEC 60099-4) Conditioning
4 groups of 5 impulses at In 8/20 µs, superimposed on 1,2 x Uc
1 high current 1 high current impulse 4/10 µs impulse 4/10 µs
Ur for 10 seconds Uc for 30 minutes
Time 1 minute apart
Preheat to 60 °C
Cool down to ambient temperature
Time interval not specified
max. 100 ms
Test evaluation (pass criteria): • Decrease of temperature, power loss, resistive component of the leakage current • No significant change of residual voltage (max. 5%) • No puncture, flashover or cracking of MO blocks
Fachgebiet Hochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 101 -
LongDuration Current Impulse Test (IEC 60099-4)
6 5 4 3 2 1 0 -1 -2 -3 -4
1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 -0,2
Test procedure: 6 groups of 3 impulses = 18 impulses (MO blocks in open air) I [kA]
U [kV]
Long duration current impulse (2,4 ms, 1200 A)
0 0,5 1 1,5 2 2,5 3 3,5 4
t [ms]
1 minute apart Cool down to ambient temperature
Typical 2 ms-values for single MO blocks from 200 A (distribution class arresters) to 1600 A (station class arresters), may be increased by connecting several blocks in parallel
Fachgebiet Hochspannungstechnik
Time
Test evaluation (pass criteria): • No significant change of residual voltage (max. 5%) • No puncture, flashover or cracking of MO blocks
Overvoltage Protection and Insulation Coordination / Chapter 5 b
- 102 -