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CUSTOMER PRESENTATION — OCTOBER 2019

Shielded surge arresters

Applied in underground distribution systems
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Agenda

Definitions
Standards
Types of arresters
Protection on underground distribution systems

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Definitions
What is a surge?

A surge, or transient, is a sub-cycle overvoltage with a duration of

less than a half-cycle of the normal voltage waveform. Surges can
damage, degrade or destroy electric/electronic equipment.
What can result from surges in distribution systems?
Voltage surge
– Breakdown of insulation
– Aging of insulation (pre-damage)
– Malfunction

Normal level

Short period

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Definitions
Causes of surges

Switching surges
– Demand power load switching
– Utility power load correction
– Capacitor bank switching (the most
common switching phenomena)
Lightning surges
– Nearby lightning strikes
– Direct lightning strike on the power lines
(the majority lead to faults)

Severity of transients in distribution

On 15.0 kV class, typical transients are:
~10.0 kV to 80 kV with duration of ~8 to 20 μs

Switching surge

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Definitions
Global lightning density

2019 ABB
All rights reserved. Slide 5 Source: https://lightning.nsstc.nasa.gov/data/query/mission.png
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Definitions
US lightning density

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All rights reserved. Slide 6 Source: www.vaisala.com/en/products/data-subscriptions-and-reports/data-sets/nldn
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Definitions
Economic considerations

Accurately applied surge protection reduces:

– Outage of lines and substations
– Interruptions of critical manufacturing processes, which demand high voltage stability
– Costs due to interruptions in the energy supply
– Costs for the replacement and repair of electrical equipment
– Aging of insulation (e.g., cables)
– Maintenance work

The aim of overvoltage protection is to guarantee an uninterrupted supply of electrical energy

with high voltage stability to the greatest degree possible.

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Definitions
Surge arrester

A surge arrester is a protective device

for limiting surge voltages on
equipment by discharging or bypassing OPERATING EYE
surge current. It limits the flow of Molded stainless
power following current to ground and steel core
is capable of repeating these functions
as specified. MOV DISK SHIELD GROUND EYE
Silver epoxy-bonded Maintains the housing
Surge arresters are installed phase-
shunted spring shield ground connection
to-ground on the system. connections for the best after failure
circuit connection

BRAIDED GROUND LEAD

SEMICONDUCTIVE SHIELD Flexible copper ground
Fully shielded and lead tethered to the
fully submersible jacket withstands
10,000 A for 10 cycles
without fusing
BOLT AND
LOCKWASHER

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Definitions
Metal oxide varistor (MOV)

– A varistor is sometimes called a “metal oxide resistor” and

is made of different metal oxides in powder form, which
are compressed and sintered in the form of round blocks.
– The zinc oxide grains create diode junctions that are
interconnected.
– When enough voltage activates a varistor, reaching the
breakdown voltage for the junctions, it provides a low
impedance path.
– This action redirects the energy away from the circuit,
providing protection.

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All rights reserved. Slide 9 Source: https://ec.kemet.com/varistor-mov-voltage-protection
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Definitions
Maximum continuous operating voltage (MCOV)

– The maximum continuous operating voltage (MCOV) of an

arrester is typically in the range of 75% to 85% of the duty-
cycle voltage rating.
– At MCOV, the arrester current is usually not more than a
few milliamperes, typically less than 10 mA.
– If the arrester is operating at a voltage level greater than
its MCOV, the metal oxide elements will operate at a
higher-than-recommended temperature. This may lead to
premature failure or shortened life.

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Definitions
Duty-cycle rating

– Duty-cycle rating is the designated Parking stand arrester (200 A) Bushing surge arrester (200 A)

maximum permissible voltage between Part no. Voltage MCOV Duty cycle rating Part no. Voltage MCOV Duty cycle rating
class (kV RMS) (kV RMS) class (kV RMS) (kV RMS)
terminals at which an arrester is 167PSA-3 2.55 3 167BSA-3 2.55 3
designed to perform its duty-cycle test. 167PSA-6 5.10 6 167BSA-6 5.10 6
167PSA-9 7.60 9 167BSA-9 7.60 9
– The duty-cycle test subjects an arrester 167PSA-10 15 kV 8.40 10 167BSA-10 15 kV 8.40 10
to an AC RMS voltage equal to its rating 167PSA-12 10.20 12 167BSA-12 10.20 12
167PSA-15 12.70 15 167BSA-15 12.70 15
for 24 minutes, during which time the 167PSA-18 15.30 18 167BSA-18 15.30 18
arrester must withstand lightning 273PSA-10 8.40 10 273BSA-6 5.10 6
273PSA-12 10.20 12 273BSA-9 7.60 9
surges at 1-minute intervals. The 273PSA-15 25 kV 12.70 15 273BSA-10 8.40 10
magnitude of the surges is 10 kA 273PSA-18 15.30 18 273BSA-12 25 kV 10.20 12

(10,000 amps) for station class 273PSA-21

375PSA-24
17.00
19.50
21
24
273BSA-15
273BSA-18
12.70
15.30
15
18
arresters and 5 kA for intermediate 375PSA-27 35 kV 22.00 27 273BSA-21 17.00 21
and distribution class arresters. 375PSA-30 24.40 30 375BSA-24
35 kV
19.50 24
375BSA-27 22.00 27
375BSA-30 24.40 30

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Definitions
Duty-cycle rating

Elbow surge arrester (200 A) Elbow surge arrester (600 A)

Part no. Voltage MCOV Duty cycle rating Part no. Voltage MCOV Duty cycle rating
class (kV RMS) (kV RMS) class (kV RMS) (kV RMS)
167ESA-3 2.55 3 K655ESA-10 8.40 10
167ESA-6 5.10 6 K655ESA-12 10.20 12
167ESA-9 7.60 9 K655ESA-15 12.70 15
167ESA-10 8.40 10 K655ESA-18 25 kV 15.30 18
15 kV
167ESA-12 10.20 12 K655ESA-21 17.00 21
167ESA-15 12.70 15 K655ESA-27 22.00 27
167ESA-18 15.30 18 K655ESA-30 24.40 30
167ESA-21 17.00 21 755ESA-18 15.30 18
273ESA-3 2.55 3 755ESA-24 19.50 24
273ESA-6 5.10 6 755ESA-27 22.00 27
273ESA-9 7.60 9 755ESA-30 35 kV 24.40 30
273ESA-10 8.40 10 755ESA-33 26.80 33
25 kV
273ESA-12 10.20 12 755ESA-36 29.00 36
273ESA-15 12.70 15 755ESA-40.5 32.50 40.5
273ESA-18 15.30 18
273ESA-21 17.00 21
375ESA-10 8.40 10
375ESA-18 15.30 18
375ESA-21 17.00 21
375ESA-24 35 kV 19.50 24
375ESA-27 22.00 27
375ESA-30 24.40 30
375ESA-36 29.00 36

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Definitions
Maximum discharge voltage

A lower level Protective characteristics

maximum Voltage class

MCOV Duty cycle rating Maximum discharge voltage (kV crest) 8 x 20 microsecond current wave

discharge voltage (kV RMS) (kV RMS) 1.5 kA 3 kA 5 kA 10 kA 20 kA

indicates better 2.55

5.10
3
6
8.06
16.12
8.48
16.95
8.74
17.47
9.36
18.72
10.40
20.80
protection. 7.60 9 24.18 25.42 26.20 28.08 31.20
15 kV 8.40 10 28.21 29.66 30.57 32.76 36.40
10.20 12 32.24 33.90 34.94 37.44 41.60
12.70 15 40.30 42.38 43.68 46.80 52.00
15.30 18 48.36 50.85 52.41 56.16 62.40
2.55 3 8.06 8.48 8.74 9.36 10.40
5.10 6 16.12 16.95 17.47 18.72 20.80
7.60 9 24.18 25.42 26.20 28.08 31.20
8.40 10 28.21 29.66 30.57 32.76 36.40
25 kV
10.20 12 32.24 33.90 34.94 37.44 41.60
12.70 15 40.30 42.38 43.68 46.80 52.00
15.30 18 48.36 50.85 52.41 56.16 62.40
17.00 21 56.42 59.32 61.14 65.52 72.80
8.40 10 28.21 29.66 30.57 32.76 36.40
15.30 18 48.36 50.85 52.41 56.16 62.40
17.00 21 56.42 59.32 61.14 65.52 72.80
19.50 24 64.48 67.80 69.88 74.88 83.20
35 kV 22.00 27 72.54 76.28 78.62 84.24 93.60
24.40 30 80.60 84.75 87.35 93.60 104.00
26.80 33 88.66 93.23 96.09 102.96 114.40
29.00 36 96.72 101.70 104.82 112.32 124.80
32.50 40.5 108.81 114.41 117.92 126.36 140.40

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Definitions
Protection on underground distribution systems — impulse wave example

T1 = 1.67 x T
100%
T1 = Virtual front time
Amplitude (kV)

90% T2 = Virtual time to half

Written as T1 / T2 wave

50% Typical is 8/20 wave

30%

0
T T2
O1
Time (µs)

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Definitions
Protective levels

– The protective level of an arrester is the maximum crest

voltage that appears across the arrester terminals under

Crest voltage (kV)

specified conditions of operation.
– Curve A: Demonstrates the strength of insulation
on equipment. A
– Curve B: Is the protective level provided by an arrester.

Time (µs)

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Definitions
Cable BIL deterioration and temporary overvoltage (TOV)

Cable BIL deterioration

The progressive weakening of cable insulation will lead
to cable deterioration and eventually its failure. Each surge
impulse on the cable will contribute with other factors toward
cable insulation strength deterioration. Ultimately, the cable
can fail with an overvoltage level below the cable’s basic impulse
level (BIL) rating.
Temporary overvoltage (TOV)
A TOV is an oscillatory overvoltage associated with switching or
faults (for example, load rejection, single-phase faults) and/or
nonlinearities (ferroresonance effects, harmonics) of relatively
long duration, which is undamped or slightly damped.

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Standards
Applicable standards and guides for protection of equipment (including cables) on underground systems

C62.11
– 2012
• IEEE standard for metal oxide surge arresters for AC power circuits (>1 kV)
C62.22
– 2009
• IEEE guide for the application of metal oxide surge arresters for alternating-current systems
Std 386™
– 2016
• IEEE standard for separable insulated connector systems for power distribution systems rated 2.5 kV through 35 kV

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Types of arresters
According to IEEE Std C62.22-2009

Types
– Station (utility/power company) — What voltage level?
– Intermediate (utility users/power company)
– Distribution (utility/power company)

Classes
a) Heavy-duty class: An arrester most often used to protect overhead distribution systems exposed to severe lightning currents.
b) Light-duty class: An arrester generally installed on and used to protect underground distribution systems where the major portion
of the lightning strike current is discharged by an arrester located at the overhead line/cable junction.
c) Normal-duty class: An arrester generally used to protect overhead distribution systems exposed to normal lightning currents.

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Protection on underground distribution systems
Key points

– The use of surge arresters is not an exact science, and there are many variables involved in protecting
the system.
– Reliable surge protection for underground distribution circuits should incorporate some margin
of protection to take into account unknowns variables. IEEE C62-11 recommended protective margin
for impulse coordination is 20% (for transmission and distribution applications).
– Surge voltages enter the underground system from the overhead feeder at the riser pole.
– The magnitude of surge voltage entering the cable is limited by the arrester on the riser pole.
– Surge voltage in excess of the protective level of the riser pole arresters can occur on the cable and at
equipment locations remote from the riser pole because of amplification by reflection from the open point.
– When the ongoing surge from the riser pole arrester meets an endpoint in the underground circuit,
it will double in magnitude at that point in the circuit. This is known as the voltage doubling effect.

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Protection on underground distribution systems
Location and application of surge arresters example — 15 kV system

– Assume no attenuation. This assumption becomes conservative for cable lengths greater
than 3,000 ft (900 m).
– Assume that incident voltages will double at open points and terminating transformers.
– The 10 kA crest surge is used when considering protection schemes for a shielded system.
– Suitable margin of protection is 20%.
– The BIL of the system is equal to 95 kV.

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Protection on underground distribution systems
Location and application of surge arresters example — 15 kV system

– Overhead arrester is
designed to limit the
system voltage surges. Overhead
arrester
– Part of the surge is
diverted to ground.
– Part of the surge
Riser pole
is let through to
the system.
– The maximum voltage Pad-mounted
Open/end point
at the open end will transformer
be twice the arrester Vmax=2 x VRP
discharge voltage.

Transition point different

surge impedance

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Protection on underground distribution systems
Surge impedance change

OVERHEAD SURGE IMPEDANCE

@ 300–500 ohms/support surges of 200–500 kV
Propagation speed 1,000 ft/µs
Lightning
Overhead strike
line
Riser pole TRANSFORMER SURGE IMPEDANCE
@ 2,000–4,000 ohms
Line terminates in a transformer,
representing an open point circuit

Underground
cable
T1 T2 T3 T4

UNDERGROUND SURGE IMPEDANCE

@ 25–75 ohms
Propagation speed of 300–500 ft/µs

2019 ABB
All rights reserved. Slide 22 Source: Surge Protection of Cable-Connected Distribution Equipment on Underground Systems IEEE COMMITTEE REPORT
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Protection on underground distribution systems
Arrester selection — 15 kV system example

Determine the maximum discharge voltage Maximum discharge voltage (kV crest)
– From the overhead arrester product specification 8 x 20 µs current wave
• Rating of the riser pole arrester (10 kV) Arrester
1.5 kA 5 kA 10 kA 20 kA
• Initial surge magnitude (20 kA discharge current) rating

– The lead length will increase surge voltage about 10.00 24.50 27.50 29.00 35.00
2 kV per foot. Lead length on the riser pole arrester
(4 feet). Additional discharge voltage: 2 kV x 4 ft = 8 kV 18.00 45.50 52.50 55.00 66.00

27.00 64.00 72.00 76.00 91.00

Maximum discharge voltage = 35 + 8 = 43 kV

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Protection on underground distribution systems
Arrester selection — 15 kV system example

Elbow arrester applied

at the open/end point.
Overhead
arrester

Riser pole

Maximum
discharge
Open/end point
voltage
35 + 8 = 43 kV

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Protection on underground distribution systems
Arrester selection — 15 kV system example

Maximum discharge voltage (MDV) with elbow arrester Maximum discharge voltage (kV crest)
applied at the open/end point: 8 x 20 µs current wave
– From the elbow arrester product specification Arrester
1.5 kA 5 kA 10 kA 20 kA
• Rating of the elbow arrester (10 kV) rating
• Let-through 10.00 30.50 34.50 38.50 38.50
– Coefficient of reflection (0.5)
– MDV from the riser pole = VRP 18.00 56.50 64.00 71.00 71.00

27.00 87.50 99.00 110.00 110.00

MDV with elbow arrester = VRP + (0.5)* 30.5 = 58 kV

MDV without elbow arrester = 2*VRP = 43 * 2 = 86 kV

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Protection on underground distribution systems
Arrester selection — 15 kV system example

BIL for 15 kV system 95kV

86 kV MDV with no elbow arrester
(20% margin of protection)1 79kV
(Cable BIL deterioration)* 60kV
58 kV MDV with arrester at end point
(20% margin of protection)1 50kV
15kV

To reduce the total surge voltage to a value below 50 kV, additional arresters are required in the system.

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* 60–75 kV BIL is typical
All rights reserved. Slide 26 1 ANSI recommended. Accounts for variation of surge parameters, aging of insulation, minor installation flaws.