The Challenges of Converting
Arrester Standards to
Understandable Utility Standards
Michael K. Champagne, P.E.
Member, IEEE-SPDC
What are these Challenges?
1. Personnel are not familiar with arrester ratings and
applications
• Newer engineers replacing older experienced engineers
(aging and retiring workforce problem)
• Personnel not familiar with / aware of / do not have access to
IEEE Standards and Guides.
• Budget limitations do not allow for much training
• Surge protection not perceived as important as major
equipment.
2. Standards for other equipment is more straight
forward
• Breakers and switches
– Continuous current ratings and voltage ratings are straight
forward
– Interrupting ratings have reasoning that with some
explanation, can be understood by a novice
• Transformers
– Voltage ratings are straight forward
– Power ratings only require a short explanation
3. Arrester Ratings are not as Straight Forward
Best illustrated by a question from a project manager:
“We are building a 230 kV substation. Why would you install a
192 kV rated arrester? Is this a mistake?”
It’s not obvious to a novice what arrester ratings mean
• Two voltage ratings:
– MCOV
– Duty Cycle
• Concept of Insulation coordination
• Energy Ratings: Distribution / Intermediate / Station Class
• Fault duty rating
• Temporary Overvoltage (TOV)
• Physical characteristics
• Other attributes
Confusion over what an arrester does
Common Questions are:
•
•
•
•
•
•
•
When does it work?
What does it do when it does work?
What happens when it really does work?
How do I know it worked?
What does it do when it does work?
Does it have to “fail” to work?
Do we even need arresters?
Other Sources of Confusion
• Why so many building blocks and what are their effects?
• What is meant by failure mode?
• What is collateral damage?
What happens if I don’t get it right?
• Misapplication and it’s effects
• Arrester failure
• Equipment failure
Who applies arresters?
Utilities:
Factories & Other Industry:
•
•
•
•
• Corporate Engineers
• Local Engineers
• Maintenance workers
Standards Engineers
Design Engineers
Maintenance technicians
Linemen / mechanics
In each case:
Does surge protection get enough attention?
How can these Challenges be Met?
One Approach:
Produce an Internal Application Guide
Two Objectives Today
• Explain the rationale of this approach
• Provide some examples of what an internal guide includes to
illustrate the need.
Publish an internal application guide with these objectives:
• Identify audience and keep them in mind
• Base the guide on IEEE standards, but only address the parts we need =>
keep it simple
• Address problems experienced in the past
• Answer common questions and clear up confusion
• Maintain the fewer building blocks approach
• Describe special applications to guide’s reader
• Publish and teach the guide to all personnel involved
• Publish an internal shortcut key to address 90% of applications on our
system
• Review the guide periodically and update as necessary
Consider our arrester applications
• Where should we apply arresters?
– Substations
• What are they designed to protect?
– Major Equipment
• What good can they do us => How can they help us?
– Prevent equipment outages due to failures
– Increase reliability
• Where should we not apply arresters?
– Requires development of internal philosophy
• Economical and practical approach
– Reduce building blocks
Consider Application Problems of the Past
• Internal (arrester) Failure due to
– Temporary overvoltage
– Being applied at wrong system voltage
• External (arrester) failure due to
– Solid pollution residue on housing
– Animals
– Improper mechanical forces
• Collateral damage
– Failing arrester caused damage nearby equipment
Minimize the building blocks
• Fewer options => less chance of misapplications by those unfamiliar with
standards
• Concentrate on the arrester models that solve the most problems
• Allow for Special applications
• Eliminate models that had a narrow application.
• Results in a savings of inventory costs
Results of the New Guide
• Explained using specific examples to introduce arrester
concepts to a novice
• Resulted in fewer misapplications
• Better equipment protection
Results of the New Guide
(Continued)
• Only allow Station Class arresters inside the substation to eliminates
confusion. => Zero arrester failures applied ≤ 230 kV since 2004.
• This rule was amended to require the use of energy class H arresters at
system voltages up through 230 kV and energy class J arresters at EHV
system voltages. This will harmonize with the new C62.11-2012 Test
Standard.
• Require one level of MCOV higher than the minimum recommended by
IEEE C62.22 for most applications. =>Eliminated TOV damages
• Require only polymer-housed arresters to be used. => Drastic reduction in
collateral damage risk.
Results of New Guide
(Continued)
• Required a minimum housing height for medium class voltage
applications to eliminate some animal outages
• Required a minimum creep distance for medium class
voltages to reduce risk of flashover due to environmental
contamination.
• Both of these are helping reduce external flashovers in high
pollution environments
Examples of material to include in the new Guide
Definitions
• Terminology must be understood to apply concepts.
• Not always straight forward
–
–
–
–
–
Surge Arrester
Line Terminal / Ground Terminal
MCOV, Duty Cycle, and the relationship between the two
System Voltage
Temporary Overvoltage (TOV)
• Use and explain the IEEE definitions
Proper spelling
ARRESTOR
•Somebody who puts you in jail.
•Be carful with spell check.
ARRESTER
This is the version we’re
here to learn about today.
Specific Example
How to determine proper arrester rating for a given system
voltage?
• Arresters are installed phase-to-ground on the system
• System voltages all have maximum limits where they can deviate from
nominal
• Must allow for TOV’s specific to our system.
Calculation of Minimum MCOV
VMCOV
VSYS
 1.05 
3
Where
VMCOV = Minimum MCOV rating of applied arrester, kV
VSYS = Nominal system operating voltage, kV
Utility’s specific application guide requires the use of the next higher entry
from Table 1 of ANSI/IEEE C62.11. This is to allow for a longer unanticipated
TOV on the system.
Explain the Concept of Insulation Coordination
Crest Voltage (kV)
(ABB T&D Book)
A
B
Time (s)
Curve A is the demonstrated strength of insulation on a piece of equipment.
Curve B is the protective level provided by an arrester.
Curve A is protected by the protective device of Curve B which limits the voltage to
a value level less than in insulation strength of Curve A.
Impulse Wave Example
(IEEE Std. 4)
T1 = 1.67 x T
T1 = Virtual Front Time
Amplitude (kV)
100%
T2 = Virtual Time to Half
90%
Written as T1 / T2 wave
Typical is 8/20 wave
50%
30%
0
T
O1
T2
Time (s)
Protective Levels
Transformer Insulation Levels
Arrester Protective Levels
•
Chopped Wave Withstand (CWW) 1.2s
rise time, crest value of 1.10 x BIL
•
Front of Wave (FOW) 0.5s rise time and
crest is a function of arrester rating
•
BIL = Basic Impulse Insulation Level
•
•
BSL = Basic Switching Insulation Level
BSL = 0.83 x BIL
Lightning Impulse Protective Level (LPL)
8/20 s impulse w/ 1.5, 3, 5, 10, & 20 kA
crest
•
Switching Impulse Protective Level (SPL)
classifying current w/ rise time of 45-60 s
Sources: IEEE C57.12.90
IEEE C57.12.00
Sources: IEEE C62.22
IEEE C62.11
Transformer Insulation Coordination
Per IEEE Guide (C62.22)
PRx =
Insulation Withstand Level of Equip.
Voltage at Protected Equipment
PR1 = CWW
FOW
= 1.1 x BIL
FOW
> 1.2
PR2 = BIL > 1.2
LPL
PRS =
BSL = 0.83 x BIL > 1.15
SPL
SPL
Values for FOW, LPL, & SPL can be obtained from the arrester manufacturer’s
catalogue.
Catalogue Data Example
Arrester
Rating
(kV rms)
Arrester
MCOV
(kV rms)
192
152.0
PR1 =
PR2 =
Front-of-wave
Protective
Level
(kV Crest)
TOV
(kV rms)
1 sec
10 sec
222.5
212.0
CWW
FOW
BIL
LPL
=
=
1.1 x BIL
FOW
Maximum Discharge Voltage (kV Crest)
8/20 μs Current Wave
1.5 kA
3 kA
5 kA
10 kA
20 kA
40 kA
386
403
417
444
487
544
482
=
1.1 x 825
= 1.88 > 1.2
482
825
= 1.69 > 1.2
487
Catalogue Data Example
(Continued)
Switching Surge
Protective Level
(kV crest)
125 A
250 A
500 A
1000 A
344
352
362
375
PRS = BSL = 0.83 x BIL = 0.83 x 825 = 1.82 > 1.15
SPL
375
SPL
IEEE recommends using a switching surge coordinating current
of 500 A for system voltages up to 150 kV, 1000 A up to 325 kV,
and 2000 A up to 900 kV.
Resistively-Grounded Transformer
Concern in on the secondary of the transformer
• Neutral bushing (Xo) voltage
shifts during phase-to-ground
faults
• Produces over voltage on unfaulted phases during phase-toground faults
• Requires an arrester with higher
MCOV
• Do NOT depend on TOV curve of
arrester for this application.
Why not depend on the TOV curve?
Because it’s not necessary.
Solidly Grounded
• Apply a 12 kV, 10.2 kV MCOV arrester
• PR1 = 3.36
• PR2 = 2.98
• PRS = 3.51
Resistively Grounded
• Apply an 18 kV, 15.3 kV MCOV arrester
• PR1 = 2.25
• PR2 = 1.99
• PRS = 2.34
•Both cases assume 110 kV BIL on the secondary winding of the transformer.
•Even by increasing the arrester MCOV rating by two steps, the protective ratios are still well
above the IEEE recommended value.
Transformer High Voltage Side Fault When DG is present
Scenario:
• DG is present on low voltage side of
transformer
• Ground Fault on HV bus
• HV bus cleared either by local
breakers or remote end breakers.
• Backup relaying may take up to 20
cycles to trip the LV BKR.
Question:
• Will our standard arrester withstand
TOV caused by the delta winding on
the isolated bus?
Analyze the DG Scenario
• Standard arrester applied at 230 kV is a 192 kV (duty cycle) 152 kV MCOV
• When the fault occurs and the bus is cleared from the high side, voltage
on un-faulted phases rises to 230 kV phase-to-ground. This is 1.5 per unit
MCOV.
• It was determined that that BACK UP relaying would take 20 cycles to clear
the LV breaker.
• This would exceed the TOV curve of the arrester.
What are these Challenges?
1.6
TOV Curve
1.5
1.4
1.3
1.2
`
Voltage per unit MCOV
20 cycles = 1/3 second. Yes the arrester’s
TOV curve is exceeded and it will fail.
0.01
0.1
1.0
Max Time Duration in seconds
10.0
So which arrester do we apply?
• Would an arrester with an MCOV higher than the anticipated TOV work in
this case?
• No, because the discharge voltages would be too high to coordinate with
the BIL of the transformer?
• Therefore, we have to select an arrester with low enough discharge
voltages to protect our transformer, but still be able to withstand the TOV.
Determine the proper MCOV
• From the TOV curve, we know that at 20 cycles, the previous arrester can
withstand 1.45 x MCOV for 20 cycles.
• Use that as a starting point:
MCOV ’ >
TOV
1.45
= 158.6 kV
The next available size arrester is a 198 kV, 160 kV MCOV model.
Will it work?
• TOV: It will withstand 234.2 kV for 1 sec.
• FOW = 508 kV  PR1 = 1.78
Prev. Ratio
(1.88)
• LPL = 512 kV  PR2 = 1.61
(1.69)
• SPL = 395 kV  PRS = 1.73
(1.82)
Do we need arresters at transmission line terminals in
substations?
SUBSTATION BUS
•
•
•
BREAKER
•
ARRESTER
Lightning Flash may contain many strokes
Arresters must be located on the line side
of the breaker
Mandatory at EHV, should be considered
at lower voltages
Should be based on
-Economics
-Importance of substation
-MTBF of breaker’s voltage class
-Presence of automatic tripping schemes
in areas around EHV switch yards
Conclusion
A company-specific guide is necessary to explain and
solve arrester standards challenges that are specific to
your system.
• Specific Explanations -> less confusion
• Fewer building block -> fewer mistakes
• Specific application examples -> fewer misapplications
Bibliography
[1] IEEE Std. 4-2013, IEEE Standard for High Voltage Testing Techniques.
[2] IEEE Std. C57.12.00-2010, IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and
Regulating Transformers.
[3] IEEE Std. C57.12.90, IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating
Transformers.
[4] IEEE Std. C62.11-2012, Standard for Metal-Oxide Surge Arresters for AC Power Circuits (>1 kV).
[5] IEEE Std. C62.22-2009, IEEE Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current
Systems (>1 kV).
[6] Central Station Engineers of the Westinghouse Electric Corporation, Electrical Transmission and Distribution
Reference Book, re-published by ABB.