Selecting Arrester MCOV-Uc

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ArresterFacts

ArresterFacts 010 010 The The Lightning Lightning Surge Surge and and ArrestersArresters

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Copyright ArresterWorks ArresterWorks 2008 2008 Jonathan Jonathan J. J. Woodworth Woodworth Page1Page1

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Selecting Arrester

MCOV and U

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Prepared by Prepared by Jonathan Woodworth Jonathan Woodworth Consulting Engineer Consulting Engineer ArresterWorks ArresterWorks Feb 12, 2009 Feb 12, 2009

Part 1 of Arrester Selection Guide

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Selecting Arrester MCOV and U

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Introduction

There are several necessary steps that There are several necessary steps that need to be taken when selecting an arrester need to be taken when selecting an arrester for an application. An early step in this

for an application. An early step in this selection is the determination of the voltage selection is the determination of the voltage rating of

rating of the arrester. the arrester. The only The only voltagevoltage rating of an arrester that is important is the rating of an arrester that is important is the MCOV (Maximum Continuous Operating MCOV (Maximum Continuous Operating Voltage

Voltage IEEEIEEE) ) and and Uc Uc (Continuous(Continuous

Operating Voltage

Operating Voltage IECIEC). This MCOV - Uc). This MCOV - Uc

rating however is not always obvious rating however is not always obvious without a fairly good understanding of the without a fairly good understanding of the system to which it is to be applied. The system to which it is to be applied. The objective of this ArresterFacts is to make objective of this ArresterFacts is to make this decision clearer and understandable. this decision clearer and understandable.

Definitions

MCOV rating

MCOV rating ((IIEEEEEE))- The maximum- The maximum

designated root-mean square (rms) value of designated root-mean square (rms) value of power frequency voltage that may be

power frequency voltage that may be

applied continuously between the terminals applied continuously between the terminals of an arrester.

of an arrester.

Duty-cycle voltage rating

Duty-cycle voltage rating ((IEEEIEEE))- The- The

designated maximum permissible voltage designated maximum permissible voltage between its terminals at which an arrester is between its terminals at which an arrester is designed to perform its duty cycle test. designed to perform its duty cycle test. TOV Curve

TOV Curve – – A graph that shows the power A graph that shows the power frequency withstand voltage vs. time for frequency withstand voltage vs. time for arrester from .01 sec to 100,000 sec

arrester from .01 sec to 100,000 sec ((IEEEIEEE,, IEC

IEC))

Ground Fault

Ground Fault – – An event where current An event where current flows from the power system to ground flows from the power system to ground when a system phase conductor is when a system phase conductor is

connected to earth either through a direct connected to earth either through a direct contact or through an arc.

contact or through an arc. ((IEEEIEEE,, IECIEC))

Uc - Continuous operating voltage Uc - Continuous operating voltage ((IECIEC))

The designated permissible r.m.s. value of The designated permissible r.m.s. value of power-frequency voltage that may be power-frequency voltage that may be applied continuously between the arrester applied continuously between the arrester terminals indefinitely.

terminals indefinitely.

Ur - Rated voltage of an arrester Ur - Rated voltage of an arrester ((IECIEC))

Maximum permissible r.m.s. value of Maximum permissible r.m.s. value of power-frequency voltage between its terminals at frequency voltage between its terminals at which it is designed to operate correctly which it is designed to operate correctly under temporary overvoltage conditions as under temporary overvoltage conditions as established in the operating duty tests. established in the operating duty tests.

NOTE 1 NOTE 1

The rated voltage is used

The rated voltage is used as a reference parameter for theas a reference parameter for the specification of

specification of operating characteristics.operating characteristics. NOTE 2

NOTE 2

The rated voltage as defined in this standard is the 10 s The rated voltage as defined in this standard is the 10 s power-frequency voltage used in the operating duty test power-frequency voltage used in the operating duty test after high-current or long-duration impulses. Tests used to after high-current or long-duration impulses. Tests used to establish the voltage rating in IEC 60099-1, as well as establish the voltage rating in IEC 60099-1, as well as some national standards, involve the application of some national standards, involve the application of repetitive impulses at nominal current with power repetitive impulses at nominal current with power frequency voltage applied. Attention is drawn to the fact frequency voltage applied. Attention is drawn to the fact that these two methods used to established rating that these two methods used to established rating do notdo not necessarily produce equivalent values.

necessarily produce equivalent values.

Determining Line-Gnd Voltage

and Minimum MCOV or Uc

When arresters are applied to protect When arresters are applied to protect systems from lightning or switching surges, systems from lightning or switching surges, they are installed between the phase and they are installed between the phase and earth.

earth. For this application, the For this application, the MCOV of MCOV of thethe installed arrester must be equal or higher to installed arrester must be equal or higher to the continuous voltage between the phase the continuous voltage between the phase and earth.

and earth. On three On three phase systems, thephase systems, the line to ground voltage is equal to the phase line to ground voltage is equal to the phase to phase

to phase voltage divided by voltage divided by 1.73. 1.73. ForFor example, on a 760kV transmission system, example, on a 760kV transmission system, the nominal system phase to phase voltage the nominal system phase to phase voltage is 760kV therefore the line to earth voltage is 760kV therefore the line to earth voltage would be

would be 440kV. 440kV. Since all Since all systems havesystems have some regulation error, this too must be some regulation error, this too must be taken into

taken into consideration. consideration. If the If the regulation isregulation is 10%, then for example, on the above

10%, then for example, on the above

system, the line to ground voltage could be system, the line to ground voltage could be 440x

440x 1.10 = 1.10 = 485kV. 485kV. The The MCOV MCOV or Uc or Uc oror an arrester for this system at a minimum an arrester for this system at a minimum should be 485kV.

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ArresterFacts 016 016 Selecting Selecting an an Arresters Arresters MCOV MCOV or or UcUc

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Typical IEEE System Voltages Typical IEEE System Voltages Nom Nom Line to Line to Line Line Voltage Voltage Max Line Max Line to Line to Line Voltage Voltage Max Line Max Line to Grnd to Grnd Voltage Voltage Min Min MCOV MCOV kV kV rms rms kV kV rms rms kV kV rms rms kV kV rmsrms 2.40 2.52 1.46 1.46 2.40 2.52 1.46 1.46 4.16 4.37 2.52 2.52 4.16 4.37 2.52 2.52 4.80 5.04 2.91 2.91 4.80 5.04 2.91 2.91 6.90 7.25 4.19 4.19 6.90 7.25 4.19 4.19 8.32 8.74 5.05 5.05 8.32 8.74 5.05 5.05 12.0 12.6 7.28 7.28 12.0 12.6 7.28 7.28 12.5 13.1 7.57 7.57 12.5 13.1 7.57 7.57 13.2 13.9 8.01 8.01 13.2 13.9 8.01 8.01 13.8 14.5 8.38 8.38 13.8 14.5 8.38 8.38 20.8 21.8 12.6 12.6 20.8 21.8 12.6 12.6 22.9 24.0 13.9 13.9 22.9 24.0 13.9 13.9 23.0 24.2 14.0 14.0 23.0 24.2 14.0 14.0 24.9 26.2 15.1 15.1 24.9 26.2 15.1 15.1 27.6 29.0 16.8 16.8 27.6 29.0 16.8 16.8 34.5 36.2 20.9 20.9 34.5 36.2 20.9 20.9 46.0 48.3 27.9 27.9 46.0 48.3 27.9 27.9 69.0 72.5 41.9 41.9 69.0 72.5 41.9 41.9 115.0 115.0 121 121 69.8 69.8 669.89.8 138.0 138.0 145 145 83.8 83.8 883.83.8 161.0 161.0 169 169 98 98 97.797.7 230.0 230.0 242 242 140 140 140140 345.0 345.0 362 362 209 209 209209 500.0 500.0 525 525 303 303 303303 765.0 765.0 800 800 462 462 462462

System Configurations

Once the system voltages are understood, Once the system voltages are understood, the next step in the selection process is to the next step in the selection process is to determine the system configuration to which determine the system configuration to which the arrester w

the arrester will be ill be applied. applied. In other In other words,words, one must determine if it is a wye or delta one must determine if it is a wye or delta system

system (star or (star or delta in delta in thethe IECIECworld). world). AlsoAlso needed for selection is to know how the needed for selection is to know how the system neutral conductor is used in the system neutral conductor is used in the circuit if there is

circuit if there is one. one. The power The power sourcesource transformer and the neutral bonding transformer and the neutral bonding scheme determine how high the line to scheme determine how high the line to ground voltage of the unfaulted phases ground voltage of the unfaulted phases

Typical IEC System Voltages Typical IEC System Voltages Nominal Nominal Line to Line to Line Line Voltage Voltage Typical Typical Max Line Max Line to Line to Line Voltage Voltage Max Line Max Line to Grnd to Grnd Voltage Voltage Minimum Minimum Uc Uc kV rms kV rms kV kV rms rms kV kV rms rms kV kV rmsrms 3.3 3.3 3.7 3.7 2.1 2.1 2.12.1 6.6 6.6 7.3 7.3 4.2 4.2 4.24.2 10.0 10.0 11.5 11.5 6.6 6.6 6.66.6 11.0 11.0 12.0 12.0 6.9 6.9 6.96.9 16.4 16.4 18.0 18.0 10.4 10.4 10.410.4 22.0 22.0 24.0 24.0 13.9 13.9 13.913.9 33.0 33.0 36.3 36.3 21.0 21.0 21.021.0 47.0 52 47.0 52 30.1 30.1 30.130.1 66.0 72 66.0 72 41.6 41.6 41.641.6 91.0 100 57.8 57.8 91.0 100 57.8 57.8 110.0 110.0 123 123 71.1 71.1 71.171.1 132.0 132.0 145 145 83.8 83.8 83.883.8 155.0 155.0 170 170 98.3 98.3 98.398.3 220.0 220.0 245 245 142 142 142142 275.0 275.0 300 300 173 173 173173 330.0 330.0 362 362 209 209 209209 400.0 400.0 420 420 243 243 243243 will rise

will rise during a during a ground fault. ground fault. FortunatelyFortunately the number of system configurations are the number of system configurations are limited.

limited.

The most common IEEE configuration is the The most common IEEE configuration is the 4 wire solid multi-grounded neutral as

4 wire solid multi-grounded neutral as shown in

shown in figure 2a. figure 2a. This is also This is also known asknown as an effectively grounded system.

an effectively grounded system.

Figure 2a

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Figure 2b Impedance or Resonant Grounded System Figure 2b Impedance or Resonant Grounded System

A common in

A common industrial andustrial and very comd very common IECmon IEC configuration is the 3 wire impedance

configuration is the 3 wire impedance grounded wye

grounded wye (or star). (or star). The reason The reason forfor popularity of this system is that the fault popularity of this system is that the fault current to earth is limited by the impedance. current to earth is limited by the impedance. When low impedance is used, it can limit When low impedance is used, it can limit the fault current to levels that allow for lower the fault current to levels that allow for lower fault current rated equipment to be used on fault current rated equipment to be used on the system. This is often a cost savings the system. This is often a cost savings configurati

configuration. on. When the When the impedance is impedance is high,high, a Petersen coil is used which can offer fault a Petersen coil is used which can offer fault extinguishing capabilities without using extinguishing capabilities without using breakers to break the fault. This is breakers to break the fault. This is sometimes referred to as a resonant sometimes referred to as a resonant grounded system.

grounded system. A third com

A third common system mon system configuratioconfiguration is ann is an isolated or

isolated or ungrounded system. ungrounded system. This canThis can be either delta

be either delta or wye or wye configured. configured. Figure 2cFigure 2c and 2d show these two systems.

and 2d show these two systems.

Figure 2c

Figure 2c Ungrounded Ungrounded systems (isolated systems (isolated neutral)neutral)

A common

A common transmission transmission line configuline configuration isration is the single grounded Wye as seen in Figure the single grounded Wye as seen in Figure 2d .

2d .

Figure 2d Single grounded neutral system

Figure 2d Single grounded neutral system (Uni-grounded(Uni-grounded system)

system)

Determining Phase Voltage Rise

due to Earth or Ground Faults

When a three phase power system

experiences a fault to earth on any one of experiences a fault to earth on any one of its phases, the two unfaulted phases its phases, the two unfaulted phases experience an increase in the voltage experience an increase in the voltage between

between the the phase phase and and ground. ground. SinceSince arresters are most often applied between arresters are most often applied between the phase conductor and earth, then they the phase conductor and earth, then they also see this increase in voltage across their also see this increase in voltage across their terminals.

terminals. This increase This increase in in voltage willvoltage will remain across the arrester until a system remain across the arrester until a system breaker operates and breaks or interrupts breaker operates and breaks or interrupts the fault.

the fault. This is a This is a very significant event invery significant event in the life of an arrester and must be

the life of an arrester and must be accounted for during the voltage rating accounted for during the voltage rating selection of an arrester.

selection of an arrester.

The determination of a voltage rise during a The determination of a voltage rise during a ground fault is not an easy task if a precise ground fault is not an easy task if a precise value is

value is desired. desired. There are some There are some rules ofrules of thumb and graphs that can be used, but thumb and graphs that can be used, but these are quit crude and difficult at best to these are quit crude and difficult at best to use.

use. Annex C oAnnex C of IEEE standard f IEEE standard C62.22 andC62.22 and Annex

Annex A of IEC 60A of IEC 60099-5 co099-5 cover this subver this subject.ject. For distribution systems where the system For distribution systems where the system and transformer impedances are relatively and transformer impedances are relatively unknown, a worst case scenario is used for unknown, a worst case scenario is used for each type

each type of system. of system. The voltage The voltage riserise during a fault in these cases is determined during a fault in these cases is determined by multiplying the line to ground voltage by by multiplying the line to ground voltage by

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a ground fault factor or earth fault factor. a ground fault factor or earth fault factor. Figure 3 lists the ground fault factors used Figure 3 lists the ground fault factors used to determine the unfaulted phase voltage to determine the unfaulted phase voltage rise during a ground fault.

rise during a ground fault.

Type of System Type of System Ground Ground Fault Fault Factor Factor Solidly Grounded 4 wire

Solidly Grounded 4 wire systems systems 1.251.25 Uni-grounded 3 wire Uni-grounded 3 wire systems systems 1.41.4 Impedance grounded Impedance grounded systems systems 1.731.73 Isolated Ground Systems

Isolated Ground Systems and Delta Systems

and Delta Systems 1.731.73

Figure

Figure 3 3 Ground Ground Fault Fault FactorsFactors

For example in a 13.8kV multi-grounded For example in a 13.8kV multi-grounded system, the maximum continuous line to system, the maximum continuous line to ground voltage

ground voltage is 8is 8.38kV. .38kV. The voltageThe voltage during a ground fault on the unfaulted during a ground fault on the unfaulted phases can reach 8.38 x 1.25 or 10.47kV phases can reach 8.38 x 1.25 or 10.47kV rms.

rms. This This is is the the voltage voltage an an arrester will arrester will seesee across its terminals for as long as the fault across its terminals for as long as the fault exists.

exists.

Mixed Configurations Mixed Configurations

It is also important to note that the It is also important to note that the grounding of the neutral at the source grounding of the neutral at the source transformer is the configuration referred to transformer is the configuration referred to in determining the voltage rise of the

in determining the voltage rise of the system.

system.

For example as seen in Figure 5, a For example as seen in Figure 5, a delta/delta transformer is tied to a solidly delta/delta transformer is tied to a solidly grounded wye

grounded wye system. system. In this In this case MOV1case MOV1 should be sized for a solidly grounded should be sized for a solidly grounded system, and MOV 2 should be sized for an system, and MOV 2 should be sized for an isolated ground system.

isolated ground system.

Figure

Figure 5 Mixed 5 Mixed Configuration Configuration Use Use the the sourcesource transformer grounding scheme to determine the MOV transformer grounding scheme to determine the MOV rating

rating

Using the TOV Curve to Select

an Arrester

’’

s MCOV

After the

After the system consystem configuration figuration and poteand potentialntial overvoltage is determined, it must be

overvoltage is determined, it must be compared to the arrester TOV curve. compared to the arrester TOV curve.

Figure 6 shows TOV curves of several types Figure 6 shows TOV curves of several types of

of arresters. arresters. Figure Figure 6 6 shows shows a a comparisoncomparison of system overvoltage and arrester TOV of system overvoltage and arrester TOV capability.

capability.

Figure

Figure 4 4 Potential Potential System System OvervoltagesOvervoltages

Source Source Transformer Transformer

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In the example in Figure 7, the selected In the example in Figure 7, the selected distribution arrester would not withstand an distribution arrester would not withstand an overvoltage of an ungrounded or delta overvoltage of an ungrounded or delta system, but would withstand an overvoltage system, but would withstand an overvoltage from a uni-grounded and multi-grounded from a uni-grounded and multi-grounded system.

system. However However if if a a gapped gapped MOVMOV arrester was selected, it could withstand arrester was selected, it could withstand even an ungrounded system overvoltage. even an ungrounded system overvoltage.

For distribution systems

For distribution systems, the process of, the process of comparing the potential system overvoltage comparing the potential system overvoltage and the arrester withstand capability is and the arrester withstand capability is seldom completed because the time of the seldom completed because the time of the overvoltage is

overvoltage is unknown. unknown. Because of Because of thisthis issue, for all systems other than the multi issue, for all systems other than the multi grounded system, the MCOV or Uc of the grounded system, the MCOV or Uc of the arrester is selected to equal or exceed the arrester is selected to equal or exceed the line to

line to line voltage. line voltage. Most manufacturersMost manufacturers also offer a quick lookup table to select the also offer a quick lookup table to select the arrester rating based on the system to arrester rating based on the system to which it is

which it is attached. attached. See Figure See Figure 8 for 8 for thisthis recommendation.

recommendation.

For substation applications For substation applications, the, the comparison of the potential system comparison of the potential system overvoltage and the arrester overvoltage overvoltage and the arrester overvoltage withstand capability is essential in selecting withstand capability is essential in selecting the arrester MCOV or

the arrester MCOV or Uc. Uc. In the In the case ofcase of transmission systems and substations, the transmission systems and substations, the expected system overvoltage magnitude expected system overvoltage magnitude and duration are known quantities so this and duration are known quantities so this comparison is quite accurate.

comparison is quite accurate.

The best means of obtaining the expected The best means of obtaining the expected overvoltage during a fault on a transmission overvoltage during a fault on a transmission system is to ask the persons responsible for system is to ask the persons responsible for relay settings.

relay settings. They They have usually have usually modeledmodeled the system extensively with proven

the system extensively with proven

software, they can supply both magnitude software, they can supply both magnitude and durations of faults at most location on and durations of faults at most location on the

the system. system. Use Use this this information information toto compare

compare against the target arresters’ TOVagainst the target arresters’ TOV curve.

curve.

Transmission Line Arresters

The selection of transmission line arresters The selection of transmission line arresters (TLA) MCOV rating or Uc rating is different (TLA) MCOV rating or Uc rating is different than a

than a distributiodistribution n or or substation arrester. substation arrester. InIn the case of TLA’s the objective is to

the case of TLA’s the objective is to onlyonly protect insulators from the undesirable protect insulators from the undesirable backflash during a switching or lightning backflash during a switching or lightning surge. Since overhead insulators are surge. Since overhead insulators are

generally a self-restoring type of insulation it generally a self-restoring type of insulation it is not imperative to have the lowest possible is not imperative to have the lowest possible clamping voltage for the arrester to mitigate clamping voltage for the arrester to mitigate

Figure 7

Figure 7 Comparing TOV Comparing TOV Curve and Curve and PotentialPotential System Overvoltage

System Overvoltage

Figure 6 Example Arrester TOV Curve Figure 6 Example Arrester TOV Curve

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flashover.

flashover. Sometimes it Sometimes it is also is also desirable todesirable to size the arrester so that it does not absorb size the arrester so that it does not absorb any significant energy during a switching any significant energy during a switching surge.

surge. In this In this case increasing the case increasing the MCOV orMCOV or Uc rating is an effective means to do just Uc rating is an effective means to do just this.

this. However However if if the the TLA TLA is being is being applied applied toto mitigate switching surges, then the arrester mitigate switching surges, then the arrester MCOV should be similar to that of the MCOV should be similar to that of the substation arresters.

substation arresters.

Summary

Selection of an arrester MCOV rating or Uc Selection of an arrester MCOV rating or Uc rating can be daunting at times, but once rating can be daunting at times, but once the system configuration and overvoltage the system configuration and overvoltage potentials are known it is a simple

potentials are known it is a simple comparison.

comparison.

***************************** *****************************

Figure 8a

Figure 8a IEEE MCOV IEEE MCOV SuggesteSuggested Ratings d Ratings (based on (based on historical prefehistorical preference and Trence and TOV anaOV analysis)lysis)

Typical IEEE System

Voltages

Suggested IEEE Arrester MCOV Rating

Nom Nom Line to Line to Line Line Voltage Voltage Max Line Max Line to Line to Line Voltage Voltage Max Line Max Line to Grnd to Grnd Voltage Voltage Solid Solid Multi-grounded grounded Systems ( 4 wire) Systems ( 4 wire) Uni-grounded Uni-grounded Systems Systems (3 wire) (3 wire) Impedance Impedance grounded, grounded, Ungrounded and Ungrounded and Delta Systems Delta Systems Transmission Line Transmission Line Arresters for Arresters for Lightning Lightning Protection Only Protection Only kV

kV rms rms kV kV rms rms kV kV rms rms MCOV MCOV MCOV MCOV [*] [*] MCOV MCOV [*][*]

2.40 2.52 1.46 2.40 2.52 1.46 2.552.55 4.16 4.37 2.52 4.16 4.37 2.52 2.55 2.55 5.1 5.1 5.15.1 4.80 5.04 2.91 4.80 5.04 2.91 5.15.1 6.90 7.25 4.19 6.90 7.25 4.19 7.657.65 8.32 8.74 5.05 8.32 8.74 5.05 5.1 5.1 7.657.65 12.0 12.6 7.28 12.0 12.6 7.28 7.65 7.65 10.210.2 12.5 13.1 7.57 12.5 13.1 7.57 7.65 7.65 12.7 12.7 [7.65][7.65] 13.2 13.9 8.01 13.2 13.9 8.01 8.4 8.4 12.7 12.7 [8.4][8.4] 13.8 14.5 8.38 13.8 14.5 8.38 8.4 8.4 12.7 12.7 [8.4] [8.4] 15.3 15.3 [8.4] [8.4] 15.315.3 20.8 21.8 12.6 20.8 21.8 12.6 12.7 12.7 15.3 15.3 [12.7] [12.7] 2121 22.9 24.0 13.9 22.9 24.0 13.9 15.3 15.3 19.5 19.5 [15.3] [15.3] 22-2422-24 23.0 24.2 14.0 23.0 24.2 14.0 15.3-17 15.3-17 24.4 24.4 [15.3] [15.3] 22-2422-24 24.9 26.2 15.1 24.9 26.2 15.1 15.3 15.3 22 22 [15.3] [15.3] 24-2924-29 27.6 29.0 16.8 27.6 29.0 16.8 17 17 24.4 24.4 [17] [17] 24-2924-29 34.5 36.2 20.9 34.5 36.2 20.9 22 22 29 29 [22] [22] 36-39 36-39 [22] [22] 29-3629-36 46.0 48.3 27.9 46.0 48.3 27.9 29 29 39 39 29-3929-39 69.0 72.5 41.9 69.0 72.5 41.9 42-48 42-48 53-67 53-67 48-6748-67 115.0 115.0 121 121 69.869.8 70-76 70-76 84-98 84-98 76-9876-98 138.0 138.0 145 145 83.883.8 84-98 84-98 106-115 106-115 98-11598-115 161.0 161.0 169 169 9898 98-115 98-115 115-131 115-131 115-131115-131 230.0 230.0 242 242 140140 140-152 140-152 182-190 182-190 152-190152-190 345.0 345.0 362 362 209209 209-245 209-245 230-289 230-289 245-289245-289 500.0 500.0 525 525 303303 318-452 318-452 >452>452 765.0 765.0 800 800 462462 462-490 462-490 >490>490

[*] MCOV rating of a Gapped MOV arrester [*] MCOV rating of a Gapped MOV arrester

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Figure 8b

Figure 8b Suggested Suggested Uc for Uc for IEC syIEC systemsstems

Typical IEC System

Voltages

Suggested Uc for IEC Systems

Nominal Nominal Line to Line to Line Line Voltage Voltage Typical Typical Max Line Max Line to Line to Line Voltage Voltage Max Line Max Line to Grnd to Grnd Voltage Voltage Solidly Earthed Solidly Earthed Neutral at the Neutral at the Source Source Transformer Transformer Impedance Earthed, Impedance Earthed, Isolated and Delta Isolated and Delta

Systems Systems Transmission Line Transmission Line Arresters for Arresters for Lightning Protection Lightning Protection Only Only kV rms kV rms kV kV rms rms kV kV rmsrms Uc Uc UcUc 3.3 3.7 2.1 3.3 3.7 2.1 2.4 2.4 4.04.0 6.6 7.3 4.2 6.6 7.3 4.2 4.8 4.8 7.27.2 10.0 10.0 11.5 11.5 6.66.6 7.2 7.2 1212 11.0 11.0 12.0 12.0 6.96.9 9.6 9.6 12 12 1212 16.4 18.0 10.4 16.4 18.0 10.4 12 12 18 18 1818 22.0 24.0 13.9 22.0 24.0 13.9 16.8-24 16.8-24 24 24 2424 33.0 36.3 21.0 33.0 36.3 21.0 24-36 24-36 36 36 3636 47.0 52 30.1 47.0 52 30.1 33-43 33-43 53 53 43-5343-53 66.0 72 41.6 66.0 72 41.6 43-58 43-58 72 72 58-7258-72 91.0 100 57.8 91.0 100 57.8 66-77 66-77 102 102 77-10277-102 110 123 71.1 110 123 71.1 77-86 77-86 125 125 86-12586-125 132 145 83.8 132 145 83.8 96-115 96-115 145 145 115-145115-145 155 170 98.3 155 170 98.3 110-125 110-125 170 170 125-170125-170 220 245 142 220 245 142 154-188 154-188 245 245 188-245188-245 275 300 173 275 300 173 182-192 182-192 300 300 192-300192-300 330 362 209 330 362 209 221-230 221-230 360 360 230-360230-360 400 420 243 400 420 243 269-288 269-288 420 420 288-420288-420 500 550 318 500 550 318 420-440 420-440 550 550 440-550440-550

Other ArresterFacts Available Other ArresterFacts Available

Arrester Lead Length

Field Testing Arresters

Infrared Thermometer

Guide for Selecting an Arrester Field Test Method

VI Characteristics

The Externally Gapped Arrester (EGLA)

The Disconnector

Understanding Mechanical Tests of Arresters

What is a Lightning Arrester?

The Switching Surge and Arresters

The Lightning Surge and Arresters

Understanding the Arrester Energy Handling

Issue

Understanding Discharge Voltage

What is a Riser Pole Arrester?

ArresterFacts Usage ArresterFacts Usage ArresterFact

ArresterFacts are Copyrighted dos are Copyrighted do cuments intended forcuments intended for the educati

the education of arreon of arrester users aster users and stakeholdernd stakeholders. s. IfIf you choose to copy any part of this d

you choose to copy any part of this d ocument forocument for teaching purposes you have my permission, however teaching purposes you have my permission, however please give ArresterWorks proper credit.

please give ArresterWorks proper credit. Thank you for using

Thank you for using www.ArresterWorks.comwww.ArresterWorks.comas youras your source of information on high

source of information on high voltage surge arresters.voltage surge arresters. Jonathan Woodworth Jonathan Woodworth Principal Consultant Principal Consultant ArresterWorks ArresterWorks

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Selecting Arrester MCOV-Uc

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Selecting Arrester

Selecting Arrester

MCOV and U

MCOV and U

cc

Part 1 of Arrester Selection Guide

Part 1 of Arrester Selection Guide

Selecting Arrester MCOV and U

Selecting Arrester MCOV and U

Contents

Contents

Introduction

Introduction

Definitions

Definitions

Determining Line-Gnd Voltage

Determining Line-Gnd Voltage

and Minimum MCOV or Uc

and Minimum MCOV or Uc

System Configurations

System Configurations

Determining Phase Voltage Rise

Determining Phase Voltage Rise

due to Earth or Ground Faults

due to Earth or Ground Faults

Using the TOV Curve to Select

Using the TOV Curve to Select

an Arrester

an Arrester

s MCOV

s MCOV

Transmission Line Arresters

Transmission Line Arresters

Summary

Summary

Typical IEEE System

Typical IEEE System

Voltages

Voltages

Suggested IEEE Arrester MCOV Rating

Suggested IEEE Arrester MCOV Rating

Typical IEC System

Typical IEC System

Voltages

Voltages

Suggested Uc for IEC Systems

Suggested Uc for IEC Systems

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