Arc Flash Hazard in w Pp

8/10/2019 Arc Flash Hazard in w Pp

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Abstract The topic of this paper is the arc-flash hazard in

Wind Power Plants (WPP). A brief introduction of the concept

of arc flash is followed by the presentation of a methodology to

perform an arc-flash hazard analysis on a WPP collector system.

Issues such as faults being fed by multiple sources, as well as the

modeling of the fault current of the wind turbine generator are

addressed. The paper concludes with two examples using the

presented methodology.

Index Terms Arc-flash hazard, shock hazard, wind powerplants.

I. INTRODUCTION

This paper investigates and discusses the arc-flash hazard

in a Wind Power Plant (WPP) collector system. It will define

an arc-flash calculation methodology for multiple sources and

provide two examples of the methodology.

The approach this paper will be as follows: Section II dis-

cusses the arc-flash hazard in general the causes of arcs, the

available models to calculate incident energy levels and cer-

tain concerns, which are specific to wind power plants. Sec-

tion III describes the possible mitigation strategies defining

an arc-flash protection boundary, the types of personal protec-

tive equipment (PPE) available, and possible means of reduc-

ing incident energy levels through various technologies. Sec-

tion IV presents a detailed, structured method to calculate arc-

flash incident energy levels in a WPP. Section V concludes

the paper with two examples.

II. ARC-FLASH HAZARD

A. General Description of Arc-flash Hazard

An electric arc is the result of the electrical breakdown of

an insulator (typically air) resulting in current flowing through

the insulator. An arc-flash fault is often caused by:

Human mistake (e.g., dropping a tool, accidental con-tact with live parts)

Environment (e.g., contamination, water vapor)

Equipment failure (e.g., insufficient insulation, deteri-orated insulation, corrosion)

Overvoltage conditions

A combination of the above.

In power systems the path of the arc can be between two

phases, multiple phases, single phase and ground, and multiple

phases and ground. The arc flash is surrounded by a conduc-

tive plasma cloud and often vaporized conductive material,

which increases the likelihood of a single-phase fault making

contact with nearby phases and escalating into a three-phasefault. This is more likely to happen on systems with low insu-

lation level and at locations with small clearance between

conductors, such as low-voltage systems and switchgear

equipment. For these cases a single-phase fault often escalates

into a three-phase fault within a few milliseconds (Schau and

Stade, 1995).

A large amount of energy is released during an arc flash,

primarily in the form of heat. The burn hazard during an arc

flash is the main concern for worker safety (e.g. Lee, 1982).

Additionally, the energy released in the form of pressure is of

concern for worker safety since the pressure wave can directly

injure the worker or can destroy objects resulting in shrapnel

that can injure the worker (Lee, 1987). The part of the arcflash that is associated with the release of a pressure wave is

commonly referred to as the arc blast (Dugan, 2007).

The arc-flash fault current is generally smaller than the

bolted fault current of the system due to the impedance of the

arc. The incident energy is the energy impressed on a surface

at a certain distance from the arc and is used as a measure to

quantify the burn hazard from an arc-flash.

Arc-flash energy is transferred to the surroundings by con-

duction, convection, and radiation energies (Wilkins et al.,

2004). For enclosed equipment, a substantial part of the

arc-flash energy is also converted to pressure. Figure 1 illu-

strates the energy dissipation for open-space and enclosed-

space configuration. For arcs in open spaces, the geometry of

the energy emission is spherical and consequently the fraction

of the total arc energy that is emitted as radiant energy is pro-

portional to 1/D2. On the other hand, there is a focusing effect

for the enclosed-space configuration, which increases the

energy emitted in the direction of the opening. Consequently,

the radiation emitted from the box is less divergent than for

the spherical geometry resulting in a distance relationship of

1/Dxwith the distance exponential x being smaller than 2.

Arc-Flash Hazard in Wind Power Plants

IEEE PES Wind Plant Collector System Design Working Group

Contributing Members: M. Bradt, M. R. Behnke, T.A. Bellei, W. G. Bloethe, C. Brooks, E.H. Camm,

W. Dilling, B. Goltz, J. Li, J. Niemira, K. Nuckles, J. Patio, M. Reza, B. Richardson, N. Samaan, J. Schoene,T. Smith, I. Snyder, M. Starke, K. Tay, R. Walling, G. Zahalka

978-1-4244-6547-7/10/$26.00 2010 IEEE


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Figure 1: Distance dependence of incident energy for open-space and

enclosed-space configurations.

B. Arc-Flash Models

Arc-flash models estimate the incident heat energies a per-

son near an arc fault is exposed to. The incident energy levels

calculated in an arc-flash hazard analysis determines arc-flash

hazard categories, which in turn guide the decision regarding

the appropriate Personal Protective Equipment (PPE) for a

person that works near energized equipment. The calculatedincident energies are vastly model dependent (e.g., Ammer-

man et al., 2008) and there is currently no consensus on which

model to employ in an arc-flash hazard analysis.

Models that are based on empirical data include the IEEE

1584 model for system voltages below 15 kV, the Doughty

model, sometimes referred to the NFPA 70E model, (Doughty

et al., 2000), and the Wilkins model (Wilkins et al., 2005).

The IEEE 1584 and Doughty models are purely empirical

while the Wilkins model is based both on empirical data and

circuit theory making it a semi-empirical or behavioral model.

In general, empirical and semi-empirical models are fitted to

test data and consequently are only applicable for the tested

range of the relevant parameters and for conditions that re-semble the test conditions.

Models that are based on theory include the Duke Power

model, which is available in the public domain, the commer-

cially available ARCPRO model, and models that are based on

theory published by Lee (1982). The Duke Power model and

the ARCPRO models are the models integrated into the Heat

Flux calculator software and the ARCPRO software, respec-

tively. The models were developed for single-phase arc faults

in open air. The single-phase, open-air incident energies can

be converted to incident energies during three-phase faults and

faults in enclosed spaces using adjustment factors. Note that

most arc faults start as single-phase faults and escalate to

three-phase faults within a few milliseconds. A complete de-

scription of the theory behind the Duke Power model and the

ARCPRO model is not publicly available and consequently it

is difficult to evaluate the physical soundness of the model.

The ARCPRO model was internally verified for part of the

accepted range of input parameters (Kinectrics, 2004) inde-

pendent verification for the completed range of input parame-ters is lacking. IEEE 1584 recommends using a theoretical

model for system voltages of 15 kV and above. This model is

based on the very conservative maximum power transfer as-

sumption (Lee, 1983). Lee does not present equations for the

incident energy calculations in his paper and there is an inter-

pretation of Lees work for calculating incident energies that is

different than the IEEE 1584 interpretation (Martin and Beat-

tie, 2005). These Lee-based models are different from all oth-

er models presented in this paper in that the incident energies

calculated with the Lee-based models are proportional to the

system voltage; all other models show no or very little direct

dependence of incident energy and system voltage above 5

kV. The proportionality of incident energy and system vol-tages in the Lee-based models results in apparently unrealisti-

cally large incident energy levels for large system voltages.

Input parameters for all arc-flash models are the available

bolted fault current and the arc duration. The bolted fault cur-

rent can be determined in a short-circuit analysis and the arc

duration is typically determined by the time it takes for the

protection device (typically fuses and/or protective relays) to

clear the fault. The incident energy is also sensitive to the

working distance and the arc length1. An arc-flash hazard

analysis is often performed with arc lengths and working dis-

tances from IEEE 1584 which gives typical values for given

system voltages and equipment types (open air, switchgear,

etc.).

Note that none of the models discussed here seems to prop-

erly account for the arc-flash energy balance. Arc-flash ener-

gy in the form of convective heating inside the plasma cloud is

ignored in the IEEE 1584 theoretical model used for system

voltages of 15 kV and above, which results in an overestima-

tion of the incident energy for working distances outside the

plasma cloud. The effect of the plasma cloud is also ignored

in the calorimetric measurements from which the IEEE 1584

data were obtained since the sensors were located outside the

plasma cloud, where the arc-flash energy is primarily radiative

(Wilkins et al., 2005). This should not affect the accuracy of

the IEEE 1584 empirical model for working distances outsidethe plasma cloud, but will likely result in an underestimation

of the incident energies predicted by the IEEE 1584 empirical

model if the working distance is inside the plasma cloud

boundary. This is a concern if the plasma cloud expands far

enough to reach the worker thereby exposing the worker to

1The arc is often assumed to be straight and under this assumption the arc

length is equal to the distance between bus bars. However, for long arcs thatcan develop in systems with high voltages and large bus-bar spacing, this

assumption is not accurate since the arc is often warped and therefore consi-

derably longer than the bus bar distance.


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energy levels that are potentially much higher than predicted

by any of the models discussed here. There is no consensus in

the literature about the dimension of the plasma cloud. Lee

(1982) assumed a spherical dimension for the plasma cloud

and predicted for one configuration an arc plasma diameter of

170 mm. On the other hand, for the same configuration,

Stokes and Sweeting (2005) experimentally determined a

much larger plasma expansion they measured an arc plasma

dimension of 3m x 1.5m from a photograph. Also, for en-closed space configurations the plasma cloud is likely to ex-

pand farther in the direction of the worker due to the focusing

effect (see Section IIA)

C. Arc-flash Concerns specific to Wind Plants

Typically, during wind plant commissioning, the equip-

ment inside the wind turbine tower has to be approached in an

energized state. This is a problem if the arc-flash analysis

predicts large incident energies at locations inside the turbine.

Temporary protection settings (e.g., relays set on instantane-

ous trip) may be applied to reduce the incident energy at loca-

tions with excessively high incident energy levels.

In particular, the arc-flash hazard inside the wind turbinetower may be more severe than predicted by the arc-flash ha-

zard analysis because of the following concerns:

Convective heat transfer that is not properly accountedfor in models used for the arc-flash hazard analysis in-

creases the incident energy if the worker is inside the

plasma cloud (see Section IIB). A worker location insidethe plasma cloud is likely due to (1) the focusing effect of

the arc-flash in the enclosed space configuration, which

directs the plasma towards the worker and (2) the tightspace inside the turbine tower, which may result in a re-

duced working distance.

The arc-blast hazard (the hazard due to the pressure

from the arc fault) is potentially more severe inside theturbine tower because of (1) the focusing effect of the

blast in the enclosed-space configuration, which increasesthe pressure exerted on the worker, (2) the inability of the

worker to move away from the blast, and (3) the fall ha-

zard inside the turbine tower. Note that the arc-flash ha-zard analysis does typically not assess the blast hazard.

The two-second rule in IEEE 1584 (i.e., using twoseconds as the maximum time a person is exposed to an

arc-flash because the person will be able to move to safety

within that time) does not necessarily apply due to the re-stricted ability to move inside the turbine tower.

The duration of the arcing fault current contribution

from the turbine may depend on the turbine protection on-ly (i.e., there may not be any fuses/relay protection be-

tween the turbine and the arc fault location that discon-

nects the turbine from the fault). Consequently, to prop-erly account for the fault current contribution from the

turbines, some insight into the protection mechanism of

the turbine is required, which may not be always availableto the person performing the arc-flash analysis.

III. ARC-FLASH HAZARD PROTECTION

A. Protection Boundary

IEEE 1584 defines the arc-flash protection boundary to be

the area around an energized object in which a person without

PPE is at risk of receiving at least second degree burns from

an arc-flash originating from the energized object. Skin expo-

sure to energy levels that exceed 1.2 cal/cm2 can cause

second-degree burns. Persons within this area are required to

wear PPE. The flash protection boundary is determined in an

arc-flash analysis.

B. Protection Equipment

NFPA 70E (2004) classifies the arc-flash hazard according

to maximum incident energy a person can be exposed to. The

NFPA 70E hazard categories are listed in Table 1. Protection

requirements, such as Personal Protective Equipment (PPE),

are selected based on the hazard category. The PPE should

limit the energy exposure of the chest and face during an arc-

ing fault to curable burn energies (below 1.2 cal/cm2accord-

ing to IEEE 1584). In some cases the maximum incident

energy level may exceed 40 cal/cm2. For these cases, risk

consideration will play a major role. There is PPE available

above 40 cal/cm2, however the preferred approach is to always

work such high levels de-energized.

TABLE 1:NFPA70EHAZARD CATEGORIES

Category

Energy

Level

(cal/cm2)

Protective Clothing/PPE

0


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Figure 4: Scope of paper.

The dynamics of the generators behavior creates asyn-

chronous fault values and how that impacts quantification of

an arc-flash energy and on the response of the LVCB and its

trip logic is beyond the scope of this paper, which is focusing

on the collector system. Instead, a constant conservative fault

current from the WTG is assumed for the examples in Section

V.

B. Short-Circuit Study

1) Collect the system and installation data

It is imperative that the component data used for the

short-circuit study be accurate. The study must consider all

sources (e.g. utilities, generators, and motors) as well as the

impedances of the connecting system, transformers, and

cables. A single-line diagram is essential in finding the avail-

able fault currents at each WTG site and the WPP substation

bus.

2) Calculate arcing fault currents

Bolted fault currents can be calculated using any commercial-

ly available power engineering software that is capable of per-forming a short-circuit analysis. The reader must consider all

possible scenarios during operation and then utilize the com-

ponent data, along with the single-line diagram to obtain the

bolted fault current at each piece of equipment. Also all three

initial short-circuit conditions must be calculated, which arecommonly called: momentary, interrupting, and time-delayed

(or steady-state). For the example below the momentary will

be estimated at five time steady-state and interrupting will be

estimated at three times the steady-state.

Using the IEEE 1584 empirical model for the low-voltage

electrical equipment, only three-phase fault currents are neces-

sary to calculate arcing-fault currents or other standard percen-

tages can be used. For software such as ARCPRO and the

Duke Heat Flux calculator use SLG fault currents instead of

three-phase fault currents in their theoretical models. The

impact of a three-phase event using ARCPRO can then be

accomplished with the suggested multipliers to adjust the out-

put results to the three-phase open-air or cabinet (in-a-box)conditions.

3) Fault currents fed from multiple sources

In WPP, a fault almost anywhere will result in the fault be-

ing fed by two or more sources (e.g. a single generator, a

group of WTGs, and/or the external utility system). In such

scenarios, fault current contributions from various sources

need to be considered separately based on their protecting

device for use in the next subsection.

C. Coordination Study

1) Determine the fault clearing times

Using the time-current characteristic (TCC) curves and the

arcing-fault current, it becomes straightforward to determinethe time taken for a protecting overcurrent protective device to

clear a fault. This can be determined by drawing a vertical

line representing the arcing fault current and then determining

where it intersects with the maximum clearing time TCC

curve for the protecting device. For fuses this would be the

total clearing curve, because it represent the maximum time to

complete the open. For the LVCB, this could be on the manu-

factures overcurrent clearing curve in either direction or from

a signal from the WTG control module to trip, which will have

a different time delay than the overcurrent. Such LVCB time

delays could include logic responding to the low voltage ride-

through (LVRT) or other generator abnormal conditions. For

the MVCB relays at the collector feeder exits this will be theselected TCC curve, which must include the maximum break-

er opening/clearing times and any intentional coordination

delays.

At most WPP substations, there are differential protective

schemes which will detect faults within the differential zones.

The respective clearing devices within those zones will define

the clearing times for fault and arc-flash events within their

reach with the maximum time decay being associated with the

slowest breaker.

2) Clearing times for faults with multiple sources

For faults being fed from multiple sources, clearing times

for each source will need to be determined. For each fault

current calculated from subsection IV.B, a clearing time can

be found using the method discussed in IV.C.(1). The fault

current and its associated clearing time will be used to com-

pute the incident energy in the next section.

D. Arc-Flash Hazard Study

The method presented here is a simplified approach and

should provide a conservative value for the total incident

energy from an arc-flash event. The steps are:

1) Determine locations where the arc-flash is to be esti-

mated, such as the generic ones indicated inFigure 5.

Generator

Low-Voltage

Circuit Break-

er

Step Up

Transformer

Medium VoltageCircuit Breaker

(MVCB)

Low Voltage

(LV) equip-

ment locatedin or near the

wind turbine

tower

Medium Vol-tage (MV)

equipment

located on the

feeders and in

the Substation

: Possible fault locations


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2) Determine and/or establish the parameters and assump-

tions at each location, such as open air or cabinet situation,

likely working distance and arc gap distance. Use actual val-

ues for the distances or typical values from IEEE 1584.

The next three steps will be iterated at each selected fault

location based on how the multiple sources of fault current

contribute to the total fault current at that location through

time. The only step that may be skipped may be step 3, which

is the need to rerun the fault calculation after each deviceclears. Engineering judgment regarding the impact on values

after each loop may be small enough to allow working only

with each of the separate fault flows that would be contribut-

ing to the event. The initial fault calculation run may be ade-

quate.

3) Perform a short circuit fault calculation run on a particu-

lar location to obtain its fault flows for the momentary, inter-

rupting, and steady-state conditions from all sources and de-

termine how much is flowing through the protecting devices to

the fault location.

4) Determine the total clearing times for all the protecting

devices that are allowing fault flow to the fault location, such

as:a) At the collector feeder breaker relay use the TCC curve

and find the respective time for the fault flow passing through

it (taking into account a faster trip of the breaker due to a

higher momentary current) from the substation and external

power system, or

b) In the LV secondary cabinet of a wind turbine step-up

transformer use the transformer fuses, the LVCB TCC, or the

control logic to the LVCB to estimate the time depending on

the fault flow direction use either the transformer fuses or

the control logic to trip and clear the LVCB to estimate the

time.

5) Determine the amount of incident energy occurring at

this location by using an arc-flash model (such as the IEEE

1584 model, the ARCPRO model, or another model) with all

the respective contributing fault current sources (step 3) and

the clearing time of the next fastest clearing device (step 4).

For instance:

a) At a 34.5kV substation collector feeder exit - use

ARCPRO with the parameters from step 2, such as the open-

air three-phase case at 15-inch working distance and a 6-inch

arc gap (NESC Table 410-1), or

b) in a 600V secondary cabinet of a step-up transformer

use IEEE 1584 with the parameters from step 2, such as the

under-1000V and in-a-box options that will provide a 24-inch

working distance and an 1.25-inch arc gap (IEEE 1584 Tables2 and 3).

6) Loop steps 3 though 5 for each successively slower pro-

tecting device as it removes its respective amount of contribut-

ing fault flow from this location from the quickest device to

slowest device, until all the fault flow is eliminated.

7) Sum the arc-flash incident energy from each of the suc-

cessively passes for this location. This sum will be the total

incident energy for this location.

8) Finally, repeat the steps 3 through 7 for all selected loca-

tions.

V. EXAMPLES

Example 1 A fault and arc-flash occur at a 34.5kV

MVCB breaker exit on the collector-side of a collector feeder

with two turbines generating at an LV of 600V. Each WTG is

rated 2 MW, uses a 2500 kVA step-up transformer, and has a

rated current of about 33A at 34.5 kV. SeeFigure 5.

Figure 5: Example of fault and arc-flash in air at MV feeder.

There are three sources contributing to the fault: the system

and each of the two turbines. Since this is an open-air loca-

tion, the NESC default values from Table 410-1 offer a good

baseline. Fault flows to this location will determine the loops,

which are two in this case, Flow 1 and 2. The fault flow from

the substation bus (Flow 1) will be seen by the MVCB relay

and it will clear its portion of the fault flow first. For this ex-

ample (Figure 5), a fault flow for Flow 1 will be 5 kA and the

clearing time, which was obtained from reading the TCC plot

for the collector feeder relay at 5 kA, will be 0.10 seconds.

However, there is a second delayed fault flow (Flow 2)

that continues from the two turbines. At the wind turbines the

clearing devices are the LVCBs at 600 V and the two internal

transformer fuses on the 34.5-kV side. If the contributing cur-

rent from any one turbine is not large enough to trip the LVCB

on overcurrent, then the control scheme for the LVCB will

respond to a low-voltage condition and wait a predefined

amount of time based on the actual voltage that each turbine

sees against the predetermined low voltage ride-through

(LVRT) envelope. Note that the LVRT time delay is depen-dent on how low the voltage drops. Typically, if it goes below

15% of nominal it will be at its shortest delay, which will be

0.15 seconds in this example. However, the delay could be

longer if the voltage during the fault is higher than 15%. For

this example, the assumption will be that the control schemes

on all WT LVCBs on the collector feeder will simultaneously

see a sustained zero voltage to initiate a trip to their LVCB at

the minimum time delay. The total time delay for Flow 2 will

be 0.35 seconds. In this example, the 0.35 seconds consists of

0.15 seconds delay from the LVRT envelope and 0.10 seconds

Crow BarWT TowerTop

WT TowerMiddle

WT TowerBaseLV CB

Crow BarWT TowerTop

WT TowerMiddle

WT TowerBaseLVCB

Exp.Fuse

C.L.Fuse

WTTransf

FeedThruw/ Sw.

OutsideTowerStep-upTransformerTank

Exp.Fuse

C.L.Fuse

WTTransf

FeedThruw/ Sw.

OutsideTowerStep-upTransformerTank

Wind Turbine 1 Wind Turbine 2

Sub Transf

SYSTEM

MV CB

CollectorSub

Flow 1

HV

MV

LV LV

Flow 2

MV

: Possible fault location


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for the control circuit and LVCB clearing time to respond to

an external trip signal, as well as the initial 0.1 seconds for the

feeder circuit breaker to clear. As mentioned, it will be as-

sumed that both turbines will respond identically and at the

same time. However, this methodology is flexible enough to

allow for multiple delayed devices clearing at different times.

It is understood that the fault current from the WTG for the

initial few cycles will be obtained from the momentary condi-

tion of the short circuit, or around five times the rated current,and then drop off very quickly as the turbine responds electri-

cally. However, fault current from the WTG, before it drops

off as seen on the 34.5-kV system at the MVCB will be small

compared to the contribution from the substation and external

system. By the time the MVCB clears, the WTG contribu-

tions will either be at the interrupting or steady-state condi-

tion. For our example, the interrupting condition will be used,

or about 99 Amps (three times the rated current of 33 A).

Since both turbines are contributing to the fault flow, the de-

layed contribution is approximately 198 Amps. With these

values the incident energy is calculated with the respective

calculator, which is this case for both loops of the method

produced the values in Figure 6 for a total of 8.4 cal/cm2.

Figure 6: Arc-flash results for a fault in air at MV feeder ((not-to-

scale).

Example 2 Using the same WPP setup, the fault and arc-

flash now occurs in the LV (600 V) cabinet of the first wind

turbine step-up transformer. See Figure 7.

At this location there are also three sources, but two fault

flows. One flow is from the generator associated with this

transformer (Flow 3), and the other is from the collector feeder(Flow 4), which represents the contributions from the other

turbine, the substation and the external power system. Since

this location is in a cabinet (a.k.a. in-a-box) and is on the low-

voltage side, the assumptions and equations from IEEE 1584

empirically will be the best choice and will provide a good

baseline. Therefore, the working distance, gap size, and de-

fault values will come from their respective tables in the IEEE

1584 document. Because this fault is at 600 V, the Ampere

level of the fault flows (Flows 3 and 4) will be much higher

compared to a similar power level on the 34.5-kV system.

Since the fault currents are much higher on the 600 V side, the

arc-flash values are certain to be larger as well.

Assuming the MVCB feeder relay, the transformer fuses

and the LVCB are all coordinated, then the sequence of clear-

ing can be determined from the TCC plot that was used in

their coordination. That coordination would have the trans-

former fuses clearing before the feeder breaker to keep the

feeder energized while the generator is taken off-line. There-

fore the clearing sequence for this location will be between theLVCB and the fuses, with the fuses generally taking the longer

time and the LVCB tripping first to clear the local generator.

The LVCBs clearing time will be defined the same way here

as it was in the first example by the LVRT with a total time of

0.35 seconds. The clearing time will be shorter if the overcur-

rent mechanism responds before the LVRT trip.

Figure 7: Example of fault and arc-flash in an LV cabinet.

The fault flow from the wind turbine generator, Flow 3, in

Figure 7, will be the momentary condition fault current value

which could be nearly five times the rated current, or about

10,000 Amp plus the steady state fault flow from the collector

feeder, Flow 4, of 35 kA. The momentary condition is used

because it represents a conservative value. Thus, a total fault

flow of about 45 kA will result for 0.35 seconds. After the

LVCB clears the fault flow (Flow 3) from the local WTG, the

fault flow from the collector (Flow 4) will still be contributing.

The total clearing time for this portion is found by locating

this fault flow of 35 kA on the TCC of the transformer fuse set

and finding where it crosses the total clear curve of the firstfuse in the transformer to open. For this example 0.55 seconds

will be used. However, this delayed clearing will have its arc-

flash contribution bounded by the duration of the difference

between the fuse total clearing time and the LVCB clearing

time of 0.35 seconds, which will provide a final interval of 0.2

seconds of fault flow from the collector feeder, before the

transformer fuse opens. Figure 8 shows both intervals and

their respective incident energy contributions with the total

being about 34.2 cal/cm2.

Time Duration of Arc-flash (sec)

0.0 0.10

5kA

0.21kA

0.10 sec

0.25 sec

Total 8.4 cal/cm2

7.8 cal/cm2

0.6 cal/cm

2

FaultCurrentat theSite ofthe Arc-flashEvent

0.35


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Figure 8: Arc-flash results for a fault in an LV cabinet (not-to-

scale).

VI. CONCLUSIONThis paper has investigated and discussed the arc-flash ha-

zard on a WPP collector system. A brief discussion of the arc-

flash hazard and its causes were presented along with a me-

thodology and two examples for tallying the total incident

energy from multiple sources.

The use of the various conditions of fault current in the me-

thodology, are presented as a conservative measure for esti-

mating the arc-flash incident energy, but it must be understood

that the real behavior of the fault current from the WTG is

very unpredictable and situation dependent. From these two

brief examples it can be seen that one of the highest levels of

the arc-flash hazard in a WPP collector system can be on theLV cable and inclusive cabinets between the LVCB and the

step-up transformer. However, these results could be very

different if another arc-flash calculator were used, such as the

IEEE 1584 theoretical model, which has a dependence on vol-

tage.

VII. REFERENCES

[1] Ammerman, R.F., T. Gammon, P.K. Sen, and J.P. Nelson, ComparativeStudy of Arc Modeling and Arc-flash Incident Energy Exposures, Pe-

troleum and Chemical Industry Technical Conference, pp. 1-12, Cincin-

nati, OH, 22-24 Sept. 2008.

[2] Dalziel, Charles F., The effects of electric shock on man, IRE Trans-actions on Medical Electronics (PGME-5), May 1956.

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Fault

Currentat theSite ofthe Arc-flashEvent

0.0 0.35

45kA

0.55

35kA

0.20 sec

0.35 sec

23.6 cal/cm2

10.6 cal/cm2

Total 34.2 cal/cm2

Time Duration of Arc-flash (sec)

Documents

Arc Flash Hazard in w Pp