single-pole operation leads to hazardous

7/26/2019 Single-Pole Operation Leads to Hazardous

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AbstractBC Hydro recently developed a radial 287 kV

Northwest Transmission system which includes a long (340 km)

line. After the terminal station it connects to two shorter lines.

Short time after when the system went into the service, the long

line experienced multiple line-to-ground faults due to icing and it

led to single-phase trip protection and auto-reclose operations.

During open-pole condition phase duration, the floating phase on

the short lines experienced unsafe over-voltages causing

transformer and reactor protection trips. This paper will use

disturbance records to explain the sequence of events and present

the detailed waveform analysis. It was found that the sensitive

phase-to-phase fault protection operated on the shunt reactor.

The transformer protections operated on excessive magnetizing

current due to the differential restraint element fifth harmonic

currents dropping below the setting threshold (35% on three

phases). It appeared that the harmonic restraint dropped on

higher voltage due to excessive saturation causing flux to transfer

from transformer core to tank. The disturbance has been

simulated with EMTP and this helped to identify the causes of

the over-voltage. The paper will also discuss the simulation

results and some recommend solutions to avoid re-occurrence of

the over-voltages problem.

Index Terms Single-Pole Operation, Temporary Over-

Voltage, Transformer over-excitation

I. INTRODUCTION

he BC Hydro transmission system, in a remote corner ofthe province, had a sizeable addition brought into service

near the end of 2014. To spur economic activity in the region a

series of new transmission lines were constructed to

accommodate both non-utility generation and large industrialloads. The main 287 kV transmission line to the area is very

long and had significantly more faults than anticipated in

months following the first energization. The protectionsystems had been very dependable during all the faults in the

initial months and in the time since then as well. The security

of the relaying system has also been quite good. It was tested

though under a severe unintended operating condition for a

fault that occurred on January 7 th 2015. This paper outlines

how multiple faults that day left the system in the unintendedoperating configuration. This condition resulted in

approximately 1.7 pu voltage at multiple substations. Next the

paper will discuss how protection relaying in the regionresponded while the system was operating in a critical state.

Three protection relays operated while there was no fault

Submitted September 2015

Mukesh Nagpal e-mail BC Hydro, Burnaby, BC V3N 4X8, Canada

[email protected]

within their protection zones. The paper includes detailedsteady-state and high frequency analysis to re-create the

conditions witnessed in the field. Finally, the paper will briefly

describe potential remedies to prevent further abnormal

conditions in the system.

II. BCHYDRO SYSTEM

BC Hydro, the third largest utility in Canada, possesses

major hydro-electric generation assets. These resources,

primarily located in the northern (Peace River) region of theprovince and in the south eastern (Columbia River) region, are

remote from the south-west corner of the province where most

of the demand for electricity is concentrated.

A. Northwest Transmission System

Figure 1 shows geographic one-line diagram of the

Northwest Transmission System (NTL). It consists of a new

287-kilovolt (kV), 340 km long transmission line, 2L102,connecting the existing BC Hydro Skeena (SKA) Substation

near Terrace with a new substation Bob Quinn (BQN) near

Bob Quinn Lake.

The system was expanded to provide a secure

interconnection point for clean generation projects via 39 km

long 287 kV transmission circuit 2L379. The three connected

non-utility generating clusters are Forrest Kerr (FKR), andVolcano Creek (VOL), all on the Iskut River near Forrest Kerr

Creek, north of Stewart in northwestern BC. The total outputfrom these clusters would be 305 MW from run of river

generation units. These generators supply clean electricity to

support development in the area.

The system is also serving the industrial and residential loadvia a three terminal 287 kV 110 km long transmission line

2L374. The transmission system one - line diagram including

existing BC Hydro northern region transmission network, the

NTL, new Bob Quinn substation and IPP generation andtransmission system is shown in Figure 2. The area can now

reduce greenhouse gas emission by enabling communities now

relying on diesel generation to connect to the BC Hydrotransmission grid as well.

B. Detail of a 287 kV Line in Northwest System

Figure 3 shows a simplified one-line diagram showing

circuit 2L102, which was involved in the incident. As shown

in Figure 1, this line is the only transmission path betweenSkeena (SKA) Substation and Bob Quinn (BQN) switching

stations. The line is 340 km long and is fully transposed. There

is an optical ground wire (OPGW) cable run between the topsof high voltage electricity towers. The optical fiber within the

Mukesh Nagpal, Terry Martinich, Ska-Hiish, Tyler Scott, Gurinder Hundal and Apollo Zhang

BC Hydro, BC, Canada

Single-Pole Operation Leads to Hazardous Over-

Voltage on Adjacent Lines

T


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cable is used for high speed protection and SCADA functions.

Tower construction, conductor data along with the line

parameters determined from the construction data are listed in

Appendix I. There is 35% series compensation at the BQN endof line and 72% positive sequence shunt compensation using

two reactors at SKA and one at BQN. The shunt reactors at

SKA (2RX1 & 2RX2) are fixed and the one at BQN

(2RX231) is switchable.

2L102 is protected by modern microprocessor-based relayswith a high speed, sub-cycle, current differential scheme. The

line breakers are rated as having a three cycle interrupt time.Therefore overall fault clearing time is less than four cycles

for all bolted faults. This speed is within the performance

target specified in NTL system planning studies.

Figure 1: BC Hydro Northwest Transmission SystemGeographical Map.

Figure 2: Northern Region BC Hydro Transmission System

One-Line Diagram.

To maintain the system stability, single-shot high speed

automatic reclose is attempted after line trips. The reclose

scheme is designed to initiate single-pole trips for single-

phase-to-ground faults and three-pole trips for all multi-phasefaults. The SKA bus is the lead or master end for auto-reclose

and the associated breakers 2CB7 and 2CB8 are equipped with

point-on-wave (POW) closing to minimize the line pickuptransients. 2CB7 is the first breaker to close followed by

2CB8. The BQN bus is the follow end with 2CB3 closing first

and 2CB4 closing second.


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Figure 3: Simplified 2L102 One-Line Diagram NTL

System.

III. EVENT DESCRIPTION

This section is divided into two subsections. The firstsection describes a series of incidents which includes five

individual faults at different times and the nature of these

faults. The events with time stamps are listed in sequence inTable 1. The second subsection focuses specifically on the

fifth event. During this event the entire system north of BQN

experienced significant over-voltage on one phase. Thesubsection presents detailed analyses of the waveforms

recorded by the high speed digital fault recorders during this

incident.

A. Overview of the Incident

Table 1 lists the sequence of events for this series of events.On 7th January, 2015 at 05:38:39 PST, the first Phase C-to-

ground fault occurred on 2L102 about 2 km from BQNstation. The line protection responded correctly to trip single-

pole (Phase C) in three cycles and executed an auto-reclose

after the one second open pole interval. The fault was caused

by an OPGW wire sagging under the heavy snow

accumulation on the wire. Since the sagging wire reducedclearance between the phase conductor and ground wire, it

took longer for the fault to self-extinguish than expected.

Hence, the line was auto-reclosed onto a persistent fault. The

failure of auto-reclose resulted in a three-pole trip at both line

terminals (SKA and BQN). Referring to system one-line

diagram in Figure 2, 2L102 protection operation keys direct

transfer trip (DTT) to the downstream line protection relays,

2L374 and 2L379, to isolate the remote generation andtransmission customer load upon disconnection from BC

Hydro integrated system. On receipt of DTT, 2L374 tripped at

BQN terminal and RDC entrance circuit breakers. Similarly,

2L379 tripped BQN terminal as well as FKR and VOL

entrance circuit breakers. Note that RDC load remaineddisconnected and 2L379 remained open-end at FKR and VOL

throughout the rest of events that morning.

A second Phase C-to-ground fault occurred at 05:44:42.732

PST; shortly after BC Hydro control center restored 2L102.

The control center had not yet restored 2L374 and 2L379.

Similar to the first event, the line tripped single-pole and then

ended up tipping three-pole trip due to the auto-reclose failure.The third and fourth events are failed attempts to energize

2L102 from SKA station by BC Hydro control center. They

both failed due to a persistent fault on the line.

Before the fifth event, BC Hydro control center was in the

process of restoring the Northwest Transmission system. It

was restored to a point such that 2L102 was fully restored atboth ends, 2L374 energized from BQN to TAT and open

ended at RDC, and 2L379 energized at BQN but open endedat FKR and VOL. In this system configuration, 2L102 from

SKA is the only source in the Northwest system. A Phase C-

to-ground fault on 2L102 reoccurred at 06:21:21.972 PST at

the same location as the previous events - 2.8 km from BQN.Breakers associated with Phase C of 2L102 were tripped by

the protection. Because non-utility generation was not

reconnected after the previous fault, opening of Phase Cbreakers on 2L102 led to loss of source on that phase for all

three circuits in the Northwest Transmission system. In

absence of regulated source on Phase C, the voltage on that

phase in the BQN-2L374-2L379 sub-system experienced atemporary over-voltage exceeding 1.7 pu. The high voltagecaused one shunt reactor and two transformer protections to

operate. This event is the main subject of analysis being

reported on this paper. The remaining paper will discussprotection response during this event, analytical simulations

replicating the event and methods to avoid its reoccurrence.

B. Over-Voltage Waveforms

Figure 4 shows three phase-to-ground voltages captured by

the digital fault recorders (DFR) at the BQN bus. Phase C-to-ground voltage exceeded 1.6 pu within two cycles after

opening of Phase C beakers on 2L102. It is interesting to note

that, during the temporary over-voltage (TOV), Phase B-to-ground and the C phase-to-ground voltages are nearly 180

degrees out-of-phase. Figure 5 shows phase-to-phase voltages

which indicate that the BQN T3 delta-connected windingbetween Phases B and C was subjected to the over-voltage and

saturation of that winding. This over-voltage resulted in BQN

T3 tripping in about 10 cycles after the single-phase opening.

Since BQN T3 and 2RX22 share the tripping zone, 2RX22

was disconnected from the system at the same time. This leadto the voltage increasing yet again, this time to more than 1.7

pu. About 8.5 cycles after tripping of BQN T3 and reactor


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IV. PROTECTION AND CONTROL DESCRIPTION

In two months following Northwest Transmission system

energization, 2L102 had several phase-to-ground faults and

the protection performed correctly during all faults. Previous

sections detailed how the system ended up in an undesirableoperational state on the morning of 7 thJanuary 2015.

The following protection section will detail the protection

operations in the NTL system that morning besides the 2L102

operations. It will also discuss the protection operations thatdid not occur. Section V will discuss the measures taken to

quickly take action in the protection system to reduce the

chance of a high temporary over-voltage in the future.

A. Duration of Over-Voltage Condition

The 2L102 line protection had single-phase tripping (SPT)

enabled on January 7th, which opens only the faulted phase

for any single-phase-to-ground fault. If the fault persists whenthe open phase is closed (unsuccessful reclose), then the line

protection would open all phases with three-phase tripping

(3PT) logic, and send direct transfer trips to open entrance

breakers of RDC, FKR and VOL. The single-phase openinterval of the line is approximately 60 cycles (1 second). Thefirst phase-to-ground fault occurred at 5:38 AM and it was

persistent so, a direct transfer trip was sent to RDC, FKR, and

VOL taking them offline for the remainder of this time period.During the 6:21 AM event 2L102 line protection detected the

single-phase-to-ground fault. During the approximately 1

second single-phase open (SPO) period, a number of additionprotection operations occurred, some unexpectedly.

B. BQN Transformer T3 Protection Operation

BQN T3 is a 10 MVA transformer with an HV delta

winding and an LV wye winding. The transformer serves a

fourth harmonic filter bank and the station service transformerat BQN substation.

As shown in Figure 3, the voltage between Phase B and C

became very high (more 1.6 pu) during open pole period. It

saturated the delta winding of BQN T3 connected between the

two phases. Figure 6 shows the disturbance records from thetransformer differential relay. Three analog traces on top are

three-phase line currents processed by the 60-Hz digital filter

embedded in the relay. Two analog traces in the middle of thefigure are fifth harmonic frequency content relative to the

fundamental frequency in differential current measured by the

relay for the B and C phases. In bottom part of the figure,digital traces are illustrating responses various relay elements

to the differential currents measured when the B-to-C windingwas overexcited by over-voltage. To illustrate distorted nature,

Figure 7 shows the unfiltered analog traces of the line currents

into the transformer. T3 primary (287 kV side) currentsdemonstrate that, with harmonic distortion considered, these

currents were about 3 times the 20 Arms rated primary

current. Though not shown, negligible currents were comingout of the transformer low-voltage windings confirming that

the high-side currents were transformer magnetizing currents.

In Figure 6 and Figure 7, Phase B and C line currents werepractically 180 out-of-phase which confirmed the saturation

of the B-to-C winding transformer core. There was negligible

line current in Phase A.

The magnetizing currents on high-side appeared as Phase B

and C differential or operate currents. However, the relay

operation was initially blocked for approximately three cyclesby the 2nd and 5th harmonic elements as shown by digital

traces in Figure 6. The relay was set to restrain the trip

operation when the 2ndharmonic component of the differential

current exceeded 15% of the fundamental frequency current inone or more phase. Likewise, 5thharmonic restraint was set to

35%. Once the 2nd and 5th harmonic current content droppedbeyond their individual setting threshold, the relay tripped.

The BQN T3 tripping zone trips 287 kV circuit breakers

2CB2 and 2CB3. This protection operation also tripped reactor

BQN 2RX22 as collateral since they share a tripping zone. It

is likely that BQN 2RX22 would have eventually tripped aswell if given more time.

Figure 6: From the BQN T3 Protection Event Report,

Showing the Filtered Primary Currents.

Figure 7: From the BQN T3 Protection Event Report,

Showing the Unfiltered Transformer Magnetizing

Currents.

C. TAT Transformer T1 Protection Operation

TAT T1 is a 16.6 MVA transformer with an HV wye

winding and an LV wye winding. The transformer has aburied delta tertiary winding. The transformer serves the small

amount of distribution load in the area at 25 kV.

TAT T1 was also exposed to high voltages well above the

knee point voltage of the saturation characteristic. T1

conducted a relatively high current for 8 cycles before itsprotection tripped the transformer. From the event report, the


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filtered primary currents are shown in Figure 8 and the

unfiltered currents appear in Figure 9. The maximum

instantaneous currents (Phase B and C) were about 170 A

peak, due to severe harmonic distortion. As a comparison, therated primary current is 33 Arms (47 A peak).

Like BQN T3, a high percentage of 5th harmonic current

blocked the transformer from operating instantaneously when

it began to saturate from the high voltage. This event report

also shows the 5th harmonic current dropping below 35% andtripping shortly afterwards. Compared to BQN T3, this

transformer took nearly 8 cycles longer to saturate to the pointwhere 5th harmonic current dropped below the inrush

threshold.

The unfiltered event report shows that the harmonic current

started to reduce while the fundamental current increased four

cycles after the relays event report was triggered. This alignswith the tripping of BQN T3 and RX22 and the subsequent

voltage rise that was recorded in the area. The even higher

voltage drove the TAT transformer core deeper into saturationcausing the magnetizing flux to leak out of the core and setting

up eddy currents in the non-laminated parts of transformer. As

a result, the fifth harmonic current dropped relative to thefundamental frequency component and contributed to

transformer tripping. Similar to other transmission anddistribution transformers in BC Hydro, the transformers in the

new NTL system were neither equipped with over-voltage nor

Volt-per-Hertz protection. Trips by the differential protection

saved the transformers from possible damage.

Figure 8: From the TAT T1 Protection Event Report,

Showing the Filtered Primary Currents

Figure 9: From the TAT T1 Protection Event Report,

Showing the Filtered Primary Currents

D. BQN Reactor 2RX25 Protection Operation

BQN 2RX25 is a 20 MVA oil filled reactor. The primarypurpose of the reactor is to compensate line charging

capacitance for 2L374.

The reactor protection consists of primary high impedance

differential protection as well as primary and standby phaseand ground over-current protection. The differential protectionis able to detect phase-to-ground faults and trip

instantaneously. It is unable to detect turn to turn faults

though. We deploy two sets of over-current protection toensure we have redundant protection to detect turn to turn

faults with the reactor.

The reactor was subject to a 1.7 pu voltage, which translates

to a higher than 1.7 pu current due to saturation. Currentsobserved during the over-voltage were 3 pu and were

sufficient to activate the inverse-time over-current protection.

Unlike the transformers discussed earlier there was no

differential current in the reactor. All current entering the

reactor left the corresponding low voltage terminal of thereactor. This reactor has a phase over-current element set to

pick-up at 1.2 times nominal phase current with an inverse

time tripping element. It was initially assumed that this wasthe element that tripped 2RX25. Upon investigating the event

reports from the protection relays it was determined that the

phase over-current element did not actually trip the reactor.

BC Hydro has devolved a specialized element to detect phase-to-phase faults deep within multi-phase reactors. A phase-to-

phase fault will result in an increase in phase-to-phase current

along with a corresponding decrease in phase-to-phase

voltage. Our element is looking for a 25 percent increase incurrent along with and 20 percent decrease in phase-to-phase

voltage. Figure 10 is an event report for the reactor over-

current protection. Element 50BCS is the Phase B to C over-current and Element 27CA is the Phase A to C under-voltage

element. Element SV5T is an 8 cycle pick-up timer required

for the phase-to-phase fault detector to operate.


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Figure 10: From the BQN 2RX25 Protection Event Report.

The unfiltered event report in Figure 11 shows significantly

less harmonic current than either of the two transformers

experienced. More than 1.7 pu of phase-to-ground temporaryover-voltage was present at the transformer terminal at the

time of protection operation. The slope of the flux-current

characteristic of 2RX25 in the fully saturated region is

significantly higher than that of the transformer (air-coreinductance). Hence, the smaller harmonic content in thereactor currents.

Figure 11: From the BQN 2RX25 Unfiltered Event Report.

E. Observations on Protection Operations

The operation of the protection systems helped to reduce theseverity of the over-voltage in the area. This is especially true

following the clearing of TAT T1. Figure 12 shows an

immediate decrease in voltage following TAT T1 breakers

opening.

It is also interesting to review the breaker clearing times for

these operations. The three protection operations were nearlyuniform in their breaker clearing times as shown in Figure 12.

All the breakers in this system are rated at a 2.4 cycle nominal

clearing speed. In actual operation under these conditions theclearing time recorded by the protection relays was 6 cycles

more than double the rated time. All breakers are rated at 362

kV, but were exposed to voltages above the voltage rating. Allcurrents were well below the breaker rated interrupting current

of 40 kA. Higher than nominal breaker interrupting times are

expected at the lower fault currents. It must be taken into

account for breaker failure timer settings. An event report

from the BQN 2L374 protection relay nearly capture the entire

event with filtered currents and voltages. The clearing points

of various protections are easily identified with changes in

currents and voltages at the BQN terminal.

Figure 12: BQN Composite Protection Operations.

V. SYSTEM ANALYSIS

A. Simplified Steady-State Analysis

Simplified steady-state analysis for the unbalanced open

phase conditions is given in this section to estimate the natural

resonance frequency provided by the open phase condition.

When the natural resonance frequency is near the powerfrequency (60Hz), it is highly possible [1-5] that this will lead

to the over-voltage phenomenon during the incident reported

in this paper.

Figure 13 shows the three-phase circuit diagramrepresenting BQN-2L374-2L379 sub-network. For simplicity,

there are a few assumption made to the network. They are asfollows:

Assume the healthy phase voltages (A and B) are equal

and 120 degree apart

Assume both lines are fully and properly transposed

Ignore non-linear effects, i.e. surge arrestor conduction,

transformer or reactor magnetic saturation, or coronaeffects

Lump phase-to-ground capacitance and interphase

capacitance on both lines as one set of capacitance

Ignore the TAT primary to secondary coupling since the

load is very small


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Figure 13: Simplified BQN-2L374-2L379 sub-system with C

phase open.

The symbols used on Figure 13 are self-explanatory. The

shunt reactor 2RX25 at BQN can be represented by the shunt

inductance (Lg). The transformer TAT T1 leakage impedance

between Primary winding and Tertiary Winding can berepresented by the inductance LT. For each transmission line,

the phase-to-ground capacitance (Cg) and the inter-phase

capacitance (Cm) can be obtained from the line parameters Positive Sequence Capacitance (C1) and Zero Sequence

Capacitance (C0):

3

01 CCCm

, 0CCg

The two transmission lines 2L374 and 2L379 are in parallel.

Therefore, their inter-phase mutual capacitance (Cm) and

ground capacitance (Cg) can be lumped together and berepresented by a total Cmand Cg.

Figure 14 (a) shows the equivalent network representationfor one open phase condition in Figure 13. It can be further

simplified by finding its Thevenin Equivalent circuit which is

shown in Figure 14 (b). The equivalent circuit is a simple LCcircuit, and the natural resonance frequency of this circuit can

be derived as follows:

Hz

LL

CCLLf

Tg

mgTg

6.62)2(

2

1

The simplified circuit natural frequency is 62.6Hz which is

very close to the power frequency of 60Hz. With the

consideration of the transformer saturation, the leakage

impedance will become larger and hence change the resonancefrequency still closer to 60Hz. It is highly possible that the

resonance phenomenon could result in the open-pole voltage

rising above the source voltage level (1p.u.). Therefore, it

gives a general indication of how the system voltage couldpossibly behave in the open pole condition.

Tg

Tg

LL

LL

Figure 14: Simplified Thevenin Equivalent Circuit.

This simplified analysis is only for the purpose of

understanding. It does not include non-linear components

which will be considered in the following sections for moreaccurate modelling and simulation.

B. EMTP Linear Analysis with and without TAT T1

To establish the dominant causes of the high over-voltages

during the 2L102 SPO period, all the nonlinear effects

(arrestor conduction, magnetic saturation, and corona losses)

are neglected; only the linear effects are simulation. Through aprocess of elimination, each transformer and reactor is

removed one by one and the 2L102 SPO period is simulated.The C phase voltages are then observed. It was determined

that TAT T1 was the dominant cause of the high C Phase

over-voltages. See Figure 15 for simulation with TAT T1 as

well as without TAT T1.

Other than the opening of 2L102 Phase C at BQN 3 cyclesafter fault inception, no other switching occurs during the

simulations. For simplicity, in the simulations the small station

service load supplied from BQN T3 was neglected and theTAT distribution load was assumed to be only 300 kW. Since

the instantaneous Phase C-to-ground voltage is of primary

interest, only that phase is plotted.a) Linear Case with TAT T1

This case assumes the same initial conditions as on 7thJanuary Phase C fault near BQN and the same SPO switching

times. All shunt reactors and the BQN and TAT transformers

are in service. As can be clearly seen in Figure 15 (a), as soon

as 2L102 Phase C is disconnected at BQN, the magnitude ofthe fundamental frequency voltage in Phase C of the BQN-

FKR-RDC system escalates dramatically, to more than 5 pu

after six cycles. This indicates the presence of a nearfundamental frequency resonance for this open-phase

condition. The Phase C voltage waveform is actually the first

part of a ring-down waveform. The waveform results from the

modulation of two frequencies, one being the power frequencyor forcing frequency and the other being the natural (orresonant) frequency of the circuit. Capacitive and magnetic

coupling to two phases energized from the grid provides the

sustained source at power frequency. The transient resonantresponse of Phase C will be shown to be close to 60 Hz.

Increasing the EMTP simulation time shows a beating effect

in the waveform where the modulation would have eventuallyreached a minimum voltage (less than 1 pu) and then repeated

but with reduced magnitudes.


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TOV of abo

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ere is an imm1 pu, which p

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ilar to the c

ut the maxim

exceeds 1.0ust have pla

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event.

ithout TAT T

n with the nthe digital f

9. The DFR

e-to-ground)

alues are shocurred on 2L

at BQN openhalf cycle la

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t 1.6 pu. At

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diate increasersists until T

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Figure

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voltages. A

waveforms arms. The goo

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for phase A iis 7.39%. Th

ration the err

In addition, t

cording and sifor A phase

re, the EMT

tem has beeations.

16: EMTP No

228kV rated

xide arrester

ion capabilityarrester is the

ion of the 2S

neous voltagduring the S

accumulation

e that TAT T

, the arrester h

ty. Once a m

ation of the

equence of ev the three pl

s can be see

re in good agness of fit of t

uared Error (

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e Pearson cor

mulation valu, B phase, a

model of th

n verified an

n-linear Anal

urge arresters

s rated IEC

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A25 Phase C

e across thePO. As can b

occurs after

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as absorbed 1.

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phase-to-gro

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hile consideri

elation coeffi

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linear and n

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sis with TAT

2SA25 on B

Class 4 wit

kJ/kVr. The3 MJ. Figure

energy accu

arrester, ande seen, the hi

3 and 2RX22

ding the tem

94 MJ, or 84

ster is subject

9

nd voltages

as a series ofsured BQN

ted Phase C

the recordedtermined by

is the square

ording. The

4%, and foran take into

ng the phase

ients for the

0.9944, andrespectively.

onlinear 287

for further

T1.

QN 2B5 are

an energy

rated energy17 shows the

ulation, the

the arresterhest rate of

trip off. By

orary over-

ercent of its

ed to energy


10/12

ab

loco

Fi

En

ter

A.

Imph

soltri

A

Di

sorption abov

ses may responents and

ure 17: EMT

ergy Absorpti

V

This sectionm over-voltag

Immediate A

mediately aftase trip and

utions couldand auto-recl

vantages:

This solutio

temporary

investment isadvantages:

Any single-l

of the Nortloss of rev

Chris Mine,

of service to

its rating, th

lt in thermathe arrester fai

P Simulation

n.

. MITIGATIO

escribes thee mitigation al

tion

r 7th January

reclose mod

be developed.ose three-pole

prevented a

over-voltage

hardware an

ine to ground

hwest Transnue for the

loss of station

distribution c

internal heati

runaway ofls.

of BQN Surg

ALTERNATIV

short-term, internatives.

2015 incidee was disabl

The 2L102 rfor all detecte

repeat of the

event wit

communicati

ault causes a

ission systemnon-utility ge

service at BQ

stomers.

ng due to ene

the zinc ox

Arrestor 2S

ES

terim, and lo

t, 2L102 sined until furt

lays were setd faults.

January 7th h

out additio

ons.

omplete brea

, disruptionnerator and

N, as well as l

gy

ide

25

g-

le-her

to

igh

nal

up

nded

oss

B. Lo

Analyti

generat

of a se2L102.

to prov

It wa

dynamiloadingtesting

MW in

chosenNUG a

connec

single-

EMP18. A

possibl

enable/

This m

relay b

Advant

Disadv

g Term Soluti

cal studies

ion and/or loa

ere over-voltFaults betwee

e these results.

s decided that

cally controllat BQN subsit was decide

low into BQ

as this guarare operating a

ion from the

ole tripping o

T studies anaurther long t

use rem

isable single-

ay achieve m

sed solution.

ages:

This solutio

additional

operational i

ntages:

This soluti

resonant circ

n

identified tha

in the BQN

ge during sinn October 201

single-pole tr

ed by moniation. To simd to focus so

substation.

tees at least tt their full ou

L379 to 2L10

n and off.

yzing this solrm solution i

dial action

pole tripping

re dependabil

n does not r

ajor equip

n the least tim

n does not

uit.

t if there i

ystem then th

gle-pole open4 and January

ipping of 2L1

toring real tlify protectioely on monit

threshold of

wo generatingtput. A simpl

2 protection r

ution are shos being explo

scheme co

ased on area

ity than a pu

equire the in

ent, is expe

and at the le

detune the

10

s sufficient

ere is no risk

intervals on2015 helped

02 would be

ime systemsetting and

oring 2L379

23 MW was

units at thehard wired

lays toggles

n in Figureed that will

trollers to

ower flows.

e protection

vestment in

cted to be

st cost.

fundamental


11/12

Fi

2L

C.

de

dein

A

Di

ure 18: EM

379 and Singl

Equipment R

For this optio

ta-grounded

signed, single-SPO and all ot

vantages:

This option

During SP

system wou

temporary o

A STATC

problem inperiod of th

sadvantages:

There couldBQN 25 k

two of the p

SPO conditi

pumps, sewby the oscill

The over-vo

installs a n

connect the

will have a

create a sim

P Simulation

e-Phase Trip.

eplacement

, the existing

tar transform

line to grounher faults wou

etunes the re

, the voltag

ld be similar

er-voltage.

M that wou

the distributiSPO

be a power qsystems ther

ase-to-groun

on. Rotating

ge treatmentting electrom

ltage problem

ew 287/69 k

future McLy

delta-connec

lar problem a

of 23 MW

AT T1 woul

er, the same

faults on 2Lld result in 3P

onance and sh

waveforms

to Case 6,

ld reduce th

n voltages at

ality concern.e will be seve

voltages duri

achinery (e.g

umps, etc.) cagnetic torque.

may re-emerg

autotransfo

ont project.

ted tertiary

s found for T

f Generation

be replaced b

as BQN T3.

102 would reO.

ifts it to 53 Hz

on the 287

aving negligi

power qua

TAT during

On the TATre modulation

g the 1.1 sec

. water treatm

ould be impac

e when the N

mer at FKR

This transfor

inding and

T T1. Howe

on

y a

As

ult

.

kV

ble

ity

the

ndin

nd

ent

ted

G

to

er

ill

er,

if

traCo

an

aut

A.

Eff

Over

priority

in a r

plannervariety

configu

reactor

B. Eff

Trippin

The

This p

couplin

the prisystem.

networ

studiesespecia

subsyst

C. Pr

Damag

Withthe 1.7

cycles.

voltage

was ex

area woperati

arrestor

effectethe hig

D. Qu

Proble

Mod

in a mOnce t

identifi

modific

when stime fo

conduc

the 2L379 te

sformer wilnsequently, a

problem

otransformer,

cts of Single-

-voltage miti

when consid

mote or radi

s to considerof intent

rations when

and transfor

cts of Magnet

g Schemes

effects of L-

per highlight

g of a transfo

ary cause oThis effect is

analysis and

when desiglly in a radi

ems.

tection Syst

e

out the threepu over-volt

The protectio

to 20 cycles.

eriencing an

s experiencinns helped to

s from prolo

equipmentlighted incide

ick Protection

s

ern multi-func

nner beyonde source of t

ed BC Hydr

ations to rest

stem configur further studi

ed without im

minal breake

not be c operating o

created by

if Alternative

II. CONCLU

ole Tripping

ation should

ring using a s

al system. It

the system reional and

specifying eq

ers

ic Coupling of

circuit reson

d that a prev

rmers buried

f the over-vnot easily de

highlights th

ning single-pal system th

em Operatio

perations in tge condition

n relays reduc

Although non

nternal fault,

g a severe ovave the transf

ged over-volt

as shown lasnt.

Solutions to P

tion relays ha

he original inhe January 7t

was able to

re single-pol

ation will safes such as eq

mediate time

s at FKR ar

nnected toder can prob

the additio

is implemen

SIONS

n Radial Syst

be a prima

ingle-pole trip

is important

onance frequunintentional

ipment such

Equipment in

ance are well

iously unkno

delta tertiary

ltage experieonstrated by

e need for det

ole trippingt supplies o

n Prevented

e BQN protewould have l

ed the length

e of the trippe

all of the equi

er-voltage. Tormers, reacto

age. To date,

ing negative

revent System

e the versatili

tention of relover-voltage

quickly mak

tripping to t

ly allow. Thisipment repla

onstraints.

11

e open, this

the system.bly prevent

n of this

ed.

ms

ry planning

ping scheme

for system

ncy under aoperating

s line shunt

Single-Pole

understood.

n magnetic

inding was

ced by theonventional

ailed EMPT

schemes ne or more

Equipment

ction systemasted for 60

of the over-

d equipment

pment in the

e protections, and surge

none of the

effects from

Operation

y to be used

y engineers.was clearly

e protection

e area only

has allowedement to be


12/12

12

VIII. APPENDIX I

A. 2L102 Construction

Figure I-1 shows a typical steel-Y type monopole tower for

this flat-configuration circuit. The average height of the

conductor above ground at the tower is 15.0 m. Each phasecomprises a bundle of two 2B-1590 KCMIL ASCR Lapwing

conductors in a 45.7 cm arrangement.

Figure I-1: 2L102 Tower Configuration

IX. REFERENCES

1. F. Iliceto, E. Cinieri and A. Di Vita, Overvoltages Due to

Open-Phase Occurrence in Reactor Compensated EHV

Lines, IEEE Transactions on Power Apparatus and

Systems, Vol. PAS-103, No. 3, March 1984, pp. 474-482.2. Marta Val Escudero and Miles Refern, Effects of

Transmission Line Construction on Resonance in Shunt

Compensated EHV Lines, Presented at the InternationalConference on Power Systems Transients (IPST05),

Montreal, Canada, June 19-23, 2005, Paper No. IPST05-

09.

3.

M. Nagpal, Terry Martinich, Amitpal Bimbhra and Dave

Sydor, Damaging Open-Phase Overvoltage Disturbanceon a Shunt-Compensated 500 kV Line Initiated by

Unintended Trip, IEEE Transactions on Power Delivery,

Vol. 30, No. 1, February 2015.4. M. Nagpal, Terry Martinich, Amitpal Bimbhra, Dave

Sydor and Jerry Wen, Damaging Open Pole Over-

Voltage Disturbance Initiated by Personnel Incident,Western Protective Relaying Conference in October 2013,

Spokane, WA, USA.

5. Terry Martinich, M. Nagpal and S. Manuel, Analysis of

Damaging Open-Phase Event on a Healthy Shunt

Compensated 500 kV Line Initiated by Unintended Trip,

Presented at the International Conference on Power

Systems Transients (IPST2015), Cavtat, Croatia June 15-18, 2015, Paper No. 15IPST200

single-pole operation leads to hazardous

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