Rail Incident Report - Circuit Breaker Failure - DPTIdpti.sa.gov.au/__data/assets/pdf_file/0009/287298/Rail_Incident... · RAIL INCIDENT REPORT Circuit Breaker Failure, ... The NCA

Rail Commissioner

RAIL INCIDENT REPORT

Circuit Breaker Failure, Lonsdale

28th April 2016

Knet #10833444 V.3

Circuit Breaker Failure, Lonsdale 28th April 2016

Summary of the ReportAt 6:53 hrs on 28th April 2016 an incoming 66kV gas-insulated circuit breaker (CB1081) at the Rail

Feeder Station (RFS) experienced an internal short-circuit resulting in ionisation of the gas insulating

medium, this led to an uncontrolled arc-fault. The magnitude of the fault was approximately 13kA,

with a duration of 455 milliseconds (ms).

The 66kV RFS protection system detected the fault initially as a busbar zone differential fault, the

protection system initiated a command to trip CB1081. Due to the location of the arc-fault on the

incoming side of the Circuit Breaker (CB), CB1081 interrupter was unable to clear the fault. After

300ms Circuit Breaker Fail (CBF) initiated an inter-trip to the Lonsdale substation up-stream breaker,

Lonsdale substation protection system had already detected the fault and after a programmed

timer delay of 400ms the Lonsdale substation protection system tripped the upstream CB, the fault

Current was cleared at 455ms after fault detection.

The root cause of the fault was a loss of insulation integrity, however due to the damage to the CB it

has not been possible to determine without doubt the reason for this loss of dielectric integrity, it is

considered that the fault may have been due to the introduction of a contaminant during the

manufacture and assembly process or re-gassing during the commissioning process on-site.

A contributing factor to the extent of damage to the CB was the performance of the CBF protection

system. This ultimately led to a prolonged fault duration of 455ms with the Lonsdale substation

back-up distance protection operating as designed for a non-cleared down-stream fault. This

prolonged fault resulted in the heating and expansion of the Sulphur Hexafluoride (SFs) insulating

gases within CB1081 chamber. The pressure increased to such an extent the pressure relief system

that is designed to protect the CB from an over pressure event operated. The operation of this

pressure relief device occurred within the 455ms fault duration and resulted in decomposed SFs by-

products of the arc-faultto be expelled from the CB fouling the switchroom.

The pressure from the release of the safety relief system was sufficient to blow open the

switchroom door. First responders on arrival at the switchroom noted the doors open and smoke

emanating from the building. They initially suspected vandalism and requested power be de-

energised to the RFS. The action of the switchroom doors being blown open allowed natural

ventilation to disperse the SFs and combustion by-products to the greater environment. Due to the

isolated location of the switch-room and the relatively srpall volume of combustion by-products

released, there was no health or environmental impact to the community.

With confirmation that the 66kV equipment was de-energised, the first responders entered the

switchroom. The first responders have been subsequently counselled on their exposure to

decomposed SFs and by-products, however any adverse health outcomes are unlikely.

The Original Equipment Manufacturer (OEM) product specialist assisted with the coordination of

the clean-up and retesting of equipment prior to the back-up supply being brought into service.

DPTI, in conjunction with the RFS OEM, has undertaken a review of the safety risks and is currently

in progress to ensure that the system operates in accordance with the design thereby minimising

any damage to equipment or the operation of the pressure relief device in the unlikely event a

similar fault occurs.

Document #: 10833444 Version: 3 Page 2 of 13

Author: Rail Risk & Assurance

Circuit Breaker Failure, Lonsdale 28tn April 2016

The Incident

Location

The Rail Feeder Station (RFS) is located off Meyers Rd Lonsdale adjacent the Adelaide to Seaford Rail Line.

The Lonsdale substation is located to the west of the RFS as detailed in Figure 1 DPTI Rail Feeder Station

location.

Figure 1 DPTI Rail Feeder Station location

Rail Feeder Station Configuration

There are two incoming supplies from Lonsdale substation configured as primary and back-up to the RFS, of

which only one can be supplying power at any one-time. The configuration provides duplication of the supply

from Lonsdale substation but the two supplies must never be tied together through the GIS switchgear. The

RFS monitors, manages power quality and distributes the supply to duplicated 66/25kV transformers that

provide supply to the Seaford Rail overhead line traction system.

The 66kV Gas Insulated Switchgear (GIS) system can be configured to manage power availability, power

quality or various degraded or emergency feeding arrangements in response to maintenance requirements

or equipment fault and is monitored and controlled by a Supervisory Control and Data Acquisition (SCADA)

system located remotely in the rail Operational Control Centre.

The 66kV Switchroom is a modular type building located within the RFS compound as detailed in Figure 266kV switchroom, five vents are provided within the building to manage the pressure that may result from

the operation of the pressure relief device.

5 GIS Bays within the 66kV

Figure 2 66kV switch room

Document #: 10833444 Version: 3


Page 3 of 13


Equipment involved

The GIS switchgear detailed in Figure 3 Switchroom layout contains 5 CB bays, configured as:

• two incoming supplies from Lonsdale substation (CB1081 & CB1085),

• two outgoing supplies to 15/20MVA, 66/25RV Transformers (CB1082 &CB1084)

• Single outgoing circuit to the Static Var Compensator (CB1083).

The GIS system also includes:

• busbar sections,

• high-speed earth switches,

• Voltage transformers & Current transformers,

• lightning surge arrestors,

• local control panel and operating mechanism.

The GIS was designed in Europe and manufactured in Shanghai, China. Routine testing was undertaken as

required by relevant Australian & International Standards and Contract arrangements; manufacturing and

test records were provided for review.

Sulphur Hexafluoride

GIS switchgear contains an insulating and arc suppressing medium Sulphur Hexafluoride (SFe), the SFs is at

pressure within the CB, bus zones and chambers and is used as an insulator, arc suppressant and cooling.

The volume of gas in the CB represents a small fraction of one percent of the volume of the room. When

the burst disk ruptured, the pressure pulse was directed towards the building vents. The use of a dense,

air-filter medium prevented an uninhibited release of pressure and thus the rise in pressure forced open

the doors to the switch room, allowing any gaseous products to rapidly escape the room. There would have

been no asphyxiation risk to anyone entering the room even if the doors hadn't opened.

Solid by-products from the decomposed sulphur hexafluoride are the least toxic and would predominantly

have been mild corrosives with the potential to cause minor skin irritation if unprotected skin came into

contact with them for a period of time.

Incoming Circuit Breakers

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Figure 3 Switchroom layout 66kV Switch room

Document#: 10833444 Version: 3


Page 4 of 13


The FaultThe fault developed within CB1081 as detailed in Figure 4 Gas Insulated Switchgear-Bay (plan and section

View), the type of fault which is thought to have developed at the top of the CB and between the

interrupter and Current Transformer assembly (as detailed Figure 5 Graphical overview of the fault

location) is rare for GIS. The GIS OEM has no previous experience that can be referenced in support to

determine the root cause of the fault.

The performance of the GIS during this arc-fault and the operation of the pressure relief device was in

accordance with IEC62271 Part 203 Gas-insulated metal-enclosed switchgearfor rated voltages above 52

kV.

Pressure relief

system A

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1 Busbars and combined disconnectors2 Circuit-brf3 Current transformer4 Cable connection module5 High-speed earthing switch6 Voltage transformer7 Local control cabinet8 CB operating mechanism Page 60 of 345

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Page 5 of 13


Design Requirements

Fault Clearance Requirements

A requirement of the Network Connection Agreement (NCA) is that the Distribution Network is protected

by protection devices which "effectively and safely disconnect any faulty circuit within a time specified". The

maximum clearance time for a 66kV fault is 100ms. The NCA also requires that breaker fail protection is

provided to clear faults that are not cleared by the primary protection system within 250ms.

Due to the location of the fault, it is considered a dead zone1 fault and therefore was to be cleared within

the NCA breaker fail clearance time of 250ms.

Pressure Relief Device

The pressure relief device in accordance with IEC62271 Part203 Gas-insulated metal-enclosedswitchgear

for rated voltages above 52 kV; may operate for a fault Current of <40kA within 200ms, with no external

effect, i.e. no burn through of the chamber. It is calculated that the CB0181 pressure relief device operated

at 196ms and no burn through of the chamber occurred, although there was evidence of internal pitting.

System Safety Engineering

Requirements Management

The requirements management activities, as part of an effective systems engineering processes, did not

effectively capture all the interface requirements contained within the NCA. In particular the fault clearance

times and the breaker fail protection requirements.

Hazard identification

The hazard identification process considered the likelihood and consequence of the following 66kV GIS

events;

• Pressure release into an unsafe area,

• Insulation failure,

• Leakage of SFs,

• Failure to trip on fault condition.

The hazards were considered "low' and "Broadly acceptable" and mitigation focussed on the structure of

the building and venting arrangements to manage the risk.

A short zone which is not protected by the protection system, (see Glossary for detail)




Summary of the incidentAt approximately 6:53 hrs on 28th April 2016 a 66kV Circuit Breaker (CB1081) in bay FA01 within the RFS

66kV switchroom experienced an internal arc-fault on the incoming side of the interrupter in the dead zone

of the CB.

The RFS 661<V protection system; specifically the bus zone protection relay detects a fault on two incoming

phases and commands a trip ofCBlOSl; as the fault was on the incoming supply side of the CB the opening

of the circuit breaker interrupter has no impact on clearing the fault, see Figure 6 for the time line of

events.

Key events:

• 06:53:22 fault on two phases (L2 & L3),

• +12ms the RFS 66kV bus zone protection system detects the fault condition and issues a trip

command to CB1081,

• +16ms the Lonsdale substation 66kV Cable protection system detects a down-stream fault and

commences timing,

• +53ms CB1081 is detected to mechanically open and interrupt the fault Current,

• At approximately 190 - 250ms the pressure in the CB chamber expands to a level that results in the

rupture of a pressure relief device,

• +308ms the RFS 66kV CBF protection system initiates a trip to the upstream CB in the Lonsdale

substation,

• +415ms the Lonsdale substation66kV distance protection system times out and issues a trip

command to CB5697 (upstream circuit breaker),

• +455ms the fault Current clears (CB5697 opens),

• Power is lost to the 25kV overhead line traction supply.

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Page 7 of 13


The ResponseThe power outage was observed by the Electrical Control Officer (ECO), on the SCADA system located

remotely in the Rail Operations Control Centre. The ECO in discussions with the Electrical Engineer

immediately commenced reconfiguring the system to an alternative feeding arrangement and after

discussion with Lonsdale substation controller, commenced re-energising the back-up Lonsdale substation

66kV feeder, reconfiguring the 66kV switchgear and reinstated supply to the 25kV overhead line traction

supply.

• 06:53 CB1081 displays "Open" status and multiple alarms displayed on the SCADA. The ECO

identifies loss of power and advises Seaford Line Controller (Operations Controller) and rail Shift

Manager of loss of supply,

• 06:58 ECO tiaises with Lonsdale substation Controller to identify issue and restores power to

standby circuit (Feeder 2),

• 07:08 power restored to the 25kV overhead line traction supply,

• Electrical Engineering interrogate the SCADA system to understand fault and decide to despatch an

Electrical Engineer to site to investigate,

• 07:42 Electrical Engineering, confirm attendance at Lonsdale. Electrical Engineering observes the

doors open and smoke emanating from the 66kV switchroom. Electrical Engineering contact the

Electrical Engineer Manager and a decision is made to immediately shutdown the supply to the RFS,

• 07:49 CB1085 is opened, stranding electric trains on the network,,

• 08:16 Lonsdale substation are contacted to isolate power from Feeder 2, so Electrical Engineers can

enter switch room,

• 08:30 Electrical Engineering enter switchroom and observe burn-marks on the CB1081 and damage

to adjacent 66kV GIS CB Bay,

• 09:30 The OEM supplier is contacted and advised of the incident,

• 10:45 The OEM supplier is contacted and requested to attend site,

• 15:00 On arrival on-site Lonsdale RFS OEM, product specialist advised the potential hazards of

coming into contact with the decomposed SFs by-products,

• 16:40 OEM product specialist advises the needs to thoroughly clean the switchroom to remove the

traces of the decomposed SFe by-products.




The Recovery and InspectionThe OEM product specialist oversaw the recovery and dismantling of the CB. Following removal of the CB

from the switchroom and inspection at Tonsley Park CB1081 was sent to Grenoble, France for further

analysis.

Onsite SFg gas in three other compartments was analysed for moisture or contamination; no issue was

identified.

Observations were made during disassembly of the CB for missing, damaged, worn or loose items, the gas

tightness between chambers and function of the drive mechanism; no issue was identified.

Possible causes of an internal arc included;

• Contamination during manufacture,

• Contamination as a result of re-gasing during installation,

• Internal discharge during operation,

• Flashover resulting from over-voltages.

Following analysis of the CB at the OEM facility, OEM confirmed that the fault observed on CB1081is the

first recorded fault of this kind in the 8DN8-4 GIS and can be considered a singular event.

Figure 7 Top of circuit breaker chamber



Page 9 of 13


Key facts and analysisThe Control and Protection Study produced at time of design by the Contractor, considered the concept of

separability and system grading.

Event recordings of the supply show that a Current of 12.9KA flowed for 455 milliseconds.

There was no indication of any defect in the CB1081 prior to the incident.

Summary of Conclusions

Root cause

The root cause of the incident was the sudden loss of the insulation integrity leading to an internal arc in

the dead zone of CB1081.

Whilst it is not possible to determine without doubt, the cause fault is an insulation failure within the circuit

breaker.

Escalation factors

Escalation factors include:

• The extended duration of the fault, resulting in excess pressure within the CB chamber resulting in

the operation of the pressure relief device.

The following factors were also related:

• The CBF signalling scheme from DPTI RFS to Lonsdale substation was not established by DPTIand

its contractors in the most effective manner.

• The Systems Engineering process did not identify the criticality of the requirement for clearing a

fault within 250ms as detailed in the NCA nor its relationship to the operation of the pressure relief

device.

Actions reported as already taken or in progress relevant to this report.

As an interim measure DPTI with Lonsdale substation modified the upstream protection to

"instantaneously trip for fault", rather than the 400ms Distance Trip delay that was in place on the 28th

April 2016. Whilst in the interim this may have resulted in a greater chance of nuisance tripping it affords

greater protection to the GIS CB should an internal fault occurred.

DPTI has undertaken a review of the design of the RFS protection system, the interface with Lonsdale

substation back-up protection system and the redundancy of the system. This review identified a number

of improvements to the protection system design to reduce the probability of an arc-fault being sustained

for sufficient time and magnitude to reduce the likelihood of the operation of the pressure relief device to,

so far as reasonable practicable (SFAIRP), these changes were implemented progressively and completed in

November 2016.

A modified design and protection settings was implemented on the secondary protection system for Feeder

No. 1 (CB1081), with a full functional test being carried out including the interface with Lonsdale substation

to confirm compliance to the NCA requirements, in particular the fault clearance times. This test was

successfully completed on Feeder No. 1 on the 16th October prior to CB10181 being put back into service;

modifications to Feeder no. 2 secondary protection system were completed on the 20th November 2016.

Restrictions on access to the 66kV switchroom whilst the 661<V equipment was energised, has been lifted;

the RFS OEM has reviewed the safety arrangements within the 66kV switchroom and completed the

following inspections or modifications to address safety concerns:




• Inspection of the in-service 8DN8-4 circuit breakers to identify any contamination or internal

damage to the CB upper chamber

a Review the venting arrangement within the room to ensure in the case of a rupture of the pressure

relief device that the vents operate

• Confirmation of the direction of the blast deflectors

• Modification to the protection system so that the fault duration will be limited to less than

approximately 150ms

• Update the Contractor RFS Safety Assurance Report.

Recommendations

Item

1

2

3

4

5

6

7

8

Recommendation

Modification to the 66RV Protection system to reduce the duration of any fault to

less than 150msec.

Review the redundancy and single points of failure of the control and protection

system and upgrade as required to improve compliance with the NER, NCA and

industry practice

A technical assessment be conducted on the RFS systems as a whole to identify any

potential latencies

The ONRSR Major Project Guideline assurance principles be adopted byInfrastructure Delivery for all rail projects

Review of Construction Contracting specifications to reflect systems engineering and

safety assurance practices

The DPTI Rail Systems Engineering Management Plan (SEMP), procedure should beupdated to align with industry best practice and ONRSR Major Project Guideline andbe mandatory for all new rail projects

A methodology for monitoring partial discharge should be investigated with the

equipment supplier

SFs gas management procedures to be documented



Page 11 of 13


Appendices

Appendix A - Glossary of abbreviations and acronyms

CB Circuit Breaker

CBF Circuit Breaker FailDPTI Department Planning Transport and Infrastructure

ECO Electrical Control OfficerGIS Gas Insulated Switchgear

IEC International Electrical Commission

kA 1000 Am pskV 1000 Vo ItsLS Lonsdale substation

NCA Network Connection Agreement

NSP Network Service Provider

NER National Electrical Rulesms Millisecond (.001 second)OEM Original Equipment Manufacturer

RFS Rail Feeder StationSCADA Supervisory Control and Data Acquisition

SFAIRP So Far As Is Reasonably PracticableSFe Sulphur Hexafluoride




Appendix B ~ Glossary of terms

Term

Busbar

Bus Zone

Protection

Circuit Breaker

Fail Protection

Dead zone

Network

Connection

Agreement

Protection

Reasonably

practicable

Redundancy

SFAIRP

SulphurHexafluoride

Trip

Description

A metallic strip, usually of a large cross-sectional area that is used to conduct

electricity in a switchboard or switchgear over relatively short distances. Their large

cross-sectional area in comparison to cables helps to reduce losses due to corona

effect.

The primary form of protection used to detect faults internal to the switchgear zone

designated as the Bus.

The backup protection system designed to detect an unsuccessful trip of a circuit

breaker

A short zone which is not protected by the protection system, in the case of CB1081

there is a small area between Circuit Breaker interrupter and the Current

Transform er

The Network Connection Agreement is an agreement between SAPN Lonsdale

substation owner and DPTI that detail the obligations on both parties, including

technical and commercial obligations and requirements.

A definition relating to the concept of power system .fault detection and isolation

In the context of SFAIRP, reasonably practicable means that which is, or was at a

particular time, reasonably able to be done to ensure safety, taking into account and

weighing up all relevant matters including:

• the likelihood of the hazard or the risk concerned occurring,

• the degree of harm that might result from the hazard or the risk,

• what the person concerned knows, or ought reasonably to know, about the

hazard or risk, and ways of eliminating or minimising the risk,

• the availability and suitability of ways to eliminate or minimise the risk,

• after assessing the extent of the risk and the available ways of eliminating or

minimising the risk, the cost associated with available ways of eliminating or

minimising the risk, including whether the cost is grossly disproportionate to the

risk.

Applied to protection systems, the NER stipulates that the failure of a single element

within the protection scheme should not prevent fault clearance within the

applicable clearance times.

Under section 46 of the RSNL, DPTI Rail is required:

s to eliminate risks to safety so far as is reasonably practicable,

• if it is not reasonably practicable to eliminate risks to safety, to minimise those

risks so far as is reasonably practicable.

The concept of SFAIRP is to achieve the best possible safety outcomes, to the extent

that is 'reasonably practicable'.

Sulphur hexafluoride (SFs) is an inorganic, odouriess, colourless and non-toxic gas

that is 5 times more dense than air. It is used in High Voltage switchgear as an

insulator and arc quenching medium due to its excellent insulation strength.

Sulphur hexafluoride breaks down during arcing but it is self-healing, meaning most

of the decomposition products reform into SFc. A lot of energy is absorbed in the

decomposition process and once the decomposed products cool outside the arc, the

molecules reform releasing the absorbed heat, rapidly transporting heat away from

the arc, making it an efficient cooling medium.

Sulphur hexafluoride has low thermal conductivity so although it can rapidly conduct

heat away from an arc by dissociation, it has an insulating effect beyond the arc.

The automatic opening of a circuit breaker when a fault is detected by the

protection system in the circuit it is supplying.



Page 13 of 13

Documents

Rail Incident Report - Circuit Breaker Failure - DPTIdpti.sa.gov.au/__data/assets/pdf_file/0009/287298/Rail_Incident... · RAIL INCIDENT REPORT Circuit Breaker Failure, ... The NCA