cired2007 Directory

1
OPERATOR AND PUBLIC SAFETY REVISITED THE
APPLICATION OF IEC 62271-200/202 WITH SPECIFIC
FOCUS ON INTERNAL ARC TESTING OF METAL-ENCLOSED
SWITCHGEAR AND CONTROLGEAR (PAPER 0256)

• R A Kelly (Eskom SOUTH AFRICA)
• B Meyer (Previously Eskom SOUTH AFRICA)

2
Introduction

• Purpose to share Eskoms philosophy behind the
  recent developments in the re-testing of
  metal-enclosed switchgear products to meet the
  safety requirements of the South African
  Occupational Health and Safety Act with
  particular respect to internal arc compliance
  utilizing the recently published IEC 62271-200
  and IEC 62271-202 as reference.
• Operator and public safety has been put under the
  spotlight in Eskom following various catastrophic
  failures of metal-enclosed switchgear.

3
Introduction

• Users in South Africa have a duty, in terms of
  safety legislation (most notably the Occupational
  Health and Safety Act 85 of 1993 1) to their
  employees and the public to provide an acceptably
  safe environment and to take reasonable measures
  to mitigate against possible dangers.
• With developments in both technology and
  knowledge, it is now possible to specify and use
  switchgear that is tested not only to withstand
  the effects of, but to safely vent the
  emissions generated by an internal (arc) fault.

4
History of MV S/G in SA EDI

• For many years primary insulation/interrupting
  medium was oil
• Historically maintained on an interval and
  event-based maintenance schedule
• Alarming trend inadequately maintained
• Maintenance simply not being scheduled
• pressure on maintenance budgets
• increasingly difficult to schedule onerous
  outages required for maintenance
• In some cases run-to-failure philosophy

5
History of MV S/G in SA EDI

• The result
• gradual deterioration in the insulating and
  interrupting properties of oil
• increased probability of mechanism failure
• increased risk and number of failures with
  associated injuries / fatalities

6
History of MV S/G in SA EDI

• As a direct result, numerous switchgear failures
  have occurred which have been accompanied, in
  many instances, by serious injuries, and in some
  more severe cases, fatalities.
• Issues pertaining to internal arc testing have
  emerged in the process of addressing the safety
  concerns around increasing switchgear failure
  risks.

7
History of MV S/G in SA EDI

• Prior to the advent of suitable alternatives to
  oil-filled switchgear (e.g. air/gas-insulated
  metal-enclosed switchgear), requirements such as
  internal arc classification could not be
  seriously considered.
• IAC only possible with dry-arcs
• can be simulated in laboratory
• associated with air, SF6 filled switchgear
• Simply not practical for oil-filled switchgear
  damage to surrounding property

8
History of MV S/G in SA EDI

• In general, oil-filled switchgear has a proven
  record of reliability and performance. Failures
  are rare but, where they occur, the results may
  be catastrophic. Tanks may rupture, resulting in
  the ejection of burning oil and gas clouds,
  causing death or serious injury to persons and
  major damage to plant and buildings in the
  vicinity of the failed equipment. Accident
  experience has shown that failure usually occurs
  at, or shortly after, operation of the equipment.
  Thus, the way switchgear is operated, its
  condition and the circumstances existing in the
  system at the time of operation, to a large
  extent, determines whether the equipment will
  safely perform its duty.
• Clause 5, HSE 483/27 Oil-filled electrical
  distribution and other switchgear

9
History of MV S/G in SA EDI

• The now well known concept of IAC involves
  designing and testing equipment that, should an
  internal short circuit fault (arc) should occur
  in any of the switchgear enclosures, it will fail
  in a safer and predictable manner.

10
Safety Eskoms approach

• Safety is achieved by reducing risk to a
  tolerable level.
• freedom from an unacceptable risk (IEC 51)
• Tolerable risk is determined by the search for an
  optimal balance between the ideal of absolute
  safety and the demands to be met by a product,
  process or service, and factors such as benefit
  to the user, suitability for purpose, cost
  effectiveness, and conventions of the society
  concerned.
• Risk is considered to be the combination of the
  probability of occurrence of a harm and the
  severity of the harm.

11
Safety Eskoms approach

• It follows that there is a need to continually
  review the tolerable level of risk in
  particular when developments in both technology
  and knowledge can lead to economically feasible
  improvements in order to greatly reduce the
  risk associated with the use of a product,
  process or service.

12
Internal arc

• Arc energy f (voltage, S/C current, time)
• Incident energy f (arc energy, distance)
• Energy absorbed by person f (incident energy,
  PPE)

13
Internal arc

• Result of inadequate pressure release mechanisms

14
Risk Reduction (IEC 51)

• It is emphasized that the additional protective
  devices, personal protective equipment and
  provision of information to users should not be
  used as substitutes for design improvements

15
Risk Reduction

• PPE only to be used last line of defence
• not as a replacement for appropriate equipment
  design and testing (e.g. internal arc
  compliance), safe work practices or engineering
  controls that can help limit exposure to
  arc-flash hazards
• SA OHS Act has a general duty clause reasonable
  precautions
• Currently no local electrical safety regulations
  relating to internal arc in South Africa
• Eskom chosen to follow recommendations of NFPA
  70E
• standard for electrical safety in the workplace
• adopted by the US DoL

16
Risk Reduction

• Arc flash hazard risk analysis, requiring
• arc flash protection boundary be established
  based on the incident energy in order to manage
  the risk of injury and ensure that personnel have
  adequate PPE.
• employees are trained and aware of potential
  hazards when operating, changing the position of,
  or working in the proximity of energized
  electrical equipment.

17
Risk Reduction
18
Risk Reduction

• If an employee needs to enter a flash boundary to
  perform work that could possibly cause an arc
  flash, then appropriate PPE (personal protective
  equipment) needs to be worn.
• The type of PPE depends on the amount of energy
  to which an employee could be exposed.

19
Risk Reduction
20
Risk Reduction

• For new equipment, through the specification and
  design of internal arc classified switchgear,
  where the energy and emissions resulting from and
  internal arc are suitably vented away from the
  operator and/or people in the vicinity, the
  safe working distance (flash boundary) can be
  effectively managed
• without the need for excessive PPE (category 0)
• IEC IAC provides a tested level of protection
• under normal operating conditions
• not under maintenance conditions
• not concerned with service continuity

21
Risk Reduction

• additional supplementary measures
• arc detection, arc eliminators / suppressors,
  CLDs (e.g. ACRs, NERs), pressure relief devices,
  remote control, motorised racking devices,
  transfer of withdrawable parts with front doors
  closed
• requires a co-ordinated approach
• Measures are continually sought to mitigate
  against internal arc faults caused by known
  common problems.

22
Specifications for new S/G

• 1998 internal arc testing of primary S/G
• 2002 specification of IAC secondary switchgear
  (e.g. RMUs)
• 2005 present - Eskom has recently been involved
  in the development and re-testing of switchgear
  products to meet the safety requirements of the
  Occupational Health and Safety Act and
  industry-aligned requirements utilising the
  recently published IEC 62271-200 as well as IEC
  62271-202 (prev IEC 61330) as reference
• IAC philosophy revisited

23
Specifications for new S/G

• IEC 62271-200 caters for two relevant categories
  of IAC based on the type of accessibility
  required by the user.
• Type A accessibility is restricted to authorised
  personnel only and
• Type B accessibility caters for unrestricted
  accessibility including that of the general
  public.
• IEC 62271-202 defines accessibility Type A and B
  as follows
• Type A accessibility protection of operators
  (authorised personnel) performing normal
  operations
• Type B accessibility protection of public
  unrestricted accessibility (doors closed)

24
Specifications for new S/G

• Primary switchgear
• AR-BFL (IEC 62271-200)
• 25kA 0,2 s (12kV 24kV)
• transfer of withdrawable parts with front doors
  closed
• venting upwards, room dimensions specified
• pressure relief devices in switchroom
• supplementary measures
• arc detection system (2/2)
• remote switching (separate room for control
  panels)
• motorised racking devices with remote control
• Secondary switchgear
• AB IEC 62271-202 (AF-BFLR (IEC 61330))
• 20kA 0,5 s (12kV) 16kA 0,5 s (24kV)
• venting upwards 2 m duct

25
Specifications for new S/G

• Recently tested secondary switchgear

26
Conclusions

• Ever increasing focus on human safety, service
  delivery and cost reduction.
• Eskom and other major utilities have responded to
  the changing risk profile in the light of
  developments in both technology and knowledge
• The introduction of mandatory type testing for
  internal arc classified (IAC) switchgear as
  detailed in IEC 62271-200 and IEC 62271-202,
  together with the implementation of safe working
  practices (such as those detailed in NFPA 70E),
  has greatly enhanced Eskoms ability to specify
  acceptable equipment that significantly improves
  both operator and public safety.