Session Three: Arc Flash – Safety by Design in LV Switchgear

Electrical Safety & Power System Protection Forum 1

Session Three:

Arc Flash - Safety by Design in LV Switchgear

David Stonebridge ABB Australia

Abstract The Australian WH&S regulations & codes of practices have undergone dramatic changes in recent years. In 2012 the state & territory governments have to some degree harmonised the WH&S requirements, however when it comes to Arc Flash the debate continues with no firm national harmonised recommendations. Many mining companies in Australia have adopted the US regulations which have also undergone changes when it comes to protecting workers against Arc Flash. The focus of this paper is to look at safety by design in LV switchgear to protect workers against arc flash and to eliminate the need for PPE levels higher than category 2.

Introduction The new Work Health & Safety (WH&S) acts and codes of practices makes the person conducting the business or undertaking (PCBU) & the worker responsible for maintaining safety in the work place. This raises the question, what are the safety hazards and how do you provide protection?

ACB Operation with compartment door closed

For 20 years the racking and closing of circuit breakers has been performed without the necessity for the worker to wear arc rated PPE (Personnel Protective Equipment)

ACB Operation with compartment door closed

Is it now necessary under the WH&S requirements to wear full arc rated PPE to perform the same operations on the same switchgear?

Session Three: Arc Flash – Safety by Design in LV Switchgear

Electrical Safety & Power System Protection Forum 2

LV Switchgear Standards for voltages up to 1000V

(The Australian LV Standard AS/NZS 3439.1:2002. The International LV Standard IEC 61439-1/2)

The objective of the Standards is to define the service conditions, construction requirements, technical requirement and type testing requirements for LV switchgear. The primary safety focus is to prevent persons from making contact with live parts. Basically the requirement of the standards has not changed significantly from AS1136 which was published in the 1970’s. When performing an ACB racking operation with the door closed there is no danger of making contact with “Live” parts while there is a remote possibility that the operation could cause an internal arcing fault which could put the worker in a hazardous situation. The standards provide guidance to the purchaser they don’t recommend the safety requirements. For example arguably the most important safety requirement for switchgear is internal arc fault containment (IAC).The testing requirements for IAC were included in AS1136 in the form of guidelines for the manufacturer and the purchaser to come to an agreement on the increased security required. IAC was not a mandatory requirement and this has not changed in AS/NZS 3439.1.2002.

The objective of the Internal Arc Fault Containment (IAC) testing is to verify the safety of anyone standing in front of the switchgear against an internal Arc fault. Tests are conducted to the guidelines in Annex ZD AS/NZS 3439.1.2002 or IEC/TR 61641 for the nominated prospective fault current at a certified testing laboratory.

To verify the safety of anyone standing in front of the switchgear cotton screens are fitted around the switchgear to simulate clothing.

Each functional unit is tested by initiating an arc inside the unit with a piece of wire across all 3 phases.

To verify maximum safety against internal arcing faults the complete switchgear should be tested. Incoming Breaker, line and load side, main busbars and the line side of the functional units.

WH&S Requirements

The Australian WH&S regulations & codes of practices have undergone dramatic changes in recent years . In 2012 the state & territory governments have to some degree harmonised the WH&S requirements ,however when it comes to Arc Flash the debate continues with no firm national harmonised reccommendations. The US NFPA 70E regulations have aslo undergone dramatic changes, when it comes to protecting workers against Arc Flash the US requirements are clear .

Session Three: Arc Flash – Safety by Design in LV Switchgear

Electrical Safety & Power System Protection Forum 3

Many mining companies in Australia have adopt the US regulations

IEEE Standard 1584 Guide for Performing Arc Flash Hazard Calculations

NFPA 70E 2012 Standard for Electrical Safety Requirements for Employee Workplaces

These US regulations are being adopted in countries outside of America as part of the national OH&S acts and codes of practice, as is becoming the case in Australia. The US OH&S regulations IEEE1584-2002, Guide for Performing Arc Flash Hazard Calculations and NFPA 70E-2012, Standard for Electrical Safety requires an arc flash analysis to be conducted to calculate the incident energy levels. Once calculated this information is used to develop strategies to minimise burn injuries. The strategies include:

The specific rating of PPE ( personal protective equipment)

Working de-energised

Applying arc-resistant switchgear - IAC (internal arc fault containment)

If you don’t have Internal Arc Fault Contained (IAC) switchgear or switchgear where you can’t work “live” then this information is used to determine the level of PPE required to partially protect workers when working or operating electrical equipment. IEEE1584 indicates even if you have IAC switchgear which requires you to open the door to remove the functional unit from the bus you first should test to verify the switchgear is not alive. To conduct live testing the appropriate PPE must be worn. The inadequacy of this PPE is recognized in both IEEE1584 and NFPA70E which emphasizes that PPE is the lowest in the hierarchy of controls.

It must be recognised that PPE alone does not provide 100% protection against

Example: On the right US Regulations NFPA – 4 cals/cm sq. PPE

2009 requirements below –Flame retardant

2012 requirements right – Arc rated

Session Three: Arc Flash – Safety by Design in LV Switchgear

Electrical Safety & Power System Protection Forum 4

an arc flash as it only protects against the heat. PPE does not protect against the toxic gases or the appreciable pressure waves or the associated shrapnel which may attain velocities of 300m/s. Australian users are finding that Category 4 PPE is cumbersome and uncomfortable and affords limited mobility and visibility creating its own safety hazards. This has resulted in users demanding safer and more user friendly arc fault protection solutions. Users are looking at ways to eliminate the need for PPE levels higher than category 2.

The goal of the US regulations is to protect workers against burn injuries. Safety by design is promoted in IEE1584 to improve personnel safety:

Internal arc fault containment

Operating with the doors securely closed

Remote control and remote racking

Safe isolation and de-energisation

Minimising fault current and duration

Alternative work practice

Arc Fault Protection - Safety by design

The focus of this paper is to look at safety by design in LV switchgear to eliminate the need for PPE levels higher than category 2. The following is an example of where the arc flash hazards were calculated and category 4 PPE was implemented before looking at safety by design.

An arc flash analysis was conducted at an Aluminium Refinery on the 415V main power switchboards. The design of the switchboard requires that the electrical worker open the compartment door, take hold of the 2 racking levers and pull the breaker off the live bus. The aluminium process does not allow the switchgear to be shut down to perform this operation. The result of the arc flash engineering assessment was that there was a significant risk of arc flash when inserting and removing a circuit breaker and therefore Category 4 PPE had to be worn.

The owner recognised not only the hazards and limitations of wearing Cat 4 PPE, but in the event of an arc explosion the resultant pressure could turn the breaker into a deadly projectile. This was motivation to look at a safer design and develop their design requirements for LV switchgear.

Session Three: Arc Flash – Safety by Design in LV Switchgear

Electrical Safety & Power System Protection Forum 5

Owners ‘Safety by Design’ Requirements:

Withdrawable, Form 4 compartmented construction All control terminals & instruments located in the top

compartment away from high fault level conductors. Breaker operation whilst standing and the door

closed Thermography with the cable compartment door

closed ACB tag- out in disconnect position & door closed Provision for local manual and remote operation Unlimited arc fault containment ( special tests to

AS/NZS 3439)

Fully insulated bus system to minimise the risk of arcing faults

Summary

Many companies have employee protection policies with zero harm targets. These policies need to be supported with detailed safety strategies. It is not enough to say we need to protect workers against arc flash injuries and insist the workers wear arc rated PPE when working on LV Switchgear. It is also not enough to say internal arc fault containment switchgear is a mandatory requirement.

To protect workers from arc injuries under all conditions an engineering arc hazard risk assessment needs to be conducted. The switchgear IAC test reports need to be reviewed to clearly establish under what circumstance workers will or will not be protected. Clearly if a worker removes a cover to do Thermography on a live bus he needs to wear the appropriately rated PPE. If the switchgear is well maintained and operated under normal conditions with all the doors securely closed and has the appropriate Internal Arc Fault Containment test reports then arc rated PPE is not required to operate the switchgear.

Safety needs to be built-in to the culture of the company to fully mitigate the risk of arc burn injuries. The following is a suggested basis for a safety strategy.

TOP Safety Strategy - Safety by Design

Technical: Built-in Safety in the switchgear design o Fully Withdrawable o Closed door operation o Internal arc fault containment on the complete switchgear

Incomers, Main bus, Outgoing units line & load

Operational: Built- in Safety into the culture of the business o Safety strategy with clear responsibilities & instructions o Work permits o Safety reviews & training programs

Personal: Built-in Safety in the people o Qualified switchgear product trained people o Equipped with the appropriate tools and PPE to do the task