Ex NA and Ex e Motore Risk Assessment_RevC

7/24/2019 Ex NA and Ex e Motore Risk Assessment_RevC

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ABB GroupApril 1, 2011 | Slide 1

Safety of Ex nA, Ex e and Class IDivision 2 motors


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Standard with verification requirements

Only the latest editions of the IECand EN standards specify theproblem!

Many countries implement the IEC-standards into their nationalstandards.

Various countries define the edition

of the standards by internal rules

=> Many countries do not fol lowcontemporary the latestrequirements and therefore they arenot addressing the sparkingphenomena today.

Which international standards are addressing the sparkingphenomena?


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Which international standards are addressing thesparking phenomena?


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History of accident in theU.K.


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Actions taken by Authorities

Initiated several studies

Based on studies, they gave series ofrecommendation to users mainly in the UK

The development of international standardswere initiated

Actions taken by End Users

Required gas environment testing in practiceand experience from the tests

Comparison between different practices tofulfill the standard requirements

Inspection and overhaul of electric motors onfield

Actions taken by standardizationcommittees

ENV 50269

Risk assessment requirements implementedto IEC/EN standards

History of accidents involving electric motors in the UK


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Where and when sparkingcan occur


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When and Where it can occur?

All the time when the motor isrunning

Partial discharges (PD) at thesurface of the winding

Partial discharges at the surfaces ofconnection cables

Main reasons for stator sparking

High voltage and improper stressgrading

Inadequate clearance distances

Direct contact between groundenclosure and high voltage cable

Heating wires mounted on coiloverhangs

Aging of the windings Voltage transients

Dirty surfaces of windings

Stator sparking in respect of safety


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When and Where can it occur?

During the first cycles when motorsare started

Between rotor bars and rotor core

Close to end of rotor core packs orclose to the first radial cooling ducts

Main reasons for rotor sparking

Leakage current from rotor bar to rotorcore is switching due to possiblemovements of the rotor bars in the

slots

Rotor sparking in respect of safety


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Circulating currents

Where and When can it occur?

Between separate parts of enclosures

When motor magnetized and running Over-voltages

Main reasons for circulating current

Parts get charges due to magnetic fluxcreated by the stator

Parts are not equip-potential bondedand they floating on own potential

Improper grounding Equip-potential cables are

disconnected


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Note, waiver from some dutytypes where the motor isstarted once per week orless.

Non-sparking motors (IEC 60079-15:2005 and EN 60079-15:2005)

When risk assessment is applicable?

Increased safety motors (IEC 60079-7:2006 and EN 60079-7:2007)


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Stator risk assessmentIncreased safety motors


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Risk assessments for the Ex nA stator

constructions shall be if the sum of

risk factors is greater than 6:

Stator design shall be pass the required

non-sparking tests, or

Motor shall be equipped with a provision

pre-start ventilation (Note! operatorneeds to make decision to use it or not

based their possibility accept the risk)

Note, the table will be moved to IEC 60079-14 in the future, and the stator

gas testing will be compulsory for all random-wound high-voltage stators

and all high-voltage form-wound stators in gas groups IIC and IIB, as well as

in gas group IIA if the nominal voltage is greater than 6.6kV

Stator risk assessmentNon-sparking motors


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Non-sparking motors (IEC 60079-15:2005and EN 60079-15:2005)

Increased safety motors (IEC 60079-7:2006 and EN 60079-7:2007)

Special measures shall be applied if the sum

of risk factors is greater than 5

Special measures shall be applied if the sum

of risk factors is greater than 6

Rotor risk assessment


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Tests to verify that thedesigns are non-sparking

per IEC 60079 standards


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Stator testSinusoidal voltage test

Sinusoidal voltage test continuousoperation

Insulation systems and connectioncables shall be tested in an explosivegas mixture comprised of (21 5) %hydrogen-in-air or (7,8 1) % ethylene-in-air, v/v

U = A sinusoidal voltage of 1,5 timesthe rated r.m.s. line voltage for 3 min

The maximum rate of voltage rise shallbe 0,5 kV/s

In this test will be tested insulationbetween

Phase and earth

Phase and other phases


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Stator testVoltage impulses test

Voltage impulses test transient conditions

Insulation systems and connection cables

shall be tested in an explosive gas mixture

comprised of (21 5) % hydrogen-in-air or

(7,8 1) % ethylene-in-air, v/v

U = 10 voltage impulses of three times peak

phase voltage with

a tolerance of 3 %

A voltage rise time between 0,2 s and 0,5

s

A time to half value which is at least 20 s

but normally not exceeding 30 s

Electrical connection same as a sinusoidal

voltage test

In this test will be tested insulation between

Phase and earth

Phase and other phases


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Rotor test

Aging

The rotor cage shall be subject to an

ageing process comprising a minimumof five locked rotor tests

The maximum temperature of the cage

shall cycle between the maximum

design temperature and less than 70C

The applied voltage shall be not less

than 50 % of the rated voltage


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Rotor test

Tests

The same gas mixtures as for stator testing

Motors shall be subjected to 10 direct-on-line uncoupled

starts or 10 locked rotor tests. These tests shall have a

duration of at least 1 s

No explosion shall occur

During the tests, the terminal voltage shall not fall below 90

% of the rated voltage. The concentration of hydrogen or

ethylene shall be confirmed after each test


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Scenarios to users andtheir pros and cons


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Three scenarios for end users

1. To perform Risk Assessment for each case together with

Manufacturer and keep fingers crossed, or

2. To have a Provision for Pre-Purging if Risk factors limitsare exceeded, or

3. To require manufacturers to carry out gas testing and

provide certification based on that


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Scenario 1To perform risk assessment for each case

Easiest and most attractive procedure from Manufacturer, butin practice its brings couple of issues

In most of the cases, the risk factor limits are exceeded, and

special measures are needed.

Lack of information flow

Effective co-operation is needed between End User andManufacturer during the motor design phase (through

mech.vendor and contractor) All information is not typically available at that time

Changing specification

Risk assessment results might change many times during

tendering Varying conditions during the machines life time

Certificate will have limitation of use per risk assessmentresults


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Scenario 2Provision for Pre-Purging when Risk Factor Limits Exceeded

Another easy and economical solution formanufacturers

Manufacturer provides flanges and End User / Operator

takes the responsibility to decide to use them or not

Safety engineers typically require purging if the risks areindicated

If pre-purging is selected by end user

Does NOT protect against stator partial discharges,which can occur all the time. Thats the reason why IEC60079-7:2006 requires stator testing for all motorsabove 1kV

10 to 60min delay in the start Additional investments to purge control device, piping

and air compressor

Additional cost for operator to run air compressor

Overall reliability is reduced due to additionalcomponents

S


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Scenario 3Gas testing and Certification

To required that Gas testing is carried out for Rotor &

Stator is probably the best way for End Users &

Operators

No ones responsibility on end user of motor safety

To get confirmation that the design is non-sparking per

international standards

Not to have any limitations of the use of a need to review

risk assessment if factors are changing e.g. starting

frequency or maintenance strategy

Longer life-time for stator insulation due to no surfacedischarges


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ABB approach

Th i d t t f d f t f


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The gas test covers

LV Motors: M3_P motors produced in Vaasa(rotor test)

Induction Machines: HXR, AMA, AMI, M3produced in Helsinki or Shanghai (stator &rotor test)

Synchronous Machines: AMG and AMZproduced in Helsinki (stator test)

Results of the test

All rotor test passed (LV & HV)

Stator test passed (HV)

13.2 kV with IIC gases

15 kV with IIA and IIB gases

Other Ex nA motors which are not coveredby the type testing are equipped with aprovision for pre-start purging

Purge control units are always available asan option

The required gas tests are performed for most ofHV motors

B fit f t t d t f O t / E d U


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Benefits of gas tested motor for Operators / End Users

Streamlining the risk assessment process

(not need of risk factor calculations)

Re-inforce the insulation system increase the

time life of products

The alternative to testing and certification

involves equipping the motor with provision

for pre-purging

Investment in a higher capacity air

compressor, piping, and a purge control

unit

Requires an additional operation

purging every time the motor is started



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Benefits of the ABB approach thereforeinclude reduced

Initial capital expenditure

Lower operating costs

Faster starting

Higher reliability is improved as no

additional components are required

Most importantly, ABBs certified motorsoffer proven safety, as testing representsthe only way to verify that equipment is

really safeDanger is often marked with black and

yellow.Thats why our machines are blue!



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