intrinsic safety concepts, applications & … presentations/2014... · intrinsic safety...
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INTRINSIC SAFETY CONCEPTS,
APPLICATIONS & INSTALLATIONS
Roelof Viljoen
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Index
- Intrinsic Safety Concepts- Installation of Intrinsic safety in (flameproof) enclosures- System / Loop installations
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Intrinsic safety concepts
- Principles- Fault conditions- Gas groups- Temperature classes- Ratings of components- Construction
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A circuit in which no spark or thermal effect in any part of the equipment or circuit intended for use in a hazardous area is capable of causing ignition.
Fault conditions are applied in the circuit. Therefore, safety components are in many cases duplicated / triplicated.
Intrinsic safety is the only techniques considering faults IN the CONNECTING CABLES.
The system / interconnecting of different certified intrinsically safe units effect the overall safety and needs to be approved.
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Basic principles:
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Intrinsic Safety Categories (“ia”, “ib” & “ic”)
1,5 times safety factor on rating per component
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Intrinsic Safety Categories (“ia”, “ib” & “ic”)
(Ga, Ma) (Gc)(Gb, Mb)
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Spark Test Apparatus
Ignition Curves
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Resistive curve
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Ignition Curves
50 % safety factor is applied when using the curves.
Ignition graphs exist for:
resistive energies, (50% safety factor on current)
capacitive energy, (50% safety factor on voltage) and
inductive energy, (50% safety factor on current)
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A 5C to 10 C safety factor is applied to the surface temperature of a component.
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Interesting INFO
Gas Ignition energy Ignition Temperature
Methane Group I (250µJ) 537˚C (T1 gas)
Hydrogen Group IIC (20µJ) 560˚C (T1 gas)
Temperatures
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►Group I: IP54 housing: Components with surface area <20 mm2 may reach 950 °C @ 40 °C ambient.
Components with surface area >20 mm2 may dissipate 3,3 W @ 40 °C ambient.
150 °C still applicable on outside of housing
►Group I: NOT IN AN IP54 housing: 150 °C still applicable on inside components.
►Group II: No allowance is made for IP rating / sealing of enclosures and
therefore the surface temperature is measured on the inside of the equipment on internal components / tracks.
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Temperatures
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HOW HOT DO INTERNAL COMPONENTS ACTUALLY GET?
Approximately 20 mm2 surface areaand
340 °C @ 1 W and 40 °C ambient
Approximately 20 mm2 surface areaand
220 °C @ 1 W and 40 °C ambient
>>20mm2 surface area
Temperatures
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Safety components must be sufficiently rated:
- 150% rating required- Derating of semiconductor components e.g. Zener diodes
according to:• Assembly conditions (e.g. TL = 75°C, derate 40mW/C above
75°C• Ambient conditions (affects TL)
e.g. A 5W Zener diode is typically <2.5W
Use of components in parallel to share power?
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Some construction features include:
- IP rating- Electrostatic hazard (Plastic)- Drop test (typically no impact test)
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Installation of Intrinsic safety in (flameproof) enclosures
- Connections inside (flameproof) enclosures- Ambient temperatures- Internal Wiring / Installation in (flameproof) enclosure (including
empty enclosure)- ia equipment / double protection vs. 1.4% methane isolation
requirement
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A 50 mm separation I.S. To Non-I.S. (A partition may be used)
I.S. To earth ≥ 3mm
I.S to I.S. ≥ 6mm
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Connections inside (flameproof) enclosures
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Default ambient temperature:
(-20 ºC to +40 ºC)
e.g. Ex d I or Ex ib I/IIA T4
OR
[Ex ib] I/IIC T6 (-20°C < Tamb < 55°C)I.S. PSU or Barrier[Ex ib] I/IIC T6(-20˚C<Tamb<55˚C)
Heat generating
Components
What temperature will the I.S equipment be
exposed to?
Typically -20˚C to 40˚C Ambient outside temperature
Ex d Enclosure
Mine or Plant
Ambient Temperatures
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Internal Wiring / Installation in (flameproof) enclosure (including empty enclosure)
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Intrinsic safety requirements include:
• Separation Distance between:o Non-I.S. and I.S.o I.S. and I.S.o I.S. and earth.
• Safety Parameters (Um)• Earthing requirements for I.S.• Internal wiring requirements
o Bundling / Trayso Constructional / insulationo Ferrules
• Gland requirements for I.S. wiring• Internal temperature rise. (Ambient for I.S)
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Internal Wiring / Installation in (flameproof) enclosure (including empty enclosure)
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Internal Wiring / Installation in (flameproof) enclosure (including empty enclosure)
Flameproof requirements include:
o Energy storing componentso Pressure pilingo Temperatures (Temp. classification / ambient / temp. at
gland entries and branching point of cable / ratings of components (e.g. bushes) etc.)
Relabeling for empty enclosure certification / new certificate number. Do not remove empty enclosure certification label.
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Examples of Category Ma Equipment having two forms of protection
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>1.4% methane in air • flameproof equipment must be switched off. • Intrinsically safe category “ia” equipment or double protected
equipment allowed to remain energized.
Questions• Ex d [ia] I, may this remain on?• How is batteries in flameproof enclosures handled?
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Hazardous area in a mine (Zone 0)
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System / Loop Certification
- I.S. Loops / Systems- Simple apparatus- Earthing / Isolation requirements- Use of I.S. certified multimeters- Battery powered equipment
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I.S. Loops / Systems
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TransmitterEx ib IIC T3
(-20<Tamb<55)
Ui = 30VIi = 120mAPi = 0.7W
Ci = 0Li = 0
Hazardous area (Zone 1, Group IIA, T3 gas, ambient temperature 50 degC)
Safety Parameter rules:
Uo ≤ UiIo ≤ Ii
Po ≤ Pi
Co ≥ Ccable + CiLo ≥ Lcable + Li
Barrier device[Ex ia] IIA
(-20<Tamb<55)
Uo = 28VIo = 93mA
Po = 0.65W
Co = 83nFLo = 4.2mH
OR
Simple apparatus
Cable:
Capacitance / km
Inductance / km
Resistance / km
Safe area, ambient 10°C to 25°C
Non-certified
electronics
Safety Parameter rules:
Um = 250Vrms
(Limit on voltage from isolation transformer or
UPS)
IS LOOPS (MUST be approved by an approved tests laboratory)
Guidelines for more than one interface connected in a single loop may be obtained from SANS 10086-1
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• System certification required for I.S Loops / Systems • Mine machines are approved without intrinsic safety systems
certification / installation requirements.
• RS485 / Data signals not protected with barrier devices e.g. Return from fixed gas sensors in a mine to a PLC.
• Direction of barrier devices.• Multiple barrier devices / I.S. sources in a single loop.• Common ground return for multiple barrier devices / I.S. sources.
Machine certification / Misconceptions
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Common misconceptions:
When a barrier / I.S. Power Supply is used, the whole circuit is intrinsically safe.
USE OF RELAYS
CERTIFIEDSolenoid or relay(Usaully potted with diodes
Creepage and clearances Inductance / temp NEVER connect an i.s. circuit to a non-certified relay
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Interconnection of non-certified equipment in an I.S. Loop e.g.
- Non-certified relays- Solenoids- Indicators etc.
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Combination of capacitance & Inductance
Typical condition on a barrier device (LINEAR) for handling
of Co and Lo
• Li < 1% of Lo or Ci < 1% of Co
• Or inductance & capacitance is distributed (cable)
-- No restriction to Co and Lo use
Or
Li ≥ 1% of Lo and Ci ≥ 1% of Co -- 50% of Co and 50% of Lo allowed
• The reduced capacitance of the external circuit (including cable) shall not be greater than:
• 1μF for Groups IIB, IIA & I and
• 600nF for Group IIC.
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Simple apparatus
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Simple Apparatus:Connected to I.S. equipment
Resistor Potentiometer /
RTD Switch LED Photo
Sensor
Passive Components
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• conform to all relevant requirements of the Standard but
o need not be certified and
o need not be marked with i.s. marking
NB: 500V Isolation requirement to earth / body
Mine machines?
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Simple Apparatus shall:
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Earthing / Isolation requirements
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Typical protection by a barrier device / High quality earth (HQE):
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Mains FaultPower Supply / Electronics fault
elElectro-
nics /
Power
Supply Hazardous
location
Electronics /
power supply
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Typical protection by an isolator / Isolation:
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Mains Fault Power Supply / Electronics fault
EEleElectr
o-nics /Electronics /
Power Supply
Hazardous Location
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ISOLATION REQUIREMENTS FOR I.S. CIRCUITS
• 500 V isolation between i.s. circuits and earth• 1500 V isolation between i.s. and non-i.s. circuits.• 500 V isolation is required between i.s. and i.s. circuits.
Electronics/
Power supply
Certified equipment
Possible fault into hazardous location
Mains fault to positive line
Mains fault to i.s. enclosure Mains fault to negative line
PD = Fault current x earth resistance
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Earthing for I.S. Circuits
Supply Transformer
Barrier Device
Arm
ou
rin
g /
Scre
en
Main earth buster
HQE (High Quality Earth
Optional I.S. Link for testing
I.S. busbarO
vera
ll Sc
reen
Barrier Device
Arm
ou
rin
g
Junction box
500V isolation between I.S. And earth
Screened pairs
Scre
ened
pai
rs
Armouring
Terminals
500V isolation required
500V isolation required
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Use of cables for intrinsic safety on mine machines:
- Mechanical protection?- HQE on mine machines / inside flameproof boxes?- 500V isolation on mine machines e.g. junction boxes,
connection to earth etc.- Handling of screen?
- HQE- 500V isolation
- Multiple I.S circuits in a single cable?
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Use of I.S. Certified multimeters
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Intrinsically- safe multi-meters
Spe
cial
co
nd
itio
ns
of
use
“X
”
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Battery powered equipment
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Special conditions for safe use (X)
Use only Duracell plus AA 1.5V Alkaline MN1500 batteries
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B+
Charge
OV
B+
Charge
OV
Fuse Resistor
Charge
B+
Blocking diodes
OV
Typical examples of handheld units are radios,
multi-meters and gas sensors.
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Typical protection circuit for lithium batteries
Intrinsically safe?