Tuesday, December 01, 2020

STANDARDS

AS 1668, AS 1359, BS 7349, BS 4999, BS 5000, IEC 34, IEC 72.

GENERAL

Western Electric Smoke Spill motors are designed to meet the requirements of Bitish and Australian Standards.

AS 1668. 1 states that the objectives of Smoke Control are:

        a) to vent smoke from the fir-affected compartment: and

        b) to reduce the spread of smoke to fire isolated exits and other compartments.

 

In general Smoke Spimm motors are required to continue to operate driving extraction fans in a building, in the case of a fire. Usually these motors operate air circulation fans as part of the normal operation of the building, however if a fire occurs they must continue to operate for a period of time to extract smoke and\or dangerous fumes from the building and allow rescue services some assistance in rescuing any occupants still in the building. it is expected that hte fumes being extracted will be at high temperatures, well above normal ambients. These motors must be able to operate for a short period in high ambient temperatures - usually 250deg C. for 2 hours.


 

AS 1668.1 defines a Smoke-Spill fan as follows:

Each Smoke-Spill fan, complete with its drive, flexible connections and control gear, shall be constructed and installed so that it is capable of continous operation at it’s rates capacity as required as follows:

        a) Except as required be b), the fan shall operate for a period of not less that 2 hours with a smoke-spill air temperatures of 200 deg C.

         b) Where the smoke-spill fan serves as a single compartment and is located at the same level as the compartment. it shall operate for a period of not less that 30 minutes with a smoke spill air temperature of 300 deg C.

If the building has an approved aprinkler system installed throughout and fire isolated exits are pressurized, the need only comply with a), as above.

Motors driving such fans may be mounted in the air stream provided -

        i) They are capable of operating at the appropriate temperatures and for the specified period : and

        ii) any intergral high temperature cut-outs fitted are electrically isolated during a smoke control operations

 

STANDARD ELECTRIC MOTOR SPECIFICATIONS

Voltages 380v, 400v, plus other options.

Frequency 50Hz, (60Hz)

Speeds - single speed or 2 speed

Connections - 2.2 Kw and below- 240v Delta/ 415v Star.

3Kw and above - 415v Dleta with 6 leads for Star and Delta startings.

2 speed motors are supplied for DOL starting only. If star/ delta starting is required it must be specified with the inquiry and the order.

Protection - TP55, (IP56, IP65, IP66).

Shaft Hole - all motors are supplied with a drilled and tapped hole to DIN standards, in the end of the shaft.

Cooling - TEFC, (Totally Enclosed Fan Cooled), TEAO, (Totally Enclosed Air Over). TEAO motors are supplied without a cooling fan and rely on the air flow from the ‘load’ fan they are driving for their cooling.

Terminations/Connections - Standard Terminal box and terminal block oe extended leads and a blanking plate.

Special Requirements for Smoke Spill motors.

Bearings with C3 or C4 radial clearances.

High Temperature Grease.

Stainless Steel Nameplates.

Special Stator Windings - Class H or Class F, depending on the time and termperature rating specified by the customer. Class H windings with special materials are also available.

 

The following information is Required when ordering a Smoke Spill motor.

Kw ratings (or rating for 2 speed)

Speed or Speeds.
Voltage

Frequency

Temperature Rating in deg. C.

Time Requirement

Mounting - foot or flange

TEFC or TEAO.

Standard Terminal Box or Blanking Plate and Extended leads

With or without fan.

With or without fan cowl.

With or without anticondensation heaters.

(Only to be operated when the motor is off)

With or without thermistors. (Thermistor circuit will need to be disabled in the case of a fire)

Type of motor starter or if using a variable frequency drive.

 

Motor Testing

Sample motors, prepared to Western Electric Smoke Spill Specifications, have been tested, and independently witnessed, to ensure compliance with the following requirements:

200 deg C. for 2 hours

250 deg C. for 3 hours

300 deg C. for 30 minutes.

 

The motors were run in a normal ambient temperature at full load driving a fan until the temperature stabilized at normal operating temperature. The motor/fan units were then placed into a large oven at the required temperature and continued to operate for the required time. The motors were closely monitored during these tests, and all data was recorded. Copies of the test reports on these motors are available on request.

 

The Future

Australian Standards have produced a new Draft Standard called "Methods of Test and Rating Requirements for Smoke Spill Fans". This standard is based on the requirements of the European Standard EN BKXF-3 "Specifications for powered smoke and heat exhaust ventilators"

The following sections are all taken from the new draft standard.

The foreword to the draft standard states:

 

Smoke and heat exhaust ventilation systems are used widely to create smoke free areas beneath a buoyant smoke layer and to create negative pressures in fire affected compartments. These actions assist in evacuating people from a building, reducing fire and smoke damage, facilitating firefighting and retarding the lateral spread of the fire.

 

When air and the products of combustion are exhausted from a building by mechanical means in the event of a fire, a powered fan (known as a smoke spill fan) is generally used. It is therefore essential that the smoke spill fan temperature conditions when called upon to do so.

 

Dual Purpose smoke-spill fan - a smoke spill fan that has provision to allow its use for day to day comfort ventilation.

 

Smoke spill fan motor range - a range comprising smoke spill fan motors from the same manufacturer, which are physically similar, using the same form of construction and material and manufacturing method for the carcass, the cooling impeller when fitted, and end covers; the same insulation specification which includes insulation used for coil separation and slot insulation, winding impregnation materials (varnish or resin, tec. lead insulation, terminal blocks and other materials that could affect the integrity of the insulation): same bearing type, internal radial clearance, class of fit, lubricant and arrangement. The motor windings shall also be based on the same maximum winding temperature and class of insulation, in accordance with IEC34.1

The following may vary across the range -

a) the frame size;

b) the rotational speed;

c) the electrical windings, including multispeed;

d) he form of mounting, e.g. foot, flange, pad, clamp

 

Motor Rating/Motor Selection. The motors shall be selected for continuous operation at the power level required or the sir density at normal ambient temperature, not just for operation at elevated temperatures and lower densities.

 

Motor Rating/Insulation Integrity. The integrity of the insulation in motors is very dependent on the operational temperature of the windings. Relatively small decreases in the temperature rise above ambient will significantly extend the life of the insulation. Motor ratings for smoke spill fans shall be limited by the temperature rise for one class lower that the insulation class of the motor, as defined in IEC34.1 and given in the table below:

Notes:

1. It is recommended that motor ratings for all smoke spill fans be limited by temperature rise for one class lower that the insulation class of the motor.

2. The mechanical integrity of smoke spill fan motors placed in the airstream or subject to thermal conduction effects in determined largely by the ability of the lubricated bearings, supporting the motor shaft, to function satisfactorily at elevated temperatures. This mechanical integrity is enhanced by selecting the appropriate class of fit, internal radial clearance and lubrication for the rated smoke spill operating time and temperature. As a guide, bearings used in smoke spill fans which are exposed to elevated temperatures should have a C3 radial clearance and the appropriate high temperature lubricant suitable for the time/temperature rating.

 

Alternative Insulation. As an alternative for motors with Class B or Class F insulation, the motor rated power output should be 15% above the absorbed power for an air density of 1.2kg/m3.

 

Time/Temperature Ratings

Test Time and Temperature According to Rating

Notes: Rating 3 & 4 are not called for in AS 1668. 1, but are included within this Standard to accommodate ratings which may be specified by overseas markets. The special ratings may include other ratings requested by the supplier. (Refer to table below)

 

Summary

In the past there has been some confusion about exactly what tests and test procedures should be conducted on motors and fans to ensure that they will meet the requirements of Smoke spill standards. When this new standard is adopted (probably in 1998) it will ensure uniformity and compliance with the requirements of the standard for all motors that have been tested to this standard.

 

Another area of concern is that although new motors and fans will pass the requirements of the standard there is some doubt that they would comply with the requirements after they have been operating for 5 years. It has been suggested in Australia that all smoke spill motors should be replaced with new motors after a period of time - maybe 5 or 10 years. The new draft standard tries to address this problem by keeping the temperature rise of the motor during normal operation well below the rating of the materials. The bearings and grease are still probably the weakest link and will probably fail first without good maintenance.

 

Western Electric Australia plan to set up a test rig as specified in the new draft standard for combined motor and fan testing in compliance with the proposed new standard, so that when the new standard is released we will be ready with a range of motors tested to the requirements and independently witnessed. We will also offer this test facility to the fan producers to test the compliance to their fans.

 

Western Electric have always tried to ensure that the motors we supply for smoke spill applications are of the highest quality and designed to give reliable performance over many years. Smoke spill motors need to be well made and reliable because people’s lives are at stake if these motors do not perform to Smoke Spill Standards when they are needed.

 

The following tables and comments are an attempt to cross reference between different National standards for Hazardous Location Definitions. We note that there is a world wide trend towards IEC standards in the electrical industry and that even the American manufacturers are gearing up to produce products to IEC standards in IEC metric dimensions.


COMPARISON OF ZONES FOR ELECTRICAL EQUIPMENT

IEC/CENELEC/U.K.
GERMANY/JAPAN
U.S.A.
ZONE 0 DIVISION 1
ZONE 1 DIVISION 1
ZONE 2 DIVISION 2

COMPARISON OF CLASS II CLASSIFICATIONS - DUSTS

B.S.6467 & A.S. 2236
-CLASS II
U.S.A.-CLASS II
DIP - NO SUB - GROUP GROUP E - METAL DUSTS

GROUP F - COAL DUSTS

GROUP G - GRAIN DUSTS

COMPARISON OF GAS GROUPINGS FOR ELECTRICAL EQUIPMENT

IEC
CENELEC
AUSTRALIA
U.KBS4683 GERMANY & JAPAN

VDEO171

RIIS-TR-TR-79-1

U.S.A.
NATIONAL
ELECTRIC
CODE
Representative Gases
II IIA II IIA 1 D Propane
IIB IIB 2 C Ethylene
IIB IIC 3n 3a B Hydrogen
IIB 3b None Carbon Disulphide
IIB 3c A Acetylene

COMPARISON OF ZONES FOR TEMPERATURE CLASSIFICATIONS FOR ELECTRICAL EQUIPMENT.

IEC/CENELEC
AUSTRALIA
JAPAN
(RIIS - TR - 79 - 1)
U.S.A.
(NEC 1984)
MIN
IGNITION
TEMP
DEG C
Class Maximum Surface
Temp. deg.C.
Class Maximum Surface
Temp. deg.C.
Class Maximum Surface
Temp. deg.C.
T1 450 G1 360 T1 450 450
T2 300 G2 240 T2
T2A
T2B
T2C
2TD
300
280
260
230
215
300
280
260
230
215
T3 200 G3 160 T3
T3A
T3B
T3C
200
180
165
160
200
180
165
160
T4 135 G4 110 T4
T4A
135
120
135
120
T5 100 G5 80 T5 100 100
T6 85 G6 70 T6 85 85

The tables above are a compilation of information from various sources which we believe to be correct, however, we can accept no responsibility for any inaccuracies.


EXPLOSION PROOF VS FLAMEPROOF

Americans refer to “Explosion Proof”, while the UK and IEC refer to “Flameproof” motors or equipment. In IEC definitions this is an Ex d piece of equipment. Ex d equipment is designed to contain an internal explosion to escape between the “flamepaths”, but cool any flame in the hot gases so that no flames escape from the enclosure to ignite any external flammable gases - hence “Flameproof”.

Although Ex e equipment is designed to be used in a Zone 1 area it cannot be described as “Explosion Proof” or “Flameproof”, as it will not contain an explosion if one did occur. Ex e equipment is manufactured to an approved “Explosion Proof Technique”.


Saturday, June 06, 2020

The typical fuse consists of an element which is surrounded by a filler and enclosed by the fuse body.
The element is welded or soldered to the fuse contacts (blades or ferrules).

The element is a calibrated conductor. Its configuration, its mass, and the materials employed are selected to achieve the desired electrical and thermal characteristics. The element provides the current path through the fuse. It generates heat at a rate that is dependent upon its resistance and the load current.
Mersen (Gould Ferraz Shawmut) Fuse Construction

The heat generated by the element is absorbed by the filler and passed through the fuse body to
the surrounding air. A filler such as quartz sand provides effective heat transfer and allows for the
small element cross-section typical in modern fuses. The effective heat transfer allows the fuse to carry harmless overloads. The small element cross section melts quickly under short circuit conditions. The filler also aids fuse performance by absorbing arc energy when the fuse clears an overload or short circuit.

When a sustained overload occurs, the element will generate heat at a faster rate than the heat can be passed to the filler. If the overload persists, the element will reach its melting point and open. Increasing the applied current will heat the element faster and cause the fuse to open sooner. Thus fuses have an inverse time current characteristic, i.e. the greater the over-current the less time required for the fuse to open the circuit.

This characteristic is desirable because it parallels the characteristics of conductors, motors,
transformers and other electrical apparatus. These components can carry low level overloads for
relatively long times without damage. However, under high current conditions damage can occur quickly. Because of its inverse time current characteristic, a properly applied fuse can provide
effective protection over a broad current range, from low level overloads to high level short circuits.

Monday, March 02, 2020

Level sensors have been a part of manufacturing processes for several decades, in industries as diverse as food and beverage, semiconductors, and pharmaceutical. However, equipment manufacturers and users may be surprised at both the breadth and sophistication of level sensing alternatives currently available. 

Measurements and actions that used to require large, mechanical, and expensive devices can now be performed using advanced, highly versatile technologies that are also durable, precise, and easy to implement. What’s more, a variety of level sensing technology options work well with what have traditionally been challenging substances such as sticky fluids (e.g., molasses, glue, ink) and foam(beer, pulp, hydraulic fluid, soap). 

Some users may question the need for such technology - or any level sensing device, for that matter - arguing that existing, “tried-and-true” methods are well-suited for the basic nature of most level sensing tasks. But today’s manufacturing environment is hardly that simple. Given the increasingly competitive nature of the marketplace, plus the ongoing drive to minimize inefficiencies and waste, no operation can afford processes that are merely “close enough.” Dependability is also paramount if caustic or otherwise hazardous materials are involved.

In other words, level sensing is like any other part of the manufacturing process; it has to be precise, reliable, and cost-effective.

SICK Level Sensing

Level sensing 101 

To determine the best sensor for a particular application, it’s important to first understand what technology options are available, as well as their advantages and limitations. Following are some of today’s most frequently used level sensing methods. 

Laser.

This technology offers the broadest availability of offerings, flexibility, ease of set-up and alignment, and cost. While lasers work well for bulk and liquid, continuous, and switching applications, it’s not as well-suited for clear materials, foam (light loss due to dispersion), or sticky fluids (lens contamination).

Microwave. 

Because of its ability to penetrate temperature and vapor layers that may cause problems for other techniques, guided microwave technology (also known as guided radar)compares well with lasers as they don’t need calibration and have multiple output options.Guided microwave is also among the handful of technologies that works well with foam and sticky materials. However, guided microwave sensors do have a limited detection range in some applications.

Tuning Fork. 

This vibrating-style sensor technology is ideal for solid and liquid detection,including sticky substances and foam, as well as bulk powders. However, tuning forks are limited to detection applications (i.e., overfill and dry run), and do not provide continuous process measurement. The mounting position of the devices is also critical.


Ultrasonic. 

These devices, which gauge levels by measuring the duration and intensity of echoes from short bursts of energy, share the same capabilities as lasers and offer flexibility in mounting and outputs. The technology is ideal for many types of liquids, but performance drops off in applications involving foam. Range is more limited than laser offerings and alignment of the emitting/detection and reflection components is also critical.

Optical Prism.

Inexpensive and simple to set-up and operate, optical sensors detect variations in emitted light. However, optical prisms work only in clean translucent to transparent liquids,while their limited “on/off” functionality also restricts their use to protecting from overflows and dry runs. 

Pressure. 

Used for a variety of liquids, pressure sensors measure the hydro-static pressure of the liquid at the bottom of the tank with respect to atmospheric pressure to determine the level of the liquid. Though highly accurate, pressure sensors’ setup and calibration requirements make them more of a specialty solution in situations where all other options are not viable due to the type of liquid, or configuration of the tank itself. For example, the tank bottom may have a funnel or cone shape, or there may be a motor or agitator positioned in the middle that prevents a straight-down view. 

Capacitance. 

Capacitance level sensors operate with a variety of solids, liquids, and mixed materials. There are also a wide range of device types, some of which can be attached outside the vessel. Users need to be cautious when selecting a device, as not every capacitance senor works with every type of material or vessel. In addition, some capacitive probes can give continuous output much the way guided microwaves or conductive probes do, but need to be calibrated to the material being measured. And because capacitance probes are a contact-based measurement system, the technology is not always suitable for use with sticky fluids. 

Floats.

The oldest and simplest measuring technology can still be found in automated manufacturing processes. Being a mechanical device, however, floats offer little other advantage to users for all but the most basic applications.

SICK Level Sensors


Decision time

In some respects, matching a level sensor with a particular application may seem relatively simple. One question - the desired result, is usually a matter of either switching/detection for dry-run and overflow protection, or continuous monitoring for process management.

Here, the continuum from basic performance to “smart” sensors is rather straightforward. Tuning forks, optical prisms, and some capacitance sensors are restricted to switching applications. Other technologies work for both switching and measurement - laser, guided microwaves, ultrasonic, pressure, and float.

But the other key consideration - what is being measured - is not so simple. Solids and liquids have multiple dimensions and characteristics, any one of which can influence its ability to be accurately measured. 

For example, both solids and liquids can be clear, translucent, or opaque. Minute texture variations of some powdery substances may also affect how a sensor reacts, as can a liquid’s viscosity and density. 

Color variations may also be an issue with some types of level sensors. And, as noted earlier,particularly challenging applications further restrict the range of options. When dealing with foam, sticky liquids, or clear liquids, for example, guided microwaves and vibrating forks may well be the only option.

The table below can serve as a helpful starting point to find the best level sensor technology for a particular application. In making these evaluations,users and equipment manufactures should also ask operations-related questions.

For example, what kind of control capabilities do the sensors have, and what training operator training is required. Will the material being measured affect the sensor’s performance over time, requiring maintenance for cleaning and/or replacement? If so, how often should preventative work be scheduled,and what are the downtime implications? What is the expected life of a particular sensor? And if the process involves multiple types of materials with varying characteristics, will changeovers be an issue? 

The above information is designed to provide a basic guide to the growing range of level sensing technology. Because most of these approaches continue to evolve with the introduction of new and enhanced products, the best way to ensure a full evaluation of available options - especially for unique or challenging applications - is via a collaboration involving the manufacturing system owner, machine builders, and technology suppliers. Thorough and thoughtful assessments of sensor technologies will lead to better decisions, resulting in better product quality and optimized production efficiency.