Moeller Electric T rotary switches and P switch disconnectors are suitable for use as main, maintenance and emergency-stop switches that can be locked in the off position with up to three padlocks. Moeller Electric T rotary switches and P switch disconnectors are available in ten different basic switch types with several mounting forms and both standard and customised contact configurations. This makes them a compact, convenient, dependable and cost-effective solution for virtually any application involving uninterrupted currents of up to 315A.
Both ranges are available in versions with 400/415V AC23A ratings from 6.5 to 132kW and with uninterrupted current ratings from 20 to 315A. They are suitable for use as main, maintenance and emergency-stop switches rated to IEC/EN 60204 and IEC/EN 60947 and can be locked in the off position with up to three padlocks. They are available in their own enclosures or for mounting in control cabinets, either on the door or rear of the panel with a cover interlock. The T range is also available as motor load switches for changeover, multispeed, reversing and star-delta switches.
T0 switches can be supplied with up to 22 contacts and 12 switching positions and are suitable for many different switching and control functions, such as on/off, hand/auto, changeover, step, coding and instrument selector. Compact TM switches are designed to save space but also to be particularly easy to install and wire. They have an AC23A rating of 3kW and an uninterrupted rating of 10A. Moeller Electric supplies a full range of enclosures for use with its rotary switches and switch-disconnectors.
These enclosures are available in insulated and stainless steel versions with ingress protection ratings up to IP65 and in sheet steel with ingress protection ratings up to IP55, making them suitable for use in the food industry. ATEX-compliant insulated enclosed versions of T rotary and P switch disconnectors are available up to 100A. All types and ratings are approved for use in dust areas, zone 22 and category 3 and all are approved for device group II.
Students Race Low-Carbon Fuel Vehicles
Among the teams entering cars in the low-carbon fuel category are the University of Hertfordshire with a hydrogen-powered car and Oxford Brookes University with a parallel hybrid. Teams from across the world have entered the Formula Student competition, which is backed by the Institution of Engineering and Technology (IET) and takes place at Silverstone the weekend after the British Grand Prix This year, for the first time, there is a category for cars powered by low-carbon fuel.
Formula Student is aimed at building future engineering talent and there are five different classes that can be entered. Those taking part design and manufacture a single-seater racing car. Among the teams entering cars in the low-carbon fuel category are the University of Hertfordshire with a hydrogen-powered car and Oxford Brookes University with a parallel hybrid.
Robin McGill, Chief Executive of the IET, said: "Environmentally friendly fuels are the fuels of the future and it's for this very reason that the IET has pushed to have a low-carbon vehicle category in the competition". "We have been a partner in Formula Student for three years and recognise the vital role the competition plays in promoting careers and excellence in engineering".
With three weeks to go, both teams are gearing up for the challenge. It is the 11th car that the University of Hertfordshire has entered in the competition. The team of nine students, who are all final year MSc students, is looking to build on the previous years' results of 7th and 5th.
The Hertfordshire car is hydrogen powered with an adapted 250cm3 internal combustion engine. Leader of the Hertfordshire team, Professor Howard Ashe, said: "The students are keen to take part in the competition as they are only too aware that it provides them with hard to come by real world practical and business skills". "It helps them to gain valuable team working and individual skills". "It also gives them an appreciation of real world skills".
"Now that their exams are over, the team are working all day, every day, including working into the night, to ensure the car is fit for purpose for its launch on 3rd July". The Oxford Brookes team is entering an electricity-powered parallel hybrid car. The team is led by James Larminie and it's the seventh year that the university has taken part in the competition. Made up of undergraduate and postgraduate students, the team is currently busy putting the finishing touches to the car.
Formula Student is aimed at building future engineering talent and there are five different classes that can be entered. Those taking part design and manufacture a single-seater racing car. Among the teams entering cars in the low-carbon fuel category are the University of Hertfordshire with a hydrogen-powered car and Oxford Brookes University with a parallel hybrid.
Robin McGill, Chief Executive of the IET, said: "Environmentally friendly fuels are the fuels of the future and it's for this very reason that the IET has pushed to have a low-carbon vehicle category in the competition". "We have been a partner in Formula Student for three years and recognise the vital role the competition plays in promoting careers and excellence in engineering".
With three weeks to go, both teams are gearing up for the challenge. It is the 11th car that the University of Hertfordshire has entered in the competition. The team of nine students, who are all final year MSc students, is looking to build on the previous years' results of 7th and 5th.
The Hertfordshire car is hydrogen powered with an adapted 250cm3 internal combustion engine. Leader of the Hertfordshire team, Professor Howard Ashe, said: "The students are keen to take part in the competition as they are only too aware that it provides them with hard to come by real world practical and business skills". "It helps them to gain valuable team working and individual skills". "It also gives them an appreciation of real world skills".
"Now that their exams are over, the team are working all day, every day, including working into the night, to ensure the car is fit for purpose for its launch on 3rd July". The Oxford Brookes team is entering an electricity-powered parallel hybrid car. The team is led by James Larminie and it's the seventh year that the university has taken part in the competition. Made up of undergraduate and postgraduate students, the team is currently busy putting the finishing touches to the car.
Pressure And Temperature On The Record
The PRTC210 pressure and temperature recorder is compact, portable and easy to use.
New from MadgeTech, the PRTC210 is a pressure and thermocouple based temperature recorder with a 0.125in NPT fitting. The external thermocouple channel allows for insertion into a pipeline with a compression fitting, and the 0.125in NPT can be connected to a female fitting.
This provides an instant temperature and pressure response of what is flowing through the pipeline. The PRTC210 accepts thermocouple types J, K, T, E, R, S, B and N and is available with pressure ranges of 0-2, 0-6.9, 0-21, 0-34.5, 0-69 and 0-345bar.
The device can measure and record 21,844 readings per channel and has a battery life of up to 2 years. The PRTC210 is compact, portable and easy to use. It can be started and stopped directly from a PC, and its small size allows it to fit almost anywhere. As with all MadgeTech products, the data are downloaded and viewed using the MadgeTech software. The PrTC210 is priced at US $649.
New from MadgeTech, the PRTC210 is a pressure and thermocouple based temperature recorder with a 0.125in NPT fitting. The external thermocouple channel allows for insertion into a pipeline with a compression fitting, and the 0.125in NPT can be connected to a female fitting.
This provides an instant temperature and pressure response of what is flowing through the pipeline. The PRTC210 accepts thermocouple types J, K, T, E, R, S, B and N and is available with pressure ranges of 0-2, 0-6.9, 0-21, 0-34.5, 0-69 and 0-345bar.
The device can measure and record 21,844 readings per channel and has a battery life of up to 2 years. The PRTC210 is compact, portable and easy to use. It can be started and stopped directly from a PC, and its small size allows it to fit almost anywhere. As with all MadgeTech products, the data are downloaded and viewed using the MadgeTech software. The PrTC210 is priced at US $649.
Threadform Duplication Adds Life To Worms
Simon Chipchase explains his company's pioneering methods for replicating threadforms for worms and worm gears. Worms and worm gears have been manufactured since ancient times In modern times the profile or tooth form of gearing has been standardised for most types of gears.
Helical or spur gear teeth can be defined in terms of pressure angle and NDP (or module for metric units). Worm gearing has evolved along a different path where pitch, profile or form and proportions of tooth size and height are somewhat arbitrary and determined by the manufacturer and/or the method of manufacture. When equipment is maintained and worm gears are replaced as matched sets then the threadform may not be an issue. But if owners or users of equipment need only one element or need interchangeable spare parts then there is a need to duplicate the original threadform.
The article discusses a method where a sample or artefact can be measured in order to quantify the tooth geometry. The worm, wormwheel or gear set can be duplicated so as to be identical to the original where either or both elements could be used. The tooth geometry of worm gears has many variations usually depending on manufacturer or intended use. In early times the worms were made to resemble a simple screw thread which could be chased on a lathe. If the worm was cut with a straight sided tool the form would resemble that of an acme screw, where the threads would have straight form in the axial plane.
If the tool were tilted to be normal to the thread helix then the form would be straight sided in the normal plane. Later developments included grinding the worm threads for superior finish and to improve distortions from hardening. The simplest method is to dress a conical grinding wheel which has a straight form, that wheel in turn generates some profile on the worm thread which varies somewhat based on the wheel diameter and also based on the helix angle or lead of the worm. Another form is the involute helicoid where the worm is essentially a helical pinion with only one or very few teeth.
Also there is a concave tooth form where the worm is similar to a ball screw. These threadforms are described by industry standards as type A for straight axial, type N for straight normal, type I for involute, type K for straight form on wheel or cutter, and type C for the concave form. In practice the manufacturer would determine whatever form to use usually based on the type of equipment or machine tools that were available. If the worms were to be ground a type K form may be easier to produce but would vary slightly as the diameter of the grinding wheel changes. Regardless of which profile was used there would be established tolerances with controls or measuring systems.
What typically happened was the cutter for the worm gear would be developed along with the first worm or a master worm. Often slight adjustments were made to the worm profile. Depending on the vintage or the culture of the manufacturer the worm profile may be altered or modified for a number of reasons. If the hob was less than perfect in terms of profile then the worm could be modified to make the tooth form conjugate. Or some profile modification could have been made proactively, such as tip relief or some variation from true theoretical form. Either way it is often the case that worm profile is slightly different than true theoretical.
So as worm gears were produced over time by different manufacturers there exists a variety of defined threadforms as well as some deviation from those theoretical definitions. It follows that there are worms being used all over the world which are difficult to quantify in terms of tooth profile. If an existing piece of machinery or an old worm gear reducer needs new gearing then there are several courses of action. The simplest is replace with OEM parts. For some wormgears the original manufacturer may be difficult to identify or no longer exists. Or an alternate source may be needed because of economics or logistics.
If worm gears are substituted as a matched pair then the flank form may not matter. But for a number of reasons it may be necessary to duplicate exactly the original flank form, where the need arises to quantify and duplicate the tooth geometry of an existing worm. The endeavour to duplicate can take several forms, depending on which flank form the worm has. Once identified it may be more or less difficult to match because it may or may not suit the capability or culture of the manufacturer who is trying to make the replacement part or parts.
Historically products have been purchased with the sole intention of dissection and analysis in order to determine how to make a better mousetrap. That works on large scale or high volume products and can be applied for limited or single unit applications, but it requires getting a sample sent to the lab for measurement and analysis. A worm shaft would be made available for an indefinite period of time and sent to the shop to be measured or mapped out in terms of tooth size and shape.
Once quantified it could be duplicated and used to check with a new mating worm gear as well. Of course this would mean the worm remains available for analysis. In many cases the end user cannot be without the sample worm for so long because it is still being used for its intended purpose. The following method can be used to quantify thread size and shape or form by performing a simple procedure in the field. Typically in manufacturing a worm has a finish grinding operation where the stroke of the grinder extends somewhat beyond the active contact zone.
For a used worm with considerable wear, there is an area just beyond the contact zone, either on approach or recess end, where there is a ground thread of original size and shape. So if a new spare worm is not available a used worm may be duplicated. A small fixture with two ground faces which function as a V-block is made. The subject worm which is to be duplicated is either removed from its housing or somehow there is access to the finished thread area. Simple measurement of the worm outside diameter, thread depth, and tooth size at some known depth are made and recorded.
Next the threads are cleaned and a casting is made of the tooth space using an epoxy material. The casting is moulded between the V-block fixture and two tooth flanks. The fixture rests against the worm outside diameter fixing the alignment of the casting in relation to the axis of the worm. The casting is a full size model of the tooth space. It could be thought of as analogous to the casting a dentist makes before building the post on a damaged tooth in order to duplicate it with a cap or crown. Once the casting has been made it is carried or sent by courier to Renold Gears' factory in Milnrow, UK.
The cast plug is mounted on the same or an identical V-block fixture. Next it is measured on a co-ordinate measuring machine using a specialised software package to map the precise geometry. From these measurements the geometry for the worm thread is established and the design and processing of a new worm and/or worm gear cutter can begin. The worm thread can be duplicated exactly or modified while at the same time the worm gear tooth can have profile modification and/or face crowning at the discretion of the manufacturer.
The duplication process may also require determination of additional parameters because either a detail drawing is not available or it does not have all the pertinent information. Typical measurements of diameters and lengths are made judiciously where the function as well as dimension is taken into consideration. For example a diameter could have ISO tolerance applied for a standard lip seal where the same diameter could have a different tolerance applied for bearing fit. The more difficult determination would be for a dimension which interfaces with a mating part which is not a commodity item.
An effort is made to determine the function and dimensions of the mating part so the proper fit is achieved. For the case where other tooth design parameter(s) must be determined there is a device which can be made for field measurement of lead and/or axial pitch. It consists of a ground V-block fitted with ball probes mounted on slide. The pitch measurement is more accurate if made over several threads and the dimension divided by the number of threads spanned. Quite often worms drive in one direction so the measurement may be made on the nondrive flank.
Alternatively the measurement can be made on one end if at least one pitch is not worn significantly. Also the measurement can be made from one end to the other, each point being out of the contact zone where wear is not an issue. Or several measurements can be made over one or more pitches within the contact zone and compared with determine if the wear is significant. Of course several measurements can be used to compare, average, and/or to determine if there is significant pitch variation or variation in the measurements themselves.
Helical or spur gear teeth can be defined in terms of pressure angle and NDP (or module for metric units). Worm gearing has evolved along a different path where pitch, profile or form and proportions of tooth size and height are somewhat arbitrary and determined by the manufacturer and/or the method of manufacture. When equipment is maintained and worm gears are replaced as matched sets then the threadform may not be an issue. But if owners or users of equipment need only one element or need interchangeable spare parts then there is a need to duplicate the original threadform.
The article discusses a method where a sample or artefact can be measured in order to quantify the tooth geometry. The worm, wormwheel or gear set can be duplicated so as to be identical to the original where either or both elements could be used. The tooth geometry of worm gears has many variations usually depending on manufacturer or intended use. In early times the worms were made to resemble a simple screw thread which could be chased on a lathe. If the worm was cut with a straight sided tool the form would resemble that of an acme screw, where the threads would have straight form in the axial plane.
If the tool were tilted to be normal to the thread helix then the form would be straight sided in the normal plane. Later developments included grinding the worm threads for superior finish and to improve distortions from hardening. The simplest method is to dress a conical grinding wheel which has a straight form, that wheel in turn generates some profile on the worm thread which varies somewhat based on the wheel diameter and also based on the helix angle or lead of the worm. Another form is the involute helicoid where the worm is essentially a helical pinion with only one or very few teeth.
Also there is a concave tooth form where the worm is similar to a ball screw. These threadforms are described by industry standards as type A for straight axial, type N for straight normal, type I for involute, type K for straight form on wheel or cutter, and type C for the concave form. In practice the manufacturer would determine whatever form to use usually based on the type of equipment or machine tools that were available. If the worms were to be ground a type K form may be easier to produce but would vary slightly as the diameter of the grinding wheel changes. Regardless of which profile was used there would be established tolerances with controls or measuring systems.
What typically happened was the cutter for the worm gear would be developed along with the first worm or a master worm. Often slight adjustments were made to the worm profile. Depending on the vintage or the culture of the manufacturer the worm profile may be altered or modified for a number of reasons. If the hob was less than perfect in terms of profile then the worm could be modified to make the tooth form conjugate. Or some profile modification could have been made proactively, such as tip relief or some variation from true theoretical form. Either way it is often the case that worm profile is slightly different than true theoretical.
So as worm gears were produced over time by different manufacturers there exists a variety of defined threadforms as well as some deviation from those theoretical definitions. It follows that there are worms being used all over the world which are difficult to quantify in terms of tooth profile. If an existing piece of machinery or an old worm gear reducer needs new gearing then there are several courses of action. The simplest is replace with OEM parts. For some wormgears the original manufacturer may be difficult to identify or no longer exists. Or an alternate source may be needed because of economics or logistics.
If worm gears are substituted as a matched pair then the flank form may not matter. But for a number of reasons it may be necessary to duplicate exactly the original flank form, where the need arises to quantify and duplicate the tooth geometry of an existing worm. The endeavour to duplicate can take several forms, depending on which flank form the worm has. Once identified it may be more or less difficult to match because it may or may not suit the capability or culture of the manufacturer who is trying to make the replacement part or parts.
Historically products have been purchased with the sole intention of dissection and analysis in order to determine how to make a better mousetrap. That works on large scale or high volume products and can be applied for limited or single unit applications, but it requires getting a sample sent to the lab for measurement and analysis. A worm shaft would be made available for an indefinite period of time and sent to the shop to be measured or mapped out in terms of tooth size and shape.
Once quantified it could be duplicated and used to check with a new mating worm gear as well. Of course this would mean the worm remains available for analysis. In many cases the end user cannot be without the sample worm for so long because it is still being used for its intended purpose. The following method can be used to quantify thread size and shape or form by performing a simple procedure in the field. Typically in manufacturing a worm has a finish grinding operation where the stroke of the grinder extends somewhat beyond the active contact zone.
For a used worm with considerable wear, there is an area just beyond the contact zone, either on approach or recess end, where there is a ground thread of original size and shape. So if a new spare worm is not available a used worm may be duplicated. A small fixture with two ground faces which function as a V-block is made. The subject worm which is to be duplicated is either removed from its housing or somehow there is access to the finished thread area. Simple measurement of the worm outside diameter, thread depth, and tooth size at some known depth are made and recorded.
Next the threads are cleaned and a casting is made of the tooth space using an epoxy material. The casting is moulded between the V-block fixture and two tooth flanks. The fixture rests against the worm outside diameter fixing the alignment of the casting in relation to the axis of the worm. The casting is a full size model of the tooth space. It could be thought of as analogous to the casting a dentist makes before building the post on a damaged tooth in order to duplicate it with a cap or crown. Once the casting has been made it is carried or sent by courier to Renold Gears' factory in Milnrow, UK.
The cast plug is mounted on the same or an identical V-block fixture. Next it is measured on a co-ordinate measuring machine using a specialised software package to map the precise geometry. From these measurements the geometry for the worm thread is established and the design and processing of a new worm and/or worm gear cutter can begin. The worm thread can be duplicated exactly or modified while at the same time the worm gear tooth can have profile modification and/or face crowning at the discretion of the manufacturer.
The duplication process may also require determination of additional parameters because either a detail drawing is not available or it does not have all the pertinent information. Typical measurements of diameters and lengths are made judiciously where the function as well as dimension is taken into consideration. For example a diameter could have ISO tolerance applied for a standard lip seal where the same diameter could have a different tolerance applied for bearing fit. The more difficult determination would be for a dimension which interfaces with a mating part which is not a commodity item.
An effort is made to determine the function and dimensions of the mating part so the proper fit is achieved. For the case where other tooth design parameter(s) must be determined there is a device which can be made for field measurement of lead and/or axial pitch. It consists of a ground V-block fitted with ball probes mounted on slide. The pitch measurement is more accurate if made over several threads and the dimension divided by the number of threads spanned. Quite often worms drive in one direction so the measurement may be made on the nondrive flank.
Alternatively the measurement can be made on one end if at least one pitch is not worn significantly. Also the measurement can be made from one end to the other, each point being out of the contact zone where wear is not an issue. Or several measurements can be made over one or more pitches within the contact zone and compared with determine if the wear is significant. Of course several measurements can be used to compare, average, and/or to determine if there is significant pitch variation or variation in the measurements themselves.
Image Sensor Resolves For Microscopy
The ProgRes C7 is suitable for any illumination technique in light microscopy and excels with high light sensitivity and natural reproduction of colours. The new ProgRes C7 from Jenoptik, equipped with instantaneous SXGA live image, mechanical shutter and 7Mpixel CCD sensor, records even the tiniest specimen structures in a precise and detailed fashion. The ProgRes C7 is particularly suited to macro shots in addition to microscopy applications.
The instantaneous live image makes precise specimen positioning and focusing much easier. Thanks to the integrated shutter, it takes only a single shot to capture objects in motion and easily accommodates flash illumination techniques. Another advantage of the shutter is that it allows the camera to be triggered directly and precisely. Integration into automated process sequences or applications involving, for example, a motorised stage are made easy.
The ProgRes C7 is suitable for any illumination technique in light microscopy and excels with high light sensitivity and natural reproduction of colours. C-Mount and IEEE1394 FireWire provide standard interfaces for connection with all common types of microscopes and computers. Powerful easy-to-handle ProgRes CapturePro image acquisition software for Microsoft Windows and Apple Macintosh operating systems is included.
The instantaneous live image makes precise specimen positioning and focusing much easier. Thanks to the integrated shutter, it takes only a single shot to capture objects in motion and easily accommodates flash illumination techniques. Another advantage of the shutter is that it allows the camera to be triggered directly and precisely. Integration into automated process sequences or applications involving, for example, a motorised stage are made easy.
The ProgRes C7 is suitable for any illumination technique in light microscopy and excels with high light sensitivity and natural reproduction of colours. C-Mount and IEEE1394 FireWire provide standard interfaces for connection with all common types of microscopes and computers. Powerful easy-to-handle ProgRes CapturePro image acquisition software for Microsoft Windows and Apple Macintosh operating systems is included.
Cables Handle Domestic And Industrial Jobs
YY, SY and CY flexible control cables are used as an interconnecting cable for measuring, controlling or regulation in control equipment for assembly and production lines. Anixter Components has added six new ranges of domestic mains and flexible control cables to its 2008/2009 product catalogue The range of mains cable includes industry standards such as 2192Y, 218Y and 318Y.
The 2192Y range is available in 0.5 and 0.75mm2 conductor sizes and the 218Y and 318Y are available from 0.5mm2 to 2.5mm2. These provide power for many domestic appliances including lightweight portable appliances, such as radios and table lamps, as well as those supporting heavier loads such as washing machines, spin dryers and refrigerators. For industrial applications, there is a range of YY, SY and CY flexible control cables.
These are used as an interconnecting cable for measuring, controlling or regulation in control equipment for assembly and production lines. The durable galvanised steel braiding on the SY types offers extra armouring for demanding applications such as machine tools, control gear and industrial conveyor installations.
Additionally, the CY types are enhanced by a copper screening, ensuring their suitability for installations where signal interference is a consideration. "It has always been our goal to offer our customers a one-stop-shop service for cable management products". said Andrew Fletcher, Technical Director, Anixter Components. "The introduction of wire and cable to our range is simply a natural progression".
The 2192Y range is available in 0.5 and 0.75mm2 conductor sizes and the 218Y and 318Y are available from 0.5mm2 to 2.5mm2. These provide power for many domestic appliances including lightweight portable appliances, such as radios and table lamps, as well as those supporting heavier loads such as washing machines, spin dryers and refrigerators. For industrial applications, there is a range of YY, SY and CY flexible control cables.
These are used as an interconnecting cable for measuring, controlling or regulation in control equipment for assembly and production lines. The durable galvanised steel braiding on the SY types offers extra armouring for demanding applications such as machine tools, control gear and industrial conveyor installations.
Additionally, the CY types are enhanced by a copper screening, ensuring their suitability for installations where signal interference is a consideration. "It has always been our goal to offer our customers a one-stop-shop service for cable management products". said Andrew Fletcher, Technical Director, Anixter Components. "The introduction of wire and cable to our range is simply a natural progression".
Toshiba Vacuum Contactors
In vacuum circuit breakers or vacuum contactors, current making and breaking is performed in the entirely sealed vacuum chamber. So, they poses various features such as (1) Excellent arc-extinguishing ability, (2) Less contact wear, and long life, (3) Safety, no fire or explosion hazard, (4) Less maintenance, (5) Compact and lightweight. Then the vacuum circuit breakers and vacuum contactors have been becoming major switching apparatus throughout the countries around the world.In 1965, Toshiba put the first vacuum switching devices in the market. Since then, various efforts have been made to increase their application fields. Regarding switching surge, analysis of generating mechanisms, measurement of the switching surge, development of the surge suppressors have been achieved. Based on those results this application guide was compiled.
Toshiba Low & Medium Voltage Vacuum Contactors are all "low surge type". As contactors are mainly applied for a motor switching, low surge characteristic is essentially required. So Toshiba developed a special contact material of the low chopping level, and employed for all vacuum contactors.
It was considered that as circuit breakers must interrupt a high current, low surge contact material can not be employed. However, Toshiba invented a "axial magnetic field type electrode" which can interrupt a remarkable high current. So by combining this type of electrodes and the low surge contact material, development of low surge type vacuum circuit breakers can be successfully achieved.
As the oil-immersed transformers have high lightning impulse withstand voltage, and insulation life is fairly long, surge protection is considered to be not required. However, in case of interrupting exciting inrush current, or switching dry type transformers or other equipment of which insulation level is considerably low, surge protection is advisable, such as to install surge arresters. However, the limiting voltage of the surge arrester shall be evaluated to be effectively lower than the insulation strength of the load equipment. If there is a possibility of encounter to lightning, the arrester must have enough capacity. Same caution should be taken for gapless surge absorbers using nonlinear resistors. When a vacuum circuit breaker switches a transformer, in which loads of low insulation levels (such as power electronics equipment) are connected to the secondary side, surge protection at primary and/or secondary side is advisable.
As stated above, surge protection is not required for the Toshiba vacuum contactors or the low surge type circuit breakers. However when starting inrush current is interrupted, installation of surge suppressor is recommended. Generally the impulse withstand voltage is not specified for motors, and insulation deterioration is not negligible. Therefore, it is a general rule to install surge suppressors, when the conventional vacuum circuit breakers are used for switching the motors. Toshiba recommends to use CR type surge suppressors in which a capacitor and a resistor are connected in series.
Toshiba Low & Medium Voltage Vacuum Contactors are all "low surge type". As contactors are mainly applied for a motor switching, low surge characteristic is essentially required. So Toshiba developed a special contact material of the low chopping level, and employed for all vacuum contactors.
It was considered that as circuit breakers must interrupt a high current, low surge contact material can not be employed. However, Toshiba invented a "axial magnetic field type electrode" which can interrupt a remarkable high current. So by combining this type of electrodes and the low surge contact material, development of low surge type vacuum circuit breakers can be successfully achieved.
As the oil-immersed transformers have high lightning impulse withstand voltage, and insulation life is fairly long, surge protection is considered to be not required. However, in case of interrupting exciting inrush current, or switching dry type transformers or other equipment of which insulation level is considerably low, surge protection is advisable, such as to install surge arresters. However, the limiting voltage of the surge arrester shall be evaluated to be effectively lower than the insulation strength of the load equipment. If there is a possibility of encounter to lightning, the arrester must have enough capacity. Same caution should be taken for gapless surge absorbers using nonlinear resistors. When a vacuum circuit breaker switches a transformer, in which loads of low insulation levels (such as power electronics equipment) are connected to the secondary side, surge protection at primary and/or secondary side is advisable.
As stated above, surge protection is not required for the Toshiba vacuum contactors or the low surge type circuit breakers. However when starting inrush current is interrupted, installation of surge suppressor is recommended. Generally the impulse withstand voltage is not specified for motors, and insulation deterioration is not negligible. Therefore, it is a general rule to install surge suppressors, when the conventional vacuum circuit breakers are used for switching the motors. Toshiba recommends to use CR type surge suppressors in which a capacitor and a resistor are connected in series.
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