The simple and ubiquitous fuse still provides a primary means of protecting electrical circuits against overcurrent. In this second article, by Cooper Bussmann’s Gordon Newbury, he examines some recent fuse developments:
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Despite the age of the fuse as a technology, it would be wrong to think that the mechanism of operation of today's high performance fuse is as simple as its distant ancestor. Performance has been improved through better understanding of fuse behaviour using computer-modelling techniques. Moreover, such improved performance characteristics now uniquely enable fuse-based systems to protect high-tech equipment. An example is the use of high-speed fuses to isolate Insulated Gate Bipolar Transistors (IGBTs) in electronic equipment. Some recent developments are notable:
LV fuses - Despite the comments on the need for standardisation enhancements on traditional fuses, there is still scope for evolution. Cooper Bussmann has addressed this challenge with a new fuse system. Called Cube Fuse, this has great potential for the International market and is a new dimensional system, having the electrical characteristics of traditional North American IEC fuses but giving both general industrial and motor circuit protection. A major feature is that no fuse carrier or replaceable handle is needed. The fuse is fitted or withdrawn, using finger pressure only, into or out of the fuse base – all in a touch-safe IP20 manner.
Three Cube Fuse fuse holders can be dovetailed together to produce a roughly cubic three-phase unit. For example, a three-pole 60A assembly occupies only about 75 mm cubed. This dimension is very compact compared with their large North American counterparts and is comparable with UK and Mainland European fuse systems. The Cube Fuse is currently available in 30 and 60A packages. Other features include:
- 35 mm DIN rail fitting.
- 30A and below fuses inserted into a 60A fuse base.
- Patented blown fuse indication.
- 300kA breaking capacity - IEC gD characteristics.
Future developments will cover higher current ratings and gG characteristics. For further information, visit www.cubefuse.com.
Miniature fuses - These protect electronic equipment such as consumer electronics. They are mainly used at the input, providing protection for the whole equipment with 6.3 x 32mm (0.25 x 1.25 inch) fuses or the smaller 5 x 20mm type. The demands for secondary protection have changed significantly with the development of associated electronic circuits. LV circuits and circuit board miniaturisation, using first wire ended, through-hole, then surface mount technology, have led to compatible circuit components including fuses. This includes 1608 package (1.6 x 0.8mm) surface mount applications up to 24V DC. In this application, the fuse’s role is to limit any damage and prevent fire. The whole board is replaced after a fault, because fault diagnosis can be lengthy. For further information visit www.cooperelectech.com.
High voltage (HV) Automatic Sectionalising Links - HV fuses are mainly used by the Network Distribution Operators (NDOs) for the protection of overhead line rural systems and underground urban systems. In the case of overhead line protection, the NDO's are under severe pressure from the regulator to improve power quality. The overhead lines are particularly vulnerable. Falling branches, wind, clashing of conductors, lightning and birds flying into the lines are common causes of disruption. The simplest protection method is group fusing of the spur lines using expulsion fuses. However, the faults above are transient, leading to nuisance operation of the expulsion fuse. The extensive use of auto-reclosers has addressed this issue, but when the auto-recloser locks out, many customers lose power. A successful solution is the UK invention of the Automatic Sectionalising Link (ASL). This retrofits into the expulsion link cut-out and works in conjunction with the auto-recloser. It only operates on a permanent fault on the spur line and its electronic logic circuits give operation in the dead time of the auto recloser, For this reason, it does not have to clear any overcurrent.
HV full range fuses – Traditionally for urban systems, ring main units are used with fused switches on the ‘T' off connections to protect the associated transformer. These use back-up current limiting fuses with striker tripping to clear all low overcurrents, so giving ‘fulI range’ performance. A recent development has been the Full Range fuse. This will clear all overcurrents that cause the fuse elements to melt. A popular method of achieving this is to combine current limiting fuse elements (high fault currents) and expulsion fuse elements (low fault currents) in a standardised fuse cartridge.
An interesting new application using Full Range fuses is in a fused end box directly attached to the transformer bushings. This simple and compact package, costing much less than a ring main unit, does not have any switching capability, but can be integrated into a modern urban system.
Telecommunications and automotive - These are two fields outside of the traditional markets where significant strides in technology are taking place. New fuse protection requirements are evolving in both these areas, mainly in Europe and the USA.
The big upsurge in international demand for telecommunication products is not only in the equipment (mobile phones) and email, requiring surface mount fuses, but also in the power supplies. These include main primary and secondary distribution and remote supplies such as relay stations. These are typically up to 60 V DC. The fault levels can be high, with numerous branch circuits are fed from high input currents. Specially designed fuses (in purpose designed fuse holders) provide the best solution to meet these technical demands.
The electrical systems in automotive applications are undergoing significant change, including the introduction of 42V systems, hybrid and fuel cell energy sources, added comfort features, plus safety and environmental issues. Fuse protection is the preferred solution to meet these future needs.
For further information, visit www.bussauto.co.uk.
Cooper Bussmann Burton-on-the-Wolds, Loughborough,
Leicestershire LE12 5TH
Tel: 01509 882737
Fax: 01509 882794
Web: www.bussmann.com
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