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Three main systems are used on the continent of Europe and in many other countries throughout the world where continental European low-voltage equipment is generally used. These three systems are described in terms of the contact arrangements of the fuselinks. These are:

(a) blade contact – ‘NH’ type

(b) end contact or screw type – ‘D’ type (c) cylindrical cap contact.

Each type employs cartridge fuselinks and no equivalents of the British semi-enclosed fuses are produced.

4.3.1 Blade-contact-type fuses

These are generally referred to as NH fuses, NH being an abbreviation of Nieder-spannungs Hochleitungs which is German for low-voltage high-breaking-capacity.

They are for use by authorised persons, mainly for industrial applications, and are used in factory distribution systems and also in the distribution cabinets of the ESI in power-distribution networks.

A range of these fuselinks is shown in Figure 4.24. The fuse elements are generally made from copper strip. The body is usually made of ceramic but high-temperature thermosetting plastic materials have been used. Bodies often have a rectangular out-side cross-section with a circular longitudinal hole through them, and end plates, complete with the blade contacts, are attached to the body with screws. To allow the

Figure 4.24 NH fuselinks

fuselinks to be mounted in close proximity to each other, even in the absence of insu-lating separators, the end plates are normally confined within the outside dimensions of the fuselink body. The blade contact surfaces are usually silver plated to assist in obtaining low-resistance connections even when the forces applied on the blades by the spring contacts into which they fit are relatively low.

Some fuselinks are produced with cylindrical bodies and these are allowed in the standard specifications provided that they meet the dimensional requirements.

NH fuselinks are generally available for applications up to and including 1250 A, for AC circuits operating at levels up to 500 V and DC circuits of voltages up to 440 V. Designs with restricted current ratings are available for 690 V AC systems.

They usually incorporate operation indicators, a feature which is not now normally provided on low-voltage fuselinks used in the UK. The operation-sensing device is a fine wire which is connected in parallel with the fuse element. This wire normally carries only a tiny fraction of the total current passing through its fuselink but, when the element ruptures during clearance, the wire carries a much larger current, which causes it to melt and break very quickly. The wire is used to hold in a flag or plunger in one of the end plates. When the wire breaks, the flag or plunger is pushed out by the action of a spring and in this way an indication of operation is given.

In some installations, only the front of the fuselink is visible and there is therefore a requirement for an indicator at the centre of the front of the fuse body. In order to reduce the stocking of the two types of indicating fuselinks, designs are readily available which have a combined front and end indicator. An example is shown in Figure 4.25.

Unlike British designs, NH fuselinks are inserted into their fuse bases by a detach-able handle which is made of plastic, a particular example being shown in Figure 4.26.

Figure 4.25 NH fuselink with combined front and end indicator

Alternatively, in a widely used simple design of fuse-switch, the cover of the switch acts as the fuse handle, the fuselinks replacing the normal switch blades and being withdrawn when the cover is opened or removed. This arrangement is shown in Figure 4.27.

Traditionally, the fuse bases have been much simpler than the British designs described earlier and were not shrouded to prevent accidental contact with live parts.

However, in line with other low-voltage equipment, associated safety aspects have been addressed and fuse bases with covers and shrouds over the contacts are readily available. In addition, fuselinks with isolated gripping lugs are offered.

Figure 4.26 NH feeder pillar showing use of handle

Figure 4.27 NH fuse switch

For electricity supply industry applications, NH fuselinks are used in fuse distri-bution cabinets, including packaged substations and cable distridistri-bution cabinets. This has led to the introduction of integral three-phase shrouded units which are mounted directly onto the distribution bus bars. This system has become standardised in IEC 60269-2-1 and is referred to as ‘fuse rails’. A shrouded three-phase unit is shown in Figure 4.28.

In view of the number of fuselinks in a distribution cabinet, it is important to minimise the temperature rise within the cabinet and low power loss fuselinks are

Figure 4.28 Shrouded three-phase NH ‘fuse rail’ unit

desirable. In addition, if low power loss fuselinks are installed by a utility, then if the projected reduction in power loss is multiplied by the number of fuses installed then this can provide a measurable energy saving. As stated earlier, the ‘standard’ voltage rating for NH fuselinks is 500 V AC. However, most distribution systems outside of North America are based on a 400 V three-phase supply and consequently 400 V

fuselinks with a lower power loss than 500 V traditional designs are available in the standard NH dimensions.

In Germany and associated markets, three high-current rating fuselinks are often placed as close as is practical to the secondary terminals of the distribution transformer.

This gives added protection in the case of an accidental fault between these fuses and those downstream protecting the multi-way feeders. These fuselinks are given the designation gTr in Germany. However, to date they have not been introduced into the IEC standard. The ‘nameplate’ rating of these fuselinks and characteristics matches the kVA rating of the transformer, thus simplifying the selection of the appropriate fuselink. The gTr fuselinks allow to run the transformer at 130 per cent of its rated current over a period of 10 h, which is sufficiently long to cover the daily high-load period of power utilities.

4.3.2 End-contact or screw-type fuses

As indicated in Chapter 1, this is a very old fuse system, often referred to as the Diazed type or in some countries by the abbreviated form of this: ‘Zed’ type. Diazed was derived from ‘diametral abgestruft’, that is ‘diametral steps’. The term ‘bottle’

type is also used, this name clearly stemming from the characteristic shape of the fuselinks, an example of which is shown in Figure 4.29. The official designation, that should be used, however, is ‘D’ type which is derived from Diazed.

Production of these fuses is perpetuated by the continuous need to supply replace-ments for some of the very large number which have been installed over many years.

A sectional view of a typical fuselink is shown in Figure 4.30. They are mainly pro-duced with ratings up to 63 A for use in AC circuits operating at levels up to 500 V. The limitation in current rating is largely caused by the difficulty of producing satisfactory contact with the holders, rather than with shortcomings in the fuselink design. Higher ratings, up to 200 A, have been produced but they have not proved popular.

Figure 4.29 ‘D’ type fuselink

bottom contact

ceramic body

fuse element

granular quartz

indicator

indicator wire top contact

Figure 4.30 Sectional view of ‘D’ type fuselink

The fuselinks contain strip elements of copper or silver-plated copper and they are filled with granular quartz. The bodies, which are made of ceramic material, often have much thicker walls than British fuselinks of equivalent ratings which tends to assist with heat dissipation because porcelain has a higher thermal conductivity than granulated quartz. Each fuselink is fitted at the ends with cylindrical contacts made of brass, usually nickel-plated, and they are often of two different diameters. They usually have grooves in the ends to ensure good contact when they are fitted in the carrier.

The fuselinks are fitted with operation indicators which generally take the form of a button head that is pushed out through the end contact by a weak spring when the fine-wire operation-sensing device in parallel with the main element melts and no longer provides restraint. The button head is visible through a glass window in the screw cap.

A standard holder of the form shown in Figure 4.31 is produced to accommodate a range of ‘D’ type fuselinks. A range of gauge rings, with various internal diameters and coloured ends to indicate the maximum ratings of fuselinks which will fit into them, is available. The appropriate ring is placed into a fuse-holder to ensure that a fuselink of too great a rating for the circuit being protected may not be installed.

The fuselink is inserted before the screw cap is screwed to the fuse-holder and this produces forces between the fuselink end contacts and the spring contacts in the screw cap and fuse socket.

plan ‘x,x’

x x

screw cap

ceramic fuselink

gauge ring

fuse base

Figure 4.31 Holder for ‘D’ type fuselink

A dimensionally smaller range of fuses, designated DO, has been produced by at least two continental manufacturers. These are used in some countries, but in others, only the standard ‘D’ type is allowed in the interests of standardisation.

DO fuse-switch-disconnectors have recently been introduced which offer the following features:

• It can only be switched in when the DO fuselink is firmly screwed in position, giving high contact pressure.

• In the off position and the fuselink in situ, it isolates the fuse from the supply.

• In the off position and the fuselink is unscrewed, the fuselink is isolated from both the supply and the load. No dangerous reverse voltages are therefore possible.

• Independent manual operation of the switch.

• Ganged three-phase units with ‘DIN rail’ mounting.

An example is included in Figure 4.32.

Figure 4.32 DO products including fuse-switch-disconnectors

4.3.3 Cylindrical-cap-contact fuses

Fuse systems incorporating fuselinks with cylindrical bodies and ferrule end caps are widely used in France and associated countries for domestic and industrial applica-tions. The fuselinks are filled with quartz and usually have ceramic bodies. They are available with operational indicators if required.

For domestic applications, the fuselinks are produced in a range of diameters and lengths each having its own unique dimensions to prevent incorrect replacement after operation.

In IEC 60269-3-1 these fuselinks are referred to as Type A to differentiate these from Type B, used in the UK and associated countries, and an old Type C, which was historically used in Italy. The Type A fuselinks are standardised in the following ratings:

250 V AC up to 16 A 400 V AC up to 63 A

For industrial applications, cylindrical fuselinks are available in the following standardised ratings:

400 V AC up to 125 A 500 V AC up to 100 A 690 V AC up to 50 A

A fuse-holder widely used internationally for these fuselinks is shown in Figure 4.33.

It has an integral hinged fuse carrier, which allows the fuselink to be inserted in a safe manner. It can be mounted on a standard ‘DIN rail’ in multiple linked modules such as three-pole and neutral.

Fuse combination units incorporating cylindrical fuselinks are available for indus-trial use. Strikers, operating in a similar way to operation indicators, may be incorporated in these fuselinks. When a fuselink melts, the striker moves out through

Figure 4.33 Cylindrical fuse-holder and fuselinks

the end cap and actuates a microswitch which may initiate an alarm. In three-phase designs the strikers can operate on a common trip rod which then actuates a microswitch which can energise the trip coil of the switch, or alternatively it can de-energise the holding coil to effect three-phase clearance. This feature is valuable in certain applications, such as the protection of motors, where single-phase operation is unacceptable.

4.3.4 Semiconductor fuses

The majority of these fuses are used to protect power semiconductors and usually rated at 690, 1000 or 1250 V AC, but other voltage ratings will be found. Square-ceramic-body designs are very popular, the Square-ceramic-body lengths being shorter than those of fuselinks used for industrial applications. End terminations suitable for bolted connections with fixing centres at 80 or 110 mm are widely used, but alternative versions with tapped holes in the ends are available. The latter design has the advantage of being more compact and is often used for ratings above 1000 A.

The overall dimensions of semiconductor fuses are specified in IEC 60269-4-1, Section IB (DIN 43653) and a selection of the designs available are shown in Figure 4.34.

Many semiconductor fuses used in Continental Europe incorporate operation indicators. These are similar to those used in industrial fuselinks and they may be either at one of the ends or in the central regions of the bodies. As well as giving local indications, these devices may be adapted to operate microswitches so that remote indication of fuse operation may be provided. Examples of these fuselinks are shown in Figure 4.35.