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GROUP FUSING/PROTECTION Fuse ratings are available up to 100Amp at 12/24kV and this equates to transformer loads of the order of 2 or 4MVA, which could represent a substantial number of polemounted units on a single feeder. The T.A.P. FUSE-SWITCH provides an opportunity for designing using group fusing of a feeder, incorporating load-break switching for maintenance/isolation and a trip-all-phase facility in the event of a single-phase fault. SECTIONALISING FUNCTION The combination can of course be used in conjunction with ARC units in the classical way as a sectionaliser by correct grading of the fuses, but yet providing three-phase isolation in the event of a sustained fault. SENSITIVE EARTH FAULT PROTECTION As in the case of the TRISEC, Sensitive Earth Fault (SEF) protection can be introduced by incorporating the TRANSPOST current sensors and the TFI micro-energy digital logic circuitry, with long life lithium battery to power the logic and provide the trip energy. The TFI is in this case programmed to respond only to the low level earth fault, which is user selectable over the range 2.5 to 20 Amps in 2.5Amp steps, with an appropriate time delay to cover the possibility of transient disturbances causing nuisance tripping. The time delay is a nominal 3 seconds to coordinate with a recloser SEF setting of 5Amps on a definite time delay of 6 seconds. |
SENSITIVE EARTH FAULT PROTECTION (cont) Additionally, the earth-fault protection is programmed to inhibit the tripping of the fuse switch in case the SEF evolves to a higher fault level. The blocking of the tripping pulse would then ensure that the main fuses would interrupt the fault and prevent the switch attempting to operate during this time. 50Amp fuses are recommended for the SEF application. TRANSFORMER PROTECTION Other common forms of transformer protection are Buchholz gas detection and winding temperature alarm, and these protective devices can be also connected to the trip-coil circuit to open the switch when required. This combination unit offers all the features of the conventional Ring Main Unit fuse switch plus the SEF protection and represents a significant saving on the only other available equipment for this purpose, namely the outdoor circuit breaker. It is believed that this combination can fill the needs of many spot networks and townships, where SEF and fused protection in conjunction with the load-break switch is a far more economic solution than any available circuit breaker. |
| SPECIFICATIONS |
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T.A.P. FUSE-SWITCH : Combination 200/400Amp, 24kV fused disconnector with trip-all-phase feature. ARCTRAP tested 630Amp @ 12kV and 200Amp @ 24kV. LINEGEAR cycloaliphatic resin or silicone insulators, 600mm or 750mm creepage, 150kV BIL, 5kA symmetrical rating. Options: TRANSPOST CTs and programmable logic for Sensitive Earth Fault protection. 5/40Amp settings. Buchholz and Winding Temperature trip contacts are available. |
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INTRODUCTION The T.A.P. FUSE-SWITCH has a trip-free mechanism and a spring energy opening device. When any one of the drop-out fuses operates and falls out, it strikes an insulated trip assembly, which is connected by a rod to the trip-free mechanism. This opens all three phases of the load-break switch, interrupting the load current in the other two phases. |
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SECTIONALISERS The problems of operating medium voltage reticulation systems in areas prone to lightning are well known and opinions vary widely as to what is the optimum solution. One thing is certain, that low value fuse links are totally unsuited due to the effects of inrush current or their susceptibility to blowing on what turns out to be a non-damage fault.
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