Handbook of Electrical Engineering

164 HANDBOOK OF ELECTRICAL ENGINEERING models are provided with a comprehensive solid-state module for creating the protection f ...

SWITCHGEAR AND MOTOR CONTROL CENTRES 165 Figure 7.6 Cut-off and prospective current curves for a 40 A fuse and a 40 A moulded ca ...

166 HANDBOOK OF ELECTRICAL ENGINEERING Figure 7.7 Clearing time versus fault current for fuses and moulded case circuit breaker ...

SWITCHGEAR AND MOTOR CONTROL CENTRES 167 situation and is called ‘partial coordination’. What is called ‘complete coordination’ ...

168 HANDBOOK OF ELECTRICAL ENGINEERING Solution: a) Choose the upstream MCCB at the switchboard and its settings. From a manufac ...

SWITCHGEAR AND MOTOR CONTROL CENTRES 169 h) Find the fault current at the distribution board, point B. From a manufacturer’s dat ...

170 HANDBOOK OF ELECTRICAL ENGINEERING Figure 7.9 Coordination of MCCBs at a distribution board. Add Zc 2 to Zfcto give the faul ...

SWITCHGEAR AND MOTOR CONTROL CENTRES 171 Hence the peak making capacity of the 32 A MCCB is well in excess of the let-through pe ...

172 HANDBOOK OF ELECTRICAL ENGINEERING The fault making current Ifdis:- Ifd= Vp Zfd = 440. 0 1. 732 ( 0. 049 +j 0. 00468 ) = 516 ...

8 Fuses 8.1 General Comments Fuses are used when it is possible to use a simple and economic method of protection against overcu ...

174 HANDBOOK OF ELECTRICAL ENGINEERING Rated voltage. Rated current. Rated frequency. AC and DC service and type of load curren ...

FUSES 175 Table 8.1. Characteristic currents that are related to the X-to-R ratio of a circuit Ratio to rms symmetrical current ...

176 HANDBOOK OF ELECTRICAL ENGINEERING its maximum possible value, called the ‘maximum asymmetrical’ (US) or ‘asymmetrical prosp ...

FUSES 177 Figure 8.2 Melting, nominal and clearance time curves versus current for a typical 250 A fuse. The melting time and cl ...

178 HANDBOOK OF ELECTRICAL ENGINEERING time range of 0.01 to 1000 seconds. For times less than 0.01 sec it is better to seek the ...

FUSES 179 8.4.1 Worked example An example of fuse selection:- A 6600 volt induction motor is fed from a fuse-contactor starter. ...

180 HANDBOOK OF ELECTRICAL ENGINEERING Figure 8.3 Peak cut-off current versus prospective symmetrical rms current for typical fu ...

FUSES 181 Figure 8.4. Protection of an induction motor and its feeder cable. about 1200 amps. A 125 amp fuse would reduce this t ...

9 Cables, Wires and Cable Installation Practices Cables provide a highly reliable and compact method of transmitting power from ...

184 HANDBOOK OF ELECTRICAL ENGINEERING 9.1.1 Copper and aluminium Copper and aluminium are used in their highly refined form for ...