FUSES
I.E.E. Regulations define a fuse as: “A device for opening a circuit by means of a conductor designed to melt when an excessive current flows. The fuse comprises all the parts that form the complete device.”
- An electronic device used to protect circuit from over current, overload and make sure the protection of the circuit.
- Excessive current in any electrical circuit can be hazardous and it is caused by overloads and short-circuit.
- Contains a length of filament which melts when exposed to an abnormally high current, breaking the circuit.
- Consist of low resistance metallic wire enclosed in a non-combustible material.
- When there is over current, the thin wire in the fuse melt due to heat generated by the heavy current flowing through it. Thus, disconnected power supply from connected system.
- Fuses are one-use only, however,
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RCD do not offer protection against current overloads.
Nuisance tripping of RCS
• Sudden changes in electrical load can cause a small, brief current flow to earth. RCDs are very sensitive and operate very quickly
RCD will not protect against a socket outlet being wired with its live and neutral terminals the wrong way round.
RCD will not protect against the overheating that results when conductors are not properly screwed into their terminals.
RCD will not protect against live-neutral shocks, because the current in the live and neutral is balanced.
Advantages and disadvantages between fuses and circuit breakers
Circuit-breakers are more advantageous compared to fuses because circuit-breakers respond quicker, are more sensitive and reliable and they can be reset unlike fuses which can only operate once.
Advantages of circuit breaker over the fuse:
1. When tripped it can be reset easily.
2. Faulty circuit is easily identified.
3. It has an accurate tripping
measurements of three-phase voltage and current samples obtained from the PSCAD/EMTDC. Fig. 8 depicts the 220 kV, 50 Hz simulated system one-line diagram. The other related parameters of the simulated system are shown in Table 1, transmission lines are assumed completely transposed. Fig. 9 & 10 show 3ph voltages and currents waveforms for 3ph to ground fault at 50% of the second line without and with UPFC respectively. It is clear that when UPFC is involved in the fault loop, the the voltage and current signals would be deviated from the actual value.
Filtering circuitry is initiated by spurious signals causing logic errors in electronic devices. This is due to noise. IS equipment is designed to withstand brownouts that lasts slightly more than 20% i.e. a few milliseconds. Under voltage does not cause damage but services are terminated. Silicon based equipment such as memories and processor are damaged by prolonged overvoltage due to power surge. This is after the surge protector equipment has be held conduit power intensity and prolonged exposure.
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