Protective Measures In Electrical Power Lines And Electronic Appliances

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Every appliance be it mechanical, electrical or electromechanial needs protection measures from potential hazards which might be threatening to the efficiency and operation of the appliance, Even human beings and animals need protection from dangers too; that is why we leave in houses and not bush.

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Introduction

Protective measures in electrical/electronic systems are precautions taken and components incorporated in any appliance or system so as to shield it from impending hazards. This hazard might be a natural occurring hazard (thunder storm, lightning bolt); hazard due to human error like inappropriate bridging of wires (short circuit) during electrical connections ; or hazard due to fault in machines which include, the secondary part of a transformer supplying a very high or low voltage/current due to some internal/external fault in the transformer system. Hazard which is harmful to electrical appliances might arise from where it is not even expected at certain times.


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Due to the afore-mentioned impending hazards which has the potency to reduce the efficiency or totally damage an electrical system or appliance, various components are incorporated in order to protect this systems and appliance from damages. The major benefit of this protective measures is that it reduces cost; the protective component in the system can simply be changed when it cuts instead of going through the inconvenience of changing checking faults and perhaps changing a more expensive component damaged by the hazard or even in the worst scenario, replacing the entire appliances or systems with a new one which is non-economical.

Fuse

Electrical fuse is a component incorporated in electrical/electronic appliances for safety purposes. fuse is attached in the primary side of most electronic appliances, and is connected between the A.C source and the rectifying part of the circuit. In a lay man's understanding, the fuse serves as a connection between the Ac source and the diode(rectifier)

Fuse is basically a metallic conductor or stripe of wire which melts when excess current passes through it, this strip of wire is enclosed in a glass or ceramic cylindrical in shape and two circular metallic conductors is used at the terminal for continuity. This melting is caused by heat due to excess current and is given by the equation below

H= IRt
where I is current
R is the resistance of the material measured in ohms
t is the time usually in seconds

From the equation, it is visible that heat produce is directly proportional to the current flowing through the fuse. the more current passing through, the more the heat generated. However, at a critical current, the heat generated becomes too much for the strip of wire and causes it to melt.

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The melting of the strip causes a break in the circuit or open circuit in the complete circuitry. Once this happens,current stops flowing and the appliance would not work until the fusee is replaced with a new one because it is a sacrificial component

it is is a sacrificial component sacrificial component in the sense that it can be used only once; once it cuts, it is replaced with a new one. Although some fellows would wound a wire between the two metallic terminal of the fuse, but this is not electrically advisable as it night cause fire outbreak.

Similar thing happened to me while I was new to electronic repair learning process. My DVD player got faulty that it could not be powered, then I unscrewed it and conducted some test using my digital multi-meter. I tested for continuity on the fuse and discovered it has damaged already.
So, I replaced the fuse with a new one, however it cut immediately. Out of curiosity, I changed the fuse again from the much fuses in my possession. unfortunately for me, the fuse cut again. Due to my low knowledge then in electronics, I thought this repeated cut was because my DVD needs more current that the fuse can supply, so I used a thick wire to bridge the two terminals of the fuse. I connected it to A.C source and almost instantly, fire outbreak occurred. I quickly disconnected the appliance PCB from the source and other tests on it.
Finally, I detected that the diodes are faulty, then changed the diodes and used a new fuse. This time, the DVD started functioning as usual.

Faults in diodes is causes by excess voltage. When a very high magnitude of negative voltage(breakdown voltage) is passed across a diode, the diode gets to its breakdown region and eventually get faulty. Normally diodes allow current to flow in only on direction which is from anode to cathode. However when the diode becomes faulty, it conducts in two directions which are from anode to cathode and the vice versa. This is critical because this diode tries sending back voltage to the source. However the fuse cuts to maintain safety and avoid further electrical hazards.

It is worthy of note to know that the braking of fuse is automatic.

Circuit Breaker

Circuit breaker is an electrical circuit which automatically interrupts the flow of electric current in cases of over current, over load or short circuit.

In my experience as an electrical engineer, I have encountered some unnecessary short circuiting during some electrical maintenance. An unforgettable experience I had was the one I encountered while during a maintenance in my house. I was working on wall sockets and forgot to switch off the source, at a time the live wire and the earth bridged thereby causing a short circuit. A visible spark of fire emitted and stopped almost instantly. Thanks to the circuit breaker for saving me from fire out break or any other electrical hazard. I continued my maintenance and after went to the switch box to complete the circuit via turning on the CB.

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In any case of overload, over current or short circuit, the CB automatically disconnects or interrupt the flow of current. However, over current is relative, a current of 1A can cause some CB to switch off while a current of 4A can still be normal for some CB. Hence, Circuit breakers has different ratings and different places of application. The circuit breaker used is a switchyard is different form that used at residential home and also different from the one used in industry and transformers. There are high voltage circuit breakers like the ones used in power transmission companies, medium voltage circuit breakers and low voltage circuit breakers like the ones used in residential houses

Depending on the make of circuit breaker, some required to break manually switched to logic 1(turn on) even after rectifying the cause of the interruption while some would automatically "turn on" whenever the problem is rectified.
Just like the fuse, the purpose of circuit breaker is to avoid further damages caused by any electrical hazard. However, the major difference between a fuse and circuit breaker is while a fuse is sacrificial component, circuit breakers can be used many times. That is to say, that over current or short circuit damages the fuse totally but does not damage circuit breakers.

Voltage Stabilizer

This is another electrical appliance designed to protect electronic appliances from hazards.
A voltage stabilizer is designed to give out a constant voltage output irrespective of the incoming voltage form the A.C source. Electronic chips, Micro chips and other intelligent enhancing chips like sensors are incorporated in voltage stabilizers thereby making it intelligent, for this reason voltage stabilizers are called intelligent voltage regulator.


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In the case of over voltage from the source, the stabilizers reduces the voltage to the normal; in the case of low/under voltage supply, the stabilizers boosts the voltage to the required and in case of fluctuating voltage, the stabilizers makes the output voltage still constant and safe to use for other electronic appliances. Fluctuation in voltage can create fault in electronic appliances. However, using the output of a voltage stabilizers as the voltage source of other appliances, reduces or even eliminates the risk caused by fluctuating voltage, low voltage and over voltage to appliance.

Thunder Arrestor And Surge Arrestor

Have you ever wondered what would happen to an electrical/electronic appliance, electrical power line if lightning bolt comes in contact with it?

During thunderstorm there exists a tendency that thunder bolt or lightning bolt would occur. This posses a very high voltage and current which is capable pf causing electric shock. In my past publish "generating electricity to thunder storm and lightning bolt, I detailed out how i was shocked by a metallic conductor at the instant of lightning bolt. You can check it out here

The current of possessed by lightning bolt is about 30KA, this is such a high magnitude of current that can cause to much heating in the panel and components of any electronic device thereby causing irreparable damage to that electronic appliances.

Sometimes ago in electronic repair workshop where I learnt electronic maintenance, a man brought his faulty television for repair. On opening the enclosure, my boss asked the man what happened to the television?. The man replied that he was just watching his television during rainfall, then he saw some flash of lightning which was later accompanied by some thunder claps, instantly, the television went off. Unfortunately for the man, the television spoilt beyond economical repair. The whole panel has to be changed and this is relatively expensive.

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To avoid all these up and downs, and enhance safety. Thunder arrestors are introduced in electrical power lines and top of buildings while surge arrestors are incorporated in various electrical/electronic devices. So the major difference between thunder arrestor and surge arrestor is that thunder arrestor operates externally while surge arrestor operates internally(in devices).

Whether thunder arrestor or surge arrestor, the both get hold of lightning both and channel it to the earth through a predetermined path. However, it is advisable to use electrical extensions with surge arresting feature should the thunder arrester in buildings and power lines fail to work efficiently.

Conclusion

"Safety first" is the watchword of engineers and this should be upheld religiously and even at all cost. Protective measure enlisted below is among safety procedures and should be upheld at all time. Failure to think of safety first at any instant might cause exceeding damage and might even lead to fire outbreak and at its worst death.

Electronic appliances manufactures always adhere to this safety rules and measures. However everyone has a part to play to be safe. For instance, when the fuse in your device cut, replace it with a new one instead of using some strips of wire.

Thanks for your time

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References

• Heating effect of electric current
• Understanding Electrical fuse and safety
• Thunder arrestor and surge arrestor principle
• Guide to voltage stabilizer
• Heating in an electrical fuse
• The working principle of circuit breakers
• Short circuiting in an electric circuit
• Direction of current flow in a diode