BASIC KNOWLEDGE - SHORT CIRCUITS The basics of short circuits in power electronics systems

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In general, the term short circuit is commonly used to refer to a situation whereby a live or ‘hot’ wire carrying a current comes into contact with a neutral wire. This article explains the several types, causes, and consequences of short circuits in power electronics.

When a short circuit occurs, resistance quickly reduces and a large volume of current flows through an unexpected pathway. Depending on the strength of the current, this can cause crackling, smoke, and flames—this makes a short circuit a dangerous possibility.

What are short circuits in power electronics?

More technically, short circuit refers to a specific condition where electricity flows and stays outside of the established pathway of an electrical circuit.

A short circuit will occur where there is a low resistance connection between two conductors that are providing a circuit with power. This leads to the generation of an excess of voltage streaming and causes an excessive current to flow through, which will go via a ‘short’ (unexpected) route and cause a short circuit.

There are two main types of short circuit:

‘Normal’ short circuit

A normal short circuit is where a live wire touches a neutral wire. This causes resistance to instantly drop and force a large volume of current through an unexpected pathway.

‘Ground’ short circuit

A ground fault short circuit is where the live wire comes into contact with a grounded portion of an electrical system, such as a wall box or ground wire. This also causes resistance to quickly drop which forces a large amount of current to flow through an unexpected pathway.

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What causes short circuits in power electronics?

A short circuit usually comes about due to abnormal system conditions or internal and or external effects.

Internal effects are caused by things like the breakdown or degradation of components, the breakdown of transmission lines from the deterioration of insulation in a generator, or inadequate design. External effects include short circuits caused by lightning surges, system overloading, and mechanical damage (i.e., improper use, vandalism, improper maintenance).

Short circuits can occur in both battery-powered and electrical mains-powered systems. In battery-powered devices, short circuits happen when the positive and negative terminals are connected with a low-resistance conductor. This causes the same short circuit situation outlined above: where a high current causes resistance to drop and leads to the delivery of a large amount of energy in a short period of time.

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What are the consequences of short circuits?

The main consequences of a short circuit are, depending on the current strength, damaged components, electric shock, and a fire, explosion, or release of harmful chemicals. What happens is of course dependent on the device or power system that has shorted, and the materials and components used within it.

This is because when a short circuit occurs, the system’s current increases to a high level while the voltage decreases. This heavy current causes excessive heating which overheats the wires and the power system, potentially causing a fire or explosion. Sometimes, short circuits can take the form of an arc and cause considerable damage to a power system. This occasionally happens with power lines; if the arc is not quickly cleared it will burn the conductor and cause severe long-term damage.

The low voltage created by a short circuit also has a harmful impact on the power system. If voltage remains low, systems can become unstable and shut down.

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