When learning about electronics as well as starting to learn about electricity, or have a lot of exposure to electrical systems. Surely you have heard a lot about the concept of short circuit, electrical overload. So what is a short circuit? What is overload? Are they dangerous? The cause of this image. Let’s find out with Hong Phuc right in this article!

Short circuit concept

A short circuit (also known as a short circuit) is a phenomenon in which an electrical circuit is short-circuited at a certain time. Make the circuit impedance smaller. The current in the circuit will increase suddenly the voltage will be reduced. When the current increases too much, it will cause serious effects. The short-circuit current with respect to time can be decomposed into two components as periodic and non-periodic. The non-cycle component turns off after some time only the cycle component remains. Short circuit is also known by its English name Short Circuit.

Viewing: What is a short circuit?

Short circuit phenomenon

There is a transient process that changes the current and voltage. The total impedance of the electrical system is reduced

The current increases while the voltage decreases. When the current increases significantly, it is a short circuit current. Therefore, if the short-circuit point is not released, the system will soon go into sustained (steady) short-circuit mode.

Causes and consequences of short circuit

Cause of short circuitDue to the insulating ability of the wire. Electrical equipment is poor or damaged without our knowledge. Overvoltage due to weak power source and due to too many electrical devices used at the same time causes overload. Other causes such as: wrongly connected circuits together. Or when connecting circuits together is not calculated in advance. Consequence of short circuit Electrical equipment will heat up. More electromotive force between conductors and damage to electrical equipment Voltage drop and unbalance: conduction: affecting the load. A voltage drop of 30 to 40% can cause equipment to stop working. Production activities are delayed. High risk of product damage.Communication line interference

Short Circuit Classification

There are different types of short circuits such as:

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3-phase short circuit: 3 phase short circuit 2 phase short circuit: 2 phase short circuit 1 phase short circuit: 1 phase ground short or medium short 2 phase ground short circuit: 2 phases short together and ground short

Among them, 3-phase short circuit is the most dangerous

Normally, circuit breakers must be isolated from the system. Particularly in the 35 -10 6kV voltage grid is the medium grid. How to calculate small 1 phase short circuit current area. Allow it to continue operating for 2 hours since short circuit. If after 2 hours, the problem cannot be detected and fixed, the power must be cut off. In order to detect the fault date, a three-phase delta transformer is required.


When a short circuit occurs, if not handled and released in time. It will most likely lead to the failure of the entire system and cause enormous consequences for the business. Individuals or households have many economic losses. Not only that, it can lead to danger to human life.

Short circuit parameters you need to know

In the actual electrical system. To be able to calculate the short circuit is extremely difficult and very difficult to be precise. Therefore, depending on the purpose and calculation requirements, we have different experiments. But the general pattern of experiments will look for the basic parameters are:

Short circuit voltage Short circuit loss Short circuit current

These parameters are converted to 3-phase short-circuit voltage values. The converted short circuit tests are also specified as the three phase short circuit tests. A short-circuit test on a single-phase transformer is made 3 times and the rules are tested:

Important Rules

Rules when the power is applied and the end of the coil is connected to Y:

Rule for converting result to rated value at measuring temperature

In there:

(%) short circuit voltage(W) is short circuit lossNote: all converted to rated value at t°C.

When the power is on, the solution is put into the terminal D coil, with the third coil turned off:

Average values ​​at measuring voltage

Formula to convert result to rated value at measuring temperature

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In there:

UKt(%): short-circuit voltagePKt (W): short-circuit power lost Note: values ​​converted to rated values ​​at t°C

Formula to convert result to standard temperature (75 degrees Celsius)

In there:

UK75 (%): short-circuit voltagePK75 (W) short-circuit power lossK: temperature correction factor

From the short-circuit solution we can determine

Short circuit resistanceShort circuit impedanceShort circuit reactance

In the case that considers a 1-phase 2-coil transformer as a 2-pole network unit. We have short circuit voltage calculated as a percentage equal to the total impedance calculated in percent. Therefore, the short circuit resistance of a transformer in English is “The perentage impedance of a transformer”.

What is overload?

Overload has the English name Overload, this is a term related to power capacity. For example, generators, alternators or power transmissions such as transformers and conductors. Overload is the current phenomenon of the discharge loads too large for the rated current of the conductors, switches or power supply.

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Overload is a term related to amperage. The basis of calculation is A (ampere). Overcurrent can occur in any machine or power tool, regardless of source or load. Overcurrent occurs when the amperage exceeds the rated amperage. Examples include short circuit (short circuit), lightning strike, or magnetic resonance (for wound devices). In essence, both are current phenomena that exceed the rated amperage.

Cause of overload

To visualize the cause of electrical overload, let’s look at the following circuit diagram:

At that time, the amperage flowing through the load will increase beyond the allowable threshold or the rated value of the fuse, causing the fuse to break or be damaged.

Overcurrent prevention method

In order to limit electrical fires caused by overloads and overcurrents, many people have used devices such as circuit breakers, aptomats, fuses, relays, etc. These are common devices for switching and protecting electricity. when the above situation occurs. In addition, you can use a number of other devices such as UPS Online or Lioa voltage stabilizer, etc. to stabilize the current.

Requirement against overload

Requires protection against overload in accordance with national regulations on electrical systems of houses and public houses.

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In the residential electrical system, overload protection devices must be used that satisfy 2 conditions IB In Iz (3) and I2 1.45 x Iz (4) simultaneously.

In there:

IB: circuit design calculation current, in amperes (A)In: rated current of the protective device, in amperes (A). For adjustable protective devices, the rated current In is the rated current.IZ: allowable long-term continuous load current of the conductor. It is expressed in amperes (A)I2: effective operating current for the conventional time of the protective device, in amperes (A). series I2 specified in the product standard or provided by the manufacturer.

Installation of overload protection device:

Overload protective devices should be installed at places where there is a change, causing the allowable current-loading capacity of the conductor to be reduced, except for the cases specified at point B of section and in section 2.6.4…The overload protection device can be installed on the part of the conductor between the point of change and the installation position of the protective device, etc.


After learning about short circuit and overload, Hong Phuc came to the following conclusion:

Short Circuit:

Is the phenomenon of a circuit that allows current to flow when the impedance of the circuit is zero or very small This is an electrical problem that occurs when two anodes and cathodes are in direct contact with each other without passing the load. The voltage value will return to 0 and the current flowing through depends on the impedance of the circuit


This is an electrical problem that occurs when the amperage flowing through the circuit exceeds the permissible value or the rated value of the circuit. When the circuit is overloaded, its voltage value may be reduced but will does not fall to 0.

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Above are the knowledge about short circuit and overload that Hong Phuc has gathered. Hope this article will bring you useful information.