What is the definition of a short circuit, and what are the several cases of a short circuit?

A short circuit is when a circuit or part of a circuit is shorted. If the load and the power supply are connected together by wires, it is called a short circuit, the current provided by the power supply during the short circuit will be much larger than the current provided by the path, and the short circuit is generally not allowed, if the short circuit is serious, the power supply or equipment will be burned out.

Power system. The so-called "short circuit" refers to the connection between phases or between phases (or neutral wires) outside the normal operation conditions of the power system. The basic forms of short circuits in three-phase systems are:

Three-phase short circuit, two-phase short circuit, single-phase ground short circuit, two-phase ground short circuit. An abnormal connection (i.e., short circuit) occurs between phases or between phases (or neutrals), sometimes when a very large current flows. Its current value is much greater than the rated current.

and depends on the electrical distance of the short-circuit point from the power supply. A short circuit is a low-resistance short circuit between conductive parts of different potentials, which is equivalent to a closed circuit directly connected by the wire without passing through the load. (Usually this is a serious and should be avoided as much as possible in the fault of the circuit, which will cause the circuit to burn out due to excessive current and cause a fire).

A short circuit in the power supply means that in the circuit, the current does not flow through the electrical appliance, and is directly connected to the positive and negative poles of the power supply. According to Ohm's law.

i=u r knows that since the resistance of the wire is small, the current on the circuit will be very large when the power supply is shorted. Such a large current, the battery or other power sources cannot withstand it, which will cause damage to the power supply; What's more, because the current is too high, the temperature of the wire will rise, and in severe cases, it may cause a fire.

The current flows directly from one end of the power supply to the other end of the power supply without flowing through the load, which is a "short circuit".

The phenomenon that two points with different potentials in a circuit are directly in contact or connected by conductors, resulting in a larger current.

A short circuit is a phenomenon in which two points with different potentials in a circuit are directly in contact or connected by a conductor, causing the current to increase.

A short circuit in the power system is characterized by a high current, which can damage electrical equipment or cause a fire, and should be avoided.

The physical definition of a short circuit is that a circuit or part of a circuit is shorted.

A short circuit is a condition in which the wires leading from a power source to an electrical device (also known as a load) are directly connected to each other without passing through the load (or with zero load).

There is also a kind of short circuit that is also commonly used, that is, there are more than two electrical appliances in series, and one is short-circuited with a wire (connected to both ends of the electrical appliance) to increase the current of the other.

"Short circuit" is an important concept in electricity. Many students are confused about the identification of "short circuit" and the harm it causes, and the following is explained from the concept, classification and judgment method of "short circuit".

1. The concept and classification of short circuits.

Depending on the composition of the circuit, there are two types of short circuits: "power supply short circuit" and "local short circuit".

1) Power short circuit The current starts from the positive pole of the power supply, does not pass through any electrical appliances, and returns directly to the negative pole of the power supply, which is called a short circuit of the power supply.

In actual circuits, wires, switches, ammeters, rheostats, etc., can be incorrectly connected directly to the power supply poles. All four conditions constitute a short circuit, and all of them are short circuits in the power supply.

The switch is disconnected, and the bulb L1 and L2 are connected in series; After the switch is closed, the current starts from the positive pole of the power supply, passes through the closed switch, and returns to the negative pole of the power supply, and there is no current passing through the bulb L1 and L2, that is, the bulb L1 and L2 are short-circuited, which belongs to the short circuit of the power supply.

2) Local short circuit In a series circuit, if the wire (or closed switch or ammeter) is connected in parallel with a certain electrical appliance, the current will go through the wire, and the electrical appliance will be short-circuited, which is called a local short circuit. After the switch is closed, the lamp L1 is short-circuited, which is a local short circuit.

Second, the judgment method of short circuit - line drawing method.

1) "Trace method" to judge the short circuit of the power supply is to use a pen to start from the positive pole of the power supply, along the circuit (including each branch) to trace the line, as long as a line can be traced between the positive and negative poles of the power supply is not through any electrical appliances, then this circuit must belong to the short circuit of the power supply. Observe and analyze the circuit.

Using the trace method, we trace each circuit from the positive electrode in the direction of the current as follows:

From the black line shown in Figure 8, it can be seen that after the switch is closed, the three circuits A, B, and C can trace a thick line that does not pass through the electrical appliance from the positive and negative poles of the power supply, so they all belong to the power supply short circuit, and the D circuit must pass through the electrical appliance (light bulb) no matter how it is described, so it does not have a short circuit.

2) "Drawing method" to determine local short circuit In a series circuit, if you can use a pen to trace another road without electrical appliances at both ends of a certain electrical appliance, the electrical appliance is short-circuited, which is a local short circuit. When the circuit only closes the switch S1, the circuit is shown in Figure 9, L1 is short-circuited, and L2 emits light; When the switch S2 is closed only, L2 is short-circuited and L1 emits light.

Circuit short circuits are divided into short circuits of power supplies and short circuits of electrical appliances. The details are as follows:

Power short circuit: It is to connect the two ends of the power supply directly or indirectly with wires, without passing through any electrical appliances in between. If in a complex circuit, find a way that can go directly from the positive pole of the power supply to the negative pole without passing through any electrical appliances, it is regarded as a short circuit, because the current always takes the shortest route, and the short circuit of the power supply is very dangerous, which is easy to cause the power supply to burn out or even fire.

Short circuit of electrical appliances: It can be simply said that it is to take a wire to connect the two ends of the electrical appliances, the current passes through the wire, there is no current through the electrical appliances, and the electrical appliances do not work, which is regarded as a short circuit.

What are the main types of short-circuit faults?

1. The current increases sharply. The current during the short circuit is much larger than the normal working current, and in serious cases, it can reach more than ten times the normal current. The three-phase short-circuit current at the outlet end of a large generator can reach tens of thousands or even hundreds of thousands of amperes. Such a large electric current will produce a huge impact force.

Deform or damage electrical equipment, and generate a lot of heat.

Damage caused by overheating the device. Sometimes the arc generated by the short circuit point can burn out the equipment directly.

2. The voltage drops sharply. When a three-phase short circuit, the voltage at the short-circuit point is zero, and the voltage near the short-circuit point also drops significantly, which will cause the electrical equipment to not work properly, such as asynchronous motors.

The rotational speed decreases, or even stalls.

3. It is possible to make the power system.

The stability of the operation was disrupted. After a short circuit occurs in the power system, the electromagnetic power output of the generator decreases, and the mechanical power input of the prime mover does not have time to decrease accordingly, resulting in unbalanced power, which will cause the generator rotor to accelerate.

Some generators accelerate fast, while others accelerate slowly, so that the angular difference between generators is getting bigger and bigger, which may cause generators running in parallel to lose synchronization, destroy the stability of the system, and cause power outages in large areas.

4. When the asymmetric short circuit is asymmetrical, the unbalanced current will flow through the system, which will induce a high electric potential and a large current in the adjacent parallel communication lines, which will interfere with the communication and may also cause danger to equipment and people. Among the above consequences, the most serious is the destruction of the stability of the parallel operation of the power system, which is described as the national economy.

followed by a sharp increase in the current.

A short circuit is when the power supply is directly connected to a closed circuit by the conductor without passing through the load. The short-circuit current refers to the current when the electrical appliance is not connected, which is equivalent to the current when the positive and negative phases of the battery are connected directly by finding a wire.

(Usually this is a serious and should be avoided as much as possible in the fault of the circuit, which will cause the circuit to burn out due to excessive current and cause a fire).

In parallel circuits, wires or switches are used to connect the two ends of a circuit component or load directly. (This is a safety connection that does not cause burning due to excessive current, and is a short-circuit that is partially or partially discreet.) For example, in order to prolong its service life, when a filament of his brother high school is broken and damaged, the special structure inside it will automatically connect the two ends of the small light bulb to make other small bulbs work normally.

Quite simply, short circuit means that you used to have to pick up your children from work and go home. Now you don't have to pick up your child and go straight home, which is called a short circuit.

Mine the easiest!

That is, the current is directly returned to the power supply without passing through the electrical appliances, such as directly connecting the positive and negative poles of the battery, which will short-circuit and burn the battery.

There is also a kind of short circuit called electrical short circuit, such as in a parallel circuit, and a large resistance and a small bulb due to the resistance of the resistor, so the resistance is short-circuited, and the current does not pass through him.

Friends, the two power lines are directly short-circuited or the two-phase power supply is formed without passing through the load, which is called a short circuit. You may wish to refer to it.

The path that can constitute the flow of current and form a closed loop (that is, the current can flow out of the positive pole of the power supply and then flow in from the negative pole) is called the path; Some of the circuits are disconnected, and the circuit is called open when there is no current on the circuit; If there is no resistance in the branch through which the current passes (no electrical appliances) or if the two poles of the power supply are directly connected with wires, it is called a short circuit.

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