Physical problems with short circuits, problems with short circuits?

There are two kinds of short circuits in junior high school: (1) The first one is that there is no electrical appliance on the circuit, and the current is directly from the positive pole to the negative pole, that is, the positive and negative poles are directly connected, and the short circuit is at this time. It is known as a power short-circuit. There will be a large current, which can burn out the power supply, and it is strictly forbidden to occur in experiments and life.

There is a current passing through the same large resistance, but the current wants to ignore the small resistance electrical current, and there is no strict demarcation. Moreover, after a circuit generates a large current due to a short circuit, the output voltage of the power supply will be reduced. The decrease in output voltage is due to the existence of resistance in the power supply, but the current must be much larger than the normal application state of the circuit, and the heat generated by excessive current will be large, and some parts will burn out.

2) A local short circuit is between two points in the circuit, one of which passes through the branch without electrical appliances, and the current flows through this branch without electrical appliances. The short-circuited electrical appliances have no (should be very small, small enough to be negligible) current, and the entire circuit is still working with electrical appliances.

Since you have used the wire to connect to both ends of the electrical appliance, so that the newly connected wire will form a new circuit with the power supply, because the resistance of the wire is much smaller than that of the electrical appliance, so the current is only through the wire, and the ohm's law obtains i=u r, so the current will be very large, and the circuit you are talking about will produce a large current refers to the current in the new circuit!

If the electrical appliance is short-circuited, there will be no current passing through the short-circuited electrical appliance, which is equivalent to one less electrical appliance or no electrical appliance in the circuit, and the electrical appliance itself has resistance Now the total resistance has become smaller or very smaller, according to the expression of Ohm's law, the current has become larger, and the current resistance is inversely proportional.

Because the electrical appliances have resistance, the wires have no resistance, so the current goes through the wires, and the electrical appliances do not go through the electrical appliances, so there is no current through the electrical appliances at this time.

Because the current passes through the wires at both ends of the appliance, it will not pass through the appliance.

Figuratively speaking, electrical appliances have resistance to the current, there is an obstruction effect on the current, the resistance of the wire is almost zero, according to the series shunt, the proportion of the current size is opposite to the resistance ratio, the electrical resistance has a few ohms to several thousand ohms The wire is generally not a few thousandths of a euro, so it is not that there is no current to use the electrical appliance, but it can be ignored.

This should be idealized. When there is a wire directly connected to the two ends of a certain electrical appliance, we all know that the resistance of the wire is very small for the electrical appliance, and then all the current flows through the wire. In our opinion, it can be considered that there is no current flowing through the electrical appliance.

Short circuits are a common and serious failure of the system. The so-called short circuit is a short circuit between various types of abnormal phases or between phases and ground in the system. There are many reasons why a short circuit can occur, the main ones are:

1) Damage to electrical equipment and components. For example, the insulation part of the equipment is naturally aging or the equipment itself is defective, and it is broken down and short-circuited during normal operation; and equipment defects caused by improper design, installation, and maintenance, which eventually develop into short circuits, etc.

2) Natural causes. For example, the weather is bad, and the overhead line is broken due to strong winds and low temperature wire icing; Due to direct lightning or lightning induction, equipment overvoltage, insulation breakdown, etc.

3) Man-made accidents. For example, the staff violates the operating procedures and pulls the brake with load, resulting in a short circuit between the phases of arc light; Violation of electrical safety work regulations with grounding knife switching, resulting in gold dust short circuit, human negligence to connect the wrong line caused by short circuit or poor operation management caused by small animals entering live equipment to form a short circuit accident, etc.

1) A short circuit is a closed circuit when the power supply is directly connected by the wire 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 fault that should be avoided as much as possible, which can cause the circuit to burn out and fire due to excessive current.)

2) In a hybrid circuit, wires or switches are used to connect the two ends of a circuit component or load directly. (This is a local or partial short circuit that is required for a safety connection that does not cause burnout due to excessive current.) For example, in order to prolong its service life, when one of the filaments is broken and damaged, the special structure inside it will automatically connect the two ends of the small bulbs to make the other small bulbs work normally. )

The total resistance connected to the circuit is too small, and the current is too large, and it will be short-circuited.

Short circuits in life, for example, if the rice cooker is boiling, foam comes out of the lid, and the soup runs down the outer wall and soaks into the power plug, which may cause a short circuit, and for example, when the classroom uses a plug, the table leg accidentally presses against the power line, and the insulation layer of the power cord leaks, and the two wires come into contact with each other, which can also cause a short circuit, and so on.

In physical experiments, if you are not careful when connecting the circuit, the burrs of the wires of the two binding posts will collide together, causing a short circuit, and so on.

In the case of a short circuit, the current does not pass through the electrical appliance, and directly returns from one pole of the power supply to the other pole at the short circuit, so the current will be very large, and it is easy to burn out the power supply.

There are two cases of ordinary short circuits: Power short circuits. That is, the current does not pass through any electrical appliances, and flows directly from the positive electrode back to the negative electrode through the wire, which is easy to burn out the power supply.

A short circuit with an electrical appliance is also called a short circuit in a part. That is, a wire is connected to both ends of the electrical appliance, and the electrical appliance is short-circuited, which is easy to burn other electrical appliances.

The positive and negative poles of the power supply are directly connected without electrical appliances.

There are several cases of short circuit, now let's take a look.

There are 4 situations that can occur in three phases, two phases, single-phase and two-phase grounding. The above-mentioned three-phase short circuit is a symmetrical short circuit, and other forms of short circuit are asymmetric short circuits. In the power system, a single-phase short circuit is the most likely to occur, while a three-phase short circuit is the least likely.

The reason for the short circuit: the communist power supply system requires the production area to supply uninterrupted power to the electrical load to ensure the normal production and life of the factory. However, due to various reasons, it is inevitable that failures will occur, and the normal operation of the system will be destroyed, and the most common fault in the system is a short circuit.

A short circuit is a low-impedance short circuit between conductive parts of different potentials. The cause of the short circuit: the insulation of the current-carrying part of the electrical equipment is damaged.

This damage may be due to the long-term operation of the equipment, the natural aging of the insulation or the breakdown of the normal voltage due to the unqualified ability of the equipment, the insufficient dielectric strength, or the normal insulation of the equipment and the overvoltage breakdown, or the insulation of the equipment is damaged by external force and causes a short circuit.

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.

The main causes of short circuits are:

1. Short circuit caused by aging of the line and damage of insulation;

2. The power supply is overvoltage, resulting in insulation breakdown;

3. Small animals (such as snakes, hares, cats, etc.) are connected on the bare wire;

4. Caused by a variety of man-made random pulling;

5. The line of the outdoor overhead line is relaxed, and it collides under the action of strong wind;

6. The line is installed too low and collides with various transport items or metal objects, resulting in short circuit.