The Distribution Box Is Mainly Composed Of Two Parts

One is the complete set of components, that is, the enclosure of the distribution box and its related accessories. The second is electrical components and related accessories, that is, air switches and their required accessories.

The cabinet consists of the following parts 1. Circuit breaker Circuit breaker: both the switch and the main components of the power distribution cabinet. Commonly used are air switch, leakage switch and dual power automatic transfer switch

1. Air switch:

A. The concept of air switch:

The air switch is also an air circuit breaker, which is used to connect, break and carry the rated operating current and short circuit, overload and other fault currents in the circuit, and can quickly break the circuit when the line and load are overloaded, short circuited, undervoltage, etc. For reliable protection. The dynamic and static contacts and contact rods of the circuit breaker are designed in various styles, but the main purpose is to improve the breaking capacity of the circuit breaker. At present, using a certain contact structure, the current limiting principle of limiting the peak value of the short-circuit current during breaking has a significant effect on improving the breaking capacity of the circuit breaker, and is widely used.

B. The working principle of the air switch:

The automatic air switch is also called a low-voltage circuit breaker, which can be used to connect and break the load circuit, and can also be used to control the motor that starts infrequently. Its function is equivalent to the sum of some or all of the functions of the knife switch, over-current relay, voltage loss relay, thermal relay and leakage protector. It is an important protective device in the low-voltage distribution network.

The automatic air switch has multiple protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action value, high breaking capacity, convenient operation, safety, etc., so it is widely used at present.

  2. Leakage protection switch: A. Leakage protection switch concept:

It not only has the function of leakage protection, but also trips when people touch the electrified, which is the main function of the leakage protector to ensure personal safety; if the electrical equipment is not well insulated and leaks electricity to the casing, the leakage protector will also trip to prevent human body from getting an electric shock. At the same time, it has the functions of current on-off, overload protection and short-circuit protection.

B. The working principle of leakage protection switch:

Schematic diagram of the working principle of the leakage protector. LH is a zero-sequence current transformer, which consists of an iron core made of permalloy and a secondary coil wound on the annular iron core to form a detection element. The phase wire and neutral wire of the power supply pass through the round hole to become the primary coil of the zero-sequence transformer. The rear outlet of the transformer is the protection range.

C. The function of leakage protection switch: 1. When leakage or grounding fault occurs in electrical equipment or lines, it can cut off the power supply before people touch it. 2. When the human body touches a charged object, it can cut off the power supply within 011s, thereby reducing the degree of damage to the human body caused by the current. 3. It can prevent fire accidents caused by electric leakage.

3. Dual power automatic transfer switch: the concept of dual power automatic transfer switch:

The dual-power automatic transfer switch is an automatic switching system for selecting one of the two power sources. When the first circuit fails, the dual-power automatic transfer switch automatically switches to the second circuit to supply power to the load. If the second circuit fails, the dual-power automatic transfer switch automatically switches to the first circuit. circuit to supply power to the load.

It is suitable for UPS-UPS, UPS-generator, UPS-mains, mains-mains, etc. for continuous power conversion of any two power sources.

2. Surge protector:

A. The concept of surge protector:

A surge protector, also called a lightning protector, is an electronic device that provides safety protection for various electronic equipment, instruments, and communication lines. When the electrical circuit or communication line suddenly generates a peak current or voltage due to external interference, the surge protector can conduct the shunt in a very short time, so as to avoid the damage of the surge to other equipment in the circuit.

B. Basic knowledge of surge:

The main function of the surge protector system is to protect electronic equipment from "surge" damage. So if you want to know what a surge protector does, you need to ask two questions:

What is a surge? Why do electronic devices need their protection?

Surge is also called surge. As the name implies, it is an instantaneous overvoltage exceeding the normal working voltage. Essentially, a surge is a violent pulse that occurs in mere millionths of a second. Surges can be caused by heavy equipment, short circuits, power switching, or large motors.

A surge or transient voltage is a voltage that substantially exceeds its rated level during the flow of electrical energy.

The standard voltage for wiring in general homes and office environments is 120 volts. If the voltage exceeds 120 volts, it can cause problems, and a surge protector can help prevent this problem from damaging the computer.

C. The function of surge protector:

The first line of defense

It should be a large-capacity power surge protector connected between each phase of the incoming line of the user's power supply system and the ground. It is generally required that the power protector of this level has a maximum impact capacity of more than 100KA/phase, and the required limiting voltage should be less than 2800V. We call it CLASS I power surge protector (SPD for short). These power surge protectors are specially designed to withstand the high current and high energy surge energy absorption of lightning and induced lightning strikes, shunting a large amount of surge current to the earth. They only provide medium-level protection for limiting voltage (when the surge current flows through the SPD, the maximum voltage that appears on the line becomes the limiting voltage), because CLASS I protectors are mainly for absorbing large surge currents. They alone cannot fully protect the sensitive electrical equipment inside the power supply system.

The second line of defense should be the power surge protector installed at the branch power distribution equipment that supplies power to important or sensitive electrical equipment. These SPDs can more perfectly absorb the remaining surge energy that has passed through the surge arrester at the entrance of the user's power supply, and have an excellent suppression effect on transient overvoltages. The power surge protector used here requires a maximum impact capacity of 40KA/phase or more, and the required limit voltage should be less than 2000V. We call it CLASS II power surge protector. The general user power supply system can meet the requirements for the operation of electrical equipment when the second level of protection is achieved.

The last line of defense can use a built-in power surge protector in the internal power supply of the electrical equipment to completely eliminate the transient overvoltage of small transients. The power surge protector used here requires a maximum impact capacity of 20KA/phase or lower, and the required limit voltage should be less than 1800V. For some particularly important or sensitive electronic equipment, it is necessary to have a third level of protection. At the same time, it can also protect the electrical equipment from the transient overvoltage generated inside the system.

3. Watt-hour meter: A. The concept of watt-hour meter: The watt-hour meter commonly used by electricians is an instrument for measuring electric energy, commonly known as a watt-hour meter.

B. The working principle of the watt-hour meter:

①Working principle of mechanical watt-hour meter:

When the watt-hour meter is connected to the circuit, the magnetic flux generated by the voltage coil and the current coil passes through the disk, and these magnetic fluxes are out of phase in time and space, and eddy currents are induced on the disk respectively due to the interaction between the magnetic flux and the eddy current. The rotating torque is generated to make the disk rotate, and the rotation speed of the disk reaches a uniform motion due to the braking effect of the magnet steel. Since the magnetic flux is proportional to the voltage and current in the circuit, the disk is proportional to the load current under its action. Speed movement, the rotation of the disc is transmitted to the counter through the worm, and the indication of the counter is the actual electric energy used in the circuit.

②Basic principle of electronic watt-hour meter:

Electronic watt-hour meters use electronic circuits/chips to measure electrical energy; use voltage divider resistors or voltage transformers to turn voltage signals into small signals that can be used for electronic measurement, and use shunts or current transformers to turn current signals into For the small signal of electronic measurement, use a dedicated electric energy measurement chip to perform analog or digital multiplication on the transformed voltage and current signals, and accumulate the electric energy, and then output a pulse signal whose frequency is proportional to the electric energy; the pulse signal drives the stepping motor to drive Displayed by a mechanical counter, or digitally displayed after being processed by a microcomputer.

4. Ammeter: A. The working principle of the ammeter:

The current meter is made according to the action of the magnetic field force on the current-carrying conductor in the magnetic field. When a current flows, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic induction line. Therefore, under the action of the magnetic field force, the coil is deflected, which drives the rotating shaft and the pointer to deflect. Since the magnitude of the magnetic field force increases with the increase of the current, the magnitude of the current can be observed through the degree of deflection of the pointer.

This is called a magnetoelectric ammeter.

B. Rules for using the ammeter:

①The ammeter should be connected in series in the circuit (or short circuit.); ②The measured current should not exceed the range of the ammeter (you can use the method of test touch to see if it exceeds the range.); ③It is absolutely not allowed to connect the ammeter to the On the two poles of the power supply (the internal resistance of the ammeter is very small, which is equivalent to a wire. If the ammeter is connected to the two poles of the power supply, the pointer will be crooked if it is light, and the ammeter, power supply, and wire will be burnt if it is serious.). ④. See the needle clearly Stop position (must be viewed from the front)

5. Voltmeter:

A. The concept of voltmeter:

A voltmeter is an instrument for measuring voltage. Commonly used voltmeters - voltmeter symbol: V, there is a permanent magnet in the sensitive galvanometer, and a coil composed of wires is connected in series between the two terminals of the galvanometer. The coil Placed in the magnetic field of a permanent magnet and connected to the pointer of the watch through a transmission. The voltmeter is a fairly large resistor, ideally considered an open circuit.

B. Working principle of voltmeter:

The voltmeter is assembled with an ammeter. The internal resistance of the ammeter is very small. Then, a large resistor can be connected in series to directly connect two points that need to measure the voltage. According to the relationship of Ohm’s law, the current displayed by the ammeter is proportional to In the external voltage, so you can measure the voltage

C. Use of voltmeter:

The voltmeter can directly measure the power supply voltage. When using the voltmeter, it should be connected in parallel in the circuit. When using the voltmeter, the following points should be noted: (1) When measuring the voltage, the voltmeter must be connected in parallel at both ends of the circuit under test;

(2) Correctly select the range, and the measured voltage should not exceed the range of the voltmeter. When used, it is connected in parallel in the circuit; if it is connected in series, the electromotive force of the power supply is measured.

However, the components mentioned above are the most basic components in the distribution box. In the actual production process, other components will be added according to the different uses of the distribution box and the requirements for the use of the distribution box. ,

Such as: AC contactor, intermediate relay, time relay, button, signal indicator light, KNX intelligent switch module (with capacitive load) and background monitoring system, intelligent fire evacuation lighting and background monitoring system, electrical fire/leakage monitoring detector and Background monitoring system, EPS power battery, etc.