First, three-phase four-wire system and three-phase five-wire system symbol meaning to answer:
(R yellow, S green, T red, N blue or black, ground yellow and green two color lines) three-phase five-wire system
(R yellow, S green, T red, N blue or black wire,) three-phase four-wire system
(R yellow, S green, T red, ground yellow and green color lines) Three-phase four-wire system
Three-phase four-wire system: phase lines A, B, and C, protection neutral line PEN, PEN line through the working current, PEN in the access to electrical buildings to do repeated grounding; belongs to TN-C grounding system. Three-phase five Line system: phase lines A, B, C, neutral line N, protective grounding line PE, N line has working current passed, PE line usually has no current (only in case of earth leakage or short circuit has fault current); The TN-S grounding system is used for power distribution.
Second, three-phase four-wire system why a three-phase five-wire system more than one line
Transmission Line Three-phase Power Supply Electrical Connection Diagram
In low-voltage distribution network cables, three-phase four-wire systems are commonly used for transmission lines, including three-phase four-wire systems.
The three lines respectively represent A, B, and C phases, and the Other three are neutral three-wire and four-wire.
The three-phase five-wire system includes three phase lines (A, B, and C lines), a neutral line (N line), and a ground line (PE line) for three-phase power, and therefore is distinguished by one more ground line.
The three-phase five-wire system has one more ground wire than the three-phase four-wire system and is used in places where safety requirements are high and equipment requires uniform grounding.
The knowledge of the three-phase and five-wire system lies in these two and “zero linesâ€. When used in the power grid of more sophisticated electronic instruments, if the neutral wire and the ground wire share a single wire, it will have an effect on the working zero in the circuit. Although, in theory, they are all zero potential points, if there is an occasional surge pulse impacting the working zero line, and the zero line and the ground line are not separated, for example, this kind of pulse is caused by the phase line leakage. In some electronic circuits, if the zero drift phenomenon is serious, then the electrical enclosure may be charged, which may damage the electrical components, or even damage the electrical appliances, resulting in danger of personal safety.
The fundamental difference between the zero line and the ground line is that one constitutes a working loop, and one protection function is called a protective earthing, a return network, and a ground return. In an electronic circuit, these two concepts are to be distinguished. In a regular company, The two lines are to be separated.
In practice, there is also a three-phase and six-wire connection method. In addition to the working neutral line and the protective grounding, it is also specially equipped with a grounding line. This line is connected separately from the equipment ground line and is not connected to any other line. Used to protect the equipment, because the damage of electrical parts is often only a few microseconds, so the fault current will be quickly back to the earth, the need for direct grounding equipment.
In the same power system, it is absolutely not allowed to have a protective earth and a protective zero at the same time.
In the three-phase four-wire power supply system, the two functions of the zero-main line are separated, that is, one line is used as the working zero line (N), and the other line is used to protect the zero line (the point of the connection line is: The working neutral N and the protective neutral PE have no electric connection at all except for the neutral point of the transformer.Because this type of tie can be used for single-phase loads, there is no three-phase load derived from the neutral point. The three-phase load derived from the neutral point has been widely used, and in the case where the three-phase load is not fully balanced, the working neutral line N has a current passing through and is charged while the protective neutral line PE has no electricity. Therefore, the grounding system of this power supply mode completely has a safe and reliable reference potential.
Third, the principle of three-phase five-wire power supply
Three-phase five-wire supply diagram
It is well known that in three-phase four-wire cable and power supply, when the three-phase load is unbalanced and the zero line of the low-voltage power grid is too long and the impedance is too large, zero-sequence current will flow through the zero line. An excessively long low-voltage power grid is caused by the environment. Deterioration, wire aging, moisture and other factors, the leakage current of the wire through the zero line to form a closed loop, resulting in the zero line also has a certain potential, which is very unfavorable for safe operation. In the special case of disconnection of the zero trunk line, the single-phase equipment and all equipment connected to zero after disconnection generate dangerous voltages, which is not permitted. If a three-phase five-wire system is used, the working neutral N and the protective neutral PE connected to the electrical equipment are laid separately. The potential on the working zero line cannot be transmitted to the housing of the electrical equipment. The dangerous voltage caused by the three-phase four-wire power supply mode is effectively isolated, and the potential on the casing of the electric equipment is always at the “ground†potential, thus eliminating the hidden dangers of generating dangerous voltage from the equipment.
Fourth, the three-phase five-wire laying requirements
(1) When wiring with insulated conductors, protect the neutral line with yellow-green two-color lines. Normally, the working neutral line is black. In the vertical wiring along the wall, the protection zero line is set at the bottom, and when horizontal wiring is used, the protection zero line is against the wall.
(2) At the power transformer, the working neutral line is led out of the neutral porcelain casing of the transformer, and the protection neutral line is led out from the lead-out line of the grounding body.
(3) Repeated grounding shall be connected to the protection neutral line as required, and repeated grounding on the working zero line is prohibited.
(4) Five-core low-voltage power cables should be used when using low-voltage cables.
(5) The working neutral and protection neutral lines at the terminal's electricity (such as gates, sockets, wall distribution panels, etc.) must be connected to the zero trunk respectively.
(6) The transformation of old enterprises shall gradually implement the method of separating the zero line of protection and the zero line of work. For example, in the workshop, zero-line trunks are repeatedly grounded, and after the repeated grounding, the working zero line is laid separately, and the protection zero line is repetitively grounded. The four-pole leakage protection circuit breaker is used in front of the circuit breaker. After the circuit breaker was changed to three-phase five-wire system; In the overhead line power supply and the implementation of power and lighting electricity separately erected (two Shed lines), can use the zero line with the lighting line cross-stretched to work for the zero line, with The neutral line erected on the power line is used to protect the neutral line.
V. Application range of three-phase and five-wire power supply
All the low-voltage power supply wire systems that are protected by zero are all the applications of three-phase five-wire power supply. Relevant state departments stipulate: All new construction, expansion, enterprises, commerce, residential buildings, smart buildings, infrastructure construction sites and temporary lines shall implement the three-phase and five-wire power supply methods, so that the protection zero line and the work zero line will be laid separately. Existing enterprises shall gradually change the three-phase, four-wire system to three-phase, five-wire power supply. The specific measures shall be implemented in accordance with the requirements for laying three-phase and five-wire systems.
Kirisun radios,Portable Two Way Radio,Motorola Vhf Handheld Radio,Multi Band Portable Radio
Guangzhou Etmy Technology Co., Ltd. , https://www.digitaltalkie.com