In the daily work of electricians, sometimes it is necessary to convert three-phase electricity to two-phase electricity to meet production needs. So what are the methods for converting three-phase electricity to two-phase electricity, and how to wire three-phase electricity to two-phase electricity? Let's find out together.
Three-phase alternating current is a form of electrical energy transmission, also known simply as three-phase electricity.
A three-phase AC power supply is a power source composed of three AC potentials with the same frequency, equal amplitude, and phases that differ by 120° from each other.
Three-phase alternating current has many uses. Most AC electrical equipment in industry, such as electric motors, uses three-phase alternating current, which is often referred to as a three-phase four-wire system. In daily life, however, single-phase power, also known as lighting electricity, is more commonly used.
When using lighting electricity, one phase of the three-phase power is used to power the electrical equipment, such as household appliances, while the other wire is the fourth wire in the three-phase four-wire system, which is the neutral wire, drawn from the neutral point of the three-phase power.
How to connect a three-phase power supply to a two-phase power supply:
The colors of three-phase electricity are yellow for phase A, green for phase B, and red for phase C. Currently, there are several ways to name them: A, B, C, L1, L2, L3, or U, V, W, all in the same order.
The three-phase power can be evenly distributed to the top terminals of the six circuit breakers. Specifically, the three-phase power under each circuit breaker, from left to right, is 1, 2, and 3; the top terminals of the first two-phase circuit breaker are connected to 1 and 2 respectively.
The second two-phase circuit breaker is connected to terminals 2 and 3 respectively; the third two-phase circuit breaker is connected to terminals 3 and 1 respectively; the fourth circuit breaker is connected in the same way as the first circuit breaker; the fifth circuit breaker is connected in the same way as the second circuit breaker; and the sixth circuit breaker is connected in the same way as the third circuit breaker. In this way, the three phases under the three-phase circuit breakers are evenly distributed.
How to wire a three-phase power supply to a two-phase power supply?
When installing electrical wires, the "three-phase four-wire" standard wiring is used, which simply means: three live wires and one neutral wire; the voltage of the three live wires is 380 volts, and by pairing any one of the live wires with the neutral wire, a voltage of 220 volts is formed; most household appliances are connected in this way.
First, you need to determine whether three-phase electricity is a four-wire or three-wire system. If it's a four-wire system, the three live wires are the live wires, and the remaining wire, which should be thinner than the other three, is the neutral wire. If there are only three wires, then the neutral wire is the ground you're standing on, which is a wire directly connected to the earth. The voltage between the three live wires in three-phase electricity is 380V, but the voltage between any one live wire and the ground you're standing on is only 220V, which is the AC mains voltage.
Simple connection method for converting three-phase electricity to two-phase electricity (judge the correctness yourself, and you are responsible for the consequences):
Green goes well with blue, and red goes well with gray. The yellow-green wire will not be connected for now; for safety reasons, it will be reconnected later when we purchase three-core electrical wire.
What is the difference between three-phase and two-phase electricity?
Note: There are only single-phase and three-phase electricity. There is no such thing as two-phase electricity.
One live wire and one neutral wire constitute a single-phase 220V circuit. This is the most common input wiring method for household lighting.
Two live wires indicate a single-phase 380V circuit. This input wiring method is commonly used in BX series welding machines, resistance series welding machines, and most modern inverter DC dual-power welding machines. If one phase of a three-phase 380V circuit is missing, it is considered a single-phase 380V circuit and cannot be referred to as a two-phase circuit.
Three live wires constitute a three-phase 380V circuit. This wiring method is commonly used for electric motors and most 380V electrical appliances.
Three-phase electricity consists of three phase wires, with a voltage of 380V between them. It is used for three-phase power supply equipment, such as three-phase motors. Two-phase electricity consists of two phase wires, with a voltage of 380V between them. It is commonly used in AC welding machines. Single-phase electricity consists of one phase wire and one neutral wire, with a voltage of 220V. It is mainly used in household appliances.
A generator that can produce electric potentials with equal amplitude, equal frequency, and a phase difference of 120° is called a three-phase generator.
Using a three-phase generator as a power source is called a three-phase power supply;
A circuit powered by a three-phase power supply is called a three-phase circuit;
U, V, and W are called three phases. The voltage between phases is the line voltage, which is 380V.
The voltage between the phase and the neutral line is called the phase voltage, which is 220V.
1. The difference between three-phase power supply and single-phase power supply:
The power generated by the generator is three-phase. Each phase of the three-phase power supply and its neutral point can form a single-phase circuit to provide electrical energy to the user. Note that in this AC circuit, the terminals should not be called positive or negative; they should be called the line terminal (called the live wire in residential electricity) and the neutral wire (called the neutral line in residential electricity).
2. According to regulations, the neutral point of a 380V (three-phase) residential power supply should not be grounded at the incoming end (it should be grounded at the transformer end. This grounding is to prevent the voltage level from being higher than the power supply voltage due to the floating point. There is a certain resistance between the grounding at the user end and the grounding at the transformer end in the earth). The power supply method is to form a circuit with one live wire and one neutral wire (neutral point lead-out wire). A grounding wire is also connected in the single-phase three-core power socket.
This is to ensure the proper functioning of the residual current device (RCD). (The working principle of an RCD: If a person touches the live wire of the power supply, or if there is an internal leakage in the electrical equipment, the current flows from the live wire through the person or the casing of the electrical equipment into the ground, instead of flowing through the neutral wire. The current in the live wire and the neutral wire will be unequal. The RCD detects this current difference and immediately trips to protect the safety of the person and the electrical equipment. This differential current is usually selected in the tens of milliamperes.) If the neutral point of the power supply is directly grounded (which is not allowed in civil electrical construction), the RCD will lose its function and will not be able to protect the person and the electrical equipment from short circuits.
3. The concept of "three-phase electricity" is: When a coil rotates in a magnetic field, the conductor cutting the magnetic field lines will generate an induced electromotive force, and its variation can be represented by a sine curve. If we take three coils and position them 120 degrees apart in space, and the three coils still rotate at the same speed in the magnetic field, they will definitely induce three induced electromotive forces with the same frequency.
Because the three coils are 120 degrees out of phase in space, the resulting current is also a three-phase sinusoidal change, called three-phase sinusoidal alternating current. Industrial electricity uses three-phase electricity, such as three-phase AC motors.
The voltage between any two phases is 380VAC, and the voltage between any phase and ground is 220VAC. It is divided into phase A, phase B, and phase C. On the circuit, they are represented by L1, L2, and L3. (Three-phase AC power supply also includes 660VAC and 6000VAC power supplies depending on the application).
3.1 A generator capable of producing electromotive forces of equal amplitude, equal frequency, and a phase difference of 120° is called a three-phase generator; a power source using a three-phase generator is called a three-phase power source; a circuit powered by a three-phase power source is called a three-phase circuit. U, V, and W are called the three phases. The voltage between phases is the line voltage, which is 380V. The voltage between a phase and the center line is called the phase voltage, which is 220V.
3.2 Connection method for three-phase electrical loads
It is divided into delta connection and Y connection.
The load leads of a delta connection consist of three live wires and one ground wire. The voltage between the three live wires is 380V, and the voltage between any live wire and the ground wire is 220V.
The load leads in a Y-connection consist of three live wires, one neutral wire, and one ground wire. The voltage between the three live wires is 380V, and the voltage between any live wire and the neutral wire or the ground wire is 220V.
The total power of a three-phase electrical appliance = voltage per phase × current per phase × 3, that is, total power = current × voltage (220V) × 3 (W = U × I × 3).
3.2 Three-phase electricity meters come in three types: mechanical meters, ordinary electronic meters, and magnetic card electronic meters. The general specifications are: 1.5 (6), 5 (20), 10 (40), 15 (60), 20 (80), 30 (100) (voltage 3×380/220V~).
Note: The load of the meter can be adjusted by selecting inductors with different turns ratios to meet the usage requirements. For example, if a meter with a specification of 3x1(2)A is used with an inductor and the turns ratio of the inductor is selected as 1:50, then the maximum rated current that each phase can carry is 100A.
