Calculation method of three phase AC circuit, how to calculate the current of three phase circuit?

As long as one of the three phases of the three-phase power supply, the three-phase load and the three-phase transmission line is asymmetrical, it is an asymmetrical three-phase circuit. In practice, the main thing is the asymmetry of the three-phase load. There are 3 types of common asymmetrical circuits:

a three-phase, four-wire circuit supplying power to an asymmetrical star-connected load; a three-phase three-wire circuit that supplies power to an asymmetrical delta connection load; A three-phase, three-wire circuit that supplies power to an asymmetrical star-connected load. When ignoring the transmission line load, the load phase voltage of the first circuit is still symmetrical, so it can be calculated separately for three single-phase circuits (see star connection); For the second circuit, the load phase voltage is still symmetrical, so the load current can be calculated first, and then the line current (see triangle connection); For the third circuit, the neutral point of the load is to be displaced, and the voltage and current of the three-phase load can be calculated from the obtained neutral voltage (see neutral point).

Three-phase circuit is a multi-supply AC circuit, Kirchhoff's law for solving sinusoidal steady state circuits is fully applicable to three-phase circuits, and the common method for solving three-phase circuits is the (kcl kvl vcr) equation. Because of the symmetry of the three-phase power supply, the guerrilla method is sometimes used to solve the three-phase circuit. For the three-symmetrical circuit, the circuit is converted into a y-y form, the line current, phase voltage, and line voltage of phase A are obtained, and the line current, phase voltage, and line voltage of phase B and C are written according to the symmetry.

For three-phase asymmetrical circuits, the moving voltage u(n n) from the midpoint of the load to the midpoint (ground) of the power supply is usually required, commonly known as the midpoint potential displacement.

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The power factor cos of the inductive load is generally calculated between the average of the state hunger; The resistive load is 1) a power supply system consisting of three voltage sources (or electromotive force) with the same frequency, equal amplitude, and 120° phase difference.

Three-phase generators have 3 windings. They form a symmetrical three-phase power supply, each of which is called a one-phase. The instantaneous values of the voltages of each phase have the same amplitude um and frequency, but the phases of the three are 120° different from each other (i.e., 1 3 periods), and the phasors of the three-phase voltage or traces are respectively the effective value (<) where up is the phase voltage u

The instantaneous value and phasor of the phase voltage can be expressed by the following formulas, respectively:

p represents power, unit: w (watts); 3=fixed); U represents the line voltage, unit: V (volt) I represents the line current, unit: A (A); COS stands for Power Factor, <>

About the power factor of three-phase equipment:

Different devices have different power factors. For resistive (heat) equipment, the general power factor is taken as 1, and for inductive (coil) equipment, the general power factor is taken.

A three-phase motor with a rated voltage of 380V and a rated power of 22kW, calculate its rated current?

Solution: Three-phase motor is an inductive load, so the power factor is taken.

For three-phase 380V motors, the power factor is generally taken, so the simple current size of the 1KW power beam is:

So, the current of 1kW of 380V motor is about 2A, which is how it comes from.

A three-phase electric furnace with a rated voltage of 380V and a rated power of 22KW, calculate its rated current? The hole is late.

Solution: The three-phase electric furnace is a resistive rubber trouser load, so the power factor is taken as 1.

Alternating current is to consider the power factor, p=uicosq, which is single-phase alternating current. For three-phase balanced circuits, multiply by root number 3, where you and i are the effective values of line voltage and line current.

Alternating current power calculation method.

Power (DC) Current Voltage.

Power (single-phase AC) Voltage, Current, Power factor.

Power (three-phase AC) Voltage, Current, Power factor

Note that three-phase AC and 380 power supply are two general silver failures

If the power cord of the electrical equipment is 3 wires (excluding the grounding wire), the equipment is a three-phase AC device.

If the power cord of the electrical equipment is 2 wires (excluding the grounding wire), even if the dry pin is powered by a three-phase power supply of 380V, the equipment is still a single-phase AC device p=ui=i 2*ru - the voltage at both ends of the loaded conductor, the unit is volts i - the current in the conductor, the unit is ampere r - negative front medium load resistance, the unit is ohm p - electric power, the unit is watts.

Formula p= 3uicos, where p-sakura-symmetrical three-phase circuit electrical power (watts), u - line voltage (volts), i - line current (amps), cos - the rate factor of the gonglu shout, cos = 1 when the pure resistive load is removed; cos = 0 for pure inductive load or pure capacitive load; Usually the three-phase circuit COS based on the motor can be taken.

The three-phase alternating current power is calculated as follows: the actual power of the alternating current p uicos where: 1. "cos": is the power factor, which is generally taken.

2. "P": the actual power of alternating current, unit: kw.

3. "U": the actual voltage of AC electricity, unit: kv.

4. "i": the actual current of alternating current, the average value of the three-phase electric spike flow can be taken, and the single fissure is buried: a.

The calculation formula is as follows:

1. Three-phase active power: p=.

2. Three-phase reactive power: p=.

3. Apparent slag bridge rate: s=.

Electrical power of three-phase AC circuit:

1. In the pure resistive circuit, the power factor of the resistive load is basically equal to 1, and the power of the resistive element is divided into instantaneous power, average power or active power.

Since the voltage and current in the AC circuit change with time, the power also changes, and the product of each instantaneous voltage and current is called instantaneous power.

Since the instantaneous power is inconvenient to calculate and measure, it is usually expressed as the average value of the instantaneous power in a cycle, which is called the average power or active power, i.e., p=ui=i r=u r.

2. If it is a pure inductive load (such as transformer, three-phase asynchronous AC motor, etc.), the voltage at both ends of the circuit is 90 ahead of the current flowing through the inductor, and the effective value relationship between voltage and current satisfies Ohm's law, that is, i=u xl xl is the inductive reactance ( ) and its magnitude is determined by the formula xl= l=2 fl. <>

How to use current in a three-phase AC circuit?

Looking at the structure of the circuit, the magnitude of the voltage, and the magnitude of the impedance determine the current.

If the symmetrical three-phase AC circuit, the line voltage is U, and the load impedance of each phase is Z, then the line current is i=i plant 3 Z.

In star wiring, the phase current is the line current.

In the triangle wiring, the phase current is 1 of the line current and 3.

Calculate the current in a three-phase AC circuit according to this, <>

The three-phase alternating current power is calculated as follows: the actual power of the alternating current p = where : cos :

is the power factor, generally taken, p: the actual power of alternating current, unit: kw, u:

The actual voltage of the alternating current, unit: kv, i: the actual current of the alternating current, the average value of the three-phase current can be taken, unit:

Mountain Hood A. 1》The power supply voltage is AC three-phase electricity, each phase voltage is 220V, the rated voltage of the motor is 380V, the rated current is 15A (should be 15KW connected), the motor can be changed to Y connection to adapt to the three-phase 220V operation, the calculation formula is U 220V, the voltage is low, the current is large, and the power remains unchanged.

2》When the three-phase voltage is 380V, the three-phase asynchronous motor is connected to Y or connected in the original connection, and the calculation formula is U 380V.

3》When the three-phase voltage is 380V, the three-phase asynchronous motor was originally changed to the Y connection, because its winding was originally to withstand 380V, after the change of the Y connection method, the winding can withstand 380V voltage 3 times (that is, 380, the winding can withstand 660V voltage in 380V voltage operation, and its root number 3 needs to be increased to the 3rd power. i.e.: i p (

p is equal to.

The actual power p of alternating current is equal to, wherein: cos: is the power factor, generally taken as the actual power of alternating current, the unit is the actual voltage of alternating current, the unit is the actual current of alternating current, and the average value of three-phase current can be taken, and the unit is a.

Calculation of three-phase unbalanced current:

1. (Maximum Current-Minimum Current) Maximum Current.

2. max (phase current - three-phase average current) three-phase average current.

For example, the three-phase current is ia=9aib=8aIC=4A, the three-phase average current is 7A, the phase current - three-phase average current is 2A, 1A, 3A, and the largest difference between the remaining bucket is taken, so Max (phase current - three-phase average current) = 3A, so the three-phase current is uneven and the balance = 3 7. <>