How to calculate the current of AC motor
Low-voltage 380/220V three-phase four-wire system is a widely used power supply system throughout China. All types of low-voltage appliance nameplates generally indicate the capacity. How to quickly calculate the rated load current according to the size of the capacity to fit the appropriate fuse (melt), switches, wires, etc. is the most common calculation problem encountered by electricians. .
1 three-phase motor
Current 380V three-phase motor, power factor is generally about 0.8, its rated current is about 2 times the rated capacity, when the motor power is below 2KW, can be considered 2.5 times.
For a 220V three-phase motor, its rated current is about 3.5 times the rated capacity. When the motor power is below 2KW, it can be considered as 4 times.
The specific formula is I=KP
Type I --- Rated current of three-phase asynchronous motor (A)
P---The motor's power (KW)K---coefficient
Related question and answer:
Three-phase motor current calculation formula I=P/1.732/U/cosΦ, what is cosΦ and why is there a cosΦ.
Is the formula I=P/1.732/U correct or wrong? Under what circumstances will use cosΦ.
The formula I=P/1.732/U is wrong, and it should be I=P/(1.732*U*cosΦ).
CosΦ is in the AC circuit, the cosine of the phase difference (Φ) between the voltage and current is called the power factor, expressed by the symbol cosΦ, in the numerical value, the power factor is the ratio of active power and apparent power, that is, cosΦ=P/ S
The size of the power factor is related to the load nature of the circuit, such as the power factor of the resistance load of incandescent light bulbs, resistance furnaces, etc., and generally the power factor of circuits with inductive or capacitive loads is less than one. Power factor is an important technical data of the power system. Power factor is a factor that measures the efficiency of electrical equipment. The low power factor indicates that the circuit has large reactive power for the alternating magnetic field conversion, which reduces the utilization of the equipment and increases the line power loss. Therefore, the power supply department has certain standards for the power factor of the power-using unit.
cosΦ = what S in P/S represents.
S indicates active power, and active power is also called average power. The instantaneous power of alternating current is not a constant value. The average value of power in a cycle is called active power. It refers to the power consumed by the resistive part of the circuit and refers to its output to the motor.
To calculate the three-phase current, the power factor of the power unit must be taken into consideration, so the power factor is expressed by cosφ.
If cosφ is 1, the formula may not be considered.
CosΦ (that is power factor) is translated:
The power factor of the motor is not a fixed number. It is related to the quality of the manufacturing and also depends on the size of the load. In order to save energy, the state mandated that motor products increase the power factor from the original 0.7 to 0.8 to the current 0.85 to 0.95, but the load rate is the user's grasp and is not uniform. In the past, the power factor was often taken as 0.75 in the calculation of the motor current. Now it is often 0.85.
Current is 144.34A, what copper cable is needed? What is the calculation formula?
Need 50 square meters of sight line.
The record is: 10 in the next five, 100 in 2; 2535 four and three circles; 7095 two and a half; wearing tube high temperature 80% off; bare line plus half; copper upgrade
2 single-phase motor current
The rated current of a 220V single-phase motor is approximately 8 times the rated capacity. Such as electric fans, hand drills, blowers, washing machines, refrigerators, single-phase 220V motor power load
The formula is I=8P
Where I--- single-phase asynchronous motor
Rated current (A)P---motor power (KW)
Both star and corner connections are P=1.732*U*I* power factor
Star line voltage = 1.732 phase voltage, line current = phase current
Corner line voltage = phase voltage, line current = 1.732 phase current
note
These formulas are certainly familiar to you. The key is to understand clearly that the measured or given current or voltage is a line or phase problem.
In the actual three-phase load circuit, due to the convenience of measuring the external power supply of the load, if it is a star connection method, the voltage generally refers to the line voltage. If it is an angle connection method, the current generally refers to the line current, so the first calculation is used. Formula (3 times the root number).
If there are special circumstances, the phase voltage and phase current, then the second formula must be used (3 times the relationship)
Rated current calculation
For AC three-phase four-wire power supply, the line voltage is 380, the phase voltage is 220, and the line voltage is the root number 3 phase voltage.
For a motor, the voltage of one winding is the phase voltage, and the voltage of the conductor is the line voltage (refers to the voltage between phase A and phase B, phase C, the current of one winding is the phase current, and the current of the conductor is the line current.
When the motor star is connected:
Line current = phase current;
Line voltage = root number 3 phase voltage.
The tails of the three windings are connected and the potential is zero, so the voltage of the winding is 220 volts.
When the motor is angled:
Line current = root 3 phase current;
Line voltage = phase voltage. The winding is directly connected to 380. The current of the conductor is the sum of the vectors of the two winding currents.
Power calculation formula p = root number three UI multiplication power factor is right
Using a clamp ammeter to measure the line current on any one of the ABC lines
1, three-phase calculation formula:
P=1.732×U×I×cosφ
(Power factor: resistive load = 1, inductive load ≈ 0.7 to 0.85, P = power: W)
Single-phase formula: P=U×I×cosφ
The air-opening selection should be based on the load current, and the air-opening capacity should be 20-30% larger than the load current.
The formula is universal:
P=1.732×IU×power factor×efficiency (three-phase)
Single-phase non-multiplication 1.732 (Gen. No. 3)
The choice of air-opening is generally 1.2-1.5 times the overall rated current.
The empirical formula is:
380V voltage, 2A per kilowatt, 660V voltage, 1.2A per kilowatt, 3000V voltage, 4kW 1A,
6000V voltage, 8 kW 1A.
Above 3KW, current = 2* power;
3KW and below current = 2.5* power
2. Power factor (divided by active power divided by reactive power, the tangent value is calculated after the inverse tangent)
Power factor cosΦ = cosarctg (reactive power / active power)
Apparent power S
Active power P
Reactive power Q
Power factor cos@ (the symbol cannot be replaced with @)
Apparent power S = (square of active power P + square of reactive power Q) reopen squared
The power factor cos @ = active power P / apparent power S
3, find the calculation formula of active power, reactive power, power factor, please elaborate below. (Transformers are single-phase transformers.) In addition, the reduction of reactive power will reduce the active power. Conversely, the increase in reactive power will also increase the active power?
Active power = I * U * cos φ is the rated voltage times the rated current and then multiplied by the power factor
The unit is watts or kilowatts
Reactive power = I * U * sin φ, the unit is the lack of or kilograms.
I*U is capacity in volt-ampere or kVA.
When the reactive power decreases or rises, the active power remains unchanged. However, when the reactive power decreases, the current decreases and the line loss decreases. On the contrary, the line loss increases.
4. What is the leading or lagging reactive power? Why does the asynchronous motor absorb the lagging reactive power from the grid during operation?
The inductive current is the leading current, and the capacitive current is the hysteresis current.
Reactive power is relatively abstract. It is used for the exchange of electric and magnetic fields within a circuit and is used to establish and maintain the electric power of magnetic fields in electrical equipment. It does not work outside, but it is transformed into other forms of energy.
All electrical equipment with electromagnetic coils must use reactive power to create a magnetic field. For example, 40 watt fluorescent lamps, in addition to the need for more than 40 watts of active power (ballasts also need to consume some of the active power) to light, but also need about 80 percent of the reactive power for the ballast coil to establish the alternating magnetic field.
Because it does not do work outside, it is called "reactive." The sign of reactive power is denoted by Q in units of Var or kVar.
5, three-phase motor 11KW motor marked current 22.6A, there are single-phase 0.75KW marked with 4.5A speed 2860r \ min how to calculate?
Three-phase motor power calculation P = UI * power factor (0.75)
Rated current I=P/(U*0.75)/1.732=11/(0.38*0.75)/1.732=22.28A
0.75KW single phase (220V)
Calculated as: .0.75/(0.22*0.75)=4.54A
The 0.22 of the above and the 0.38 of the first are kV of voltage, 0.22KV=220V0.38KV=380V
2860r/min said that the motor is the speed of the two-pole motor per minute.
Four-pole motors like 1450 rpm are mainly used for the selection of special motors with different required speeds.
Like bipolar motors used in axial fans and some devices that require higher speeds, quadrupole motors are often equipped with variable speed machines with variable flow lines and some glass edge grinders, etc.
6. How to calculate the wattage of a motor. A motor, it has the following information: 1430 speed, 380V, 5 minutes 7.5A, then it is a few kilowatts?
According to the three-phase motor power formula P=1.732UIcosφ can be calculated
P - power WU - voltage VI - current Acosφ power factor is generally taken as 0.8
Result P=1.732*380*7.5*0.8=3948.96W is approximately 4KW
There is also an empirical formula that is 380V three-phase motor current is twice the power, which is 2KW 4A, 3KW 6A, 4KW 8A 50W 100A
7, three-phase motor to increase the power factor to use several capacitors?
Generally, the natural power factor of a three-phase motor is about 0.7. If the power factor is to be increased to 0.9, the compensation capacitance is: Q≈0.5P, that is, the compensation amount of the capacitor is about half of the rated power of the motor.
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Coaxial Power D-Sub Solder Cup Contacts with Mixed or Full Layout
Transmit Radio Frequency Signals
The Coaxial D-Sub have like the Power D-Subr replaced the two rows in a Standard Density connector with a coaxial contact that take up about the same size as the two rows of signal contacts. The Coaxial D-Sub is exactly the same size as the Standard Density connector but instead of example 9 positions of signal pins it has 2 power contacts , or instead of 37 positions of signals it has 8 coaxial contacts.
The Impedance for the coaxial contacts are 50Ω or 75Ω
The Coaxial D-Sub with Mixed Layout mixes both coaxial contacts and signal contacts in the same connector. For example the same size as a 15 position Standard Density D-Sub you can have what we call a 7W2, which means there is 7 contacts where 2 of them are coaxial contacts, which means there are 5 signal contacts, so 5 signals and 2 coaxial. See the Layout in the Tech Specs on the bottom, there are a lot of combinations of the Mixed Layout alternative.
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Features
Coaxial d-sub for a variety of applications in cable mount.
Signal contacts come pre-loaded. Coaxial contacts supplied - Not Pre-Loaded.
Available in 5 standard shell sizes with 23 multiple contact arrangements: 1W1/ 2V2 /2W2 /3V3/ 3W3/ 5W1/ 5W5
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Allows combination of signal and coaxial d-sub contacts.Materials
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Insulator: PBT + 30% fiber-glass - Black, U.L. rated 94V-O
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Notes
Panel Cut-Outs
5W1 = Standard 9 Pin Shell
3W3 / 3W3K / 7W2 / 11W1 = Standard 15 Pin Shell
5W5 / 9W4 / 13W3 / 17W2 / 21W1= Standard 25 Pin Shell
8W8 / 21WA4 = Standard 37 Pin Shell
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