Calculation method of rated current of motor
First, the academic school: calculation formula.
1. Calculation formula for rated current of three-phase motor:
P=1.732×U×I×cosφ
(power factor: resistive load = 1, inductive load ≈ between 0.7 and 0.85, P = power: W)
2. Calculation formula for rated current of single-phase motor:
P=U×I×cosφ
The choice of protective air switch should be selected according to the load current. Generally speaking, the capacity of the protective air switch is 20~30% larger than the load current.
3, the general calculation formula.
P=1.732×IU×power factor×efficiency (three-phase)
Single phase does not multiply 1.732 (root number 3)
The choice of protective air switch is generally 1.2-1.5 times the overall rated current.
Second, the experience of the faction: the empirical formula.
1. The empirical formula is classified by voltage:
380V voltage, 2A per kW.
660V voltage, 1.2A per kW.
3000V voltage, 4 kW 1A.
6000V voltage, 8 kW 1A.
2. The empirical formula is classified by power:
Above 3KW, current = 2* power;
3KW and below current = 2.5* power.
Understand the calculation method of the rated current of the motor, we analyze and calculate by example: the rated current calculation of the three-phase motor 15KW.
1. The empirical formula calculates the current I: 15 × 2 = 30 currents.
2, the college formula calculation: P = 1.732 × IU × power factor × efficiency (power factor and efficiency are taken as 0.9), U = 380, P = 15000, substituted into the formula can be calculated current I = 28.1 current.
Third, the concept of rated current. Www.dgzj.com
1. 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 3-phase voltage.
2. For the motor, the voltage of one winding is the phase voltage. The voltage of the wire is the line voltage (refers to the voltage between phase A and phase C, phase C, the current of one winding is the phase current, and the current of the wire is the line current.
3. When the motor is connected by star: 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.
4. When the motor is connected at the corner: line current = root 3 phase current; line voltage = phase voltage. The winding is directly connected to 380, and the current of the wire is the vector sum of the three winding currents.
5, the clamp ammeter card is measured on any line of A, B, C line current.
