欧姆定律与功率
V、I、R 和 P 中任意两项可求出其余两项。
尝试一个工程 4
每项工作都会预填示例数值。请替换为您自己的数值。
- Find the resistance of a heater elementThe working resistance and current of a 2 kW heater on 230 V.
- Find the current of a 12 V lampThe current a 50 W lamp draws on 12 V d.c.
- Find the power of a three‑phase heater bankThe kW of a star heater bank of 20 Ω per phase on 400 V.
- Find the voltage across a resistorThe volts across 470 Ω carrying 20 mA d.c.
输入
使用默认输入值的示例计算。
- 供电
- 单相交流
- 您已知道
- 电压和功率
- 电压
- 230 V
- 有功功率
- 2,300 W
- 功率因数
- 1
电流
10A
- 阻抗
- 23Ω
- 视在功率
- 2.3kVA
此结果仅供设计参考。请对照现行标准进行核验。
计算步骤
- 公式
I = P ÷ (V × pf)
- 电压230V
- 电流结果10A
- 阻抗23Ω
- 有功功率2,300W
- 视在功率2.3kVA
- 无功功率0kvar
- 电阻分量，Z × pf23Ω
- 电抗分量，Z × sin φ0Ω
关于此计算器
How this is calculated
Ohm's law says the voltage across a resistance is the current through it times the resistance. The power formula says the power is the voltage times the current. Together they link four quantities, so any two of them give the other two. You pick the pair you know, and the tool solves for the rest.
On d.c. the four are voltage, current, resistance and power, and nothing else enters. On a.c. the current and voltage can be out of step, so two things change. The opposition to current is the impedance, Z, which the tool uses wherever d.c. uses R. The real power is the voltage times the current times the power factor. The tool then splits the impedance into its resistance part, Z times the power factor, and its reactance part, and gives the apparent and reactive power too.
On three phase the tool takes the line voltage, between two phases, and the line current. The real power is the square root of three times the line voltage times the line current times the power factor. The impedance it gives is one phase of a balanced star load: the voltage from line to neutral over the line current. A delta load with the same line current has three times that impedance in each branch.
No standard is read. These are the physics every electrician learns, and the tool shows the formula it used for the pair you gave.
| Step | Table or clause | What it decides |
|---|---|---|
| d.c. | V = I × R and P = V × I | The two unknowns from the pair you know |
| Single‑phase a.c. | V = I × Z and P = V × I × pf | The current or voltage, the impedance and the real power |
| Three‑phase a.c. | V = √3 × I × Z and P = √3 × V × I × pf | Line values and the impedance per phase of a star load |
| Power from resistance and current | P = I² × R | The power when the voltage is not given |
| The parts of the impedance | R = Z × pf and X = Z × sin φ | The resistance and reactance on a.c. |
Worked examples
- A 2 kW heater on 230 V draws 8.7 A. Its working resistance is 26.45 Ω.
- A 50 W lamp on 12 V d.c. draws 4.17 A through 2.88 Ω.
- A star heater bank of 20 Ω per phase on 400 V draws 11.55 A in each line and gives 8,000 W.
- A 470 Ω resistor carrying 20 mA has 9.4 V across it and gives off 0.188 W.
- A motor on 400 V drawing 32 A at 0.85 power factor looks like 7.22 Ω per phase and takes 18,844.71 W.
Limits
The tool treats every load as linear and balanced. It does not model harmonics, an unbalanced three‑phase load or a load whose resistance changes with temperature, such as a lamp filament or a cold heater element. A meter reading on a cold element is lower than its working value.
For a cable's voltage drop, use the voltage drop tool: it reads the cable's resistance and reactance at its operating temperature from AS/NZS 3008.1.
See also: Three phase power, Full load current and Voltage drop.
问题
结果仅供设计参考。请依据现行标准核对。
欧姆定律是什么？
电阻两端的电压等于流过的电流乘以该电阻：V = I × R。结合 P = V × I，它将四个量联系起来，知道任意两个即可求出另外两个。
交流时功率因数如何影响结果？
在交流中，对电流的阻碍为阻抗 Z，而不仅是电阻。单相有功功率为 V × I × 功率因数。工具还给出电阻分量 Z × pf 及电抗分量。
本工具如何计算三相？
它以线电压和线电流为输入。有功功率为 √3 × V × I × 功率因数。给出的阻抗为平衡星形负荷的一相阻抗。三角形负荷每个分支的阻抗为该值的三倍。
为何加热元件冷态时电阻读数较低？
金属发热元件的电阻随温度升高而增大。仪表测得的冷态读数低于工作电阻。工作数值请使用额定电压和额定功率计算。
可以用它计算电缆的电压降吗？
只是粗略估算。电缆电阻随温度变化，交流还会增加电抗。请使用电压降工具，该工具依据 AS/NZS 3008.1 读取电缆参数。
计算示例
背景
相关工具
这是否有用？
有问题，或数值看起来有误？联系我们。