Characteristics of electrical equipment - power and current consumption. If only one of these values is indicated, then it is required to convert amperes to kilowatts. These conversions are needed to determine the ratings of circuit breakers and select the cross section of the supply conductors, calculate and design the power supply system, and account for the consumed electricity.
All the necessary concepts for calculations are available in the school physics course, with the exception of the nuances of using a reactive load. How many amperes per kilowatt is determined for direct and alternating current in the same way, provided that active consumers are used. An inductive or capacitive load requires the power factor to be taken into account. There are several formulas for how to convert amperes to kilowatts, and they do not require complex calculations.
Content
Translation for 220 volt networks
The power formula relates the supply voltage, current consumption and power:
P=U•I
In circuits with reactive loads, where there are inductive and capacitive loads, the value of active power is corrected by entering the power factor into the expression:
Pa=U•I•cosø
The conversion of amperes to kilowatts for single-phase networks is carried out by substituting the initial values into the above formulas. The first is used in the case of active load, and the second - with reactive (electric motors). Substituting current and voltage in volts and amps, power is obtained in watts. For a powerful load, watts are taken to translate into more convenient values:
1000 W = 1 kW.
These are the basic rules for the translation of electrical quantities.
380 volt networks
The conversion of current values to power for a three-phase network does not differ from the above, only it is necessary to take into account the fact that the current consumed by the load is distributed over three phases of the network. The conversion of amperes to kilowatts is carried out taking into account the power factor.
In a three-phase network, you need to understand the difference between phase and line voltages, as well as line and phase currents. There are also 2 options for connecting consumers:
- Star. 4 wires are used - 3 phase and 1 neutral (zero). The use of two wires, phase and zero, is an example of a single-phase 220 volt network.
- Triangle. 3 wires are used.
The formulas for how to convert amperes to kilowatts for both types of connection are the same. The difference is only in the case of a delta connection for the calculation of separately connected loads.
Star connection
If we take a phase conductor and zero, then there will be a phase voltage between them. Linear voltage is called between the phase wires, and it is greater than the phase:
Ul = 1.73•Uf
The current flowing in each of the loads is the same as in the network conductors, so the phase and line currents are equal.Under the condition of load uniformity, there is no current in the neutral conductor.
The conversion of amperes to kilowatts for a star connection is made according to the formula:
P=1.73•Ul•Il•cosø
Delta connection
With this type of connection, the voltage between the phase wires is equal to the voltage on each of the three loads, and the currents in the wires (phase currents) are related to the linear (flowing in each load) expression:
Il \u003d 1.73•If
The conversion formula is the same as above for "star":
P=1.73•Ul•Il•cosø
Such a conversion of values is used when choosing circuit breakers installed in the phase conductors of the supply network. This is true when using three-phase consumers - electric motors, transformers.
If separate loads connected by a delta are used, then the protection is placed in the load circuit in the formula for calculation using the value of the phase current:
P=3•Ul•If•cosø
The reverse conversion of watts to amperes is carried out according to inverse formulas, taking into account the connection conditions (connection type).
It will help to avoid the calculation of a pre-compiled conversion table, which shows the values for the active load and the most common value cosø=0.8.
Table 1. Converting kilowatts to amperes for 220 and 380 volts with cosø correction.
| power, kWt | Three-phase alternating current, A | |||
| 220 V | 380 V | |||
| coso | ||||
| 1.0 | 0.8 | 1.0 | 0.8 | |
| 0,5 | 1.31 | 1.64 | 0.76 | 0.95 |
| 1 | 2.62 | 3.28 | 1.52 | 1.90 |
| 2 | 5.25 | 6.55 | 3.,4 | 3.80 |
| 3 | 7.85 | 9.80 | 4.55 | 5.70 |
| 4 | 10.5 | 13.1 | 6.10 | 7.60 |
| 5 | 13.1 | 16.4 | 7.60 | 9.50 |
| 6 | 15.7 | 19.6 | 9.10 | 11.4 |
| 7 | 18.3 | 23.0 | 10.6 | 13.3 |
| 8 | 21.0 | 26.2 | 12.2 | 15.2 |
| 9 | 23.6 | 29.4 | 13.7 | 17.1 |
| 10 | 26.2 | 32.8 | 15.2 | 19.0 |
