# Advice 1: How to calculate starting current

The launcher is called the currentconsumed by the motor during power supply. Since the value of the starting currentand can be many times higher than nominal, it is necessary to limit, choosing the circuit breakers with the required currentnovel feature that protects the line of inclusion of the electric motor or their group. To do this you need to calculate the inrush current.
You will need
• Technical documentation on the motor.
Instruction
1
Identify the type of motor. It could be the motor constant currentor three-phase alternating current. Calculate the nominal current of the motor DC currentin amperes, using the formula: IH=1000PH/(ηHUH), and the nominal current of the motor three-phase currentand using the formula: IH=1000PH/(UHcosφH√ηH), where:Rn is the nominal engine power, kW;UH — the motor rated voltage, V;ηH is the nominal efficiency of the engine;cos Fn is the nominal power factor of the motor. Data on nominal power, nominal voltage, efficiency and power factor take from the technical documentation of the motor.
2
Calculate the value of the starting currentin amperes after the calculation of its nominal value. To calculate use the formula:IN=IH*KP, where IH is the nominal value of currenta, and KP - the rate constant currentand its nominal value. Review the technical documentation on the motor, it must be specified the multiplicity is constant currentand its nominal value (CP). Multiply this number by the resulting value of the nominal currentand and get the value of starting currentin amperes. Calculate for each motor in the chain.
3
Pick up a circuit breaker to protect the line of inclusion depending on the magnitude of inrush currentas all the motors in the circuit. Please know that circuit breakers can be type of off, C and D. the Switches with the feature of disconnecting type suitable for lighting networks of General purpose, with the feature disable-type are used for disconnection of lighting circuits and systems with moderate starting current ofAMI (motors and transformers). For circuits with an active-inductive load, and also for protection of electric motors with large starting currentAMI typically used to use switches with characteristics of type D. Identifying the type of switch, adjust depending on the magnitude of the inrush current.
Note
Plug-in circuit breakers with characteristic type With overload capacity magnetic circuit breaker twice as high compared to circuit breakers with characteristic type b

# Advice 2: As current to calculate power

Electrical power is physical quantity that determines the rate of conversion of electrical energy. Power is measured in watts (W) and, depending on the considered operation AC or DC can be determined by the relevant rules.
Instruction
1
It is known that a current of 1 a at A voltage in the electrical network 1 delivers power to 1 watt. But this ratio can be used to find power only in the constant values of the potential difference and current strength. Ie, when determining the power (P) in a DC network. To do this, use one of the following formulas, depending on the task parameters: P = I*U, P = I2*R, where I is the value of the DC current, U – voltage, R – resistance.
2
However, it is often required to determine the power in an alternating electric field in circuits sinusoidal current. Thus for full power of the circuit taking the product of the values of voltage and current in accounting for the phase shift between these values, i.e., the reactive and active components of power and power factor.
3
Find the active power of the alternating field. For this, in addition to current values, it is necessary to know the resistance (R) of the circuit. Substitute the given values in the formula P = I2*R and calculate the value. If in an electrical circuit there are several individual parts (resistors), determine the active power for each of them. Fold the values of the active capacity of the entire chain.
4
Calculate the reactive power of the AC circuit. It approximately describes the energy conversion processes in the fields of inductances and capacitances. And reactive power the active-inductive load element is a positive value, and conversely, negative when the active-capacitive nature of the load. This means that if the circuit inductor reactive power will have positive sign and the capacitive power capacitor – negative. To calculate the reactive power element of the inductor (RL) or capacitor (RS) use the same formula P = I2*R , where R is the resistance of the particular element. Sequentially calculate power for each element. Determine the total reactive power of the circuit. Fold values found, in this case, consider the sign of the reactive power of the capacitor: RR = Рл1 + Рл2 – RS.
5
Determine the full capacity of the AC circuit. It is associated with an active and reactive capacity by the following relationship: S = √(RA2 + PP2). Substitute into the formula the values of capacities and calculate the final result.
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