Inrush Current Là Gì

While inrush current has a peak current value, the term “Inrush Current” is commonly used vĩ đại describe the current that is required mập mạp energize an AC powered device or hàng hóa when first applying voltage và power bự it. This is especially true for inductive sầu loads such as transformers, Inductors và electric motors. It also applies to khủng AC/DC power supplies that use a simple rectifier/capacitor nguồn vào stage. These initial currents can surge và be quite a bit higher than the normal operating current or what is called “steady state” current. An example of an electric motor inrush current is shown in Figure 1. It shows the peak current for the first half cycle as being cthua trận to mập 30 amps và then decaying over subsequent half cycles as the motor spools up.Bạn đã xem: What is inrush current là gì, nghĩa của trường đoản cú inrush current trong tiếng việt


A different example of inrush current is an AC/DC đầu vào stage that uses a rectifier, capacitor circuit where the capacitor needs đẩy đà be charged up khủng its nominal voltage as shown in Figure 2. In both cases, it is apparent that the inrush current is considerably larger than the steady state current.

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Peak current on the other applies to phệ all AC currents, either inrush or steady state. An AC current wavekhung has an RMS value representing the effective or DC equivalent current but it also has a peak value, both positive sầu và negative sầu peaks where the current reaches it maximum cùng minimum value during each cycle. The absolute ratio between the RMS value với the peak value is called crest factor (CF). For a sinusoidal current as encountered with a resistive load, the crest factor will be the square root of 2 or ~1.4142 to đùng 1. This crest factor or ratio is shown in Figure 3.



Why Does it Matter?

When using an AC nguồn source bự determine the required inrush current for a unit under chạy thử, it is important to cảnh báo that the AC source should be capable of delivering significantly more current for a short period of time than is required to béo run the unit under khám nghiệm in a steady state condition. In the case of Motors và Inductors, the inrush current can be 10 to 30 times the nominal current. For toroidal inductors, this value may be up to khủng 50 times nominal.

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Source current limitation may be both in terms of RMS current rating và peak current rating. For motors cùng inductor loads, the crest factor of the inrush current is only 1.414 so if the source can support the RMS current, the peak value will be supported as well. For rectified AC nguồn vào equipment, the current crest factor is generally much higher than 1.414, up khổng lồ 2 or 3 to phệ 1 so not only the RMS rating but also the peak current rating must be considered. Most available AC nguồn sources will support current crest factors from 2.5 lớn 4 at max RMS current output.

Current Limiting Effects

If the source is unable khổng lồ deliver the required inrush current, it may still be used for testing normal operation but the required inrush current cannot be determined as the power source will go into phệ current limit – either RMS or Peak or both – với limit the voltage in doing so. This means the unit under demo will typically still start up or turn on but not as fast as it would when operated from the utility.

AC Source Voltage Distortion

High peak currents và distorted current wave sầu forms also impact the AC power source distortion as they work against the output impedance of the nguồn source. The lower the power nguồn source’s output impedance, the less this effect will be. Figure 4 shows the effect of highly distorted current on output voltage distortion. As the current reaches its peak near the đứng top of the voltage wavesize, the voltage is pulled down causing some flat topping to béo occur.


To alleviate this effect, a programmable đầu ra impedance feature may be offered on some AC source models that allows the output impedance the be reduced. See our expert blog post called “What is Prog Z on an AC power nguồn source & why does it matter” at