The Power of Crest Factor – What is it and Why is it Important

Have you ever wondered why sometimes when you plug-in your hairdryer into a power outlet may all the sudden circuit breaker tripped? Of course, there may be reasons such as circuit overload, short-circuit, or a ground fault. In this issue, we will be exploring the same phenomenon as “circuit overload”, but in the AC power source field. Where we will be exploring the importance of the need for crest factor or inrush current.

What is Crest Factor?

In the AC power source field, the crest factor simply is the waveform ratio between the peak value and its Root Means Square (RMS) value, most of the time it is measured in current or voltage. In the sinusoidal signal waveform, the crest factors equal to √2. Yet, non-sinusoidal signals, can either be greater than or less than √2. Most of the electric products produce some level of a high and short duration of the initial current, also known as inrush current. Inrush current is what caused the circuit breaker to trip in the scenario mentioned in the previous section. Different products act very differently on the inrush current drawn. Figure 1 illustrates some examples of crest factors in different products. Such as in typical compact fluorescent lamps, the crest factor may be up to 3.75, the electrical appliance may be up to 1.4, and the computer and IT equipment may have up to 3.

Figure 1 Image with various of product and its crest factors.

Why is it Important?

Because powering the electric product initial current peak is high and short, sometimes you don’t need to get a next-level power up when come to AC power source selection. For example, on metric, 1kVA power rating with a crest factor of 6 can have similar performance as a 2kVA power rating with a crest factor of 3. The crest factor may already cover the peak current for your DUT. For some, it may have cost-saving effects.

Greater the better?

It’s a yes and no answer. Yes, theoretically as it can power up most inrush demand product. Yet, at the same time, the function has also become limited to a narrower product. Rather, by using the same example mentioned above. A similar performance can be reached with next-level up power source. Further, as the based power rating is greater. It is capable of powering more dynamically. And sometimes, it is priced very similarly.

What considered “optimal” crest factor value?

Your application will determine the “optimal” crest factor value. Take EEC 6620 programmable power source for example. It has a specified crest factor of greater than 3. The maximum allowable current for this source at 110VAC is 18.4A. This means the power source can handle 3 or more times the rated current for a short period of time. The power source can actually output at a peak current of 55.2A. This would be a good fit if the user’s application requires this amount of inrush current.

The bottom line is, you need to examine the loads you need or potentially need when selecting a power supply. And yet, the crest factor is only just one of the important criteria when selecting a power source. Among others, the waveform simulation performance in compliance with IEC standards such as IEC 61000 or size and weights or power reliability may be equally or more important for the task you are seeking.

Extech Electronics Co. (EEC) will be presenting the next generation high performance, powerful and reliable AC Power Source next month. The EAL-5000 series programmable AC power source. The new series offers a complete line-up from 500VA to 6000VA, crest factor greater than 3. Extensive functionalities including waveform simulations. Built for manufacture, R&D, quality, and service teams. The intuitive user interface, SCPI protocol command, and flexible performance packages meet on different functions and budget needs. With high durability and TÜV safety certification. Made the series a dependable and ideal solution for ATE and manufacture applications.