Electrical transients, or transient voltages, are exactly what they sound like: Short, sudden energy disturbances that may occur within an electrical system when an incident triggers storage elements (such as inductors and capacitors) to release pent-up electrical energy. Lightning strikes are one type of transient incident, but more often it not so dramatic. Arcing, the switching of circuit breakers, relay or motor activation, or simple electrostatic discharge can all generate transients within a product.
My first foray into the world of electromagnetic compatibility (EMC) involved designing a transient protection solution for a RS-485 duplex communication circuit. This experience over 15 years ago served as more than just an introduction to the complex world of EMC. It also instilled a lasting respect for the intricacies and nuances of working with electrical transients, especially the importance of circuit protection. Just because these voltages are transient doesn’t mean they can’t do a lot of damage—both to sensitive equipment, and to yourself. Transients are dangerous entities with the potential to shock or kill. That’s why you need Shockingly Good Protection!
In this blog mini-series on electrical transients, I have four aims:
Throughout this mini-series I will focus on the IEC 61000-4-x transients. This initial post will introduce each type and explain their differences. Later posts will build upon that understanding as we learn how to protect against each of these transients.
The IEC61000-4-x transient standards exist to guide us in the complex world of industrial transient immunity. Industrial systems demand high levels of EMC immunity to operate in harsh conditions where high noise levels, surges, and transient voltages are commonplace. Thus, meeting these requirements is not just a matter of regulatory compliance; it's a crucial step towards ensuring that your products can withstand the rigors of industrial environments.
We'll begin with three key transients defined by the IEC61000-4-x standards: electrostatic discharge (ESD), electrical fast transients (EFT), and surges. Each of these transients has unique characteristics, with surge being particularly destructive due to its higher energy levels comparted to ESD and EFT. Let's examine these transients side by side, focusing on the speed and energy associated with each one.
|
Transient Type |
Electrostatic Discharge (ESD) |
Electrical Fast Transients (EFT) |
Surge |
|
IEC Standard |
IEC 61000-4-2 |
IEC 61000-4-4 |
IEC 61000-4-5 |
|
Summary |
Sudden transfer of electrostatic charge between bodies at different potentials. Extremely fast with a pulse width of >60 ns |
Switching of inductive or capacitive loads. A single EFT pulse is comparable to an ESD pulse. Note that EFT pulses occur in bursts during testing, with energy levels up to 100s of milli-Joules. |
Energy spikes caused by lightning strikes or power system switching. Surge energy can be many orders of magnitude larger than that of ESD or EFT. |
|
Rise Time |
0.8 ns |
5 ns |
1.5 us |
|
Energy |
1-10 mJ |
4 mJ |
10-80 J |
As you can see above, ESD and EFT pulses are similar in speed, which means they can often be mitigated with similar techniques. However, the surge pulse is very different. The rise time is 1.2 µs, a lot slower than that of the ESD or EFT single pulse, but don’t let that fool you! With a pulse width of 50 µs, a surge can inflict 10 to 80 Joules of energy depending on the voltage level. This is considerably higher than that of the ESD or EFT pulse. Therefore, surges require more complex protection solutions to mitigate the higher energy inflicted on the system.
Hopefully it’s clear by now that these transients, especially surges, can blast your circuit with a lot of unwanted energy—but what does that look like in the real world? Why is circuit protection so important in the industrial environment?
Consider a bus transceiver like RS-485 or CAN-FD. That’s where I started! These transceivers may have cables running out into the real world, sometimes spanning the entire length of a factory floor. Transients can run rampant in industrial environments such as this, and that unwanted energy can couple onto a cable, travel its length, and damage the transceiver device. Even the installation process can trigger electrostatic discharge (ESD) events and damage communication ports. Therefore, circuit protection is crucial to ensure reliable operation and safeguard sensitive equipment.
If you still don’t believe me, see Figure 1 below. This is what happened when I subjected a 4kV surge pulse to the differential lines CANH and CANL of a CAN transceiver with no surge protection. The result was significant damage, so bad that the moulding compound was blown off the device!
Figure 1. Result of a 4 kV surge pulse applied to CAN transceiver bus pins
In this post, we've built a better understanding about the types of electrical transients and why they matter for your product. Next, we’ll explore ways of protecting electronic circuits against these harmful energy pulses to ensure your product’s reliability in an industrial environment. We’ve got a lot of ground to cover, so I’ll be churning out new blog posts a bit faster than usual. Be sure to check back in two weeks’ time for the next installment, Shockingly Good Protection: Designing Circuit Protection!
