Transient voltage protection

There are many different methods of infrastructure power distribution used around the world, which presents many challenges to power engineers as they design products that rely on high voltage power sources. But regardless of the distribution method, the nature of the power source alone can cause transient high voltages to exist in the distribution system. Transient voltages can be caused by the discharge of stored energy due to a variety of reasons, such as switching generators, arcing, or lightning strikes.

In order to protect electrical equipment connected to the power distribution system from the dangers and hazards caused by transient voltages, the International Electrotechnical Commission (IEC) implemented the IEC 60204-1 standard, which classifies equipment according to its tolerance to transient voltages and the conditions required. The standard is "Safety of Machinery - Electrical Equipment of Machines - Part 1: General Requirements", which defines four categories of transient voltage tolerances under different working voltages.

Table 1: Allowable transient voltage values ​​under different operating voltages

The table outlines the transient voltage thresholds allowed for different working voltages and categories. For example, if a device operating at 300V can withstand 3500V transient voltages, it would be classified as a Class III device.

Overvoltage Category (OVC) Requirements

The main purpose of IEC-60204-1 is to set requirements for different conditions for equipment to achieve a specific category rating to ensure safe use. As shown in the table above, all power equipment and wiring must be classified according to the OVC level. Depending on the connection conditions the equipment is subjected to, IEC may require it to meet a specific OVC level. For example, if a robotic machine is directly connected to a switchboard, IEC-60204 will require that the wiring between the switchboard and the equipment must comply with OVC III, and the power supply within the machine must also comply with OVC III.

If the robot machine power supply cannot meet the requirements of OVC III, an OVC III Class isolation transformer must be installed between the switchboard and the machine. In this way, the isolation transformer reduces the voltage of the switchboard, which reduces the category requirements of the robot machine power supply and OVC II wiring. In many similar cases, the choice of power supply may have cost and space impacts on the equipment owner, as they may need additional isolation equipment to support the end user's specifications.

As defined in IEC 60204-1:2016 , the installation categories range from the least likely to be exposed to high voltage transients to the most likely to be exposed to high voltage transients as follows:

Class I Requirements apply to equipment connected to circuits where measures are taken to limit transients and temporary overvoltages to suitably low levels, such as transient/overvoltage protected circuits.

Class II Requirements apply to energy consuming devices supplied from fixed installations such as appliances, portable tools, household loads, sockets, lighting and connections more than 10 meters from Class III sources.

Category III Requirements apply to equipment in fixed installations and where reliability and availability of the equipment are subject to special requirements, such as isolating transformers, switchgear and equipment directly connected to switchboards.

Category IV Requirements apply at the point of installation into the electrical network, such as meters, overcurrent protection systems, utility transformers, and switchboards. Category IV applications are likely to experience high voltage transients.

OVC III Power Supply

Systems that do not require additional auxiliary equipment support are clearly more cost competitive than alternatives. In addition, reducing the number of components in critical applications can also reduce possible failure points, which can prove to be very beneficial when using qualified OVC power supplies in appropriate environments. For example, RECOM's RAC05-K/480 series and RAC03E-K/277 series of AC/DC power supplies are both OVC III compliant and have ultra-wide input ranges. The RAC05-K/480 offers a nominal input range of 100-480VAC and 5W output, with 4kV isolation voltage and 5, 12 or 15V output voltage. The cost-effective RAC03E-K/277 has an input range from nominal 100VAC to enhanced 277VAC, making it suitable for applications in automation control, Industry 4.0, IoT and home automation. The RAC05-K/480 can be directly connected to the power distribution line to support a variety of 5V applications, such as smart grid, renewable energy, smart metering and IoT applications.

Applications that require higher power can choose RECOM's RAC10-K/277 series, which has 10W output power, an input voltage range of 85V to 277V, and an output voltage of 3.3V to 24V. The RAC05-K and RAC10-K power supplies are ideal for always-on and standby mode applications such as process automation, IoT and smart building systems. In addition, both the RAC20-K/277 series and the RACM40-K series can be built to meet OVC III requirements on a project-specific basis. Using OVC III compliant power supplies in always-on IoT applications can reduce overall cost, BOM, product complexity and installation requirements, making your product stand out from your competitors.