• • • EDITOR’S CHOICE • • •
Surge protection in industrial applications
Aneesh VN, associate product line manager for MTL surge products at power management company Eaton, explains why surge protection is an essential consideration when designing electrical equipment for industrial applications
controls and instrumentation could result in major health and safety issues, environmental fines, downtime, public perception issues, revenue loss, and budget depletion caused by emergency repairs and overtime cost. Protecting against surge events is therefore vital for minimising any damage and maximising uptime.
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Designing in surge protection Surge protection should always be deployed as part of a systematic approach, which includes surge protection of AC power to critical equipment and other services including data, telecom and signal lines. All services should be protected using suitable Surge Protection Devices (SPDs) and connected to an equipotential bonding bar with the least wire length (<0.5meters). The selection of SPDs depends upon some of the key parameters, such as:
•Maximum continuous operating voltage (MCOV) (Uc): MCOV of SPD shall be greater than the maximum operating voltage of the power system or equipment;
•Voltage protection level (Up): Up of SPD should be less than the impulse voltage rating of the protected equipment;
•Protective distance: If the distance between the SPD and the equipment to be protected is too large, oscillations could lead to a higher voltage at the equipment terminals. This can cause failure of equipment, despite the presence of an SPD. An acceptable distance (Protective distance) depends upon the SPD characteristics; however, in general, oscillations may be disregarded for distances less than 10 metres;
•Installation location: The surge rating In, Iimp, Imax shall be determined based on the installation location and the LPZ inside the building. The category/test class of the SPD is selected based on the LPZ and where it is installed. The table below shows the relationship of the SPD classification, according to IEC61643- 11 and IEC61643-21; and
•Telecom and signalling SPDs must conform to the application-specific requirements such as capacitance, series resistance, losses and NEXT for example, because some of these parameters can influence the transmission characteristics of the network.
electricalengineeringmagazine.co.uk
ransient surge events can have costly and devastating consequences for an industrial plant. Any electrical disruption to critical
Figure 1 illustrates a typical industrial process
layout and highlights those areas which are most at risk from lightning and surge damage, or most likely to pass induced currents into sensitive or critical equipment – and where, therefore, surge protection should be considered essential. Eaton’s range of MTL surge products provides a complete solution from the AC power service entrance down to the individual equipment and all the control and communication lines in between. Fuses and circuit breakers are not recommended
for surge protection since they cannot react quickly enough to prevent surge damage. SPDs designed using components – such as spark gaps, suppression diodes and metal oxide varistors – are better suited to add surge protection to any systems already in place. SPDs react in nanoseconds diverting the surge current to earth, limiting the voltage and restoring normal operation to receive the next surge automatically. It is important to choose surge protection
carefully for maximum effectiveness. Having an understanding of the relevant standards and specifying surge protection that is designed for ATEX, IECEx and North American certification requirements are essential to ensure the safety of the plant and employees.
Surge protection in
hazardous locations Another important design consideration is the operating environment. Transients are just as likely to affect systems located in or connected to hazardous areas as those in safe areas of an industrial plant. However, the certification and approvals needed before electrical and electronic systems can be used in potentially explosive atmospheres makes the application of surge protection in these environments a little more complicated.
Surge protection devices in intrinsically
safe circuits must meet the same standards of design and construction as the intrinsically safe equipment, i.e. SPDs must be certified as being within the safety parameters of the intended application. SPDs can be inserted into any part of an IS loop
between the IS interface and a field device. In the safe area, SPDs and IS interfaces should
be mounted close to each other but separately – even when the mounting hardware is the same. For example, SPDs and barriers should be mounted on separate DIN-rails (as shown on the left side in figure 2) and NOT on the same DIN-rail (as shown on the right) because there is a requirement for a 50mm clearance between safe-area and hazardous- area terminals and the intertwining of the connections to the devices creates confusion.
In the hazardous area, SPDs can be mounted
in weatherproof enclosures to protect a number of field devices associated with one local area, or, more commonly, individual process transmitters can be provided with individual surge protection devices.
In summary The installation of quality surge protection from a reputable supplier such as Eaton and a properly designed surge protection plan are vital steps in improving plant reliability, increasing availability and hence maximising Return on Assets. The cost of reliable surge protection is a small price to pay to safeguard the significant investment in today’s ever more complex process systems.
ELECTRICAL ENGINEERING • APRIL 2022 5
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