Capacitor-Based DC Back-up Power Provides Unique Solution for Harsh Environments
Finding the right industrial-grade solution to provide back-up power for your plant in the event of an interruption to the main power supply is critical, especially if you are dealing with a particularly hostile environment.
Until recently, the generally accepted industry standard solution has been to deploy a DC UPS (uninterruptible power supply) system that uses lead gel batteries to provide an emergency back-up power source that makes sure the plant has enough power to park its machines in safe positions and shut down under control, to provide a bridge while the back-up generator kicks in, or even to power right through and hope that the mains come back before the batteries die. The choice of which path to follow is a strategic one and differs from one plant to the next, but at the end of the day the mission is to ensure safety, save critical process data, minimize downtime and maximize profitability.
“Ultimately, the costs associated with a power interruption are not limited to the disruption to the production process,” says Kai Bronzel, a spokesperson for Siemens Industry in Alpharetta, GA. “Some people may think that when the power goes out the machines stop and when it comes back on they start again, just like your TV at home. But the reality is that industrial machines are a lot more like digital clocks than TV’s. When the power goes out they have to be reset properly.
“If they shut down in the middle of a batch then the whole batch is probably waste, but even if you are talking about a discrete factory with an SMT line populating circuit boards for an electronics producer you don’t want machines spinning up on their own, creating unsafe working conditions that may lead to catastrophic failure, damaged equipment and injured workers.”
Over the years industry has devised methods to minimize the impact of power disruptions, the most common of which is the aforementioned lead gel battery-supported DC UPS system. When main power fails, the UPS kicks in to take whatever action plant managers have determined is appropriate to minimize the impact of the interruption. For large operations this DC UPS is an ideal solution and can provide power for problems that last from several minutes to an hour. However, the battery-powered back up isn’t right for everyone. To start with lead gel batteries need periodic replacement, meaning ongoing maintenance and replacement costs have to be part of the total cost of ownership (TCO) equation.
“Also,” adds Bronzel, “the battery-powered solution that is commonly deployed today isn’t good in harsh industrial environments where the temperature typically rises above +20° C. This causes severe degradation of the service life of the battery which leaves you with an unreliable system. Once you go above +40°C you can’t use batteries at all.”
There is also a concern with ventilation, adds Bronzel. Lead gel batteries tend to leak gases and so must be located in a ventilated control cabinet, which can be a problem in a dusty or dirty environment.
Siemens Industry has introduced an industrial-grade capacitor-based DC UPS as an alternative for users with operations that aren’t well suited to the battery-based options currently available. The capacitor-based system can’t maintain operations for as long as the batteries, as it stores a shorter charge, and the initial cost is higher. However, it requires no replacement batteries and is almost maintenance-free which reduces the cost of the system over its lifecycle.
One example of a capacitor-based UPS system is Siemens’ SITOP UPS500S. Typically, a SITOP deployment would include basic units with add-on modules. The basic unit is equipped with 15A maximum backup current, integrated energy store with options at 2.5 kWs and 5 kWs, a USB interface and is IP20 rated. Further, each add-on module supplies a supplementary energy store of 5 kWs to extend the backup period and can be configured to cascade – up to three modules can be connected in parallel with the basic unit. The unit has a small footprint in the control cabinet and can be easily monitored with a Windows-based HMI interface which processes all signals from the UPS module.
Says Bronzel, “In the case of harsh environments, +40° C or higher as you commonly see in oil and gas or metals, the capacitor-based solution experiences only minor degradation to service life – somewhere around 10 percent – so it is very reliable in environments that currently don’t have any solution at all. And it will last. In environments lower than +50° C the system will degrade only about 10 percent after eight years of service. Once you go higher than +50° C that goes up to 20 percent.”
Ultimately companies want to make sure that they maximize productivity and one way to do that is by optimizing their operational uptime, says Bronzel. “These days if you want to be competitive then your manufacturing operation is a 24 x 7 x 365 proposition and every minute your plant isn’t operating as planned costs money. The new capacitor-based system helps users navigate their shutdowns in a way that minimizes their impact on the operation. Critical process data is protected, machines are parked in safe positions from which they can be restarted easily and overall safety is maintained throughout the plant. When you factor in the ongoing savings realized from the batteries you no longer need to replace (at $200 per throw per year) then it all comes together in a significant value proposition for users.”
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