The cost of AC Inverters has dropped dramatically over the last 10 to 15 years, and, as a result, it now makes good sense to consider changing over the older technology DC drives in your plant to modern, efficient AC drives, and replacing older across-the-line motor starters with superior soft-start units or inverters.
Recore Electrical Contractors, Inc., and RCT Division has worked with a number of customers to accomplish these conversions. There are a number of benefits associated with operating your equipment with AC inverter controllers.
Energy Efficiency. Typically, DC drive systems have efficiencies in the 80-85% range compared to newer AC drives with efficiencies in the mid-90's, and many DC drives keep power applied to field windings even when the motor is not being used, generating heat and wasting energy. Over the lifespan of the typical electric motor, increasing the efficiency even slightly results in considerable savings in power costs.
Improved Power Factor. Power factor on DC drives may be in the 50% range whereas power factor for AC drives is approaching unity (power factor of 1 = 100% of input energy converted into useful work). This results in much more actual work being done for a given amount of power consumed.
Reduced Maintenance Costs. Most DC motors utilize carbon brushes which transfer power to the rotating commutator ring. These are wear items that require periodic maintenance, resulting in added costs and downtime. AC motors do not have brushes, and they are lighter in weight.
Improved Control. AC drive systems can provide superior performance over DC units. The variable speed on AC drives is digitally controlled, meaning much higher control accuracy and fewer concerns about calibration.
Lower Power Costs. Power rates charged by utility companies for industrial customers are frequently based upon a plant's overall power factor. Electric motors can typically represent 50% or more of a factory's overall power consumption, so by increasing the efficiency (and thus your power factor) of your motors and drives, you may receive improved power rates from your utility company.
Environmental Benefits. The new energy-efficient motors reduce electrical demand, thereby reducing the environmental impacts of electricity generation. Many utility companies and electrical providers have programs to help pay for part of the costs of upgrading their customer's motors and drive systems.