Water Well Journal
Issue link: http://read.dmtmag.com/i/543740
Develop a procedure for checking the various operating conditions that lead to excessive heat, whether a submersible or T- or U-frame motor, and check for these conditions on every service call. The few added minutes will often pay dividends to you and your customer. Be Ready for the New Motors The U.S. Department of Energy has regulated the energy efficiency level of electric motors since 1997. When oper- ating, the electrical energy is transferred as useful mechanical energy to some driven device such as a fan, pump, blower, compressor, or conveyor. The Energy Policy and Conservation Act, as amended by the Energy Inde- pendence and Security Act of 2007 (EISA), covers three broad categories of electric motors: general purpose, definite purpose, and special purpose. These broad categories include a variety of motors. Single-speed, con- tinuous-duty polyphase motors with voltages not greater than 600 volts. Motors with or without mounting feet. Motors built in a T- or U-frame. Motors built with synchronous speeds of 3600, 1800, 1200, or 900 rpm (two, four, six, or eight poles). NEMA Design B motors from 1 to 500 hp. NEMA Design A and C motors from 1 to 200 hp. Motors that are close-coupled pump or vertical solid-shaft normal thrust motors. With its most recent final rule—one which has a compliance date of June 1, 2016—the Department of Energy is ex- panding its regulation and establishes energy conservation standards for a number of different groups of electric motors that DOE has not previously regulated. Although EISA does not currently apply to submersible motors, within a few years you may no longer be able to purchase a standard efficient pump motor. Everyone so impacted may say this change will be for the best in the long run and everyone will benefit. But those who routinely deal with motors for cen- trifugal or vertical turbine pumps will need to consider a few items. The new motors will be wound with more efficient wire and wraps. This means the new motors will draw less amperage when running but will also draw more locked-rotor or starting cur- rent. If you retrofit an existing installa- tion with a new premium efficient motor, there's a good chance the exist- ing circuit breaker will trip upon start- up. This may entail the replacement of this circuit breaker if it cannot be ad- justed to withstand this higher inrush current. That can get expensive in a hurry. In other cases, the new motor's frame may not fit onto the existing discharge head or pump bracket. The important thing will be to consider all aspects of the change-out and make sure your cus- tomer knows all possible pitfalls before you start. Using 230-Volt Motors on 208-Volt Power Supplies You have been told dozens of times you can run a standard 230-volt, three- phase motor on a 120/208-volt, wye power supply. When you consider an al- lowable 10% voltage drop for a 230-volt rated motor ending up at 207 volts, that's close for a 208-volt installation, right? In most cases, you can get away with this. But remember our earlier part of this discussion about the great killer of motors—heat? A 208-volt power supply is often the level of three-phase power provided in an urban or city setting where the voltage is often compromised due to a lot of single-phase loading. This often results in unbalanced volt- ages and the resultant voltage drop on the three-phase circuits as well. Also remember this narrow window of operating voltage provides no safety factor for the long length of wire runs or branch circuits, such as submersible mo- tors or long offsets. This is when you need to increase your wire sizes, down the well and to the motor starter, to limit the voltage drop to less than 1%. This is another factor of cost your customer may not appreciate finding out at the end of the job rather than the start. Once again, remember the result from low voltage—more motor heat— and verify all aspects of this type of installation. Also, if possible, increase the amount of water or air flow past the motor to keep the motor cooler and less vulnerable to the inevitable increase of heat. Beware of Voltage Imbalance Times have changed and what was once acceptable is not acceptable now. This tenet certainly applies to voltage imbalance. Utilities are now stretching their existing power supplies farther and farther as well as lengths from power plants or substations. One of the results of this action is often voltage imbalance. The impact that just 1% of voltage imbalance can have on a three-phase submersible pump motor can be devas- tating (see Figure 1). In many cases use of a variable frequency drive can have a ENGINEERING from page 36 Figure 1. Effect of voltage imbalance on motor temperature. waterwelljournal.com 38 August 2015 WWJ