Applications Immersible Dry Pit Design Considerations Scott Hansen & Andrew Stein Dave Heiner Associates Always submerged Immersible Can be submerged for a finite amount of times. Dry Pit submersible Located in a Dry Pit and can be submerged. Typical Installation Environment Wet Well Motor Cooled by fluid in wet well Pump should always be submerged to promote cool running. Heat dissipates through the casing. Municipal wastewater markets use submersible motors for both wet and dry pit applications. These are totally enclosed, non ventilated (TENV) motors. Wet pit motors use the effluent for cooling and are designed to run continuously while submerged. These standard designs are also rated to run in air for 15 minutes when conditions require it. These motors can also be designed for continuous operation in dry pit applications by de rating a larger horsepower motor frame. This allows the motor to dissipate heat while running continuously in a dry pit application that only experiences flooding under unusual conditions, such as heavy rains or a backup in the system. 1
Explosion Proof Design motors are rugged and corrosion resistant, making them suitable for demanding applications. The motors have cast iron frames and end plates. Most motors come standard with 316 stainless steel hardware and 416 stainless steel shaft material. designs are available for hazardous and nonhazardous locations. An example of a hazardous location is a sewage application where flammable gases might be present. These locations may require an explosion proof motor design. Explosion proof motors are UL (Underwriters Laboratories) listed and CSA (Canadian Standards Association) certified for Division 1, Class 1, Groups C and D with a 1.0 Service Factor and T2A temperature code. Design motors use cast iron frames that are precision machined for tight fits between the parts. Machined fits have grooves with O rings to prevent water ingress to the motor. An epoxy filled, non wicking cable cap assembly protects the motor from moisture that could enter through the opposite drive end of the motor. Typically, two separate cables exit the cable cap epoxy potting compound; a four conductor power cable and a five conductor control cable. Standard lengths vary from 25 to 30 feet, but other lengths are available upon request. This cable should never be used to lift the motor. The drive end of submersible motors is a critical part of the design. Since the motors are designed to run continuously while submerged in water or effluent, they include features to keep water out. An oil filled chamber and a mechanical seal serve this function. Also, a moisture monitoring probe is used to detect moisture entering the chamber. The drive endplate has a special design that includes a chamber filled with oil. The oil acts as a barrier to trap moisture and provide sufficient time for shut down if water enters the motor. It also lubricates the upper part of the mechanical seal. The mechanical seal keeps moisture out of the motor. Some companies use a Type 21 mechanical seal as its standard submersible motor seal. This seal uses an inner and outer seal arrangement. It has both a stationary face and a rotating face. As previously stated, the upper part of the mechanical seal is lubricated by the oil in the endplate chamber. However, the lower part is lubricated by the pumped liquid. Carbon ceramic is the standard seal face material and is used in applications with relatively clean effluent. Tungsten carbide, which is used with more viscous fluids, is the most popular seal face material. For the most demanding slurry type applications, seal faces with tungsten carbide are an option. Pump manufacturers specify what type seal is necessary. Immersible Motor Ideal for dry pit applications where there is the possibility of flood plain type flooding events Exceeds IP67 requirements for submergence Can withstand up to 30 feet of submergence for a 2 week period, far exceeding industry standards Some models only allow immersion for 30 minutes at a submergence of 3 feet 2
Immersible Pump and Motor Immersible Features Ease of maintenance and serviceability No level controls, monitors, recirculating pump or piping needed Excellent efficiencies No cooling jacket necessary Designed to run submerged for limited time periods Lower thrust due to bearing frame which means longer bearing life The shaft penetrates the bottom only and is sealed using a triple redundant sealing system Another mechanical feature of the immersible design is an explosionproof style conduit box that uses a sealing compound and a nonwicking epoxy sealed cable assembly to prevent water from entering through the electrical connection at the motor. These motors use the same power and control cable configuration as the submersible motor design. Other standard features include: two normally closed thermostats, motor space heaters and a regreasable lubrication system. Immersible Cooling The TEBC design runs continuously in air and has a separate 1/2 horsepower motor running an external fan for constant velocity cooling. An end user supplied float switch turns off the blower motor if the water reaches a level near the cooling fan. The opposite drive end is totally enclosed, and the fan and blower motor are mounted separately to ensure that moisture will not enter the motor from the opposite drive end. These motors are also built with precision machined cast iron frames and endplates with grooves and O rings to prevent water ingress to the motor. Immersible Advantage Lastly, the immersible design has the benefit of reducing costs over the traditional immersible pump configuration, which uses a nonimmersible vertical pump motor mounted more than 20 feet above the pump and employs a jack shaft to reach it. The immersible motor mounts directly to the pump. This configuration eliminates the construction and installation costs incurred by building a motor support structure. Motor & Pump Coupled Dry Pit with Drive Shaft 3
Dry Pit Old Style Drive Shafts Rotate Require Guards Need to be aligned. Wear out and wobble Shaft Support and Design Shafted Pumps Drive Shaft Running Motor Mounting Dry Pit Lift Station Drive Shafts Couplings Alignment 4
Dry Pit Dry Pit Station Dry Pit Mounting Options Optional Cooling for Dry Pit s Layouts Product Cooled Sewage is used to cool the motor. As the pump runs the coolant flows. Other options for cooling Close Loop Cooling Glycol or other cooling media is circulated through the motor for cooling. Jacket Cooling Close Loop Cooled Cooling 5
How a cooling system works High Efficiency Motors Motor Efficiency Optimization Purchase motors with an inherently high power factor. Do not select over sized motors (the power factor decreases with reduced motor load) Install power factor correction capacitors (Motor running capacitors*) in parallel with motor windings Draws leading current which offsets some lagging current. Can increase full load PF to 95% (Max.) Convert to a Variable Frequency Drive Motor Efficiency Optimization Motor Running Capacitors are one of the more popular methods to increase motor power factors, and has the following list of benefits: Increase Power Factor Reduce reactive current flow from electric utility through cables and motor starters Less heat dissipation and kw losses (3% of motor demand) Savings potential increases as motor load decrease, and PF drops below 60% 70% (10% savings possible) Reduces utility PF penalty charges Increase total system capacity Intelligent Electric Motor Control Variable frequency drives Starting Methods Design Features Controls Variable frequency Drive 6
Design VFD Design Features Energy Savings Harmonic Filters VFD Protection Bearing Protection Grounding VFD Protection Harmonic Attenuation Eliminate Shaft Voltages Fluting Pitting Craters Level Control Transmitter Installation 7
Floats Seals Probes Alarms Moisture probes are necessary because seals wear, and the potential for moisture to enter the motor increases over time. This sensing system, consisting of two probes with a resistor between them, is placed in the oil inside the endplate. The probes are connected to a customer supplied control module that sounds a warning alarm or shuts down the motor if a change in resistance is detected. This ensures that the motor is shut down before any damage occurs. Worn seals will need to be replaced. This motor configuration is predominantly used for applications in which the motor will be submerged at all times. Pump Seal Failure Relay Questions? When is lunch? 8