Solar Power for Subs: Sizing the System

In the third post in our series on solar pumping systems, we’ll start our discussion with sizing a submersible solar pumping system. With today’s web tools, sizing is usually remarkably easy, as most solar manufacturers offer some type of online sizing tool. For our example, we’ll use Franklin Electric’s SolarPak Selector. To find it, go to www.franklin-electric.com/solar, which will take you to Franklin’s solar home page.

Solar sizing1

From here, click on “Solar Selector”. You should see the following page:

Solar sizing2

There are three things we need to specify on this page in order to properly size our solar pumping system:

1. Where is the installation located? (This will help determine how much sun is available.)
2. How much water is needed in terms of pressure and volume? (Just like a conventional system.)
3. What are the electrical characteristics of my solar panels?

In the first step, the system calculates how much sun should be available based on the latitude and longitude of the installation. Chances are, you don’t have those numbers handy, but that’s not a problem. Although you can enter the latitude and longitude of the installation directly, an easier way is to select “Look up Your Latitude and Longitude”. With this option, a map will pop up and give you two options: 1) move the crosshairs on the map to the location or 2) simply enter the name of your location in the box at the top of the page and the SolarPak Selector will do the rest. If you do enter the latitude and longitude directly, don’t forget that in the Western Hemisphere, longitude is expressed as a negative number. You also have the option to use the device’s location (iPad, laptop, etc.). As soon as you open the SolarPak Selector page, you should see a pop-up menu that asks for permission to track your physical location, as you can see on the bottom of the screen shot above. If you allow this, your coordinates will automatically load into the SolarPak Selector. Of course, your device should be somewhat close to the installation’s location for this to work properly.

If you choose to use the map to look up your coordinates, you should see this screen:

Solar sizing3

For our example, we’ll use Amarillo, Texas, which we would enter into the box at the top left of the screen.

Solar sizing4

The SolarPak Selector calculates that on average, Amarillo receives 5.35 hours of usable sunlight each day for our solar pumping system.

Solar sizing5

Step 2 (and actually, the order here doesn’t matter) is to specify how much water we need per day and at what total dynamic head. Note that our volume requirement per day can be expressed in cubic meters (m3), gallons, or liters. The drop down box allows you to select your unit of measure. Similarly, Total Dynamic Head can be expressed in meters, feet, or PSI, again specified with the adjacent drop down box.

For our example in Amarillo, we’ll say that on average, we need 900 gallons per day at 200 feet of head. We enter this into the Output Requirements section on the left of the SolarPak Selector page.

Solar sizing5

Once we enter this information, the SolarPak Selector goes to work and provides us with a wealth of information, including which Franklin system is recommended for this installation.

The only input we haven’t covered is solar panels. Simply enter the manufacturer-listed Wmpp, Vmpp, and Voc values (covered in our last post) into the boxes provided in the section called Solar Panel Characteristics. The SolarPak Selector will do the rest, helping you define your array.

That’s all the information the Solar Selector requires to size the system. In our next post, we’ll move on to what information the Solar Selector does with that information.

Solar Power for Subs: Part 1

solar installHarness the power of the sun; over time, that age-old dream has become a reality. With solar technology, we can use the sun’s energy to do work, to move things and drive machines. Today several manufacturers, including Franklin Electric, offer solar pumping systems that harness the power of the sun to get water from the ground—even where there’s no power grid.

Over the next several weeks, Franklin AID will examine in detail how these systems work, their sizing, their proper application and set-up, and their advantages and disadvantages. By the end of this series, you will have a very complete understanding of where solar pumping fits into your product portfolio, along with how to install one of these systems.

Why Solar?

To begin with, why use a solar pumping system? There are two simple answers: 1) because there’s no power where the water well is located, and 2) because the power is free. But there can be other reasons to use a solar pumping system that may be less obvious. Perhaps power is available where you need water, but it’s unreliable. If that location is remote, the end user may not even be aware when the power is off. Couple that with a critical water supply and the simple reliability of solar pumping can make a strong case for it. A prime example here is open range livestock.

In other cases, there may be power nearby, but the well is several hundred feet away from the power source. The cost of trenching and running copper to the wellhead could often outweigh the cost of a solar pumping system. In other areas, electrical power may available but very expensive. Since the sun shines for free, solar simply makes the economic sense.

Finally, some people want to use greener products as much as possible and nothing fits the bill better than solar. Marketing reasons can even enter the picture. For example, organic farm operations that market themselves as such may want to use solar pumping for irrigation in order to be able to promote this to their customer base. In such cases, electricity from the grid may be readily available.

Why Not Solar?

Of course, solar pumping by definition has a big drawback: it needs the sun to operate.  As a result, pumping systems that are strictly solar can’t deliver water 24 hours a day. But irrigation normally isn’t required 24 days a day, and in other applications, a storage tank or cistern may store more than enough water when the sun is down or the weather doesn’t cooperate.

In a residence or business, however, we do want water to be available under pressure 24 hours per day. So although stand-alone solar pumping systems aren’t likely to completely replace conventional residential systems, that doesn’t mean they can’t be combined with battery-powered systems or traditional grid systems. We’ll cover these options later.

In summary, where solar systems really come into their own are in applications such as livestock watering, irrigation, vineyards, and anywhere a grid power is unreliable or nonexistent. That’s a pretty exciting development for our industry.

Stay tuned for the next post in this series, where we’ll cover the starting point of all solar pumping systems: the panels.

SubMonitor: What it CAN’T do

In the last few Franklin AID posts, we’ve discussed how SubMonitor protects a 3-phase submersible installation against a wide variety of potentially harmful conditions. It does this by continuously monitoring voltage, current, and a heat sensor in Subtrol-equipped motors.

On the mechanical side, however, there are a few things that SubMonitor just can’t protect against. One of these is water hammer. Water hammer most often occurs when a check valve is not used, has been improperly installed, or leaks. As a result, when the pump stops, the water drains back down through the pump inlet and creates a vacuum in the discharge piping. When the pump restarts, water rushes to fill that vacuum at a high velocity. When it strikes the hardware or stationary water above, it causes a hydraulic shock that can split pipes, break joints, and damage the pump/motor. The picture below shows a thrust bearing that was destroyed by water hammer.

Water Hammer

Another mechanical condition that SubMonitor won’t protect against is radial side loads. The most common cause of side loading is misalignment of the pump and motor. This creates a side which, depending on the how extreme that load is, can cause a rapid failure in the radial motor bearing near the top of the pump.

Radial bearing

Finally, another condition that SubMonitor won’t protect against is upthrust. As the name implies, upthrust occurs when a large volume of water pulls the impellers upward. This carries across the pump coupling/motor shaft assembly and pulls the shaft up with it. This generally occurs at start-up, and the pump and motor are designed to handle this on a momentary basis. However, if the pump is operating on the far right-hand side of the curve for long periods of time, the resulting upthrust can damage the motor and pump.

When looking at these three mechanical failure modes, it may seem obvious that no electronic protection device could guard against these types of failures. These situations underscore the importance of using good installation procedures. Combined with the protection that SubMonitor offers against events that you can’t control, your submersible installation will reliably deliver water for years to come.

A Timely Topic – Using a Generator with a Franklin Sub

As a result of the recent weather events on the east coast, Franklin Electric’s Water Systems Technical Hotline has been receiving a high number of calls concerning the use of generators with submersible installations. In order to provide an easy reference for all, it makes sense to review generator sizing here in Franklin AID.

Note: The use of generators must follow all local, state, and national electrical codes. ALWAYS consult these codes before installing a generator. In addition, make sure the generator is properly ventilated and that you are familiar with its operating instructions before putting it into use.

Guidelines specific to using an engine driven generator with a Franklin submersible motor can be found on page 5 of the Franklin Electric AIM (Application, Installation, and Maintenance) Manual.

To determine proper sizing, refer to Table 5 on page 5 of the AIM Manual. (Click the illustration above for a close-up view.)Note that the numbers in the sizing chart apply to both 3-wire and 3-phase motors. If it’s a 2-wire installation, the minimum generator sizing is 50% higher than listed in the chart. This is because of the higher starting current required for 2-wire motors.

Also note that the sizing chart only applies to one submersible motor. If other devices are being powered, they must be identified along with their power consumption. Even though some of these items may not run continuously, they still need to be taken into account, per the generator manufacturer’s recommendations.

The frequency of the voltage delivered by the generator will be a function of the engine’s RPM. Motor speed varies with the frequency of the output voltage, and since pump affinity laws relate power to performance, generator sizing can have significant impact on pump output. For example, if the generator is putting out a voltage at a frequency that is below 60 hertz, the pump will not meet its performance curve. Likewise, if the frequency is above 60 hertz, it may overwork the motor and trip its overloads. The generator manufacturer’s instructions will contain guidance on how to adjust the generator’s frequency. Of course, you’ll also need a voltmeter that measures frequency. Most of today’s digital voltmeters contain this function.

The thrust bearing in a submersible motor requires a minimum speed of 30 hertz (about 1800 RPM), so it is important to start the generator before starting the motor. Likewise, it is equally important to stop the motor before the generator is shut down. Failure to do so may result in damage to the motor’s thrust bearing during start-up and coast down. The installation of a simple transfer switch will allow the motor to be turned on and off independently of the generator. (Note: circuit breakers should NOT be used for this function.)

More critically, a transfer switch also functions as a safety device to isolate the utility electrical supply from the generator. Without a transfer switch, the generator can back feed into the utility lines and, in a worst case scenario, cause serious injury or death. Unfortunately, the transfer switch is one of the more commonly overlooked safety devices required by the National Electrical Code (NEC).

Code also requires that the generator be properly grounded in order to protect against electrical shock in the event of a fault. Like all electrical conductors, the ground wire must be correctly sized for the load it is designed to carry.

Hopefully, you won’t find yourself in a no-power situation that necessitates using an engine-driven generator. In the event that you do, taking appropriate precautions and following this protocol will help make sure you can get your Franklin sub back online.

Reduced Voltage Starters (RVS) and Franklin Submersible Motors

REDUCED VOLTAGE STARTERS
This month’s technical topic is REDUCED VOLTAGE STARTERS. One of the misconceptions about these devices is that their function is to protect the motor. This is not the case, and as a matter of fact, all Franklin 3-phase submersible motors are suitable for full-voltage starting. Under this condition the motor speed goes from zero to full speed within a half-second or less. Simultaneously, the motor current goes from zero to locked rotor amps, then drops to running amps at full speed. Although it doesn’t harm the motor, this may dim lights, cause momentary voltage dips to other electrical equipment, and shock load power distribution transformers.

Reduced voltage starters limit this voltage dip, and power companies often require them. Another reason for a reduced-voltage starter is to reduce motor starting torque. That, in turn, reduces the stress on shafts, couplings, and discharge piping. In addition, reduced-voltage starters slow the rapid acceleration of the water on start-up. This helps to control upthrust and water hammer. Continue reading

Overload Protection of Three-Phase Submersible Motors

The characteristics of submersible motors are different from standard, above ground motors. Submersible motors require special overload protection. In order to properly protect a three-phase submersible motor, ambient-compensated, quick-trip overload protection must be used. This can be either a fixed heater or adjustable overload relay, as long as it is ambient-compensated and quick-trip. Franklin Electric?s Subtrol-Plus system can also be used to protect Subtrol-equipped motors.

Ambient-Compensated: Ambient-compensated overload protection must be used to maintain protection in both high and low air temperature areas. Three-phase pump panels are typically suitable for indoor and outdoor applications within temperatures of +14°F (-10°C) to +122°F (50°C). Pump panels should never be mounted in direct sunlight or high temperature locations as this will cause unnecessary tripping of overload protectors. A ventilated enclosure, painted white to reflect heat, is recommended for outdoor high temperature locations.

Quick-Trip: If the motor is stalled or the shaft cannot turn, the overload protector must trip quickly to protect the motor?s windings. In some areas, it is customary to specify that the overload must trip within 10 seconds with 500% normal current (IN). Quick-trip heaters and overload relays shown here, will respond within 10 seconds. Franklin?s Subtrol-Plus responds within 3 seconds. Heaters marked ?Standard Trip? are typically Class 20 or 20 second response time. Standard Trip, Class 20 and some Class 10 overloads will allow submersible motor burn-out before tripping. Quick-trip overload protection must be used.

The time-current trip curve, as shown in Figure 1, shows the response time for different classes of overloads under different running scenarios. The bottom axis of the chart shows different multiples of normal currents. The side axis shows ?Time? in seconds. The first bold vertical line represents the amperage if the power source single-phases on the motor side of the transformer (secondary side). This can occur if a fuse blows or a contact fails. This condition causes the normal line amperage to increase to 173% of normal in two phases and drop to zero in the third phase. The second bold vertical line represents the amperage if the power source single-phases on the incoming side of the transformer (primary side). This can occur if a power line is broken in a storm or car accident. This condition causes the normal line amperage to increase to 230% of normal in one phase and 115% of normal in two phases. The third vertical line represents a locked rotor or bound shaft condition. As you can see from the motor burnout curve or shaded area, the motor must be disconnected with a quick-trip device or severe motor damage can occur. The best protection, as the bold horizontal line shows, is Franklin?s Subtrol-Plus which disconnects the power within 3 seconds. Continue reading