Drought Insurance

Even with reliable brands and installation, some conditions are simply out of our control. For instance, half of the U.S. is currently experiencing a drought and has been for some time. During drought conditions, water levels in a well may drop below pump intake, causing an underload situation. With the lack of snow during the past winter and little rain during the spring and summer, wells could experience this drop either temporarily or long term.

Without significant rainfall to recharge aquifers, many private well systems are susceptible to the adverse impact of dry well conditions. If a well goes dry, the underload condition it causes can destroy the pump and/or motor.

Monitoring and diagnosing load issues can save a pump from damage and potential system failure caused by drought. Investing in a protection device before trouble hits can save a lot of time and money for you and your customer in the long run by shutting down the system to prevent damage when a dry well occurs.

Pumptec, for example monitors motor load and power line conditions to provide protection specifically against dry well/underload, as well as for waterlogged tanks and abnormal voltage. Upon detecting a fault, it interrupts power to the motor to give the well a chance to recover.

Franklin Electric wants to help make guarding systems from dry well conditions as easy as possible and Pumptec products are an ideal way to ensure a long and reliable pump life. During a lack of precipitation like we are currently experiencing, wells are more prone to going dry, due to either a drop in the water table or the fact that the well is getting used more. Sometimes the best investment isn’t the product itself, but what you do to protect it. We encourage you to protect your investment and make sure that once you put a pump downhole, you won’t have to see it again.

For more information about Pumptec, please visit our website, or get more information on how to protect a submersible water system from adversity, contact our Hotline at 800.348.2420 or hotline@fele.com.

 

Column-by-Column: Greatest Hits

This week, as we wrap up our column-by-column series on single- and three-phase motor specifications, we’d like to touch on what you might call the “greatest hits” from the series. The specification tables on pages 13 – 14 (single-phase) and pages 22 – 28 (three-phase) are very complete, but in the field, there are only a few columns that are used day-to-day. This post will highlight these columns.

Keep in mind that much of the information specifically mentioned in this post concerns single-phase motors. However, as we know from our post Understanding Three-Phase Motors, although there are more three-phase tables, looking at the column headings you can see that it’s the same information.

The first column on our most used list is Maximum Load, which has two parts, Amps and Watts. Amps in this context is often referred to as service factor amps or max amps. Maximum Amps is important because it tells us how hard the motor is working. The more water we’re moving, the more current we will need. This translates into where you’re operating on the pump curve. It can also be very helpful in troubleshooting issues and tell us if we’re overloading the motor.

The maximum power in watts value doesn’t play into troubleshooting; generally, we don’t measure watts in the field directly. Watts are important to know when calculating the cost to operate a submersible system. For more on that topic take a look at the Franklin in the Field post Deal of a Lifetime.

Moving along in our recap, next comes Winding Resistance in Ohms. Always remember that winding resistance is a power-off check. Power must be disconnected and locked out.

All single-phase motors (2- and 3-wire) have two windings: a start winding and a run winding. However, on 2-wire motors we don’t have access to the start winding; therefore, in the AIM Manual, only the winding resistance for the run winding is listed. In the case of a 3-wire motor, winding resistance is listed and can be measured for both the start and run windings.

Three-phase motors, on the other hand, have three identical windings, and therefore current and resistance measurements are the same. That is why in the AIM Manual, under three-phase motors, we only need one line of information.

Regardless of motor type, what does winding resistance tell us? It tells us the electrical condition of the motor and other conductors, such as the drop cable and splices. When troubleshooting and measuring winding resistance, we’ll generally get one of three readings: zero, infinity, or close to the table value. If the reading is zero, the winding (or some other part of the conductor) has shorted. A reading of infinity indicates the winding is open. In either of these cases, the motor or other failed conductor will need to be replaced or corrected.

Continuing on in our column-by-column review, we reach Locked Rotor Amps. Sometimes abbreviated as LRA, Locked Rotor Amps is exactly what the name implies: the amount of amps drawn if the rotor is locked and can’t move while electrical power is applied. These amperages generally run about five times higher than maximum running amps.

One example of LRA is a bound pump; however, LRA also occur at the moment of start up. Every time a motor is started, it pulls Locked Rotor Amps for a split second. Even though this start up amperage occurs for only a short time, it could be enough to trip the system. Knowing the value of Locked Rotor Amps can be an important aspect on some installations, especially in terms of making sure the system has appropriate electrical service.

Locked Rotor Amps is also important in the aspect of sizing reduced voltage starters (RVS). To specify a reduced voltage starter we need information located in our next column, KVA Code.

The KVA Code lets us know which reduced voltage starter is needed for a specific motor. This code defines a group of motors based on a combination of their voltage, locked rotor amps, and horsepower. An RVS allows a system to ramp up to full voltage instead of applying power to the motor all at once, thereby reducing the amount of in-rush current.

KVA Code wraps up page 13 for single-phase motors, but we don’t want to forget about single-phase fuse sizing, located on page 14 of the AIM Manual.

Remember that fuses and circuit breakers are not overloads. Overloads protect a motor and are found in either the motor or the control box. Fuses and circuit breakers primarily only protect the electrical system. That is, they protect the wiring by tripping or blowing due to excessive current.

Although fuses and circuit breakers have the same function, they operate differently. A fuse is a type of low resistance resistor that acts as a sacrificial link to provide over-current protection. A circuit breaker is a mechanical over-current protection device, using an electromagnet to literally flip a switch off and cut power. Circuit breakers can be reset, whereas fuses must be replaced.

 

On page 14 one of the first things we come to under amperage of fuses or circuit breakers is Maximum Per NEC and Typical Submersible. Franklin Electric recommended fuses are found under the Typical Submersible column and fall within the requirements of the US National Electric Code (NEC). These fuses and circuit breaker amps are calculated specifically for typical Franklin Electric submersible motor performance. Electrical codes require that fuse or circuit breaker protection be provided as part of an installation, and it’s critical these components be sized correctly.

The Franklin AIM Manual offers a wealth of information on all aspects of motor specifications, but there are a few key sections of information that are used more frequently. In the day-to-day of a water systems professional, the above mentioned topics are what you are going to see the most. While some of the information may be available on a motor nameplate, once it’s in the ground the AIM Manual keeps it readily available for reference.

For more in-depth and specific information on the above topics, please take a look at their individual posts within the column-by-column series, and, as always, if you have further questions or need help with troubleshooting, please call our Technical Service Hotline at 800.348.2420 or email at hotline@fele.com.

Column-by-Column: KVA Code Decoded

During our Column-by-Column series on single-phase motors, we talked about Locked Rotor Amps and briefly touched on KVA Code, saving it for a three-phase discussion. Since we discussed the three-phase motors specifications listed on pages 22 – 28 of the Franklin Electric AIM Manual in our last post, now is the perfect opportunity to revisit KVA and where that code letter comes from.

KVA Code is most commonly used to specify a reduced voltage starter. Reduced voltage starters are more common and important for higher horsepower, three-phase motors since they pull more amps than single-phase motors. As submersible installations and the motors in them get larger, Locked Rotor Amps get much larger as well.

For example, a system with a 6-inch, 50 hp, 460 V motor has a maximum running load of 77 amps. However, that same motor has locked rotor amps of 414. As we discussed in the post Locked Rotor Amps and KVA Code, if the motor is started directly across the line (called DOL for direct-on-line), it will try to pull 414 amps at the moment of start-up. In many cases, this is far more amperage than the electrical service can provide.

That’s where reduced voltage starters come in. Reduced voltage starters allow the system to ramp up instead of applying full voltage to the motor all at once. The reduced voltage starter aids a system pulling too many amps at start up; in this case, the motor will never see the locked rotor amps of 414, saving the system from tripping and possible overload.

The KVA Code is used to specify which reduced voltage starter is needed for a specific motor. This code letter defines a group of motors based on a combination of their voltage, locked rotor amps, and horsepower.

So how do we get a specific KVA Code letter? This range of numbers is found using the following equation:

K = Kilo (1000)

V = Voltage

A = Amperage (Locked Rotor AMPs)

(Volts x Amps) / 1000 = KVA                          single-phase

(Volts x Amps x 1.73) / 1000 = KVA              three-phase

KVA / HP = Rating (Code Letter)

Each KVA Code letter corresponds to a universal KVA/HP range, as defined by NEMA.

Going back to our 6-inch, 50 hp, 460 V motor:

(460 x 414 x 1.73) / 1000 = 329

329 / 50 hp = 6.6

By referencing the KVA Code chart we see the corresponding letter is H, and we have reached the correct KVA rating. Luckily, the math is already done for us and all KVA Codes are located in the AIM Manual, as well as on the motor nameplate.

That wraps up our discussion on Locked Rotor Amps, KVA Code, reduced voltage starters and the columns of three-phase motor specifications, starting on page 22. Come back next week when we will review “what you really need to know” from this series.

Column-by-Column: Understanding Three-Phase Motors

Over the last several weeks, we’ve examined each column in the single-phase motor specification table on pages 13 and 14 of the Franklin Electric AIM Manual. This week, we’ll take a quick look at the equivalent three-phase information found on pages 22 – 28.

With so many pages of three-phase motor specifications, at first glance it may look as if three-phase motors must have more going on than their single-phase counterparts. However, the “more” that’s going on here is because three-phase motors come in far more ratings than single-phase. Single-phase power has some limitations, and as a result, Franklin single-phase motors are only offered from ½ to 15 hp. Franklin three-phase motors are available in ratings all the way from ½ to 200 hp.

In addition, there are more three-phase voltages. Whereas single-phase motors are either 115 or 230 V, three-phase motors can have five voltages: 200, 230, 380, 460, and 575 V. So, more hp and voltage ratings mean more models. In fact, Franklin offers three-phase submersible motors for just about every application.

However, although the tables are larger, looking at the column headings you can see that it’s the same information that we already covered for single-phase. Specifications such as maximum load, line (winding) resistance, and locked rotor amps all have the same meaning whether we’re talking single- or three-phase.

There is one difference to note. Notice that all of the three-phase motors only have a single line of data, whereas most of the single-phase motors have 2 or 3 lines of data. This is because single-phase motors have two different windings, a start (auxiliary) winding and a main (run) winding, and there are physical and electrical differences between them. So, when measuring maximum load, for example, in a single-phase motor, there are three readings to take (run, start, and common), and each of these measurements will be different. However, three-phase motors have three identical windings. Therefore, current and winding resistance of each will be the same. So, although there are still three readings to take with a three-phase motor, the expected value is the same for each one since each winding is the same. Therefore, a single line in the table applies to all three windings.

Another difference between single- and three-phase motors is that 3-wire single-phase motors require a control box. Although a panel of some type is generally used, three-phase motors do not require a control box. As a result, we don’t need to make a distinction between the standard control box and a CRC control box.

All of this makes three-phase motors actually simpler than single-phase motors. If you know the information from our series on single-phase motors, then you already know three-phase motors. The differences in the tables don’t actually complicate things, but simplify the system and may even offer you new business and product opportunities.

No matter what kind of Franklin motor you are working with, if you have application, installation, or troubleshooting questions, contact our Technical Service Hotline at 800.348.2420 or email at hotline@fele.com.

Column-by-Column: Single-Phase Fuse Sizing

In our column-by-column series over the last few weeks we’ve been looking at Table 13 of the Franklin Electric AIM Manual on Single-Phase Motor Specifications. Opposite this page is Table 14, Single-Phase Fuse Sizing. In this post, we’ll examine the six columns in this table listed for each submersible motor.

As a first step, it’s important to understand that fuses and circuit breakers are not overloads. Overloads, which are found either in the motor or the control box, protect the motor. Fuses and circuit breakers, on the other hand, protect the electrical system. That is, they protect the wiring in the circuit and trip or blow to interrupt excessive current. This prevents against wire damage from overheating or even fire.

Although fuses and circuit breakers have the same function they operate differently. A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over-current protection. When the current gets beyond a certain threshold a small link inside the fuse gets hot enough that it melts, thereby “blowing the fuse” and causing power to be cut from the system.

Fuses are offered as standard or dual element / time delay fuses. A standard fuse is a fast response fuse, which means it will trip instantly any time the amperage exceeds the fuse rating. In any system the standard fuse offers the least amount of protection, as it allows the current to run higher before tripping. One can think of a standard fuse as providing catastrophic protection.As the name implies, dual element / time delay fuses combine two elements into one package. One element operates like a standard fuse. However, a second element reacts at a lower current but is far slower to react. This time delay element provides better system protection and allows the momentary start-up current to pass through. Although not an overload per se, this arrangement offers some secondary overload protection to the motor.

A circuit breaker is a mechanical over-current protection device, using an electromagnet to literally flip a switch off and cut power. Being electromechanical, circuit breakers can be reset whereas fuses are sacrificial and must be replaced.

With that as background, let’s take a closer look at Table 14.

The first thing you may notice is that there are two broad categories, Maximum per NEC and Typical Submersible. The column Maximum Per NEC represents maximum fuse and circuit breaker size requirements as recommended by the US National Electric Code. The NEC offers a broad, general rating system that applies to all motor types. Amperages in these columns are calculated by the NEC using factors including Locked Rotor Amps and Maximum Load Amps. The amps recorded here are the highest amount of amps recommended for a fuse or circuit breaker.

Moving to the right we find the column labeled Typical Submersible, specifying the same three categories below but at lower amperages. These Typical Submersible sizes are Franklin Electric-recommended, calculated specifically for typical Franklin Electric submersible motor performance by engineers utilizing decades of experience in the field.

Turning our attention to the three columns below, we see values for the three types of over-current protection we previously discussed: Standard Fuse, Dual Element Time Delay Fuse, and Circuit Breaker.

The idea behind the recommended over-current protection amps is to get the lowest amp fuse or circuit breaker that will allow the brief start-up amps to pass through without tripping and still provide some protection for the motor.

For example, the Maximum Per NEC Standard Fuse on a 4-inch, 2-wire, 115 V motor is 35 amps. This means that a 35 amp standard fuse is the smallest able to withstand the brief 64.4 start-up amps (or Locked Rotor Amps) of the motor without nuisance-tripping. However, it also means that this motor, with a maximum load of 12.0 amps, has the potential to run at up to 35 amps before tripping the fuse, possibly overloading the system and offering little motor protection.

The Maximum Per NEC Dual Element Fuse recommended for this motor is 20 amps while the recommended circuit breaker size is 30 amps.

Franklin’s Typical Submersible columns recommend a standard 30 amp fuse, a 15 amp dual element fuse, or a 30 amp circuit breaker. Based on experience, these sizes work, protect the wire, and offer the motor some secondary overload protection. If the amps were any smaller, our system could nuisance-trip at start-up.

Electrical codes require that fuse or circuit breaker protection be provided as part of the installation, and it’s critical that these components be sized correctly. Hopefully, this post has shed some light on how each submersible motor listed can have six different fuse or circuit breaker sizes listed and where these numbers come from.

Column by Column: Power Factor

As we continue our column-by-column review of the single-phase motor specifications on page 13 of the AIM Manual, this week we find ourselves at the column marked PF, or Power Factor. If you read the recent post, Most Missed Question, you’re already a step ahead.

In an AC (alternating current) system, voltage and current are not completely in phase. That is, their peaks and valleys don’t line up in perfect phase.This difference in phase between the voltage and the current is the power factor. As it turns out, the more in phase the voltage and current are, the higher the power factor. As a matter of fact, in the perfect world picture, the power factor is 100% (expressed as 1.0). In the real world picture, the power factor is around 75% (expressed as 0.75).

Note that because the voltage and current can never be more than 100% in phase, power factor can never be greater than 1.0. Conversely, it can also never be smaller than 0.

So what? Why does power factor matter?

Power factor is important because it affects our motor’s power consumption. Back in school, you probably learned that

Volts x Amps = Watts (Power)

While that is true in a DC (direct current) system, an AC system never gets quite as much power out of a system as is put into it. That lag between volts and amps we discussed above is the reason for that. Therefore, when calculating power consumption for an AC system, the equation looks like this:

Volts x Amps x Power Factor = Watts (Power)

By the way, you may also note that the more efficient the motor, the higher the power factor.

Hopefully by now you’ve realized that everything on this page works together. Next week we’ll move to the right to the Locked Rotor Amps column as we get closer to wrapping up the series.

Column-by-Column: Efficiency %

As we return to page 13 of the AIM Manual this week, this week’s post will focus on the column labeled Efficiency %.

Simply put, electric motors take electrical energy and convert it into mechanical energy. That is, we put electricity into the motor and out comes the rotation of a shaft that powers a pump. However, it’s not a “one-for-one” conversion; we don’t get the same amount of energy out of the motor that we put into it. The energy that is lost in the conversion process gets turned into heat. This happens not just with motors, but with all devices that convert energy from one form to another. Perhaps the most obvious everyday example is a light bulb. Only a small portion of the electricity that goes into a light bulb comes out as light energy. The rest becomes heat, as anyone who has touched a lit bulb knows.

This ratio between the amount of energy that we get out of something versus what we put into it is called efficiency. It’s generally stated as a percentage, but it can also be stated as a decimal.

The efficiencies of Franklin Electric’s single-phase submersible motors are listed on page 13 of the AIM Manual. Like several of the other columns on page 13, there’s a column for full load (FL) and one for maximum load, also called service factor load (SF). [For an explanation of service factor, see the Franklin AID post on Full Load Amps and Max Amps.] Since the motor operates at or near service factor most of the time, we’ll limit our focus to efficiency at service factor, or the SF column in the table above.

Using the 1 hp, 3-wire motor as an example, the table shows that the motor is 65% efficient. Once again, this simply means that 65% of the electrical energy that goes into the motor is available to turn the pump.

We can even calculate this ourselves as follows:

This is a 1 hp motor, but to keep the units consistent, we’ll use the equivalent value in kilowatts, in this case 0.75. We’ll also convert this to watts by multiplying by 1000 (kilo=1000). So, mechanically, this is a 750 watt motor. Since there’s a service factor involved of 1.4, this motor is actually a 1050 watt motor (750 x 1.4 =1050).

Now we know what we get out of the motor in terms of mechanical energy, but how much do we put into it in terms of electricity? That is found in the Maximum Load column under watts. That value is 1600 watts. So, we put 1600 watts of electricity into the motor and get 1050 watts out. That means the efficiency is:

1050 watts / 1600 watts = .65, or 65%

(output     /      input      =  efficiency)

This matches the 65% listed in the efficiency column.

Keep in mind that so far, we’ve just covered motor efficiency. The pump’s not going to be 100% efficient either, but we’ll cover that in another post.

In actual practice, the efficiency of smaller single-phase motors is generally not too critical. Because it actually costs so little to run a residential single-phase motor [refer to the Franklin in the Field post The Deal of a Lifetime], efficiency gains may only result in pennies of savings per day. Efficiency becomes more important, however, in applications with greater power consumption.

Next week we’ll move on to power factor in our attempt to make the numbers make sense, column-by-column.