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.

SubMonitor: Over/underload detection

In the last post, we reviewed how SubMonitor protects a three-phase motor against high or low voltage and how the default settings of plus or minus 10% nameplate voltage provide the optimum protection in just about every installation. However, if for some reason more voltage tolerance is required, we covered how SubMonitor’s DETAILED SETUP allows the voltage trip points to be set up to plus or minus 20% of the motor’s nameplate voltage.

In this post, we’ll look at how SubMonitor protects against overload and underload conditions. The classic case of an overload is a bound or dragging pump. In this scenario, the motor is being asked to do more than it has been designed to handle and must pull an excessive amount of current. This higher amperage overheats and damages the motor.

At the other end, an underload can be caused by a dry well, a broken coupling, a loose impeller, or a blocked inlet. In these cases, the motor is saying, “I’m not working nearly as hard as I should be. That means I’m not moving as much water as I should be and something must be wrong.” An underload condition won’t damage the motor, but it can indicate a dry well condition which will destroy the pump. An underload condition could also indicate a lack of cooling flow past the motor.

In any case, an overload or underload condition indicates that something is wrong with the installation and corrective action is needed. A reliable indication of both an overload and an underload is the amount of current the motor is consuming. SubMonitor measures current via three current transformers built-in to the unit. These are sometimes called the sensor coils. These coils continuously measure the amount of current in each motor leg. One can almost think of the three sensor coils as three separate Amprobes, one for each leg, continuously measuring current.

Using its three sensor coils, SubMonitor is always monitoring for an overload or underload condition. The default setting for an overload condition is 115% of the motor’s service factor amps. For example, from the Franklin Electric AIM Manual, a Franklin 6-inch, 460V, 40 horsepower submersible motor has service factor amps of 61.6. So, in the default mode, SubMonitor will take this motor off-line if any leg exceeds 70.8 amps (61.6 x 115% = 70.8). If this occurs, SubMonitor will leave the motor off-line for 10 minutes and then attempt a restart. SubMonitor will do this three times, but if after three attempts, the motor is still overloaded, SubMonitor will keep the motor off-line until the issue is corrected and SubMonitor is manually reset.

Just like the voltage protection, the above settings can be customized using DETAILED SETUP. The overload trip point can be set from 80% to 125% of service factor amps. The off-time can be customized from the default setting of 10 minutes to anywhere between 5 and 60 minutes. The number of attempted restarts can adjusted from 0 to 10.

Underload works the same way, but of course, with different numbers. The SubMonitor underload default is 75% of service factor amps. So, in the case of our motor above with service factor amps of 61.6, the underload trip point will be 46.2 amps (61.6 x 75% = 46.2). If SubMonitor senses an underload, it will leave the pump shut down for 30 minutes. In the case of a dry well, this may allow the well to recover. Once again, three restarts will be attempted before a manual reset is required. If a shorter or longer off-time is needed, it can be adjusted from 10 to 120 minutes, and the number of restarts set from 0 to 10. In terms of the underload setting itself, it can be adjusted all the down to 30% of service factor amps (less sensitive) and up to 100% of service factor amps (more sensitive).

Even though SubMonitor offers a great deal of customization on the overload and underload settings, note that in nearly all cases, the default settings are the optimal settings and will do the best job of protecting the installation while minimizing false trips.

SubMonitor’s overload and underload monitoring deals with the values in each leg of a three-phase motor. But there’s another current parameter here that is just as important, and that’s the balance between the three legs. We’ll look at that in the next post.

FranklinTECH goes on the road: Southeastern US

Throughout the year, Franklin holds all-day training seminars at our three FranklinTECH campuses and other selected locations across the country. These seminars focus on water system basics, the proper application of Franklin Electric submersible products, and troubleshooting. As always, these are provided at no cost to you, and lunch is even included.

As part of this training commitment, Franklin Electric is pleased to announce the following dates and locations for upcoming all-day seminars in the Southeast Region:

These seminars count toward Certified Contractor status for the 2013 Key Dealer program, and in most cases, qualify for Continuing Education credit as well.

You can also take advantage of the next session at our training center in Wilburton, Oklahoma on September 11- 12.

To register for a session, contact our Hotline at 800.348.2420 or hotline@fele.com. Space is limited and registrations are handled on a first come, first served basis, so get your spot reserved as soon as possible. We hope to see you soon at a FranklinTECH seminar this fall!

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.