A product lineup of various Siemens VFD drives used for industrial motor speed control.

Siemens VFD Drives: A Beginner’s Selection Guide

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Estimated reading time: 10 minutes

Introduction: Your Guide to Selecting the Right Siemens VFD Drives

Selecting the right Siemens VFD drives is a critical decision for any industrial application. It directly impacts operational efficiency, energy use, and equipment longevity. These advanced motor controllers provide precise regulation of an AC motor’s speed and torque. Siemens offers the comprehensive SINAMICS family of drives to meet these needs. According to Digi-Key: VSDS Installation, this family is engineered to cover the full spectrum of motor control applications. Consequently, a thorough understanding of this portfolio is essential for engineers aiming to optimize their systems.

The primary advantage of a Siemens variable speed drive is its effect on energy efficiency. It works by matching motor speed to the actual load demand instead of running constantly at full power. In addition, these industrial VFD systems deliver smoother startups and stops. This process reduces mechanical shock and extends the life of belts, gears, and couplings. The SINAMICS platform is exceptionally broad and scalable. As highlighted by Precision Electric, it offers everything from basic drives to high-performance motion control solutions. This ensures a perfectly matched Siemens motor controller is available for any task.

However, navigating the extensive options requires a clear assessment of your application. You must understand technical needs like voltage, horsepower, and control features. Important factors also include environmental conditions and safety functions like Safe Torque Off (STO). Compliance with standards like NFPA 70E is also critical. As noted by RS Components & Siemens Industrial Drives, newer drives offer enhanced performance and specialized functions. Therefore, this guide will break down the key specifications across the SINAMICS family. We will provide a practical framework to help you confidently select, install, and maintain the ideal Siemens VFD.

Step 1: Understanding Your Motor and Load Requirements

The foundational step in selecting the right siemens vfd drives is a thorough analysis of the motor’s nameplate. This data dictates the drive’s essential specifications, so you must identify the voltage, full-load amperes (FLA), horsepower (HP), and operational frequency. Furthermore, the service factor is a critical detail, as a value greater than 1.0 may necessitate a drive with a higher current capacity to prevent overload faults. According to Digi-Key: VSDS Installation, matching these core parameters is non-negotiable for ensuring system compatibility and safe operation.

Following the motor analysis, understanding the application’s load profile is equally important. Loads are typically classified as either variable torque (VT) or constant torque (CT). For instance, centrifugal fans and pumps are common VT loads, where torque needs are low at low speeds. In contrast, applications like conveyors or crushers are CT loads, requiring consistent torque across all speeds. This distinction is vital, as Precision Electric notes that heavy-duty applications require drives with superior overload capabilities.

A product lineup of various Siemens VFD drives used for industrial motor speed control.

Choosing the correct model from the wide range of Siemens VFD drives is the first step in optimizing your industrial motor’s efficiency and performance.

Finally, you must synthesize this information to select an appropriately rated Siemens variable speed drive. The drive’s continuous amp rating must exceed the motor’s FLA, and its duty rating must match the load type. A constant torque application, for example, requires a “heavy-duty” rated drive capable of handling at least 150% overload for one minute. Properly sizing the drive not only prevents nuisance tripping and thermal damage but also maximizes energy efficiency, a key benefit of modern adjustable frequency drives as emphasized by sources like Eaton and Globalindustrialsupplies.

Step 2: Decoding the Portfolio of Siemens VFD Drives

Once you have defined your application’s needs, the next step is to navigate the extensive portfolio of Siemens VFD drives. The cornerstone of their offering is the SINAMICS family, a comprehensive range of Siemens inverter drives designed to address nearly any motor control challenge imaginable. According to Digi-Key: VSDS Installation, this platform scales from basic speed control for a single motor to complex, multi-axis systems for sophisticated machinery. Consequently, understanding the primary SINAMICS sub-series is essential for making an informed selection that aligns with your technical and budgetary requirements.

The SINAMICS family is broadly categorized to simplify selection based on application complexity. For instance, the SINAMICS V series, including the popular V20, provides a simple, cost-effective solution for basic tasks like pumps, fans, and conveyors, as noted by Siemens Converters. Moving up, the SINAMICS G series is designed for general-purpose industrial applications requiring more versatility and a wider power range, as detailed by Precision Electric. Finally, for the most demanding tasks involving high-dynamic performance and precision, such as in robotics or CNC machining, the SINAMICS S series offers advanced servo drive capabilities.

A key advantage of the Siemens portfolio is its modularity, particularly within the SINAMICS G120 platform. This design separates the drive into a Control Unit (CU) and a Power Module (PM), which allows for greater flexibility in design and maintenance. For example, an engineer can standardize on a specific Control Unit with PROFINET communication while selecting from various Power Modules to match different motor sizes, a concept explained by Precision Electric. In other words, this approach enables you to tailor the drive configuration precisely to the machine’s requirements, optimizing both cost and performance without over-engineering the solution.

Step 3: Correctly Sizing Siemens Frequency Converters

Correctly sizing Siemens frequency converters is a critical step that extends beyond simply matching the motor’s horsepower rating. For reliable operation of your Siemens VFD drives, you must analyze the motor’s Full Load Amps (FLA), system voltage, and the application’s specific load characteristics. An undersized drive will lead to nuisance tripping, while an oversized one is an unnecessary capital expense. Therefore, a precise calculation is essential for system efficiency and longevity.

Engineer examining a motor nameplate to determine the specifications for compatible siemens vfd drives.

Careful analysis of your motor’s nameplate is the essential first step in selecting the correct Siemens variable speed drive for your application.

A crucial factor is determining the correct duty rating based on the load profile. Variable torque loads like pumps and fans, for instance, can often use a Normal Duty (ND) rating. In contrast, applications with high starting torque or potential overloads, such as conveyors or crushers, require a Heavy Duty (HD) rating to handle the stress. As explained by Precision-Elec, many AC motor drives from Siemens feature dual ND/HD ratings, providing flexibility but requiring careful selection based on the application’s peak demand.

Furthermore, you must account for environmental factors, which can significantly impact a drive’s performance. For example, high ambient temperatures and operating at high altitudes diminish the drive’s cooling capacity, necessitating a current output reduction, or “derating.” Failing to apply these derating factors can lead to premature failure from overheating. Consulting documentation for specific models like the G120 is vital, as noted by Precision Electric, and the SINAMICS family covers a vast power range according to Siemens SINAMICS V20 Converters. Ultimately, using official engineering tools like the Siemens SIZER software, as recommended by DigiKey VSDS Installation, automates these complex calculations for a precise match.

Step 4: Selecting Control and Interfacing Options

After sizing your drive, the next step involves selecting the control and interfacing options for your Siemens VFD drives. This decision fundamentally impacts how the drive integrates into your broader automation architecture, ranging from simple hardwired start/stop commands to sophisticated, high-speed network control. For instance, basic applications might only require digital and analog I/O for standalone operation. In contrast, complex coordinated systems demand seamless data exchange for diagnostics, parameterization, and real-time process control, making network capability a critical consideration for these industrial VFD systems.

For tightly integrated systems, leveraging an industrial network is the most effective approach. Most SINAMICS drives natively support leading Siemens protocols, and as noted by Precision Electric, this includes robust support for PROFINET and PROFIBUS. This integration simplifies commissioning and diagnostics significantly, especially when using the Totally Integrated Automation (TIA) Portal. In other words, this single software environment allows engineers to configure and manage the entire system, from the PLC to the Siemens frequency converter. This holistic approach, described by Precision Electric as “Integrated Automation,” reduces engineering time and minimizes potential communication errors between components.

Beyond network control, consider the local interface and safety requirements for your application. Operator panels, such as the Basic Operator Panel (BOP) or Intelligent Operator Panel (IOP), provide direct access for monitoring, diagnostics, and on-site adjustments. Furthermore, for facilities with multiple identical drives, features like an SD card slot can be invaluable. This allows for quick and easy parameter cloning between units, which, according to Precision Electric, streamlines commissioning. Finally, always ensure your drive includes essential safety functions like Safe Torque Off (STO), which is a critical, non-negotiable feature for protecting personnel and equipment in accordance with NFPA 70E standards.

Step 5: Safety Considerations for Siemens Inverter Drives

A lineup showing the diverse portfolio of Siemens VFD drives, from compact to large industrial models.

Siemens offers a wide range of VFDs, from the compact SINAMICS V20 to the powerful G120 series, ensuring a perfect fit for any application.

Ensuring personnel safety is the highest priority when installing and maintaining Siemens inverter drives. These industrial VFD systems operate with hazardous voltages, and consequently, all work must be performed by qualified technicians following established safety protocols. Adherence to standards such as the National Electrical Code (NEC) and NFPA 70E is not merely a suggestion but a mandatory requirement for preventing electrical shock and arc flash incidents. Furthermore, Siemens emphasizes a comprehensive approach to safety, integrating protective features directly into their SINAMICS drive platform, as noted by Precision Electric.

Before performing any hands-on work, always implement rigorous lockout/tagout (LOTO) procedures to isolate the drive from its power source. After disconnection, it is crucial to wait for the internal DC bus capacitors to fully discharge, a process that can take several minutes. Technicians must use a properly rated multimeter to verify a zero-energy state before proceeding with any service. This step is critical because the stored energy can remain lethal long after the main power is cut. Many Siemens motor controllers include integrated safety features, which as Precision Electric highlights, complement but do not replace these fundamental procedural safeguards.

In addition to procedural safety, many SINAMICS series drives feature integrated functions like Safe Torque Off (STO). The primary role of STO is to prevent the VFD from generating torque in the motor, thereby averting an unexpected startup without needing to open the main power contactors. According to Precision Electric, this is especially critical in applications like machine tools or presses where operator access is required. While STO enhances machine safety for certain tasks, it is important to remember that it is not a substitute for complete electrical isolation via LOTO during maintenance.

Avoiding Common Mistakes with Ac Motor Drives From Siemens

Selecting the correct Siemens VFD drives involves more than just matching the motor’s horsepower and voltage; consequently, overlooking critical application details is a frequent source of error. A primary mistake is choosing a drive based solely on nameplate data without a thorough analysis of the load type, duty cycle, and operational environment. For instance, a drive perfectly suited for a simple fan application might fail prematurely if used on a high-inertia crusher. Therefore, a comprehensive evaluation of the mechanical system is essential for ensuring the reliability and longevity of the motor control solution.

Siemens Vfd: Normal Vs. Heavy Duty Ratings

Another common pitfall is misinterpreting the drive’s overload ratings. Siemens, like many manufacturers, offers drives with both “Normal Duty” (ND) and “Heavy Duty” (HD) ratings, which are sometimes referred to as variable torque and constant torque ratings. As an illustration, ND ratings are suitable for applications like centrifugal pumps where the load decreases with speed, while HD ratings are necessary for constant torque loads like conveyors that demand high starting torque. According to Precision Electric, failing to account for these distinctions can lead to frequent tripping on overcurrent faults or even damage to the VFD. The application may also Digi-Key VSDS Installation notes, require features not available on a basic drive.

Finally, environmental and electrical system compatibility are often neglected. Ambient temperature, altitude, and enclosure ventilation must be considered, as excessive heat is a leading cause of failure in power electronics. In many cases, drives must be derated for operation at high altitudes or in elevated temperatures, a critical step that is frequently missed. In addition, ignoring the potential for harmonic distortion can disrupt other sensitive equipment on the same power network. It is crucial to verify if the selected drive includes the necessary internal filtering to meet emission standards and ensure system-wide compatibility, as noted by Precision-Elec. Proper planning prevents these issues from causing unexpected downtime.

Conclusion: Making Your Final Siemens VFD Drive Selection

Selecting the right Siemens VFD drives is a critical decision that culminates from a careful analysis of your application’s specific needs. Throughout this guide, we have navigated motor and load requirements, the extensive SINAMICS portfolio, proper sizing, control integration, and essential safety protocols. Ultimately, the goal is to choose a drive that not only meets but exceeds operational demands. As noted by industry experts, the Siemens SINAMICS family is designed to cover a vast range of motor control needs, from basic speed control to complex, high-performance systems, as highlighted by Digi-Key VSDS Installation Article. This ensures a tailored solution is always within reach.

By systematically applying these steps, you can confidently specify a Siemens frequency converter that enhances system performance, improves energy efficiency, and ensures long-term reliability. For instance, a well-matched drive prevents premature motor failure and reduces operational downtime, directly impacting your bottom line. While Siemens offers a robust portfolio, it is also beneficial to be aware of other major players in the market. According to Precision Electric, brands like ABB, Yaskawa, and Eaton ATIC White Paper provide competitive alternatives worth consideration. In conclusion, leveraging manufacturer documentation, as advised by RS Components Siemens Drive Migration, and consulting with technical specialists will ensure your final selection is the optimal choice for your industrial application.

Read The Full Siemens VFD Drives Research:

The Full Siemens VFD Drives ResearchDownload

Reading VFD Nameplate Data Off Of Your SMVector Drive (Video)

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For those of you who are familiar or unfamiliar with Lenze / AC Techs SMVector series drive they have come a long way since their conception. All AC Tech products are manufactured in Uxbridge Massachusettes. Today we discuss how to read the nameplate data off of the drive. It is not as complicated as most might think. This is a great way to determine what voltage inputs, frequencies, phases are required and how to determine whether the Variable Frequency Drive itself is an adequate enough size for the motor you want to connect to it. Enjoy!

News :: Industrial | Economy Drives Markets to Seek Online Alternatives

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It has become common knowledge that the poor economy is causing businesses all over the United States to suffer.  As a result of the credit crunch, industrial manufacturing, automation, processing, and other related markets have been seeking alternatives, and found them online.  Historically, industrial markets have relied heavily on the local businesses they have been accustomed to for decades.

The enormous growth of the internet as a form of research and alternative shopping has begun to drive these industrial markets to seek online alternatives.  Many are learning they have been losing thousands of dollars over the past 20 years by seeking no other alternative.  Now many are taking a chance.

“It really is an exciting time,” states Craig Chamberlin, marketing manager of VFDDistributing.com, “many of our customers are reluctant to try alternatives because they assume online businesses will not provide the quality of service they find in their local shops.  Now we have an opportunity to show we’ve stayed successful for 20 years by looking out for our customers.”  VFDDistributing.com offers online drive sales but they are expanding all their services to their online customer base.

Excited, Craig states, “If they give us a chance, we can show them that we are extremely experienced in working in the field and offering extremely competitive pricing.”  Their parent company, Precision Electric, is a one stop shop for everything ranging from Motor Repair to Panel Building and Complete Automation.  All of these services which are made available to the customers they make online.

People are excited about it. Industries such as OEMs, industrial manufacturing, food, wood and steel processing, automation have a new way to cut costs, save time, and have the technical support they deserve. One customer says, “All I did was a google search looking for a particular piece of equipment I was looking for, and many choices came up, it’s definitely a more competitive world out there for our vendors.  If they aren’t paying attention and staying competitive, they are going to lose alot of work.”

There are a long line of reasons customers are seeking internet for purchasing and repair work in the industrial world. Many argue that not only is it the issue of price, but also technical support as well as repair and service work.  Many local vendors have had these customers ‘trapped’ into a corner for so long, local repair centers have lost their excellent customer service and support which they once targeted these customers with.

Precision Electric, Inc. and VFD Distributing is a family owned business that offers excellence in industrial support and service work, and have been doing so since 1984.  Simply inquire for a free quote or if you are in need technical support.


FAQ :: VFDs | Are There Things to Consider When Operating 50 Hz Equipment at 60 Hz?

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Machinery imported into the United States is often rated at an operating frequency of 50 Hertz. Unless engineered for operation at 60 Hz., this can be problematic for electric motors. This is especially true when operating pump and fan loads. Too often the distributors and purchasers of this machinery assume that the Original Equipment Manufacturer has taken this into consideration. In the repair business we frequently realize this when motors are received for repair roasted out from overload.

A Variable Frequency Drive (VFD) can be used to properly address the issues associated when operating 50 Hz equipment at 60 Hz.

Motor speed is directly proportional to the operating frequency. Changing the operating frequency on a pump or fan increases the operating speed, and consequently increases the load on the motor. A pump or fan load is a variable torque load. A variable torque load varies by the cube of the speed.

A 50 Hz motor operating on 60 Hz will attempt to rotate at a 20% increase in speed. The load will become 1.23 (1.2 x 1.2 x 1.2) or 1.73 times greater (173%) than on the original frequency. Redesigning a motor for that much of a horsepower increase is not possible.

One solution would be to modify the driven equipment to decrease the load.

This may include trimming the diameter of the fan wheel or impeller to provide the same performance at 60 Hz as the unit had at 50 Hz. This will require consultation with the equipment manufacture. Possibly the same manufacture who chose to install 50 Hz rated on a machine to operate on 60 Hz. (your confidence in them should already be suspect). There are other considerations associated with an increase in speed besides the increase in load. These include mechanical limitation, vibration limits, heat dissipation, and losses.

The best solution is to operate the motor at the speed for which it was designed.

If that is 50 Hz., then a variable frequency drive can be installed. These drives will convert the 60 Hz line power to 50 Hz at the motor terminals.

There are numerous other benefits that will be realized with this solution. These benefits include:

  • improved efficiency
  • power regulation (often better than the utility will supply)
  • motor over current protection
  • better speed control
  • programmable output to perform other tasks
  • improved performance.

The same load formula above can be used when speed of a variable torque load is reduced using a Variable Speed Drive. Therefore a 20% decrease in speed will require 58% of the original Horsepower.

 

FAQ :: VFDs | Should I Use An Inverted Rated Motor On VFD Applications?

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Many electricians apply Variable Frequency Drives (VFDs) to AC Motors that are not inverter rated. Many are not even aware that inverter rated motors exist.

Inverter rated motors are not required for inverter applications, however, when a VFD is applied to an inverter rated motor, the inverter rated motor has less chance of premature winding failure. Inverter rated motors have unique windings designed for voltage spikes up to approximately 1500 Volts.

Variable Frequency Drives (VFDs) create artificial sine waves which allow an AC Motor to function; normal AC Motor windings are designed for voltage up to around 600 volts. When these spikes exceed the maximum, the winding insulation starts to break down and eventually will burn up. Inverter rated motors are optimized with higher rated insulated (pulse-shielded) copper windings.

These type of windings can handle voltage spikes up to 1500 volts and higher before the insulation will begin to break down. Inverter rated motors also have tighter bearing air gaps than normal AC Motors.  These tighter air gaps are designed to prevent voltage buildup in the proximity of bearing housings which can cause bearing failure.

The greater the distance the motor is from the drive the more profound the effects of inverter generated voltage spikes.  When the wire from an inverter to the motor is 50 ft or longer, an Inverter rated motor should always be applied.  Always chose an inverter rated motor on new applications.

Operating a Non-Inverter rated motor with an inverter will void the warranty.  When the warranty claim is evaluated by a qualified service shop and/or manufacturer, they will determine the cause of failure to be “Operating of a Non-Inverter rated motor with an Inverter.”

Consult with a professional prior to making a decision on what type of motor to use in your VFD application. Many customers tend to use an existing AC motor for the VFD application if the motor is already available, and replace it with an inverter-rated motor when the original motor fails.  There is some risk in this practice should the failed motor damage your new inverter.

The general lifespan of an AC Motor is dependant on several factors such as:

  • Environment
  • Routine Maintenance
  • Using the correct type of motor and VFD for application.

Many electricians today apply Variable Frequency Drives (VFDs) for numerous reasons on AC Motor applications.  One advantage of using a VFD is to extend the lifespan of an AC Motor. VFDs allow soft-start which in turn creates less wear and tear on a motor, however, if the motor being applied is non inverter rated, some of these benefits may not apply.

This does not mean you should only use a VFD on inverter rated motor only, this just means you have overall greater benefits on inverter motors than basic AC motors.

VFDs Reduce Energy Costs Up To 60% Using an Industrial Drive

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A properly applied Variable Frequency Drive (VFD) will significantly reduce operating costs.  This is particularly true for variable torque loads such as:

  • Fans
  • Blowers
  • Pumps

Blowers, for example, are often used with dampers to control air flow.  These dampers may be operated either manually or automatically.  When dampers are closed, 50% motor current will drop to approximately 60% of Full Load nameplate current.  By utilizing a Variable Frequency Drive (VFD) in this application, current draw in the motor will be reduced 30% for every 10% drop in speed.  The same motor operating from a Variable Frequency Drive (VFD) at 50% speed will draw approximately 20% of FLA.

An example application:

A 10 HP AC motor rated 90% efficient running across the line with the dampers operating between 50 – 70% for 2000 hours per year will require 11,996 KWH.  If your KWH charge is $.08 per KWH, the cost to run this motor will be: $1,248.00 annually.

The same motor operating from an ASD between 50 – 70% speed for 2000 per year will require 4,676 KWH.  Operating cost at the same KWH rate will be:  $ 432.00 per year.  This represents a savings of $ 816.00 per year and should be enough to pay for the investment into a drive and installation costs in the first 12 months of operation.

If the application operates more hours than in this example and/or the KWH charge is higher the savings will compound very fast.

Reduce Energy Costs Up To 60% Using a Variable Frequency Drive
Reduce Energy Costs Up To 60% Using a Variable Frequency Drive

Another factor to consider is mechanical wear.  Because the motor and blower in this application is running at a lower speed mechanical wear will be proportionally less.  You should also expect less vibration and heat that may affect other equipment nearby.

Most VFD’s will accept a 4-20 Ma input signal for speed reference and control.  Most pressure transducers and automatic controllers can be wired directly into the same control position as your automatic damper.  (also  4 – 20 ma)

The same theory will apply to all variable torque loads.  A variable torque load is one that the load on the motor shaft increases when speed increases, or decreases when the speed decreases.

FAQ :: VFDs | How Do I Test The IGBT Power Section On My Drive?

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One of the more common problems seen in our Variable Frequency Drive (VFD) repair division is the failure of the IGBT (Insulated Gate Bi-polar Transistor) power section modules.

If the Variable Frequency Drive (VFD) is blowing fuses, or the VFD simply is not turning on, the following test may aid you in finding the root of the problem.

A digital voltmeter test can tell if a short exists from the input side of your IGBT power section modules to the output side without having to take the whole VFD apart to inspect them.  An alternative, more costly test is done by simply replacing the fuses that have blown, then turning the power on.  This is costly because if the short exists, after turning on the power you can expect a boom that will hit you yet again for $100.00 fuses. The digital voltmeter test could save money, fuses and the embarrassment of aVFD blowing up in your face.

Digital Voltmeter on Diode Test:

Every AC Variable Frequency Drive (VFD) has a section called the DC buss. This section is the output of the IGBT‘s. The terminals are often labeled DC+ and a DC-. The preliminary requirements to the Digital Voltmeter test include:

  1. Locating the DC+ and DC- terminals on the VFD. They are usually located near the input and output terminals.
  2. Locating your input and output terminals, and if you located your buss already you have found these terminals.
  3. Make sure that there are no input or output leads connected to the VFD because this will effect the readings on your meter.

Now that the right terminals have been located, proceed with the following steps to test the IGBT power section:

  1. Turn the voltmeter settings to Diode check. It looks like this  ->I-
  2. Take the positive lead on the voltmeter and put it on the DC- terminal of the VFD.
  3. Now take the negative lead and put it on each input and output terminal of the VFD one at a time.
  4. If a terminal is good, it should return anywhere from a 0.299 volt to a 0.675 volt reading on the meter.
  5. Now repeat the same process the opposite way.
  6. Take the negative lead and put it on the DC+ terminal.
  7. Now take the positive lead and put it on each input and output terminal of the VFD.
  8. Again, one should expect the same readings as in step 4.
  9. If the meter returns a reading of 0.000 – 0.100, the IGBT is shorted and needs changed.  These readings could result in blown fuses or even more costly damages.
  10. If the meter returns a reading of more than 0.750, it is possible the contact is open or there could be other devices with issues between the IGBT and the terminal. If this is the case one should contact their local electronics repair shop or contact us during our store hours to resolve the issue.

There are many things that can go wrong with Variable Frequency Drives (VFDs).  The failure of the IGBT power section is one of the most common.  Educating yourself and understanding how the technology works is the first step in saving both you and your company money.  Often times, you will find the electronics repair shop who does work for you will appreciate the preliminary troubleshooting you have done before you called.  This can result in less cost to you and less diagnostics work for them.

FAQ :: VFDs | How Can I Troubleshoot A Variable Frequency Drive On A Network?

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Engineering technicians have many nightmare stories when it comes to on-site troubleshooting.  In this instance, I was called to help troubleshoot a Closed Loop (Sensorless Vector) Variable Frequency Drive (VFD) on a production line that was so large, it seemed to go so far down the plant, it never ended.

After overcoming the intimidation associated with the sheer size of the line, it became a question of focusing on just the Variable Frequency Drive (VFD) causing the issue.  The maintenance technicians on site not only had home court advantage, but were on the phone with the Original Equipment Manufacturer (OEM) technical support.  Everything on the line ran great, right up to the point where the VFD on the network in question was supposed to start turning a set of rolls.

The VFD was a proprietary brand that was made in Japan with the rest of the machine.  After speaking with technical support from Japan, a list of discrete inputs to the Programmable Logic Controller (PLC) on the network were determined that could be checked.  The maintance guys at this site were pretty sharp so they had already checked the same list twice. It is still good practice when troubleshooting these types of problems to check these discrete inputs.

The problem most have with troubleshooting a Variable Frequency Drive (VFD) controlled by a network is that it seems so intangible.  There are no wires going to the start terminal to throw a meter on.  This VFD, like most others, had a keypad on its front.  These circumstances brought a phrase to mind that was often published on the cover of Love temperature controllers stating, “If all else fails, please read these instructions.”  The customer had a manual on the VFD, looking to the manual is always a good first step to discovering the root of the issue.

When troubleshooting communications between a VFD and a PLC on the network it is necessary to look at the VFD‘s “read only” parameters and look for the answers to these two important questions:

  • Is the Variable Frequency Drive (VFD) getting a run comand?
  • Is the VFD getting a speed referance?

After getting familiar with the keypad, the customer was requested to get the machine running again.  With the information learned from the manual, through the keypad it was determined the VFD was getting a run command and was, in fact, going into run.

However, it was also discovered that the speed reference was running at 0%.  Normally a speed reference on a VFD will run between 0% and 100%.  So in this instance, it was running at 0%.  So the VFD was running great at 0 speed, but 0 speed is not moving.  After discussing it over the phone with the OEM technical support, it had turned out the rung within the PLC on the network turning on the speed reference was not giving the proper speed reference to the VFD.  Now the customer had something to work with and were able to resolve the issue through the PLC.

Keypads can be very useful when troubleshooting Variable Frequency Drives (VFDs) controlled by networks.  Sometimes it is just a question of getting familliar with the way each unique VFD handles network communications.

FAQ :: VFDs | How Do I Derate Three Phase Inputs For Single Phase Applications?

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Often times those using a Variable Frequency Drive (VFD) may find themselves needing to connect a higher horsepower VFD to a single phase input power source.  Since most higher horsepower VFDs only accept three phase input as a power source, they are left with little options or alternatives. Don’t fret, there is a solution.

If you are using a Variable Frequency Drive (VFD) rated for three phase input and the only power source you have available to you is single phase input, then you can derate the Variable Frequency Drive (VFD) to accept the single phase input power source.   You can almost always use a VFD rated for three phase input with a single phase input power source.  Of course, if it is available, try to use a single phase input rated VFD if your power source is single phase.

When only a three phase input VFD is available, it is acceptable and common practice to derate the VFDto work with a single phase input power source.  Variable Frequency Drive (VFD) availability and installation procedures may vary from one manufacturer to another.

Before you derate your VFD, it is most important to ensure the VFD you are using is properly suited for your application.  The following are some basic guidlines to help you in determining whether or not your Variable Frequency Drive (VFD) is suitable for your application:

  1. Gather motor nameplate data including horsepower (HP), current (Amps),  motor voltage, input line voltage and power source phase.
  2. Determine which type of VFD your application will require. The type will fall under the category of either Volts per Hertz (V/Hz), closed-loop vector, or open-loop vector (Sensorless Vector).

The internal components of the three phase input Variable Frequency Drive (VFD) is rated for the appropriate current expected when three phase input power is applied.  When using single phase inputinstead, the line side current from the single phase is always higher.  To “derate” is the process of ensuring that these component are rated for the higher current that will flow from the single phase input instead of the three phase input.

You can derate a VFD by:

  1. Determining the Horsepower of the Motor the VFD will be connected too, then
  2. Choosing VFD with a Horsepower higher than the Horsepower of the motor to compensate for the additional input current from the single phase power source.

The simplest formula used for these types of applications is:

VFD Input Current > Motor Current Rating * 1.73

The VFD input current must be equal to or greater than the Motor Current Rating * 1.73.

When installing most three phase input Variable Frequency Drives (VFDs) on an application where single phase input power is used, you will almost always connect the input line leads to L1 and L2 of the VFD.  L3 will be left open with nothing connected.  Consult with the VFD manufacturer or knowledgeable integrator to be sure.

Example Application to Derate a Three Phase Input Variable Frequency Drive (VFD) to work with a Single Phase Input power source:

An application has a 230 VAC single phase input power source and needs to connect it to a conveyor that has a Variable Frequency Drive (VFD) connected to a 10 Horsepower 230 VAC 3 phase induction motor. Let us assume it has been determined that this application will operate well with a simple Volts per Hertz (V/Hz) VFD. The issue is, since there are no VFD manufacturers that offer a 10 Horsepower (HP) single phase input Variable Frequency Drive (VFD), we will need to derate a VFD with a three phase input forsingle phase input. Most manufactuers of VFDs only offer products up to 3 Horsepower (HP) for single phase input, three phase output; some products such as AC Tech SCF series do offer standard single phase input, three phase output products available up to 5 Horsepower (HP) range.

The 10 Horsepower (HP) AC motor nameplate reveals that the motor is rated for approximately 27 amps at 230 VAC. We must use the equation above:

  • VFD Input Current > Motor Current Rating * 1.73
  • VFD Input Current > 27 Amps * 1.73
  • VFD Input Current > 46.71

Now it has been determined this application will need a 230 VAC 3 phase Volts per Hertz (V/Hz) Variable Frequency Drive (VFD) with an input current rated at or above 47.0 amps.

Our company’s VFD of choice is the AC Technology/Lenze SMVector (SMV) product.  Although this VFD is open-loop vector capable and this application only requires a standard Volts per Hertz (V/Hz) VFD, the AC Tech SMVector (SMV) VFD is a great alternative to any manufacturer of Volts per Hertz (V/Hz) products because the SMV is often the same price or cheaper as any other Volts per Hertz (V/Hz) product and can operate in either Volts per Hertz (V/Hz) mode or open-loop vector.  These VFDs are also available in both Nema 1 and Nema 4x enclosures.

Looking into the product catalog, we find an SMV model fitting the requirements available rated at 15 Horsepower (HP) that has a 230 VAC three phase input rated for 48 input amps.

FAQ :: VFDs | How Does A Variable Frequency Drive Work?

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An AC Variable Frequency Drive (VFD) is commonly referred to as an “Inverter”. This is because of the way a VFD works.  The following details the inner workings of a VFD:

  1. Alternating Current (AC) power is applied to the input of the VFD and feeds a bridge rectifier.
  2. The rectifier converts the Alternating Current (AC) voltage into Direct Current (DC) voltage.
  3. The Direct Current (DC) voltage then feeds the Direct Current (DC) buss capacitors on the VFD where it is stored for use by a transistor or Insulated-Gate Bipolar Transistor (IGBT).
  4. Direct Current (DC) from the capacitors feed the input of the transistor(s).
  5. The transistor(s) then continuously turns on and off at the appropriate frequency to build a new sine wave for use by the motor connected to the output of the VFD.

The process above is often referred to as inversion because it changes from one form to another then back again.

The voltage frequency, as distributed in the USA, is 60 cycles per second and the unit of measurement is Hertz (Hz). The output frequency and voltage of an AC Variable Frequency Drive (VFD) is variable and controlled by the speed at which the output transistor is continuously turned on and off.

The variable speed is controlled digitally in modern VFDs and changed by the operator through programming, an operator interface, or by changing an analog input to the VFD that is programmed as “speed reference input”.

 

FAQ :: VFDs | How Do I Pick A Variable Frequency Drive for My Application?

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When applying a Variable Frequency Drive (VFD) to a new or existing application there are many factors to consider prior to making a firm decision on what type of Variable Frequency Drive (VFD) should be used. If one already has an existing application where VFDs seem to consistently fail, they should look to using a different VFD type for potential success. For a new VFD application one should:

  • Research the motor and VFD specifications.
  • Research your application requirements.
  • Learn more about the VFD products that are available to you.
  • Understand the features of those VFD products to determine what is an appropriate solution for your application.

There are a several different types of Variable Frequency Drives (VFDs). Not all drive manufacturers offer every type of VFD available in the market. So if one has their heart set on a specific product line, one must first do research to ensure the desired manufacturer offers the type of VFD needed by the application. The following is a short summary of the three different types of VFDs that are available and when these types of drives should be considered in an application:

V/Hz (Volts per Hertz) Variable Frequency Drives (VFDs)

The most commonly used and most basic VFD available; this product is for a basic application in pumps, fans, conveyors, blowers and others.  These applications do not require high starting torque, full motor torque at low rpm, and/or speed feedback.  Most V/Hz VFDs have adequate programming features for manyapplications.  Be certain adequate I/O and programming features are available to meet your applicationrequirements.  This product is an inexpensive alternative to a phase converter since they will accept single phase input while providing three phase output.

Sensorless (Open Loop) Vector Variable Frequency Drives (VFDs)

The next VFD type that is commonly used in a lathe, mill or any application where full torque is require throughout the motor speed range. Sensorless Vector VFDs are are also referred to as open loop vector drives; these drives are more complex than V/Hz drives and should always be applied to applications where high starting torque and/or full torque operating at low RPM is required. If speed feedback and/or extremely complex programming must be considered in your application you CANNOT use a sensorless vector VFD. Sensorless vector/open-loop vector VFDs do offer complex programming to a certain degree, but when your application exceeds sensorless vector programming features, there is a third solution.

Closed Loop Vector Variable Frequency Drives (VFDs)

This next level of VFDs are more advanced. Applications that require accurate speed regulation and feedback from the motor and/or require complex programming will require a closed-loop vector drive. This type of VFD is often offered as a “three in one” and able to operate in all operating modes.

  • V / Hz (Volts per Hertz)
  • Sensorless (Open Loop) Vector and
  • Closed Loop Vector

These products are complex and extremely efficient when properly applied. Used in the most complex, advanced manufacturing facilities across the world, closed-loop vector technology has few limits in drive technology. The product features are phenominal.  Applications where these products are utilized provide superior speed regulation and torque performance.

Before choosing a VFD for your application consult with a qualified integrator, distributor, or manufacturer who will ask all the right questions and make an appropriate recommendation.  Be sure you will be able to get proper service and telephone support from them when you, or your qualified electrician, are setting up the drive for your application.