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

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.

AVariable 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 become1.23 (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 avariable frequency drivecan 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?

Many electricians applyVariable Frequency Drives (VFDs)toAC Motors that are not inverter rated. Manyare not even aware that inverter rated motors exist.

Inverter rated motors are not required for inverter applications, however, when aVFD 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 beforethe insulation will begin to break down. Inverter rated motors also have tighter bearing air gaps than normalAC Motors. Thesetighter 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 evaluatedby a qualifiedservice 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 yourVFD application. Many customers tend to use an existingAC motor for the VFD application if the motor is already available, and replace itwith 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 anAC Motor is dependant on several factors such as:

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

Many electricians today apply Variable Frequency Drives (VFDs) for numerous reasons on AC Motor applications. One advantage of using aVFD is to extend the lifespan of anAC 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 aVFD on inverter rated motor only, this just means you have overall greater benefits on inverter motors than basicAC motors.

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

A properly applied VariableFrequency 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 aVariable 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 froma Variable Frequency Drive (VFD)at 50% speed will draw approximately 20% of FLA.

An example application:

A 10HP 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.

Ifthe application operates more hours than in this example and/orthe 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 VFDs 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?

One of the more common problemsseen in ourVariable Frequency Drive (VFD) repair division is the failure oftheIGBT (Insulated Gate Bi-polar Transistor)power section modules.

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

A digital voltmetertest cantellifa short existsfrom the input side of yourIGBT power section modulesto the output side without having to take the wholeVFD apart to inspect them.An alternative, more costlytest 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 againfor$100.00 fuses.The digital voltmetertest could savemoney, fusesand the embarrassment of aVFD blowing up in your face.

Digital Voltmeter on Diode Test:

Every ACVariable Frequency Drive (VFD) has a sectioncalled theDC buss. This section is the output oftheIGBT‘s.The terminals are oftenlabeledDC+ and a DC-. The preliminary requirements to the Digital Voltmetertest include:

  1. Locating the DC+ and DC-terminals ontheVFD. 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 theVFD because this will effect the readings on your meter.

Now thatthe right terminals have been located, proceed with the following steps totest theIGBT power section:

  1. Turnthe voltmetersettings toDiode check. It looks like this ->I-
  2. Takethe positive lead on the voltmeter and put iton the DC- terminal of theVFD.
  3. Now takethe negative lead and put it on each input and outputterminal of theVFD one at a time.
  4. If a terminal is good,it should returnanywhere from a0.299 volt to a 0.675 volt reading onthe meter.
  5. Nowrepeat the sameprocess the opposite way.
  6. Takethe negative lead and put it on the DC+ terminal.
  7. Now takethe positive lead and put it on each input and output terminal of theVFD.
  8. Again,one shouldexpect the same readings as in step 4.
  9. Ifthe meter returnsa reading of 0.000 – 0.100,theIGBT is shorted and needs changed.These readings could result in blown fuses or even morecostly damages.
  10. Ifthe meter returns a readingof more than 0.750, it is possiblethe contact is open or there could be other devices with issuesbetween theIGBT andtheterminal. 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 withVariable Frequency Drives (VFDs). The failure of theIGBTpower 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 beforeyou 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?

Engineering technicianshave many nightmare stories when it comes to on-sitetroubleshooting. In this instance, I wascalled to helptroubleshoot a Closed Loop (Sensorless Vector)Variable Frequency Drive (VFD)on a production line that was so large, itseemed to goso far down the plant, it never ended.

Afterovercoming theintimidationassociated withthe sheersize of the line, it became a question of focusing on just theVariable Frequency Drive (VFD)causing the issue. The maintenance technicianson sitenot 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 pointwhere theVFD on thenetwork in question was supposed to start turning a set of rolls.

TheVFD was a proprietary brandthat was made in Japan with the rest of the machine. After speaking with technical supportfrom Japan,a list of discrete inputs to the Programmable Logic Controller (PLC) on thenetwork were determined that could be checked. The maintanceguys 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 withtroubleshooting aVariable Frequency Drive (VFD)controlled by anetwork is that it seems so intangible. There are no wires going to the start terminal to throw a meter on. ThisVFD, likemost others, had a keypad on its front. These circumstances brought aphrase to mind that was often published on the cover of Love temperature controllers stating, “If all else fails, please read these instructions.” The customerhad a manual on theVFD, looking to the manual is always agood first stepto discovering the root of the issue.

When troubleshooting communications between aVFD and a PLCon thenetwork it is necessary to look at theVFD‘s “read only” parameters and look for the answers to these two important questions:

  • IstheVariable Frequency Drive (VFD)getting a run comand?
  • IstheVFD 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 keypadit was determined theVFD was getting a run command and was, in fact, going into run.

However, it was also discovered that the speed reference was running at0%. Normally a speed reference on aVFD will run between 0% and 100%. So in thisinstance, it was running at0%. So theVFD was running great at 0speed, but 0 speed is not moving.After discussing it over the phone withthe OEM technicalsupport,it had turned out the rung within the PLC on thenetwork turning on the speedreference was not giving the proper speed reference to theVFD. Now the customerhad something to work with and were able to resolve the issue through the PLC.

Keypads can be very useful whentroubleshooting Variable Frequency Drives (VFDs)controlled bynetworks. Sometimes it is just a question of getting familliar with the way each uniqueVFD handlesnetwork communications.

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

Often times those using a Variable Frequency Drive (VFD) may find themselvesneedingto connect a higher horsepowerVFD to asingle phase input power source.Since most higher horsepowerVFDsonly acceptthree phaseinput 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 forthree phase input and the only power source you have available to you issingle phase input, then you canderate theVariable Frequency Drive (VFD)to accept thesingle phase input power source. You can almost always use a VFD rated forthree phase input with asingle phase input power source. Of course, if it is available, try touse asingle phase input rated VFD if your power source is single phase.

When only athree phase input VFD is available,it is acceptableandcommon practicetoderate theVFDto work with asingle phase input power source.Variable Frequency Drive (VFD)availability and installation procedures may vary from one manufacturer to another.

Before youderate yourVFD, it is most important to ensure theVFD 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 andpower sourcephase.
  2. Determine which type ofVFD your application will require. The type will fall under the category of eitherVolts per Hertz (V/Hz), closed-loop vector, or open-loop vector (Sensorless Vector).

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

You canderate aVFD by:

  1. Determining the Horsepower of the Motor theVFD will be connected too, then
  2. ChoosingVFD with a Horsepowerhigher than the Horsepower of the motor to compensate for the additionalinput currentfrom the single phase power source.

The simplest formula usedfor these types of applications is:

VFD Input Current > Motor Current Rating * 1.73

TheVFD input current must be equal to or greater thanthe Motor Current Rating * 1.73.

When installing mostthree phase input Variable Frequency Drives(VFDs)on an application wheresingle phase input power is used, you will almost always connect the input line leads to L1 and L2 of theVFD. L3will be left open with nothing connected. Consult with theVFD manufacturer or knowledgeable integrator to be sure.

Example ApplicationtoDerate aThree Phase Input Variable Frequency Drive(VFD) to work with aSingle Phase Input power source:

An application has a 230VACsingle phase input power sourceand needs to connect it to aconveyorthat has a Variable Frequency Drive(VFD) connected to a 10Horsepower 230 VAC 3 phase induction motor.Let us assumeit has been determined that this application willoperatewell with a simple Volts per Hertz (V/Hz)VFD.The issue is, since there are noVFD manufacturersthat offer a 10Horsepower (HP)single phase input Variable Frequency Drive (VFD),we will need toderate aVFD with athree phase input forsingle phase input. Most manufactuers ofVFDs only offer products up to 3 Horsepower (HP) forsingle phase input,three phase output; some products such as AC Tech SCF series do offer standardsingle phase input,three phase output products available up to 5 Horsepower (HP) range.

The10 Horsepower (HP)AC motornameplate reveals that the motor is rated for approximately 27 ampsat 230 VAC.We must use theequation 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 phaseVolts per Hertz (V/Hz)Variable Frequency Drive (VFD) with an input current rated at orabove 47.0 amps.

Our company’sVFD of choice is theAC Technology/LenzeSMVector (SMV) product. Although thisVFD is open-loop vector capable andthis application only requires a standard Volts per Hertz (V/Hz)VFD, the AC Tech SMVector (SMV)VFD is agreat alternative to any manufacturer ofVolts per Hertz (V/Hz)products because the SMV is often the same price or cheaperas any other Volts per Hertz (V/Hz) product andcan operate in eitherVolts per Hertz (V/Hz) mode oropen-loopvector. TheseVFDs are also available in both Nema 1 and Nema 4x enclosures.

Looking into the product catalog, we find an SMV model fitting the requirementsavailable rated at15Horsepower (HP) that has a230 VACthree phase input rated for 48 input amps.

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

An ACVariable Frequency Drive(VFD) is commonly referred to as an Inverter.This is because of the way aVFDworks. The following details the inner workings of aVFD:

  1. Alternating Current (AC) power is applied to the input of theVFDand 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 theVFDwhere 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 theVFD.

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 ACVariable Frequency Drive(VFD) is variable and controlled by the speed at which the output transistor is continuously turned on and off.

The variable speedis controlled digitally in modernVFDs and changed by the operator through programming, an operator interface, or by changing an analog input to theVFDthat is programmed as speed reference input.

 

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

When applying aVariable Frequency Drive (VFD) to a new or existingapplication there are many factors to consider prior to making a firm decision on what type ofVariable Frequency Drive (VFD)should be used. Ifone already has an existingapplication whereVFDs seem to consistently fail,they should look tousing a differentVFD typefor potential success. For a newVFD application one should:

  • Research the motor andVFD specifications.
  • Research yourapplication requirements.
  • Learn more abouttheVFD products that are available to you.
  • Understand thefeatures of thoseVFD products to determinewhatis an appropriate solutionfor yourapplication.

There are a several different types ofVariable Frequency Drives (VFDs). Not all drive manufacturers offer every type ofVFD availablein the market. So ifone has their heart set on a specific product line,one must first doresearch to ensure thedesired manufactureroffers the type ofVFD needed by theapplication. The following is a short summary ofthe three different types ofVFDsthat are availableand when these types of drives should be considered in anapplication:

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

The most commonly used and most basicVFD available; this product is for a basicapplication inpumps, fans, conveyors, blowers and others. Theseapplications do not require high starting torque, full motor torque at low rpm, and/or speed feedback. Most V/HzVFDs have adequate programming features for manyapplications. Be certain adequate I/O and programming features are available to meet yourapplicationrequirements. This product is an inexpensive alternative to a phase converter since they will acceptsingle phase input while providingthree phase output.

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

The nextVFD type that is commonly used in a lathe, mill or anyapplication where full torque is require throughout the motor speed range.Sensorless VectorVFDs areare also referred toas open loop vector drives; these drives are morecomplex than V/Hz drives and should always be applied toapplicationswhere high starting torque and/or full torque operating at lowRPM is required. If speed feedback and/or extremely complex programming must be considered in yourapplication youCANNOT use a sensorless vectorVFD. Sensorlessvector/open-loop vectorVFDsdo offer complex programming to a certain degree, but when your applicationexceeds sensorless vectorprogramming features, there is a third solution.

Closed Loop Vector Variable Frequency Drives (VFDs)

This next level ofVFDs 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. Thistype ofVFD 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, advancedmanufacturing facilitiesacrossthe world, closed-loop vector technology has few limitsin drive technology. The product features are phenominal.Applications where these products are utilized provide superior speed regulation and torque performance.

Before choosing aVFD for yourapplication 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 yourapplication.

FAQ :: VFDs | What Is A Variable Frequency Drive (VFD)?

Variable Frequency Drives (VFDs) are electronic devices used to control the speed of an Alternating Current Motor (AC Motor). Variable Frequency Drives (VFDs) are also commonly known as adjustable frequency drives, adjustable speed drives, AC drives and inverters.
Variable Frequency Drives (VFDs) have a wide range of application use that include, but are not limited too:
Variable Air Volume Systems
Circulating Pumps for Hot Water Heating Systems
Chilled Water Circulating Pumps
Geothermal Heat Pump Systems
Injection-molding Equipment
Air Compressors
Conveyors
Chillers
Cooling Towers
Variable Frequency Drives (VFDs) operate as load controls within these applications that may accomplish up to a 50% reduction in energy costs. In general, an electric motor will turn at a rate proportional to the frequency of the alternating current (AC) applied to it. The majority of Variable Frequency Drives (VFDs) in the market today contain electronic circuitry that converts a 60Hz Line power into direct current. The VFD converts this line power into a pulsed output voltage that duplicates varying alternating current to a desired frequency.
Advances in technology over the past decade have allowed for Variable Frequency Drives (VFDs) to become a very cost efficient way to reduce energy costs and increase system efficiencies. More and more companies within a wide range of industries are finding more ways to apply Variable Frequency Drives (VFDs) to their applications.
For an even more in depth explanation of Variable Frequency Drives (VFDs), it is highly recommended that you visit: http://en.wikipedia.org/wiki/Variable-frequency_drive

Variable Frequency Drives (VFDs) are electronic devices used to control the speed of an Alternating Current Motor (AC Motor). Variable Frequency Drives (VFDs) are also commonly known as adjustable frequency drives, adjustable speed drives, AC drives and inverters.

Variable Frequency Drives (VFDs) have a wide range of application use that include, but are not limited too:

  • Variable Air Volume Systems
  • Circulating Pumps for Hot Water Heating Systems
  • Chilled Water Circulating Pumps
  • Geothermal Heat Pump Systems
  • Injection-molding Equipment
  • Air Compressors
  • Conveyors
  • Chillers
  • Cooling Towers

Variable Frequency Drives (VFDs) operate as load controls within these applications that may accomplish up to a 50% reduction in energy costs. In general, an electric motor will turn at a rate proportional to the frequency of the alternating current (AC) applied to it. The majority of Variable Frequency Drives (VFDs) in the market today contain electronic circuitry that converts a 60Hz Line power into direct current. The VFD converts this line power into a pulsed output voltage that duplicates varying alternating current to a desired frequency.

Advances in technology over the past decade have allowed for Variable Frequency Drives (VFDs) to become a very cost efficient way to reduce energy costs and increase system efficiencies. More and more companies within a wide range of industries are finding more ways to apply Variable Frequency Drives (VFDs) to their applications.

For an even more in depth explanation of Variable Frequency Drives (VFDs), it is highly recommended that you visit: http://en.wikipedia.org/wiki/Variable-frequency_drive