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