Did you know?

Did you know?

Line Reactors:

In this “Did You Know” article we will discuss line reactors. Reactors, also known as “inductors,” are coils of wire wound around a chunk of iron.

Depending on where they are used whether on AC or DC, you might hear other terms such as: AC Reactor, DC Link Inductor, or choke. 

The older school guys will call them “chokes” because that’s exactly what they do.  They choke currents in electricity.  The largest use for reactors is VFDs.   VFDs have a bank of capacitors internally.  Think of these as batteries.  When the power is supplied to these batteries, the last thing you want to happen is to instantly charge them.  One, it’s bad on the capacitors, and two, it causes a short burst of current.  Both cause extra heating in VFDs.  VFDs also draw non-linear current. For the power company, this is seen as harmonics.  By adding a reactor in front of the VFD you extend the life of the drive and reduce harmonics.  The placement of the reactor in front of the drive on the line side is referred to as a “Line Reactor.”

The products used for Line Reactors are the KLR and KDR series from TCI.

Reactors come in 3% ratings and 5% ratings.  The larger the %, more the “choke” you get.

So, who uses Reactors?

Any user of VFDs is a good place to start. Reactors are an economical solution to extend the life of the VFD and reduce harmonics. Reactors have other uses on the output section of a VFD as well. This will be covered in another “Did You Know” article, titled Load Reactors.

Load Reactors:

In this “Did You Know” article, we will cover Load Rectors and their uses for the output section of a VFD.

As you can recall, Line Reactors are used to extend the life of the drive and reduce harmonics.  Load Reactors are placed after the drive and perform some perks for the motor.  VFDs do not produce a sinewave like you would get directly from the power company.  They produce a distorted, almost square-like waveform.  The motor however works okay with this distorted waveform due to its inductive electrical characteristics.  But when the length of the motor leads start exceeding 75ft, then a phenomenon known as “voltage ring-up” or “voltage doubling” occurs.  That means a 480V motor would see close to 1000V spikes.   The insulation of the motor cannot handle this and will sooner or later breakdown and destroy the motor.  These spikes can also lead to bearing failures as the larger voltage can arc thru the bearing.  This is called “bearing pitting” or “bearing fluting”.  If you get voltage ring-up, a short circuit in the motor will occur.  With bearing failures, you get excessive noise and finally bearings lock up. 

This is where Load reactors come into play.  Adding a load reactor to motors above 75ft will reduce this phenomenon.  It also smooths out the VFD waveform somewhat, thus providing a cleaner sinewave.  This cleaner sinewave produces less losses in the motor, which leads to less heat in the motor.  The result?  An extended life for the motor.

The product used for Load reactors is the KLR and KDR series from TCI.

So, does the KDR fix all long motor lead problems? 
No, it doesn’t, but we have a solution for that too.  We’ll save that one for another “Did You Know” article, Motor Lengths.

Motor Lengths:

In this “Did You Know” article, we will continue touching on Long Leads for motors. 

In our Load Reactor article, we learned that once the VFD and motor distance becomes greater than 75ft, it’s time to consider a load reactor.  But what about when it’s much greater than 75ft, are there other choices?  Yes, there are, generically known as “dv/dt” filters.  dv/dt filters are nothing more than some extra circuitry added to the load reactors. 

These are generally good for up to 400ft or so.  So what about beyond that?  Well, then comes in the generically known, “sinewave filter” which is meant for super long leads up to 10,000 ft (that’s about 2 miles of cables).  This is a highly engineered product that makes the VFD output look like a near-perfect sinewave.  It is quite larger than the load reactor and dv/dt filter and as you might guess quite a bit of cost difference as well.

So here are some general rules of thumb, and if you ask other folks the lengths may change around somewhat, depending on which marketing team got to them first.

One question that is asked a lot is “can I use a filter even though the length may be shorter than what is required?” 
Yes, you can, but most won’t spend the extra money.  Some OEMs simply supply a V1K filter because they know it will be “a few hundred feet” to the motor.  That’s a good insurance policy to avoid breakdowns and possible liabilities.

Passive Filters:

This “Did You Know” article will deal with VFD input filters.

In simple terms, the power company supplies a sinusoidal waveform, nice and clean.  Traditionally consumers have used motors operating without a VFD.  This causes no problems with the waveform, but for the consumer, it limits the motor to only one speed.

Introduce the VFD, and now the consumer has a method to change the motor speed.  However, the VFD doesn’t consume power perfectly as seen by the utility. VFDs produce “non-linear” power and/or “harmonics”.  Add a few of these VFDs to your facility and you may not notice much changes to the power source.

Convert your entire facility to all VFDs and you can create a harmonics mess, or “poor power quality”.  So, no big deal, not a consumer problem, right?

Well, yes and no.  The utility will take note of the poor usage of their power source and may complain with a slap on the wrist or may go with a penalty charge. (As a reminder, a VFD without any filtering can have harmonics as high as 70%.)

So what are some of the tools we have to fix these issues?
In this article we will only consider the Harmonic Guard series.  For many years, the HG7 series has been around from TCI, reducing harmonics down to the 7% range.

TCI recently introduced its HGP filter.  This one reduces the harmonics down to the 5% level. 

One thing that should get you excited is that the price difference between the HG7 and HGP is almost negligible.   And the hardest standard to meet is the “5%” rating.  So, you now have a product to get down to this tough standard.

Ok, that’s been a lot of words, so let’s summarize it.  If you are selling a VFD and the customer is concerned with harmonics, then add a HG7 or HGP filter to it.

So today we covered what is termed in the industry as “passive filters.” In another “Did You Know” article we will cover, “active filters”.

Active Filters:

This “Did You Know” article will discuss active filters.

So first what’s the difference between passive and active?  
Passive filters are just pieces of electrical hardware that are tuned to remove a single harmonic frequency or possibly 2 frequencies.

Active filters have a “brain” and electronics that actively adjust to remove many harmonic frequencies.

Passive filters are “in series” with the VFD, meaning they must be sized exactly as the VFD.

Active filters are “in parallel” with the VFD(s), meaning their size is based on total harmonics to be removed.

In our case, passive filters are working with 60Hz. (Send a passive filter overseas and that will change to 50Hz and your State-side filter is a worthless chunk of scrap iron!)

Active Filters though are much “smarter” and can adjust as power usage fluctuates and harmonic frequencies move around.  As you would guess, these filters are much more costly than a passive filter.  A passive filter is meant for one VFD load, where an active filter could possibly filter multiple VFD loads.

Another way to look at the Active Filter is a set of Bose™ noise-cancelling headsets.   If you’ve ever worn these headsets, you notice that it’s much quieter and really knocks out the noise.  But how does it remove a sound headed straight for your ear?  It actually sends a negative sound to your ear.  The result?  A sound that gets cancelled out.

A TCI active filter does exactly the same thing.  It sees harmonics and injects negative harmonics back to the grid.

The result?  The harmonic gets removed. 

These are actually easier to size, you simply look at the harmonic content and size to remove that much “noise”.  Add more harmonics later to the facility, just add another Passive filter module.  Remove loads in the plant and the filter just reduces its workload.

So there you go.  We have covered Line Reactors, Passive Filters, and Active Filters, all meant for the input of a VFD to reduce harmonics.  Now it comes down to how much reduction does your customer need and how much he or she is willing to spend to get it.

Buzz Words:

This “Did You Know” article is some random Buzz Words heard in the VFD marketplace.

Here goes:

  • VFD, VSD, ASD, VVVF, Drives:  All of them mean the same thing: a Variable Frequency Drive.
  • VFD-Variable Frequency Drive
  • VSD-Variable Speed Drive
  • ASD-Adjustable Speed Drive
  • VVVF-Variable Voltage Variable Frequency Drive
  • Freq Drive (Typically pronounced “Freak-Drive”)

IEEE519 or IEEE519-1992, IEEE519-2014.  In laymen’s terms, all the same thing.  This a “recommendation document” from IEEE that defines how clean the power must be supplied and consumed.  From our past history lessons, VFDs cause poor quality and TCI has correction products. 

Typical statement might be, “We need to meet IEEE519, do you have a product?”  Yes.

PWM- Pulse Width Modulation.  This is the method that VFDs use to supply power to the motor. 
V/Hz (Volts per Hertz) and V/F (Volts per Frequency) mean the same thing.

The voltage to the motor varies as the frequency varies.  The way all VFDs perform for the most part.
Closed Loop Vector control, Closed Loop control, and Encoder feedback control refer to the same thing.
In simplest terms, this means you have a “speedometer” (aka encoder) on the motor and it sends a feedback signal to the VFD to make corrections.  With encoder feedback, you get extreme precision on speed control. 

Open Loop Vector Control, Sensorless Vector Control, and Encoderless Vector Control are the same thing.
This means the VFD can “estimate” the speed of the motor and makes corrections to it. 

Constant Torque vs. Variable Torque:

Our next topic for the “Did You Know” article series is a question that is thrown out quite a bit for VFDs. 

Do I need a Constant Torque Rated Drive or a Variable Torque Rated Drive? 
Sometimes simply referred to as CT and VT.

This has to be the most ridiculous concept for a “drive”, because drives have no twisting ability, which is exactly what torque is.  But what they are really referring to is the loading profile of the motor.

Variable Torque is probably the easiest to describe first.  This means that the faster the motor spins, the more load the motor sees.  Two applications fit this one perfectly, fans and pumps.  The faster the fan spins the more amperage it takes to do so. These drives have very little overload built into them, typically 110 to 115%.  Why so little overload capability?  Well, that’s because it very rare that all of a sudden a fan gets overloaded.

Now onto Constant Torque drives.  These are drives that see near constant loading throughout the speed range, but might see overloads on occasion.  The drive has at least 150% overload rating for 1 minute and around 175% for 3 or more seconds.  This means the drive keeps going with these types of overloads.  Probably one of the best examples is a conveyor that is being loaded with dirt.  Each time a new load of dirt gets dropped on the conveyor the motor sees this as a shock load, but has enough overload to keep going.

Drives are rated in HP for convenience, but in reality they are rated in amps and that’s what you need to make sure is covered. See the HP vs. Amps “Did You Know” article for more info.

Amps or HP:

This topic for the “Did You Know” article series is Amps or HP, which one is important?

Almost all drives manufactures that sell in the U.S. will rate their drives in HP at least from a marketing standpoint.

Go overseas and you will see kW ratings instead.  Both mean essentially the same thing, but can get a salesman (or saleslady) in trouble pretty quick.

First  1 HP = .75kW
So if you have an OEM that sells both to the US and overseas, he might ask for a 40HP/30kW drive.  Just jot down the conversion. 1HP = .75kW

But do drives really have “HP” in them?  No, drives are segregated into voltage categories and then by amperage. Most commonly 230V/460V/575V.   The “convenient” HP rating is to help you hone in on the right drive.  And for the most part if you have a standard off the shelf motor built in the last 30 years you are probably ok using HP.  However, if the motor is custom designed, then the amps might not align with the ratings published for standard motors.  And remember from our last “Did You Know” article, Constant Torque vs. Variable Torque, drives produce AMPS, not HP.

So, a 480V, 100HP standard motor might be rated for about 132A.  But a 100HP custom motor used on a crane or hoist might be rated upwards of 155A. 

You will find a 100HP drive is rated for about 150A.  If we didn’t ask for the motor amp rating, this one would be undersized.

Just remember that 95% of the time, you will be okay with the HP rating, but the drive is really rated to handle xxx Amps and the drive must be rated equal or greater to that amperage.