Chapter 2: Frequency Inverter

[Mike Johnson]

So according to the video the delta configuration (or was it the star) has a huge starting amperage requirement. Is this a problem for you Emiliano?

Wye/Star - Delta motor starting is used for several reasons and solves a couple of problems that various applications create. For a starting a heavy load that takes time to come up to speed, a Wye/Star winding is used to reduce the voltage drop and handle high currents on the electrical system. Once the motor and load comes up to speed the starter switches the motor over to the Delta windings which is the more common mode used for running 3 phase motors. This method requires 6 leads going out to the motor and a starter with several contactors and a timer or load sensing circuit that switches the contactors between the Wye/Star configuration and the Delta configuration.
One of the most common applications is a centrifuge that takes time to come up to speed and draws high currents during the start up, if high currents are allowed to take place on your electrical system you end up with voltage drops affecting other equipment on the same electrical system. The Wye/Star start winding method reduces the voltage drop issue.

 

[Bill Boehme]

I have read the attachment and would like to highlight one paragraph: {The insulation system on a 208/230-V motor is identical to that of a 460-V motor. Thus, voltage spikes produced by inverters on 208- or 230-V systems are unlikely to cause insulation damage at any cable length or drive carrier frequency.} Also I would note that the majority of 3 phase motors are dual voltage 230 / 460 volt. In my own shop I have 6 VFDs all of which I personally purchased and connected to ordinary 3 phase motors. The motors on my Lablond lathe and Bridgport mill have been around longer than VFDs without any apparent problems. As a side note the VFDs purchased in the last 10 years all cost under $300.00 and are still operating without problems as are the motors they are connected to.

I think that you missed one important part ... the paragraph that you cited refers to inverter duty motors. If the nameplate doesn't state that it is rated for inverter duty then the insulaton class might not be sufficient to withstand the high dV/dt transients under all conditions.

 

[Bill Boehme]

Wye/Star - Delta motor starting is used for several reasons and solves a couple of problems that various applications create. For a starting a heavy load that takes time to come up to speed, a Wye/Star winding is used to reduce the voltage drop and handle high currents on the electrical system. Once the motor and load comes up to speed the starter switches the motor over to the Delta windings which is the more common mode used for running 3 phase motors. This method requires 6 leads going out to the motor and a starter with several contactors and a timer or load sensing circuit that switches the contactors between the Wye/Star configuration and the Delta configuration.
One of the most common applications is a centrifuge that takes time to come up to speed and draws high currents during the start up, if high currents are allowed to take place on your electrical system you end up with voltage drops affecting other equipment on the same electrical system. The Wye/Star start winding method reduces the voltage drop issue.

What you say is true for heavy starting loads, but for a woodturning lathe application where three phase motors are only used with inverters there is generally not a heavy inertial load starting torque and no large starting current surge because of the ramp up to speed time.

 

[Don Wattenhofer]

I think that you missed one important part ... the paragraph that you cited refers to inverter duty motors. If the nameplate doesn't state that it is rated for inverter duty then the insulaton class might not be sufficient to withstand the high dV/dt transients under all conditions.

The paragraph that I referenced had only one reference to inverters as follows {voltage spikes produced by inverters on 208- or 230-V } and that is clearly not referring to inverter duty motors.

 

[Bill Boehme]

The heading of the seven paragraphs that follow says "Inverter-Duty Motor Design". It appears that the paragraph that you are referencing is the one that I have circled. If so, I would say that it refers to inverter duty motors.

While certainly not obvious I see the paragraph as being basically about cable length and frequency ... implying an environment such as inverters remotely located (typically in an electrical equipment cabinet) and the cable run from inverter to motor might be a hundred feet or more in some settings. Long cable runs increase the amplitude of standing wave transients that increase the risk of insulation arc through of the field windings. The drive carrier frequency is the frequency of the PWM pulses that go to the motor windings. Higher carrier frequencies result in higher amplitude voltage spikes especially on long cable runs. These are the operating conditions that are the design requirements of inverter duty motors.

None of that is especially applicable to our situation because we are dealing with cable runs of just a few feet ... not enough for cable length to be a factor.

The paper is rather brief and quickly glosses over some things without explanation. An example is mentioning insulating the bearings and grounding the motor shaft. In larger higher voltage motors driven by inverters the transients are high enough that they result in induced currents inside the motor housing that cause currents to flow through the motor shaft bearings. This causes arcing that pits the balls and results in premature bearing failure. A common solution is to electrically insulate the bearings from the frame and shaft and use a brush to ground the shaft to the frame.

 

[Emiliano Achaval]

I've forgotten what the original problem was. I'm sure that it wasn't caused by the jumpers swapping around from a delta to a Y all by themselves. Seems like I recall that there was a question of whether the motor or the inverter went bad and you wound up replacing both. Are you still waiting on your Stubby 1000?

My original problem was loss of torque. I ordered a new all wired, ready to go VFD. I hooked it to my old motor. Still no torque! Then I ordered a new 2HP WEG motor. Hired a college graduate engineer to hook this new motor up. Still No torque. Rod Caddeye, owner of Omega Lathes, at his cost, sends me a new, 3HP rated SEW VFD. Hired Einstein again. Still No torque! Guilio Marcolongo tells me he has a friend that can help me. Honestly, I did not believe him. Enzo Vermec, owner Vermec Manufacturing, with 2 emails, notices my motor is not connected right. In 5 minutes I change the configuration and now my lathe is back with a vengeance!! I just had a video conference with Guilio Marcolongo, I love this guy. He's a great friend, a mentor and my partner in doing projects for Woodturning Magazine, I just told him I love him!! LOL, He and his good friend Enzo, fixed my lathe!!!

 

[Emiliano Achaval]

So according to the video the delta configuration (or was it the star) has a huge starting amperage requirement. Is this a problem for you Emiliano?

I told to everyone that would listen to my sob torque story, that the lathe worked for 14 years without a hitch. But, just to make sure, I hired a professional electrician, to check my 220 lines, 2 of them, check circuit breakers, and all the wiring in my shop. I had forgotten that electricians charge as much as some lawyers do. He did fix some minor things but overall told me my shop was ok. That took one more thing out of the equation, the vfd was getting the required power.

 

[Emiliano Achaval]

The AAW should have a list of volunteers, such as retired rocket scientists, electrical engineers, electricians to give advice when a member like me needs help replacing a vfd, where to buy it, how to wire it, what steps to follow in troubleshooting. Maybe not the AAW, but perhaps here. Just rambling... I guess asking here you do get lots of answers. I need a retired lawyer to help me recover what I paid to the electrical engineer, I still insist he should have known how to hook up my new motor in Delta configuration the very first day... I appreciate all the help I got here. However, LOL nobody mentioned Delta, Y or Star...

 

[Don Wattenhofer]

My original problem was loss of torque. I ordered a new all wired, ready to go VFD. I hooked it to my old motor. Still no torque! Then I ordered a new 2HP WEG motor. Hired a college graduate engineer to hook this new motor up. Still No torque. Rod Caddeye, owner of Omega Lathes, at his cost, sends me a new, 3HP rated SEW VFD. Hired Einstein again. Still No torque! Guilio Marcolongo tells me he has a friend that can help me. Honestly, I did not believe him. Enzo Vermec, owner Vermec Manufacturing, with 2 emails, notices my motor is not connected right. In 5 minutes I change the configuration and now my lathe is back with a vengeance!! I just had a video conference with Guilio Marcolongo, I love this guy. He's a great friend, a mentor and my partner in doing projects for Woodturning Magazine, I just told him I love him!! LOL, He and his good friend Enzo, fixed my lathe!!!

The motor must have been connected for 460 volt which is about 7.6 volt per Hz and the VFD is set up with a 230 volt input that would send the motor about 3.8 volts per Hz therefore it would only be getting about half the voltage required at any given speed setting. That would definitely explain the low torque but not how the mistake was made.

 

[Doug Rasmussen]

The motor must have been connected for 460 volt which is about 7.6 volt per Hz and the VFD is set up with a 230 volt input that would send the motor about 3.8 volts per Hz therefore it would only be getting about half the voltage required at any given speed setting. That would definitely explain the low torque but not how the mistake was made.

Don, that was my thought too.

IMO, this should have not been such a confusing and expensive situation. You buy a VFD (and not an $1800 version) rated for your voltage and horsepower needs. Connect to the motor using the motor terminal connection diagram shown on the motor specific to your voltage. It's about that simple since a wood lathe is not a particularly demanding application.

 

[Mike Johnson]

You need to be selective when hiring a person that is experienced with motors and drives, there are many electricians and engineers that rarely work with these systems in the field. Some motor shops will have an experienced technician that works on these systems daily, the larger electrical contractors usually have an industrial or commercial electrician working for them that works with these systems on a daily basis. Larger HVAC shops will have a technician that is trained in motors and drives used on HVAC systems these days. The markets and technologies have grown rapidly over recent decades and it is impossible for one person to be proficient and knowledgeable in all things (electrical) . A doctor specializes in one area, you would not go to a podiatrist to have heart surgery or a heart surgeon to remove a bunion. Electricians come with varied knowledge and experience based on their schooling and who they worked for and the projects they worked on over the years. A typical residential electrician will rarely ever work on 3-phase motors and drives, commercial and industrial electrical contractors will usually have a limited number of experienced drive and controls technicians on staff. Most industrial and commercial refrigeration contractors will be experienced working on these systems. There are smaller contractors that work in small communities and rural areas that usually do farm work which usually involve motor and drives work. Many of these rural shops work with small manufacturing companies in these areas and have experience working with 3.phase systems.

 

[Bill Boehme]

The motor must have been connected for 460 volt which is about 7.6 volt per Hz and the VFD is set up with a 230 volt input that would send the motor about 3.8 volts per Hz therefore it would only be getting about half the voltage required at any given speed setting. That would definitely explain the low torque but not how the mistake was made.

As far as I can see, the only change that Emiliano made was to change the motor winding configuration from a Y to a delta.

An interesting tidbit that I just found out is that motors that can be configured for either a Y or delta are called star-delta motors even though wye is used everywhere else. Maybe the reason could be that it sounds like a question ... "why delta?"

Well, I say, Y not wye?

For the smaller motors that we use that don't require starting contactors I don't see any significant advantage of one winding configuration over the other (Delta is claimed to be better for start-stop operation while wye is claimed to be better for for constant load, but that mainly applies to very large motors).

 

[Don Wattenhofer]

As far as I can see, the only change that Emiliano made was to change the motor winding configuration from a Y to a delta.

An interesting tidbit that I just found out is that motors that can be configured for either a Y or delta are called star-delta motors even though wye is used everywhere else. Maybe the reason could be that it sounds like a question ... "why delta?"

Well, I say, Y not wye?

For the smaller motors that we use that don't require starting contactors I don't see any significant advantage of one winding configuration over the other (Delta is claimed to be better for start-stop operation while wye is claimed to be better for for constant load, but that mainly applies to very large motors).

In a delta connected motor the voltage supplied to the 3 power wires will be directly applied to the windings and the only reason for the Y connection would be to reduce the voltage to the windings for starting purposes or maybe it is designed as a Y motor. The voltage to the windings is in a Y connection is calculated by dividing the voltage by the square root of 3 (1.732) so in the case of a 240 volt system the Y voltage would be 138.564 volts which would work if the motor windings were designed to operate on a Y connection. The motor in question obviously is not designed to operate as a Y so that should answer the question Y not wye.
The other question is why would a manufacturer even make a motor with Y connection unless it is a European thing (380 volt 3 phase Y power systems are common because single phase 220 volt power is available from any of the 3 main lines and the center tap), where common house hold power is 220 volt. So are we having fun yet or should we stick to wood turning.

 

[Mike Johnson]

The industrial facility I work at has about 5000 motors on site, a number of these motors use the Wye/Delta starting configuration. Most of these are for larger slow starting loads that run at a constant speed when they come up to full power. With large motors stopping and starting the large ones tend to create voltage drops when the motor inrush current is high when starting. To address these issues the motor uses the Wye on starting and a timer or sensor switches the motor over to Delta for running at full speed. For large and small motors that need to vary in speed for the application a VFD is usually used to control the motor ramping up to speed and ramping down in speed, this method also reduces voltage drops on a large electrical network that can not tolerate voltage dips which can cause damage to electrical equipment and create problems in the control of the processes.

 

[Emiliano Achaval]

You need to be selective when hiring a person that is experienced with motors and drives, there are many electricians and engineers that rarely work with these systems in the field. Some motor shops will have an experienced technician that works on these systems daily, the larger electrical contractors usually have an industrial or commercial electrician working for them that works with these systems on a daily basis. Larger HVAC shops will have a technician that is trained in motors and drives used on HVAC systems these days. The markets and technologies have grown rapidly over recent decades and it is impossible for one person to be proficient and knowledgeable in all things (electrical) . A doctor specializes in one area, you would not go to a podiatrist to have heart surgery or a heart surgeon to remove a bunion. Electricians come with varied knowledge and experience based on their schooling and who they worked for and the projects they worked on over the years. A typical residential electrician will rarely ever work on 3-phase motors and drives, commercial and industrial electrical contractors will usually have a limited number of experienced drive and controls technicians on staff. Most industrial and commercial refrigeration contractors will be experienced working on these systems. There are smaller contractors that work in small communities and rural areas that usually do farm work which usually involve motor and drives work. Many of these rural shops work with small manufacturing companies in these areas and have experience working with 3.phase systems.

Mike, Einstein works at a government facility on top of the Haleakala Crater. To get in looks something out of a James Bond movie. He's in charge of all the motors that move whatever they use to track the missiles they shoot from Barking Sands. His credentials are good, maybe is just that he doesnt know what we need for woodturning...

 

[Mike Johnson]

There are a large variety of starter designs and motor winding designs used across many industries. Most people are familiar with the common methods used, it is the specialty motors and starter designs that cause problems for people that have little experience with the special application designs. As far as Einstein goes Tesla always considered him to be an idiot.

 

[Mike Johnson]

Be happy you don't play with 12-lead and 18-lead motors, those can be intimidating the first time you pull the cover off the motor junction box and find a bundle of wire leads that need to be wired correctly before it will run.