Understanding Motors

[George Stolz]

Help me out, motors are not my strong suit. How would I use this information?

This label in inside the cover of a 60 HP, 200V fire pump motor. There was another diagram on the housing of the motor that I went by before I noticed this label inside the cover. The motor is connected to a VFD.

I just don't understand why I have two diagrams for the same voltage. Are there starters that have different run and start terminals that would make use of this?

I recognize that this is a dumb question for those of you who know the answer.

 

[GeorgeB]

Since you show the WYE START, DELTA RUN, I'll assume that is what you are considering in "I just don't understand why I have two diagrams for the same voltage. Are there starters that have different run and start terminals that would make use of this?"

When starting current must be kept lower than the (approximate) 6x run configuration full load, there are multiple options; one, and perhaps the best, is your VFD. But the use of WYE-DELTA can be done with any motor which has all winding connections available (6 leads on single voltage, 12 leads on dual voltage). You ask if there are starters with different terminals ... yes. Further, there are 2 different WYE-DELTA schemes, open and closed transition ... each with advantages and disadvantages.

If I start in WYE, I'm effectively "running" the motor at 1/sqrt(3) of nominal voltage. This "allows" only about 1/3 of rated torque so time to speed is increased ... by close to 3 times. Once this time (usually a timer) passes, the starting contactors are reconfigured to the run (DELTA) configuration.

The lower part of that photo shows the wiring of the contactors.

Did I correctly understand your question.

 

[George Stolz]

Yes, you understood my question.

I will stop to process this info later today, thank you.

 

[Besoeker]

Help me out, motors are not my strong suit. How would I use this information?

This label in inside the cover of a 60 HP, 200V fire pump motor. There was another diagram on the housing of the motor that I went by before I noticed this label inside the cover. The motor is connected to a VFD.

I just don't understand why I have two diagrams for the same voltage. Are there starters that have different run and start terminals that would make use of this?

I recognize that this is a dumb question for those of you who know the answer.

If you are looking at the highlighted top left hand set of connections there are four arrangements.
A set of two for start run on low voltage and a set of two for start and run on high voltage.
For operation on a VFD I think you need to use the RUN configuration for the voltage you intend to use.

Just my thoughts. I don't come across 12-lead motors here.

 

[Joethemechanic]

Think of it this way,

With the windings connected in a wye, you have a 346 V motor

The motor starter (controller) connects your 208 V line to your motor while it is wired for 346 V (start mode)

This lessens the torque the motor produces, and also lessens the current drawn by the motor. But only for a brief instant.

The motor starts to spin overcoming the inertia of the rotor and the pump impeller

At some predetermined elapsed time, the contactors in the controller change the motor configuration to delta.

In delta your motor is now a 200 V delta motor and it's connected across the line to your 208 V source (run mode)


In a lot of ways it is the the electrical version of slipping your clutch when starting out in your car / truck / tractor. And just like when you slip your clutch, if you do it for too long, you produce too much heat and burn things up

 

[Joethemechanic]

You also might want to look at "Starting Compensators". That was another way of doing the same thing,,,,,, Way Way Way back in the day. But it kinda gives you another perspective.





http://books.google.com/books?id=PXwhAQAAMAAJ&pg=RA1-PA130&lpg=RA1-PA130&dq=motor+starting+compensator&source=bl&ots=FK0z1hf6Kz&sig=uyc9jO7yTEemjxqjJme3JSXa74E&hl=en&sa=X&ei=f0UcT4SPO4X40gHTyvyxCw&ved=0CHQQ6AEwCQ#v=onepage&q=motor%20starting%20compensator&f=false

 

[kwired]

Today this is usually done with solid state soft starters.

 

[Joethemechanic]

Centrifugal pumps are typically not hard starting devices anyway. The pump itself acts like a fluid coupling or "torque converter"

Now positive displacement fire pumps like on this 1927 Ahrens-Fox 1000-GPM Piston Pumper are a whole different story.

 

[kwired]

Centrifugal pumps are typically not hard starting devices anyway. The pump itself acts like a fluid coupling or "torque converter"

Hard starting - no, but they are still energized with a locked rotor condition, and sometimes there are advantages to reducing this surge of current, as well as possible mechanical advantages to soft starting.

 

[Joethemechanic]

Hard starting - no, but they are still energized with a locked rotor condition, and sometimes there are advantages to reducing this surge of current, as well as possible mechanical advantages to soft starting.

Hard starting, like the time my miscalculation blacked out an entire city block :ashamed:

 

[renosteinke]

The type of motor is rather common in Europe. First, let's look at the operation:

To start the machine, the operator will turn the 'start' knob to the "Y" position. He will leave it there as the motor comes up to full speed (without any load). Once at full speed, he will turn that same knob to a 'Delta" setting, and start working.

That's the 'practical' side of things. Now, for th reasoning behind it:
Plow through enough motor performance graphs, and you will see that "Y" wired motors are very much 'constant RPM' motors. Think of this as a primitive 'soft start.' The motor wants to spin, but doesn't have much torque at low RPM's.
"Delta" wired motors, by comparison, have lots of torque, over a much broader RPM range. So, the motor is run in 'delta' configuration when it is under load. For anyone who has ever used a cheap hand-held wood router, or an angle grinder, you can understand that having a lot of torque at start-up might be tough on the machine.

"Y" and "Delta", as used here, have nothing to do with the power supply- it's strictly about the way the motor windings are connected.

 

[kwired]

The type of motor is rather common in Europe. First, let's look at the operation:

To start the machine, the operator will turn the 'start' knob to the "Y" position. He will leave it there as the motor comes up to full speed (without any load). Once at full speed, he will turn that same knob to a 'Delta" setting, and start working.

That's the 'practical' side of things. Now, for th reasoning behind it:
Plow through enough motor performance graphs, and you will see that "Y" wired motors are very much 'constant RPM' motors. Think of this as a primitive 'soft start.' The motor wants to spin, but doesn't have much torque at low RPM's.
"Delta" wired motors, by comparison, have lots of torque, over a much broader RPM range. So, the motor is run in 'delta' configuration when it is under load. For anyone who has ever used a cheap hand-held wood router, or an angle grinder, you can understand that having a lot of torque at start-up might be tough on the machine.

"Y" and "Delta", as used here, have nothing to do with the power supply- it's strictly about the way the motor windings are connected.

I don't know if delta wound has more torque than wye wound or not, But you do not have same same thing electrically if you connect same windings in wye vs delta.

Assume a 480 volt input: connect the windings in wye configuration and you will have 277 volts across each winding, connect same windings in delta configuration and you have 480 volts across each winding.

 

[Joethemechanic]

With a given line voltage, and a given set of motor windings, if you connect the windings in a wye, torque will be less. This is because each individual winding will be seeing a lower voltage connected in a wye.

Contrary to popular belief, motors do not have to be connected in either a wye or a delta

 

[Besoeker]

To start the machine, the operator will turn the 'start' knob to the "Y" position. He will leave it there as the motor comes up to full speed (without any load). Once at full speed, he will turn that same knob to a 'Delta" setting, and start working.

In bygone days maybe. I can remember seeing Ellison mechanically operated star delta starters when I first got into the electrical business somewhat over forty years ago - and they were old hat even then. The idea of leaving it up to a machine operator to judge the interval between star and delta wouldn't pass muster these days. I neither designed nor seen one manufactured during my ime in this field that was anything other than electromechanical contactors to give the two configurations and a timer to set the changeover delay.

Plow through enough motor performance graphs, and you will see that "Y" wired motors are very much 'constant RPM' motors. Think of this as a primitive 'soft start.' The motor wants to spin, but doesn't have much torque at low RPM's.
"Delta" wired motors, by comparison, have lots of torque, over a much broader RPM range. So, the motor is run in 'delta' configuration when it is under load.
"Y" and "Delta", as used here, have nothing to do with the power supply- it's strictly about the way the motor windings are connected.

Not strictly true, or maybe just not true.

Here is a picture of a nameplate I found on my desk:

It's 230V delta or 400V star connected.
In both cases the output power is 2.2kW at 2850rpm.
Which means the same torque in both cases.

 

[Besoeker]

Contrary to popular belief, motors do not have to be connected in either a wye or a delta

No. But your arrangement requires six conductors rather than the three it would require for direct on line.

 

[Joethemechanic]

No. But your arrangement requires six conductors rather than the three it would require for direct on line.

Well it is not a real world solution, it is just an example. I tried to use it to illustrate that the windings only really know the current that is flowing through them. Whether a motor is a wye or a delta, is really just how you make the connections on the outside of the armature

Polyphase motors do not have to have interconnected phases. Case in point, two phase,,,,,,,,,

 

[Besoeker]

Polyphase motors do not have to have interconnected phases.

I agreed with you on that point.