Motor Control Education Questions

Hello All,
I know this is more of a PLC forum but I feel like you guys would be the most knowledgeable about motor controls, etc. I'm a mechatronics instructor near Annapolis and our program has always needed more Motor and controls curriculum. We're trying to fix that now. Here is a video of a trainer we built - we're planning on building another 3 of them for classroom use.

https://www.youtube.com/watch?v=PMT30Z2BOa8

I do have some questions about motor controls and would appreciate any advice or suggestions at all.
1) I hear and see a lot of curriculum about Wye Vs Delta 3 phase configurations - In terms of wiring up a simple 3 phase motor like we're doing in the video are these configurations important. Does it have something to do with the Low Voltage vs High Voltage wiring diagram on the motor?

2) Before we move onto VFDs, PLCs and HMIs - what motor control fundamentals are we missing - We're going to cover manual motor starters, contactors, Overload relays, Solenoid braking of the motor, timing relays, etc - Is there anything important we're missing?

Any other advice relating to teaching motor controls at the college level would be appreciated. Thanks for your time.
Tim

others can reply as well, here is what I look into when dealing with motors and other things.

if using a non NEMA rated motor starter, how often does the motor start per hour? these starters have a start / stop per hour rating even though they do not say that on the specs. 5 or more, I go 1 size up.

what is the advantage of an interlocked motor started over two independent starters? an interlocked starter will not allow both contactors to be made at the same time even though both coils may be energized.

discuss the sudden reversal of a motor from running forward to powering in reverse. the inrush current can be 10 times the normal current to stop the motor and then reverse the motor. discuss what happens to the motor mounting plate and connected hardware. lots of mechanical stress.

discuss what happens when you get European tapping machines in and wire L2 to the wrong phase - the motor smokes - 1989 incident - things may have changed.

what happens when you get 50 hz motors on a 60 hz power system.
what happens to solenoids designed for 50 hz on a 60 hz system? they typically burn up in 6 months.

discuss the different voltages used in the USA, y, delta, open delta, floating systems - L2 to ground can be 240 volts when you have a 3 phase 220 volt system.

discuss NFPA 70 - national electrical code, NFPA 79 - electrical standard for industrial machinery, hazardous locations and installation procedures.

DISCUSS ARC FLASH !!!!

this is a start.
james

James Mcquade said:

others can reply as well, here is what I look into when dealing with motors and other things.

if using a non NEMA rated motor starter, how often does the motor start per hour? these starters have a start / stop per hour rating even though they do not say that on the specs. 5 or more, I go 1 size up.

what is the advantage of an interlocked motor started over two independent starters? an interlocked starter will not allow both contactors to be made at the same time even though both coils may be energized.

discuss the sudden reversal of a motor from running forward to powering in reverse. the inrush current can be 10 times the normal current to stop the motor and then reverse the motor. discuss what happens to the motor mounting plate and connected hardware. lots of mechanical stress.

discuss what happens when you get European tapping machines in and wire L2 to the wrong phase - the motor smokes - 1989 incident - things may have changed.

what happens when you get 50 hz motors on a 60 hz power system.
what happens to solenoids designed for 50 hz on a 60 hz system? they typically burn up in 6 months.

discuss the different voltages used in the USA, y, delta, open delta, floating systems - L2 to ground can be 240 volts when you have a 3 phase 220 volt system.

discuss NFPA 70 - national electrical code, NFPA 79 - electrical standard for industrial machinery, hazardous locations and installation procedures.

DISCUSS ARC FLASH !!!!

this is a start.
james

Click to expand...

Great list, for starters. I would politely suggest hiring an person with an actual electrical background to design and teach this course.

Would you be OK having a painter teach the mechanical portion of this class? Not trying to sound too snarky, just emphasizing the point.

^^^ I agree ^^^

I see from the video that you are using a VFD but that's only a small part of the motor control
you need to look at and understand
Part winding start, Why start Delta run, Part winding start, multi winding motors,
step start. and others that they may run into in the field
Not to mention there are still a lot of DC motors out there you have shunt wound, series
field control
Motor connections used in UE and here in states
As for running a 50HZ motor on 60HZ that's rarely a problem in most cases they actually run better the higher speed makes for better cooling if the higher speed doesn't cause problems in system
then you should talk about speed follower and torque follower
just to point out a few things to be aware of with motors
if you think I may be ore help PM me

Besides working in the field, I teach some continuing Ed classes at our local Community College. An important part of Motor Controls classes is troubleshooting. Find ways to "bug" circuits, such as with bad wires, open connections, shorts to ground, bad switch contacts, etc. Make sure that the control circuit fusing is low level. In the trainers that I build, I have backup overload protection, in case students neglect to fuse a circuit.

+1 qualified electrician.

You have an interesting motor in that it is not a normal "Wye delta" motor, it is a dual voltage motor.

A Wye Delta has six terminals plus earth, and if you wire according to the Y diagram on the box, you get nominal voltage 1, and if you wire according to the delta diagram you get nominal voltage 2. For these, V2 is always V1/√3.

Your setup however is a dual voltage. You will notice it can run at 208 or 480. 480/√3 is not 208. Your motor has 9 terminals. I don't see nor use these often enough that I can recall the exact internal wiring, but I know it has at least twice as many windings, some of which aren't used.

Now onto a third topic, star delta starters. You will notice above I deliberately said "nominal voltage". You can supply it different voltages and it will have less torque, and less current. Normally when you start a motor at full voltage, it's startup current is up to 10 times that of its nameplate. It's torque is around 2.5 times the motor nameplate torque. Maybe your mechanical system doesn't like 2.5x nominal torque? Maybe your electrical supply doesn't like supplying 10 times what you said you wanted?
So we have a device called a star delta starter. Essentially 3 contactors and a timer, 2 of which are interlocked. You press the start button, and 208 volts is applied to the wye configuration. When the time expires, the contactors switch over and 208 volts is applied to the delta configuration. Now in this motor nameplate, the delta would be nominal 208 and the wye would be nominal 360. So you see we were underpowering the motor for the first say 30 seconds. Your start current is reduced by a factor of 3 (still 10/3=3.3 times higher than nameplate current), and similarly your starting torque goes down by a factor of 3.

My final point is that a 400V supplied motor can either be a 400V Delta /690V star motor, and sometimes a 230V delta / 400V star motor. You wire them differently for DOL. Only the 400/690 can be used for star delta starting on a 400V system. Attempting to do so for the 230/400V variant will lead to nominal starting, and either "cooked-motor-running" or circuit breaker trips. Preferably the latter.

I always "assume" the top side of a Circuit Breaker, Disconnect, motor starter, overload, etc. is the "LINE" side, and the lower side is the LOAD side. If I turn an overload (motor circuit protector), or circuit breaker/disconnect OFF, I assume that the bottom section is de-energized.

I may be viewing the video wrong, but it looks like you are doing the opposite of that. The wiring should follow the schematic.

I picked up on a forward/reversing motor w/physical and electrical interlocking, plus jog and run functions somewhat easily. Once I understood those functions, and could conceptualize and wire (or at least draw a schematic), I found that a bunch of other PLC logic/interlocking/safety/fail safes became very easy to understand.

I would implement a forward reversing motor starter with interlocks, jog and run features - AND AN E-STOP, and then progress toward a sort of transfer switch between the VFD/PLC and the motor starter.

Another thought. Consider including a NEMA style motor starter, so that students will be familiar with them, and understand the differences with IEC style starters.

Good catch bulletin blues I missed that before
deffenetly need to pay attention to that

We had an experienced electrician killed because somebody wired a 13K disconnect with incoming to the bottom
from what I read he opened the switch and failed to verify the power
They found him the next morning when the crew showed up for work


You should always teach safety first

bulletin blues said:

I always "assume" the top side of a Circuit Breaker, Disconnect, motor starter, overload, etc. is the "LINE" side, and the lower side is the LOAD side. If I turn an overload (motor circuit protector), or circuit breaker/disconnect OFF, I assume that the bottom section is de-energized.

I may be viewing the video wrong, but it looks like you are doing the opposite of that. The wiring should follow the schematic.

I picked up on a forward/reversing motor w/physical and electrical interlocking, plus jog and run functions somewhat easily. Once I understood those functions, and could conceptualize and wire (or at least draw a schematic), I found that a bunch of other PLC logic/interlocking/safety/fail safes became very easy to understand.

I would implement a forward reversing motor starter with interlocks, jog and run features - AND AN E-STOP, and then progress toward a sort of transfer switch between the VFD/PLC and the motor starter.

Click to expand...

I worked with a lot of European made equipment used on food processing when I was in Alaska. Most of it had the line side wired to the bottom of any breakers, contactors, terminal strips, etc. Very difficult to get used to. Anything I re-wired I wired it to U.S. wiring methods that were used by all electricians in this country and drew the prints accordingly. Having been in motor controls since the early 90's I could certainly see how someone would get hurt or killed working on this equipment.

saultgeorge said:

I worked with a lot of European made equipment used on food processing when I was in Alaska. Most of it had the line side wired to the bottom of any breakers, contactors, terminal strips, etc. Very difficult to get used to. Anything I re-wired I wired it to U.S. wiring methods that were used by all electricians in this country and drew the prints accordingly. Having been in motor controls since the early 90's I could certainly see how someone would get hurt or killed working on this equipment.

Click to expand...

I won't argue that it is more common to see the line coming into the top of the breaker and the load out of the bottom, but should we be teaching that the line should be in the top and the load out the bottom or that you need to check to see which is the line and which is the load?

Motors are usually connected to something. Pumps, fans, compressors etc. I would suggest teaching some basic pump affinity laws (NPSH).

Generally in the UK at least, the line comes into the top of any disconnect in industry, however, in domestic installations the consumer units (that hold the disconnects) are commoned using a busbar at the bottom of the disconnects.


Steve

A few thoughts:

1. The motors class should be teaching basic ladder logic (with actual relays / hard wired controls). This should be a pre-requisite for the PLCs class (or taught in tandem) and the start/stop circuit should be well understood after leaving the class. There are many, many applications for a single motor, and it simply isn't economical to have a single motor controlled by a PLC/HMI. Motor starter panels are very common, and are almost always hard wired.

2. Hand-off-Auto, while a bit antiquated is still prevalent in industry (at least mine!). Basic H-O-A controls should be taught.

3. Don’t focus too much on the torque graphs/curves/etc – unless this class is specifically being given to mechanical designers as well. Most electrical / controls people never pick the motor from the torque curves, they are simply asked to control it. That is the mechanical designer’s job, IMO. Understand that they exist, but don’t make it the main focus.

4. Understand NFPA 70 requirements for a motor circuit (circuit breakers / fuses and the understanding that they protect the wires, NOT the motor, at-the-motor disconnects, motor overload protection, etc)

5. Understand some basic interlocks involved with a motor control schematic – ie how can I tell if the motor is actually running, the circuit breaker/overload is tripped, and how to wire them to an indicator light or PLC/etc.

6. Type E/F control vs contactor / overload circuits etc. Search for Bussman SPD (selective protective devices) which is a great reference for fuse sizing, wire sizing, etc for motor circuits by horsepower.

As to the top / bottom of a circuit breaker:
The contactor / circuit breaker typically has labels. “L1, L2, L3”, etc are line side, and “T1, T2, T3” etc are load side. If the schematic doesn’t call these out, the L terminals will almost always be assumed to be at the line and T at the load.

For a regular circuit breaker they are usually numbered 1, 2, 3, 4, 5, 6 and skip so 1, 3, 5 are on one side and 2, 4, 6 on the other. I would agree with most here that your panel (to me) seems incorrectly wired.