Connecting a motor up incorrectly

[roukel01]

Morning All

We were called to a motor on a printing press yesterday, basically it had burnt out.

The press is on a transformer and is supplied by 200V 3 phase.

When we checked the motor connections against the data plate it seemed to us that the motor had been conneted incorrectly (i.e direct on line connected in star rather than delta) and so the voltage was wrong.

We've connected the replacement motor in delta and it seems to be running fine

What happens in these circumstances when a motor is connected up incorrectly because the old one lasted 18 months

 

[Deleted member 26818]

Motors can be run in either star or delta.
The output torque of the motor is different depending upon whether it's in star or delta.
If a motor is chosen for it's output torque in delta, and is then run in star, the motor will be overloaded.
Then again, if the output torque is very high, the motor bearings can be stressed if it is started in delta, which will eventually overload the motor.
With high torque output motors, a star delta starter is used,
The motor starts in star, and then ideally when the motor reaches 75% of the delta speed, the unit changes from star to delta.
Not very usefull though, if a fast start is required.

 

[Darkwood]

If you check the motor plate find out if its a duel voltage and if so which voltage range it covers?
Is the press running the motor through an inverter and if so is its output 3ph 220v?
You seem supprised it was connected in star so am i to assume there just 3 wires and not 6 as found in a star/delta start up?
Also its usual to establish the cause of the burn out before you replace the motor or refit the rewound motor.
What is the motor doing?,
What size is the motor?

Fill in all the above and we can answer you more accurately.

 

[roukel01]

I'm not worried about finding out what happened to the motor, all I wanted to know was>

Example: A motor plate says Delta Connection 230V, star 400V. If 230V is applied but connected in Star what happens?

 

[Knobhead]

The main effect will be torque will be reduced to .577 of full rated output.

 

[Darkwood]

I'm not worried about finding out what happened to the motor, all I wanted to know was>

Example: A motor plate says Delta Connection 230V, star 400V. If 230V is applied but connected in Star what happens?

Running at 230v long term on 400v winding isnt a good idea if heavy load as well as torque issues you may experience slippage too and slower speed, it is usually used to soft start a motor as its load limiting on the supply (star/delta) but to run constantly in this manor may eventually damage the motor only a lighter load will give no adverse effects.
If i recall if the current demand is less than a third of motor rating its fine to run in star but if it exceeds this then long term you will damage the motor which is what i suspect has happened.

 

[Knobhead]

Something’s just crept out of the horrible dark recesses of my mind. What’s this motor used for on the press? Presses usually use DC motors for web speed control.
Let me know please.

 

[roukel01]

Its just air supply to sepearte the paper

 

[netblindpaul]

Tony,
At a previous employer of mine we "invented" a shaftless synchronisation system for printing press motors so that they would all run synchronised on 3 ph supply and be able to offer registration offsets and speed control to fractions of an rpm and synchronisation to around 3 decimal places of a degree across all motors, across all towers and the folders across the whole press, no lineshaft required, Goss took the system of us for all of their presses globally, so not always d.c. mate.
Harmsworth Quays at London was one of the big press users of this system.

 

[Knobhead]

Paul, I didn’t say all presses. I’ve worked on German, Italian and Belgian presses all were DC. Modern design so no line shafts.

 

[Inteificio]

I thought the reason for using a star/delta starter was due to the coils melting if started delta due to the inrush current?

Once the coils are warmed up and spinning the impedance increases, letting you pump up the voltage with delta.
The impedance is too low from cold so putting 400v straight in could cause too much current to run melting the windings.

I might be completely wrong, so someone please affirm or contradict me!

 

[Deleted member 26818]

That could be one reason.
A lot depends on the current rating of the motor, it's output torque, and what load it's turning.

 

[netblindpaul]

Paul, I didn’t say all presses. I’ve worked on German, Italian and Belgian presses all were DC. Modern design so no line shafts.

Tony,
I only ever worked on our kit on printing presses, have worked on other presses, but only printing on the kit that we made, so thus Goss.
Mind they are made in UK, Germany, France, Italy & Belgium IIRC!
What motors were they dc brushed or dc permag?
Can you remember the makes of the motors & drives?
Just out of curio.

 

[Darkwood]

I thought the reason for using a star/delta starter was due to the coils melting if started delta due to the inrush current?

Once the coils are warmed up and spinning the impedance increases, letting you pump up the voltage with delta.
The impedance is too low from cold so putting 400v straight in could cause too much current to run melting the windings.

I might be completely wrong, so someone please affirm or contradict me!

The reason we start in star and then to delta is to dampen current demand on the supply as star config limits the current. This is used with medium to large motors, dont know where you heard that but kinda forget it, the windings usually have a few ohms resistance before energised but the instant magnetic field on power up stops its low resistance creating a near short circuit, alot of smaller motors are started and run DOL. (direct on line) no star to delta config so power straight on.

 

[Knobhead]

DOL can be used on quite large motors. I was on a safety visit to another plant in our group. I wondered why I was very carefully stood next to a motor for a photograph, soon bloody found out! 2000HP DOL, in the photograph I looked like I had S**T myself when it started!
If the supply is up to it then there’s no need for fancy starters

Paul sorry I can’t remember the makes of the presses. I was the new boy so the Italian one was my baby. The biggest pile of sh*te out. The German presses came with perfectly translated manuals and drawings, not this baby. My Italian was and still is as good as that bloody machine.
All the motors were brushed.

 

[Darkwood]

DOL can be used on quite large motors. I was on a safety visit to another plant in our group. I wondered why I was very carefully stood next to a motor for a photograph, soon bloody found out! 2000HP DOL, in the photograph I looked like I had S**T myself when it started!
If the supply is up to it then there’s no need for fancy starters

Think on this occasion your experience is far field of the general sparkies/engineers, but with respect i can imagine that beauty wasnt on a 32amp type (c) mcb--- would have probably arced over the top of it with the inrush :Oo