3 Phase Brook Crompton Gryphon Motor

[Beekeeper2003]

I have a 3 phase 400v only Gryphon Motor dating from 1965. A previous owner has found the star point so as to enable it to run at 220v and brought this out as 3 separate (I'm not sure why)cables which are purple in colour. However, there are also two small much thinner gauge original yellow cables the purpose of which I do not understand. Picture attached. Any help or thoughts would be greatly appreciated. William

 

[rtbcomp]

Welcome to the forum. He probably used three wires to enable it to be switched between star & delta.

Are those yellow ones connected to any of the other wires on the terminal strip?

Try a continuity check between the yellows and the others to see if there's an internal connection?

Measure the resistance between the two yellow wires.

 

[arther dailey]

probably heat sensative strip, same as you would have on a transformer welder, when it overheats it will go open circuit normally.set up is then wired up so if it overheats power is switched off to mtr saving burn out in theory.

 

[arther dailey]

ps, it still needs 220volt with three phase supply though! cant be run on single phase..sorry

 

[Beekeeper2003]

Welcome to the forum. He probably used three wires to enable it to be switched between star & delta.

Are those yellow ones connected to any of the other wires on the terminal strip?

Try a continuity check between the yellows and the others to see if there's an internal connection?

Measure the resistance between the two yellow wires.

Thanks for the welcome to the forum.

One of the wires is connected to one of the 3 phase input live feeds together with one side of a motor winding, the other wire is connected to a terminal by itself though I have five core feed cable with the spare core also connected to this terminal.

There is no resistance between the wires i.e it is closed circuit. I have tried putting a heat gun on the case to test if it will go open circuit with heat but it isn't really practical as I risk burning the paint off the case but the possible explanation Arther Dailey suggests sounds plausible to me. The motor is off A Tom Senior Major Milling machine.

As an aside/supplementary I wonder if anyone has any experience/thoughts on LS Starvert Inverters.

 

[WorkshopChris]

There is no resistance between the wires i.e it is closed circuit. I have tried putting a heat gun on the case to test if it will go open circuit with heat but it isn't really practical as I risk burning the paint off the case but the possible explanation Arther Dailey suggests sounds plausible to me. The motor is off A Tom Senior Major Milling machine.

Thermal protection of motors to protect the winding is common in industrial situations, if that is a thermal switch more modern motors often have thermocouple built in with the winding's. As a motor in normal use will run hot i would not expect you to be able to put enough heat externally into the motor to operate any thermal switch.

Often fitted to pumps as a rise in internal temp can indicate a blocked filter, triggering an alarm to alert maintenance before isolating the motor if temp continues to reach a cut of point.

 

[rtbcomp]

I'd go along with thermal trip too, if so the two yellow wires would normally be connected in series with the holding coil in a No Volts Release starter &c.

 

[Rig Pig]

It might be an anti condensation heater winding?

 

[arther dailey]

I rewound hundreds if not thousands,my monies on thermocouple

 

[rtbcomp]

It might be an anti condensation heater winding?

It would have some resistance in that case, post #5 says it has zero resistance.

I rewound hundreds if not thousands,my monies on thermocouple

If it's a thermocouple would it need some electronics to operate it? As one of the yellow wires is connected to a live I'd go for an on/off trip controlling an NVR

 

[daleyd]

It's more usual to have a thermistor (a type of thermal switch) rather than a thermocouple (temperature sensor) in the windings, thermocouples can be affected by the currents in motors (they operate on extremely low voltages) so tend not to be as widely used.

 

[rtbcomp]

A thermistor is a temperature sensitive resistor, so I guess it would still need electronics for it to work, unless it had a very large resistance swing?

 

[daleyd]

A thermistor is a temperature sensitive resistor, so I guess it would still need electronics for it to work, unless it had a very large resistance swing?

If it's a true thermistor yes, it will need some form of device on the end to turn the resistance change into an alarm or to cut the power (would usually be wired into a drive or a dedicated alarm block with contacts to knock off the main contactor and/or signal a fault), though it would be unusual for it to pull power from the motor windings itself.

Another possibility is a bimetallic element, though I've never personally come across these used in a motor.

 

[rtbcomp]

^^ Interesting, I would have thought a bi-metallic element would have been the obvious choice.

 

[daleyd]

Yeah, I guess perhaps a bimetallic strip can't really cope with much current at the size needed to be embedded within motor windings, but certainly I've only ever really come across thermistors used in motor protection (ive seen a couple of applications where pt100 sensors have been used to give an actual measurement, but not often). I've really got more experience with industrial kit (usually 3 phase) rather than single phase stuff though so there may well be other methods I'm not aware of?

Quite often if using a decent make of vfd they can "guesstimate" the winding temperature from its characteristics even without a sensor, though how accurate this is I'm not 100% sure.

 

[daleyd]

Just had a thought - a bimetallic strip may be affected by vibration in a motor?

 

[Pete.]

No point speculating. Could be a thermistor, could be a thermocouple, could be a thermal switch. Since it's a 3 phase motor and since the wires are so thin it's not designed to interrupt the motor power directly but through a control relay. Cut the wires off and forget about them.

 

[daleyd]

Well, there's no harm in a bit of speculation, it's not really needed but if there's something that's useable then why not for the sake of 5 mins checking? If after that you decide it's no use then I'd be inclined to stick the ends in some chock block and leave them in the terminal box.

 

[Robotstar5]

I sometimes wonder what the manufacturers think an excessive temperature is, I've found some of our conveyor motors running that hot you can't touch them and you can smell the oil in the gearbox cooking, but no sign of an overtemp alarm (yes, they are connected)

 

[Pete.]

Well, there's no harm in a bit of speculation, it's not really needed but if there's something that's useable then why not for the sake of 5 mins checking?

I suppose it's fine as an academic exercise and the OP was asking for any help or thoughts. I just offered up my most helpful thought and that was chop 'em off you don't need them.