Motor Start Up Current

All sounds good. Go for it.

Star-delta needs 6 conductors between the starter and the motor windings.

Is your two-speed by pole changing?

let me check it.

It sounds as though a variable speed drive is a candidate for investment - provided there's a payback, of course.

Peak demand tariff considerations, perhaps?

Star delta starting on a 2 speed motor is tricky at best, not somethoing for the uninitiated to even begin to attempt. Stick to using a solid state soft starter. You will need to evaluate how you are using the 2 speed capabilities first. If you ALWAYS will start it in low speed and then change to high speed, you would select a soft starter based on the amperage rating in the slow speed, thjen use a bypass contactor that removes the soft starter once it is at full speed, then use a standard electro-mechanical 2 speed starter that is appropriate for your type of motor.

If you need to be able to start the motor in either speed, then you must select a solid state soft starter that has "dual ramps" because the acceleration parameters will be different depending on the motor speed configuration.

But as PWSlack suggested, by the time you get done with all of this it's often better to consider a Variable Frequency Drive and just use the high speed configuration of the motor.

thanks guys, i will give your suggestion to our electrical maintenance section. It seems okay. I will be pleased if you can send and electrical diagram showing the set up you had mentioned.

I agree that a VSD would be a better option, as for a diagram, the VSD would be connected between the supply and motor. An easy item to connect in, six connection for three phase, (not including the secondary connections for control, emergency stop etc).

As for the diagram of the VSD, you would get that from the supply/manufacturer.

But as PWSlack suggested, by the time you get done with all of this it's often better to consider a Variable Frequency Drive and just use the high speed configuration of the motor. Jraef,just an enquiry, on a 2 speed motor , the higher speed is normally a lot less power.Will a vfd be able to accommodate for the torque needed at the lower speed.

A VFD only does current. It cannot do torque.

Try connecting a suitably rated capacitor during starting,to reduce the starting current

If your two speeds are in a ratio of 1:2 and if your load is a fan or pump load, the running current at low speed will be 8 times lower than that at high speed. The starting current too will likewise be less. You can therefore start at low speed and once it is running steadily switch over to high speed.

As the cooling effect of shaft-mounted fan is low at low speed will the HP delivered be same at low as well as at high speeds.

The first thing I would consider is knowing the required starting torque of your application.

If you need a certain amount of starting torque (like in an elevator), there is no way to use a soft start or a Wye / delta starter. Both devices lower the start current which results in a lower starting torque. The problem will be that your application will not accelerate…..

I good suggestion will be a three phase capacitor connected over the motor windings, this improves the power factor and lowers the starting current.

The other solution will be using a frequency drive. A sensorless vector drive will give your motor its starting torque from almost still stand up nominal speed.

Keep in mind to select it according the motor current, because a two speed dahlander motor has a motor current that is higher than an one speed motor.

Further keep in mind that the nominal torque of a two speed dahlander motor is different in the low and the high speed.

This again makes it unavoidable to know the correct required torque of your application.

Or you could start the motor unloaded with a MagnaDrive coupling. www.magnadrive.com

The least expensive method since you have a two speed motor may be to go start-delta to reduce starting current. If you have a two speed motor and the proper leads coming out, you can start the motor with a star winding configuration and then after a preset time switch to wye for full torque. This will require a special starter that switches the leads to change the configuration and timer control. You must also be careful to have enough starting torque especially if you have a high inertia load.

The second option is a reduced voltage starter either solid state (soft start) or resistive or reactive. The solid state is probably the least expensive nowadays and takes up less space than the old resistive or reactive type. It is also most flexible since you can shape the starting curve to match the load characteristics.

The ultimate approach is to use a VFD which is only slightly more expensive than the RV starter but provides maximum versatility and protection.

Have you contacted the motor/equipment manufacture?
This would seem to be a common problem that the motor/equipment manufacture has been through many times.