Starting a large motor
Starting a large motor
(OP)
Starting a large motor such as 16MW, 11kV when the existing power system is not strong poses a problem. Reactor starting can reduce the starting current and thus limit the voltage drop in the system. I can see it is simplicity. Are there any better ways which are also economical as well as robust to stand desert conditions.
Thanks in anticipation.
Thanks in anticipation.





RE: Starting a large motor
I am sure you know that you need to perform a analysis on a motor staring transients to see if the resultant voltage dip is acceptable to rest of the system. Unless this is tied to a 11kV large generaotor bus, the motor alone will need a 20MVA or better transformer, rather too big for 11kV distribution system.
There may be medium voltage electronic (SCR) reduced voltage starters that some manufacuter can make upon custom order, but may not be suitable for desert conditions. (There are medium voltage static transfer switches made).
RE: Starting a large motor
Are there better ways ? Certainly. Are they more expensive (less economical) ? Of course. More Robust ? Very likely.
But there is considerable cost associated with them.
Rbulsara's medium voltage electronic (SCR) reduced voltage starters is one...
Another would be a VFD ...transformer down to meet input voltage limitation of medium voltage VFD and transformer up at output to meet motor requirement of 11 kV.
Special system ... very costly ... but reduced stress not only on plant distribution supply, but also on motor and machine.
Could be considered as a one time investment with payback over time with elimination of maintenance costs and lost production ...
RE: Starting a large motor
RE: Starting a large motor
RE: Starting a large motor
The large VFDs or soft starter will experience heating problems, if not cooled properly. They will have to be custom made. The reliability may be lower than the simpler approaches mentioned.
RE: Starting a large motor
http://fie.engrng.pitt.edu/fie2002/papers/1499.pdf
for: soft start addressing resistors
http://webs.mn.catholic.edu.au/physics/emery/hsc_motors...
for: It is interesting to note that when the motor is first turned on and the coil begins to rotate, the back-emf is very small, since the rate of cutting flux is small. This means that the current passing through the coil in the forward direction is very large and could possibly burn out the motor. To ensure that this does not happen, adjustable starting resistors in series with the motor are often used, especially with large motors. Once the motor has reached its normal operating speed, these starting resistors can be switched out, since by then the back emf has reached a maximum and has thereby minimised the current in the coil.
RE: Starting a large motor
The staged resistor method of reduced current starting... is more ammenable to low voltage applications.
Can you imagine the special resistors and contactors required for this 11 kV motor....? If available, very special... and very expensive too.
RE: Starting a large motor
RE: Starting a large motor
Also, What type of motor are you talking about, Synchronous or Induction?
Is the motor, to be started, under load ( such as a fan or compressor or conveyor, or is there some sort of unloading device such as a clutch?
If the motor is to be started unloaded and it simply has to accelerate it's own inertia then you could use a VFD to do the starting for you. the power required for the starting would be no where near the 11 MW. If it is a Synchronous motor, you can actively synchronize it to the line, before closing the motor breaker, Eliminating any surges at all. This type of synchronizing these days is a " No Brainer"
If the motor is an Induction Motor, Again VFD's can do the job. Synchronizing is also possible and again provides a smooth bumpless transfer to the line.
if your application requites the motor to be started fully loaded, then the VFD route becomes much more expensive.
Tom Grayson
RE: Starting a large motor
Reactor starting is being considered but I am not sure that is the best thing to do. I heard of flux compensated magnetic amplification (FCMA) drives that can limit the starting current to about 200%. But, I am not sure of economics and relative merits.
Any help welcome. Thanks once again to every one.
RE: Starting a large motor
http://www.gehealthcaresolutions.com/MotorStarting.pdf
RE: Starting a large motor
RE: Starting a large motor
RE: Starting a large motor
RE: Starting a large motor
Generally Reactor / Auto transformer starting is used for pump/fan/compressor application. For such loads, a lot of energy can be saved if V/f drive is used, but depends on flow characteristic.Generally the payback period is 18 months.
For crushers/conveyors/kilns, reactor / auto transformer/soft starter starting is not suitable as the starting torque requirement is more.Necessarily starters like Vector drive which can provide higher starting torque and smooth acceleration should be used.
Simson
RE: Starting a large motor
www.magnadrive.com
Magnadrive requires electronic control of the magnetic coupling, a motor soft starter, at least; and a contactor bypass of the soft starter.
The Active Front End (AFE) drives, although still about 60% more expensive than the isolation (phase shifter) transformer drives, appear to be simpler solutions than the magnadrive.