power generator

[hasanhadi]

hi
1- i having load 500kw working at 400volt
and have motor 360kw working 6600 by using step-up transformer
2- how choose power step-up transformer?
3-at starting motor 360kw how many time need to stability for generator i mean at starting voltage generator is reducing the governor and AVR will work to rising voltage the voltage generator at starting is reducing after that rising after that return to rated value equation here i need know max. time from reducing voltage at starting until return to rated value

 

[GEORGE2311]

For the step up transformer you have to see what will be the voltage drop across the impedance for the motor start up current. Use as uk=5% as it is typical until 1000kva. A 1000kva transformer has a short circuit aprox. 28kA. Your motor if we assume it has 6 times nominal it will reach during start up aprox. 4kA The voltage drop will be 4/28=0,14=14%. If this value is ok with your specification then you are ok. If not choose a 1250kVA transformer.
What is your generator rating? Check with the capability curves if it can give the start up current.

G.F.

http://www.engineering-services.gr

 

[hasanhadi]

hi
the generator rated 1250kw
i need konw too max time to need generator to stability at starting motor

 

[GEORGE2311]

For a detail answer on the time needed for stabilization after starting such a motor you have to ask the generator vendor.
From my experience, a 1,2MW four stroke diesel generator running in lets say 10% load can start without any problems or significant voltage dips a 350kW motor. Depending on the machine, I will expect maximum a 10% voltage dip for less than one second.
Last month we make a similar test with a CUMINS 1110kVA in 50Hz/400V, equipped with a STAMFORD alternator where we start up a 430kVA load (PF ~1). The little monster took the load while we didn't notice any difference in voltage or even the sound of the machine.

G.F.

http://www.engineering-services.gr

 

[GEORGE2311]

Have a look in the attached file. It is from the generator i mention in my previous post.

G.F.
www.engineering-services.gr

 

[iop995]

To find start-up time need to know details about motor load also. Torque and inertia at least. From diagrame, at 4kA start-up current, dip voltage is above 30%. That will reduce start-up current and also start-up torque and will increase start-up time. It's important to know if motor start with or without load. For no load I think will be no problem, a small increase in start-up time. With load start-up is very important torque load and inertia. At such dip voltage (35-40%) torque is also reduced with 80-90% and is very probable that motor can't start-up load.