Rating of motor or generator like when we say a 50 KW motor or 50 MVA generator what it means ?

Question

does it means
1. the maximum output power of motor or generator is this much(given rating) or
2. is it like that it will run at this input (given rating)
When we give rating in MVA and when in KW ?

Answer 1

It is closer to 1.



These are the normal rated RMS values for the device. All devices create heat and heat is generally the cause of failure for electrical devices. It is the rating that the device can safely operate at continuously (if rated continuous). That is, the amount of power the device can safely generate while the heat is safely dissipated. For short periods of time, especially at the start up of motors, these values for real power (P in kW) and apparent power (S in V•A) can be exceeded. So the maximum output the device can deliver continuously.



A 50kW motor puts out up to 50kW of mechanical power. Input has to be slightly larger to deal with mechanical (windage and bearings) and electrical (winding I²R losses).



A 50MV•A generator puts out up to 50MV•A of electrical power.



A 11kV rating is the rated RMS voltage for the device. The device operates at 11kV.

Answer 2

A motor or generator converts energy between electrical and mechanical. In both cases, the input will reflect the (output) load. This is a relationship between the torque and the current. I.e. if you draw more current from a generator, it will require more torque to turn. If you resist a motor, ie more torque, the motor will draw more current. All the same time the voltage and speed remain related and constant up to the point where the resistance etc causes significant wasted power. The bigger the motor or generator, the less resistance it will have, but at some point it causes enough power wastage to overheat the motor/generator, so there has to be a limit. Most specs are for continuous duty but they also often give a short temp maximum.

Note that W = VA *pf where pf will be ~80% so MW = 1000KW, MVA = 1000KVA, MVA ~= 800KW



11KV is the (nominal) operating voltage (11,000 Volts) , which means the wiring has to be good for at least 11,000Volts, ie not for amateurs. These power levels are strictly for teams of trained professional using elaborate safety protocols since mistakes result is large and lethal electrical explosions.

https://en.wikipedia.org/wiki/Arc_flash

Answer 3

I have NEVER SEEN a 50 KW generator that runs on GASOLINE... anything that big will run on either Diesel or Propane or LNG... and usually Diesel. You don't figure it in cost per KWH, anyway... a 50 KW genset will probably be driven by at least a 100 HP cat and at 1800 RPM that would be about 10 to 12 Gallons per hour.. or 288 to 300 gallons a day... maybe more... it would depend on a lot of things, like how old the diesel was and how heavily loaded the generator was..

Answer 4

Generators and motors are rated in volt amps (VA). The reason for this is that there are magnetic and copper losses in them. Magnetic losses are directly rated to voltage and I^2R losses are (obviously) dependent on the current. The power they can put out is VA cos(theta) where cos(theta) is the power facgtgor (PF) and theta is the angle between the voltage and current. If the PF is 1, then the VA and power rating are the same.