Hydropower Unit Inertia Requirement 1

[QCE]

I have been to help out with some info regarding a hydropower unit.

What are they talking about when they say inertia requirement in MWs/MVA in ton m2 for a hydropower unit?

What can one do in order to meet inertia requirement?
what is a reasonable value or a upper limit value and what kind of costs would be expected?

What is the mathematical relationship between tonm2 and MWs/MVR?

Thank you very much in advance!

 

[Marmite]

It's a measure of the stored kinetic energy in the generator which will determine how quickly a generator reacts to system disturbances.
The stored kinetic energy is 1/2xJxWxW
J is moment of inertia in kg m(sqd)
W is rotational speed in rad/s

If you divide by the generator VA

Stored kinetic energy/VA = 1/2xJxW(sqd)/VA

When rotating at nominal frequency, the ratio of stored kinetic energy to VA on the left hand side is known as the generator inertia constant, H. For hydro, H is usually in the region 2-5. A lighter more efficient newer machine will have a lower H than an older machine.
Regards
Marmite

 

[Marmite]

I forgot to say that the stored kinetic energy is measured in Megawatt Seconds, which is where the MWs/MVA comes in. This is H, the generator inertia constant.
Regards
Marmite

 

[QCE]

Thank you, thank you, thank you.

So the H value is dependent on m,r and w of the machine. Would you normally add or reduce weight to the rotor or change the diameter of the rotor to adjust the H?

You say newer machines have a lower H but isn't it better to have a higher H value for system stablity?

I believe you but how do you go from kgm^2/s^2 to MWs - I missed something???

 

[Marmite]

The formula is the standard formula for kinetic energy of a rotating mass. Energy is Joules.
Volts= Joules/Coulomb
Amps=Coulombs per second
Watts= VxA = Joules per second
Watt seconds =Joules (same as kWh on your meter at home =energy)

Newer machines have lower H because advances in manufacturing technology mean there is less metal in them and they are more efficient. Bigger H is better for stability but worse for fault contribution as the machine can contribute more energy to a fault. Are you designing this thing from scratch?!

Regards
Marmite

 

[QCE]

Are you designing this thing from scratch?!

Actually the owner was asking for options for differnt H values so they could consider using one or two lines for distribution. I was just asked to look into it.

Thanks again for your help.

 

[QCE]

Hello,

I hope that Marmite is around or anyone else with comments.

I would like to get comments on the following:

It has been suggested that if the generator has a H=3.5 then we need 2 power lines for stability of the grid but if the generator has H=5 then we would only use 1 line.

Is it normal to adjust the inertia of the generator to meet grid requirements?

Do you see any problem with raising the H value?(lower efficiency, more stress on generator bearings or brackets)

I am guessing it would be cheaper to raise the H instead of building another line but what would you recommend in this situation?

 

[Bahram7]

Hydro units have usually H values between 3 to 4.5.
While higher values of H will certainly help the transient stability of the network, they are not usually adjusted to meet network requirements. Factors such as the type of the excitation, system stabilizers, circuit-breakers reclosings, etc affect more the stability of the system following perturbations.
If data are provided, the system can be soundly designed with a standard transient stability program.

Bahram7

http://www.Simtech-Intl.com