Total System Inertia (H) - power system 2

[element230]

Hello guys,

I've been asked to provide the total system inertia (H) of my power system. This is for a dynamic stability study. Any ideas on how to calculate this number?

Thank you!

 

[mgtrp]

What does your electrical system consist of?

 

[7anoter4]

For H constant calculation:
H=0.231*WR^2*(rev/min)^2/MVA/10^3 [J/VA] Eq.88
See:IEEE 399/1990 ch.4.9.3.3.2 The H Constant

 

[element230]

mgtrp:
It's a rather large system >2000 MW of installed capacity with a 230/115kV transmission system.

7another4:
I have the individual H values for each unit. I'm looking for an equivalent value (or aggregate) of the system.

Thank you for your help!

 

[QBplanner]

I recall there is a IEEE paper talked about whole WECC system inertia.It may be helpful. For such a request system inertia,it is difficult to calculate the exact value. There will be too many scenarios.

 

[element230]

Can you recall the title of the paper? If its a IEEE paper, I might be able to get it.

Thank you!

 

[mgtrp]

You need to convert each of your H values to the same base, and then add them all together to get a total inertia.

Presuming that you have loads connected within your system - these will also have inertia from any rotating machinery.

 

[element230]

MGTRP:

This was actually the only way I was thinking I could do it.... so your response confirms my assumption.

Thank you for your help!

 

[mgtrp]

We are able to do this on our system by observing the initial rate of change of frequency after large load/generation trips (much like you would do for measuring H in an individual generator), but we are islanded from other networks; I'm presuming that you're interconnected, so this wouldn't be practicable.

 

[electricpete]

If you have a mass/spring system with N masses, can you replace it by one mass which has a mass equal to the sum of the individual mases?

For most dynamic studies, the answer is no. In order to simplify the system requires modal analysis and Guyan reduction.

The mass/spring/Force system has direct mathematical analogy to the linearized H / X / Power system (linearization required to convert an X to a single value of K).

A little thought will tell you it is valid to simply add together the masses (H's) only when studying transients that involve frequencies which are much lower than the resonant frequencies of the multi-degree of freedom system. In that case the springs act rigid (the interconnecting X's act like short ciruits).




=====================================
(2B)+(2B)' ?

 

[mgtrp]

For most dynamic studies that I've seen, the answer seems to be yes. Even Kimbark - who wrote the book, so to speak, on power system stability - adds the unit inertias together in his examples.

 

[QBplanner]

For a simple islanded system you can do what Kimbark's way. Such as a generator cluster. But for a system with both generation (could be mixed type and motor loads), it would be very difficult to calculate.
The IEEE paper search "WECC" "system" "inertia"