Short Circuit MVA on transmission systems
Short Circuit MVA on transmission systems
(OP)
Can someone give typical realistic SCMVA levels on 230kV station bus and 115kV station bus of transmission networks from experience?
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Short Circuit MVA on transmission systems
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Short Circuit MVA on transmission systemsShort Circuit MVA on transmission systems(OP)
Can someone give typical realistic SCMVA levels on 230kV station bus and 115kV station bus of transmission networks from experience?
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RE: Short Circuit MVA on transmission systems
As I encountered, on 110 kV [50 Hz] -close to the center- 30 kA was expected.
220 kV may be up to 50 kA. 160 kV may be 63 kA- top and 400 kV from 50 to 63 kA also.
I think these data may be considered for 60 Hz system too.
RE: Short Circuit MVA on transmission systems
Anybody has experience numbers in North America?
RE: Short Circuit MVA on transmission systems
I think it's a little bit difficult to say.
a client is connected to a transmission network and the SCMVA is 2000 MVA. A other client is on the SAME line, but at the end of the line, and the SCMVA is 500 MVA. This is for a 120 kV network
RE: Short Circuit MVA on transmission systems
Take the transformer MVA, divide it by the transformer impedance and you'll have an upper limit for a three-phase fault. 200 MVA transformer, 10% impedance - 2000 MVA. The transformer impedance is primarily a function of the primary voltage and BIL. ANSI has standard impedances based on the BIL.
"The perfect is the enemy of the good." -- Voltaire
RE: Short Circuit MVA on transmission systems
"The perfect is the enemy of the good." -- Voltaire
RE: Short Circuit MVA on transmission systems
However, I am more interesting on the transmission grid level, i.e. 230kV and 115kV ring buses other than a tapping transmission customer, any ideas?
Thanks!
RE: Short Circuit MVA on transmission systems
"The perfect is the enemy of the good." -- Voltaire
RE: Short Circuit MVA on transmission systems
I am working on a protection study for one of our transformer stations. The station (DESN) is tapped on the 230kV transmission lines. The normal operation is to run two transformers in parallel with the bus tie closed. If there is a fault on one 230kV line, as a backup, the directional distance element will prevent the back feed from the healthy 230 line to the fault through the paralleled transformers. So, my first step is to do a fault flow calculation. However, I don't have the fault level at the supply authority's ring bus. We had a similar study done by a consultant 7 years ago and the consultant didn't have that info either, what they did is to assume 6600MVA (I have no idea where they took this estimation from)at the 230kV bus - 17kA 3Ph fault at the nominal voltage 220kV, which I thought is underestimated.
RE: Short Circuit MVA on transmission systems
3-phase MVA: 4390 - 4460 MVA (depending on transmission config)
Z1,Z2: .0022+.0234j - .0022+.0237j
Z0: .0118+.0542j - .0118+.0542j
Ian Dromey - www.dromeydesign.com
RE: Short Circuit MVA on transmission systems
Do you have some typical values for a 115kV station on the grid?
RE: Short Circuit MVA on transmission systems
RE: Short Circuit MVA on transmission systems
RE: Short Circuit MVA on transmission systems
A rural location will be different than in an urban core; near generation will be different than far from generation; the Atlantic seaboard will be different than the wide open spaces of the inter-mountain west. You need to be working from a system model of the specific system you are planning to interconnect with.
If made up values are really all you need, go ahead and make them up, but there are no usable "typical" values.
RE: Short Circuit MVA on transmission systems
3-phase MVA: 1715 - 3431 MVA
Z1,Z2: .0029+.029j - .0058+.058j
As duly noted by davidbeach, sample data is just sample data.
Ian Dromey - www.dromeydesign.com
RE: Short Circuit MVA on transmission systems
RE: Short Circuit MVA on transmission systems
Substation circuit breakers are rated for voltage, continuous current, and fault interrupting capability. In transmission substations (69 kV and up), typical fault current ratings include 25, 31.5, 40, 50 and 63 kA, and some manufacturers now can attain 80 kA.
This should give you some indication of what the market supports. As the engineer, you have to know what conditions you are going to encounter to decide how much of a breaker to buy. This is where the fault study comes in.
In my rural California utility, 40 kA is plenty for every part of my system. In fact, I've got old OCB's from the 70's at 14.5 kA and 19 kA that are still adequate *for my system*. But it would be foolish for my counterpart at the utility next door to try to apply what works for me to his system (not to mention the big urban utilities nearby).