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Gas Turbine Package Power Output Unit

12/21/2020 4:15 AM

Greetings All,

1) Why the output of a gas turbine-generator package is mentioned in “Watts electric”, as in MWe or KWe and not in Volt-Ampere, as in MVA or KVA?

2) Why the alternator rating is to exceed turbine output power at all conditions in such packages?

Thank you all in advance.

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Guru
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#1

Re: Gas Turbine Package Power Output Unit

12/21/2020 5:52 AM

A1) Reactive power does not appear as torque x speed on the rotating shaft for the turbine to drive. So its VA rating is unrealistic.

A2) If it didn’t, then there would be a risk of burning out the alternator <...in such packages...>.

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#2
In reply to #1

Re: Gas Turbine Package Power Output Unit

12/21/2020 6:10 AM

A2) it is better for the turbine to run out of puff before the alternator goes phut.

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#3
In reply to #1

Re: Gas Turbine Package Power Output Unit

12/21/2020 1:04 PM

A1) Only electrical equipment has a <...VA...> rating.

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#5
In reply to #3

Re: Gas Turbine Package Power Output Unit

12/21/2020 1:46 PM

Thanks for your fast responses PWSlack.

So as per below, the rating 8.734 MW shown in Screenshot-1 is of gas turbine and that's the maximum power output the coupled alternator can generate which is even though rated higher as 11568 kVA. And finally 8.734 MW is power output MWe as per Screenshot-3. Please let me know if my understanding is correct about all of these. Thanks in advance.

Screenshot-1

Screenshot-2

Screenshot-3

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#6
In reply to #5

Re: Gas Turbine Package Power Output Unit

12/21/2020 2:25 PM

Additionally Power Output in MWe shown in Screenshot-3 is the rating of the power turbine within the gas turbine and not of the alternator. Am I correct?

Just sharing a reference found in the web.

https://www.electricaltechnology.org/2014/05/power-plant-capacity-rated-mw-not-mva.html

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#7
In reply to #5

Re: Gas Turbine Package Power Output Unit

12/22/2020 3:24 AM

It is difficult to put #1, #2 and #3 above any simpler.

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#11
In reply to #5

Re: Gas Turbine Package Power Output Unit

01/09/2021 1:53 PM

The 8.734 MW is the electrical power output of the generator. The turbine shaft output is that plus the generator mechanical and electrical losses.

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#4

Re: Gas Turbine Package Power Output Unit

12/21/2020 1:33 PM

1) Put simply, To avoid confusion, the electrical output from the generator is often referred to as kWe (or ekW) which is the actual generator output after efficiency losses within the generator. Electrical power is usually measured in Watts (W) or thousands of Watts (kilowatts, kWe). kWe is sometimes referred to as “real power” while kVA (kilovolt-amperes) is apparent power.

link

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#8

Re: Gas Turbine Package Power Output Unit

12/22/2020 9:29 AM

1) There is no difference in power rating when specified in watts (for that matter Kilo watts or Mega watts) or watt written as We or KWe or MWe. Nuclear power station have a fancy of adding "e" after W, KW and MW. I as a designer, had handled contracts of thermal and nuclear power stations and supplied same generator to them against their demand in MW and MWe.

2) As regards rating of turbine, which is always specified in watts, (as prime movers supply only active power and no reactive power, which is supplied by the generators.) Therefore generator rating is always specified in KVA which is called apparent power. Active power is product of apparent power and "Power factor". Power factor is always less than one. So Apparent power which is given in MVA, is always more than active power in MW. Therefore rating of prime mover in MW is always less than generator rating in MVA. Ratings of turbine and generator must be compared in same units MW and not MW of turbine with MVA of generator. But if one compares ratings of turbine and generator in MW, then rating of the turbine in MW, will be higher as the turbine has to supply power equal to the generator output in MW plus the generator losses in MW.

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#10
In reply to #8

Re: Gas Turbine Package Power Output Unit

12/22/2020 9:20 PM

I really liked your answer, so GA!

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#9

Re: Gas Turbine Package Power Output Unit

12/22/2020 7:55 PM

1. The turbine is rated in mechanical output, normally kW, but could be HP, BTU or Joule. There are no electrical quantities in the turbine output rating.

2. The generator is solely rated in electrical quantities, volts & amperes. Each generator has an ampere rating that cannot be exceeded without eventual damage. Typically generators are sized to take all of the mechanical power developed by the turbine, plus have capacity to provide reactive or voltage supporting power that is invariably required by the power system it is serving. It is possible to operate the generator at its full rating, where kVA = kW, 1.0 power factor, but the generator loses the opportunity to stabilize the power system for upsets and transients when operating in this mode. So it is traditional to specify the generator at either 105% or 125% of the size needed for the turbine, i.e. 0.95 PF or 0.8 PF, depending on the configuration of the power system it is applied on.

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