[Milsurplus] Even Worse
Peter Gottlieb
nerd at verizon.net
Mon Jul 5 15:14:10 EDT 2010
Not the *source* but the reactive component can be changed
instantaneously if the path now goes through a large inductance.
P
J. Forster wrote:
> Hi Peter,
>
> Clearly, power grids are not just wires, but must be treated as
> transmission lines. One wavelength of 60 Hz is about 3100 miles, so many
> power lines are a significant fraction of a WL long.
>
> However, my point is that you cannot change the phase of a source
> instantly with the flip of a switch. It takes seconds or tens of seconds,
> which makes control very hard.
>
> Any disturbances do not die out quickly either, complicating matters.
>
> -John
>
> ===============
>
>
>
>> This is not necessarily true. Long transmission lines are very
>> inductive, and dense cities (Boston, Detroit, NYC) with metal shielded
>> underground transmission lines can be quite capacitive. One real-life
>> situation that we modeled was the loss of a local feeder which caused
>> power flow through much longer transmission lines. This caused a step
>> change in reactive to higher inductance and was enough to de-stabilize
>> the system. These changes play out over seconds or tens of seconds,
>> surprisingly enough.
>>
>> As models get larger, due to limited computational power,
>> simplifications have to be made. There is a lot of work being done now
>> to make sure the simplifications made are correct!
>>
>> Peter
>>
>>
>> J. Forster wrote:
>>
>>> The real issues in network stability are that, because of the large
>>> rotating inertias of generators, a rapid phase change is all but
>>> impossible. To change the phase of a machine with respect to the
>>> network,
>>> you have to speed it up a tad (more steam), let the phase change, and
>>> then
>>> slow it back down (less steam). This cannot be done quickly.
>>>
>>> Furthermore, in a simplified case, if you have just two AC generators
>>> connected together, the can "rock" against each other in phase (rocking
>>> is
>>> a variation of the relative phase of the rotors), and the rocking is
>>> very,
>>> very lightly damped. Extend this issue to a network with hundreds of
>>> machines and you have a giant mess.
>>>
>>> -John
>>>
>>> =================
>>>
>>>
>>>
>>>
>>>> The real use of synchrophasors is not for power setting (that can
>>>> easily
>>>> be done by far less complex methods) but for early indication of grid
>>>> disturbances. This is getting more valuable as the control of the grid
>>>> is moving to a model-based design. Humans just can't interpret and
>>>> respond fast enough to prevent cascading problems.
>>>>
>>>> Peter
>>>>
>>>>
>>>> J. Forster wrote:
>>>>
>>>>
>>>>> Ah, yes. Phase shifting is easy in a polyphase system. For example, a
>>>>> Scott connected transformer can change 2 phase to 3 phase, or the
>>>>> inverse.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> -John
>>>>>
>>>>> ==============
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> Yes, it's done with a specialized tap-changing transformer called a
>>>>>> Phase
>>>>>> Angle Regulator. This paper describes how they're used:
>>>>>> http://www.npcc.org/viewDoc.aspx?name=Phase+Angle+Regulator+Operation+-May+2
>>>>>> 000.pdf&cat=LEER
>>>>>>
>>>>>> Albert
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: milsurplus-bounces at mailman.qth.net
>>>>>> [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Larry Godek
>>>>>> Sent: Sunday, July 04, 2010 6:10 PM
>>>>>> To: nerd at verizon.net; Milsurplus at mailman.qth.net
>>>>>> Subject: Re: [Milsurplus] Even Worse
>>>>>>
>>>>>> Do power companies share power back and forth according to peak
>>>>>> periods
>>>>>> by
>>>>>> changing the phase slightly? Where did i come up with this idea? I
>>>>>> really
>>>>>> don't remember.
>>>>>>
>>>>>> Larry
>>>>>> W0OGH
>>>>>>
>>>>>>
>>>>>> --- On Sat, 7/3/10, Peter Gottlieb <nerd at verizon.net> wrote:
>>>>>>
>>>>>> From: Peter Gottlieb <nerd at verizon.net>
>>>>>> Subject: Re: [Milsurplus] Even Worse
>>>>>> To: jcoward5452 at aol.com
>>>>>> Cc: jfor at quik.com, milsurplus at mailman.qth.net
>>>>>> Date: Saturday, July 3, 2010, 1:46 PM
>>>>>>
>>>>>> The power companies already do that and is able to compare phasors
>>>>>> across the grid. Check out NASPI, the North American SynchroPhasor
>>>>>> Initiative.
>>>>>>
>>>>>> I set up a PMU (Phasor Measurement Unit) at my plant already, it uses
>>>>>> GPS for time sync.
>>>>>>
>>>>>> Peter
>>>>>>
>>>>>>
>>>>>>
>>>>>> jcoward5452 at aol.com wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Here at our secret development Lab, we phase lock the 60~ to a GPS
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> receiver. This is how you make all the frequencies in the audio
>>>>>> spectrum
>>>>>> exact. This is really no secret as most Laboratories have a "house"
>>>>>> standard
>>>>>> derived from a GPS receiver.
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Jay
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: J. Forster <jfor at quik.com>
>>>>>>> To: Richard Brunner <brunneraa1p at comcast.net>
>>>>>>> Cc: milsurplus <milsurplus at mailman.qth.net>
>>>>>>> Sent: Sat, Jul 3, 2010 1:06 pm
>>>>>>> Subject: Re: [Milsurplus] Even Worse
>>>>>>>
>>>>>>>
>>>>>>> There is a thread on another list about radioactive tubes. I
>>>>>>> replied:
>>>>>>> "And, isotopically pure Thorium likely costs $millions / pound.
>>>>>>> What an opportunity for the Audiophools! Now, your Tube Amp can be
>>>>>>> onstructed with eviro-pure tubes. No harmful radiation to
>>>>>>> contaminate
>>>>>>> the
>>>>>>> larity of the sound. We at, PT Barnam AudioLabs, use only
>>>>>>> isotopically
>>>>>>> ure Thorium cathodes!!"
>>>>>>> :-)))
>>>>>>> -John
>>>>>>> =============
>>>>>>>
>>>>>>>
>>>>>>> This is beyond witless. Who are these people with so much money
>>>>>>> and
>>>>>>> so
>>>>>>> little sense? I notice they also can't spel, so it's consistent.
>>>>>>> Imagine, three brass spikes!
>>>>>>>
>>>>>>> Richard, AA1P
>>>>>>>
>>>>>>>
>>>>>>> On Sat, 2010-07-03 at 08:57 -0700, J. Forster wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> http://www.cruzefirstaudio.com/tripoint.htm
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>>>
>>>>>>>
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>>>>>>
>>>>>>
>>>>> ______________________________________________________________
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>>>>>
>>>>>
>>>>>
>>>> ______________________________________________________________
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>>>>
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>>>>
>>>
>>>
>>>
>>
>
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