[Milsurplus] Even Worse

J. Forster jfor at quik.com
Mon Jul 5 15:15:12 EDT 2010 

By raising or lowering the field current, you can make the reactive power
look capacitive or inductive respectively, but not instantaneously. The
L/R time constant of the field circuit is nowhere near zero. The L is
huge.

-John

===============


> 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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