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Patrick

Sun Sept 19 2010, 09:12PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

radiotech wrote ...

Try and get the standard; from page 9 to 43 is all the stuff on PT's. Schools can get it from IEEE if they pay the 'standard subscription'

yes my school has the database rights to the IEEE and others. i will post here when i get it tonight.

EDIT: so far i find no results on EBSCOhost, for "C57.13 - 1978" or "c57.13-1993"

radiotech

Sun Sept 19 2010, 10:41PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I am using: C57: Complete 1990 Edition - Distributing, Power and Regulating Transformers . C57.13-1978 Instrument Transformers is one of about 50 in the book I just logged on to IEEE and found the 2008 CD of the book.

[edit] the link doesnt work so--

Replaces STDVU136, Power Distribution and Regulating Transformer Standards: 2005 VuSpec. Includes active IEEE Power Distribution & Regulating Transformers Standards, Guides, and Recommended Practices in PDF format.

Thats what you are looking for

Member and Affiliate Price: $769
Non-Member Price: $963

Part Number: STDVU177 Format: CD-ROM ISBN (13 DIGIT): 978-0-7381-4918-9

Patrick

Mon Sept 20 2010, 03:16AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i couldnt find digital or physical copies at the meriam library, ill try again tomarrow.

Patrick

Mon Sept 20 2010, 09:56PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i cant get the IEEE c57.13-1978 standard its too expensive for the subscription so my college interservice dropped it. and its too expensive to buy, i cant find illegal downloads either. one of my professors said that there "money whores". i think hes right ANSI is easier to deal with.

I did find this

radiotech

Tue Sept 21 2010, 12:00AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I have to agree with your professor about the cost of standards. One thing is cetain though, the costs of reviewing and upgrading those standards, the endless committee meetings and the industry input needed to identify how old standards meet modern needs has to paid by someone. Added to this is the data-explosion and piracy
draining the resourses of the issuing agency. Just think of how easy it is to burn coipies of the $800. CD. The basic membership iption to IEEE gives you the offers only a slight discount.

The other thing is Pts are used by utilities for revenue billing under a wide range of laws and treaties. The next lower spec is for them is protective relaying that keeps the system up.

I really doubt that using it backwards as a step up transformer will permit any of the accuracy specs to hold .

Patrick

Tue Sept 21 2010, 02:37AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

radiotech wrote ...

I have to agree with your professor about the cost of standards. One thing is cetain though, the costs of reviewing and upgrading those standards, the endless committee meetings and the industry input needed to identify how old standards meet modern needs has to paid by someone. Added to this is the data-explosion and piracy
draining the resourses of the issuing agency. Just think of how easy it is to burn coipies of the $800. CD. The basic membership iption to IEEE gives you the offers only a slight discount.

yes i agree with the cost / difficulty for the IEEE to produce this stuff, but screwing college staff and students wont help there cause.

radiotech wrote ...

I really doubt that using it backwards as a step up transformer will permit any of the accuracy specs to hold .

i dont plan to use it in an abnormal way, they are intended to be step down right? so the billing measurements of high voltage or monitoring of HV is done at a lower voltage, right?

my plan: [120V socket] -> [NST] -> (12000V) -> [ PT ] -> [400Vac meter]

so... lets say the PT primary input is 12.43kV, and "Y" volts on secondary, Y = 12.430 Vac, my CVD at "X" volts is adjusted to bring itself to 1.243 volts AC. "X" and "Y" are monitored via oscope channels. this is my calibration setup, i think its good.is it?

radiotech

Tue Sept 21 2010, 03:55AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

i plan to use a PT to figure out my NST (12kv on the name plate) exactly, then use the PT + NST to calibrate my CVD to +-1%

Ok I misunderstood this statement. So, the NST will be paralled to PT, which will be provided with a burden as they indicate, and then you will use a dvm to read the 120 volts and assume the nominal primary voltage of the PT divided by the ratio will your 1 PU. voltage. I'm using Per Unit because that what distribution systems use. The voltage will be the actual voltage across the PT. Your nst would have the burden of the PT (what it needs to operate the iron and copper losses) + the standard burden of the load it needs to be accurate. With your variac you can standardize it, but as you saw from the PT test data, they seem to have accuracy over a limited range of voltages within a range of specific burdens.
The instrumentation of metering is done within the ranges of voltages the systems operates at & the relaying kicks it off line on overvoltage or undervoltage.

Patrick

Tue Sept 21 2010, 04:45AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok let me think about the operating conditions, im about to conduct one more experiment with the resistors under corn oil, if the resistors dont work then ill commit to the PT idea.

EDIT: look at this,

ok this is as the experiment was conducted, under 1.5L corn oil. the probe one is a DMM on uA scale, the Probe two was also a DMM, both were making simultanious measurements. i calculated the 7.651kV from the 125uA number. the 177uA was indicated, the 52 uA that are missing can be acounted for by the 146M resistor.but i dont know if ive isoltaed all the relavent variables.

the only buzzing came from the transformer itself, a little corona i think. i started the test with the container empty of oil, then turn the variac upto 145Vac. the currents were 177uA, and 125uA, then filled the container slowly with oil, hissing and corona went away, but none of the meters changed from empty to full. when full i had the same measurements as when empty or on any of the previous nights.

im certain about the 177uA, 125uA and the 61.21M numbers. however the 7,651V and the 146M ohms are of unkown validity.

radiotech

Tue Sept 21 2010, 05:13PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

PT conclusions; 1.best answer if you meet all operating conditions
2. PT is known to be good
3. use only between .9 and 1.1 PU
Do you think a PT used backwards for a Jacobs ladder could be damaged? (might be a problem with an ebay one)

As to the variac operated in boost ratio mode , ie 145 volt output
from 120 volt source, there is an issue with that connection on variacs that provide a line input tap before full winding turns. The core operates at a higher flux than at the full winding, i.e. variac providing 0-100 % of line voltage. They make less core noise this way. Less overdrive of core at low output current.
The next thing is the NST operating at 145 volts primary instead of its nameplate rating. Your voltage on your diagram is 7651 <0 V. Given that large leakage current, How much of it is reactive and due
to electrostatic coupling to a 60 &/or harmonics? This would make the current lumped in the leakage I<?A. (unknown angle refered to voltage)

The key is in the precise definition of leakage currents.

When a transformer makes a noise you can hear as a buzz it isn't 60 Hz,.sin waves that you hear loudly.

If you use an oscilloscope to check voltages, an idea would be to to connect a bridged T filter for 60 Hz across the input, that way you see the proportion of harmonics in the waveform. An active filter using an op amp is much better for this.

Patrick

Tue Sept 21 2010, 08:27PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

radiotech wrote ...

PT conclusions;
1.best answer if you meet all operating conditions
2. PT is known to be good
3. use only between .9 and 1.1 PU

yep, agreed

radiotech wrote ...

Do you think a PT used backwards for a Jacobs ladder could be damaged? (might be a problem with an ebay one)

yeah over current / saturation and internal heating can cause all kind of problems. if a previous owner did so.

radiotech wrote ...

As to the variac operated in boost ratio mode , ie 145 volt output
from 120 volt source, there is an issue with that connection on variacs that provide a line input tap before full winding turns. The core operates at a higher flux than at the full winding, i.e. variac providing 0-100 % of line voltage. They make less core noise this way. Less overdrive of core at low output current.
The next thing is the NST operating at 145 volts primary instead of its nameplate rating. Your voltage on your diagram is 7651 <0 V. Given that large leakage current, How much of it is reactive and due
to electrostatic coupling to a 60 &/or harmonics? This would make the current lumped in the leakage I<?A. (unknown angle refered to voltage)

well then the variac does not need to be used , my wall socket is 122.6 Vac.

radiotech wrote ...

The key is in the precise definition of leakage currents.

ok, is it possible to mathimatically quantify my R_leakage ? then back calculate to make my resistor appear more ideal ?

radiotech wrote ...

When a transformer makes a noise you can hear as a buzz it isn't 60 Hz,.sin waves that you hear loudly.

ok, maybe im losing current (uA) through corona internal to the transformer connections? the transformer was the only thing not under oil.

radiotech wrote ...

If you use an oscilloscope to check voltages, an idea would be to to connect a bridged T filter for 60 Hz across the input, that way you see the proportion of harmonics in the waveform. An active filter using an op amp is much better for this.

ok, ive never done such a thing before, ill need to wiki / google look this. can you recommend a type of T bridge, given my app?

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