Low secondary burdens on HV CVTs

[shodder]

Would anyone happen to know if there have been any studies looking at the effect of placing small secondary burdens (less than 5 VA) on high voltage CVTs?

The main issue is whether or not CVT transient effects are aggrivated by having little burden on the output of the CVT tuning circuit. The utility I work for is undertaking an extensive work program that is replacing older electromechanical protections (fairly large burdens) with digital relays (extremely small burdens) and currently there is no plan to refurbish/retune the CVTs. Is this necessary?

Any help/advice would be appreciated.

 

[jbartos]

Suggestion: Visit

http://www.wattnode.com/products/current_trans.html

etc. for more info

 

[scottf]

It can depend on the design, but in general, the CCVTs transient performance is improved as the connected burden is reduced. I.e. there is less delay with less burden connected. It is not exactly linear. For example:

If the CVT is rated <=10% at 100 VA after 1 cycle, then the performance at 10VA is going to be between 1-2% after 1 cycle.

Unless you have one of the older CVT designs that have adjustable ranges (i.e. one setting for 0-100 VA and one setting for 100-200 VA) then there should be no need for readjustment. The CCVT's accuracy is checked at zero and full burden per standard.

The other concern would be for internal ferroresonance suppression. Most CVTs with a passive suppression design have an internal stabilizing burden that is always connected across 1 seconday winding and then a second resistance that is switched in to help dampen out ferroresonance.

 

[scottf]

jbartos-

I don't see anything on the link you suggest that concerns CVTs...it looks like a link to 600 V CTs??

 

[jbartos]

scottf, thank you for the correction (I beg your pardon):
Voltage and current instrument transformers for low power may be called Low Power Instrument Transformers. Visit

http://198.173.130.4/Main/trench/tr...403F8B872E742685256B6E0052E9FD/$FILE/E900.pdf

etc. for more info
Also, visit

http://www.hut.fi/Yksikot/SJT/Vk-2002.pdf

Section 3.4.6
The ratio and phase displacement were compared with nominal
burden of 1 VA at unity power factor.
Visit

http://www.thomasregister.com

and type Transformers: Instrument under Product or Service, which will return 115 companies to approach to

 

[scottf]

Jbartos....note that this discussion is concerning CVTs, which are capacitive voltage transformers. Not really talking about low power instrument transformers, i.e. sensors.

The hut reference is about impulse measuring equipment, which again is not the topic here.

Worldwide CCVT manufacturers are Ritz, Trench, Alstom, ABB, Arteche, Passoni Vila.

 

[jbartos]

Comment: I am aware of the CCTV, e.g. Trench post was posted, however, for some reason, it does not work now.
Visit

http://www.geindustrial.com/products/brochures/CPO-9804.pdf

http://www.geindustrial.com/products/applications/GET-97D.pdf

for GE Bushing Voltage Transformers
There is a capacitance of the bushing involved

 

[jbartos]

Suggestion: Here are better links to the Trench CCTV

http://www.trench.de/_FramesPages/Instrument_transformers_Overview.htm

http://www.trench.de/_FramesPages/Capacitor_Voltage_Transformers.htm