My question is related to High Tension system. What will happen if we use out of three PTs, one will be having different Burden Voltage specification?
What is the effect if grounding screws (Sealed red painted) of primary or secondary winding is open?
What is the effect of non grounding?
What will happen if I keep secondary open?

 

Responding to Anonymous' Tue, Jul 12, 6:51pm query:

A1) Are you talking about the Burden Rating (capability) of one is different than the other two? Or, the actual burden (load) of one is different than the other two?

A2) Depends on what the PTs are used for, and their circuit configuration!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

Dear Mr. Phil,

Yes my question is if out of three PTs if one is having different Burden value the what is the effefct in circuit?
Also let me know what will be the result of keeping one of the grounding either it may be primary or secondary at time.

 

Responding to Anonymous' Thu, Jul 14, 6:42pm comments:

1) As long as the connected burden (load) doesn't exceed PT capability, then the stated accuracy will not be compromised. For example, suppose the 3 PT's are connected to a protective relaying circuit. Presumably the secondary circuits are balanced, consisting of equal impedances. Adding another voltmeter or the like in one phase, could unbalance the secondary circuit. Nevertheless, as long as the burden magnitude (ohms) and PF (power-factor) are within the manufacturer's spec, then errors should not exceed warranty values.

Caution:
BTW, I'm not advocating that protective relaying circuits be "compomised" by adding non-protective functions.

2) I'm unclear about your grounding question. If the low-potential side of the primary is physically terminated at the metal case or junction box, then the PT is used in a wye configuration having a solidly-grounded neutral. Can you send a schematic of what you are proposing?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

hai,

1. If you dont ground the star point of the primary or secondery of PT, the system will face the same problem of ungrounded system. Your PT fuse or mcb will never act when there is a first line to ground fault in your PT. Instead it may misguide you by operating some other relay if your main transformer or generator's star point is grounded.

1. as such there is no problem if your pt secondary is opened, but your protection or metering will not work in that case.

Rajan

 

Responding to Rajan's Tue, Jul 19, 6:41pm comments:

I disagree with your comment about the open-circuited secondary:

Unless the primary and secondary windings are separated by a grounded electrostatic shield, the two windings will be capacitively coupled. If the secondary is left ungrounded a dangerously high voltage will exist in the secondary circuit, and flashover is possible.

This possible scenario is the reason the grounded terminations are sealed!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])