Hi-Z on LV Overhead Line

[eskim]

Dear All,

Sorry if this question has been posted before, I have found 2 thread about E/F protection on D-Y transformer, but not cover my question below.

1. We have experience Hi-Z fault on LV(400V) O/H line which is supplied by 11/0.4kV Delta-Star with solid grounded pole XFMR around 50kVA. At the secondary side of XFMR we have cut-out fuse and can not available to provide Hi-Z protection. Could anyone give me the best solution for this situation ? (see attached file)

2. We would like to trip the 11kV breaker in substation which 1500 mtr away from the pole XFMR as illustrated above. Should I use radio relay or fiber optic converter?

3. What data should I provide to calculate the protection device for above case?

Thank you in advance and if you need some calrification please contact me. Sorry for my english.

Regards,
Eskim

 

[davidbeach]

You will have to have something on the 400V line that can detect the fault condition and send a trip to the 11kV breaker. It might be easier to put an 11kV recloser just ahead of the transformers and trip it. You could have a relay with a fancy hi-z algorithm or if broken line near the source end is your primary concern you might be able to look at negative sequence current. Not an easy fault to find, and fuses certainly aren't the answer; neither from the standpoint of detecting and clearing the fault, nor in the ability to send a trip command elsewhere.

 

[wareagle]

Why not extent the primary conductor to the end of the 400
volt secondary and hang the transformers there. No secondary involved. If the primary goes down it should trip the sub breaker.

 

[ausphil]

You will have a hard time detecting a fault like that, especially if the lv system is not interconnected - ie the phase that has gone down does not have a fault on the supply side as per your picture (ie has an open circuit and the line side of the open circuit is on the ground).

The best indication we have on our low voltage system is when the customer realises that he has lost 3 phase supply, or a single phase customer rings up without supply.

There are low voltage fault location units around that look for intermittent faults on underground cables. They basically sit there putting a time domain reflectometry pulse on the line and constantly calculate what the line "looks like" from a reflectometry point of view. When the line changes - either a phase to earth fault or open circuit or phase to phase fault - the unit will trigger some signal to the user (either hardwired or mobile phone sms) so that you can do something about it. The unit may work on overhead lines, but may not have as great a sensitivity as on underground cables. Might be worth a try. - try the Kelman Rezap Fault Master.

Phil

 

[slavag]

Hi.
Only two possibility detect this type of fault: or NPS current or NPS voltage protection on the end of 400V line.
NPS voltage is better, becouse NPS current detect also single phase load.
BTW, we had thread on the topic.
NPS voltage will detect all type of faults, include same type of fault ( broken conductor) on the 11kV side .
In case of broken conductor you can send trip to the 400V CB only ( if you have of course).
Regards.
Slava

 

[eskim]

What does NPS (voltage/current) mean?

"BTW, we had thread on the topic."
What is the topic subject title..?

Can I use 59G relay with input comes from broken delta PT tapped from 400V line directly?

Eskim

 

[slavag]

Hi Eskim.
NPS is negative phase seq or at ANSI code 46 function.
Yes, against fault as describe in your OP, you can use 59G.
you can use simple undervoltage relay 27.
Intresting discussion was at the attached thread
thread238-201894
Regards.
Slava