Hi Prot123,
The 10 ohm figure was an internal utility requirement. Unfortunately I'm
not aware of any public documents which list a frame insulation resistance.
New switchgear installations designed for FL were mounted on an insulating
mat and achieved far better than 10 ohms. Some FL...
Hi Prot123,
A major Australian utility where I used to work applied earth leakage
protection quite extensively on double bus 11 kV metalclad switchgear.
Frame leakage was used because of the difficulty of applying high impedance
protection on a board where breakers could be racked to either...
Hi,
The oscillographic fault records in the 7UT6 will almost
certainly confirm:
(a) Whether the switchgear is likely to be healthy.
(b) The probable cause of the trip.
Download the records with DIGSI and get an appropriate
person to have a look at them.
Thanks,
Alan
Hi Hans,
This is a very interesting problem. My previous employer used air cored
reactors fairly extensively, and I did spend some time considering how
to protect them.
I generally dislike the idea of discounting certain fault types just
because those present can't envisage how they might...
Hi,
A few questions:-
Is the reactor at one of the line ends, or somewhere in the middle?
Will it have an earthed or unearthed starpoint?
What kind of line protection are you using? Is optical fibre comms
available?
Thanks,
Alan
Hi,
These used to be available by distance education, and the one
course I did was pretty good:
https://www.qut.edu.au/study/short-courses-and-professional-development/short-courses/postgraduate-electricity-supply-training-course-pestc
Thanks,
Alan
Hi Rockman,
The factors in favour of high Z are in my opinion:
- Simpler to set, configure, prove, debug.
- Very long life - the CTs and wiring will last as long as the switchgear.
- If you use an electronic relay, you may need to factor in one replacement, but it is a simple...
Hi,
I agree with waross regarding the loss relationship.
To make a sensible decision, I think you should model
the system using a load flow program (or excel if
you're desperate).
It seems that you have option (1): run with 36kV at the
sending end and, say, 33kV at the receiving end or...
Hi prismpower,
I believe that 36kV cables can sustain 36kV continuously, based
on the definitions for "highest voltage for equipment" in the
IEC standards. You may want to check the applicable standards
if you are not in IEC land, and/or confirm with your cable
manufacturer.
A potential issue...
Hi mbk2k3,
The utility where I worked would always re-test (by secondary injection)
the full function of a relay after re-loading a setting file. If the wiring
was untouched, testing to links or a tripping (lockout) relay was sometimes
accepted depending on circumstance.
With modern relays, it...
Hi,
You can't do that. There is one continuous secondary winding
on the CT with taps at 40 turns and then 60 turns. The primary
has one turn. The (amps * turns) on the primary needs to equal
the (amps * turns) on the secondary, and if you attempt to use
both ratios at once, the amp turns won't...
Hi Scottf,
If the CT, the load, and the system were ideal (which they are not), the
output voltage of the CT would be proportional to the system voltage.
The primary of the CT would behave as an open circuit, because the CT
would have a infinite magnetising impedance and all of the system...
Hi
A CT behaves the same as pretty much any other transformer - the difference
is in how the CT is connected. Suppose you have a 2000/1 CT which is open
circuit and connected in series with an 11kV supply. The CT secondary is
open circuit, so the primary "tries" to behave like an open circuit...
Hi David,
There was no bus differential - the utility which originally built
the sub chose to rely on remote protection. After a number of faults
(and replacement of breakers with ones containing BBP CTs) a project
was eventually justified to install bus protection.
Thanks,
Alan
