sympathetic inrush
sympathetic inrush
(OP)
what is the consequence or inconvenience in the system, in the occurrence of magnetic inrush of simpáthetic type in a transformer?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: sympathetic inrush
RE: sympathetic inrush
how far is the transformer from the origin of nuisance(other transformer)?
RE: sympathetic inrush
I believe there is some discussion in Blackburn's book. There may be a little discussion in here:
http
RE: sympathetic inrush
Where you have two transformers with different differentials, you should mind the senisitivy of the harmonic restraint.
RE: sympathetic inrush
I guess they had some experience about that in the past.
I lost that study.
RE: sympathetic inrush
Lot of information on the issue.
As dpc said, problem is muloperation of differential protection, but today is not problem
RE: sympathetic inrush
It was not sympatethic but normal magnetic inrush in a transformer distant 4.72 km from source:
Summary of study
AHE Stone Horse has two units of three-phase step-up transformers 13.8 / 230.0 kV - 90.0 MVA, Yn-d1.
In the initial phase, these transformers are energized by the secondary (230 kV) by TL 230 kV Governor Mangabeiras SE / SE Stone Horse (4.72 km), aiming to use the primary (13.8 kV) for powering loads of ancillary services.
The present work aims to analyze the transient electromagnetic energizing this through simulations with the "ATP - Alternative Transients Program"
slavag,
dpc said restraint is not effective. So, it could operate erroneously.
RE: sympathetic inrush
Please see thread of prc with attached document.
RE: sympathetic inrush
We have to buy synch comps on to allow the power station to come on and run fault level studies every time they need to close the 400 kV CB to come online, depending on the outage pattern and what plant is already running on the day.
May you grow up to be righteous, may you grow up to be true...
RE: sympathetic inrush
G.F.
www.engineering-services.gr
RE: sympathetic inrush
This phenomenon was first analysed and reported in 1941 by C D Hayward,the GE engineer who developed the harmonic restraining feature in transformer differential relay(1938).He called it 'prolonged in rush currents with parallel transformers' ABB termed it 'transferred saturation of core' (ABB review 1990 aug-sept) and some others (France) called it transmitted saturation of core.In mid 90's H S Bronzeado and other south American engineers started calling it sympathetic inrush current and it seems this term is gaining popularity,may be due to the emotional overtones associated with the term.
The operational consequence or disturbance effect of sympathetic inrush current is normally harmless,but sometimes can result in problems.These are
1)A prolonged humming sound in the already working transformer.Normally this will be the main complaint from user who will suspect some defect in the working unit- due to core saturation by DC current circulating between units.
Increased noise level in an upstream power transformer during energisation of a down stream distribution transformer with paralled similar unit alreay in service was also reported
2) Maltripping of differential relay. This will happen especially when one common differential relay is protecting both units.In some rare cases, tripping can occur even with individual relays esp if the connected grid is weak- The net line current,feeding the transformers will be symmetrical( sum of asymmetrical inrush current and asymmetrical sympatetic inrush current)- devoid of the second harmonic components - will result in tripping of common differential relay.
3) Tripping of undervoltage relay on transformer secondary- Inrush current produces a distorted voltage on primary/secondary bus.
Sympathetic inrush current can be explained as below:
When a transformer T2,connected to the same bus as an already energised transformer T1, is switched on, inrush current flows in T2.This asymmetrical current drawn from the generator causes a distorted voltage drop in the transmission line resistance which affects the terminal voltage of T1 unit already in service.Since the flux in the core is proportional to the area (integral)of the voltage waveform at the winding terminal,the core flux becomes asymmetrical,resulting in an inrush current in T1, a few cycles after switching in T2. Hence sympathetic inrush current depends on the resistance of the feeding line.Higher the resistance(ie weaker the system) higher the sympathetic inrush current.The magnitude of this sympathetic inrush current is much lower than a normal inrush current,but stays for much longer duration in both units.
Then DC component of the inrush currents start circulate in the loop formed by the primary windings of T1&T2.Since the direction of this Dc current flow in T2 is opposite to that of T1, the cores get saturated in opposite directions and hence the current peak in the two windings occur on alternate half cycles in opposite directions.Inrush current persists untill this DC component dies down. The current drawn from the line will be sum of the inrush currents of T1 &T2 (assuming T1 is under no-load)and the same will be almost a symmetrical overcurrent, bypassing the harmonic restraining of relay.
RE: sympathetic inrush
If there was a prize for the best researched, best presented, no-nonse and informative post, it would go to you.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: sympathetic inrush
RE: sympathetic inrush
Thank you.
Yours Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: sympathetic inrush
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: sympathetic inrush
Pink is pink
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: sympathetic inrush
RE: sympathetic inrush
What would happen if before energizing T2( assuming T1 is already energized with load), a tie-in disconnect switch between secondary of T1 & T2 is closed first. These back charging currents from T1 to T2 - would these be the same as sympathetic currents? Can these cause any problems to differential relays.
Thanks in advance
RE: sympathetic inrush
The paper describes how the sympathetic inrush distorts the transformers secondary voltage and results in neutral currents which can operate sensitive earth fault protection.