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VIT Self Healing System
1. Overview
The main purpose of feeder automation are to minimize the faulted area and to minimize the outage time. The
conventional technique using current-time controlled recloser, sectionalizer and voltage-time controlled C.B,
reclosing sectionalizer are still widely used in USA, Japan and also in many countries.
But the recloser, sectionalizer scheme can not isolate the load side of faulted section, so during loop operation, it
gives unnecessary short circuit impact to the network and make it difficult to coordination each other. The
voltage-time controlled scheme can be used in loop network, but it has disadvantage of long coordination time,
frequent operation, close into fault by the LBS etc.
So, there was a trend to use computer, communication network to overcome the above problems and in this
system, the LBS (Sectionalizer or reclosing sectionalizer) operate just as passive remote switch (no active
sectionalizer functions).
The concentrated control system have disadvantage more than the distributed control system in aspect of
reliability, coordination time, investment etc.
So, there are continuous effort to develop distributed control system as likes peer to peer communication control
(S&C), and effort to improve or develop efficient self healing systems as likes loop system using dual operation
mode recloser (ABB) and pulsed reclosing system(S&C).
The VIT self healing system are developed to fulfill the feeder automation without using communication in radial
network and also in loop network. The source and load side of faulted section can be isolated before normal open
switch automation close (if this problem is solved, then the communication is no more necessary for feeder
automation). The VIT self healing system use the voltage, current and time based sequential information and as
a results it can isolate the high faulted current, sensitive earth fault current (SEF), open conductor fault through
the coordination of C.B, REC and Sectionalizers.
In VIT self healing system, the LBS do very important job (not the passive remote switch) to isolate high fault
current through fault current count, to isolate the SEF, open conductor fault by itself and to isolate the load side of
faulted section.
Of course, the control of recloser and sectionalizer have RTU functions, so it can communicate with computer,
but the feeder automatic itself will be finished without communication. The VIT self healing system is the extreme
solution to maximize the functions of recloser and sectionalizer.
Two kinds of VIT self healing system are available, and one is using reclosing sectionalizer scheme, the other is
using sectionalizer scheme. If the network is long and if needs many sectionalizing points (rural area), then the
VIT reclosing sectionalizer scheme will be the best, and if the network is not so long and if it needs 3~5
sectionalizing points, then the VIT sectionalizer scheme will be the best.
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2. VIT Reclosing Sectionalizer Scheme
2.1 Radial normal close mode, loop mode
- Best fitted for long rural network
- Infinite number of switches can be coordinated
- The sectionalizer will trip after fault current count (radial mode) or voltage count (loop mode)
- If the voltage restored, the close timer start, and if the close timer completed then close and lockout timer
start
- If the control experience loss of voltage before completing the close timer, then it goes to lock out while
maintaining open position (load side isolation of faulted section)
- If the control experience loss of voltage during lockout timer running, it will be open and lockout after
back up device open (source side isolation of faulted section)
- The normal open switch starts the close timer if one side voltage is lost and goes to lockout if the loss of
voltage count completed. If the count is not completed up to close timer, finished, then it will close.
2.2 Radial sectionalizer mode
If the radial line is not so long, the conventional sectionalizer mode can be used as follows;
- Faulted current count
- Count trip
- Inrush restraint
2.3 High Fault Current
High fault current are always cleared by first by the back up C.B or recloser. The reclosing sectionalizer or
sectionalizer isolate the faulted section after back up device clears the fault if the count is completed or
experience loss of voltage before finishing close timer or lockout timer.
2.4 SEF (Sensitive Earth Fault Current)
According to the settings, the SEF can be cleared directly by the sectionalizer before operation of back up
C.B or recloser, at the radial mode or radial sectionalizer mode.
At the loop mode, the SEF should be cleared by the back up device to isolate the load side of faulted
section.
2.5 Open Conductor Fault
The open conductor fault protection time will be longer than SEF. If the open conductor makes detective
sensitive earth fault, it will be cleared by SEF or directional SEF protection function. (For example, load
side of open conductor touches the ground and it still energized through load side 3 phase transformer).
If the open conductor do not touches the ground, it will be isolated through unbalance current (source side
of open conductor) and unbalance voltage (load side of open conductor).
3. VIT Sectionalizer Scheme
The VIT Sectionalizer doesn’t close into fault to isolate the source and load side of faulted section, but it can
isolate the source and load side of faulted section before automatic close of normal open switch.
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The C.B can coordinate with one sectionalizer and the recloser can coordinate 2 or 3 sectionalizer
according to the number of shots to lockout as follows;
- Best suited for urban network
- No close into fault by the load break switch
- The sectionalizer will trip and isolate the source side of faulted section after fault current counting (radial,
loop mode)
- The sectionalizer will trip and isolate the load side of faulted section before normal open switch close
through voltage counting (loop mode)
- The most fast and the number of operation will be minimum.
- Radial, loop network
- Automatic setting group change
- SEF, Open conductor fault isolation same with reclosing sectionalizer.
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