An Alternative Approach to Improving SAIDI and … Alternative Approach to Improving SAIDI and SAIFI Indicators Philippe Deschamps - Schneider Electric Industries - France Jean-Christophe
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An Alternative Approach to Improving SAIDI and SAIFI Indicators
Philippe Deschamps - Schneider Electric Industries - France Jean-Christophe Orsini - Schneider Electric Industries - France Kaare Seest Rasmussen - DONG Energy - Denmark
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Summary
Abstract ......................................................................................................p 1
Introduction .................................................................................................p 2
DONG Energy's network .............................................................................p 3
The concept of a SACSe substation ............................................................p 4
SACSe control unit architecture ...................................................................p 7
F200C: Possible further enhancement .........................................................p 8
Conclusion ..................................................................................................p 9
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 1
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Abstract
Under the pressure of regulating authorities, utilities are being challenged to
improve their SAIDI and SAIFI indicators. Usually, to reach this goal, more
intelligence is put inside DMS, increasing at the same time the amount
of data to be processed and the importance of communication in the
network. An alternative way, discussed in this paper, consists of using local
automation, allowing faster reactions, and therefore a drastic reduction of the
number of customers affected by permanent faults, without requiring heavy
communication infrastructure. In addition, this paper introduces a further
enhancement allowing a faster power restoration for the remaining affected
customers.
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 2
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Introduction
Challenged by the Danish authorities, DONG Energy has for a long time
experimented with several methods to optimize network management and
particularly increase power availability. An important step was reached when
it was decided to reduce the maximum time to reenergize a faulty location to
less than a minute to avoid the outage to be counted as a long one, that is
degrading the SAIDI and SAIFI indexes.
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 3
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Fig.1 - Typical feeder (neighbouring feeders in white)
DONG Energy's network
DONG Energy is a major DNO in Denmark, however this experience involves only one part of its
network.
The 10 kV grid in DONG Energy North, is a 100
per cent underground radial network, with a high
degree of access to neighbouring feeders for
backup, as shown in Fig. 1.
The grid is mainly urban and consists of
approximately 7000 substations on 600 feeders.
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C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 4
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
The goal is to put in one strategic MV/LV
substation, a line circuit breaker intended to split
the feeder into 2 segments in order to minimize
the number of customers affected by a fault, if it
happens on the downstream side. Time selectivity
is used to prevent primary substation CB from
tripping simultaneously. In some cases, there
could be up to two line CBs on the feeder: in such
a case they would use the same setting and trip
simultaneously.
The second concept is a step further. In case
of a phase-to-phase fault upstream in the same
substation, it allows the faulty segment to be
automatically isolated and the healthy ones to be
automatically resupplied. This process is based on
local automation, allowing a fast reaction, and not
needing any human intervention or communication
infrastructure. The solution was developed in
collaboration with Schneider Electric, which offers
a wide range of products for network automation.
These substations are equipped with a four-
function switchgear (Fig. 3):
• 1 fuse switch or circuit breaker for the
transformer protection. It can be forgotten since it
has no role in the concept.
• 2 circuit breakers and 1 switch distributed
among the incoming, the outgoing, and the
backup lines. There are two circuit breakers among
the three to be sure that there will be at least one in
the circuit in all network configuration cases.
First of all, let’s clarify the management of
phase-to-phase and phase-to-earth faults in the
DONG Energy network:
• phase-to-phase faults: these cause the
tripping of a breaker and therefore an outage
which explains how SACSe limits the number of
customers affected
• phase-to-earth faults: the network is
Petersen-coil grounded, allowing temporary
operation with single earth fault. However, SACSe
provides an earth-fault localization information
because a second earth fault would cause a
tripping.
SACSe means "Sectionalizing And Changeover
System enhanced". The concept of SACSe
described below is the latest evolution of the
network, which has already seen significant
improvement over the last 10 years.
A first step was taken by deploying circuit breakers
in the network [1].
First of all, in a given feeder, one or two substations
are selected to support the automation. They are
chosen because of their location: they divide the
feeder into two or three segments, each supplying
roughly the same number of customers. They are
also chosen because of the ease of upgrading
them. The principle of layout in the network of
these substations is described in the ref [2].
Second, a backup line coming from the neighbour
feeder is connected to these strategic MV/LV
substations to allow a backup supply if required
(Fig. 2).
The concept of a SACSe substation
SACSe - Main principle
Fig. 2 - Principle of a SACSe substation layout in DONGEnergy’s network
Fig. 3 - Typical make-up of a switchgear in a SACSe MV/LVsubstation
MV/LV subSACSe MV/LV sub
Backup line
MV/LVtransformerIncoming/outgoing/backup
HV/MV subFeeder 1
Feeder 2
Feeder n
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 5
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
If a fault occurs downstream, the breaker opens
instantaneously, isolating the downstream
segment(s). The status of the switchgear is then
sent to the SCADA. If a fault occurs upstream, the
switchgear acts as an auto changeover (ACO):
the circuit breaker will not trip, but the lack of
voltage releases the auto changeover process,
ordering the incoming to open and the backup
to close, which supplies the healthy downstream
segment. This is the general principle. Two cases
are shown in Fig. 4. Since the breaker in the HV/
MV substation is delayed and those in the SACSe
are not, the breaker in the HV/MV sub will only trip
when the fault is in the first segment
(Fig. 4 - case 1).
In a particular case (2 SACSe on the same feeder),
a fault downstream in the second SACSe results
in both SACSe circuit breakers tripping. In order
to resupply the segment between the two SACSe
circuit breakers, the downstream one will act as a
Reverse Auto Changeover (RACO): based on the
CB tripping information, it will keep the incoming
closed, and order the backup to close, therefore
resupplying the upstream segment
(Fig. 5).
In all cases, the time required to reconfigure is less
than 20 seconds, saving automatically up to 2/3 of
the customers normally affected by such a fault.
In addition, several logic processes are embedded
in the automation in order to avoid any improper
action in certain cases:
• once the ACO/RACO has operated, it is blocked
until there is some human interaction from the
control center to prevent further action in a non-
standard network configuration
• a logic process is in action to avoid any ACO
and/or RACO action if the network is subject to
a global outage, from the transport for instance.
This event is detected by monitoring the voltage
presence on the backup line. If an absence of
voltage is observed on both incoming and backup
lines, then no action is taken
• in case of a frequency drop, a recovery process
exists in the HV/MV substation and it, it reacts by
switching off some feeders. So in this case, the
ACO/RACO is inhibited to allow the load-shedding
process to be prioritized.
Fig. 4 - ACO - principle of fault restoration
Fig. 5 - ACO - principle of fault restoration
Trip+
reservebackup
Trip
Case 1 Case 2
Open+
backup
Trip
Open+
backup
Trip
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 6
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Infrastructure
Earth fault
Basically, the system does not require any means
of communication to react properly and fulfil its
purpose. In fact this is even an advantage in terms
of security and reliability. But of course, it is linked
with the SCADA to report the outage on the faulty
segment, in order to restore the power. In addition,
it reports its status to the operating staff, as Danish
regulations require the operator
As explained above, SACSe also integrates
directional fault passage indicators (FPIs). These
FPIs allow the staff to locate the fault in the field
more accurately and faster, and therefore prevent a
tripping due to a second fault.
to know the real status of all switches and
breakers in the network all times. By these
means, other information available in the MV/LV
substation can also be transmitted. In this case,
and thanks to good coverage of the area by GSM
infrastructure, GPRS has been chosen to transfer
data in a very economical way.
All these features are embedded in a single box
provided by Schneider Electric, which is described
below.
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 7
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
of robustness required by such an application,
openness in terms of communication protocols,
and a ready-to-use product to minimize the
settings on-site during the installation. All these
products are integrated in a single box (Fig. 7)
in a way to make it easy to integrate into DONG
Energy's existing installed base. No assembling is
needed on-site, just the mounting of one box, and
the connection of the sensors and the commands
in the switchgear.
In terms of size, the system is made to be
mounted directly on the wall of the substation. The
dimensions allow it to be used even in a compact
substation with reduced volume available.
Interfaces are designed to make installation
simple and minimize the risk of mistakes by using
prefabricated cables and connectors to link the
unit with sensors.
The box is equipped with a transparent window
on the front door, allowing all indicators of the
status of the system to be read locally. If needed,
operating staff have access to the local operation
by opening the front door. Fig. 7 - SACSecontrol unit
Fig. 6 - General architecture of the SACSe system
SACSe control unit architecture
Functional description
Design
The unit integrates the following functions (Fig. 6):
• phase-to-phase fault protection ensured by two
protection relays, for the incoming/outgoing and
backup breakers
• phase-to-earth fault detection ensured by two
directional fault passage indicators on the same
functions
• voltage presence on incoming, outgoing, and
backup cables
• automation ensuring the ACO/RACO logic
• communication with the SCADA on the status of
the substation
• power supply with batteries to supply the unit
under all conditions.
In addition, LV and MV measurement features have
been included in the unit to provide a much better
knowledge of the substation and the network load.
SACSe is designed as an industrial solution
integrating existing or slightly modified products
from the Schneider Electric Easergy offer:
• relays from the SEPAM range
• FPI for earth protection is based on the Flair
range
• automation is based on the Easergy T200 which
includes peripheral functions such as backup/main
power supply and modem.
All these products were designed specifically
for the network automation environment. As a
consequence, they comply with the specificities
of this application: harsh environment withstand
(temperature, EMC, electrical insulation -10 kV on
mains, dust, humidity, etc.), allowing the high level
ACORACOlogic
I
I
U
U I
Com
Phaseprotection
Eartdetection
Powersupply
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 8
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
Thanks to the unit presented above, the SAIDI
index is drastically reduced, but ultimate quality
requires some additional instrumentation of the
network:
• In case of a phase fault, only half (if 1 SACSe) or
one third (of 2 SACSe) of the feeder customers are
affected by an outage more than one minute.
However, the half or third of customers in the faulty
segment still need to get power back as soon as
possible.
• In case of an earth fault, the SACSe control
unit can indicate whether the fault is upstream or
downstream the SACSe substation. But a more
accurate localization is required in order to allow
faulty cable isolation without power interruption
for any customer.
Of course, for obvious cost and complexity
reasons, more than two SACSe substations on
a feeder are not possible. Increasing the number
of SACSe substations is therefore not a way to
achieve ultimate quality.
This means a device allowing accurate localization
of both phase faults and earth faults is needed
in the other substations, both upstream and
downstream from the SACSe.
Accurate localization would ideally mean knowing
which cable between the two substations is faulty.
Schneider Electric has recently launched a new
communicating fault passage indicator, the
Flair 200C, combining in a single cost-effective
product the phase-to-phase and phase-to-earth
fault detection and the GPRS communication
functions. This would suit the above purpose
particularly well. It should be noted that this new
Flair 200C embeds a new algorithm for detection
of phase-to-earth faults on compensated networks
not requiring voltage sensing. This allows the
commissioning of such devices to be drastically
simplified, especially for retrofit in existing
substations, and it reduces the global cost.
Additionally, the Flair 200C can optionally provide
measurements, further increasing the knowledge
of network load.
F200C: Possible further enhancement
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 Paper 0635 | 9
An Alternative Approach to Improving SAIDI and SAIFI Indicators
C I R E D - 20th International Conference on Electricity Distribution Prague, 8-11 June 2009
References[1] Peter Vinter, Henrik Vikelgaard, 2005, "A novel approach to distribution grid automation at NESA A/S", CIRED Conference 18th international conference on electricity distribution. Session 3.
[2] Kåre Seest Rasmussen, 2009, "A real case of self healing distribution network", CIRED Conference 20th international conference on electricity distribution. Session 3.
Conclusion
Increasing pressure on SAIDI/SAIFI improvement
usually requires more performance from DMS,
and at the same time the management of
more and more information. A complementary
solution involves the use of local automation
able to perform simple actions quickly. By this
means, when a fault occurs, a rough but fast
reconfiguration is done while the operation is
simplified.
The implementation of this requires a dedicated
device to prevent complex commissioning from
spoiling the solution, and therefore the Return On
Investment.
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