An Alternative Approach to Improving SAIDI and

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
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
An Alternative Approach to Improving SAIDI and SAIFI Indicators
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
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
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 | 2
An Alternative Approach to Improving SAIDI and SAIFI Indicators
DONG Energy's network
DONG Energy is a major DNO in Denmark, however this experience involves only one part of its
Fig.1 - Typical feeder (neighbouring feeders in white)
The 10 kV grid in DONG Energy North, is a 100
The grid is mainly urban and consists of
per cent underground radial network, with a high
approximately 7000 substations on 600 feeders.
degree of access to neighbouring feeders for
backup, as shown in Fig. 1.
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
The concept of a SACSe substation
First of all, let’s clarify the management of
The goal is to put in one strategic MV/LV
phase‑to-phase and phase-to-earth faults in the
substation, a line circuit breaker intended to split
DONG Energy network:
the feeder into 2 segments in order to minimize
••phase-to-phase faults: these cause the
the number of customers affected by a fault, if it
tripping of a breaker and therefore an outage
happens on the downstream side. Time selectivity
which explains how SACSe limits the number of
is used to prevent primary substation CB from
customers affected
tripping simultaneously. In some cases, there
••phase-to-earth faults: the network is
could be up to two line CBs on the feeder: in such
Petersen‑coil grounded, allowing temporary
a case they would use the same setting and trip
operation with single earth fault. However, SACSe
provides an earth-fault localization information
because a second earth fault would cause a
The second concept is a step further. In case
of a phase-to-phase fault upstream in the same
SACSe means "Sectionalizing And Changeover
automatically isolated and the healthy ones to be
System enhanced". The concept of SACSe
automatically resupplied. This process is based on
described below is the latest evolution of the
local automation, allowing a fast reaction, and not
network, which has already seen significant
needing any human intervention or communication
improvement over the last 10 years.
infrastructure. The solution was developed in
substation, it allows the faulty segment to be
A first step was taken by deploying circuit breakers
in the network [1].
collaboration with Schneider Electric, which offers
a wide range of products for network automation.
SACSe - Main principle
First of all, in a given feeder, one or two substations
Backup line
are selected to support the automation. They are
HV/MV sub
MV/LV sub
chosen because of their location: they divide the
Feeder 1
feeder into two or three segments, each supplying
Feeder 2
roughly the same number of customers. They are
Feeder n
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).
Fig. 2 - Principle of a SACSe substation layout in DONG
Energy’s network
These substations are equipped with a fourfunction 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
Fig. 3 - Typical make-up of a switchgear in a SACSe MV/LV
C I R E D - 20th International Conference on Electricity Distribution
Prague, 8-11 June 2009
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.
Paper 0635 | 4
An Alternative Approach to Improving SAIDI and SAIFI Indicators
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
Case 1
(Fig. 4 - case 1).
Fig. 4 - ACO - principle of fault restoration
In a particular case (2 SACSe on the same feeder),
In all cases, the time required to reconfigure is less
a fault downstream in the second SACSe results
than 20 seconds, saving automatically up to 2/3 of
in both SACSe circuit breakers tripping. In order
the customers normally affected by such a fault.
Case 2
to resupply the segment between the two SACSe
circuit breakers, the downstream one will act as a
In addition, several logic processes are embedded
Reverse Auto Changeover (RACO): based on the
in the automation in order to avoid any improper
CB tripping information, it will keep the incoming
action in certain cases:
closed, and order the backup to close, therefore
••once the ACO/RACO has operated, it is blocked
resupplying the upstream segment
until there is some human interaction from the
(Fig. 5).
control center to prevent further action in a nonstandard 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. 5 - ACO - principle of fault restoration
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
Basically, the system does not require any means
to know the real status of all switches and
of communication to react properly and fulfil its
breakers in the network all times. By these
purpose. In fact this is even an advantage in terms
means, other information available in the MV/LV
of security and reliability. But of course, it is linked
substation can also be transmitted. In this case,
with the SCADA to report the outage on the faulty
and thanks to good coverage of the area by GSM
segment, in order to restore the power. In addition,
infrastructure, GPRS has been chosen to transfer
it reports its status to the operating staff, as Danish
data in a very economical way.
regulations require the operator
Earth fault
As explained above, SACSe also integrates
All these features are embedded in a single box
directional fault passage indicators (FPIs). These
provided by Schneider Electric, which is described
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.
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
SACSe control unit architecture
Functional description
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
••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.
I protection
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.
Fig. 6 - General architecture of the SACSe system
SACSe is designed as an industrial solution
of robustness required by such an application,
integrating existing or slightly modified products
openness in terms of communication protocols,
from the Schneider Electric Easergy offer:
and a ready-to-use product to minimize the
••relays from the SEPAM range
••FPI for earth protection is based on the Flair
settings on-site during the installation. All these
in a way to make it easy to integrate into DONG
products are integrated in a single box (Fig. 7)
••automation is based on the Easergy T200 which
Energy's existing installed base. No assembling is
includes peripheral functions such as backup/main
needed on-site, just the mounting of one box, and
power supply and modem.
the connection of the sensors and the commands
All these products were designed specifically
in the switchgear.
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
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,
Fig. 7 - SACSe
control unit
C I R E D - 20th International Conference on Electricity Distribution
Prague, 8-11 June 2009
operating staff have access to the local operation
by opening the front door.
Paper 0635 | 7
An Alternative Approach to Improving SAIDI and SAIFI Indicators
F200C: Possible further enhancement
Thanks to the unit presented above, the SAIDI
Accurate localization would ideally mean knowing
index is drastically reduced, but ultimate quality
which cable between the two substations is faulty.
requires some additional instrumentation of the
Schneider Electric has recently launched a new
••In case of a phase fault, only half (if 1 SACSe) or
communicating fault passage indicator, the
one third (of 2 SACSe) of the feeder customers are
Flair 200C, combining in a single cost-effective
affected by an outage more than one minute.
product the phase-to-phase and phase-to-earth
However, the half or third of customers in the faulty
fault detection and the GPRS communication
segment still need to get power back as soon as
functions. This would suit the above purpose
particularly well. It should be noted that this new
••In case of an earth fault, the SACSe control
Flair 200C embeds a new algorithm for detection
unit can indicate whether the fault is upstream or
of phase-to-earth faults on compensated networks
downstream the SACSe substation. But a more
not requiring voltage sensing. This allows the
accurate localization is required in order to allow
commissioning of such devices to be drastically
faulty cable isolation without power interruption
simplified, especially for retrofit in existing
for any customer.
substations, and it reduces the global cost.
Of course, for obvious cost and complexity
Additionally, the Flair 200C can optionally provide
reasons, more than two SACSe substations on
measurements, further increasing the knowledge
a feeder are not possible. Increasing the number
of network load.
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.
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
Increasing pressure on SAIDI/SAIFI improvement
The implementation of this requires a dedicated
usually requires more performance from DMS,
device to prevent complex commissioning from
and at the same time the management of
spoiling the solution, and therefore the Return On
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
[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.
C I R E D - 20th International Conference on Electricity Distribution
Prague, 8-11 June 2009
Paper 0635 | 9
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