Alternative Approach to Improving SAIDI and SAIFI - Schneider Electric

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

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

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. 

An Alternative Approach to Improving SAIDI and SAIFI Indicators 


Prague, 8-11 8-11 June 2009 

Paper 0635 | 1

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. 



Prague, 8-11 8-11 June 2009 

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DONG Energy's network 

DONG Energy is a major DNO in Denmark, however this experience involves only one part of its 

network. 

FLA10-622 

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FLA10-3722 

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4956 

2928 

2365 

5199 

Fig.1 - Typical feeder (neighbouring feeders in white) 

823 

3304 

3320 

2367 

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. 

FLA03-4554 

FLA03-4553 

2366 

3568 

2726 

104 

FLA03-3972 

FLA03-3971 

FLA03-3970 

The grid is mainly urban and consists of 

approximately 7000 substations on 600 feeders. 



Prague, 8-11 8-11 June 2009 

Paper 0635 | 3 

4916 

4915 

FLA03-4524 

FLA03-4914 

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The concept of a SACSe substation 

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]. 

SACSe - Main principle 

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). 

Incoming/outgoing/backup 

MV/LV 

transformer 

Fig. 3 - Typical make-up of a switchgear in a SACSe MV/LV 

substation 

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. 

HV/MV sub 

Feeder 1 

Feeder 2 

Feeder n 

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 

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. 


Backup line 

MV/LV sub 

SACSe MV/LV sub 


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Paper 0635 | 4

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). 

Fig. 5 - ACO - principle of fault restoration 

Trip 

Trip 

+ 

reserve 

backup 

Fig. 4 - ACO - principle of fault restoration 

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 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. 


Case 1 Case 2 


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Paper 0635 | 5 

Trip 

Open 

+ 

backup 

Trip 

Open 

+ 

backup

Infrastructure 

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 

Earth fault 

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. 



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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 

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. 

Design 

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 

Fig. 7 - SACSe 

control unit 

Phase 

I protection 

I 

Eart 

detection 

U 

Fig. 6 - General architecture of the SACSe system 

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. 



Prague, 8-11 8-11 June 2009 

Paper 0635 | 7 

U I 

ACO 

RACO 

logic 

Com 

Power 

supply

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 


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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. 

References 

The implementation of this requires a dedicated 

device to prevent complex commissioning from 

spoiling the solution, and therefore the Return On 

Investment. 

[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 20 th international 

conference on electricity distribution. 

Session 3. 



Prague, 8-11 8-11 June 2009 

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