Dağıtım şebeke yatırım planlamasında çok kriterli karar verme yönteminin kullanımı
Multiple criteria decision making in distribution system investment planning
Yazar: İSMAİL ŞAHİN
Danışman: PROF. DR. MUSTAFA BAĞRIYANIK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı / Elektrik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering
Dizin: Dağıtım planlaması = Distribution planning ; Dağıtım sistemleri = Distribution systems ; Dağıtım şebekeleri = Distribution networks ; Çok kriterli karar verme = Multi criteria decision making

Özet:
Günümüzde elektrik enerjisinin kullanımı oldukça yaygın bir hale gelmiş olup, hem
günlük hayatta hem de iş hayatında bir zorunluluk haline gelmiştir. Oluşan kısa süreli
elektrik kesintileri, hayatımızı durma noktasına getirmektedir. Ekonomik büyüme,
bilimsel-teknolojik gelişme ve nüfus yoğunluğundaki artış elektrik enerji talebini her
geçen gün arttırmaktadır. Bu nedenle üretim tesislerinden iletim, dağıtım şebekeleri
ve son tüketiciye kadar elektrik enerjisinin sağlanmasında görev alan tüm birimler bu
talebe hazırlıklı olmalıdır. Bu hazırlık, gelecek dönemlerin önceden talep tahminin
yapıldığı planlama çalışması sonucunda gerçekleştirilebilir.
Elektrik enerjisinin üretiminden tüketicilere kadar ulaşmasında görev alan tüm
şebekeler incelendiğinde en karmaşık yapıya sahip şebekenin dağıtım şebekeleri
olduğu açık bir gerçektir. Dolayısıyla dağıtım şebekelerinin planlanmasında farklı
kriterlerin göz önünde bulundurulması gerekmektedir. Karmaşık şebeke yapısının
doğal sonucu olarak belirlenen kriterlerin karşılandığı birden çok çözüm seçeneği
ortaya çıkabilmektedir. Bu nedenle, yapılan planlama çalışmalarının belirlenen
kriterleri karşılamakla birlikte, kriterleri karşılayabilen olası alternatif çözümlerden
en uygun olanının seçimini de içermesi gerekmektedir.
Farklı değerlendirme kriterlerinin bulunduğu durumlarda karar verme, sadece
dağıtım yatırımları için değil tüm kararlar için oldukça zordur. Bu zorluğun aşılması
amacıyla çok kriterli karar verme yöntemleri geliştirilmiştir. Çok kriterli karar verme
yöntemlerinin amacı; birden fazla kriterin olduğu durumlarda karar verme
aşamasındaki belirsizlikleri ortadan kaldırmak ve karar verme sürecini belirli yapıya
sokarak formülize etmek ve dökümantasyona hazırlamaktır.
Yapılan bu çalışmada, ele alınan örnek bir dağıtım şebekesi için geleceğe ait tahmini
yük artışı belirlenmiştir. Hem mevcut hem de gelecek dönem yük talebi dikkate
alınarak zayıf nokta analizleri yapılmış ve problemli noktalar tespit edilmiştir. Bu
problemlerin giderilmesi için; mevcut şebekenin güçlendirilmesi, gerilim dönüşümü
ve dağınık üretim birimlerinin bağlanması şeklinde üç farklı alternatif çözüm
sunulmuştur. Alternatiflerin değerlendirilmesi için genel anlamda ekonomik, teknik
ve çevresel etkiler bazında sekiz farklı hedef ve kriterler belirlenmiştir.
Alternatiflerin değerlendirilmesinde çok kriterli karar verme yöntemlerinden TOPSIS
(For the technique for order preference by similarity to ideal solution) yöntemi
kullanılmıştır. Her bir kriterin önemi, farklı ağırlık katsayıları verilerek
belirlenmiştir.
Ağırlık katsayıları değerlendirilerek belirtilen çözümler karşılaştırılmış ve uygun
çözüm/çözümler belirlenmiştir. Her üç duruma ait karşılaştırma sonuçlarından çok
kriterli karar vermede ağırlık katsayılarının önemi görülmüştür. Bu nedenle
yatırımlara karar vericilerin hedeflerin, kriterlerin belirlenmesine ve
ağırlıklandırılmasına ne kadar önem vermeleri açıkça ortaya çıkmaktadır.

Abstract:
Nowadays, the usage of electrical energy has become a quite common. It has become
a necessity in both daily life and business life. The short term power interruptions,
bring the human life to a standstill. The demand to the electrical energy has increased
day by day regarding to economic growth, scientific-technologic improvement and
population growth. For this reason, all units which take a role from generation units
to transmission, distribution system and also to the last consumer should be ready
and well prepared for the increased demand.
When the systems which are the parts from generation to the end customer are
examined, there is no doubt that the distribution systems are the most complex one
and they are in touch with the end customer. Therefore, so many criterias are needed
to be taken into account in distribution system planning. In the past distribution
planning studies, the planners were just taking into accounts the technical criterias
like maximum voltage drop, overloading issues, technical losses etc. However,
distribution utilities have realised that criterias just only for the technical issues is not
enough in the competitive energy market. If the distribution utilites would like to
survive in this market, they need to take into account the economical criterias besides
the technical criterias. Otherwise, they can not withstand.
Recent researches show that the economics of the distribution systems can be divided
in three categories as capital cost, operation-maintenance cost and cost of losses.
Some of these criterias is directly related to the technical issues, but some of them is
related to financial problems in the utility. And also, some researches are done for
combining these two things like selection of the optimal conductor for the system.
Furthermore, technical and economical criterias are not enough to be sure about the
investments. Some new criterias are involved to this process regarding to the changes
in regulations, developments of economonics, technology. These criterias can be the
supply quality, average interruption duration, average interruption frequency,
customer satisfaction, environmental impacts (Green gas effect, CO2, NOx emission
etc.), visual esthetics, safety etc. As a result, the number of criteria are increasing
with the development of the life.
There can be so many alternative solutions as a natural result of the complex
distribution systems. Implementing the first solution into the distribution system can
cause a mistake. Thus, the distribution system planning study needs to include
selection of the best alternative solution from alternative solutions which provides
the defined criterias and goals.
Deciding in a case with too many evaluation criterias and goals is very difficult for
the decision makers in distribution utilities. However, this problem is not only for the
distribution utilities. Hence, multiple criteria decision methods are improved to
handle this problem. Recent researches show that evaluation of the real estate value,financial activities of the businesses and banks are analyzed with multiple criteria
decision methods.
The main aim of multi criteria decision methods is eliminating the uncertainties in
decision making process with multiple criteria, creating a structure to be formulized
and documentated. There are too many multi criteria decision methods regarding to
the uncertainty and alternative number constraints. One of the multi criteria decision
method TOPSIS (For the technique for order preference by similarity to ideal
solution) can be used when no uncertainty appears in the problem variables and the
comparability among the alternatives is not limited.
In this study, multi criteria decision method is used for selection of the best
alternative in distribution planning. A sample distribution system is modeled as
geographically in PSS®Sincal v9.0 which is a network analysis software. The
geographical network model let users see the routes of feeders, connections between
the feeders and problematic areas better than schematic model. This sample
distribution system is supplied from 31,5/15,8kV MV/MV substation via
10(12,5)MVA power transformer. There are 5 outgoings from 15,8kV busbar, 142
distribution transformers (15,8/0,4kV) and 141km medium voltage lines (overhead
lines and cables) in the sample distribution system. Existing active power demand of
the system is 10,11 MW.
Load growth factor is defined as 5,8% for the sample distribution system for future
power demand. The future active power demand of the systems is 13,392 MW. The
weak point analyzes are done for both existing and future term load conditions, and
the problems in the system are detected for each term. The main reason of analyzing
future term is understanding the future requirements and be ready for future with the
new investments. In weak point analyzes, Newton-Raphson load flow method is
used. As a result of weak point analyzes, the technical results and especially the
voltage drop problems are shown with colour filter regarding to the limits in the
graphics.
For solving these problems, three different alternative solutions are proposed. First
solution alternative is keeping the operating voltage as it is (15,8kV) and reinforcing
of the existing system. In this solution alternative, the mainlines are reinforced, the
overloaded distribution transformers are replaced with suitable higher capacity and
adding a new power transformer 10(12,5)MVA to the MV/MV substation. Second
alternative solution proposes a voltage conversion of the whole system. The
operation voltage of the system is converted 15,8kV to 31,5kV. All feeder outgoings
are disconnected from 15,8kV busbar and reconnected to the 31,5kV busbar. This
MV/MV substation is converted as a MV distribution substation. According to the
31,5kV operating voltage, all the distribution transformers are replaced with the new
ones. Third solution alternative proposes to add a new distributed generation units by
using the hydro potentials in the area of the distribution system. These units are
connected to the end of feeders where the voltage drop problems are seen.
To evaluate the solution alternatives for selecting the best one, the goals and criterias
are defined and can be classified as economical, technical and environmental impacts
like in recent studies. The cost of capital, operating, maintenance cost and cost of
losses are the parts of economical criterias. Maximum voltage drop, loss ratio in
medium voltage level, system constraints (maximum power capability), supply
quality (power can be supplied in an interruption case) are the technical criterias. The only criteria for environmental impact is CO2 emission because of the fossil fuel of
the generation units.
In the evaluation part, TOPSIS (For the technique for order preference by similarity
to ideal solution) method which is the common method in multi criteria decision
methods is used. The criterias are weighted with different coefficients according to
the importance in evaluation process. Regarding to the weighted coefficients in the
first evaluation case, second solution alternative is selected as the best solution. The
reason of the selection, second alternative takes the first position in the criterias
which have 60% weight, and in rest of the criterias it takes the second position with a
tiny differences from the first position. These reasons make the second alternative as
the best.
To emphasize the importance of weighted coefficients for the criterias, the evaluation
studies are done with two other weighted coefficient cases. In the second evaluation
case of the coefficients, the first alternative selected as the best alternative. The
reason of this selection is that capital cost criteria has 40% weight where the first
alternative is the best solution. And supply quality criteria which has 25% weight
where the first alternative has no solution and shares second position with its biggest
competitive second alternative solution. In other criterias second alternative solution
has advance rather than first, but this advantage is not enough to be selected the
second solution as best one.
In the third evaluation case of the coefficients, the third alternative solution selected
as the best alternative. The reason of this selection depends on the 40% weight in the
supply quality. In this criteria, just only the third alternative provides a solution. The
other two alternatives can not provide any solution, and this makes the third
alternative solution as the positive ideal solution in evaluation process. Although, the
third alternative has not taken the first position in any other criterias, it takes the
whole points from supply quality criteria and win the competition against to the other
alternatives.
In conclusion, all three alternative solutions are compared with each other with
taking into account the weighted coefficients. As a result of this comparison, the
crucial contribution of the weighted coefficients in multi criteria decision making is
shown up. Accordingly, it is absolutely clear that the decision makers in distribution
utilites have to put emphasis on defining the goals, criterias and weighted
coefficients to select the best alternative. Therefore, the distribution utilities should
create their own decision team which includes employees from different
responsibilities and experiences. However, these decision teams may not be fair. This
situation can cause an unfair competition between the distribution companies. To
prevent this problem, energy market regulatory authorities have to define the limits
for the criterias, audit each distribution companies' decision teams and check the
decisions to balance the rights with the other distribution companies. Also, the
investments which are the results of this decision process can be monitored
according to the criterias. These results can be used as a feedback for the importance
of the weighted coefficients.