Energy and Power Engineering, 2013, 5, 1303-1307
doi:10.4236/epe.2013.54B247 Published Online July 2013 (http://www.scirp.org/journal/epe)
Economic Benefit Analysis of 220 kV Energy-saving
Power Tr ansformer*
Weili Chen1, Xian Ma1, Jingtian Bi1, Zhisen Li2, Tong Jiang1
1State Key Laboratory of Alternate Electrical Power, System with Renewable Energy Sources,
North China Electric Power University, Beijing, China
2Tai’an Power Supply Company, Shandong Electric Power Corporation
Received January, 2013
ABSTRACT
Power transformer serves as one of the most widely used electrical equipments in power grid. During the operation,
terrible losses are produced. With the development of loss reduction technology of power transformers, in order to save
energy saving and reduce emissions, the old power transformer should be replaced. The paper summarizes the main
method to reduce the losses of power transformers and brings up the improved Total Owning Cost (TOC) algorithm,
which applies to 220 kV power transformers’ comprehensive benefit analysis. Using the improved Total Owning Cost
(TOC) algorithm, based on today 220 kV energy-saving power transformer manufacturing level, the economic benefits
of new energy-saving power transformer and the return period of investment are analyzed. Finally, combined with
energy-saving effect, the appropriate replacement proposal of 220 kV power transformers has been given.
Keywords: 220 kV Power Transformer; Loss Reduction Technology of Transformer; TOC Algorithm; Economic
Analysis
1. Introduction
As the transmission and distribution infrastructure, power
transformer is widely used and always run a long time.
Power transformer on the one hand is high efficiency
transmission electrical products, on the other hand is
consumption power electrical equipment. Although the
efficiency of the transformer can be as high as 99%, but
the consumption of electric energy is still very amazing
[1]. According to the statistics, the losses of power
transformer itself account for more than 3% of genera-
tion [2], therefore carrying out power transformer com-
prehensive benefit calculation and putting forward rea-
sonable replacement proposal is the important link to
reduce the power loss and to achieve the results of en-
ergy saving and emission reduction.
2. Today 220 kV Transformer Manufactur-
ing Leve
According to GB/T 6451-2008, specification and techni-
cal requirements for oil-immersed power transformers,
the highest rated no-load active loss of 180000 kVA/ 220
kV three winding on-load changer transformer is Po =
156 kW, and the highest rated load reactive loss is Pk =
630 kW[3]. Now, through inputting new materials and
manufacturing technology improvement, the load and
no-load losses of 220 kV power transformers have been
greatly reduced. The main reduction means mainly con-
sists of the following:
2.1. Reduce the No-load Loss of Power
Transformers
Now the mainstream of technologies to reducing the
no-load loss of transformers are using new type of core
material; using best quality core manufacturing process;
using high quality insulation structure; reducing the
technology coefficient; improving core structure; reduce-
ing the core window size; designing no resonance core;
using wound core transformer, etc. [4]The most effective
method is using new type of core material and using
wound core transformer. Due to the cost, low saturated
flux density, easy to produce debris and other reasons,
amorphous alloy is not suitable for large power trans-
former. Similarly, because the today’s technology is still
unable to meet the requirements of the large size core be
winded continuously, wound core currently only suitable
for small and medium distribution transformer. For 220
kV power transformers, high-quality silicon steel sheet is
suitable to reduce the unit loss of the core, such as
23ZH90. The relationship between silicon steel sheet and
*Supported by the National High Technology Research and Develop-
ment of China 863 Pro
g
ram
(
2012AA050208
)
.

W. L. CHEN ET AL.
1304
power transformer no-load loss is calculated. The results
are shown in Table 1 . With the reduction of no-load loss,
the cost is increasing.
2.2. Reduce Load Loss of Power Transformers
The common methods to reduce load losses are using
improved core structure to reduce the coil turns; calcu-
lating ampere-turns balance of coil to control the radial
leakage; using low loss low resistance wire; using ad-
vanced insulation structure; choosing appreciate conduc-
tor transposition way, etc.[3]Among them, the most fun-
damental method to reduce load losses is reducing the
resistance of conductor, which can be achieved by in-
creasing the cross-sectional area of the wire, namely se-
lect the wire in accordance with the requirement of larger
capacity transformer.
2.3. Reduce the Additional Loss of Power
Transformers
The measures to reduce additional loss are using transpo-
sition wire and composite wire reasonably to reduce ed-
dy-current loss, stray loss and additional loss; opti- miz-
ing parallel wires’ transposition to reduce circulation loss
caused by magnetic flux leakage; taking effective shiel-
ding measures in the structure.
Table 1. Different silicon steel sheet and no-load active
losses Comparison.
Specifications of silicon
steel sheet
The no-load active
losses(kW) Drop rate(%)
0.3mm Common silicon steel sheet
30Q150 204.5 0
0.3mmHI-B High permeability
silicon steel sheet 30QG130 177.3 13
0.3mmHI-B Laser processing high
permeability silicon steel sheet
30RGH120
163.6 20
0.27mm Common silicon steel
sheet 27Q140 190.9 6.67
0.27mmHI-B High permeability
silicon steel sheet 27QG110 150.0 26.7
0.23mmHI-B Laser processing
high permeability silicon steel
sheet 23ZH90
122.7 40
Table 2. Transformers’ parameters and prices.
Transformers’ parameters and prices
Id Pk（kW）P0（kW）I0% Uk% Sn(kVA) price(yuan)
1 520 84 0.20 14 180000 6660000
2 500 86 0.20 14 180000 6780000
3 480 87 0.20 14 180000 6720000
4 460 88 0.20 14 180000 6960000
5 430 94 0.20 14 180000 7500000
6 400 102 0.20 14 180000 8190000
Shandong Electric Power Equipment Company have
made some research achievements in the loss reduction
technology of power transformers, typical SSZ-180000/
220 products’ rated load active loss dropped gradually
from 600 kW to 390 kW, rated no-load reactive loss from
130 kW to 90 kW, there are some actual products in this
interval.
The price of transformers is estimated, setting the typ-
ical transformers’ rated load active loss to constant value,
using the most advanced no-load loss reduction tech-
nique, which guarantees the lowest no-load loss. Trans-
formers’ parameters and prices are estimated such as
Table 2 shows:
3. Select 220 kV Power Transformer Using
Total Owning Cost (TOC) Algorithm
3.1. Total Owning Cost (TOC) Algorithm and Its
Improving
The Total Owning Cost (TOC) algorithm is the tradi-
tional method to make economic analysis and evaluation
of distribution transformer. TOC value = initial invest-
ment of distribution transformer + the power losses’ cost
during the life of distribution transformer. According to
the TOC value of different transformers, choose the low-
est as the optimal solution [5].
When using The Total Owning Cost (TOC) algorithm
to choose 220 kV power transformers, there are some
defects, which mainly embodied in the calculation for
reactive economic equivalent. Reactive economic equiv-
alent is determined by the position of transformer in
power grid. For the distribution transformer, Reactive
economic equivalent is generally assigned k = 0.1
kW/kVAR. Because 220 kV power transformers mainly
used for transmission line, reactance value far outweigh
the resistance value, so the value should be less than 0.1.
Improved TOC algorithm calculate reactive economic
equivalent of transmission transformer.
1) Calculation formula of TOC
TOC=C+A×NL+B×LL
where, NL is rated no-load losses, kW; LL is rated load
losses, kW; A is the capital cost per kilowatt of no-load
losses during life of transformer, yuan/kW; B is the capital
cost per kilowatt of load losses during life of transformer,
yuan/kW; C is the price of transformer;
2) Parameters
0
000
%
N
L(
100
%
LL( )
100
n
kn
kkk
)
I
S
PkQ Pk
US
PkQPk
 
 
where, P0 is no-load rated active loss, kW; Q0 is rated
no-load exciting power, kVAR; Pk is load rated active

W. L. CHEN ET AL. 1305
loss, kW; Qk is rated load exciting power, k”VAR; I0% is
no-load current,%; Uk% is impedance voltage,%; Sn is
transformer rated capacity, kVA.
k is reactive economic equivalent. Reactive economic
equivalent means transformers’ reactive power consump-
tion increase or decrease per 1 kVAR formed the heat
losses increase or decrease kW value in higher level
electricity grid. The Heat losses increase or decrease in
value only by Reactive power consumed power itself
Current Square caused. Reactive economic equivalent is
calculated as follow:
The active losses of higher level electricity grid with
no transformer accessed in:
22
23 3
0
PQ
PQ
P3IR10R10 R10
UU
PP

 
 
 
 
 
3
where, 0 is the active losses of higher level electricity
grid with no transformer accessed, kW; I is system cur-
rent, A; U is system voltage, kV; R is line resistance, Ω;
P is system active power, kW; Q is system reactive pow-
er, kVAR; P is the active power losses caused by De-
livery active power, kW; Q is the reactive power
losses caused by Delivery reactive power, kVAR..
P
P
P
The active losses of higher level electricity grid when
transformer accessed in:
2
3 11
PP QQ
PR10 R
UU

 
 
 
 
 
2
3
10

where, ΔP is the active losses of higher level electricity
grid when transformer accessed, kW; ΔQ1 is reactive
losses of transformer, kVAR; ΔP1 is active losses of
transformer, kW.
The active loss changes of higher level electricity grid
when transformer accessed in:
22
11 1
b0 2
3
PQ2PP2QQ
PPP U
R10
 


1
where,
b
P are the active losses changes of higher level
electricity grid when transformer accessed in.
So, the reactive economic equivalent is:
b
1
P
kQ


Assume that the system power factor cos0.9


,
load rate is 70%. Using per-unit value, estimate the value
of reactive economic equivalent. Because 220 kV trans-
mission line resistance value is about 20% of reactance
value, and the reactance value generally take for 0.1Ω, so
resistance value is 0.02. The reactive economic equiva-
lent of 220 kV new energy-saving transformers listed
equal 0.04.
3) Coeffici
above can be calculated. The values are approximately
ent A and B
a



2
12 )
B(12)
1 1/1/1
PW PY
PW
PW
ELh
kEJLEL P
kain


 
A(kEJL 

 

where, kpW is present value; EJL is the basic tariff in dual
3.2. The Example of Improved Toc Algorithm
rithm, the economic bene-
fit
hat the average loss parameters of 220 kV
po
, Pk =520
kW
tariff system, yuan/kW·month; EL is the Power tariff,
yuan/ kWh; hpY is Annual operating hours, generally is
8760h; τ is annual maximum load loss hours; P is Trans-
former maximum load factor; i is Annual interest rate; a
is inflation rate; n is useful life.
1) The Total Owning Cost
Using improved TOC algo
s of 220 kV power transformers listed above can be
analyzed.
Assume t
wer transformers using in power grid approximated as
the loss parameters specified in GB/T 6451-2008. P0 =
156 kW, Pk = 630 kW, I0% = 0.49, Uk% = 14.3. the price
is estimated ￥6000000. Other new energy-saving
transformers’ parameters is shown in Table 2.
Taking the transformer whose P0 = 84 kW
as an example, assume the load rate of transformer is
70%, n=20, i = 7%, a = 5%,
P
W
k = 15.72, EJL = 20, EL
= 0.52, hpY = 8760.
0
000
%
NL()98.4kW
100
%
LL 1528kW
100
n
kn
kkk
I
S
PkQ Pk
US
PkQPk
 

 


Assume the maximum load rate is 100%, the annual
m
TOC=C+A×NL+B×LL=73456434yuan
Similaformers
un
turn period of investment
placed, but se-
le
f the capital, the return
pe
aximum load loss hours τ can be calculated, τ = 4292.4
h. From the Table 2, can see the price of transformer is C
= 6660000yuan. Thus, coefficient A and B and the total
owning cost (TOC) can be calculated.
A( 12)kEJL ELh 
2
75380.54
B(12)38860.59
PW PY
PW
kE JLEL P   
rly, the TOC value of different trans
der different load rates can be calculated. As shown in
Figure 1.
2) The re
The old power transformer should be re
cting different transformer to replace, the return period
of investment is also different.
Regardless of the time value o
riod of investment = the price of transformer/the loss
cost price between old and new transformer.

W. L. CHEN ET AL.
1306
.59×(1659.6
Considering plug 8.6 into
th
Similarly, the retustment of different
transformers under different load rates can be calculated.
As shown in Figures 2 and 3, here just list the situation
of load rate is 70% and 50%.
=6660000÷{[75380.54×(192－98.4)＋38860
－1528) ]÷15.72}=8.6years
the time value of the capital,Figure 1 shows that The Total Owning Cost of typical
energy-saving transformers has greatly reduced com-
pared with old transformers. Although the differences is
small between new energy-saving transformers, but the
return period of investment and the total energy-saving
benefit can vary a lot.
e formula of kpW, Can get the return period of invest-
ment in consideration of the time value of the capital:
n=ln[1-(0.07-0.05)×8.6] ÷ ln[(1+0.05) ÷(1＋
0.07)]=10yerars
rn period of inve
Figure 1. The TOC of different transformers under different load rates.
Figure 2. The return period of investment of differe nt transformers under 70%load rates.

W. L. CHEN ET AL. 1307
Figure 3. The return period of investment of differe nt transformers under 50%load rates.
If the average load rate of local 220 kV transformers is
ab
r assume that the average loss parameters of
22
4. Conclusions
ent of the energy-saving technology
illustrated by an example in which the load rate is 70%.
REFERENCES
[1] B. C. Ying, “ys to Transformer
Industry Standard Expansion of
s,”
h of Economy Capacity of Me-
out 70%, choose the transformer which the return pe-
riod of investment is shortest. According the calculation,
new energy-saving transformer 3 and 4 is the most opti-
mal selection. The price of transformer 3 is lower, but the
total energy-saving effect of transformer 4 is more obvi-
ous. Choose transformer according to need. If choose
transformer 4, The Total Owning Cost lowers 13.24 mil-
lion yuan.
This pape
0 kV power transformers using in power grid approxi-
mated as the loss parameters specified in GB/T 6451-
2008. But the actual situation may be different. Therefore
the replacement proposal in the paper only applies for the
transformers whose loss parameters is equal to or higher
than the loss parameters specified in GB/T 6451-2008.
With the developm
tio
of power transformers, the losses of 220 kV transformers
reduce obviously. In order to save energy and reduce
emission, it is advised to replace the transformers whose
loss parameters is equal to or higher than the loss pa-
rameters specified in GB/T 6451-2008 by new energy-
saving ones. The replacement should base on the Total
Owning Cost, the return period of investment, energy-
saving effect, and the local load rate of transformers. It is
The calculation of several typical power transformers is
made and the conclusion is drawn. The energy-saving
effect is best if the substitution is energy-saving power
transformers whose Pk = 460 kW and P0 = 88 kW. The
initial investment is least if the substitution is energy-
saving power transformers whose Pk = 460 kW and P0 =
87 kW.
The Energy-saving Wa
and the Analysis of Its Potential,” Energy Conservation,
Vol. 4, 1992, pp. 4-7.
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Specification and Technical Requirements for
Oil-immersed Power Transformers GB/T 6451-2008.
China ISBN, Beijing: Standards Press of China, 2008.
[4] J. L. Xu, “Method to Reduce Power Transformer Los
Vol. 3, 2012, pp. 26-35.
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