Energy and Power Engineering, 2013, 5, 689-692
doi:10.4236/epe.2013.54B133 Published Online July 2013 (http://www.scirp.org/journal/epe)
Design and Application of Optimization Software for
Substation Operation Mode Based on EMS
Nannan Gao, Jinxin Huang, Hongbo Li
State Grid of China Technology College, Jinan, China.
Received March, 2013
ABSTRACT
This paper proposes a kind of optimization software for substation operation mode, which can not only read data on-line
from EMS, but also calculate total loss of substatio ns in parallel op eration, split op eration or individua l operation mode.
It can also select the most optimized way and feed the conclusion back to EMS to make substations operate in the most
optimized way. The software is suitable for optimization of substation in rural power grid.
Keywords: Optimization; Substation Operation Mode; On-line; Closed Loop
1. Introduction
The rural power grid is one of the important parts of
electric power system. It generally has the character of
small-scale, even non-network [1]. Therefore, the em-
phasis of rural power grid optimization should be laid on
substation operation mode. The substation operation
mode has a large impact on the loss of rural power grid
because of the large variation of load [2]. Accordingly
when substations operate in the most optimized way,
they can obtain obvious economic b e nefit.
The present Energy Management System (EMS) has
not the function which can optimize the operation mode
of substations. So we design a kind of optimization soft-
ware for substation operation mode on the basis of EMS.
It can not only select the most optimized substation op-
eration mode according to the on-line data, but also real-
ize the closed loop con trolling which feed the conclusion
back to EMS. EMS will regulate the operation mode of
substation correspo ndingly to make it op erate in the most
optimized way. Moreover, the software also has conven-
ient function of statistic, accumulation, inquiry and print.
During the trial running, the software has realized obvi-
ous economic benefit.
2. Design of Software
The framework of optimization software for substation
operation mode is shown in Figure 1. The flowchart of
optimization software for substation operation mode is
shown in Figure 2.
The software reads data from two parts of EMS
through the private data interface. One co mes from Power
Application Software (PAS) including the topological
relation of all the substation equipments and their essen-
tial parameter. Another one comes from Supervisory
Control and Data Acquisition (SCADA) system includ-
ing the telemetry date and remote data of substation. All
the data will be input in the optimization module of the
software.
First the optimization module will judge the connec-
tion of all the substation equipments by their topological
PAS
Topological
relation Essential parameter
SCADA
Telemetry
date Remote data
Private data interface
Optimiz a t ion module
Data storage module Closed loop control module
Data display module
EMS
Optimization software for substation operation mode
Figure 1. Framework of optimization software for substa-
tion operation mode.

N. N. GAO ET AL.
690
Begin
Read data from EMS
Judge substation operation mode
Calculate total load of every secondary bus
Calculate to tal loss in dif ferent mode
Overloads?
N
Y
Select the most optimized mode
Exclude
Statistic, accumulati on, storage
Display?
Y
N
Inquiry, print
Closed loop control
End
Figure 2. Flowchart of optimization software for substation
operation mode.
relation. Then the optimization module will judge the
current substation operation mode which is parallel op-
eration, split operation or individual operation by the
remote data of substation. And the line which is running
in the secondary side will be judged by the same way.
After that, the optimization module can calculate th e total
load of every second ary bus by the telemetry d ate of sub-
station.
Based on these analyses, the optimization module can
calculate the total loss of the substation when it operates
in different mode, and select the most optimized way
according to the result. In addition, it can also judge
whether each transformer overloads in some way of op-
eration. If one transformer overloads in a certain way, th e
mode would not take part in the underneath preferential
selection. The calculation method of total loss when
transformer operates in the different mode will be intro-
duced in detail later.
Further more, the optimization module has the func-
tion of statistic and accumulation which can calculate th e
total loss of the substation when it operates in the current
mode or the most optimized mode every day, every
month, every year, and so on.
The optimization module will p ut all the result in to the
data storage module of the software. The data display
module of the software will realize the function of in-
quiry and print by reading data from the data storage
module.
At the same time, the optimization module will put the
most optimized operation mode into the closed loop con-
trol module, which can feed the conclusion back to
SCADA system through the private data interface.
SCADA system will regulate the operation mode of sub-
station correspondingly to make it operate in the most
optimized way.
3. Algorithm
The emphasis of a substation’s total loss should be laid
on its transformers’. Take, for example, a substation
which has two transformers and two buses in the secon-
dary side, the software uses following algorithm.
A transformer’s total loss consists mainly of iron loss
and copper loss [3-4]. Iron loss can be considered as
no-load loss because copper loss produced by no-load
current can be ignored. In addition, iron loss is decided
by the main flux in th e iron, and the main flux essentially
remains unchanged either no-load or on-load if the ap-
plied voltage remains unchanged. Therefore, iron loss
can also be considered as no-load loss either no-load or
on-load. The calculation method of total loss is shown in
equation (1) [5-6].
2
0
2
total lossk
N
S
PP
SP

 (1)
where P0 is transformer no-load loss, S is transformer
apparent power, SN is transformer capacity, Pk is trans-
former short-circuit loss.
Based on these analyses, the calculation method of to-
tal loss in the way of transformer 1 individual operation
is as equation (2) shows.
 
22
121 2
101 21 loss k
N
PP QQ
PP P
S

1

 (2)
where P01 is no-load loss of transformer 1, P1 is active
power of bus 1 in the secondary side, P2 is active power
of bus 2 in the secondary side, Q1 is reactive power of
bus 1 in the secondary side, Q2 is reactive power of bus 2
in the secondary side, SN1 is capacity of transformer 1,
and Pk1 is short-circuit loss of transformer 1.
Similarly, the calculation method of total loss in the
way of transformer 2 individual operation is as equation
(3) shows.
 
22
121 2
20222 loss k
N
PP QQ
PP P
S

 
2
(3)
where P02 is no-load loss of transformer 2, SN2 is capacity
of transformer 2, Pk2 is short-circuit loss of transformer 2.

N. N. GAO ET AL. 691
In the same way, the calculation method of total loss in
the way of split operation is as equation (4) shows.

22 22
111222
010222
12
kk
loss split
NN
PQP PQP
PPP SS

  (4)
The calculation method of total loss in the way of par-
allel operation can be obtained as follow. The relation-
ship of the two transformer apparent power is shown in
equation (5) according to the load distribution formula.
1
1
22
2
1
N
k
N
k
Su S
SS u
 (5)
where S1 is apparent power of transformer 1, S2 is appar-
ent power of transformer 2, uk1 is impedance voltage of
transformer 1, uk2 is impedance voltage of transformer 2.
The calculation method of the two transformers ap-
parent power can be obtained as shown in equation (6)
and (7) based on equation (5).
1
1
112
12
N
k
NN
kk
S
u
S
SS
uu


S (6)
2
2
212
12
N
k
NN
kk
S
u
S
SS
uu


S

(7)
The calculation method of total loss in the way of par-
allel operation can be obtained as shown in equation (8)
considering equations (1), (6) and (7).

22
121 2
01022
12
12
12
22
12
loss parallel
NN
kk
kk
kk
PP QQ
PPP
SS
uu
PP
uu

 







(8)
In conclusion, the software can calculate total loss in
parallel operation, split operation and individual opera-
tion mode by equations (2), (3), (4) and (8).
4. Example
The software has been put into operation successfully at
the Second Power Supply Bureau of Harbin since last
March. During this period, the software has characteristic
of stable operation, friendly interaction and easy to use.
Further more, the total loss average of all the four substa-
tions has dropped to 86.79 percent, which proved the
software had obvious economic benefit.
The deference of substations’ total loss every month
between they operate in original mode and in the most
optimized way is shown in Table 1.
The percentage of substations’ total loss per month has
dropped as shown in Table 2.
Table 1. Deference of total loss (kWh).
Time Lingbei
Substation Xuguang Substation Qianjin Substation Weixing Substation Monthly Average
March, 20121425.861638.45 945.16 1634.291410.94
April, 2012 1726.941048.62 1824.65 942.611385.71
May, 2012 1159.421726.48 1248.26 824.951239.78
June, 2012 824.59942.85 2045.13 1354.921291.87
July, 2012 1752.611324.58 1724.06 2049.851712.78
August, 20122195.421098.25 814.25 1348.641364.14
September, 20121628.15824.21 1248.65 2149.751462.69
October, 2012975.181725.14 1248.36 1579.481382.04
November, 20121348.90846.35 943.24 1736.481218.74
December, 20121982.101345.01 1685.95 2048.261765.33
January, 20131068.26995.42 1248.54 1647.241239.87
Average of each
Substation 1462.491228.67 1361.48 1574.221406.72
Table 2. Percentage of total loss has dropped.
Time Lingbei
Substation Xuguang Substation Qianjin Substation Weixing Substation Monthly Average
March, 201286.61%8 4.62% 91.13% 84.66%86.75%
April, 2012 83.79%90.16% 82.87% 91.15%86.99%
May, 2012 89.12%83.79% 88.28% 92.26%88.36%
June, 2012 92.26%91.15% 80. 80% 87.28%87.87%
July, 2012 83.55%87.56% 83.81% 80.76%83.92%
August, 201279.39%89.69% 92.36% 87.34%87.19%
September, 201284.72%92.26% 88.28% 79.82%86.27%
October, 201290.85%83.80% 88.28% 85.17%87.03%
November, 201287.34%92.05% 91.14% 83.70%88.56%
December, 201281.39%87.37% 84.17% 80.77%83.43%
January, 201389.97%90.66% 88.28% 84.54%88.36%
Average of each
Substation 86.27%88.47% 87.22% 85.22%86.79%

N. N. GAO ET AL.
692
5. Conclusions
The optimization software for substation operation mode
is suitable for optimization of substation in rural power
grid. It can not only read data on-line from EMS, but also
calculate total loss of substations when parallel operation,
split operation or individual operation, and select the
most optimized way, as well as feed the conclusion back
to EMS to make substations operate in the most opti-
mized way. The software has obvious economic benefit
during the trial operation.
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