The document proposes a comprehensive decision-making method for developing DC de-icing plans for power grids during ice storms. It considers two key factors: the urgency of de-icing transmission lines and maintaining power system security. It introduces indicators to evaluate the de-icing urgency of lines based on importance, existing ice levels, and predicted ice growth. It also proposes a "comprehensive index on net-ability drop" to reflect the impact on system security from groups of lines undergoing de-icing. The method aims to develop de-icing plans that equalize this index across time slots to maximize security while de-icing urgently needed lines. It was demonstrated on the Guizhou power grid in China.

1. 2014 International Conference on Power System Technology (POWERCON 2014) Chengdu, 20-22 Oct. 2014
POWERCON 2014 Paper No CP1969 Page 1/8
Abstract—When the power grid suffers a wide range of freezing
disasters, how to make a reasonable DC de-icing plan of
transmission line became a urgent problem for the dispatchers.
For the reason the DC de-icing ranking evaluating indicator of
transmission line and the comprehensive index on net-ability drop
are proposed to develop the power grid DC de-icing plan. The DC
de-icing ranking evaluating indicator of transmission line is
proposed to distinguish DC de-icing urgency of transmission lines.
The importance of transmission line, the current rate of
icing-coating and the predicted rate of icing-coating are the three
attribute factors of the evaluating indicator, the weights of which
are determined by the method of weighted average combinative
evaluation. The comprehensive index on net-ability drop is used to
reflect the system security. The transmission line DC de-icing
group which would pose a serious threat to system security will
not appear if planning the power grid DC de-icing plan based on
the proposed equivalent net-ability method. DC de-icing
comprehensive decision-making method of power grid is proposed
with overall consideration of the emergence of transmission line
DC de-icing and the power system security, the effectiveness and
Manuscript received October 9, 2001.
CHEN Liang is with Sichuan University, Chengdu, 610065, China
(corresponding author to provide phone: (0086)18048531040; fax:; e-mail:
liangchen777@hotmail.com).
FU Chuang is with Electric Power Research Institute, China Southern
Power Grid Co., Ltd., Guangzhou, 510080, China (e-mail: fuchuang@csg.cn)
LI Xing-yuan is with the Electrical Engineering Department, Sichuan
University, Chengdu, 610065, China (e-mail: x.y.li@163.com).
feasibility of which are demonstrated by the example of Guizhou
power grid. The DC de-icing comprehensive decision-making
method of power grid would be a good reference for the
dispatcher to make DC de-icing plan. g.
Index Terms—DC de-icing plan, the comprehensive index on
net-ability drop, DC de-icing urgency; power system security; DC
de-icing comprehensive decision-making method of power grid
I. INTRODUCTION
s the ice disaster damaged the power grid severely in 2008,
China Southern Power Grid (CSG) put forward a series of
measures to improve their capability of resisting ice disaster.
The soundly set DC de-icing system played a distinctive role in
the recent anti-icing relief work [1-6]. Up to now, dozens of
DC de-icing equipment have been allocated in CSG, which
could protect most of the transmission line of 220kV and above
in disaster areas.
The research on DC de-icing equipment and their
implementations were well-studied. However, how to make a
reasonable DC de-icing plan of power grid became a new
research.
The study of DC de-icing planning in power grid and DC
de-icing ranking of transmission line is still in the start-up. The
foreign researches mainly focused on the AC de-icing
strategies[7,8], which are based on the practice of the load
current de-icing and not involved with DC de-icing plan. The
research on the DC de-icing strategies was just started in China.
A de-icing decision-making model of power grid based on
Comprehensive Decision-making of Power Grid
DC De-icing Plan Based on Equivalent
Net-ability Method
CHEN Liang, FU Chuang, and LI Xing-yuan, Member, IEEE
A
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TOPSIS was proposed to judge the de-icing priority of regions
according to the micro meteorological information[9]. Another
de-icing decision-making model of transmission lines used
scoring model to decide the de-icing sequence of transmission
lines, considering three main factors that influent the power
grid de-icing sequence: the ice cladding situation, power grid
topology and the particularity of lines[10]. The above two
methods took the ice-coating situation or the micro
meteorological information as the decision-making factors,
aiming to arrange the transmission lines that are urgent to be
de-iced preferentially, but neglected the power system security
influenced by the transmission lines group of DC de-icing on
work.
The paper proposes a comprehensive decision-making method
of power grid DC de-icing plan based on equivalent net-ability
method. The critical transmission line will be arranged its DC
de-icing plan preferentially, with the target of equivalent
net-ability, to avoid the transmission lines group of DC de-icing
that threats the operating security of power grid heavily; Then,
the common transmission line will be arranged its DC de-icing
plan in accordance with its urgency. The proposed method will
reduce the operating security risk of power grid under that some
transmission lines are in DC de-icing working mode, on the
basis of transmission line in relatively safe status, which will be
useful in the anti-icing work in power grid.
II. FACTORS RELATED TO DECISION-MAKING OF POWER GRID
DC DE-ICING PLAN PROCEDURE FOR PAPER SUBMISSION
Two factors need be taken into account when drawing up DC
de-icing plan of power grid. On the one hand, the DC de-icing
urgency of transmission line is necessary to be considered, in
order to avoid the collapse of tower and the breakage of
transmission line caused by heavy ice-coating during the ice
disaster; on the other hand, power grid security shouldn’t be
ignored, to avoid the transmission line DC de-icing group that
threat the security operating of power grid heavily.
A. Importance of transmission line
The DC de-icing plan of critical transmission lines should be
arranged preferentially when drawing up DC de-icing plan of
power grid. On the one hand, the influence to power grid
security and the economic loss caused by outage of critical
transmission lines are more than outage of common
transmission lines, for the reason of heavy ice-coating on lines,
so the critical lines should be DC de-iced earlier in principle.
On the other hand, if a number of critical lines are planned to be
DC de-iced at the same time, the power grid would operate at
high risk and the de-icing work would threat the system
security and cause a lot of economic loss, so the critical lines
are better to be arranged at the different time intervals. There
are certain contradictions in these two aspects, therefore the DC
de-icing time slots of transmission lines will be arranged with
overall consideration.
B. Existing rate of ice-coating of transmission line
The system for monitoring and predicting icing events has
been established in CSG after the extreme ice disaster in 2008.
More than 300 on-line monitoring terminals have been installed
in CSG till 2013, which can monitor ice-coating of
transmission line in the heavy and medium icing area [11,12]..
The existing rate of ice-coating is used to measure the order
of existing ice-coating in this paper. The definition of existing
rate of ice-coating 2a is the ratio of existing thickness of
ice-coating to the limited thickness of ice-coating:
2 /a h s (1)
The lines with bigger value of 2a are arranged earlier than
the lines with smaller value in principle.
C. Predicted rate of ice-coating
The prediction of ice disaster need be focused except the
existing rate of ice-coating. The transmission line in the area
that ice storm continues or becomes more serious are better to
be de-iced early.
The predicted rate of ice-coating 3a in decision-making
period can be obtained through weather forecast information
and ice-coating prediction model with the help of the system
for monitoring and predicting icing events[13,14].
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D. DC de-icing plan of de-icer
Transmission lines need to switch to DC de-icers to implement
DC de-icing and one de-icer can only implement DC de-icing
on one overhead line meanwhile, so to make DC de-icing plan
of power grid is actually to draw up DC de-icing plan of each
de-icer. In order to avoid causing confusion in every de-icer
planning, it needs to be done for each transmission line that
confirming de-icing means and de-icers before planning de-ici
ng work.
III. DC DE-ICING URGENCY OF TRANSMISSION LINE
A. DC de-icing urgency indicator of transmission line
DC de-icing ranking evaluating indicator iF is used to
distinguish DC de-icing urgency of transmission line in this
paper:
1
n
i ij j
j
F r (2)
Where ijr represents the j th attribute factor of line i ; m is
the number of transmission line to be DC de-iced; j
represents the weight of the attribute factor ja .
The importance of transmission line 1a , the current rate of
ice-coating 2a and the predicted rate of ice-coating 3a are
three attribute factors. The value of 1a of lines could be
decided by dispatchers by importance sequence principle of
CSG de-icing lines and the experiences
The greater the value of iF is means the higher the urgency is
of DC de-icing of transmission line. The line with high iF
would be dc de-iced normally.
B. Weighted average combinative evaluation
The specific steps of calculating the weight j by the
method of weighted average combinative evaluation are as
follows[15]:
1 generate the reference sequence 1 2, , , nC C C C ,
which is the arithmetic mean value of ranking evaluating
indicator of lines,
1
q
ik
k
j
F
C
q
(3)
Where ikF represents the ranking evaluating indicator of line
i based on the k th simple evaluation method q is the
number of simple evaluation method used. Dephi[16],
AHP[17], entropy weight method[18] and maximizing
deviation method[19] are simple evaluation methods used in
the paper.
2 take C as the reference sequence, then calculate the
Spearman correlation coefficient k as the weight of simple
evaluation method k :
1
k
k q
k
k
(4)
3 calculate the combined weight cW :
1 1 2 2c q qW w w w (5)
IV. The method of EQUIVALENT net-ability
net-ability drop
1) net-ability
The net-ability was first introduced by Arianos and Bompard
as a measure of performance of a power transmission grid
under normal operating conditions[20,21]. The net-ability YA
of power grid Y is defined as:
,
,
1 1
g d
Y g d
g B d Bg d gd equ
A C
N N Z
(6)
, ( ) ( )
gd
gd equ gg gd gd dd
g
U
Z z z z z
I
(7)
where gB and gN are sets of generator and load nodes
respectively; likewise gN and dN are the total numbers of
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generators and loads respectively. ,gd equZ is the equivalent
impedance of the circuit whose ends are node g and node
d ; gdU is the voltage between g and d ; gI is the current
injected at node g and extracted at node d ; gdz is the g-th,
d-th element of the impedance matrix; ,g dC is the maximum
transfer capacity between node g and node d , the definition
of which is as follows[22,23]:
max
,
,
min l
g d
l L
l gd
P
C
a
(8)
Where L is the set of transmission line; max
lP is the flow limit
of line l ; ,l gda is power transfer distribution factors (PTDF).
Supposing we increase the power injection at node g until
the first line reaches its line flow limit: ,g dC is equal to the
power injection in that moment.
2) Net-ability drop
Net-ability drop Y lr is defined as follows:
* *
*
100%Y Y l
Y l
Y
A A
r
A
(9)
Where Y lr represents net-ability drop caused by outage(cut) of
the line l
B. Objective function
Comprehensive index on net-ability drop is used to evaluate
power system safety in this paper. Comprehensive index on
net-ability drop is defined as:
( )
t
Y Y l
l t
R r (10)
Where t
YR is the comprehensive index on net-ability drop of
power grid Y at the time slot of t ; ( )t is the set of outage of
transmission line.
The method of equivalent net-ability is proposed in the paper
to help making DC de-icing plan of power grid. The
objective function of the method of equivalent net-ability is:
, , , 1,2, ,m n
Y YR R m t n t t T (10)
where m
YR and n
YR are the comprehensive index on net-ability
drop at the time slot m and at the time slot n respectively; T is
the number of time slots in the planning period.
The target of the objective function can be described as to
equate the comprehensive index on net-ability drop at different
time slot to the greatest extent, thus making the minimum
comprehensive index as higher as possible in the period of DC
de-icing.
C. Constrains
1) DC de-icing time slots
For some reasons, de-icing of a transmission line has to be
arranged in certain time slots as shows in eq.(11):
i i (11)
Where i is the time slot to implement DC de-icing for line i ;
i is the set of time slots in which line i is allowed to be
de-iced.
2) Rules of simultaneous de-icing
Some transmission line cannot switch directly to de-icer but
can connect to de-icer via another line, and therefore when the
lines are to be implemented DC de-icing, the cascaded lines
need to do the same operation simultaneously.
So the lines aiming to be de-iced by cascading should be
arranged with the other lines they cascadedly connecte to de-ic
e together. eq.(12) Represents line i and line j are to be
implemented dc de-icing simultaneously.
i j (12)
3) Rules of mutually-exclusive de-icing
Some transmission line cannot to be implemented DC
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de-icing simultaneously. For instance, the lines used the same
de-icer are not available to be arranged in the same time slot, so
the planned time slots of the lines are mutually-exclusive.
eq.(13) Represents line i and line j are not allowed to be
implemented DC de-icing simultaneously.
i j (13)
V. COMPREHENSIVE DECISION-MAKING METHOD OF POWER
GRID DC DE-ICING PLAN BASED ON EQUIVALENT NET-ABILITY
On the basis of DC de-icing urgency of transmission line and
security of power system, comprehensive decision-making of
power grid DC de-icing plan based on equivalent net-ability is
proposed in this paper as in Fig.1.
Set of lines waiting for be de-iced
A(a1,a2, ,an)
Analyze net-ability drop of Power grid Y. The m
lines with AY>rthd form the critical lines set
S1(s1,s2, ,sm) in order; other lines form the
common line set S2(sm+1,sm+2, ,sn),
Set k=1
Update the allowed time slots for DC de-icing k of every
line according to constrains and the existing plan Pk-1
Add the de-icing time slot of the restricted lines which have not
yet be arranged into the existing plan Pk-1, obtain plan Pk-1
*
Has line sk been arranged
Arrange DC de-icing time slot of line sk based on the
method of equivalent net-ability and plan , obtain plan
K=m?
Arrange DC de-icing time slots of the common lines S2 according
to DC de-icing ranking evaluating indicator Fi and plan
Output DC de-icing plan Pfinal
of power grid
Fig.1 DC de-icing comprehensive decision-making flow of power
grid
In Fig.1, the restricted line refers to the lines that can be only
arranged to DC de-iced in a certain time slot, according to the
existing dc de-icing plan and constrains. A important part of
DC de-icing comprehensive decision-making flow of power
grid showed in Fig.1 is to set a decision threshold thdr . The
lines that Y l thdr r are considered as critical lines, DC
de-icing time slot of which will be decide based on the method
of equivalent net-ability; The lines that Y l thdr r are
considered as common lines, DC de-icing plan of which will be
made by DC de-icing ranking evaluating indicator iF .
By controlling the threshold value of thdr can optimize the
decision results. By decreasing the threshold value of thdr can
reduce the de-icing safety risk in operation, but risks of pouri
ngpole tower and line have been increased, so as to time to m
ake decisions. And vice versa.
VI. CASE STUDIES
In this section we will try to make DC de-icing plan of Zunyi
regional power grid (CSG) based on the comprehensive
decision-making method proposed above. There are 3 DC
de-icers(220kV) deployed at substation of Yaxi, Zunyi and
Tongzi and 19 transmission lines( include cascaded lines) are
planned to be de-iced by the 3 DC de-icers.
Table.1 220kV transmission line to be de-iced in Zunyi region
In table 1, we show the constrains, the DC de-icers used,
Y lr standing for the net-ability drop of CSG caused by
outage(cut) of the line in the table and iF which is calculated
iFY lr
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based on the information at the moment of decision.
Lines Wujnan / can only switch to the DC de-icer at
substation of Zunyi via lines Nanzun / , and therefore DC
de-icing of line Wujnan and line Nanzun should be arranged in
the same time slot; Wujnan and line Nanzun are in the same case.
Dc de-icing time slots of lines Yaxnan / are constrained in the first
two time slots for heavy ice-coating and continues ice weather.
Table.2 DC de-icing plan of 220kV transmission line in Zunyi region
Y lr Y lr
Therefore. As restricted lines, lines Yaxnan / are arranged directly
in the 1st
and 2nd
time slot of dc de-icer at substation of Yaxi.
Then, dc de-icing time slots of other lines are arranged according to
comprehensive decision-making method proposed in chapter 4.
The DC de-icing plan based on two methods shows In table 2.
The method 1 refers to method based on equivalent net-ability,
ignoring DC de-icing urgency of transmission line; the method
2 is the comprehensive decision-making method proposed in
chapter 4 in the case, 0.005thdr
The comprehensive indexes on net-ability drop t
YR in the
decision period is showed in table 3, according to the DC
de-icing plan in table 3.All the values of t
YR in six time slots
are not quite big and not much different from each other.There
is no time slot in which the value of t
YR is much bigger than the
value in other time slots, which means there is no transmission
lines group of DC de-icing would endanger the power system
security seriously.
Table.3 comprehensive indexes on net-ability drop of Guizhou
power grid
t
YR t
YR
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In the method 2, the DC de-icing time slots of common
lines(like Hato / and Tosh / ) are arranged based on by
DC de-icing ranking evaluating indicator iF , with the
maximum t
YR (0.0137) in the method 1 lower than the maxim
t
YR (0.0148) in the method 2, thus the whole system security is
slightly lower than the plan based on the method 1.
Compared with the method 1, the system security based on the
method 2 is slightly lower, however considered DC de-icing u
rgency of transmission line, so it reduces the chances of colla
pse of tower and the breakage of transmission line caused by h
eavy ice-coating so as to time consumption of decision.
VII. CONCLUSION
Comprehensive decision-making of power grid DC de-icing
plan based on equivalent net-ability proposed in the paper is
under the overall consideration of DC de-icing urgency of
transmission line and security of power system, based on which
the lines with high de-icing urgency is arranged to be de-iced
earlier at a certain safety level of power system which is
worth for de-icing decision-making and dispatching work.
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