CHAPTER 3 Substation Sitting
Transcript of CHAPTER 3 Substation Sitting
493 Optimum siting and sizing of substation
Chapter 3
Optimum siting and sizing of substations
Chapter content:
(1.0)Introduction
(2.0)Symbols definitions
(3.0)Calculation Sequence
(4.0)Data used in design
(5.0)Calculations
503 Optimum siting and sizing of substation
Chapter 3
Optimum siting and sizing of substations
(1.0)Introduction:
Substations are the second step in power system after the Electrical load forecast &
Starting with Substation “66/22 KV or 11 KV “the distribution network will initiate.
Substation will distribute its power using feeders on distribution voltage 22, 11 KV.
These feeders can be overhead or underground cables depend on the cost of the
system, it's nature & it's location in the Rural or in Cities.
Our concern here is to find the number of substations and its distribution on each
planning area. The selection of the number of the substations is from economical view.
We try to find the optimum number of substations to have minimum cost. We want to
equalize the cost of substations and the cost of feeders, to have the minimum total cost
for both S/S & feeders, If we have large number of substations (large S/S cost) we will
have short feeders (low cost) and if we have small number of substations (low S/S cost)
we will have long feeders (large cost). This mean increasing the number of substations
for a given load density tends to increase total cost. However, increasing the number of
substations reduces the cost of feeders and feeder losses.
Clearly then, the least total annual cost is a function of substation size, feeders cost,
capacity of feeder and load density. But there are another factors rather than the cost of
S/S & feeders effect on the selection the optimum sitting & sizing, so due to the growth
of demands and scarcity of available S/S sites, the cost of the location and spacing of
substations becoming a major economic problem also. Due to local geography,
distribution system, Security & other conditions beyond control, it may be impractical to
select the ideal substation size and spacing. So, these factors should be known so that
the ideal conditions may be approached as near as possible from all points of view. The
best size and spacing of S/S is that which results in the least annual cost of the sum of
fixed charges on S/S, feeders, operation, maintenance, and losses.
513 Optimum siting and sizing of substation
Factors affecting substation site selection:
1) Load forecast2) Land availability3) Cost of land4) Existing substation locations5) Feeder limitation6) Closeness to load centers
Factors affecting feeder routing selection:
1) Future load growth2) Physical barriers3) Voltage drop4) Total cost5) feeder
523 Optimum siting and sizing of substation
(2.0)Symbols definitions:
The following symbols will be used to determine the relationship of the above factors
in deriving an equation for total annual cost.
Using one square km as a unit area, the number of feeders required to serve this area
is,
n f=D /kVA f (1)
And the cost per feeder is given by
a+b×S /2 (2)
The substation cost to supply this unit area is:
D Load density (KVA/km2)
(kVA )s Substation KVA capacity
S Distance between substations (km)
a Fixed charge on feeder equipment LE/year
b Total cost of feeder including erection LE/Km
c That part of substation cost not proportional to substation capacity
d Cost per KVA of the capacity required to carry the load in the area S2
(kVA )f Feeder KVA capacity = √3 *V*Icc
n f number of feeders required per km2
C s Cost of substation per km2
CT Total annual cost of substation & feeders per km2
533 Optimum siting and sizing of substation
c
S2+d×D
(3)
The total cost of substation and feeders is then the product of equation (1) and (2) plus
equation (3), mathematically, the total cost is,
CT=(a+b×S /2 )×D /KVA f +c / S
2+d×D (4)
Minimizing equation (4) with respect to S:
S=1.59[ kVAf cbD ]0.333
km (5)
and the corresponding optimum substation size would be
kVAS opt=S2D
(6)
(3.0)Calculation Sequence:
KVASopt=D⋅S
2
nS=area÷S2⇒
approximated to the higher integer
KVASact
=Total Load÷nS
Loading Percent=KVASopt÷Substation rating including the reserve
Get # of transformers needed & add reserve transformer. Try to make total # of
transformers to be even for easier protection.
Feeders /Substation=Substation rating including the reserve÷KVA f
And then approximated to the higher integer giving even no of feeders / substation
543 Optimum siting and sizing of substation
Current Density = KVASact÷ ( feeder /Substation×√3×11×csa of feeder )
(4.0)Data used in design:
(4.1)Draw:
All dimensions in Km
(4.2)load density:
ZoneArea (Km2)
Maximum Load (MVA)
D
(MVA/ Km2)
1.Agricultural 25*5 140.9368 1.1275
2.Residential 15*7.5 376.5831 3.3474
3.City Center 15*12.5 1215.43 6.4823
4.Light Industrial 7.5*5 257.7087 6.872
5.Heavy Industrial 7.5*5 608.1562 16.2175
553 Optimum siting and sizing of substation
(4.3)Substations:
Cost of Outdoor substation=23,000,000 LE
Cost of Indoor substation= 30,000,000 LE
(4.4)For OHTL:
kind Aluminum conductor steel reinforced(ACSR)Cross section 120 mm2 (Stranded in 6 strands)CCC 300 ampere Price 38,400 LE/KM
Assume no derating in the OHTL
(4.5)For UGC:
Insulation level 12/20 kVKind Multicore cables, with stranded Aluminum conductors XLPE
insulated, steel tape armoured and PVC sheathedCross-section 240 mm2
CCC 340 amperePrice 166 LE/M+12% sales tax+25% erectionDe-rating factors Ground temperature derating factor , burials depth derating
factor, soil thermal resistivity derating factor
The following de-rating factors should be considered in design:
Ground temperature de-rating factor
Burial depth derating factor (1 m)
Soil thermal resistivity derating factor
D.F = 0.93 × 0.93 × 0.91 = 0.706
563 Optimum siting and sizing of substation
(5.0)Calculations:
(5.1)Agricultural area:
(5.1.1)Design aspects:
Substations used in the agricultural area are generally outdoor substations due to the low cost of land
Over Head Transmission Lines ( OHTL ) are used in the agricultural area are used for the primary distribution networks ( 11 KV ) due to The lower cost of OHTL makes it more suitable for use in the agricultural areas and UGC may be destroyed while digging or due to irrigation in the agricultural areas.
It is recommended that the number of transformers in each substation doesn't
exceed 6 transformers including the reserve.
It is recommended that the bus bars in the substation are sectionalized and
doubled to allow maneuver and that the number of transformers and feeders per
section is even number.
It is recommended that the number of feeders per transformer in agricultural area shouldn't exceed 6 feeders.
A recommended current density for the OHTL it is generally around 2 A/mm2. It is recommended that the loading percent of the substation
between 60%⇒80%
(5.1.2)Calculations:
573 Optimum siting and sizing of substation
As we use OHTL ⇒ b=38,400 LE/KM & (kVA )f=√3∗11∗300
As we use Outdoor substation ⇒ C=23,000,000*0.3 LE
D=1.1275 MVA/ Km2
S=1.59[ kVAf cbD ]0.333
km
S=15.41306768Km
KVASopt=D⋅S2=267851.8937
KVA
nS=area÷S2=0.526176979
, approximated to the higher integer (
nS=1 )
KVASact=Total Load÷nS=140936 .8
KVA
Transformers used in substation: 66/11 KV, 5×35 + 1×35 MVA
Loading percent = 67.1128%
Feeders /Substation=Substation rating including the reserve÷KVA f=36 .74
Feeders /Substation=36
Approximated to the integer giving even number of
feeders/ substation & feeders/ transformer.
Substation capacity is bigger than feeders capacity with 4.23 MVA
Each transformer supplying 6 feeders.
Current density=0.8562A/mm2
583 Optimum siting and sizing of substation
(5.1.3)Sitting of the 66/11 KV substation in agricultural area:
All dimensions in Km
593 Optimum siting and sizing of substation
(5.2.0)Residential area:
(5.2.1)Design aspects:
Substations used in Residential area are generally the indoor substations. Under Ground Cables (UGC) are used in Residential area for the primary
distribution networks (11 KV).
From the reliability point of view, it is better to replace one large substation with
some smaller substations distributed over the planning area, in spite of the
increase in the cost; yet, the increase is not that considerable amount.
It is recommended that the number of transformers in each substation doesn't
exceed 6 transformers including the reserve.
It is recommended that the bus bars in the substation are sectionalized and
doubled to allow maneuver and that the number of transformers and feeders per
section is even number.
It is recommended that the number of feeders per transformer in Residential area exceed 8 feeders per transformer.
The loading percent in each substation shouldn't exceed 80% for safety and
continuity of feeding in case of outage of any unit.
A recommended current density for the UGC is 1 A/mm2
603 Optimum siting and sizing of substation
(5.2.2)Calculations:
As we use UGC⇒ b=227420LE/KM & (kVA )f=√3∗11∗340∗0 .706
As we use Indoor substation ⇒ C=30,000,000*0.3 LE
D=3.3474 MVA/ Km2
S=1.59[ kVAf cbD ]0.333
km
S=6 .012358226Km
KVASopt=D⋅S2=121003.3264
KVA
nS=area÷S2=3.1122
, we have two solutions
solution 1 solution 2nS= 3 4
KVASact=Total Load÷nS=
125527.7 KVA 94145.775 KVA
Transformers used in substation 66/11 KV
5×35 + 1×35 MVA 3×35 + 1×35 MVA
Loading percent = 59.77% 67.247%Feeders /Substation= 45.9 ⇒ 48 30.6 ⇒ 32
Each transformer supplying8 feeders 8 feeders
Current density= 0.572 A/mm2 0.6434 A/mm2
613 Optimum siting and sizing of substation
(5.2.3)Sitting of the 66/11 KV substation in the Residential area :
Solution 1(nS=3 ):
All dimensions in Km
Solution 2(nS=4 ):
623 Optimum siting and sizing of substation
All dimensions in Km
(5.3.0)City center:
(5.3.1)Design aspects:
Substations used in City center area are generally the GIS (Gas Insulated Substations) since the land is very expensive.
Under Ground Cables (UGC) are used in City center area for the primary distribution networks (11 KV).
From the reliability point of view, it is better to replace one large substation with
some smaller substations distributed over the planning area, in spite of the
increase in the cost; yet, the increase is not that considerable amount.
It is recommended that the number of transformers in each substation doesn't
exceed 6 transformers including the reserve.
It is recommended that the bus bars in the substation are sectionalized and
doubled to allow maneuver and that the number of transformers and feeders per
section is even number.
It is recommended that the number of feeders per transformer in City center area shouldn't exceed 8 feeders per transformer.
The loading percent in each substation shouldn't exceed 80% for safety and
continuity of feeding in case of outage of any unit.
A recommended current density for the UGC is 1 A/mm2
633 Optimum siting and sizing of substation
(5.3.2)Calculations:
As we use UGC⇒ b=227420LE/KM & (kVA )f=√3∗11∗340∗0 .706
As we use GIS (Gas Insulated Substations) ⇒ C=30,000,000*0.3 LE
D=6.4823 MVA/ Km2
S=1.59[ kVAf cbD ]0.333
km
S=4 .823596935Km
KVASopt=D⋅S2=150824 .2406
KVA
nS=area÷S2=8.058593534
, approximated to integer (
nS=8 )
KVASact=Total Load÷nS=151928 .75
KVA
Transformers used in substation: 66/11 KV, 5×35 + 1×35 MVA
Loading percent = 72.35%
Feeders /Substation=Substation rating including the reserve÷KVA f=45.92
Feeders /Substation=48
Approximated to the integer giving even number of
feeders/ substation & feeders/ transformer.
Each transformer supplying 8 feeders.
Current density=0.6922A/mm2
(5.3.3)Sitting of the 66/11 KV substation in the City center area :
643 Optimum siting and sizing of substation
All dimensions in Km
(5.4.0)Light industrial:
(5.4.1)Design aspects:
Substations used in Light Industrial area are generally the indoor substations Under Ground Cables (UGC) are used in Light Industrial area for the primary
distribution networks (11 KV).
From the reliability point of view, it is better to replace one large substation with
some smaller substations distributed over the planning area, in spite of the
increase in the cost; yet, the increase is not that considerable amount.
It is recommended that the number of transformers in each substation doesn't
exceed 6 transformers including the reserve.
It is recommended that the bus bars in the substation are sectionalized and
doubled to allow maneuver and that the number of transformers and feeders per
section is even number.
It is recommended that the number of feeders per transformer in Light Industrial area shouldn't exceed 8 feeders per transformer.
The loading percent in each substation shouldn't exceed 80% for safety and
continuity of feeding in case of outage of any unit.
653 Optimum siting and sizing of substation
A recommended current density for the UGC is 1 A/mm2
(5.4.2)Calculations:
As we use UGC⇒ b=227420LE/KM & (kVA )f=√3∗11∗340∗0 .706
As we use Indoor substation ⇒ C=30,000,000*0.3 LE
D=6.872 MVA/ Km2
S=1.59[ kVAf cbD ]0.333
km
S=4 .730637488Km
KVASopt=D⋅S2=153788.0141
KVA
nS=area÷S2=1 .676
, approximated to the higher integer (
nS=2 )
KVASact=Total Load÷nS=128854 .35
KVA
Transformers used in substation: 66/11 KV, 5×35 + 1×35 MVA
Loading percent = 61.36%
Feeders /Substation=Substation rating including the reserve÷KVA f=45.92Feeders /Substation=48
Approximated to the integer giving even number of
feeders/ substation & feeders/ transformer.
Each transformer supplying 8 feeders.
Current density=0.587A/mm2
(5.4.3)Sitting of the 66/11 KV substation in Light Industrial area :
663 Optimum siting and sizing of substation
All dimensions in Km
(5.5.0)Heavy industrial:
(5.5.1)Design aspects:
Substations used in Heavy industrial area are generally the indoor substations. Under Ground Cables (UGC) are used in Heavy industrial area for the primary
distribution networks (11 KV).
From the reliability point of view, it is better to replace one large substation with
some smaller substations distributed over the planning area, in spite of the
increase in the cost; yet, the increase is not that considerable amount.
It is recommended that the number of transformers in each substation doesn't
exceed 6 transformers including the reserve.
673 Optimum siting and sizing of substation
It is recommended that the bus bars in the substation are sectionalized and
doubled to allow maneuver and that the number of transformers and feeders per
section is even number.
It is recommended that the number of feeders per transformer in City center area shouldn't exceed 8 feeders per transformer.
The loading percent in each substation shouldn't exceed 80% for safety and
continuity of feeding in case of outage of any unit.
A recommended current density for the UGC is 1 A/mm2
(5.5.2)Calculations:
As we use UGC⇒ b=227420LE/KM & (kVA )f=√3∗11∗340∗0 .706
As we use indoor substations⇒ C=30,000,000*0.3 LE
D=16.2175 MVA/ Km2
S=1.59[ kVAf cbD ]0.333
km
S=3.553198066Km
683 Optimum siting and sizing of substation
KVASopt=D⋅S2=204749.4485
KVA
nS=area÷S2=2.97
, approximated to integer (
nS=3 )
KVASact=Total Load÷nS=202718 .7333
KVA
We have two solutions:
Solution 1 Solution 2Transformers used in substation: 66/11 KV
5×50 + 1×50 MVA 7×35 + 1×35 MVA
Loading percent = 67.573% 72.399%Feeders /Substation= 65.597⇒66 61.224⇒64
Each transformer supplying11 feeders 8 feeders
Current density=0.6716 A/mm2 0.6926 A/mm2
comments1. Higher cost due to higher capacity.2.transformers of 50 MVA do not produced in Egypt.3. Lower loading percent.4. large # of feeders/ trans.
1. Lower cost.2. Transformers from Egypt.3. Higher loading percent.4. # of trans. Larger than 6 transformers.
(5.5.3)Sitting of the 66/11 KV substation in Heavy industrial area :
693 Optimum siting and sizing of substation
All dimensions in Km