Explanatory note on the Draft Amendment to General Terms and Conditions of
Supply (Enhancement of 33 kV and 11 kV Power Supply capacity):
1.
Technical Feasibility:
The technical feasibility of enhancing the capacity at 33 kV level is studied and
is explained below.
The maximum power that can be transmitted at a particular temperature and
power factor, over a conductor mainly depends on the following factors:
i) The maximum current carrying capacity of a conductor
ii) The maximum kVA-km loading limit of a conductor at the voltage at
which power is being transmitted.
iii) Power factor and ambient temperature, etc.
2.
Voltage Regulation:
(i).
The Voltage obtained from the source to the tail end under conditions of
Maximum Loading and Maximum Demand on each feeder with reference to
their capacity gives a picture of system condition. Since 33 kV and 11 kV lines
are short-lines, the voltage regulation, which is defined as the percentage rise in
voltage at the receiving end when the full load is thrown off, keeping the sending
end voltage constant is given by the following equation:
% Voltage Regulation =
(ii).
Es - Er
X 100
Es
It is the general practice to work out a constant in kW-km (Regulation
constant) on the basis of 1% voltage drop (at 600 C) at different power factors for
different voltages and conductor sizes. The length of the feeder should be such
that the kW-km loading is within permissible limits to ensure voltage regulation
as specified.
3.
MW-km can be the unique parameter for ascertaining the maximum capacity a
line can carry for the specified voltage regulation. MW-km depends on voltage
level and type of conductor under pre-defined ambient conditions, power factor
of the load and permissible percentage voltage drop specified in the regulations
issued by the Commission. As per Regulation No. 7 of 2004, the Discoms have
to maintain voltage at the Point of Commencement of supply within a limit + 6%
and - 9% for11 kV and 33 kV.
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4.
The Continuous Current, max rated current and maximum kW-km loading limits of
various types of conductors at 33 kV for 9 % Voltage Regulation are as follows.
33 kV, MW - km loading limit for 9% Voltage Regulation at 600 C conductor Temperature (0.9 pf)
Conductor
Continuous
Current rating at
MW-km loading
Continuous Power
Maximum
Current rating
450C Amb.Temp
limit at 9% voltage
at 450C (0.9 P.F)
Rated Power at
at 450C
(Thermal Loading) Reg (600C)
in MW
450C (0.9 P.F)
Amb.Temp
(Amps)
(Continuous
in MW
Rating)
(Thermal
(Amps)
loading)
(1)
Dog
(105)
Wolf
(158 Sq.mm)
Panther
(212 Sq.mm)
(2)
283
(3)
334
(4)
191.23
(5)
14.56
(6)
17.18
336.7
481
308.00
17.32
24.74
405.3
579
382.46
20.85
29.78
Regulation constants considered at 600 C of conductor temperature and at a pf of 0.9 lag are
shown in table below:
5.
Conductor Type
MW-km
Dog
21.25
Wolf
34.22
Panther
42.50
Maharashtra has permitted (vide MERC Regulation, 2014) upto 20,000 kVA on 33 kV
express feeder and upto 10,000 kVA on common 33 kV feeder. As per clause 48(5) of
CEA (Technical Standards for construction of Electrical Plants & Electrical Lines), the
maximum capacity of 33/11 kV substation shall be 60 MVA.
MERC permitted 5 MVA demand on 11 kV express feeder vide clause 5.3(a) (iii) of
MERC Regulations, 2014.
6.
The technical feasibility for 33 kV & 11 kV is explained hereunder.
Technical feasibility to extend 3 MVA power in 11 kV express feeder is furnished in the
table below.
The power factor considered here is 0.9 pf lag. But, due to prevailing kVAh tariff, all
HT consumers are maintaining power factor of near 0.98 to unity. Hence, in practice the
line length can be more.
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Conductor
Calculation of Line lengths for a capacity of 10 MW, 15 MW and 20 MW at 33 kV
Continuous
Continuous
Maximum
Max allowable
Maximum allowable
Current
Power at 45 0
MW-km
distance with
distance
rating at
C (0.9 P.F) in
loading limit
continuous ct
pf
0
0
10
15
20
45 C
MW
(60 C) For
load in km
MVA
MVA MVA
Amb.Temp
(Continuous
9% VR
col(4) / col(3)
1
Dog
(105)
Wolf
(158
Sq.mm)
Panther(212
Sq.mm)
Conductor
1
Dog
(105)
Wolf
(158
Sq.mm)
Panther(212
Sq.mm)
(in Amps)
Rating)
Amps
283
0.9
MW
14.56
MW-km
191.23
km
13.14
km
21.25
km
14.17
km
----
336.7
0.9
17.32
308.01
17.78
----
22.82
17.11
405.3
0.9
20.85
382.46
18.34
----
28.33
21.25
MW-km for 9% voltage drop at UPF for 33 kV Voltage
Continuous
Continuous
MW-km
Max
Current rating Power at 45 0
loading
allowable
at 450C
C (0.9 P.F) in
limit
distance with
Amb.Temp
MW
(600C)
continuous ct
(in Amps)
(Continuous
For 9%
load in km
Rating)
VR
col(4) / col(3)
Amps
MW
MW-km
km
283
16.18
300.65
18.59
336.7
19.24
452.59
23.52
405.3
23.17
601.29
25.96
Maximum allowable
distance
10
MW
15
MW
20
MW
km
km
30.06 20.04
km
---
45.26 30.17
22.63
---
40.09
30.06
Calculation of Line lengths for a capacity of 2500 kVA, 3000 kVA at 11 kV
Continuous
Max
Maximum
Continuous
Maximum
Power at
allowable
allowable
Current rating
kW-km
0
45 C (0.9
distance with
distance
Conductor
at 450C
pf
loading limit
P.F) in kW
continuous ct
Amb.Temp
(600 C) For
(Continuous
load col(4) /
2500
3000
(in Amps)
9% VR
Rating)
col(3)
kVA
kVA
1
Amps
pf
kW
kW-km
km
km
Km
Weasel (30
129
0.9
2211.94
8118.00
3.67
3.61
3.01
sq.mm)
Rabbit (50
178
0.9
3052.13
12204.00
4.00
5.42
4.52
sq.mm)
Dog(100
283
0.9
4852.54
23490.00
4.84
10.44
8.70
Sq.mm)
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7.
If 33 kV sales volume increases, the distribution losses would come down, technically,
the distribution losses will also be less, as the resistance of higher size conductor (Wolf
or Panther) is less compared Dog conductor. The details of calculations are furnished
below:
kV
Conductor
33
33
33
Dog
Wolf
Panther
Continuous
ct Rating(I)
283
336.7
405.3
Ac
Resistance
I²
(Ohms/km)
0.33 80089.0
0.223 113366.9
0.136 164268.1
I²R
26429.37
25280.82
22340.46
Loss in
kW
26.429
25.281
22.340
Input in
kW
14557.63
17319.98
20848.79
%
loss
0.182
0.146
0.107
Commercially, the DISCOM gets more revenue as the 33 kV tariff is considerably higher,
compared to 132 kV tariff. The tariff details are furnished;
HT-1 (a) Tariff:
132 kV tariff
33 kV tariff
-
Rs. 5.15
Rs. 5.57
The difference is Rs 0.42/unit. The revenue gain is explained below;
Consider a 15 MVA load. The load factor for this much size load would be around 80%.
Tariff
Additional
Units
Demand
LF
Pf
hours
rate
Revenue
(kWh)
Difference
(Rs.)
15000
0.8
0.98
720
8467200
0.42
3556224
The additional revenue to the DISCOM would be around Rs 35 lakhs per month from 15000
kVA demand consumers at 33 kV.
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