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DISTRIBUTION SYSTEM
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Distribution system typically starts here
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CIRCUIT BREAKERS
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Major Component of a Distribution Substation
High-side and low-side switching
In the figure high side switching is done with a simple switch
Low-side switching is done with a relay-controlled circuit breaker.
Reclosers can be used instead of circuit breakers.
Transformer for voltage transformation.
The figure has only one transformer
Other designs make use of more than one transformers.
Common voltages : 34.5 KV, 23.9 KV, 14.4 KV, 13.2 KV, 12.47 KV
Voltage Regulation
Maintains the users voltages to within acceptable levels.
The voltage is regulated by a step-type regulator 10% plus or minuson the low-side bus
Protection : In simple designs like in the diagram the automatic protection
against short circuits is by way of the high-side fuse. In more complex
designs, more extensive protection are employed.
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DISTRIBUTION FEEDER MAP
Used to determine the existing operating conditions of a feeder and
analysis can be performed. It contains most of the following information:
Lines (overhead and underground)
1.Where2.Distances
3.Details
a.Conductor sizes
b.Phasing
Distribution Transformers
1.Location
2.KVA rating
3.Phase connection
In-line transformers
1.Location
2.KVA rating
3.Connection
Shunt capacitors
1.Location
2.KVAR rating
3.Phase connection
Voltage regulators1.Location
2.Phase connection
3.Type
a.Single-phase
b.Three-phase
Switches
1.Location
2.Normal open/close status
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DISTRIBUTION FEEDER ELECTRICAL CHARACTERISTICS
The following data must be available :
Overhead and underground spacingsConductor tables
1.Geometric mean radius (GMR)
2.Diameter
3.Resistance
Voltage regulators
1.Potential transformer ratios2.Current transformer ratios
3.Compensator settings
a.Voltage level
b.Bandwidth (range)
c.R and X settings
Transformers1.KVA rating
2.Voltage ratings
3.Impedance (R and X)
4.No-load power loss
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NATURE OF LOADS
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NATURE OF LOADS
The modeling and analysis of a power system depend upon the load.
The load supplied by a distribution transformer is constantly changing.Every time a light bulb or an electrical appliance is switched on or off, the
load seen by the distribution feeder changes
LOAD GRAPHS
A load graph, or load curve, is a graphic record showing the power
demands for every instant during a certain time interval. The record may
cover a period of
one hour hourly load graph
24 hours daily load graph
one monthmonthly load graphone year yearly load graph
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The area under the load curve is equal to the energy in terms of
kilowatt hours (or watt hours) delivered to the particular load. The power
plant that supplies a particular load must have an aggregate (total)
installed capacity at least equal to the maximum demand represented onthe load curve.
One advantage of the load curve is that it can indicate at a glance the
general character of the load that is being supplied by the plant (not
readily obtained from tabulated figures)
Less installed capacity of generating equipment is needed for the plant
which has fewer number of valleys and peaks in each load graph. The
more nearly the graph of a load approximates a horizontal line, the
nearer the conditions will be ideal.
METHODS OF OBTAINING A LOAD GRAPH IN A POWER PLANT1. Use of recording graphic meters such as graphic wattmeter
2. Plotting values of power from indicating wattmeter readings at equal
time interval
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Average demand
The average of the demand over a specified period (day, week,
month, )
Must include demand interval, period, and unitsExample : the 15-minute average KW demand for the month was
350 KW
Diversified demand
Sum of demands imposed by a group of loads over a particularperiod
Must include demand interval, period and units
Example : the 15-minute diversified KW demand in the period
ending at 9:30 was 200 KW
Maximum diversified demand
Maximum of the sum of the demands imposed by a group of loads
over a particular period
Must include demand interval, period and units
Example : the 15-minute maximum diversified KW demand for the
week was 500 KW.
http://d/EE%20SUBJECTS/1ST%20SEM%202009-2010/EE%20132%20-%20POWER%20SYSTEM/POWER%20SYSTEM/all%20demand%20curve.xlsxhttp://d/EE%20SUBJECTS/1ST%20SEM%202009-2010/EE%20132%20-%20POWER%20SYSTEM/POWER%20SYSTEM/all%20demand%20curve.xlsx8/10/2019 Lecture on Distribution System
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Load duration curve
The load duration curve plots the 15-minute KW demand vs. the
percent of time the transformer operates at or above the specific KW
demand.
Example : the transformer operates with a 15-minute kw demand of 12
kw or greater 22% of the time.
Maximum noncoincident demand
For a group of loads, the sum of the individual maximum demands
without any restriction that they occur at the same
Must include demand interval, period, and units
Example : the maximum noncoincident 15-minute KW demand for the
week was 700 KW
http://d/EE%20SUBJECTS/1ST%20SEM%202009-2010/EE%20132%20-%20POWER%20SYSTEM/POWER%20SYSTEM/all%20demand%20curve.xlsx8/10/2019 Lecture on Distribution System
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Demand factor
The demand factor can be defined for an individual customer
maximum demandDemand factor = -----------------------------
connected load
Load factor
Ratio of the average demand of any individual customer or
group of customer over a period to the maximum demand over
the same period. It gives an indication of how well the utilitys
facility is being utilized.
Average demand
Load factor = -----------------------------
Maximum demand
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Utilization factor
Ratio of the maximum demand to rated capacity. It gives an
indication of how well the capacity of an electrical device isbeing utilized.
Maximum demand
Utilization Factor = ----------------------------------
Transformer rating
Diversity factor
Ratio of the maximum noncoincident demand of a group of
customers to the maximum diversified demand of the group.
Maximum noncoincident demand
Diversity Factor = ---------------------------------------------------
Maximum diversified demand
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Load diversity
Difference between maximum noncoincident demand and the
maximum diversified demand.
EXAMPLES .
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ENERGY = 58.75 KW HRSAVERAGE DEMAND = 58.75/24 = 2.45 KW
AVERAGE
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LOAD DURATION CURVE
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FEEDER LOADS
Load Allocation
In the analysis of a distribution feeder load, data will
have to be specified. The data provided will depend
upon how detailed the feeder is to be modeled, andthe availability of customer load data.
The most comprehensive model of a feeder will
represent every distribution transformer. In this case,
the load allocated to each transformer will have to be
determined.
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Application of Diversity Factors
The definition of the diversity factor (DF) is the ratio of the
maximum noncoincident demand to the maximum
diversified demand. When a diversity factor table is
available, then it is possible to determine the maximum
diversified demand of a group of customers served by a
distribution transformer.Max. noncoincidental demand
Max. diversified demand = ----------------------------------------
DFn
The maximum diversified demand becomes the allocated
load for the transformer.
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Single-phase lateral.
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Example :
A single-phase lateral provides service to three distribution
transformers as shown above. The energy in kwh consumed by
each customer during a month is known. A load survey hasbeen conducted for customers in this class, and it has been
found that the customer 15-minute maximum kw demand is
given by the equation :
Max Kwdemand= 0.2+ 0.008 * kwh
Customer#1 #2 #3 #4 #5
Kwh 1523 1645 1984 1590 1456
Max Kw 12.4 13.4 16.1 12.9 11.9
Transformer 1
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Customer
#12 #13 #14 #15 #16 #17 #18
Kwh 2098 1856 2058 2265 2135 1985 2103
Max Kw 17 15.1 16.7 18.3 17.3 16.1 17
Customer
#6 #7 #8 #9 #10 #11
Kwh 1235 1587 1698 1745 2015 1765
Max Kw 10.1 12.9 13.8 14.2 16.3 14.3
Transformer 2
Transformer 3
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N Div F N Div F N Div F
1 1.1 26 3.00 51 3.15
2 1.60 27 3.01 52 3.15
3 1.80 28 3.02 53 3.16
4 2.10 29 3.04 54 3.16
5 2.20 30 3.05 55 3.16
6 2.30 31 3.05 56 3.17
7 2.40 32 3.06 57 3.17
8 2.55 33 3.08 58 3.17
9 2.60 34 3.09 59 3.18
10 2.65 35 3.10 60 3.18
11 2.67 36 3.10 61 3.18
12 2.70 37 3.11 62 3.18
13 2.74 38 3.12 63 3.18
14 2.78 39 3.12 64 3.19
15 2.80 40 3.13 65 3.19
16 2.82 41 3.13 66 3.19
17 2.84 42 3.13 67 3.19
18 2.86 43 3.14 68 3.19
19 2.88 44 3.14 69 3.20
20 2.90 45 3.14 70 3.20
21 2.90 46 3.14
22 2.92 47 3.15
23 2.94 48 3.15
24 2.96 49 3.15
25 2.98 50 3.15
TYPICAL VULUES OF DIVERSITY FACTOR
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1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70
D
iversityFactors
Number of Customers
Series1
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Determine for each transformer the non-coincident maximum kwdemand . Using the given diversity factor table, determine the
maximum diversified kw demand.
T1 : Noncoin. max = 12.4 + 13.4 + 16.1 + 12.9 + 11.9 = 66.7 kw
Noncoin. Max 66.7
Max. div. demand = -------------------- = ------- = 30.3 kw
Div. fac. for 5 2.2
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T2 : Noncoin. max = 12.9 + 13.8 + 14.2 + 16.3 + 14.3 + 17 = 81.6 kw
Noncoin. Max 81.6
Max. div. demand = -------------------- = ------- = 35.5 kw
Div. fac. for 6 2.3
T3 : Noncoin. max = 17 + 15.1 + 16.7 + 18.3 + 17.3 +16.1 +17 = 117.5 kw
Noncoin. Max 117.5
Max. div. demand = -------------------- = ------- = 48.9 kw
Div. fac. for 7 2.4
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Series2
LOAD CURVE FOR TRANSFORMER 1
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LOAD DURATION CURVE FOR TRANSFORMER 1
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Series2
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