lecture on distribution system

8/10/2019 Lecture on Distribution System

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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.xlsx


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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.xlsx


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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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1 3 5 7 9 11131517192123252729313335373941434547495153555759616365676971737577798183858789919395

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1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96


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1 3 5 7 9 11131517192123252729313335373941434547495153555759616365676971737577798183858789919395


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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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lecture on distribution system

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