Download Electronic Devices and Circuits Lecture 2

Dated: 17 February 2016
Instructor :Kashif Mehmood
Introduction
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 The electrical utility industry was born 1882 at pearl street electric station in
New york city.
 Electrical power system includes a generating, a transmission and distribution.
 In the past, the distribution system contains 80% of total investment.
 Figure 1.1 shows Electrical utility plants in service for the years 1960 to 1978.
 Total operation and maintenance (O&M) costs for the privately owned utilities
have increased from $ 8.3 billion in 1969 to $ 40.2 billion in 1978.
 Production expense contains 64% of total O&M expenses in 1978.This is because
of rapidly increasing in fuel costs.
 In short the economic importance of distribution system is very high and the
amount of investment involved dictates careful planning ,design, construction
and operation.
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Microelectronics
Economy
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Distribution system and planning
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 System planning is necessary to overcome the demand of electricity
which can be done by the addition of distribution system.
 It should be appropriate and economical.
 The deficiency of available land in urban areas and environmental
consideration is main problem of optimal distribution system beyond
the resolving power of unaided human mind.
 Distribution system planners must determine the load magnitude and
its geographical planning.
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 The distribution system is important to an electrical
utility for two reasons:• Its close proximity to the ultimate customer.
• Its high investment cost. As the distribution system
of power supply system is the closest one to the
customer, its failure affects customer service more
directly than for example failure on the transmission
and generating system which usually do not cause
customer service.
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Logic Families
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Factor Effecting System Planning
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 The hurdles which prohibit designer have also become more difficult.
 These include shortage of land in urban areas, limitations on fuel
choices etc.
 In short , the planning problem is an attempt to minimize the cost of
sub transmission, substations, feeders and so on as well as the cost of
losses.
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Load Forecasting
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 The load growth of geographical area served by a
utility company is the most important factor
influencing the expansion of distribution system.
 There are two common time scales of importance to
load forecasting:• Long Range : with the time horizons in the order of
15 or 20 years away.
• Short range with time horizons of up to 5 yrs. Away.
• These forecast would predict future load in details.
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Disadvantages of ICs over discrete
components
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Substation Expansion
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 The planner makes a decision based on tangible and in tangible
information.
 For example the forecast load, load density and load growth
may require a substation expansion or a new substation
construction.
 In the system expansion plan the present system configuration ,
capacity and the forecasted loads can play major role.
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Substation site selection
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 The distance from the load center and from the
existing sub transmission line as well as other
limitations, such as availability of land, its cost and
land use regulation are important.
 It may be defined as territory of the utility.
 Three basic alternative uses of the consideration are
• Quantitative versus qualitative evaluation .
• Adverse versus beneficial effects evaluation.
• Absolute versus relative scaling of effects.
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Substation site selection procedure
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Substation site selection procedure
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Factor effecting total cost of the dist.
System
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Fig. 3.1 (a)
Fig. 3.1 (b)
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Present distribution system
Planning technique
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 Today, many electrical distribution planners in the
industry utilize computer programs, usually based
on ad hoc, such as load flow program , short circuit
and fault current calculation programs, voltage drop
calculation program, as well as other tools such as
load forecasting, voltage regulation, regulator
setting, capacitor planning etc.
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 The acceptability criteria representing the companies
policies , obligation to consumer : Service continuity.
 The max. allowable peak load Voltage drop to most
remote customer on the secondary.
 The max. allowable voltage dip occasioned by the starting
of motor of specified starting current characteristics at the
most remote point on the secondary.
 The max. allowable peak load.
 Service reliability.
 Power losses.
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