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Supply Harmonics [4]

论文作者:留学生论文论文属性:短文 essay登出时间:2011-04-19编辑:点击率:20848

论文字数:5901论文编号:org201104191725059753语种:中文 Chinese地区:中国价格:免费论文

关键词:Supply HarmonicsElectricity sinusoidal voltagesvoltages

n systems

having allowable harmonic content, but the extra heating typically reduces performance to

about 95% of that which would be experienced with pure fundamental sine waves [1]. It

must be stressed, however, that the above statements do not apply to the rating and

performance of electrical motors (induction or synchronous) fed from a variable speed

inverter when, depending on the type of variable speed system, the harmonic effects can be

very significant.

7.1.9 Telephone interference

One of the earliest expressed concerns about harmonics in the electricity supply system

was related to interference with telephone communications. This was particularly the case

when both telephone lines and power distribution line were mounted on common overhead

lines. For any given physical arrangement, the disturbance is a function of both the

amplitude and frequency of the harmonic components. The disturbance to the

communication system can be reduced by a number of means including minimising ground

return currents, filtering and other harmonic elimination methods.

S7: Supply Harmonics

112 EEE8044: Fundamentals

7.2 Total Harmonic Distortion

The most widely used measure or index of harmonic distortion of a power system voltage

is the Total Harmonic Distortion (THD) defined by

100%

square of the amplitude of the fundamental component

sumof the squares of the amplitudes of all harmonic components

THD = × (7.1)

or

1

50

n 2

2

n

V

V

THD

Σ=

= (7.2)

where Vn is the value of the nth harmonic voltage drop and V1 is the value of the

fundamental supply voltage.

The value of the THD is usually of interest at the point of common coupling (pcc) with

other users previously defined as the point in the public utility at which other user loads

are, or may be, connected. For example, in Figure 7.1, the pcc for users 1 and 2 is the 11

kV busbar and the pcc for users 3 and 4 is the 33 kV busbar and for customer 5, it is the

132 kV busbar.

132 kV

33 kV

11 kV

user 1 user 2

user 3 user 4

user 5

pcc

pcc

pcc

Fig. 7.1 Point of common coupling

S7: Supply Harmonics

113 EEE8044: Fundamentals

7.3 Standards and Harmonic Limits

A number of national and international standards and recommendations provide guidelines

on the amount of harmonics and harmonic distortion that can be produced or should be

allowed to flow into the power system. These standards usually specify how much of each

harmonic a customer is allowed to inject into the power distribution system as well as

setting limits for the total harmonic distortion that should be allowed anywhere on the

system.

Permitted levels of harmonics in the UK are defined by Engineering Recommendation

G5/4 which sets current and voltage harmonic levels that may exist for any one customer at

the point of common coupling to other users.

In the UK, Engineering Recommendation G5/4 “Limits for Harmonics in the United

Kingdom Electricity Supply System” has been used as the national standard for many

years. The method adopted in G5/论文英语论文网提供整理,提供论文代写英语论文代写代写论文代写英语论文代写留学生论文代写英文论文留学生论文代写相关核心关键词搜索。

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