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loads in stages, according to the rating and type of equipment under consideration. Stage 1

deals with small loads and states the maximum sizes of converters that may be connected

to the network without worrying about harmonics.

Stage 2 gives maximum permitted values of harmonic currents that a user may feed into

the network and the maximum permitted THD at the point of common coupling, providing

that the existing level of THD at the pcc is within the accepted limits. Tables 7.1 and 7.2

give Stage 2 permitted harmonic and THD levels.

Table 7.1 G5/4 Stage 2 permitted harmonic currents

System

Voltage at pcc

Harmonic order and permitted rms harmonic currents (A)

2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th 15th

415 V 48 34 22 56 11 40 9 8 7 19 6 16 5 5

11 kV 13 8 6 10 4 8 3 3 3 7 2 6 2 2

33 kV 11 7 5 9 4 6 3 2 2 6 2 5 2 1

132 kV 5 4 3 4 2 3 1 1 1 3 1 3 1 1

S7: Supply Harmonics

114 EEE8044: Fundamentals

Table 7.2 G5/4 Stage 2 permitted THD levels

System Voltage

at pcc

Total Harmonic

Distortion

(THD)

Individual harmonic voltage

distortion

Odd harmonics Even harmonics

415 V 3.75% 3.00% 1.50%

6.6 kV and 11 kV 3.00% 2.25% 1.00%

33 kV and 66 kV 2.25% 1.5% 0.75%

132 kV 1.125% 0.75% 0.375%

If a piece of equipment fails to meet stage 2 limits, it may then be considered under Stage

3. This includes a number of guidelines and THD levels 33% higher than those for Stage 2,

which should be considered together with existing distortion levels and a knowledge of the

load and distribution network. Table 7.3 gives Stage 3 permitted THD levels.

Table 7.3 G5/4 Stage 3 permitted THD levels

System Voltage at

Point of Common

Coupling

Total Harmonic

Distortion (THD)

Individual harmonic

voltage distortion

Odd

harmonics

Even

harmonics

415 V 5.00% 4.00% 2.00%

6.6 kV and 11 kV 4.00% 3.00% 1.31%

33 kV and 66 kV 3.00% 2.00% 1.00%

132 kV 1.50% 1.00% 0.50%

While G5/4 simply gives recommended limits on harmonics, it does in effect have a

statuary status in the UK. This is because it is included in the Distribution Code of the

Public Electricity Supply Licence.

For comparison, IEEE std 519-1992 “IEEE Recommended Practices and Requirements for

Harmonic Control in Electrical Power Systems”, which doubles as an American National

Standard, sets similar limits on customer harmonic currents injected into the system

expressed as a function of the ratio of system short circuit current to normal load current,

as shown in Table 7.4.

S7: Supply Harmonics

115 EEE8044: Fundamentals

Table 7.4 IEEE Standard 519-1992 harmonic current limits

Isc/Iload Harmonic order

2-10 11-16 17-22 23-34 > 34 Total

< 20 4.0% 2.0% 1.5% 0.6% 0.3% 5.0%

20-50 7.0% 3.5% 2.5% 1.0% 0.5% 8.0%

50-100 10.0% 4.5% 4.0% 1.5% 0.7% 12.0%

100-1000 12.0% 5.5% 5.0% 2.0% 1.0% 15.0%

> 1000 15.0% 7.0% 6.0% 2.5% 1.4% 20.0%

The standard also sets limits on the total harmonic distortion and the amount of an本论文由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。