Electricity + Control January 2017

DRIVES, MOTORS + SWITCHGEAR

Points to Consider to Ensure VSD Installations Meet IEEE 519

Glen Ward, ZEST WEG Group

This is an extensive subject and as such the points below are intended as an introduction to highlight relevant portions of the IEEE 519 [1] and to encourage further discussion and analysis.

A lthough the IEEE 519 [1] is not a mandatory standard, its rec- ommendations are being used as a reference to specify the harmonic distortion limits allowed by the utility companies and in the design of industrial power systems. ANSI/IEEE Standard 519 [1] was published in 1981. It recommend- ed maximum levels of Total-Harmonic-Voltage-Distortion (THDV) at the point that the utility connects to different types of users (Point of Common Coupling (PCC) (see Figure 1a )). Different maximum levels were provided for different types of buildings (see Figure 1b ).

IEEE 519 was revised in 1992 to provide recommendations on maxi- mum allowable levels of harmonic current distortion (see Figure 2 ). The new standard also defined themaximum recommended contribu- tion of individual current harmonic orders. The amount of allowable distortion is based on a ratio of the short circuit current available to the distribution system (ISC – maximum short circuit current avail- able at point of common coupling), and the maximum load current recognised by the distribution system (Il – the maximum load current of user at the point of common coupling). The larger the user’s load in relation to the utility transformer supplying that user, the greater that user’s contribution to the overall harmonic distortion will be. Hence, stringency of the limits is increased with decreasing Isc/IL ratio.

< 11 11 ≤ n < 17

17 ≤ n < 35

23 ≤ n < 35

35 ≤ n

Isc / IL

TDD (%)

< 20

4

2

1,5

0,6

0,3

5

20 < 50

7

3,5

2,5

1

0,5

8

50 < 100

10

4,5

4

1,5

0,7

12

100 < 1000

12

5,5

5

2

1

15

> 1000

15

7

6

2,5

1,4

20

Figure 2: • Maximum harmonic current distortion in percent of IL • Isc - maximum short-circuit current at PCC • IL - maximum demand load current (fundamental frequency compo- nent) at PCC Importantly PCC is the electrical connection point between the util- ity distribution system and the user's electrical distribution system. The distortion at the PCC can be evaluated by the current TDD and the voltage THD, as well as the individual order current harmonics according to the table. Often, the limits defined in IEEE 519 [1] have been applied by engineers to individual equipment instead of the system as a whole, at the intended PCC. While this approach could well be effective, it is a misapplication of the standard and can result in unnecessary use of costly and energy consuming reactors, passive filters, multi- pulse drives and active filters. It is important to understand the intent and purpose of this standard and implement it accordingly. Modern reputable VSD products share a common build typology (VSD design)

Figure 1a: PCC.

THDV Level

Applications

3%

Airports, Hospitals, Telecommunication Companies

THDV Level

General Applications

5%

Office Buildings, Schools

THDV Level

Dedicated Systems

10%

Factories

Figure 1b: THD levels.

Electricity+Control January ‘17

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