1. Applied Harmonics Control of Harmonics

2. Harmonic Distortion Evaluations
IEEE Standard
Limit harmonic current injections from end users so that harmonic voltage distortion is tolerable.
Limit harmonic voltage (responsibility of utility).

3. utility system
customer
under
study
PCC IL
other customers
utility system
customer
under
study
PCC IL
other customers

4. End users are limited at PCC in terms of
individual harmonic components and
total demand distortion
Utility is mainly responsible for limiting voltage distortion at PCC
Evaluations:
Measurement of currents injected by load (over one week period)
Calculation of frequency response of system impedances (using harmonic calculation software)

6. Table 6.1 Harmonic voltage distortion
limits in % of nominal fundamental-
frequency voltage

7. Table 6.2 Harmonic current limits

8. Ih is rms magnitude of individual harmonic current
Isc is the short-circuit current at PCC
IL is the fundamental component of the maximum demand current (average max demand over 12 months)
Individual limits apply to odd-order harmonics, even order limits are at 25% of indicated value

9. For power converters with more than 6 pulses, where q = pulse number, multiply limits in table 6.2 by

10. Controlling harmonics
Control only when harmonics create a problem. Types of problems:
load harmonic currents are too large
path for harmonic currents is too long electrically (too much impedance) producing voltage distortion or communication-line interference
response of system magnifies one or more harmonics

11. Options for control Reduce magnitude of harmonic currents from load
Add filters to do one or more of these:
short out (siphon off) the harmonic
block harmonic currents from entering part of the system
supply the harmonics locally
Modify the frequency response of the system by filters or other means

12. Reducing load harmonic current
Sometimes transformer connections can be changed, for example:
phase shift on some transformers supplying 6-pulse converters
delta windings block triplen currents
zig-zag transformers can supply triplens

13. Zig-zag transformer

14. Zig zag transformer
Place the transformer to supply balanced triplen harmonics (and any other zero-sequence currents) to load
This will unload zero sequence currents on circuits upstream of the ZZ transformer, with little or no effect downstream
Fault study results may be affected

15. Placement of ZZ transformerb c I3 n
3I3
Unloads the neutral conductor upstream

16. Filtering
Shunt passive filter: short-circuit harmonic currents close to their source
Series passive filter: block harmonic currents from power delivery system (may cause large load voltage distortion)
Active shunt filter: electronically supply low-order harmonics to a nonlinear load (used with simple passive filters for higher frequency components).

17. Passive Filters Shunt passive filters are high-pass notch filter
notch filters, tuned to a specific harmonic frequency, or
high-pass filters
high-pass
filter
notch filter

18. Modifying system frequency response
Add a shunt filter to the system
Add a reactor (e.g., in series with a pf correction capacitor) to de-tune system
Change pf correction capacitor size or placement, or remove capacitor bank entirely

19. Where to control harmonics
On utility system or end-user facility
utility system is more difficult to filter unless we can move or change the size of or reconnect a capacitor
end-user system may be easier to filter if we can access the feeder(s) where the harmonic currents are being produced

20. Filters In-line reactors (or chokes) for ASD
Isolation transformers can help
Isolation transformers can be reconnected with different phase shifts
ASD M Xs Xt
reactor 0-5%
on ASD kVA

21. Isolation transformers X~5%
480 V bus M
ASD M
ASD
Approximates a 12-pulse converter with 6-pulse converters by putting half on Delta-Delta transformers and the half on Delta-Y. 12-pulse has Ih = 0 for h = 5, 7

22. Harmonic studies Perform harmonic studies when
a problem occurs, to find a solution
planning large capacitor bank installation on either utility or industrial system
planning installation of large nonlinear load such as adjustable speed motor drives (ASD)
designing a harmonic filter or converting a capacitor to a harmonic filter