Harmonic Filters

Report
IEEE 519-2014
Mark Halpin
November 2014
What Has Stayed the Same?
• Most importantly, the overall philosophy
– Users are responsible for limiting harmonic
currents
– System owner/operator are responsible for
managing voltage quality
– All recommended limits apply only at the PCC
• Existing recommended limits are retained
– Some new ones added
What Has Been Changed?
• Philosophy of changes  Driven by 20 years of
experience with 519-1992 and increased cooperation
with IEC
• Multiple changes related to
–
–
–
–
–
Measurement techniques
Time varying harmonic limits
Low voltage (<1 kV) harmonic limits
Interharmonic limits
Notching and TIF/IT limits
• Also “editorial” changes to
– Reduce document size
– Minimize miss-use of PCC-based limits
– Better harmonize with other standards projects
Measurements
• Recommended to use IEC 61000-4-7 specifications
– 200 ms (12 cycle @ 60 Hz) window gives 5 Hz resolution
1.4
1.2
Harmonics @ 60 Hz
1
0.8
0.6
0.4
Interharmonics @ 5 Hz
0.2
X+60
X+55
X+50
X+45
X+40
X+35
X+30
X+25
X+20
X+15
X+10
X+5
X
X-5
X-10
X-15
X-20
X-25
X-30
X-35
X-40
X-45
X-50
X-55
X-60
0
Indices
• From IEC 61000-4-30
– 3 s “very short” value
Fn ,vs
1 15 2
 2  Fn ,i
15 i1
– 10 min “short” value
Fn ,sh
1 200 2
2
F( n ,vs),i

200 i1
Assessment of Limit Compliance
18
16
14
TDD (%)
12
10
8
6
4
2
0
1
5
9
13
17
21
25
29
33
37
41
45
49
53
57
61
65
T im e (h )
What value should be compared against the limit?
69
Weekly Statistical Indices
100
1 0 0 .0 %
95th or 99th
percentile
60
8 0 .0 %
6 0 .0 %
40
4 0 .0 %
20
2 0 .0 %
0
.0 %
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Frequency
80
Value to be TDD (%)
compared against limit
Changes to the Limits
• New voltage limit provision for low voltage (<1 kV)
– 5% individual harmonic, 8% total harmonic distortion
• Revised current limits for general transmission systems (> 161
kV)
Maximum Harmonic Current Distortion in Percent of IL
Individual Harmonic Order (Odd Harmonics)
Isc/IL
<11
11≤h< 17
17≤h< 23
23≤h< 35
35≤h
TDD
<25*
1.0
0.5
0.38
0.15
0.1
1.5
25<50
2.0
1.0
0.75
0.3
0.15
2.5
≥50
3.0
1.5
1.15
0.45
0.22
3.75
Percentile-Based Voltage Limits
• Daily 99th percentile very short time (3 s) values
should be less than 1.5 times the values given in
Table …
• Weekly 95th percentile short time (10 min) values
should be less than the values given in Table …
Percentile-Based Current Limits
• Daily 99th percentile very short time (3 s) harmonic
currents should be less than 2.0 times the values
given in Table …
• Weekly 99th percentile short time (10 min) harmonic
currents should be less than 1.5 times the values
given in Table …
• Weekly 95th percentile short time (10 min) harmonic
currents should be less than the values given in Table
…
Interharmonic Limits
(“Recommendations”)
• Voltage-only 0-120 Hz limits based on flicker
6
V≤1kV
V≤1kV
4
1 kV<V≤69 kV
1 kV<V≤69 kV
3
2
69 kV<V≤161 kV
V>161 kV
1
all
voltages
69 kV<V≤161 kV
V>161 kV
all
voltages
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
Voltage (% of Nominal)
5
Frequency (Hz)
Editorial Changes
• Improve definitions of all relevant terms to account
for greater understanding and improved
instrumentation
• Removal of “flicker curve”
• Removal of “tutorial” material (shorten document)
• Strengthen introductory material dealing with PCConly applicability of recommended limits
Experience So Far
• Granted, this is limited mostly to “experiments”
over the last 6-12 months
– Users with relatively stable harmonic emissions are
essentially unaffected
– Users with rapidly-changing harmonic emissions may
show reduced levels in measurements
• The 200 ms window acts as a smoothing filter
• Percentiles and multipliers appear to be relatively
consistent with “short time harmonic” multipliers
often used with 519-1992
Passive Mitigation of Power
System Harmonics
Mark Halpin
November 2014
Outline
• Passive Filters
– Basic resonance concepts
– Single-tune filters
– C-type filters
• Performance comparisons
– Sensitivities to network conditions
– Overall effectiveness
• Conclusions
Series Resonance Concept
capacitive
1 

Zeq  j L 

C 

 jX L  X C 
inductive
resonant frequency, r
r 
1
LC
Major concept: The impedance can become a very low value
Series Resonance In Practice
Harmonic
Voltages
harmonic
currents
Effects include:
1. Heating in transformer
2. Fuse blowing at capacitor bank
Typical resonances:
--500 kVA, 12.47 kV, 5%
--300-1200 kvar capacitor
--r=173-346 Hz (3rd-6th harmonic)
Parallel Resonance
inductive
capacitive
 1 

Zeq  jL // 
 j C 
XLXC
 j
X L  X C 
resonant frequency, r
r 
1
LC
Major concept: The impedance can become a very high value
Parallel Resonance in Practice
Harmonic
Currents
harmonic
voltages
Effects include:
1. Excessive voltage distortion
2. Capacitor bank fuse blowing
Typical resonances
--500 kVA, 480 V, 5%
--400 kVA load, 80% pf lagging
--pf correction to 95% lagging (120 kvar)
--r=547 Hz (9th harmonic)
Resonance Summary
• Series resonance
– Widely exploited in harmonic filters
– Can lead to (harmonic) overcurrents
• Parallel resonance
– Frequently leads to (harmonic) overvoltages
– Sometimes used in blocking filters
Single-Tuned Filters
• “Single tune” means a single resonant point
Classical Single-Tuned Filter
C-type Filter
Applications
• Classic single-tuned filters
– Common in industrial applications
• Inside facility
• At the PCC
• May use multiple filters, each tuned to a different frequency
– Traditionally used by utilities (declining)
• C-type filters
– Not common in industrial applications
– Becoming dominant in the utility environment
– Often used in conjunction with classic single-tuned designs
• Purpose is always the same—give harmonic currents a lowimpedance path “to ground”
– Results in reduced voltage distortion
Application Considerations
• Ratings
– Capacitor
•
•
•
•
RMS voltage
Peak voltage
RMS current
kVA
– Reactor currents
• Peak current
• RMS current
• Losses
Filter Application Procedure
• Use frequency scan and harmonic study to determine
requirements
– Number of filters (estimate)
– Tuned frequency for each
– Ratings (estimate)
• Start with lowest-frequency filter and work upward (in frequency)
– Each filter has parameters than can be at least partially optimized
– Consider credible system changes
– Assess impacts of filter parameter variations (±10%, maybe more)
• Evaluate total performance vs. requirements
– Consider credible system changes
– Specify required ratings (tweak design as necessary)
Comments on Frequency Scans
• These results indicate the potential for a problem
• They are extremely useful for designing filters
– Identification of high/low impedance frequencies
(resonant conditions)
– Assessment of filter impacts on frequency response
• Alteration of undesirable impedance characteristics
• Demonstration of intentional low impedance path(s)
• They are subject to the accuracy of the models used
• Complete assessments require a harmonic study
– Results subject to model accuracy and assumptions
– Limit compliance
– Ratings of components
Demonstration Case
• Basic harmonic situation and sensitivities
– Series and parallel resonance conditions
• Mitigation using filters
– Single-tuned “industrial”
– C-type “utility”
Normal Condition Frequency
Response—LV Filter Application
(Are impedances high or low at known harmonic frequencies?)
1.2
0.8
0.6
System Normal
0.4
0.2
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
1
Harmonic #
Sensitivities—Substation SC Power
(equivalent impedance at LV bus)
1.2
Increasing severity and frequency with fault MVA
0.8
0.6
Increasing severity (lower Z)
and increasing
frequency with Fault MVA
0.2
130 MVA
150 MVA
170 MVA
0.4
Decreasing severity and
Increasing frequency with fault MVA
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
1
Harmonic #
These sensitivities would be considered pretty small and insignificant
Sensitivities—Capacitor Status
(equivalent impedance at LV bus)
1.4
Low(er) frequency resonance not much affected by MV cap
1.2
0.8
All Caps
LV Only
0.6
MV Only
inductive
No Caps
0.4
0.2
capacitive
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
1
High(er) frequency
resonance significantly
affected by MV cap
Harmonic #
Low(er) frequency resonances not much affected by things that
impact high(er) frequency response—opposite not true!!
Sensitivities--Conclusions
• Large changes in system impedances,
equivalents, etc., (fault MVA) are usually
needed for significant effects
• Relatively small changes in capacitor bank
status (or size) can have major impacts
• Filters must function under all of the potential
scenarios
Design Approach
• Convert existing 480 V cap bank to filter bank by adding series
reactor
– Capacitor voltage rating often will be exceeded in the end!
– X/R ratio of reactor can have significant impact
• Losses
• Performance
– Additional resistance can be added in series if needed (losses will
increase!) for performance
1
f tune 
Note: Tuned frequency normally
taken ≈5% below target
Avoid overload
Parameter variation
2 LC
1
300 
2 L.006908
L  40.7H
X L  15.4mW
5th Harmonic Single-Tune Design
3.5
3
2
X/R=100
X/R=10
1.5
X/R=1
R=0.0770 Ohm
1
0.5
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
2.5
Harmonic #
Filter Quality (“Q”) Factor
• The “sharpness” of the frequency response of a filter
is often indicated by the filter “Q”
Q
h tune X L(60)
R

2f tune L
R
• The filter Q indicates
– Damping (less sharp characteristic—more damped)
• Lower Q, more damping
– Losses
• Lower Q, more losses
• For the previous slide
– Q=500, 50, 5, 1
A Closer Look at Q
3.5
3
2
Q=500
Q=50
1.5
Q=5
Q=1
1
0.5
Harmonic #
All this discussion of Q doesn’t look like a big deal…
10
9
8
7
6
5
4
3
2
1
0
0
Impedance (W)
2.5
Performance Evaluation
(480 V Bus Impedance)
1.2
Impedance (W)
1
0.8
No Filter
0.6
5th Filter (Q=500)
5th Filter (Q=1)
0.4
5th Filter (Q=10)
0.2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
0
5th
harmonic currents
produce much less 5th
voltage after filter
Harmonic #
Filter Q has an obvious impact on the entire response!
Performance Evaluation
(LV Filter Impact on MV System at Cap Bank)
25
Impedance (W)
20
15
No Filter
High Q (500)
10
Low Q (10)
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
0
5th
harmonic currents
produce much less 5th
voltage after filter
Harmonic #
Lower Q: Not as much filtering at 5th harmonic
much less amplification at higher frequencies
Filtering on 12 kV Network
• Discussion so far based on filtering on customer-side
(LV)
– Presumably associated with limit compliance
• If all network users are in compliance (currents),
excessive voltage distortion may still exist
– Strong resonances can create large (noncompliant)voltage
effects from small (within compliance) currents
– Solution is to filter on MV (utility) side
– Filter designs must account for LV filter presence (or not)
Same Approach for Filter Design
1
f tune 
2 LC
1
300 
2 L10.235 
L  27.5mH
X L  10.367W
Note: Tuned frequency normally
taken ≈5% below target
Avoid overload
Parameter variation
Q=100R=0.5184 W
Q=10R=5.1835 W
12 kV Filter Performance
16
14
Impedance (W)
12
10
8
No Filter
High Q (100)
6
Low Q (10)
4
2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
0
Harmonic #
Filter eliminates 5th resonance, but creates new ones that could be as bad (or worse).
Best solution probably to split 600 kvar into 2x300 kvar and make two filters—5th and 7th
The C-type Filter
• Tuning (selection of parameters) is more
difficult than for single tuned filters
• Starting from an existing cap bank Ctotal
– Step 1 Choose L to tune filter frequency as for
single-tuned designs (based on Ctotal)
– Step 2 Divide existing capacitance into two
parts
• C2 chosen so that L and C2 are series resonant (Z=0)
at the power frequency
• C1 determined from “Ctotal-C2” (C in series combines
as parallel)
– Step 3 Pick R to provide desired high(er)
frequency damping
C-type Filter Example
• Will a 12 kV C-type perform better than the
conventional single-tuned design?
• Existing 600 kvar bankCtotal=10.235F
– L=10.367 W (27.5 mH) for ftune=300 Hz (from ST
design)
– For 60 Hz “bypass” tuning, C2=255.85 F
• C1=10.66 F
– Select R for desired damping
• Note Q defined differently
R
R
Q

h tune X L(60) 2f tune L
C-type vs. ST Filter Performance
12
8
No Filter
6
ST Q=100
ST Q=10
CT Q=5
4
CT Q=10
2
Harmonic #
10
9
8
7
6
5
4
3
2
1
0
0
Impedance (W)
10
12 kV Filter Sensitivities
(LV Cap/Filter Off-line)
8
7
5
ST Q=10 (No LV)
4
CT Q=15 (No LV)
ST Q=10
3
CT Q=15
CT Q=0.5 (no LV)
2
1
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
6
Harmonic #
The real advantage of the C-type is control of HF response
Comments on Comparisons
• Both filter types are effective at the tuned frequency
• C-type has very low power frequency losses
– Single-tuned filter has resistive losses proportional to cap bank
reactive current squared
• Low Q single tuned designs are helpful to reduce secondary
resonances created by filter additions
– Alternative is to add secondary filters
• Low Q C-type designs provide good damping of secondary
resonances by default
– Much less likely to encounter “secondary” problems
• C-type designs make poor utilization of existing cap banks
– Consider using one bank for var compensation with a separate
filter installation
Passive Filter Conclusions
• Two main types exist—both work
– Single tuned
• Main advantages: Simplicity, up-front cost
• Main disadvantages: losses, can create secondary problems
– C-type
• Main advantages: Low losses, HF response
• Main disadvantage: up-front cost, poor utilization of existing
cap banks
• Frequency scans are a great tool for filter design
– A harmonic study is required to determine necessary
ratings
Backup Slides
Basic Frequency Scan Concepts
(from load to 12 kV cap bank--focus on parallel resonance)
16
1 A @ 6th harmonic produces this voltage
14
1 A @ 13th harmonic produces this voltage
10
8
Name
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Impedance (W)
12
Harmonic #
1 A @ 60 Hz produces this voltage (drop)
Magnification Factors
(a normalized frequency scan)
120
80
60
Name
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Magnification Factor
100
100% current @ 6th harmonic
produces 80X voltage!!!
6th harmonic current required to be
much smaller to produce 3% 6th
harmonic voltage (IEEE 519 limit)
Harmonic #
Normal (100%) 60 Hz current produces normal voltage drop (maybe 5-10 %)
Applying Scan Results
120
80
60
40
5th harmonic current might be 20%
(1/5) of the fundamental, but the
MF=18. 5th harmonic voltage of
(5-10%)*18/5=18% or more could be
Name
produced  A filter may be needed
if the current is this large
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Magnification Factor
100
Harmonic #
Normal (100%) 60 Hz current produces normal voltage drop (maybe 5-10 %)

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