New Methods to Mitigate Distribution System Harmonics

Transcription

1 Alberta Power Industry Consortium 214 Power & Energy Innovation Forum New Methods to Mitigate Distribution System Harmonics By Wilsun Xu Power Disturbance & Signaling Research Lab November 5, 214

2 Outline 1. Background: harmonic problems faced by utility companies 2. Example research works on harmonic mitigation Distributed micro-filter Zero sequence filter 3. Other power quality research activities in U of A

3 1. Background 1 to 15 years ago Industrial customers are the main harmonic producers Interconnection standards have been established to limit their harmonics o o Installation of harmonics filters inside the facility VFDs that generate only small amount of harmonics PCC point of common coupling Utility system I h <I limit Utilities have established limits on I harmonics flowing into their systems at the PCC (e.g IEEE Std. 519) I harmonics Harmonics filters Linear & nonlinear loads A standard design practice Nowadays, such loads inject little harmonics into power systems

4 IHD [%] IHD [%] Current [A] Current [A] Current [A] 1. Background Current situation More and more home appliances are becoming harmonic sources New appliances are also emerging such as PV panels and EVs Although insignificant individually, their collective impact can be big Blocks of residential loads have become main harmonic sources PC 1-2 PC 3-3 PC 2-4 Desktop PC Time step Microwave MW 1 on 6 MW 1 off MW 2 on MW 2 off Time step CFL PC 1 PC 3 PC Washer MW1 on MW 1 off MW 2 on MW 2 off Filling Water 6 Washing Rinsing Rinsing off Spinning Time Step Fast Spinning

5 Current Distortion (IDD, %) 1. Background Current situation 12 1 Typical spectra of a service transformer load SUB Residential feeder 8 PCC rd 5th 7th 9th 11th 13th 15th Total One neighborhood with 1 service transformers, 3MW For this block of loads, its harmonic injection at PCC will exceed utility harmonic limits. As a result, the neighborhood would not be allowed to connect to the system if it were owned by a single owner. Additional challenges: The presence of 3 rd and 9 th harmonics (zero sequence) No single entity is responsible for it So utilities own the problem

6 1. Background Potential problems Potential Impact on Transmission Systems: Overload filters of HVDC, SVC and similar equipment Inability to energize transmission capacitors Resonance associated with transmission cables Potential Impact on Distribution Systems: Overload distribution cables Shorten the life of distribution capacitors Increased capacitor/cable resonance Potential Impact on 3 rd Parties: Telephone interference Voltage induction on pipelines Overload customer capacitor or other equipment (e.g. wind farm)

7 1. Background New challenges & research needs New Challenge: Mass-distributed harmonic-producing loads 1. How to assess and predict the impact of distributed harmonic sources? 2. How to monitor harmonic levels in systems with distributed H sources? 3. How to make the impact easier for decision-makers to understand? 4. How to mitigate the harmonic distortions in distribution systems? What is the proper strategy to manage the situation? How to impose harmonic limits on individual devices? What is the role of utility-side harmonic solutions? What options are available for system-wide or problem-focused harmonic filtering schemes?

8 1. Background U of A research activities in harmonic mitigation New ideas under investigation at the Distributed low voltage filters (called micro-filters) Filters dedicated to mitigate zero sequence harmonics Filters dedicated to prevent distribution system harmonics from flowing into transmission systems Novel MV filters that may cost less than the traditional shunt MV filters Resonance-free capacitors

9 2. New method 1 Micro Filter The concept This filter is proposed for system-wide or partial system-wide harmonic filtering Feeder branch Multi-grounded primary feeder Substation Secondary feeder Distribution transformers Micro filter 3f load Service drop Secondary feeder Service drop House 1 House 2 House N Install low voltage (micro) filters at multiple secondary systems Prevents harmonics from secondary systems flowing into primary systems How to create low cost micro filters? How to install them? (installation cost can be 1x of the cost of filter!)

10 2. New method 1 Micro Filter Novel Installation Scheme Proposed solution: Meter-collar based, 24V, plug-in active filter Meter Base Revenue Meter Secondary feeder Micro Filter Filter location Point Y House 1 House 2 Filter installation scheme Filter location in circuit Active filtering: At low voltage, active filter is inexpensive and compact. Estimated cost is less than $1/each Micro filter is installed at only one of the houses in the secondary system Installation for about 3%~5% secondary systems are sufficient. Filters can be installed gradually or partially. There is no large initial cost

11 Daily Average Current IDD(%) 2. New method 1 Micro Filter Research findings Extensive studies have been conducted to 1) Determine if the proposed concept can work 2) Establish design parameters for the micro filters Secondary conductor House #1 1m Primary System 15m I h 3m Serivce conductors 5m No Filter at Service transformer at House 1 at House 2 at House 3 at House 4 at House 5 #2 2m #3 3m #4 #5 3rd 5th 7th 9th 11th 13th 15th TDD Our research findings suggest that the micro-filter scheme is a promising solution. The next step is to build a prototype device.

12 2. New method 2 Zero sequence filter The concept This filter is proposed to mitigate telephone interference problems SUB 1st neighborhood Parallel telephone circuit Filter 9 th and 15 th 2nd neighborhood A A This is essentially a a load (customer); Yg-D (service) transformer; B 25kV/6V or 25kV/48V; 3~5kVA; Can C be constructed using 3 single-phase units C B C C 1 C 2 L 2 This arrangement filters both 9 th & 15 th harmonics; It can be simplified by using C1 only to filter just the 9 th harmonic. N N (a) (b) Installing a filter = connecting a three-phase customer

13 2. New method 2 Zero sequence filter Case study 21 SU Feeder (The main source of telephone interference in 41Ave) Only one filter downstream to the telephone line attracts around 2% of the upstream harmonic load currents F 1 First Filter Z Z u L u d L ZL 2% Downstream loads Upstream loads 24/25 kv Summerside Substation d Z L u Z L F 2 Second Filter (if necessary) The Telephone line sections in parallel with overhead lines 1kVA primary and a 277 secondary, 2 HV bushings, around $5,5. 15kVA primary and a 277 secondary, 2 HV bushings, around $7,2. 2kVA primary and a 277 secondary, 2 HV bushings, around $7,7. If this is an issue, a 2 nd filter could be installed to mitigate upstream harmonics

14 Tel line Voltage(V) Tel line Voltage(V) Tel line Voltage(V) Tel line Voltage(V) Tel line Voltage(V) Tel line Voltage(V) 2. New method 2 Zero sequence filter Case study results Time of the Day: 1am Without Filter Transformer based filter Two transformer based filters Capacitor based filter One filter at location F1 is sufficient Time of the Day: 6am Total rms Time of the Day: 9am Total rms Time of the Day: 16pm Total rms Time of the Day: 2pm 1 15 Conclusions: Total rms The filter is very easy to construct and install Total rms Time of the Day: 23pm 1 5 The filter is an effective solution to mitigate 5 telephone interference problem It could be useful to reduce pipeline induction as well It costs less than the traditional shunt filters The next step is to test the filter in ATCO system Total rms

15 3. Other power quality related research at U of A Power quality analysis & measurement: Method to assess the impact of distributed harmonic sources Novel sensors for measuring distribution line harmonics Method to detect harmonic or resonance sources Synchronous closing scheme for generators Inductive coordination of distribution line and pipeline Power quality data analytics: Methods to anticipate the failure of equipment Method to monitor the condition of feeder capacitors Novel protection scheme for trip grounding

16 4. Conclusions On the technical subject of harmonic mitigation: Distributed harmonics is an emerging power quality concern It calls for new ideas for assessment, measurement and mitigation Two examples are shown to illustrate the benefits of research On U of A research activities: The APIC platform has enabled U of A to Understand industry needs and obtain technical support/feedback Undertake forward-looking projects of high-risk, high-reward nature in addition to application projects Provide excellent training opportunities to graduate students U of A has benefited a lot from the APIC platform as well We thank APIC companies for their financial and technical support!