AS NZS 61000.3.6 HARMONIC ALLOCATION CONSTANT FOR IMPLEMENTATION.pdf
《AS NZS 61000.3.6 HARMONIC ALLOCATION CONSTANT FOR IMPLEMENTATION.pdf》由会员分享,可在线阅读,更多相关《AS NZS 61000.3.6 HARMONIC ALLOCATION CONSTANT FOR IMPLEMENTATION.pdf(6页珍藏版)》请在三一文库上搜索。
1、HARMONIC ALLOCATION CONSTANT FOR IMPLEMENTATION OF AS/NZS 61000.3.6 D.A. Robinson, V.J. Gosbell, B.S.P. Perera Integral Energy Power Quality Centre School of Electrical, Computer and Telecommunications Engineering University of Wollongong NSW 2522 Australia Abstract Allocation of equal harmonic emis
2、sion rights to MV customers having the same maximum demand is a key concept in the new Australian harmonic standard AS/NZS 61000.3.6 1. Some difficulty can arise with the application of the standard when customers are spread out along a feeder with significantly different fault levels. One proposed
3、method of overcoming this problem is to reduce the allocation as the square root of the fault level 2. This method requires the calculation of an allocation constant that is applied to all customers connected to the same zone substation. This paper gives a methodology for calculating the harmonic al
4、location constant when there is incomplete data, and discusses some simplifying assumptions that can be made to optimise calculations. 1. INTRODUCTION In January 2001 Australia adopted a new harmonic standard governing emission limits of distorting loads in MV and HV power systems. The new standard
5、AS/NZS 61000.3.6 is an adaptation of the international technical report IEC 61000-3-6 3. AS/NZS 61000.3.6 comprises a number of stages and tests to determine harmonic emission allowances for customers connected to MV or HV networks. Stage 1 has three tests that base acceptance on load size as compar
6、ed to the short circuit level at the connection point. Stage 2 contains three tests of increasing complexity depending on the amount of information known about the system. There is also a Stage 3 where excessively distorting loads are allowed connection on a temporary and precarious basis. It is per
7、ceived that most distorting loads will be assessed under Stage 2 of the standard. The Integral Energy Power Quality Centre has been involved in producing and implementing practical methods for applying AS/NZS 61000.3.6. Of particular importance is the section of the standard concerning loads distrib
8、uted along a feeder having significant variation in fault level. AS/NZS 61000.3.6 briefly covers this section in Stage 2, Test 3. The application of the principles suggested by the standard for this section is poorly described and only a non- practical trivial example is provided. A more general app
9、roach follows. 2. PRINCIPLES OF AS/NZS 61000.3.6 The guidelines specified in the new standard are somewhat more difficult to apply than in the previous harmonics standard AS 2279.2 4. These guidelines attempt to ensure allocation of harmonic emission rights to customers is more equitable. A key conc
10、ept is that customers with the same agreed power and the same Point of Common Coupling (PCC) are entitled to equal harmonic emission rights. The PCC is defined as the nearest point in the power system to which another consumer might be connected. To account for time variation, customer harmonic cont
11、ributions and utility harmonic levels are assessed generally by the 95% Cumulative Probability (CP) level. As the 95% levels are statistical quantities direct summation is inadequate for combining contributions from a number of customers. Two summation laws are proposed by the standard: (i) The firs
12、t summation law makes use of diversity factors that require knowledge of the load type and is suited to more individual cases. (ii) The second summation law is a more general method that accounts for time diversity of the individual loads on a larger scale, and is given by Equation (1) i hih UU =(1)
13、 Where the exponent depends on the harmonic order h. The recommended value for the 5th harmonic is 1.4. The second summation law provides the basis for the proposed methodology for allocating harmonic emission rights to customers within an MV distribution system. The standard encourages an equitable
14、 allocation of harmonic rights to all customers having the same maximum demand. Where customers see different fault levels the question arises as to whether these rights are to equal harmonic voltage, equal harmonic current, or some other right. It can be shown that allocating equal harmonic voltage
15、 rights allows greater use of the systems harmonic absorption capability, but customers towards the end of a weak feeder receive lower current. The allocation of equal current is fairer but underutilises the harmonic absorption capability. The standard recommends a mid-way policy of equal harmonic p
16、ower, which can be shown to be equivalent to a harmonic current allocation varying with the square root of the fault level. AS/NZS 61000.3.6 assumes that the harmonic voltage at the MV level is a combination of the emissions from the MV loads and the background distortion of the HV transmission syst
17、em. Thus a fraction ThMV of the HV harmonic planning level LhHV must be included in the MV harmonic voltage planning level LhMV. Using the second summation law the acceptable global harmonic contribution GhMV from the MV distribution system alone can be calculated using Equation (2) hHVhHM hMVhMV )L
18、(TLG=(2) The fraction ThHM is assumed here as unity. For the purpose of this work only the 5th harmonic is considered as it has been shown to be the most predominant and problematic for most MV distribution systems 5-6. A full description of the principles behind the proposed methodology can be foun
19、d in 2. 3. THE ALLOCATION CONSTANT k When loads are spread out along a feeder and connected to points having different fault levels, allocation of harmonic current emissions becomes difficult. To achieve the constant harmonic power policy recommended in Section 2, the harmonic current emissions need
20、 to be allocated in proportion to agreed power Si and inversely proportional to the square root of the harmonic impedance Zhi at the PCC. A suitable strategy from 2 is to allocate harmonic current emissions EIhi using Equation (3) hi i Ihi Z kS E 1 =(3) Where k is called the allocation constant. The
21、 same value of k is used for all loads supplied from a common substation. Its value is chosen such that when the substation reaches load saturation, and all loads are contributing their maximum permitted harmonic contribution, the magnitude of the considered harmonic voltage will have a value not ex
22、ceeding the limits suggested by AS/NZS 61000.3.6. It is easy to show that this voltage will occur at the far end of the weakest feeder. Exact calculation of k is possible but complex and requires an enormous amount of data. To illustrate this process we consider a distribution system with each non-l
23、inear load modeled as an equivalent harmonic current source. At harmonic order h, the resulting voltages are related to the currents as shown in Equation (4) hhh IZV=(4) Where Vh is the unknown harmonic voltage vector, Zh is the harmonic impedance matrix, and Ih is the harmonic current vector. For a
24、 system with N nodes the expanded form of Equation (4) is as follows = hN hj h2 h1 hNNhNjhN2hN1 hiNhijhi2hi1 h2Nh2jh22h21 h1Nh1jh12h11 hN hi h2 h1 I I I I ZZZZ ZZZZ ZZZZ ZZZZ V V V V M M LL MMMM LL MMMM LL LL M M Using direct addition the harmonic voltage at node i is given by Equation (5) = N j hjh
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- AS NZS 61000.3.6 HARMONIC ALLOCATION CONSTANT FOR IMPLEMENTATION 61000.3
链接地址:https://www.31doc.com/p-3645269.html