Upon completion of this experiment, students should have the: MO1 : Ability to model transmission and distribution systems using PSS Adept. MO2 : Ability to determine the location of capacitor banks for several given val ues. MO3 : Ability to calculate voltage regulation in a distribution system. MO4 : Ability Ability to evaluate the effect of compensating capacitor placement in tr tr ansmission system.
Table 1: Standard setting for Malaysia network System Standard Base Voltage kV System 3 phase kVA Typical value 11, 22,33 or 132 kV 100000kVA Input Voltage Type Line - Line System Frequency 50 Hz ( TNB) Stability Voltage Range (p.u) 0.95
1. Fixed type capacitor banks The reactive power supplied by the fixed capacitor bank is constant irrespective of any variations in the power factor and the load of the receivers. These capa citor banks are switched on either manually (circuit breaker / switch) or semi a utomatically by a remote-controlled contactor. This arrangement uses one or more capacitor to provide a constant level of compe nsation. These capacitors are applied at the terminals of inductive loads (mainly motors) , at bus bars. Disadvantages: Manual ON/OFF operation. Not meet the require kvar under varying loads. Penalty by electricity authority. Power factor also varies as a function of the load requirements so it is dif ficult to maintain a consistent power factor by use of Fixed Compensation i.e. f ixed capacitors. Fixed Capacitor may provide leading power factor under light load conditions , Due to this result in overvoltages, saturation of transformers, mal-operation of diesel generating sets, penalties by electric supply authorities. Application: Where the load factor is reasonably constant. Electrical installations with constant load operating 24 hours a day Reactive compensation of transformers. Individual compensation of motors. Where the kvar rating of the capacitors is less than, or equal to 15% of the supply transformer rating, a fixed value of compensation is appropriate. Size of Fixed Capacitor bank Qc = 15% kVA transformer
Method Advantages Disadvantages Individual capacitors Most technically efficient, most flexible Higher i nstallation & maintenance cost Fixed bank Most economical, fewer installations Less flexible, requires switches and/or circuit breakers The size of the inductive load is large enough to select the minimum size of cap acitors that is practical. For HT capacitors the minimum ratings that are practical are as follows: System Voltage Minimum rating of capacitor bank 3.3 KV , 6.6KV 75 Kvar 11 KV 200 Kvar 22 KV 400 Kvar 33 KV 600 Kvar Unit sizes lower than above is not practical and economical to manufacture. When capacitors are connected directly across motors it must be ensured that the rated current of the capacitor bank should not exceed 90% of the no-load curren t of the motor to avoid self-excitation of the motor and also over compensation. Precaution must be taken to ensure the live parts of the equipment to be compens
ated should not be handled for 10 minutes (in case of HT equipment) after discon nection of supply. Crane motors or like, where the motors can be rotated by mechanical load and mot ors with electrical braking systems, should never be compensated by capacitors d irectly across motor terminals. For direct compensation across transformers the capacitor rating should not exce ed 90 % of the no-load KVA of the motor. C. Size of Conductor for Capacitor Connections Size of capacitor circuit conductors should be at least 135% of the rated capaci tor current in accordance with NEC Article 460.8 (2005 Edition). Placement of capacitors in Distribution system The location of low voltage capacitors in Distribution System effect on the mode of compensation, which may be global (one location for the entire installation) , by sectors (section-by-section), at load level, or some combination of the las t two. In principle, the ideal compensation is applied at a point of consumption and at the level required at any instant. Compensation by sector Principle Capacitor banks are connected to bus bars of each local distribution Panel. Most part of the installation System can benefits from this arrangement, mostly the feeder cables from the main distribution Panel to each of the local distribu tion panel. Advantages Reduces the tariff penalties for excessive consumption of kvar. Reduces the apparent power Kva demand, on which standing charges are usually based. The size of the cables supplying the local distribution boards may be reduce d, or will have additional capacity for possible load increases. Losses in the same cables will be reduced. No billing of reactive energy. Makes less demands on the supply Feeders and reduces the heat losses in thes e Feeders. Incorporates the expansion of each sector. Makes less demands on the transformer. Remains economical Limitations Reactive current still flows in all ion Boards. For the above reason, the sizing of em, are not improved by compensation by Where large changes in loads occur, on and consequent overvoltage problems.
cables downstream of the local distribut these cables, and the power losses in th sector there is always a risk of overcompensati
Application Compensation by sector is recommended when the installation is extensive, and wh
ere the load/time patterns differ from one part of the installation to another. This configuration is convenient for a very widespread factory Area, with worksh ops having different load factors
Load flow studies are performed in order to investigate:i) Flow of current, kW and kVar in the various points of the network ii) Bus bar voltages. iii) Effect of rearranging circuits and incorporating new circuits on system loa ding iv) Optimum system running conditions and loads distribution v) Optimum system losses vi) Optimum rating and tap range of transformers vii) Improvement from change of conductor size and system voltage Load flow studies are essential not only for analyzing the existing system, but also useful for the planning of future development of the system in order to know the effect of new loads and new cables/lines before they are installed. In a power system, voltage at various buses tends to increase or decrease during it daily operation. When the voltage is below the required level, reactive power produced by inductance needs to be offset by capacitance. There are several techniques can be used to i ncrease the voltage to its acceptable level. A well known technique is to use shunt capacito r in parallel to the transmission lines. The capacitor is used to provide reactive power compensation in order to achieve power and energy loss reduction, system capacity release and acceptable voltage profiles. The extent of these benefits depends on the location, size, type, and number of shunt capacito rs and also on their control settings. Hence, an optimal solution for placement and sizing of s hunt capacitors in a distribution system is a very important aspect of power system analysis. In this experiment, capacitor banks are required to be connected at the transmis sion network to help improving voltage profile for certain busbars. The PSS/Adept simulation sof tware is capable to optimise the size and the location of capacitors in the designated ne twork. 5.1 Capacitor Placement Optimization (CAPO) analysis Capacitor placement optimization finds the suitable size of the capacitors to be located in certain bus of a network. The result of the optimization process will indicate t he set of location(s) where capacitors should be placed; the size of the capacitors.
From the results of 5 and 6, evaluate the performance of the capacitors in terms of voltage stability and total power savi ng. Discuss the result with and without capacitor placement to the power transmissio n system.
CAPO places capacitors on the network as long as they are economic (i.e., as lon g as the value of the monetary savings from the placement is greater than the cost of the capacito r itself). CAPO selects the node for the n th capacitor that results in the largest monetary savings. Load snapshots are implemented in PSS/ADEPT to provide modeling of the load variations, which o ccur with time, temperature, or other factors. When switched capacitors are placed by CAPO, the capacitor switching increment for each snapshot is also calculated. The following paragraphs provide a complete description of CAPO, considering fix ed and switched capacitors and multiple snapshots. First, for each snapshot a load flow is done to let transformer taps and existing switched capacitors adjust. These transformer tap and capacito r increment settings are then saved with each snapshot. There will be no further adjustments of these transformer/capacitor settings as CAPO progresses. CAPO first considers fixed capacitors, which, by definition, are on during all l oad snapshots. All the eligible nodes in the network are then examined to see at which one the capacito r placement offers the greatest monetary savings. Since there are multiple snapshots, this reductio n is calculated as the weighted sum from each snapshot, where the weighting factor is the snapshot duration. The following conditions can then stop the capacitor from actually being placed on t he selected node: The present worth of the savings does not offset the present worth of the costs. With multiple snapshots the savings are evaluated as in the simple example considered above, except now a weighted sum over all the profiles is calculated. There are no more fixed capacitors available to be placed (actually, this can be
checked before all the nodes are searched, but is listed here for completeness). An upper voltage limit is violated in one of the profiles (the network upper vol tage limit is set from the Analysis Options Property sheet under the General tab). Fixed capacitors continue to be placed until one of the above three conditions a re encountered; at that point the fixed capacitor placement ends and the switched placement begins. This procedure is a bit more complicated, and before we begin this is probably a good point to make a comment. If only one load snapshot is used, you might expect that after the fixed capacitors are placed there will be no placement of switched capacitors. There are at least four conditions where this is not true: You had only a few fixed capacitors available, and there was still considerable opportunity for savings when these fixed units were depleted. The eligible nodes for switched capacitors are different than those eligible for fixed capacitor placement. You make the cost of switched capacitors less than that of fixed capacitors, and after the fixed capacitors are placed it will still be cost effective to place switche d capacitors. You make the size of the switched capacitor bank smaller than that of the fixed bank. The eligible nodes (for switched capacitors) in the network are reviewed to find the node, which produces the greatest savings summed over all the snapshots. There are a couple of subtleties in this evaluation. First, if placing the switched capacitor causes a voltage violation in any snapshot, the capacitor is turned off during that period. Second, if the capacitor causes a co st penalty for a snapshot, it is also turned off for that snapshot. The calculation of the present wo rth of the savings is then calculated considering only the snapshots during which the capacitor is turned o n. This process continues until a point is reached where: The savings do not offset the cost of the switched capacitor. CAPO runs out of switched capacitors to place. In summary, CAPO places fixed capacitors on the network until one of the stop co nditions are encountered. Then switched capacitors are placed until one of the switched capac itor stop conditions occurs. The total cost of the
optimization is then the installation and maintenance cost of all the capacitors placed; the total savings is the sum of the savings from each capacitor. PSS/ADEPT 5.2 U SERS MANUAL June 2005 Siemens Power Transmission & Distribution, Inc. Power Technologies International 1482 Erie Boulevard P.O. Box 1058 Schenectady, NY 12301-1058 US Phone 518-395-5000 www.pti-us.com 1) D. P. Kothari and I J Nagarath, Modern Power System Analysis , Tata Mc Graw Hil l, Third Edition, 2005. 2) Chapman,S.J, Electric Machinery and Power System Fundamentals , McGrawHill 2002 3) "PSS/ADEPT 5.2 USERS MANUAL June 2005",Siemens Power Transmission & Distributi on, Inc. Power Technologies International, 1482 Erie Boulevard P.O. Box 1058, Sc henectady, NY 12301-1058 US, Phone 518-395-5000, www.pti-us.com 4) Mohan, W.; Scott, M. "Modeling Power Electronics in Power System Using EMTP" . University of Minnesota - BPA. 1993 5) Saadat, H, "Power system Analysis Paperback", PSA Publishing; THIRD EDITION I'm just a bachelor I'm looking for a partner Someone who knows how to ride Without even falling off Gotta be compatible Takes me to my limits Girl when I break you off I promise that you won't want to get off
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