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پرسش ترانسفورماتور شماره 9 - گروه برداري ترانس
اگر دو plant مشابه داشته باشيم كي از ترانس dy11 و كي از ترانس dy5 استفاده مي كنيم؟
نویسنده : انيسه آدينه زاده - از: ايران
 
#1
ساعت: 20:19 - تاریخ: 3 اسفند 1387
1-براي ترانسهاي قدرت متصل به ژنراتورها ( GT) معمولا اتصال Ynd11

2- براي ترانسهاي كمكي واحد توليد توان (UAT) معمولاً اتصالDyn1 يا Dd0

3-براي ترانسفورماتورهاي توزيع اتصال Dyn11

4- براي ترانسفورماتورهاي متصل به اجزاء هارمونيك زا مثل مبدلهاي الكترونيك-قدرت از اتصالات Dy5 يا Dy7 نيز استفاده مي شود. 
نویسنده : حميد
 
#2
ساعت: 18:40 - تاریخ: 4 اسفند 1387
1-دليل علمي استفاده از ترانس DY11 در  سيستم توزيع و ترانس DY5 در سيستم توزيع و جگونگي تاثير اتصالات بر هارمونيك زدايي چيست؟
2-چرا ترانسفورماتورهاي توزيع كنار دكل برق داراي گروه برداري DY5 هستند؟  
نویسنده : انيسه آدينه زاده
 
#3
ساعت: 20:40 - تاریخ: 10 اسفند 1387
بد نيست نگاهي هم به معماي ترانس شماره 19 از بخش انگليسي بياندازيد.

حقيقتاً تجارب متنوعي در استفاده از گروه هاي مختلف برداري در جهان وجود دارد، و تنها بحث كلاسيك شكل گرفته حول اين مفهوم مسئله بارگذاري نقطه نوتر ترانس، امپدانس صفر آن و موضوع قابليت تركيب امواج حاوي هارمونيكهاي مختلف در ترانس و امكان حذف برخي از آنها است. مثلاً مي توان نشان داد تركيب دو موج با اختلاف فاز 60 درجه موجب حذف هارمونيكهاي مضرب 3 و با اختلاف فاز 30 درجه در برخي شرايط موجب حذف هارمونيكهاي مرتبه 5 ، 7،17 و 19   موج مي شود. 
نویسنده : حميد
 
#4
ساعت: 08:53 - تاریخ: 12 اسفند 1387
مراجع  قابل مطالعه و كاربردي در مورد گروه برداري ترانس و كاربرد ْآنهارا مي خواهم  
نویسنده : انيسه آدينه زاده
 
#5
ساعت: 17:03 - تاریخ: 12 اسفند 1387
1- همانطور كه قبلاً به عرض رسيد، الزام فني قاطعي براي جابجايي زاويه فازهاي ولتاژ و جريان در شبكه هاي قدرت وجود ندارد، مگر در موارد خاص مثل ترانسهاي مورد استفاده در سيستمهاي مبدل الكترونيكي كه الزام حذف هارمونيك تعيين كننده مي شود. البته الزامات مهمي در استفاده از اتصالات مختلف (مثلث، ستاره يا زيگزاگ) در سيستمهاي الكتريكي وجود دارد كه مشروح آنها در منابع كلاسيك وجود دارد.
در خصوص گروه برداري اتصالات مختلف با موارد زير برخورد نمودم كه بد نيست مورد توجه قرار دهيد.

ANSI standard require that wye-wye and delta-delta transformers have 0 degree displacements. Sometimes the phase difference is used to advantage, such as when supplying power to 12-pulse rectifiers or other specialized loads. European standards permit a wide Varity of displacements, the most common being DY11 (330 DEGREE).


2- همچنين بر اساس كتابچه معروف شركت آ ب ب كه مهندسان ايراني خيلي به آن رجوع مي كنند، اتصالات زير قابل توصيه است.

Also according to ABB Switchgear manual Preferred connections are:

Yyn 0  :
For distribution transformers. The neutral point can be loaded continuously with up to 10 % of the rated current, or with up to 25 % of the rated current for
a maximum of 1.5 hours. Example: for connecting arc suppression coils.
YNyn 0  :
With compensating winding, used for large system-tie transformers. The neutral point can be loaded continuously with the rated current.
YNd 5 :
Intended for machine and main transformers in large power stations and transformer stations. The neutral point can be loaded with the rated current.
Arc suppression coils can be connected (delta winding dimensioned for the machine voltage).
Yzn 5  :
For distribution transformers, used up to approx. 250 kVA for local distribution systems. The neutral point can be loaded with the rated current.
Dyn 5  :
For distribution transformers above approx. 315 kVA, for local and industrial distribution systems. The neutral point can be loaded with the rated current.
Ii 0  :
For single-phase transformers, intended for traction power supply or for three-phase banks with very high voltages and powers.

3- استانداردهاي زير نيز حاوي اطلاعات خوبي در اين خصوص هستند.

IEEE C57.105 , Guide for application of transformer connections in three-phase distribution system.

IEC 60076-8 ,
 
نویسنده : حميد - از: فیروزآباد فارس
 
#6
ساعت: 08:05 - تاریخ: 24 مهر 1388

خواهشمند است یک سری دلایل برای حذف هارمونیک در نوع اتصالات ترانسفورماتور را بیان نمائید.

 
نویسنده : مسلم - از: ایران
 
#7
ساعت: 11:12 - تاریخ: 3 آبان 1389
آیا میتوان دو ترانسفورماتور تکفاز که غیر مشابه هستند را موازی بست!؟ 
نویسنده : کیان - از: رشت
 
#8
ساعت: 10:28 - تاریخ: 8 آبان 1389
بطور کلی خیر، البته برخی رواداریها برای انحرافات مختصر در استانداردها پیش بینی شده است که در زیر به برخی از آنها اشاره شده است.

The satisfactory parallel operation of transformers is dependent upon five principal characteristics; that is, any two or more transformers which it is desired to operate in parallel should possess:
1. The same inherent phase angle difference between primary and secondary terminals.
2. The same voltage ratio.
3. The same percentage impedance.
4. The same polarity.
5. The same phase sequence.

To a much smaller extent parallel operation is affected by the relative outputs of the transformers, but actually this aspect is reflected into the third characteristic since, if the disparity in outputs of any two transformers exceeds three to one it may be difficult to incorporate sufficient impedance in the smaller transformer to produce the correct loading conditions for each unit.
Characteristics 1 and 5 only apply to polyphase transformers. A very small degree of latitude may be allowed with regard to the second characteristic mentioned above, while a somewhat greater tolerance may be allowed with the third, but the polarity and phase sequence, where applicable, of all transformers operating in parallel must be the same.
Generally three phase transformers are in parallel operation if they are connected in parallel on at least two sides. A distinction is made between busbar interconnection and network interconnection. The following conditions must be satisfied in order to avoid dangerous
transient currents:
1. Vector groups should have the same phase angle number; terminals of the same designation must be connected together on the HV and LV sides; Exception: Phase angle numbers 5 and 11 (Table below);
2. The ratios should be as similar as possible, i.e. the same rated voltages on the HV and LV sides;
3. Approximately the same impedance voltages uk maximum permissible discrepancies ± 10 %. In the event of larger differences, an inductance (reactor) can be connected ahead of the transformer with the lower impedance voltage.
4. Rated output ratio smaller than 3:1.



The theory of the parallel operation of single-phase transformers is essentially the same as for three-phase, but the actual practice for obtaining suitable connections between any two single-phase transformers is considerably simpler than the determination of the correct connections for any two three-phase transformers.
In single-phase transformers phase angle difference between primary and secondary terminals does not arise, as by the proper selection of external leads any two single-phase transformers can be connected so that the phase angle difference between primary and secondary terminals is the same for each. Consequently the question really becomes one of polarity.

It is very desirable that the voltage ratios of any two or more transformers operating in parallel should be the same, for if there is any difference whatever a circulating current will flow in the secondary windings of the transformers when they are connected in parallel, and even before they are connected to any external load. Such a circulating current may or may not be permissible.
This is dependent firstly on its actual magnitude and, secondly, on whether the load to be supplied is less than or equal to the sum of the rated outputs of the transformers operating in parallel. As a rule, however, every effort should be made to obtain identical ratios, and particular attention should be given to obtaining these at all ratios when transformers are fitted with tappings.
In passing, it may be well to point out that when a manufacturer is asked to design a transformer to operate in parallel with existing transformers, the actual ratio of primary and secondary turns should be given, as this ratio can easily be obtained exactly. Such figures would, of course, be obtained from the works test certificate for the existing transformers.
It is to be noted that this flow of circulating current takes place before the transformers are connected up to any external load. A circulating current in the transformer windings of the order of, say, 5% of the full-load current may generally be allowed in the case of modern transformers without any fear of serious overheating occurring. It is sometimes very difficult to design new transformers to give a turns ratio on, say, four tappings identical to what an existing one may possess, and while it is desirable that the ratios should be the same, it is not necessary to insist on their being identical.

 
نویسنده : حمید - از: فیروزآباد فارس
 
#9
ساعت: 17:25 - تاریخ: 6 آذر 1389
سلام. اگر چند نيروگاه توسط ترانس هاي ايزوله به يكديگر وصل باشند ، آيا ضروري است كه گروه برداري تمام ترانس ها يكي باشد؟
(اگر بخواهيم به شبكه برق سراسري برق بدهيم، حتما بايستي از يك گروه برداري خاص استفاده كنيم؟) 
نویسنده : آرش خان - از: تهران
 
#10
ساعت: 15:26 - تاریخ: 8 آذر 1389
به نظر می رسد موضوع مورد علاقه شما نقش ترانسفورماتورهای اینترکانکشن بین شبکه های تولید برق محلی و شبکه سراسری باشد. تأثیر اینگونه ترانسها و نحوه اتصالشان بر پارامترهای گوناگون الکتریکی رنج وسیعی از مزایا و معایب فنی که متوجه هر نوع اتصال است را شامل می شود. در متن زیر برخی اتصالات متداول در این خصوص و مزایا و معایب هر یک تشریح شده است.

A- Grounded-Wye (utility) –Grounded-Wye (generator) Interconnection Transformer
This connection is perhaps the most common three-phase transformer connection on some
utility systems, although not necessarily on the UI system. Advantages and disadvantages related to the use of this transformer connection with respect to DG application include:

1-General
- More economical than other connections in some applications, particularly at 25- and 35 kV class voltages.
- Less concern for ferroresonance in cable-fed installations; some core designs may be more prone than others.
- DG ‘sees’ same imbalance that utility system ‘sees’
2. Harmonic Distortion
Disadvantage(s)
- Will directly pass zero-sequence harmonic currents (such as the 3rd harmonic)
3. System Protection
Advantage(s)
- No phase shift in system voltages (relaying); can detect primary side voltages with low-voltage relays
                 Disadvantage(s)
- DG may feed into any type of fault that is on the utility system.
- Utility will supply fault current for internal generator ground faults, increasing fault damage.
- Does not necessarily provide a ground reference when islanded despite the fact that both windings are solidly grounded. Ground reference will be provided by the generator and/or load.
4. Insulation Coordination
The insulation level of the transformer provides proper insulation coordination between UI system and load-side equipment.

B- Delta (utility) – Grounded-Wye (generator) Interconnection Transformer
This is the most common connection for serving three-phase loads on the UI 13.8 kV system.
Advantages and disadvantages related to the use of this transformer connection with respect to DG application include:

1. Harmonic Distortion
Advantage(s)
- Triplen harmonics from the DG do not reach the utility system.
Disadvantage(s)
- Depending on generator neutral grounding, 3rd harmonics in the DG may cause excessive current in the DG-side neutral.

2. System Protection
Advantage(s)
- Provides some isolation from voltage sags due to utility-side single line ground
(SLG) faults, allowing the DG to better ride through voltage sags.
- Does not feed directly into utility-side SLG faults (it can contribute through other ground sources on the utility system).
Disadvantage(s)
- Cannot provide an effectively grounded system during islanding or open conductor conditions
- Difficult to detect some utility-side SLG faults from the generator side by voltage relaying alone. The delta winding tends to hold the generator side voltage magnitudes up and in the proper phase relationship. Primary-side relaying is often required to ensure rapid detection.
- Very prone to ferroresonance in cable-fed installations, especially during open conductor fault conditions. Instantaneous overvoltage relaying (59I) is often required to ensure prompt detection of this condition.

3. Insulation Coordination
Provides proper insulation coordination between UI system and load-side equipment.

C- Grounded-wye (utility) –Delta (generator) Interconnection Transformer
This connection is rarely used on utility power distribution systems to serve loads, but is considered by many as the best way to interconnect large three-phase DG. This transformer connection is often referred to as a “grounding bank” and has a number of special characteristics that must be considered in its application on utility power systems like UI’s distribution system:
1. This connection acts as a source of ground current and will supply ground fault current into the utility system as long as the transformer is connected to the utility system even without the DG connected to the transformer. This additional fault current must be considered when designing a DG application using this connection. A single UI substation may have several DG units connected to it and the ground fault current contribution must be limited by using a neutral grounding reactor (see Neutral Grounding Reactor Sizing below).
2. The normal voltage imbalances on the UI distribution system will cause current to circulate in the transformer winding continuously. This will result in transformer heating and consume a portion of the transformer capacity. This circulating current can also be limited by selecting an appropriate neutral grounding reactor size.
3. The grounding bank action serves to limit ground over voltages that can occur during momentary islanding periods when the DG system is separated from the utility system. Neutral grounding reactors selected to limit fault current contribution and circulating currents must have a sufficiently low impedance to maintain an“effectively grounded” system during periods when the connection to the main utility grid is lost.

Advantages and disadvantages related to use of the grounding bank interconnection transformer configuration for DG applications include:
1. Harmonic Distortion
Advantage(s)
- Triplen harmonic currents that might be produced by the generator are blocked by the delta winding and cannot flow on the generator side and, therefore, are not passed on to the utility power system.
Disadvantage(s)
- Triplen harmonic currents already present in the UI distribution system from other sources will tend to flow into transformers with this winding connection, contributing to transformer heating.
- The flow pattern for triplen harmonic currents on the distribution system is altered, which could be either beneficial or detrimental to telecommunications interference and neutral-to-ground voltages depending on the path taken by the currents. This alteration in flow pattern for triplen harmonics is difficult to predict prior to construction and can require mitigation after commissioning should complaints arise from other UI customers.

2. System protection
Advantage(s)
- Utility-side faults are generally more readily detected by the DG system protection because the transformer itself actually participates in all ground faults. This characteristic generally allows the DG to disconnect more quickly.
- Should the DG become isolated from the utility source (islanded), this connection helps the DG system present an effectively grounded source to the utility distribution system and avoid the resonance and overvoltage issues of other connections.
Disadvantage(s)
- Contributes strongly to all ground faults, which can increase damage due to high fault currents. A neutral impedance can minimize the impact.
- The presence of multiple DG installations supplied by the same UI substation using this transformer connection increases the complexity of coordinating transformer and neutral reactor sizing.

3. Insulation Coordination
Provides proper insulation coordination between UI system and load-side equipment.
 
نویسنده : حمید - از: فیروزآباد فارس
 
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