GÜÇ SİSTEMLERİNDE KORUMA

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1 GÜÇ SİSTEMLERİNDE KORUMA
Giriş ve Temel Başlıklar EES

2 Giriş ve Tanımlar Güç sistemlerinin temel hedefi; çok yüksek seviyede emre amadelik (süreklilik) ile enerji sunmak, tolere edilemeyecek durumlarda ise arızanın boyutunu ve süresini asgari seviyede tutmaktır Ancak, değişik arıza nedenleriyle güç kayıpları, gerilim dipleri ve aşırı gerilimler oluşur. EES

3 Arıza Nedenleri Doğal olaylar Fiziksel kazalar Teçhizat arızaları
İnsan kaynaklı hatalar EES

4 Doğal olaylar nedeniyle kısa devre
Yıldırım Rüzgar Buz yükü Deprem Yangın Ağaçlar Hayvanlar Hava kirliliği, sis, toz EES

5 Fiziksel kazalar nedeniyle kısa devre
Araçların direklere/iletkenlere çarpması İnsanlara elektrik çarpması Hafriyat çalışmaları nedeniyle yer altı kablolarının zarar görmesi İnsan kaynaklı hatalı manevralar EES

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7 31. 07. 1984’de fotoğraflanan Seattle’daki yıldırım nedeniyle 12
’de fotoğraflanan Seattle’daki yıldırım nedeniyle evde elektrik kesintisi yaşandı. Ancak, koruma sistemleri sayesinde ne büyük bir teçhizat hasarı ne de uzun süreli kesintiler yaşandı. EES

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10 Kısa devre arızası Zsc Zs
Arıza noktasından önceki tüm sistemin eşdeğer empedansı Zs Yük empedansı A simplified network comprises a source of constant AC power, a switch, an impedance Zsc that represents all the impedances upstream of the switch, and a load impedance Zs In a real network, the source impedance is made up of everything upstream of the short-circuit including the various networks with different voltages (HV, LV) and the series-connected wiring systems with different cross-sectional areas (A) and lengths. When a fault occurs between A and B, the negligible impedance between these points results in a very high short-circuit current Isc that is limited only be impedance Zsc. The current Isc develops under transient conditions depending on the reactances X and the resistances R that make up impedance Zsc EES

11 Kısa devre arıza tipleri
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13 Arıza istatistikleri Faz-toprak: %80 Faz-faz: %15 Üç faz: %5
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14 Arıza belirtilerinin görüldüğü sistem bileşenleri
Aşırı akım Aşırı/düşük gerilim Güç faktörü/faz açısı Akım yönü Empedans Frekans Sıcaklık En yaygın arıza göstergesi; akımdaki ani ve yüksek miktardaki artıştır. Dolayısıyla, aşırı akım koruması yaygın olarak kullanılır System faults usually, but not always, provide significant changes in the system quantities, which can be used to distinguish between tolerable and intolerable system conditions. These changing quantities include overcurrent, over- or undervoltage power, power factor or phase angle, power or current direction, impedance, frequency, temperature, physical movements, pressure, and contamination of the insulating quantities. The most common fault indicator is a sudden and generally significant increase in the current; consequently, overcurrent protection is widely used. EES

15 Sistem koruması Uygun röle ayarlarının uygulanarak arızalara ve istenmeyen sistem durumlarına maksimum hassasiyet Aynı zamanda, sistem açısından tolere edilebilir tüm durumlara izin Protection is the science, skill, and art of applying and setting relays or fuses, or both, to provide maximum sensitivity to faults and undesirable conditions, but to avoid their operation under all permissible or tolerable conditions. EES

16 Koruma sisteminin karar verme süreci çok hızlı olmalı
Sistemdeki sorun/arıza; hızlı müdahaleyi gerektiren tolere edilemeyecek bir durum mudur yoksa sistemin absorbe edebileceği tolere edilebilir veya geçici (transient) bir durum mudur? Eğer gerekiyorsa, koruma sisteminin çalışması sonucu sorunlu bölge hızlıca izole edilerek sistem dengesizliği (disturbance) asgari seviyede tutulmalı It is important to recognize that the ‘‘time window’’ of decision in a power system’s protection is very narrow, and when faults occur, a recheck for verification or a decision-making procedure that involves additional time, is not desirable. It is vital (1) that a correct decision be made by the protective device as to whether the trouble is intolerable and, thus, demands quick action, or whether it is a tolerable or transient situation that the system can absorb, and (2) that, if necessary, the protective device operates to isolate the trouble area quickly and with a minimum of system disturbance EES

17 ‘Temizlenmeyen’ kısa devre arızalarının olası sonuçları:
Teçhizat hasarı şiddetinin artması Ciddi yaralanmalar Uzun süreli kesintiler Patlama, yangın vb. sonucu çevresel hasar Both failure to operate and incorrect operation can result in major system upsets involving increased equipment damage, increased personnel hazards, and possible long interruption of service. These stringent requirements with serious potential consequences tend to make protection engineers somewhat conservative. EES

18 İletim hattındaki kısa devre arızası
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19 Aynı teçhizatın korunması için yedekli sistemler (Hiçbir sistem mükemmel değildir)
Aynı yerde (primary backup) Aynı merkezde (local backup) Uzak merkezde (remote backup) Problems can and do occur in protective equipment; nothing is perfect. To minimize the potential catastrophic problems that can result in the power system from a protection failure, the practice is to use several relays or relay systems operating in parallel. These can be at the same location (primary backup), at the same station (local backup), or at various remote stations (remote backup). All three are used together in many applications. In highervoltage power systems this concept is extended by providing separate current or voltage, or both measuring devices, separate trip coils on the circuit breakers, and separate tripping battery sources. EES

20 Arttırılmış yedeklilik
Arızanın temizlenme olasılığında artış (Artan ‘dependability’) Arıza yokken hatalı çalışma olasılığında artış (Azalan ‘security’) Her uygulamada amaca göre ‘dependability’ ile ‘security’ arasında bir denge sağlanmalı The various protective devices must be properly coordinated such that the primary relays assigned to operate at the first sign of trouble in their assigned protective zone operate first. Additional redundancy, however, does have a negative impact on security. As more systems are added to enhance dependability, an increased probability of incorrect operations results. Good judgment must be utilized when applying protective relaying in order to optimize the balance between dependability and security. The optimal balance will vary, depending on the characteristics and objectives of each specific application. EES

21 Röle Tipleri (Çalışma prensibine göre)
Elektromekanik röleler Elektronik röleler Dijital röleler Originally, all protective relays were of the electromechanical type. Analog type electronic relays using discreet electronic components were introduced in the 1970s. In recent years, microprocessor-based electronic relays have been developed and are being applied at an increasing rate. Microprocessor- based relays are sometimes referred to as numerical type relays since the analog inputs are converted to digital numbers that are then processed within the relay. EES

22 Kesiciler Koruma röleleri: ‘Beyin’ Devre kesicileri: ‘Kaslar’
Genel uygulama; arıza tek veya iki fazda olsa da üç fazın açılması şeklindedir. Protective relays provide the ‘‘brains’’ to sense trouble, but as low-energy devices, they are not able to open and isolate the problem area of the power system. Circuit breakers and various types of circuit interrupters, including motor contactors and motor controllers, are used for this and provide the ‘‘muscle’’ for fault isolation. the practice for many years has been to open all three phase for all types of faults, even though one or two of the phases may not be involved in the fault EES

23 Koruma sisteminin temel elemanları
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24 Tekrar Kapama İletim hattı arızalarının büyük çoğunluğu tek faz-toprak ve geçici (transient) arızalardır. Tekrar kapama yöntemi ile milisaniyeler içinde arızalı faz açılıp kapatılır ve güç akışı kesintisiz sağlanmaya devam edilebilir. Düşük gerilim seviyelerinde ( V) devre kesicisi ve röleler sıklıkla tek bir cihaz içine entegre edilmiş şekildedir. Temel koruma mantığı aşırı akıma dayanır. Because most transmission-line faults are transient single-line-to-ground type, opening only the faulted phase would clear it. With a transient fault, such as that resulting from lightning-induced overvoltage, immediate reclosing of the open, faulted phase would restore three-phase service. at the lower voltages, the circuit breaker (interrupter) and relays frequently are combined into a single-operating unit. The circuit breaker switches commonly installed in the service entrance cabinet in modern residential homes and commercial buildings are typical examples. In general, this type of arrangement is used up through 480–600 V. Primarily, the protection is overcurrent, EES

25 Röle-kesici bağlantıları
Koruma röleleri, güç sistemine akım (CT) veya gerilim trafoları (VT) vasıtasıyla bağlanır. Daha güvenli (düşük akım-gerilim) işletim Daha yüksek kesinlik (accuracy) Koruma sistemi başta olmak üzere önemli iç ihtiyaç beslemeleri için tüm Yüksek Gerilim (YG) merkezlerinde (Trafo Merkezi-TM) akü-UPS sistemleri mevcuttur (Koruma sistemi için genellikle 48 V DC) Protective relays using electrical quantities are connected to the power system through CT or voltage transformer (VT). These input devices or instrument transformers provide insulation from the high-power system voltages and reduce the magnitudes to practical secondary levels for the relays. At the higher power system voltages, each station at which circuit breakers are installed has a station battery to supply direct current to the breaker trip coils, the control and protective relay circuits as required, emergency alarms and lighting , and so on. 48 V DC is often used for electronic and solid- state devices. This DC supply is another vital part of the protection system and requires careful attention and maintenance for high system and protection reliability. EES

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27 Sistem korumasının temel hedefi
Güç sistemindeki sorunlu alanın süratle izole edilerek arızanın sistemin geri kalanına etkisini ve enerjisiz kalacak bölümü minimize etmektir. The fundamental objective of system protection is to provide isolation of a problem area in the power system quickly, so that the shock to the rest of the system is minimized and as much as possible is left intact. EES

28 Koruma sistemlerinin temel kriterleri
Güvenilirlik (Reliability) ‘Dependability’ ‘Security’ Seçicilik (Selectivity) Hız Basitlik (Simplicity) Ekonomiklik (Economics) protection does not mean prevention, but rather, minimizing the duration of the trouble and limiting the damage, outage time, and related problems that may result otherwise. The five basic facets are: 1. Reliability: assurance that the protection will perform correctly. 2. Selectivity: maximum continuity of service with minimum system disconnection. 3. Speed of operation: minimum fault duration and consequent equipment damage and system instability. 4. Simplicity: minimum protective equipment and associated circuitry to achieve the protection objectives. 5. Economics: maximum protection at minimal total cost. EES

29 Güvenilirlik (Reliability)
‘Dependability’ Röle sisteminin, gerektiği durumlarda doğru bir şekilde çalışma derecesi Test edilmesi kolay ‘Security’ Röle sisteminin, gerekmediği durumlarda hatalı çalışmama derecesi Test edilmesi pek mümkün değil. Çünkü, sonsuz çeşit olası geçici (transient) durum söz konusu olabilir Genel olarak; iki ilkeden birinin derecesi artarken diğeri azalır. Reliability has two aspects, dependability and security. Dependability is defined as ‘‘the degree of certainty that a relay or relay system will operate correctly’’ (IEEE C 37.2). Security ‘‘relates to the degree of certainty that a relay or relay system will not operate incorrectly’’ (IEEE C 37.2). In other words, dependability indicates the ability of the protection system to perform correctly when required, whereas security is its ability to avoid unnecessary operation during normal day-after-day operation, and faults and problems outside the designated zone of operation. the protection must be secure (not operate on tolerable transients), yet dependable (operate on intolerable transients and permanent faults). Dependability is easy to ascertain by testing the protection system to assure that it will operate as intended when the operating thresholds are exceeded. Security is more difficult to ascertain. There can be almost an infinite variety of transients that might upset the protective system, and predetermination of all these possibilities is difficult or impossible. As a generality, enhancing security tends to decrease the dependability, and vice versa. EES

30 Seçicilik (Selectivity)
Röle koordinasyonu olarak da bilinir 2 ve 3 nolu rölelerin ani, 2 nolu rölenin artçısı konumunda (bu arıza için) olan 1 nolu rölenin ise gecikmeli olarak açacak şekilde ayarlanması gerekir 2 nolu rölenin arızayı zamanında temizlemesi halinde 1 nolu rölenin çalışmaması istenir Selectivity (also known as relay coordination) is the process of applying and setting the protective relays that overreach other relays such that they operate as fast as possible within their primary zone, but have delayed operation in their backup zone. Operation of the backup protection is incorrect and undesirable unless the primary protection of that area fails to clear the fault. EES

31 Hız Arıza en kısa zamanda temizlenmeli. Ancak genelde, hız arttıkça rölelerin yanlış çalışma olasılığı da artar. Arıza temizlenme süresi (İletim sistemi) Röle çalışma zamanı: < 50 ms Kesici çalışma zamanı: ms Toplam (röle+kesici): ms Dağıtım sisteminde, zaman koordinasyonu gerekliliği nedeniyle röle çalışma zamanı genelde daha yavaştır 0,2-1,5 sn Röle hızı; özellikle, güç sistemi kararlılık (stabilite) açısından hassas bölgede olduğu zaman önemlidir. Arızanın daha hızlı temizlenmesi, generatörlerin senkronizmden ayrılma ihtimalini, dolayısıyla sistem kararlılığının bozulma ihtimalini azaltır. Obviously, it is desirable that the protection isolates a trouble zone as rapidly as possible. Zero-time or very high speed protection, although inherently desirable, may result in an increased number of undesired operations. As a broad generality, the faster the operation, the higher the probability of incorrect operation. A high-speed relay is one that operates in less than 50 msec (three cycles on a 60 Hz basis) Modern high-speed circuit breakers operate in the range of 17–50 msec; others operate at less than 83 msec Thus, the total clearing time (relays plus breaker) typically ranges from approximately 35–130 msec In the lower-voltage systems, in which time-coordination is required between protective relays, relay-operating times generally will be slower; typically on the order of 0.2–1.5 sec for the primary zone. Relay speed is especially important when the protected facility exists in a stability sensitive area of the power system network. Faster fault clearing reduces the amount that generators can accelerate during the fault and, therefore, improves stability margins. EES

32 Rölelerin Sınıflandırılması
Fonksiyonuna göre Koruyucu (protective) Düzenleyici (regulating) Trafo kademe değiştiricilerinde ve generatör gerilim regülatörlerinde gerilim seviyesinin ayarlanmasında kullanılan röleler Tekrar kapama, senkronizasyon röleleri (reclosing, synchronism check, synchronizing) İzleme (monitoring) Alarm üniteleri Giriş tipine göre Akım, gerilim, güç, frekans, sıcaklık Çalışma prensibine göre Elektromekanik, elektronik, dijital Performans karakteristiğine göre Mesafe, aşırı akım, yönlü aşırı akım, ters zamanlı, sabit zamanlı, toprak, düşük/yüksek gerilim vs. There are five basic functional types: (1) protective, (2) regulating, (3) reclosing, synchronism check, and synchronizing, (4) monitoring, and (5) auxiliary. PROTECTIVE RELAYS For the most part, the relays discussed are separate devices that are connected to the power system through CT and VTs from the highest system voltage (765 kV, at present) down to service levels of 480 V. In general, distribution equipment below 480 V is protected by fuses or protection devices that are integral with the equipment. REGULATING RELAYS Regulating relays are associated with tap changers on transformers and on voltage regulators of generating equipment to control the voltage levels with varying loads. RECLOSING, SYNCHRONISM CHECK, AND SYNCHRONIZING RELAYS Relays of this type are used in energizing or restoring lines to services after an outage, and in interconnecting preenergized parts of systems. MONITORING RELAYS Monitoring relays are used to verify conditions in the power system or in the protective system. In general, alarm units serve as monitoring functions. AUXILIARY R ELAYS Auxiliary units are used throughout a protective system for a variety of purposes. Generally, there are two categories: contact multiplication and circuit isolation. OTHER RELAY CLASSIFICATIONS Protective relays classified by input are known as current, voltage, power, frequency, and temperature relays. Those classified by operating principle include electromechanical, solid-state, digital, percentage differential, multirestraint, and product units. Those classified by performance characteristics are known as distance, reactance, directional overcurrent, inverse time, phase, ground, definite, high-speed, slow-speed, phase comparison, overcurrent, undervoltage, overvoltage, etc. EES

33 Röle Uygulama Prensipleri
The power system is divided into protection zones defined by the equipment and the available circuit breakers. Six categories of protection zones are possible in each power system: (1) generators and generator–transformer units, (2) transformers, (3) buses, (4) lines (transmission, subtransmission, and distribution), (5) utilization equipment (motors, static loads, or other), and (6) capacitor or reactor banks (when separately protected). EES

34 The protection of each zone normally includes relays that can provide backup for the relays
protecting the adjacent equipment. The protection in each zone should overlap that in the adjacent zone; otherwise, a primary protection void would occur between the protection zones. This overlap is accomplished by the location of the CTs—the key sources of power system information for the relays. Fortunately, the area of exposure is quite small, and the possibility of faults is low. Without this overlap, primary protection for the area between the CTs would not exist, so this overlap is standard practice in all applications. EES