AUTO_RECLOSING PROTECTION CONSIDERATIONS WITH TAPPED TRANSFORMER BANK NATHIM SHEYT RASOOL Dr. M. F. AL-KABABJIE MINISTRY OF ELECT., IRAQI NORTH REGION GRID ENGINEERING COLLEGE, UNIV. OF MOSUL nathim_rasol2000@yahoo.com al_kababjie@yahoo.com ABSTRACT The paper analyzes High speed Auto_Reclosing Protection operation considerations with setting coordination of High Voltage ( 132 kv ) Transmission Line HVTL Protection, which takes into account the effects of Tapped Transformer Bank TTB (Mobil Sub – Station) on the reach of Distance Relays at the two terminals of the TL. Those Mobile S/S s are used due to abnormal circumstances, like those in the country now a day. As a result the infeed current from the next terminal of the TL, shrinks the reach of the Relay. A case study taken from the Ring of Mosul city. Index Terms—Auto_Reclosing Relay, Transmission Line Protection, Distance Relay setting, Single-phase earth fault, Tapped Transformer Bank. 1. INTRODUCTION Auto_Reclosing protective Relays are hardware devices equipped with all HV Over Head TLs. They are responsible for restoring The TL after transient faults. Hence, more than 80% of the transmission line faults are transient in nature. Figure (1) shows the lay out of OHTL bay in Iraqi transmission system. Distance measuring protection relays are serving the abnormal conditions in the power system and tripping the circuit breakers to isolate the faulty section as soon as possible, in order to insure stability and dependability of the supplying power to the consumers. The effect of faults can be minimized by proper coordination of protective relays setting the operating parameters of such relays is a knowledge – intensive problem that very often requires the experience of senior relay engineer [1] . It also involves comprehensive and repetitive routine work dealing with a large database, tedious and time-consuming tasks [2] . The complexity of this problem is compounded when various relay types from different manufactures are involved, and this is almost all power systems, including Iraqi one. Moreover, the increasing complexity of modern power systems adds an extra burden to the relay setting process. Distance relays are the most difficult to set, because they employ non-unit measurements and require a multiplicity of setting parameters. The initiation of Figure (1): Line configuration of the switchgear & protection location for an OHTL Bay. Auto_Reclosing command is with the first zone-tripping signal and with all types of faults. The setting problem is non-algorithmic and knowledge intensive and it lends itself quite naturally to the Expert System solution [3] . 2. High Speed Auto_Reclosing Relay Statistically, the majority of system faults are of a transient nature so that once the fault has been cleared by the protection, the faulted circuit can be re-energized successfully with a likelihood of minimal disturbance to the rest of the system [4] . Auto Reclosing is commonly applied to transmission systems. The number experienced in any given year depends heavily on weather conditions, with high fault rates in a 'bad' year of lightning storms, snowstorms. Kin & fog and pollution conditions, and gales. Particularly severe weather conditions tend to result in exceptionally high fault rates over just a few hours or days, e.g. a severe lightening storm may result in several tens in of faults per hour affecting large parts of the system as it moves across the country. In an average year, approximately 80%, of all system faults occur on overhead line circuits, 7%, on generator units, 6% on transformers, and 2%, on bus bars, the 6th Jordanian International Electrical& Electronics Engineering Conference 2006