Power System Protection Part - 1 Dr.Prof.Mohammed Tawfeeq 21 Power System protection Dr. Mohamad Tawfeeq Types of Relays The main types of protective relays are summaries in the following diagram: Attracted Armature Solid Computerized State Digital Relays Plunger Type Magnetic Induction line differential relay sel-311l sel te7l-p relay control test switch its-2 differential protection and automation system schweitzer va engineering laboratories current & potential test switch 1 vc ia. 1b [b. jc 187l.p control test s'mtch PDF Tools Share Summary Despite having several modern transformer protection schemes, the protection engineer prefers the universally adopted unit-type differential protection scheme for the current transformer (CT) because of its functional flexibility. straint method. In a word, the transformer differential protection of transformer T. 2 . will not mal-operate when T. 2. operates with load and CT. 1. is saturated. According to analysis above, parallel sympathetic in-rush has a few effect on differential relay whatever the transformer operating with load or not. 4. Effect of Series Sympathetic Differential protection/Backupfunction A 87 T G M L Differential protection transformer, autotransformer, generator, motor, Small busbur, short line 49 Overload protection for one winding 86 Lockoutfunction 50/51 Time-overcurrent protection TOC phase: I>, I>>, I p, (inrushstabilization) The aim of this paper is to extend a hybrid protection plan for Power Transformer (PT) based on MRA-KSIR-SSVM. This paper offers a new scheme for protection of power transformers to distinguish internal faults from inrush currents. Some significant characteristics of differential currents in the real PT operating circumstances are extracted. Power System Protection Part - VII Dr.Prof.Mohammed Tawfeeq Al-Zuhairi 321 Differential Protection Differential protection is the best technique in protection. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers (C.T.s). If the net difference equal zero, it means no fault exist. This system is operating in Multiwinding transformer protection Provide current differential protection for up to five windings with an adaptive-slope percentage restraint for transformers at power plants, transmission substations, distribution substations, and industrial plants. The remaining three-phase current inputs can provide feeder backup protection. Transformer differential protection is simple in concept and the primary means for protecting power transformers. A transformer differential relay compares current entering the transformer to current leaving the transformer. The phasor sum of the currents is the operate (or difference) current. Page 3 of 17 Power Systems Protection To compare both currents, the ends of the CTs are joined together and across the bridged CT lines, there is a differential relay. The differential behaves as such: 1. The current coming in and out on the ends of the CTs cancels out. Therefore no current flows in the differential relay element. 2. The current coming in and out on the ends of the CTs does protection to the differential relays of generators and to the line relays of network Relay must be able to operate even when the fault With power transformer with tap change, at rated