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Transformers are critical assets of power system network and their adequate protection is a matter of vital importance. Modern protection relays are usually defined as intelligent electronic device (IED) s, and they provide huge flexibility and enhanced protection features to assure correct operation of the equipment. Transformer protection IEDs are equipped with key features such as differential and restricted earth fault (REF) protection along with several other functionalities as per the guidelines of IEEE C37.91.

In this paper, protection of a complicated bus arrangement with dual bus coupler and bus sectionalizer using low impedance differential protection applicable for very high voltages like 220kV and 400kV is discussed. In many power generation stations, several operational procedures are implemented to utilize the transfer bus as main bus and to facilitate maintenance of circuit breakers and current transformers (in each section) without shutting down the bay(s). Owing to this fact, the complications in operational philosophy have thrown challenges for the bus bar protection implementation.

Energization of a transformer results in sudden flow of current which is an effect of core magnetization. This current will be dominated by the presence of 2nd harmonic, which in turn is used to segregate fault and inrush current, thus guaranteeing proper operation of the relay. This additional security in the relay sometimes obstructs or delays differential protection in a specific scenario, when the 2nd harmonic content was present during a genuine fault. This kind of scenario can result in isolation of the transformer by Buchholz and pressure release valve (PRV) protection, which is acted when fault creates more damage in transformer. 

Transformers are critical assets of power system network and their adequate protection is a matter of vital importance. Modern protection relays are usually defined as intelligent electronic device (IED) s, and they provide huge flexibility and enhanced protection features to assure correct operation of the equipment. Transformer protection IEDs are equipped with key features such as differential and restricted earth fault (REF) protection along with several other functionalities as per the guidelines of IEEE C37.91. These functions are available with enhanced facilities such that it can incorporate the difference in phase angle based on vector rotation, ratio correction of current transformers used, interposing CT corrections etc… The increase in flexibility of the IED has also increased the complexity of programming it where a trivial error in the configuration will result in unwarranted operation causing loss of power and reduction of equipment life. 

In this paper, protection of a complicated bus arrangement with dual bus coupler and bus sectionalizer using low impedance differential protection applicable for very high voltages like 220kV and 400kV is discussed. In many power generation stations, several operational procedures are implemented to utilize the transfer bus as main bus and to facilitate maintenance of circuit breakers and current transformers (in each section) without shutting down the bay(s).

In this paper, different methods of inhibiting the unwarranted operation of busbar protection relay during the CB testing is discussed with appropriate logics. This paper also focuses on providing proper security for bus faults by implementing relay logics to ensure minimal human intervention (prevention of bus bar blocking, throwing of knife switches for CT secondary shorting etc…) and acceptable modifications to the current protection scheme layout. Various methods are recommended that can be incorporated based on the suitability of the respective system condition. The discussed methods are developed in Intelligent Electronic Devices (IED)s using the advanced logics and algorithms. 

Each issue of Electrical Tester has a range of hand-picked industry articles for high-voltage electrical engineers working on utilities.

VLF Sine Wave 62 Firmware

Grounding and ground testing are topics and practices most widely recognized by familiar terms and organizations like Fall of Potential Method, 62 Percent Rule, IEEE and NETA standards and practices, and the National Electric Code® (NEC®). These and other significant contributions to the body of knowledge form the foundation of the subject and its implementation in practice.

Grounding electrodes are typically buried metal objects; rods, interconnected arrays of rods, plates, grids, and various other designs aimed at putting a sufficient amount of metal in contact with the soil so as to safely and efficiently divert unwanted fault currents out of the electrical system and out of the protected facility. Upon construction, there is generally a ground resistance specification that is not to be exceeded. A performance test is run to assure that the system meets spec.