Grounding transformer applications and associated protectionschemes

The use of grounding transformers on three-phase ungrounded governmental, industrial, and commercial distribution systems is addressed. Ground-fault protection schemes that provide selective and reasonably fast tripping are often incorporated with these grounding transformers. The authors first review the state of the art of grounding transformers to assist electric power systems engineers in the proper understanding of the use and applications of these devices and then discuss two governmental system case studies illustrating improperly applied grounding transformers and/or associated ground-fault protection systems. In addition, they describe remedial actions taken to correct these deficiencies. The objective in presenting improper grounding transformer applications is to highlight protection concerns that are often ignored. It is stressed that a single grounding transformer is not adequate for use with a multibus configuration. A unique protection scheme for use on a multibus arrangement is presented     

Feasibility of adaptive distribution protection system usingcomputer overcurrent relaying concept

The technical feasibility and economic viability of an adaptive distribution protection system (ADPS) using a computer overcurrent relaying concept are examined. Computer overcurrent relays installed on each of the feeders and tap locations (where the reclosers are installed) continuously monitor and analyze line currents and voltages and interface with the substation and system computer to provide faster and improved protection of all distribution system components and optimized control of loads, capacitors, and reclosing sequences of associated circuit breakers and reclosers. It is concluded that, since the benefit-to-cost ratio of ADPS varies from 4.3 to 33, manufacturers will be motivated to develop the ADPS fully and utilities will be encouraged to install these systems to improve reliability, safety, and performance of the distribution system     

A new hybrid filter to dampen resonances and compensate harmoniccurrents in industrial power systems with power factor correctionequipment

A new hybrid power filter is presented for three phase industrial power systems which include passive power factor correction equipment (PFC). The hybrid filter damps resonances occurring between line impedances and the PFC. In addition, the hybrid filter topology can be used to compensate harmonic currents. The capacitors of the PFC, which generally cause resonant problems in harmonic distorted networks, can be used for passive filtering by connecting a transformer with a low magnetizing inductance in series hence creating a single harmonic trap. The primary side of the transformer is connected to a low VA-rated three-phase current controlled inverter which builds the active part of the hybrid topology. Simulation results and experimental results are presented verifying the damping and harmonic compensation performance of the proposed topology     

Multicell circuit model for high-power thyristor-type semiconductor devices

New device models for circuit simulation are developed for high-power thyristor-type devices, such as gate-turn-off thyristors, integrated gate-commutated thyristors, and MOS turn-off thyristors. These models are based on semiconductor physics, which guarantees a wide range of validity. In particular, the proposed models are based on the lumped charge approach. Coupled electrical and thermal behavior is implemented to allow transient thermal simulations. To account for the nonuniform current distribution during turn-off, several of these single-cell models are connected in parallel to simulate a complete device. Simulation results are compared with measurements.