Ljubomir A. Kojovic

Innovative Differential Protection of Power Transformers Using Low Energy Current Sensors

Traditional differential protection systems are applied on large power transformers using current transformers (CTs). However, because of high secondary currents (often exceeding 100 kARMS), differential protection systems for electric arc furnace transformers have not been applied in the past due to the lack of commercially available CTs. This paper will present differential protection systems that have been in use for many years using Rogowski coil current sensors. These protection systems use high-precision printed circuit board Rogowski coil current sensors. This paper reviews the characteristics, designs, and application of these Rogowski coil sensors for advanced protection, control, and metering systems with new multifunction relays. This paper compares performance characteristics of new solutions based on Rogowski coil sensors with the conventional differential protection systems based on CTs, demonstrating that the new systems do not have the limitations of conventional technology. Operating experience from several site applications is included.

Innovative Differential Protection of Power Transformers Using Low-Energy Current Sensors

Traditional differential protection systems are applied on large power transformers using current transformers (CTs). However, because of high secondary currents (often exceeding 100 kARMS), differential protection systems for electric arc furnace transformers have not been applied in the past due to the lack of commercially available CTs. This paper will present differential protection systems that have been in use for many years using Rogowski coil current sensors. These protection systems use high-precision printed circuit board Rogowski coil current sensors. This paper reviews the characteristics, designs, and application of these Rogowski coil sensors for advanced protection, control, and metering systems with new multifunction relays. This paper compares performance characteristics of new solutions based on Rogowski coil sensors with the conventional differential protection systems based on CTs, demonstrating that the new systems do not have the limitations of conventional technology. Operating experience from several site applications is included.

Prevention of underground cable splice failures

The failure of underground medium-voltage cable splices produce many undesired events. When water invades an underground cable splice, a series of self-clearing faults ensue. These self-clearing faults continue until complete splice failure occurs. This paper discusses the nature of medium-voltage cable splice failure in underground installations. In addition, a new methodology is described which will predict the occurrence of cable splice failures before they happen.

Comparative characteristics of iron-core current transformers and Rogowski Coils for applications for protective relaying purposes

This paper compares the operating characteristics of non-conventional current sensors, Rogowski Coils, and conventional iron-core current transformers for protective relaying applications.

Application of real-time power system simulators for testing protective relay system operational characteristics

Proper protective relay operation is essential for power system reliability. System transient conditions and instrument transformer errors are major causes for relay misoperation. Therefore, relays tests need to include both transient simulation and instrument transformer models. This paper presents two techniques for protective system testing: real-time power system simulator (RTPSS) and playback system. Both systems can simulate transient testing as well as instrument transformers.

Coiled for protection

In this article, the authors describe an advanced protection system that incorporates Rogowski coil current sensors and multifunction relays that provide primary and backup power system protection.

Innovative Differential Protection of EAF Electrical Systems Using Low Energy Current Sensors

This companion paper to that presented at the 2009 IEEE IAS Annual Meeting describes new differential protection solutions for electric arc furnace (EAF) power systems that use Rogowski Coils as current sensors. These novel solutions provide multiple protection zones, covering the entire EAF electric supply system. The protection philosophy includes multiple differential zones of protection such as cables serving the EAF vault, series reactors, EAF transformers (including all power apparatus in the protection zones), and busbars.