This article elaborates on the properly required protection and how its operation will prevent the undesired consequences to the ICG owner, the utility, and the general public. This article also discusses actions that take place when the utility supply is disrupted, creating an islanding condition and states reasons why protection required by regulatory agencies, local utilities, and documents suc...

The application of bus fault protection in industrial facilities has been primarily limited to overcurrent relays located at the upstream breaker. This does not always provide the best protection for bus faults. The protection sensitivity is limited because of the need to coordinate with other downstream overcurrent devices. This paper describes an enhanced method of applying sensitive bus fault protection using digital overcurrent relays. In addition, this method provides both downstream feeder breaker backup protection and relay backup protection.

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.

This paper reviews the principles of ground differential protection within industrial power systems and discusses the use of directional overcurrent relays in this application. Electromechanical product type relays have been the device used primarily for this application. The use of current polarized directional ground-overcurrent relays provides a novel approach in the application of ground differential protection

When paralleling generators, it is necessary to match the characteristics of the two systems as closely as possible. This is accomplished by minimizing the phase-angle difference, slip frequency and voltage difference between the two systems. Using the voltage magnitude alone to calculate this difference may not provide the expected results. When the phase angle is taken into account, the vector difference of the voltages may lead to greater values than simply using the magnitude difference. This paper discusses the application of synchronizing and introduces the concept of utilizing the voltage vector difference to ensure proper synchronizing while minimizing stress to the system.

When a fault occurs on a power system, one or more phases will experience DC offset. This DC component, which will decay dependent on the L/R time constant of the power system, can produce saturation in current transformers, as well as the input current transformers of the protective relays sensing the fault. In addition, when the fault current is interrupted, the resulting DC tail can maintain the current above the relay's pickup setting for a time dependent on the CT secondary circuit L/R time constant. This paper discusses this phenomenon and how it can affect the operation of two types of current operated relays.

Electro-mechanical (EM) relays have been used in safeguarding electrical systems since the early days of electrical power system protection. Static analog relays have been available for over 20 years and can provide multiple protective functions and tasks. They can come in single-phase or multi-phase units. Newer static digital relays utilize microprocessor technology which provides additional functionality such as communications, self diagnosis, metering, event recording, waveform capture and much more. However, advancement in technology brings the question: “Do you want all your relay eggs in one basket”? Single-phase, single-function electromechanical devices may not provide all the features, but are considered by some to provide more security and dependability. This paper discusses the advantages and disadvantages of using the latest microprocessor technology in applying protective relays in typical petroleum and chemical industry applications. Electro-mechanical, static analog and static digital relays are compared regarding features, maintainability, performance and application. The goal of this paper is to aid industrial electrical engineers to select the best application combination of relay technology and equipment for operations and maintenance personnel

The phenomenon of transformer magnetizing inrush current has been discussed in many papers throughout the years. A brief review of magnetizing inrush is given to provide the basis of need for transient testing. Previous studies have shown that inrush currents contain harmonic components of the fundamental waveform. Conventional philosophy has been to utilize the second harmonic current to provide ...

The technology of static overcurrent relays has developed very rapidly in the past few years. These developments have produced changes from electromechanical relays in the way they are applied, and further, offer many new features to provide greater utilization than possible previously. A Working Group of the Medium Voltage Subcommittee of the Power Systems Protection Committee began examining the impact of these developments several years ago. This report documents the results and describes the nature of the changes and the new areas of application. It is presented acknowledging the fact that this is really an interim report, since static relay technology is a very dynamic technology with many more innovations yet to be developed.

Differential relays are used extensively to provide protection for power transformers. Several issues must be considered in their application to ensure adequate protection. These include transformer magnetizing inrush current, relay burden and current transformer performance. The use of low ratio current transformers in high magnitude fault applications can produce distorted secondary waveforms to the relay whose performance may be directly affected. There is also a relationship between the magnetizing inrush and current transformer performance which may affect the operation of the differential relay. This paper discusses these specific applications and the testing of a transformer differential relay under conditions of saturated CTs using the Electro-Magnetic Transient Program (EMTP)

Breaker failure relaying has been generally achieved through the use of a current monitoring relay to determine whether current continues to flow into a fault after a breaker has been instructed to interrupt the circuit. If current continues to flow after a predefined period of time, the circuit breaker is considered to have failed. Steps must then be taken to trip the next set of upstream breakers in the power system to remove the faulted circuit and prevent system damage. However, with industrial power systems, this may be the utility's breakers on the feeding transmission line. Regardless, breaker failure schemes must be designed to isolate both the faulted circuit and the failed circuit breaker. This paper discusses a new and innovative method of protecting a circuit breaker from the failure described above, plus other failures that go unprotected with conventional schemes, thus providing "total" breaker failure protection.

Frequency relays are often applied on power systems either to protect generation equipment or provide load shedding capabilities. Accurate setting and operation of these relays is essential in the proper coordination of the power system equipment. Dynamic testing provides a method of assuring the proper operation of frequency relays. Along with this testing is a myriad of complexities and confusion. Dynamic tests are not always as straightforward as one might think, especially when the results are not as anticipated. The methods of testing, type of test equipment used, and the specific relay measuring techniques all play a significant role in the dynamic testing results. This paper discusses the intricacies of dynamic frequency testing along with the differences between test equipment and frequency relays and how these differences affect the testing results. A sampling of four frequency relays was tested (three solid state devices and one electro-mechanical), each using four different test sets. Results of each are discussed