Richard Hunt

Current Transformer Saturation Effects on Coordinating Time Interval

The primary function of protective devices is to remove faulted equipment from the electrical system. It is typically very advantageous for these devices to isolate as small of a section of the electrical system as possible. Overcurrent protection is the most common protection function used, as faulted equipment typically results in a large short circuit current. When overcurrent protection is employed, the overcurrent protection is typically coordinated with time so that the devices closest to the fault will operate and isolate only that section of equipment before devices farther from the fault operate and isolate larger pieces of the system. These time overcurrent devices must also be coordinated with damage curves for equipment such as buses and cables to clear the fault before the overcurrent can cause damage to the equipment. This concept of time coordination of overcurrent is well understood, and there are general guidelines applied to account for measurement error and other inaccuracies. The reduced signal levels provided to relays due to current transformer (CT) saturation are normally not considered during coordination studies. This reduced signal level will result in slower than desired operation of protective relays. Feeder relays could trip slower than upstream devices, isolating more of the power system than intended, or could allow primary equipment to be damaged before tripping. This paper will review the concept of coordinating time overcurrent relays and then discuss the concept of loss of coordination associated with CT saturation. This paper will model CT saturation from actual installations using the IEEE Power System Relaying Committee CT Saturation Calculator tool. This model data will be used to estimate the performance of protective relays. This paper will discuss methods to improve the coordination of overcurrent relays when faced with significant CT saturation.

Application of Digital Radio for Distribution Pilot Protection and Other Applications

Networked distribution lines, sub-transmission lines, and industrial facility incoming supply lines have always presented an interesting protection challenge. As the number of distributed generators and cogeneration facilities increase, directional overcurrent protection and distance protection may not be selective enough for reliable protection without the implementation of pilot protection schemes such as permissive over-reaching transfer trip and directional comparison blocking. Pilot-wire relaying has been the traditional solution at distribution voltages. Pilot-wire relaying sends a voltage signal between relays at each end of the line across copper wire. These voltages are used for differential protection. This scheme was used because of availability of copper pairs from the phone company and/or the low cost of installation of the communications wire. Today, however, copper pairs are no longer available from the phone company and the cost of installing new copper is increasingly expensive. When fiber access is available (typically at a premium cost), communication based digital protection solutions such as current differential relays and directional overcurrent relays in a pilot protection scheme are used. The modern challenge is a method to provide digital communications for pilot protection that is reliable and affordable. Digital radio is an inexpensive method to provide digital communications for pilot protection at the distribution level. Digital radio has the ability to send permissive, blocking, and transfer trip signals over short to medium distances. Relay to relay messaging protocols have now become standardized through the IEC 61850 GOOSE profile and can provide not only protection information but also metering, monitoring, and control. Practical concerns for the protection engineer include the reliability, security, and latency of digital radio communications, as this has a strong influence on selecting and setting the protection scheme. To address these concerns, this paper presents actual field data for radio signal reliability and latency. Based on this actual data, some recommendations for pilot protection schemes at the distribution level are presented. In addition, the paper also reviews the application requirements for digital radio, including design for redundancy, path concerns, antenna selection and site evaluation, and use of licensed and spread spectrum radios. Since modern digital radio also support higher communications bandwidth, the paper will explore some other innovative applications that can operate in concert with pilot protection communications.

Current transformer saturation effects on coordinating time interval

The primary function of protective devices is to remove faulted equipment from the electrical system. It is typically very advantageous for these devices to isolate as small of a section of the electrical system as possible. Overcurrent protection is the most common protection function used, as faulted equipment typically results in a large short circuit current. When overcurrent protection is employed, the overcurrent protection is typically coordinated with time so that the devices closest to the fault will operate and isolate only that section of equipment before devices farther from the fault operate and isolate larger pieces of the system. These time overcurrent devices must also be coordinated with damage curves for equipment such as buses and cables to clear the fault before the overcurrent can cause damage to the equipment. This concept of time coordination of overcurrent is well understood, and there are general guidelines applied to account for measurement error and other inaccuracies. The reduced signal levels provided to relays due to current transformer (CT) saturation are normally not considered during coordination studies. This reduced signal level will result in slower than desired operation of protective relays. Feeder relays could trip slower than upstream devices, isolating more of the power system than intended, or could allow primary equipment to be damaged before tripping. This paper will review the concept of coordinating time overcurrent relays and then discuss the concept of loss of coordination associated with CT saturation. This paper will model CT saturation from actual installations using the IEEE Power System Relaying Committee CT Saturation Calculator tool. This model data will be used to estimate the performance of protective relays. This paper will discuss methods to improve the coordination of overcurrent relays when faced with significant CT saturation.

Application of digital radio for distribution pilot protection

The traditional solutions for protecting networked distribution lines, sub-transmission lines, and industrial facility incoming supply lines use some form of pilot protection. A significant challenge for pilot protection, especially in retrofit situations, is the cost of installing pilot communications channels. Digital radio is an inexpensive method to provide digital communications for pilot protection at the distribution level. Digital radio has the ability to send permissive, blocking, and transfer trip signals over short to medium distances. Relay to relay messaging protocols have now become standardized through the IEC61850 GOOSE profile and can provide not only protection information but also metering, monitoring, and control.

Principles in Motor Protection

This article discusses the fundamentals of motor protection principle. A brief overview of the existing protection philosophy for asynchronous motors is reviewed with a special consideration of thermal protection of motors. Because large synchronous motors are used in the cement industry, a review of additional functions required for protection and control of synchronous motors is given.

Protecting Remotely Located Motors: Application Issues and Solutions to the Technical Challenges

The basic goals of motor protection are allowing the motor to operate as close to thermal limits as possible and isolating the motor when actual failures occur. The basic principles for performing this protection are well known. In most installations, the motor is located close to the protective relay and interrupting device, be it a contactor, starter, or circuit breaker. However, the motor may sometimes be located remotely from the protective relay due to the needs of the physical process or due to operational safety requirements. Distances of 1,0002,000 ft between the motor location and the protective relay are common. This large distance does not change the motor protection used, but it does require careful application engineering to ensure reliable protection performance.

Fully utilizing intelligent electronic devices capability to reduce wiring in cement industry distribution substations

Each wired termination in a substation represents a cost associated with engineering, installing and testing that wired point. These costs include the obvious financial labor costs, but also include intangible costs such as installation and commissioning time, potential for human error, panel space, increased resistive burden in circuits, and larger raceways. Additionally, each wired termination represents stranded engineering time that is used to design these terminations rather than allowing the engineering staff to solve problems.

Fully utilizing the intelligent electronic device capability to reduce wiring in rural electric distribution substations

Each wired termination in a substation represents a cost associated with engineering, installing and testing that wired point. These costs include the obvious financial labor costs, but also include intangible costs such as installation and commissioning time, potential for human error, panel space, increased resistive burden in circuits, and larger raceways. Additionally, each wired termination represents stranded engineering time that is used design these terminations rather than allowing the engineering staff to solve problems.

Fully Utilizing the Intelligent Electronic Device Capability to Reduce Wiring in Industrial Electric Distribution Substations

Each wired termination in a substation represents a cost associated with engineering, installing and testing that wired point. These costs include the obvious financial labor costs, but also include intangible costs such as installation and commissioning time, potential for human error, panel space, increased resistive burden in circuits, and larger raceways. Additionally, each wired termination represents stranded engineering time that is used design these terminations rather than allowing the engineering staff to solve problems. Most industrial electric distribution wiring design practices are taken for granted without thought as to the true cost and reliability of the practice and whether or not the function can be implemented with less wiring. Some standard Industrial electric distribution practices have evolved that seek to minimize wiring. An example of this practice is the use of multifunction microprocessor based relays that can logically develop a trip bus from protective elements rather than having to wire individual elements to create the same trip bus. This paper seeks to expose some of the hidden financial costs and reliability costs associated with copper process wiring. Additionally this paper will discuss ways in which modern Intelligent Electronic Devices (IEDs) can be fully implemented to further reduce wiring. The cost and reliability benefits associated with the reduced wiring will be discussed and quantified. Some of the solutions to be addressed include the use of breaker IEDs as an interface for breaker control, IED to DCS communications, IEC 61850 IED to IED communications, internal lockout Relays, IED pushbutton control, and process bus. Each of these solutions are currently available in todays market place and have varying degrees of acceptance within the industry. The benefits and liabilities of each solution using traditional IED implementation versus maximized IED implementation shall be discussed.

Fully utilizing the IED capability to reduce wiring

Each wired termination in a substation represents a cost associated with engineering, installing and testing that wired point. These costs include the obvious financial labor costs, but also include intangible costs such as installation and commissioning time, potential for human error, panel space, increased resistive burden in circuits, and larger raceways. Additionally, each wired termination represents stranded engineering time that is used to design these terminations rather than allowing the engineering staff to solve problems. This paper seeks to expose some of the hidden financial costs and reliability costs associated with copper process wiring. Additionally this paper will discuss ways in which modern IEDs can be fully implemented to further reduce wiring. The cost and reliability benefits associated with the reduced wiring will be discussed and quantified. Some of the solutions to be addressed include the use of breaker IEDs as an interface for breaker control, IED to SCADA communications, IED to IED communications, internal lockout Relays, IED pushbutton control, and process bus. Each of these solutions are currently available in todays market place and have varying degrees of acceptance within the industry. The benefits and liabilities of each solution using traditional IED implementation versus maximized IED implementation shall be discussed.