X. Z. Dong

Developments of transient and integrated protection for power system

The paper reviews the concept and development of the transient based protection and integrated protection for power systems. A number of new protection schemes with features of transient based and integrated protections are outlined. A new transient based integrated protection scheme for the protection of distribution system plant as well as distribution network as a whole using the transient polarity comparison technique is described. The scheme is based on the detection of fault generated transient current signals from all locations of the protected network. Comparison of the signal polarities obtained provides an indication of the actual faulted section. Like other transient based protection schemes, it is insensitive to the fault type, the fault inception angle, the fault path resistance and the line loading. In addition, it also has new features of integrated protection.

An integrated protection scheme for power line systems

This paper presents an integrated relay and its associated protection scheme for power line systems. The concept of integrated protection is firstly introduced, in which a centralized protection system or relay provides the protection for multiple power plants or a substation. A novel integrated protection relay based on a combination of a number of protection principles is described. In the proposed scheme, the specially designed protection relays are installed at each substation of a network and are responsible for the protection of every line section connected to the substation busbar. The combined algorithms with multiple settings are implemented into the relay to cover all the protected line sections. Simulation studies show that the proposed protection scheme is able to produce desirable performance and may offer many advantages over the existing one and great potential for future applications.

Combined Positional and Boundary Protection for Transmission Lines

This paper presents a novel relay for power transmission line systems, which is based on a combination of positional and boundary protection principle. The relay installed at a substation is responsible for the protection of the transmission lines associated with the substation. The relay is able to offer fast trip for any fault on its protected line sections without the need for communication link. The paper presents a detailed description to the basic principle, algorithm and design of the combined positional and boundary protection relay.

Integrated positional protection of transmission systems using Global Positioning System

This paper presents a new technique for the protection of power transmission systems by using the global positioning system (GPS) and fault generated transients, the integrated positional protection technique. The technique is based on the detection and processing of fault generated high frequency transient signals, in which a centralized protection relay provides the protection of multiple transmission lines. A specially designed integrated positional protection relay, which contains a fault transient detection system together with a substation communication network, is connected to the power line through the high voltage coupling capacitors of the CVT. The relay detects the fault generated high frequency voltage transient signals and records the time instant corresponding to when the initial travelling wave generated by the fault arrives at that busbar. The communication unit is used to transmit and receive coded digital signals of the local information to and from the associated relay(s) in the system. At each substation, the relays determine the location of the fault by comparing the GPS time stamps measured locally with those received from the adjacent substations. Extensive simulation studies presented in the paper demonstrate the feasibility of the scheme.

Transient Polarity Comparison for Integrated Protection of Distribution Network

This paper presents a novel integrated protection scheme for distribution networks using the transient polarity directional comparison technique. The technique is based on the detection and processing of fault generated transient current signals, in which specially designed protection relays are installed at each substation of a distribution network. The transient detection unit of the relay detects the faulted generated transient current signals. The transient polarity identification algorithm is then applied to the signals to identify the polarity of the signal detected. The direction of a fault is determined by comparison of the polarity of the signals derived from all the line sections connected to the substation. The actual faulted section is identified by processing the directional information from various substations. Simulation results presented in the paper demonstrate the feasibility of the scheme.

Integrated protection of distribution lines using transient comparison technique

This paper presents a novel integrated protection scheme for distribution lines based on Transient Polarity Comparison technique. In the proposed scheme, the specially designed interface units are installed at each substation and connected to the CTs on every line associated to the busbar. The unit converts the measured signals to optical format and sends to the central protection relay through a substation communication network, which is interfaced to all the interface units in the substation. A central protection relay receives measured currents from all locations in the substation and extracts the fault generated transient current signals. The super-imposed components containing in the transient signals captured from each relay are then extracted and the polarities of the signals derived. The polarity of the signals is then sent over to other end(s) of the protected line section(s). The comparison of the polarities of the signals from the line ends will determine whether a fault is inside in a protected network. Simulation results presented in the paper confirm the feasibility of the scheme.

A new integrated protection scheme for distributed generation systems

This paper presents a new integrated protection relay and its associated scheme for distributed generation systems. In the scheme, an integrated relay is responsible for the protection of both line sections associated with the substation bus. Based on conventional directional overcurrent protection technique, the basic principle of the new relay is to determine whether a fault is on the protected line section or not by detecting the operation of the remote circuit breaker on the protected line section, subsequently accelerated operation can be achieved. In addition to the conventional overcurrent protection, the relay developed consists of a number of new protection functions: the directional under voltage; the accelerated overcurrent and the accelerated directional under voltage protection. The paper presents the simulation results with respect to typical distributed generation systems. Results show that the relay and its associated protection scheme are able to not only significantly increase the speed of response of the conventional time grading based protection scheme for distributed generation system, but also provide features of integrated protection.

Life cycle assessment of energy consumption and CO 2 emission for transmission system

This paper presents a detailed study process of life cycle energy consumption and CO2 emission for transmission system. An assessment framework that consists of six stages is established, within which the energy consumption and CO2 emission contributions from all life cycle chains are considered. A typical 500kV single-circuit AC transmission system in China is taken for instance to illustrate the assessment process of the transmission system over its lifetime. The total energy transmission and CO2 emission reduction benefit of the transmission system is defined, calculated, and compared to the total energy consumption and corresponding CO2 emission over its lifetime. The resulting energy payback ratio (EPR) and CO2 emission reduction benefit can provide useful information for the cost-benefit comparison of different transmission technologies or planning schemes.

A positional polarity comparison relay utilizing global positioning system

This paper presents a new relay for the protection of power transmission systems by using the Global Positioning System (GPS) and the transient Polarity Comparison techniques, the Positional Polarity Comparison Relay. A specially designed protection relay detects the fault generated high frequency current transient signals and records the polarity of the transient signal and the time instant corresponding to when the initial travelling wave generated by the fault arrives at that busbar. A communication unit is used to transmit and receive coded digital signals of the local information to and from the associated relay(s) in the system. At each substation, the relays determine the location of the fault by comparing the polarity and the GPS time stamps measured locally with those received from the adjacent substations. Simulation studies presented in the paper demonstrate the feasibility of the scheme.