Pilot-wire Differential Protection Research Articles

Enhanced real time coordination of distance and user defined over current relays

Faults on the transmission lines are primarily cleared by pilot wire differential protection as well as from zone-1 and zone-2 of distance relays, depending upon their location on the lines. If the main distance relays fails to operate, then standard time inverse directional over current (DOCR) relays are set as backup protection in coordination with main distance relays. The desired coordination time margins between main distance relays and backup standard time inverse over current relays should be maintained at start of zone-1 and zone-2 of distance relays. Coordination of fixed zone-2 setting of distance relays with standard time inverse relays results in poor tripping time of backup DOCR.In this research article, zone -2 setting of distance relays are made adaptive, so that minimum coordination time margin is maintained for complete reach of distance relays. User defined time inverse over current relays are proposed in conjugation with flexible feature of zone-2 setting of distance for improving the operating time of backup DOCRs. The performance of the proposed algorithm is validated in real time simulation with hardware in loop testing of numerical distance and user defined DOCR. From hardware in loop simulation results, it is observed that the performance of the proposed combined distance &DOCR coordination algorithm is in close concurrence with simulated results. The sensitivity of proposed algorithm is checked for different phase as well as ground faults with different fault resistance and it is also observed that the proposed algorithm is highly robust for different fault conditions.

Laboratory Investigation of Using Wi-Fi Protocol for Transmission Line Differential Protection

Pilot wire differential protection is one of the most common methods for protecting short transmission lines. The conventional protection scheme has drawbacks, such as malfunction due to line disconnection and limited line length. A laboratory investigation of transmission line protection using Wireless Fidelity (Wi-Fi) communication protocol for data sharing between the relays located at the two ends of the transmission line is presented in this paper. The protection algorithm is based on current signals measured at both ends of the transmission line. The data is exchanged through the wireless communication network. The relay decision is based on data sharing obtained through wireless communication network. The suggested technique satisfies high degree of reliability and stability.

A new approach to digital current differential protection for low and medium voltage feeder circuits using a digital voice-frequency grade communications channel

A new approach to digital current differential protection is described which provides the capabilities of conventional pilot wire differential protection while using the limited data transfer capabilities of a digital data voice-frequency grade communications channel. This approach compares polyphase polarised current measurements taken at the feeder's terminals to detect faults and can trip in under two power system cycles. The algorithms decouple the measurements from the power system frequency and its waveform, and thereby have a high inherent tolerance to the complications introduced by communication channel delays and their fluctuations. For this project, the communications requirements have been limited to a full duplex 2400 bits/sec system suitable for operation over a voice-frequency grade channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discussion on “Circulating-current pilot-wire differential protection of multiended circuits”

Discussion on “Circulating-current pilot-wire differential protection of multiended circuits”

Circulating-current pilot-wire differential protection of multiended circuits

A general analysis is made of symmetrical multiended pilot-wire circuits terminated by impedances in parallel with the current sources. The fundamental-frequency-transmission characteristics of the pilot circuits are accounted for, and compensation for pilot phase shift is applied by a suitable choice of parallel impedance. A range of alternative amplitude-comparator relay characteristics is presented graphically on the basis of the complex ratio of the relaying current at any relay location to the phasor sum of relaying currents at the remaining terminations. A method is described by which the insertion of a simple network at the electrical centre of a system of symmetrical pilot circuits permits the application to multiterminal lines of schemes of protection requiring the correct termination of the pilot circuit in its characteristic impedance.

Circulating-current pilot-wire differential protection system

A circulating-current a.c. pilot-wire differential protection scheme is described in which compensation is provided for the phase shift of the fundamental-frequency signals transmitted over the pilot-wire circuit. Alternative relay characteristics are considered, with particular reference to the desirability of maintaining simultaneous tripping of circuit breakers at both ends of the protected section under all internal-fault conditions. Factors influencing the choice of preferred relay-tripping characteristics are examined, together with a means of modifying a practical pilot circuit to enable the preferred tripping characteristic to be obtained.

Differential pilot-wire protection systems using phase comparators

The paper provides a comprehensive account of the underlying theoretical basis of pilot-wire differential protection systems, in which, though the relaying signals are subjected neither to amplitude nor phase constraints in transmission through the pilot circuit, the final detection, and corresponding delineation of the protection characteristic, is achieved using phase comparators. It is shown that a wide range of characteristics is in this way realisable, and examples are given in which the stability zone of a complete 2-ended scheme is derived from compounding discontinuous linear or circular-arc sections. From this range, a composite characteristic is proposed that appears to give substantial discriminating margins, when used with conventional phase-current-summation circuits.

Pilot-wire differential protection systems

Pilot-wire differential protection systems

The fundamental characteristics of pilot-wire differential protection systems

In the design of pilot-wire protection systems the pilot circuit is usually considered to be either purely resistive or completely balanced and able to transmit information simultaneously from end to end. Characteristics are given for long practical circuits showing that these are invariably unsymmetrical owing to their heterogeneous composition, and it is shown that the change in pilot-circuit input admittance due to remote-end voltage variation gives a reliable indication of design parameters. A locus diagram is given for pilot-circuit admittance upon which the relay operating characteristics can be superimposed, giving complete design information for the protection scheme. By a change of axis this diagram can be redrawn in terms of power-system input currents to the relay system, showing the performance of the relays at both ends of the line. Consideration is given to the design of practical protection schemes using the longest pilot circuits, which are treated as completely unsymmetrical networks. The effect of the non-linearities in the voltage-limiting circuits is also considered. A design technique is illustrated which enables the protective scheme characteristics to be predicted and verified by simple tests. Practical limits and limitations inherent in the use of rented telephone-type circuits are discussed briefly, since these exert considerable influence on practical scheme design.

An Improved A-C Pilot-Wire Relay

Despite the fact that it is quite generally conceded that differential protection is the most desirable principle for line protection, yet few applications of relay systems of this type have been made until recently except for lines of very short length. The older forms of pilot-wire differential protection required three or four wires of low resistance; and even then, the systems were characterized by lack of sensitivity, and by high burden on the current transformers.

An improved A-C pilot-wire relay

Despite the fact that it is quite generally conceded that differential protection is the most desirable principle for line protection, yet few applications of relay systems of this type have been made until recently except for lines of very short length. The older forms of pilot-wire differential protection required three or four wires of low resistance; and even then, the systems were characterized by lack of sensitivity, and by high burden on the current transformers.