GB2155285A - Pilot wire distance compensating circuit - Google Patents

Abstract

A pilot wire distance compensating circuit including a two terminal-pair network 1,2,3,4 wherein a single unified group of capacitors CR is connected between the input terminals or the output terminals, whereby it is possible to largely decrease the number of the pilotwlre distance compensating circuit capacitors and reduce the volume and cost of the apparatus compared to prior circuits having capacitors connected across both the input and the output terminals. The circuit is used in a transmission line protection system (Figure 2) to compensate for the length of a bypass wire (21) so that relays (RC, OC) responsive to currents in the transmission line to effect the bypass connection can operate independently of the wire. <IMAGE>

Description

SPECIFICATION Pilot wire distance compensating circuit The present invention relates to a transmission line protective relay by pilot relaying as a transmission line protective relaying system having a high selectivity, more particularly it relates to a pilot wire distance compensating circuitforthe pilot wire relay.

A pilot wire distance compensating circuit such as the one as shown in Figure 1 is known.

Referring to the Figure 1, reference numerals 1 and 2 denote input terminals, 3 and 4 denote output terminals, and the circuit of Figure 1 as a whole constitutes a two-terminal pair network. R1, R2 ..., RL denote resistors and C11, C12 ...., CiM and C21, C22 ..., C2M denote capacitors, wherein the capacitors are set up with the following relationships:: Clt = C21, C12 = C22, CiM = C2M Reference numeral 10 denotes an RB-changeover switch for varying the resistance RB between the input terminal 1 and the output terminal 3, 11 denotes a CR1 changeover switch for varying the capacitance CR1 between the input terminal 1 and the input terminal 2, and 12 denotes a CR2-changeover switch for varying the capacitance CR2 between the output terminal 3 and the output terminal 4.

As a pilot wire relay incorporating such a pilot wire distance compensating circuit as shown in Figure 1, one as shown in Figure 2 is in use.

Referring to Figure 2, the portion enclosed by the dotted line 20 denotes the pilot wire distance compensating circuit of Figure 1, reference numeral 21 denotes a pilot wire, 22 denotes an insulating transformer with transformation ratio of 1: N, 23 denotes a coil, 24 denotes an input transformer, 25 denotes a CT (current transformer), 26 denotes a transmission line to be protected, OC denotes an operating coil, and RC denotes a restraining coil. And, reference numeral 30 (the portion enclosed by the chain line) denotes a so called transmission circuit.

The operation will be described in the following. The pilot wire 21 in Figure 2 can be of any length and is a distributed constant circuit having a loop resistance RP Q and a line-to-line distributed capacitance CP pF.

Since the coil 23 produces resonance at a rated frequency with the line-to-line distributed capacitance CP"F and with the capacitances CRa and CR2 in the pilot wire distance compensating circuit, the transmission circuit 30 is considered to be equivalent to the rr- - circuit as shown in Figure 4. The operating principle of the pilot wire relay is that the relay is rendered operable when the following relationship is operative between the current 1oc flowing through the operating coil OC and the current IRC flowing through the restraining coil RC as a result of superposition of the currents from CT 25 at this end and the current from CT 25 at the other end: loc - ^rl > K, where a is a rate of restraint and K is a constant.

Here, it is arranged that the distance of the above pilot wire 21 can be of any length because RB, CR1, and CR2 in the pilot wire distance compensating circuit 20 are varied case by case so that the circuit constants of the equivalent circuit to the transmission circuit 30, namely, the circuit of Figure 4, may become constant regardless of the length of the distance. By this arrangement, the characteristics of the relay such as the minimum operation current at inflow end under single end infeed condition can be made constant regardless of the length of the distance.

The formulae for calculating RB, CR1, and CR2 in the conventional pilot wire distance compensating circuit as shown in Figure 1 are, when, for example, the maximum loop resistance of the pilot wire is assumed to be 1000 Q and the maximum line-to-line distributed capacitance of the same to be 2pF: RB = (1000QRP). 1 2 2 N2 = CR, CR1 = CR2 2 where (2F - C) . .N2.

CR = 2 2 Since the conventional pilot wire distance compensating circuit was constructed as above, it was necessary that the relationship CRl = CR2 is always kept and therefore it was required to provide two each of completely identical capacitors for CRl and CR2 as physical hardware constituting the compensating circuit and also to provide two changeover switches, which involved such disadvantages that the total volume of the pilot wire relay become large and the cost for the same was high.

The present invention intends to overcome the above disadvantages. Preferably the pilot wire distance compensating circuit of the invention eliminates one of CR1 and CR2 in the circuit of Figure 1 and provides a single unified circuit having a capacitance CR equal to the sum of the capacitances CR, and CR2, so that the number of parts i.e., capacitors and changeover switches, will be decreased, and thereby the volume of the pilot wire relay and the cost of the same can be reduced.

Thus a single group of capacitors and single changeover switch are located between either the input terminals or the output terminals but not both.

According to an aspect of this invention there is provided a pilot wire distance compensating circuit including a two-terminal pair network having a first input terminal, a second input terminal, a first output terminal, and a second output terminal, wherein a plurality of groups of capacitors connected between said first input terminal and said second input terminal or between said first output terminal and said second output terminal are arranged into a unified group and connected between said first input terminal and said second input terminal or between said first output terminal and said second output terminal.

Referring now to the accompanying drawings, an embodiment of the invention will be described by way of example only, with reference to the following in which: Figure lisa circuit diagram showing a conventional pilot wire distance compensating circuit; Figure 2 is a block diagram showing a pilot wire relay to incorporate the above pilot wire distance compensating circuit of Figure 1 or that of Figure 3 to be subsequently described; Figure 3 is a circuit diagram showing the pilot wire distance compensating circuit of an embodiment of the invention; and Figure 4 is a circuit diagram of an equivalent circuit at a rated frequency to the transmission circuit 30 in Figure 2.

Referring to Figure 3, reference numerals 1 and 2 denote input terminals, 3 and 4 denote output terminals, and the network of Figure 3 as a whole constitutes a two-terminal pair circuit. R1, R2 RL denote resistor and C1, C2PV, , CM denote capacitors. Reference numeral 10 denotes an RB - changeover switch for varying the resistance RB between the input terminal 1 and the output terminal 3, and 13 denotes a CR changeover switch for varying the capacitance between the output terminal 3 and the output terminal 4.

The circuit of Figure 3, like the conventional circuit of Figure 1, is, in use, incorporated in the pilot wire relay in Figure 2. The operation of the pilot wire relay as a whole when the circuit of Figure 3 is incorporated in the circuit of Figure 2 is the same as that when the circuit of Figure 1 is incorporated in the circuit of Figure 2.

Then, while the distance of the pilot wire 21 can be of any length case by case, it is arranged that RB and CR of the pilot wire distance compensating circuit 20 may be varied for each case, so that the circuit constants of the equivalent circuit to the transmission circuit 30, that is, the circuit of Figure 4, are kept constant regardless of the distance.

By the above arrangement, the characteristics of the relay such as the minimum operating current at inflow end under single end infeed condition can be kept constant regardless of the length of the distance.

The formulas for calculating RB and CR in the pilot wire distance compensating circuit of the present invention as shown in Figure 3 are, when, for example, it is assumed that the maximum loop resistance of the pilot wire is 1000n and the maximum line-to-line distributed capacitance of the same is 2 F: RB=(1000n RP) 1, 2 2 N2 CR - (2iiF - C) ) N2 2 2 Incidentally, CR arranged into one group was connected between the output terminals 3 and 4 in the above embodiment as shown in Figure 3, but the same effect can be obtained if the same is connected between the input terminals 1 and 2.

By this invention, as described above, the capacitors in the conventional circuit have been reduced to one group, and therefore the present invention has made it possible to provide a pilot wire distance compensating circuit that largely decreases the number of component parts of the apparatus and thereby reduces the volume and cost of the apparatus.

Claims (3)

1. A pilot wire distance compensating circuit including a two-terminal pair network having a first input terminal, a second input terminal, a first output terminal, and a second output terminal, wherein a plurality of groups of capacitors connected between said first input terminal and said second input terminal or between said first output terminal and said second output terminal are arranged into a unified group and connected between said first input terminal and said second input terminal or between said first output terminal and said second output terminal.

2. A pilot wire distance compensating circuit substantially as described herein with reference to or as illustrated in Figure 3 of the accompanying drawings.

3. Atransmission line protective relay including a pilot wire distance compensating circuit according to claim 1 or claim 2.