JPS62268319A - Proportional differential relay system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a ratio differential relay system for protecting a transformer in which large-connection and Δ-connection windings are mixed.

(Prior Art) Conventionally, for example, when protecting a two-winding transformer in which the primary winding is connected to a large wire and the secondary winding is connected to a double wire by a ratio differential relay, a circuit as shown in Fig. 3 is used. The configuration is known. In this circuit, due to the high-to-high connection of the transformer 11, the transformer primary current Ipa.

Ipb, Ipc and the same secondary currents Isa, Isb, I
There is a phase difference of 30° with sc. Therefore, when these currents are input to the ratio differential relays 14a to 14c via current transformers 12a to 12c and 13a to 13c provided on each phase of the primary and secondary sides of the transformer 11, the transformer Even when there is no mismatch due to ratio and current transformation ratio, difference currents Jia to Δic flow due to the phase difference as shown in FIG. 4, and ratio differential relays 14a to 14e may malfunction.

Therefore, conventionally, as shown in FIG. 5, the secondary circuits of current transformers 12a and 12c on the primary side of the transformer 11 are connected in a △ manner in the same way as the secondary side of the transformer 11, and the current transformers 12a to 12c are 12c no 2
Next-side current I pa', I pb', I pc'
and the secondary currents of transformer 11 Isa, Isb, Isc,
In other words, current transformers 13a-13c (7) secondary current I
sa', I sb', I sc' (7
) The phase difference was eliminated. At the same time, current transformers 12a to 12
Since the magnitude of the current increases five times by making the secondary side circuits of c into △ connections, matching auxiliary current transformers 15a to 1.5c with a current transformation ratio of E:1 are installed in each of these secondary side circuits. The ratio differential relay 14 is connected to correct the magnitude of the current.
The difference current flowing through a to 14c was set to zero.

(Problems to be Solved by the Invention) However, according to this, the current transformers 1.2a to 12c on the primary side of the transformer 11 are the ratio differential relays 1-4a to 14c.
Therefore, when connecting other relays or meters that input the phase current (large current) on the primary side of the transformer 11, it is necessary to install another current transformer or There is a method such as pulling the secondary side cables of current transformers 1.2a to 2c into the building and connecting other relays, etc., and then △ connection to connect the matching auxiliary current transformers 15a to 15c. It had been taken.

For this reason, if the current transformers are installed separately, the burden of equipment costs increases, and if the current transformers 12a to 12c are also used for other relays, etc., the work of connecting a large number of cables is complicated. There was a problem. Furthermore, in any case, the matching auxiliary current transformers 15a-] and 5c are used to eliminate the differential current, which also has the disadvantage of increasing costs.

The present invention was proposed to solve the above problems, and its purpose is to eliminate the conventional method of △ connection of the secondary side circuit of the current transformer on the large connection side. , the calculation function of the microcomputer performs large -△ conversion of the secondary side circuit and correction of the current transformation ratio to zero the difference current flowing through the ratio differential relay, and connects the auxiliary current transformer for matching or a separate current transformer. It is an object of the present invention to provide a ratio differential relay system that eliminates the need for equipment, improves economic efficiency, and eliminates the complexity of cable connection work.

(Means for Solving the Problems) In order to achieve the second object, the present invention provides a ratio differential relay system for protecting a two-winding transformer, etc. having a human-△ connection. Determine the phase and magnitude of the secondary current of the current transformer connected to the connection side (primary side) and the secondary current of the current transformer connected to the △ connection side (secondary side) of the transformer. , and are set equally by a calculation based on a microcomputer program in a normal state in which there is no accident in the protected area including the transformer.

(Function) In the present invention, by taking the difference in the secondary current of the primary current transformer of the transformer for each phase, a state equivalent to Δ-connection of the secondary circuit of the current transformer is obtained. Then, the current transformation ratio is corrected by multiplying the difference in the secondary current for each phase by 115 to equalize the phase and magnitude of the secondary current of the secondary current transformer of the transformer. These operations are realized by microcomputer programs.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a two-winding transformer with a large connection on the primary side and a Δ connection on the secondary side as described above, and current transformers 2a, 2b, 2c are installed in each phase of the primary side. Further, current transformers 3a, 3b, and 3c are connected to each phase on the secondary side, respectively.

However, in the present invention, the downstream current transformer 2a of the transformer 1,
Secondary currents I pa' and I pb' of 2b and 2c
.
3b.

and the same size. In addition, in this example, each current transformer 2a, 2b, 2c, 3a, 3
A ratio differential relay 5a is connected between the secondary side circuits of parts b and 3c.

Since the functions of 5b and 5c can also be realized by the software of the microcomputer 4, these are also shown as constituent elements of the microcomputer 4 for convenience.

That is, in the microcomputer 4, the secondary currents I pa' and I of the current transformers 2a, 2b, and 2c are
After taking in pb'' and Ipc' and A/D converting them, the human-Δ conversion block 6 performs the following calculations.

The vector diagram of each of these currents is shown in Figure 2, and Ipa*, Ipb*, j:pc* are Ipa
', Ipb'.

The current transformers 2a and 2b have a phase delay of 30 degrees with respect to I pc', and are triple in size, as in the conventional case.

This is equivalent to connecting the secondary side circuit of 2c with a △ connection. After that, the following calculations are performed to correct the current transformation ratio. As is clear from Figure 2, Ipa'', Ipb', Ipc
'', the phase is delayed by 306, and the magnitudes are equal. In other words, pajj, i pb17,
IpCll is the secondary current Isa', I of the current transformers 3a, 3b, 3c provided on the secondary side of the transformer 1.
sb' and I Sc' are both equal in phase and magnitude. Therefore, ratio differential relays 5a, 5b, 5c
There is no risk that the ratio differential relays 5a, 5b, and 5c will malfunction in a state where no differential current flows and no accidents such as winding short circuits or ground faults have occurred within the protected area including the transformer 1. .

In this embodiment, the present invention is applied to a two-winding transformer, but the present invention can of course also be applied to a three-winding transformer with an adult one-Δ connection.

(Effects of the Invention) As described in detail above, according to the present invention, the conversion of the current on the large connection side of the transformer into a large one and the correction of the current transformation ratio are realized by software of a microcomputer, which is different from the conventional one. Thus, there is no need to connect the secondary side circuit of the current transformer on the large connection side and use this current transformer exclusively for the ratio differential relay. Therefore, it is possible to connect other relays and meters that input and use the phase current (large current) of the primary side of the transformer to the secondary side of this current transformer, making it possible to install new current transformers. This makes it possible to significantly improve economic efficiency by eliminating the need for

In addition, since the number of secondary cables of the current transformer can be reduced, there is no need to draw and connect a large number of cables into a building as in the past, and labor can be reduced.

17= Furthermore, since an auxiliary current transformer for matching for current transformation ratio correction is not required, further cost reduction can be achieved.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention,
Figure 1 is a configuration diagram of a differential protection circuit, Figure 2 is a vector diagram of each current shown in Figure 1, Figure 3 is a configuration diagram of a conventional differential protection circuit, and Figure 4 is a diagram of a differential protection circuit. 3 is a vector diagram of each current shown in FIG. 3, and FIG. 5 is a configuration diagram of a differential protection circuit showing another conventional example. 1... Transformer 2a~2c, 3a~3c・
...Current transformer 4...Microcomputer 58-5c...Ratio differential relay 6...Conversion block f1 E'

Claims (1)

[Claims] ■ A ratio differential relay that protects a transformer having a -△ connection by a ratio differential relay connected between the secondary circuits of current transformers provided on the input and output sides. In the ratio differential method, the phases and magnitudes of the secondary currents of each of the current transformers are set equally by a microcomputer program when there is no accident in the protected zone including the transformer. Relay method.