JPS60180435A - Transformer protecting relay - 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 [Technical Field of the Invention] The present invention relates to a protective relay that detects a failure in a transformer that performs the role of voltage conversion in a power system.

[Prior art]

Fig. 1 shows the transformer 7 to be protected and its peripheral configuration, in which 1 is the high voltage side bus bar, 2 is the low voltage side bus bar, 3a, 3
b is a breaker; 4a and 4b are a high voltage side current transformer CT and a low voltage side current transformer CT for providing current information to the transformer protection relay 5; 1. and 4 are current transformers 4a and 4, respectively.
b, which are referred to as the high-voltage side primary current and the low-voltage side primary current here. Reference numeral 6 indicates a local cable connecting between the transformer 7 and the high-voltage bus 1, and 8a to 8n are loads connected to the low-voltage bus 2.

Generally, the transformer protection relay 5 adopts a differential protection method,
The transformation ratio of the transformer 7, and the transformer ratio of the flow conditioners 4a and 4b.

A current input having a value determined by the current transformation ratio is obtained, and the vector difference between the two current amounts is used as the operating force, and the larger of the absolute value of the current z amount is used as the restraining force.

Now, for the sake of simplicity, we will not consider the transformation ratio and current transformation ratio, and the high pressure side 1
Assuming that the magnitude of the primary current I2 and the primary current I2 on the low voltage side can be treated at the same value level, it is expressed on a vector diagram as shown in FIG. 2. In FIG. 2, 1 indicates the direction of the voltage vector on the high-voltage bus 1.

The total load current I2 of the loads 8a to 8n in FIG. 1 is generally close to the power factor l and has a slightly delayed phase relationship, and in FIG. It is expressed as On the other hand, the charging current in the cable section of the premises cable 6 in Fig. 1 is not a problem if the capacity of the transformer 7 is large, but it is not a problem if the capacity is small, such as the starting transformer of a power plant. This will affect the fault detection sensitivity.

In FIG. 2, the charging current in the cable section 6 is expressed as Ic, and the composite vector of the low voltage side primary current flow and the charging current Ic is shown as the high voltage side primary current flow. In other words, if there is no charging current Ic, the high voltage side primary current and the low voltage side 1
The next currents 2 are equal, and the vector difference that becomes the operating force of the transformer protective relay 5 is zero. However, if the charging current Ic exists, this amount remains as a vector difference, and the error of the transformer protective relay 5 is reduced. It enters as. Therefore, when the value of the charging current Ic exists at a level that cannot be ignored with respect to the rated current of the transformer 7, the conventional countermeasure is to reduce the detection sensitivity of the transformer protective relay 5. there were.

FIG. 8 is an internal circuit block diagram of a conventional transformer protection relay. In FIG. 8, 51 and 52 are transformers, 56 is a maximum absolute value deriving circuit, 54 is a vector differential circuit, and 55 is a maximum absolute value This is a comparator for comparing and determining the suppression output from the deriving circuit 53 and the operational output from the vector difference deriving circuit 54, and outputting the operational output 56 if the operational force is greater. The electric current installed from the current transformers 4a and 4b in FIG.

After converter 2 is converted into an appropriate value by transformers 51 and 52, maximum absolute value deriving circuit 53 outputs the larger absolute value of currents I, L, and vector difference deriving circuit 54 outputs the current A comparator 55 outputs the vector difference between I, , I, and compares the magnitude of the two river forces. The reduction in sensitivity in the conventional method described above can be achieved by adjusting the comparator 55.

Conventional transformer protective relays are configured as described above, so when the charging current value is at a level that cannot be ignored relative to the rated current of the transformer, the detection sensitivity of the transformer protective relay is reduced. As a result, there was a problem in that it became impossible to detect minor failures such as one-turn rare inside the transformer.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by compensating for the charging current,
The purpose of the present invention is to provide a transformer protection relay that can cope with current Ic without decreasing sensitivity.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 8th
4 is an internal circuit block diagram of a transformer protection relay 50 according to the present invention, in which a charging current compensation circuit 100 and a composite output circuit 200 are added compared to FIG. ing. The charging current compensation circuit 100 is a circuit that can receive the output of the transformer 52 and output a constant amount whose phase is advanced by an angle 02 shown in FIG. 2 with respect to the vector phase of the low voltage side primary current I. , outputs a value commensurate with the charging current Ic. The composite output circuit 200 combines the output from the transformer 51 and the output from the charging current compensation circuit 100, and outputs a purely high-voltage side primary current component that compensates for the charging current.

It should be noted that a method may be adopted in which the voltage of the high-voltage side bus 1 is introduced and the charging current is compensated in a manner commensurate with this value, and the same effect as in the above embodiment can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, by combining a fixed amount advanced by a certain angle with respect to the current phase on the low-voltage side of the transformer into the high-voltage side current input, the cable charging current that exists on the high-voltage side can be reduced. Since the structure is configured to compensate, it is possible to obtain a transformer protection relay that does not require any reduction in detection sensitivity.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a transformer and its surroundings, Fig. 2 is a current relationship vector diagram, Fig. 8 is an internal circuit block diagram of a conventional transformer protection relay, and Fig. 4 is a diagram of a transformer protection relay according to the present invention. FIG. 3 is an internal circuit block diagram of an embodiment. 1...High voltage side bus bar, 2...Low pressure side bus bar, 3a, 6b
... Breaker, 4a ... High voltage side current transformer (CT), 4
b...Low voltage side current transformer (CT), 5,50...Transformer protection relay, 6...Internal cable, 7...Transformer,
8a-8n...Load, 51.52...Transformer, 56
... Maximum absolute value derivation circuit, 54 ... Vector difference derivation circuit, 55 ... Comparator, 56 ... Operation output, 1DO
...Charging current compensation direct circuit, 200...Synthetic output circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant Mitsubishi Electric Corporation Figure 1 Figure 2

Claims (1)

[Claims] In a transformer protection relay whose protection range includes a high-voltage side cable section of a transformer, a photocurrent compensates for a current in a charge-current phase of the high-voltage side cable with reference to a current phase of the low-voltage side CT circuit of the transformer. A transformer protection relay comprising: a compensation circuit; and a synthesis output circuit for synthesizing the output from the photocurrent compensation circuit and the high-voltage III CT circuit current of the transformer.