JPS6399721A - Differential protective relay - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a malfunction prevention device for a differential protection relay device consisting of a current transformer and a ratio differential relay or an overcurrent relay. Regarding.

(Prior art) Figure 8 shows the configuration of a conventional differential protection relay bag using a ratio differential relay, and Figure 9 shows the configuration of a conventional differential protection relay device using an overcurrent relay. Show about minutes. Electrical equipment 1
Current transformers 2a and 2b are installed across the current transformers 2a and 2b, and the main circuit currents Ia and Ib of the electrical equipment are connected to the current transformers 2a and 2b.
are converted into secondary currents Isa and Isb, respectively, and input to the ratio differential relay 3 in FIG. 8 via cables 4a and 4b, and the difference current Id and secondary current Is
Faults are identified based on the ratio between t+tL and Isb.
, in FIG. 9, the differential current Id is input to the overcurrent relay 6 to identify a failure.

When the electrical equipment 1 is in a healthy state such as a rotating machine, the main circuit currents Ia and Ib
If the current transformers 2a and 2b are equal, current transformers 2a and 2b having the same rating are used.

Difference between Figures 8 and 9! The protective device can be represented by the equivalent circuit shown in FIG. Resistors Ra and Rh are the eighth
In the figure, it is the sum of the winding resistance of current transformers 2a and 2b, the resistance of cables 4a and 4b, and the resistance of suppressing elements 3a and 3b of ratio differential relay 3, and in FIG. and the sum of the winding resistance of 2b and the resistance of cables 4a and 4b.

Inductances La and B are the sum of the leakage inductance of current transformers 2a and 2b, the inductance of cables 4a and 4b, and the inductance of suppression elements 3a and 3b of ratio differential relay 3, respectively in FIG. In the figure, current transformers 2a and 2 are shown, respectively.
is the sum of the leakage inductance of b and the inductance of cables 4a and 4b.

Rd and Ld are the resistance and inductance of the operating element 3d of the ratio differential relay 3 in FIG. 8, respectively, and the resistance and inductance of the operating element 6d of the overcurrent relay 6 in FIG. Lma and Lamb are the excitation inductances of current transformers 2a and 2b, respectively. Ia' and Ib' are the secondary conversions of the primary currents of current transformers 2a and 2b, respectively, and can be considered as equivalent current sources. Ima and Imb are the exciting currents of current transformers 2a and 2b, respectively. be. From the equivalent circuit shown in FIG. 10, the difference current is expressed as follows.

Id=Ia'-Ib'+ l1Ilb-Ima
- (1) If there is no abnormality in electrical equipment 1, Ia' and Ib'
are equal, so the above equation 0 becomes the following equation.

Id = Iwb - Ima -■ Therefore, the difference current when there is no abnormality in the electrical equipment 1 Id is the current transformer 2
This is the difference between the excitation currents 1 mb and Ima of a and 2b. The excitation currents Ima and Iw+b are determined by the excitation inductances Lma and Lmb of the current transformers 2a and 2b. Normally, the excitation inductance is large, so Ima and Imb are very small, and Id in the formula is also a very small value, but the current transformation When the capacitor 2a or 2b begins to saturate, the excitation inductance Lma or Lmb decreases, and Lma and LIIl
When an unbalance occurs in b, the difference between the excitation current Ima and Is+b increases, and a large difference current Id appears.

Generally, the current transformers 2a and 2b are selected so as not to saturate over a certain range of fault current, but in a normal current transformer, a large residual magnetic flux exists due to the hysteresis characteristic of the iron core, When the DC component is superimposed on the next side, the current transformer's 2
Due to the resistance on the next side, biased magnetization of the current transformer progresses, and in combination with the residual magnetic flux, it may reach saturation.

In Figures 8 and 9, when the breaker 5 is turned on, a DC component equal to the peak value of the AC current is generated at maximum, and the DC component attenuates due to the time constant of the main circuit. It also appears on the secondary side of current transformers 2a and 2b, and current transformer 2a
If 2b and 2b are not saturated, the difference current Id is very small due to the above reason, so the current transformer 2a becomes biased due to the integration of the product of the secondary conversion value of the DC component and the resistance Ra, and the current transformer 2a 2b, the biased magnetization progresses due to the integration of the product of the secondary conversion value of the DC component and the resistance Rb.

In FIGS. 8 and 9, due to the installation location of current transformers 2a, 2b and relay 3 or 6,
In many cases, the lengths of 4b and 4b are significantly different, and Ra and Rb and La and Lb in Fig. When the circuit breaker 5 is turned on, the current transformer 2a or 2b becomes saturated, and a large difference occurs between the excitation currents I+ua and In+b. This appears as a difference current, and in FIG. There is a possibility that the differential relay 3, or the overcurrent relay 5 in FIG. 9, may malfunction.

The possibility of the above-mentioned malfunction is high when the electrical equipment 1 to be protected is compared to the rated current, such as an induction motor.

In cases where the starting current when the breaker 5 is turned on is considerably large, or in equipment such as a reactor that has a long DC component decay time constant, or in a small-capacity generator or bus duct that supplies power to the induction motor or reactor, etc. This is particularly problematic in cases where

(Problems to be Solved by the Invention) In order to solve the above problems, the cross-sectional area of the core of the conventional current transformer has been increased to provide a margin against DC bias magnetism, and the core of the current transformer has been provided with a gap. Measures can be taken to prevent current transformers from becoming saturated and malfunction, such as reducing residual magnetic flux, increasing cable thickness and reducing cable resistance.

A countermeasure was taken to lock the output of the relay with a timer until the differential current that transiently occurs due to saturation disappears, but the countermeasure to prevent the current transformer from becoming saturated is to This is considerably larger than the size of the current transformer and the thickness of the cable required to prevent saturation of the relay, and the above-mentioned measure to lock the relay output with a timer requires differential protection from the time when the breaker is turned on until the above-mentioned transient phenomenon disappears. The problem is that it is not done.

The present invention has been made to address the above problems,
This is caused by the transient DC component generated when the breaker is closed and the residual magnetic flux of the current transformer, without making the current transformer size or cable thickness larger than that required to detect a certain range of fault current. It is an object of the present invention to provide a differential protection relay device that suppresses differential current and prevents malfunction.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a pair of current transformers of the same rating attached to each phase of the main circuit of the electrical equipment with the electrical equipment sandwiched therebetween; In a differential protection relay device comprising a ratio differential relay or an overcurrent relay that detects a failure in the electrical equipment based on the differential current between a pair of current transformers, the current transformer in the pair when the electrical equipment is healthy In order to suppress the differential current generated due to the difference in the saturation of the devices, a resistor or reactor of an appropriate size is inserted into the circuit through which the differential current flows.

(Function) By inserting a resistor or reactor of an appropriate size into the circuit through which the differential current flows, the differential current can be suppressed and malfunctions can be prevented.

(Example) The structure and operation of an example of the present invention will be explained with reference to FIG. FIG. 1 shows a ratio differential relay 3 of the conventional differential protection relay device shown in FIG.
A load adjustment resistor 13 is provided in series with a. The equivalent circuit in FIG. 1 is also the equivalent circuit in FIG. 10, but in this case Rd is the sum of the resistance of the operating element 3d of the ratio differential relay 3 and the malfunction prevention resistor 11, and Ld is the operating element 3d of the ratio differential relay 3. Inductance and malfunction prevention reactor 12
is the sum of

Ra is the sum of the winding resistance of the current transformer 2a, the resistance of the cable 4a, the resistance of the suppressing element 3a of the ratio differential relay 3, and the load adjustment resistor 13, and Rd is the sum of the winding resistance of the current transformer 2b and the cable 4a. 4b and the resistance of the suppression element 3b of the ratio differential relay 3. Other resistances and inductances are the same as in FIG. From the equivalent circuit in Figure 1O, the voltage Va generated in the current transformer 2a and the voltage vb generated in the current transformer 2b are expressed by the following formulad d Va=Ra・Iw+La1Isa+RdId+LdRevision 1
d - song ■ d d ■ b = Rb・engine sb + Lb ■ engineering 5b - Rd engineering d - Ld coni d...0) Here, when the electrical equipment machine 1 is healthy, the difference current Id is the exciting current Iab Since this is the difference between I+iaO and the equation (2) holds true, the equations (4 and 171) become the following equations.

Va=Ra-I sa+ La-I ga+Rd(Iw
h-I am)+ Ld-'(I mb-I ma)-
■dt dtVb=R
a・I sa+ ””■I sa+Rd(I ma-I
mb) + Ldn(I ma - I mb) = (eIf current transformer 2a starts to saturate before current transformer 2b, current transformer 2a
The exciting current Ima of the current transformer 2b becomes larger than the exciting current I++b of the current transformer 2b, and Imb-Imb becomes negative. Since the magnetic fluxes of the iron cores of current transformers 2a and 2b increase in proportion to Va and vb, respectively, the voltage drop of Rd and the voltage drop of Ld start to saturate from equations 4 and 4. This has the effect of suppressing an increase in magnetic flux for current transformer 2a and promoting an increase in magnetic flux for current transformer 2b which is not saturated.

Similarly, if the current transformer 2b starts to saturate before the current transformer 2a, the exciting current Imb of the current transformer 2b becomes larger than the exciting current a of the current transformer 2a, and Imb-Inmb becomes positive, so Rd The voltage drop in Ld and the voltage drop in Ld have the effect of suppressing an increase in magnetic flux for the current transformer 2b that has begun to saturate, and suppressing an increase in magnetic flux for the current transformer 2a that is not saturated.

In this way, Rd and Ld have the effect of reducing the unbalance of saturation between the current transformers 2d and 2b when the electrical equipment 1 is healthy. By inserting it into the current circuit, it is possible to suppress the differential current caused by the transient DC component and the residual magnetic flux of the current transformer, and prevent the (1) operation of the differential protection relay device.

In addition, since the malfunction described above is mainly caused by the difference in the load on the secondary side of the current transformers 2a and 2b, the load adjustment resistor 12 is used to equalize the secondary load of the current transformer. Connecting to the device side is effective in preventing malfunctions.

Although the load adjustment reactor is omitted in the embodiment of FIG. 1, the case where the load adjustment reactor is inserted in series with the load adjustment resistor is also included in the embodiment of the present invention. current transformer 2
Even if a and 2b have the same rating, the residual magnetic flux and saturation level of the current transformer are often not the same. By combining reactors, malfunctions can be more effectively prevented.

The embodiment shown in FIG. 2 is a ratio differential @
This is installed outside the 1'itt device, and its function is the same as that of the embodiment shown in FIG. 1, so it is included in the present invention.

3 and 4, a malfunction prevention resistor 11, a malfunction prevention reactor 10, and a load adjustment resistor 12 are inserted inside and outside a ratio differential relay via a transformer 13, respectively, and the operation is as shown in FIG. 1. This embodiment is the same as the above embodiment and is included in the present invention.

FIG. 5 shows the error it! through the transformer 13! l+ motion prevention resistance 1
1 and a malfunction prevention reactor 10 are inserted in series with the operating element 3d, and a load adjustment resistor 12 is inserted in series with the suppressing element 3a, and the operation is the same as that in FIG. 1 and is included in the present invention.

Figure 6 shows a differential protection relay device using an overcurrent relay, including a malfunction prevention resistor 11 and a malfunction prevention reactor 10.
Although a load adjustment resistor 12 is inserted, the operation is the same as that in FIG. 1 and is included in the present invention.

Figure 7 shows malfunction prevention resistor 11 and malfunction prevention reactor I.
O and the load adjustment resistor 12 are inserted through a transformer, but the operation is the same as that in FIG. 1 and is included in the present invention. The present invention also includes a case where the above embodiments are partially combined to obtain the same effect as shown in FIG. 1.

〔Effect of the invention〕

As described above, according to the present invention, even when a transient DC component is generated in the electrical equipment to be protected when the breaker is turned on, and the current transformer is saturated with the residual magnetic flux of the current transformer, , If the electrical equipment mentioned above is in good condition, the electrical equipment to be protected can be sandwiched by a resistor for preventing malfunction and a resistor for adjusting the secondary load of the reactor and current transformer inserted into the circuit through which the differential current flows. The degree of saturation of a pair of current transformers of the same rating will be equal, and the differential current will be suppressed. It is possible to provide a differential protection relay device that can prevent malfunctions without increasing the thickness.

[Brief explanation of the drawing]

1 to 7 are connection diagrams of a differential protection relay device having a malfunction prevention device according to an embodiment of the present invention, and FIGS. 8 and 9 are connection diagrams of a conventional differential protection relay device. , and FIG. 10 are equivalent circuits of the differential protective relay devices shown in FIGS. 1 to 9. 1... Electrical equipment 2a, 2b... Current transformer 3... Ratio differential relay 3a, 3b... Suppression element 3d... Operating element 4a, 4b
... Cable 5 ... Breaker 6 ...
・Overcurrent relay 6d...Operating element 7a
, 7b, 7d...Resistors 8a, 8b, 8d, 8e, 8f
- Inductance 9a, 9b...Equivalent pair flow source IO...Malfunction prevention reactor 11...Malfunction prevention resistor 12...Load adjustment resistor 13...Transformer agent Patent attorney Noriyuki Chika Hirofumi MitsumataFigure 1Figure 2Figure 3Figure 4Figure 5Figure 7

Claims (2)

[Claims] (1) A pair of current transformers of the same rating are installed in each phase of the main circuit of the electrical equipment with the electrical equipment in between, and the difference in current between the pair of current transformers prevents failure of the electrical equipment. In a differential protection relay device composed of a ratio differential relay or an overcurrent relay to be detected, an appropriate A differential protection relay device characterized in that it is constructed by inserting a resistor or reactor of a certain size into a circuit through which a differential current flows. (2) A resistor or a reactor for equally adjusting the load on the secondary sides of the pair of current transformers is provided on the secondary sides of the pair of current transformers. The differential protection relay device according to item 1.