JPS6359721A - Digital differential current 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 (Field of Industrial Application) The present invention relates to a digital current differential relay, and more particularly to a digital current differential relay that prevents malfunction due to differential current in the event of an external failure. .

(Prior art) Conventionally, in this type of current differential relay, the relay malfunctions due to the generation of differential current due to differences in current transformer characteristics or saturation of some current transformers in the event of an external failure. There is a risk of For this reason, when applying a digital current differential relay to protect a three-terminal system as shown in Figure 5, for example, a ratio differential relay is used that prevents malfunction of the relay by using the scalar sum of the currents of each terminal as the suppression amount. method is generally adopted. In this Figure 5, 51 indicates the object to be protected such as a bus bar,
52a, 52b, and 52c are the protection target 51 and the terminal A,
B.

The secondary sides of these current transformers are connected to relays (not shown).

As shown in FIG. 6, each current transformer 52a, 52b
.

The terminal currents Ia, Ib, and 〒C of 52c are input to the vector sum calculation circuit 53 in the relay, and the vector sum current (
The differences Ia, Ib, and Ic are input to the scalar sum calculation circuit 54, and the scalar sum current Σ|■n| is input to the differential determination unit 55. The current T, |■n| is set as the suppression amount by 1.
Perform the calculation Σ|■n|. Here, K represents a suppression coefficient.

As a result of this calculation, if +ic++≧1・T, |■n|, it is determined that there is an internal failure and "1" is output, and +id+
If <K/T, |■n|, it is judged as an external failure and "0" is detected.
" is output. On the other hand, the differential current d is the level detection circuit 5
6 and compared with 2 to a predetermined constant, 1ic+1
If ≧2, the level detection circuit 56 outputs “1”. The outputs of the differential determination section 55 and the level detection circuit 56 are applied to an AND circuit 57, and a relay output is obtained when both of these two inputs are "1".

In other words, in this method, if a failure occurs on the external terminal C side as viewed from the protected object 51 in FIG. 5, and the current transformer 52c near the fault point F becomes saturated due to current concentration, this method will also prevent external failure. Regardless, even if a differential current id occurs, this current +i
Malfunction of the relay is prevented by setting Σ|■n| as the suppression amount for the scalar sum current larger than d+.

(Problems to be Solved by the Invention) However, this type of digital current differential relay has the following problems.

That is, if a failure occurs at point F in Figure 5, Ia,
Ib is an inflow current to the protected object 51, and Ic is an outflow current as the sum of these currents. Now, assume that the waveforms of Ia and Ic are as shown in FIG. 7 (a) and (b). Here, if the current transformer 52c is not saturated, Ia+Ib=-Ic, and as shown in FIG.

However, 1. If the current transformer 52c is saturated, Ic
The waveform of is distorted as shown in Figure 8 (b), and Ia
+Ib#-Ic and the same figure (c) despite the external failure.
The operation amount id is generated. During the period in which this operation amount id occurs, the above-mentioned suppression amount Σ|
A period of +>xyo・Σ|■n| occurs, and as id exceeds a certain level, the output of the level detection circuit 56 also becomes "1", and the relay operates unnecessary as shown in the same figure (d). There is a possibility that it will be stored away.

Particularly in multi-terminal systems, when an external fault occurs, current concentrates on the faulty terminal (for example, terminal C) and the current transformer tends to saturate, so there is an extremely high possibility that the relay will malfunction as described above. .

The present invention was proposed to solve the above-mentioned problems, and its purpose is to prevent malfunctions of relays by preventing unnecessary operation amounts due to saturation of current transformers. The object of the present invention is to provide a highly sensitive digital current differential relay.

(Means for Solving the Problems) The present invention uses a differential current as a vector sum of terminal currents in a closed circuit network of a power system as an operating amount, and a scalar sum current of each terminal current as a suppression amount. In a digital current differential relay, the differential reactive amount (=l Idl・l Inl・s
inθn, where ■d is the differential current, ■n is each terminal current,
on is the phase difference between each terminal current and the differential current), and compares the maximum differential invalid amount among these differential invalid amounts with the above suppression amount, and selects the larger amount as a new suppression amount. It is characterized by the amount.

(Function) The present invention focuses on the fact that when a current transformer is saturated due to an external fault, only the saturated terminal current has a lead phase of approximately 90° with respect to the differential current compared to the normal terminal current. The saturation of the current transformer is determined by detecting the differential reactive amount generated from the phase relationship between the saturated terminal current and the differential current, and the larger of the differential reactive amount and the suppression amount is detected. is used as a suppression amount to prevent malfunction of the relay.

That is, considering the case where an external failure occurs at terminal C as shown in FIG. 5, each terminal current Ia when the current transformer 52c on the terminal C side is not saturated.

The vector diagram of Ib and Ic is for each current transformer 52a, 52b, 5
If the characteristics of 2c are equal, as shown in Figure 1, I
c=-(Ia+Ib), and the differential current d is zero. Next, if the current transformer 52c is saturated, the vector diagram will be as shown in FIG. 2. In other words, the saturated terminal current 〒C' is delayed in phase with respect to the non-saturated terminal current Ic, and the differential current rd=Ia+Ib+re'=Ic'-Ic
occurs. Also, the saturated terminal current Ic' is the differential current id
The phase is approximately 90' ahead of id, and the other healthy terminal currents Ia and Ib are 90' behind id.

Here, differential invalid amount D RV (D 1fferent
ialReactive Variable), this differential invalidation amount DRV is defined by the following equation 0 as described above.

DRV =lxdl ・1inl ・sinθn Town・
...Town...■In addition, ■n is each terminal current (Ia, I
b, Ic), θn respectively indicate the phase difference between each terminal current In and the differential current id, and the differential reactive amount DR
V is found inside the digital relay using the following equation.

DRV=Id(n4)-1n(n)-1n(7-?)
” 1Q(nJ・・・・・・・・・・・・・・・・
...■Here, for example, I d <n-z) indicates data 90 degrees before when sampling is performed every 30'' in electrical angle.

As is clear from the above equation 0, the differential reactive amount DRV has s
Since the term inθn is included, DR for each terminal current is
When calculating V, the following three cases can be considered as the sign of DRV.

a. If the terminal current is in a lagging phase with respect to the differential current...
・・・・・・DRV<O b, if the terminal current is ahead of the differential current and is in phase...
・・・・・・DRV>O When the terminal current is in phase or out of phase with respect to the C1 differential current ・・・・・・・・・DRV=0, that is, both current transformers in Figure 5 are saturated If not, DRV=0 for all terminal currents. In addition, if the current transformer 52c
is saturated, the saturated terminal current Ie'' becomes the differential current i
sin θC while leading phase by approximately 90″ with respect to d.
(θC is the phase difference between Ic' and id) 1, and ic'
The bitter DRV has a large positive value. On the other hand, since the healthy terminal currents Ia and Ib at this time have a delayed phase with respect to id, DRV has a negative value.

Therefore, the maximum value of the differential reactive amount DRV n for each terminal current In is detected as the maximum differential reactive amount DRVmax, and this is compared with the suppression amount T, |■n|: |■n| )
η・DRVmax・・・・・・・・・・・・・・・
・・・・・・・・・・・・■ (η is a constant) Then, let Σ|■n| be the suppression amount (Rest, ) as before, and Σ|■n|≦η・D RV 11ax ・・・...
・・・・・・・・・・・・・・・・・・■ If the current transformer is saturated, it is determined that the current transformer is saturated, and η・DRV max is set as the new suppression amount Ra5t, where it is a constant. η is selected taking into consideration the case where there is a phase difference in the inflow current, and by selecting its magnitude to an appropriate value, the amount of suppression when the current transformer is saturated is greater than the previous suppression amount: |■n| Sufficiently large amount of suppression R
e5t, can be obtained. This new suppression amount Re5
t, and the amount of movement id are compared in the differential determination section, l
I,:tl<Re5t.

Due to this relationship, the output of the differential determination section becomes "O", and malfunction of the relay can be prevented.

On the other hand, since each terminal current and differential current are in the same phase at the time of an internal failure, DRV=O.

■When the formula is applied, the previous suppression amount Σ|■n| and the operation amount Id
are compared, and a relay output can be obtained if necessary.

(Example) The present invention will be described in detail below with reference to the drawings.

First, FIG. 3 shows the first embodiment of the present invention6.
In the figure, 1 is a vector summation circuit, which calculates terminal currents 1a and Ib from a current transformer as in the conventional case.

Ic is inputted respectively, and a differential current id as a vector sum is calculated. Further, 2 is a scalar sum calculation circuit, which calculates a scalar sum current of each terminal current=11nl.

Differential reactive amount calculating circuits 3, 4.5 are connected in parallel to the output side of the vector sum calculating circuit 1, and differential current id is connected to these differential reactive amount calculating circuits 3, 4.5. Terminal currents Ia, Ib, and Ic are respectively input. Furthermore, the outputs of the differential invalid amount calculation circuits 3, 4, and 5 are applied to a maximum value detection circuit 6, and the output thereof is applied to a comparison circuit 7 together with the output of the scalar sum calculation circuit 2. and,
The output of the comparison circuit 7 is applied to the differential determination section 8 together with the differential current id.
The output of the level detection circuit 9 that detects the level of the differential current id from the relational expression (K is a constant) is added to the AND circuit 10 to obtain a relay output.

Next, this operation will be explained. First, when an external failure occurs, the terminal current I
Assuming that the current transformer c is saturated, the differential current id is generated from the vector sum calculation circuit 1 in conjunction with the generation of the saturated terminal current Ic' as described above. This differential current ■d is inputted to the differential reactive current calculation circuits 3, 4.5 together with the terminal currents Ia, Ib, Ic, and each calculation circuit 3, 4.5 calculates the terminal currents ia, Ib as described above. , Ic', differential invalid amounts DRVa, DRvb, and DRVc are calculated.

At this time, since only Ic' has a phase leading by approximately 90 degrees with respect to id, the differential ineffective amount DR applied to Ic'
Vc becomes maximum, and the maximum value detection circuit 6 in the next stage detects this DR.
It detects Vc and outputs it to the comparison circuit 7. Here, the previous ■
, If the value of η in the formula is set sufficiently large,
Σ|■n|≦η・DRVwax and is larger than Σ|■n|・DRVmax is selected as the new suppression amount Rest, and the determination result at the next stage differential determination unit 8 is I
I dl< Re5t, and the differential determination unit 8 outputs “0
" is output. Therefore, even if the output signal of the level detection circuit 9 is "1", no relay output is obtained from the AND circuit 10, and unnecessary operation of the relay is prevented.

Also, if the current transformer is out of saturation or has an internal failure, D
Since RVmax=O, Re5t,=ZI Inl
Therefore, normal differential determination is performed by a circuit substantially similar to that shown in FIG.

Next, FIG. 4 shows a second embodiment of the present invention. In this embodiment, when the differential current idO value exceeds a certain level, the switches 11, 12, and 13 are operated to take the differential current id into the differential reactive current calculation circuit 3°4.5. The switches 11, 12, and 13 are controlled by the level detection circuit 9'. The other configurations and operations are the same as those in the first embodiment, so detailed description will be omitted.

In each of the above embodiments, a digital current differential relay with a three-terminal system was described, but the present invention is applicable to other multi-terminal systems, and is also applicable to differential current relays including ratio differential relay systems. If it is a dynamic relay system, a generator, transformer, etc. may be protected. Furthermore, although +id+- is used as a determination formula for the differential relay system, the determination formula is not limited to this determination formula in general.

(Effects of the Invention) As described above, according to the present invention, the saturation of the current transformer is determined by detecting the maximum differential reactive amount, and the maximum differential reactive amount is compared with the conventional suppression amount. Since this amount is used as the new suppression amount, malfunction of the relay due to current transformer saturation in the event of an external failure can be reliably prevented.

Further, since there is no erroneous determination even in the case of an internal failure or an external failure where there is a phase difference in the inflow current, a highly sensitive digital current differential relay can be obtained.

[Brief explanation of drawings]

FIG. 1 is a current vector diagram of a current transformer in a non-saturated state at the time of an external failure, FIG. 2 is a current vector diagram of a current transformer in a saturated state, and FIGS. A block diagram showing the second embodiment, FIG. 5 is a single line diagram of a power system to which the present invention is applied, FIG. 6 is a block diagram showing a conventional example, and FIGS. 7 (a) to (d) are current transformation An explanatory diagram of the operation of the device in a non-saturated state. FIGS. 8(a) to 8(d) are also explanatory diagrams of the operation in the saturated state. 1... Vector sum calculation circuit 2... Scalar sum calculation circuit 3.4.5... Differential reactive power calculation circuit 6... Maximum value detection circuit 7... Comparison circuit 8
...Differential judgment section 9,9'...Level detection circuit 10...AND circuit 11,12.13...Switch Fig. 1 Fig. 2! c i (Figure 5 Giant 1 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] A digital current differential relay in which the operating quantity is a differential current as a vector sum of terminal currents in a closed circuit network of a power system, and the suppression quantity is a scalar sum current of the terminal currents. , Differential reactive amount (=|■d|・|■n|
・sinθn, where ■d is the differential current, ■n is each terminal current, and θn is the phase difference between each terminal current and the differential current), and calculates the maximum differential among these differential reactive amounts. A digital current differential relay characterized in that an ineffective amount and the suppression amount are compared and the larger amount is set as a new suppression amount.