JPH04255422A - Network relay system for spot network facility - Google Patents

Abstract

PURPOSE:To make possible to manage the set level within a relay unit when reverse power is interrupted through a network relay connected through a CT with a transformer, to operate the CT within a specified error range and to facilitate replace in an operating power supply facility. CONSTITUTION:A CT1 has double ratio and an automatic CT ratio switching means 3 is provided in a network relay 2. The CT1 is operated within a specified error range and the value to be set by the relay 2 is matched with the reverse exciting current of a transformer by switching the CT ratio between a case when the rated primary current is normal and the case when it is very low thus interrupting reverse power even with only the reverse exciting current of transformer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network relay system, and more particularly to a network relay system for spot network power supply.

0002

[Prior Art] The spot network power supply system is a system that supplies power to loads that require high reliability, such as buildings, without power outages. They are connected to the primary side of each network transformer, and the secondary side of the network transformer constitutes a network bus, so that even if one feeder line loses power, the remaining network transformers operate without power outage. It is designed to supply electricity.

[0003] In this power feeding system, a network relay is installed to protect the primary feeder from failure. This network relay is equipped with a reverse power cut-off function, a no-voltage turn-on function, a differential voltage turn-on function, etc. In particular, the cut-off function is such that when the primary feeder is cut off due to a failure, etc.
Since the reverse power flows from the other primary feeders through the network transformer to the transformer side of the cut-off feeder from the network bus side, this reverse power is detected and cut off, and the
It must be able to respond to the excitation current of the network transformer supplied from the network bus side after the substation circuit breaker opens due to a ground fault on the next feeder side. Therefore, a wide range of breaking characteristics is required from the short circuit current range to the reverse excitation current range of the transformer.

[0004] This short circuit current and reverse excitation current are detected by a current transformer (hereinafter abbreviated as CT) provided in the secondary circuit of the network transformer. When this current transformer is used, for example, with a current transformation ratio of 1000/5A, the reverse excitation current Ie is usually about 1% of the rated current I of the network transformer, and On the other hand, the rated primary current ICT of the CT used is approximately 150% of the rated current I of this transformer. That is, when performing a reverse power cutoff operation of a network relay using only the reverse excitation current Ie of the transformer, 1 of the rated primary current ICT of the CT
CT will be used at a value of 1/50, approximately 0.7%. On the other hand, according to the CT standard JEC-1201, the ratio error in the IPS accuracy class is 0.05In...±3.0%, 0.2In...±1.5%, 1.0In...±1%. , when the transformer excitation current is 7A, the above 1000/
In the case of a 5A current transformer, the current flowing into the network relay is 5/1000 x 7 = 0.035A,
This means that CT is being used outside the defined error range. Also, due to the characteristics of CT, 1% of the rated primary current
In the following regions, the ratio of the excitation current of the CT to the primary current value becomes large, and it is impossible to specify any error in the secondary current with respect to the primary current. For these reasons, currently, CTs and network relays are coupled, and C
Tests are conducted from the primary side of the T, and the network relay is set using actual measured values that take CT errors into account.

[0005]

[Problems to be Solved by the Invention] However, the above conventional apparatus has the following problems.

(1) It is not possible to manage the setting value of a single network relay.

(2) When managing only by the input current to the relay, the setting scale of the relay and the CT primary current no longer correspond.

(3) Since CT is used outside the specified error range, characteristics cannot be managed on its own.

(4) Combination testing is absolutely necessary, and it is not possible to replace only the CT or replace only the network relay in equipment that is in operation.

[0010] The present invention was devised in view of the above-mentioned problems, and it is possible to manage the setting value of the relay alone, and clearly specify the value as the actual CT primary current, that is, the transformer reverse excitation current value. The purpose of the present invention is to provide a network relay system that can match, use CT within a specified error range, and guarantee characteristics against this error, and that can be easily replaced with power supply equipment in operation.

[0011]

[Means for Solving the Problems] The means for solving the above problems in the present invention is to detect the current on the secondary side of the network transformer with a current transformer, and detect the current flowing back from the network side to the network transformer. In a relay system equipped with a network relay having a reverse power cutoff function that detects and cuts off reverse power, the current transformer is a double ratio with different current transformation ratios, and the network relay is equipped with this transformer. A ratio automatic switching means for switching the ratio of the current transformer is provided so that the ratio is automatically switched from large to small when the detected current of the current transformer is above or below a predetermined value.

0012

[Operation] The present invention uses a double ratio CT that takes in current signals to a network relay, and the relay itself is equipped with a CT ratio automatic switching means, so that the CT ratio can be changed between the normal state of the rated primary current (short circuit current) and the very small state (transformed current) of the rated primary current. By switching between the transformer excitation current and the transformer excitation current, the CT is used within a specified error range so that the value set by the relay matches the actual transformer reverse excitation current.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment that also serves as a basic block diagram of the present invention. In the figure, 1 is a CT and 2 is a network relay. This CT1 is provided in the secondary circuit of a network transformer (not shown) and has two windings with different current transformation ratios (double ratio). That is, the winding t of 50/5A
1 and winding t2 of 1000/5A, and if the rated current of the network transformer is 1, then
Rated primary current normal value ICT of CT1 corresponding to winding t1
1 is ICT1=I×1.5, and the rated primary current minimal value ICT2 corresponding to the winding t2 is 1/20th of that, that is, I
CT2=ICT1×0.05. A CT ratio automatic switching means 3 is disposed inside the network relay 2, and switches between the winding t1 and the winding t2. The secondary current detected from the winding t1 or the winding t2 is digitized by the A/D converter 4.

FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, a network relay 20 is a three-phase version of the network relay 2 shown in FIG.
is used in the current direction reversal detection circuit 21, operates the relay function via the determination logic circuit 22a, 22b, or 22c, and is used in the reverse power detection circuit 23. The reverse power detection function of the reverse power detection circuit 23 detects reverse power flowing backward from the network side toward the network transformer due to an accident on the high-voltage distribution line, and issues a trip command to the protector circuit breaker (not shown). It is something. Judgment logic circuit 22
a, 22b, and 22c are H elements H-R (S phase and T phase have H-S and H-T, and operate in the same way as in the R phase, so only the R phase will be described below. ) is operating, CT is 1000/5A, and when L-phase element LR is operating, CT is 50/5A. The voltage element, the current element, and the results of the determination logic circuit 22 are taken into the reverse power detection circuit 23 as an operating signal H-R or LR, and when the L element is operating, the transformer excitation current region,
If the H element is operating, the operation is determined based on the short circuit current region and the set value of each relay. Operation signal H-R due to current in the positive (negative) direction with respect to this reference voltage
, H-S, H-T, the CT ratio is 100
50 if there is 0/5A, L-R, L-S, L-T
/5A detection currents IR, IS, and IT are taken into the power detection circuit 23, and the phase difference angle between each phase and the current and the network side voltages VRS, VST, and VTS is calculated, and these single-phase outputs are algebraically divided into three. A three-phase output is obtained by combining the two, and when this output exceeds a certain level, it is integrated and a cutoff output is issued.

Further, the judgment logic circuits 22a, 22b, 22
c is L-R when the detection current IR is within 0 to 5A.
works. (At this time, CT is 50/5A), and if it becomes 5A or more in this state, H element HR is activated, L-R is inactivated, (At this time, CT is 1000
/5A), detection current IR, IS, IT is 0 to 5A,
In addition, the H-R continues to operate when the current is 0.2A or more. L
The switching contact L-R of element L-R is in the state shown by the solid line, and the detection current IR (same for other phases) is 1000/5A.
The primary current is detected using the current transformation ratio.

Next, in the above state (HR operation),
When the detected current is within 0 to 5 A and decreases to 0.2 A or less, the signal H-R becomes inactive and the signal LR becomes active, switching its switching contact L-R to the state of the dotted line, C
Set the T ratio to 50/5A. In addition, when the current direction is reversed, the reversing relay R (same as S and T) is operated, and its contact R is input to the judgment logic circuit 22a and is always L-
Current transformer ratio 50/5A for R operation and H-R non-operation
Make it.

FIG. 3 is an explanatory diagram of the current transformer ratio automatic switching operation of the present invention. Figure (a) shows the CT primary current from 0 to 1.
This is a characteristic diagram when increasing to 000A, and up to 50A it is 50
/5A ratio, the secondary current increases to 5A, but the
The automatic switching means 3 operates at 0A, and thereafter 1000/
At a ratio of 5A, the secondary current decreases to 0.25A and then increases again to 5A. Figure (b) shows that the CT primary current is 10
In the characteristic diagram when decreasing from 00 to 0A, the automatic switching means 3 operates at 40A, and the secondary current, which had previously decreased to 0.2A at a ratio of 1000/5A, temporarily returns to 4A, and thereafter. It decreases to 0A with a ratio of 50/5A. Note that the switching clearance is between 40 and 50A and between 0.2 and 0.25A.

FIG. 4 is a current characteristic diagram when reverse power is cut off due to the reverse excitation current of the transformer. In the figure, the horizontal axis is CT
The primary current (reverse excitation current) is shown, and the vertical axis shows the CT secondary current. In the figure, straight line A indicates the IPS class with a current transformer ratio of 50/5A, and the primary side is 50×0.05=2.5A, ensuring an error within ±3%. Straight line B is current transformer ratio 10
It shows IPS class of 00/5A, and the primary side is 1000×0.
05 = 50A, the error is guaranteed to be within ±3%. When the transformer excitation current is 7A, the current flowing into the network relay is 7 × (5/50) = 0.7A for straight line A, and for straight line B
In this case, 7×(5/1000)=0.035A. Conventionally, the straight line B remained at 50A or less, so it was outside the specified error range, but in the present invention, as shown in FIG. 3, it is switched to the straight line A, so it falls within the specified error range.

The following effects are evident in this embodiment.

(1) It is possible to manage the setting value of a single network relay.

(2) The value set by the network relay can be clearly matched to the value of the actual CT primary current, ie, the actual transformer reverse excitation current.

(3) CT can be used within a specified error range. Furthermore, characteristics against this error can be guaranteed.

(4) Equipment in operation can be easily replaced.

[0024]

[Effects of the Invention] As explained above, according to the present invention, it is possible to manage the setting value of a single relay, and the value clearly matches the actual CT primary current, that is, the actual transformer reverse excitation current value. It is possible to use the CT within a specified error range, to guarantee characteristics against this error, and to provide a network relay system that is easy to replace for equipment in operation.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment that also serves as a basic configuration diagram of the present invention;

FIG. 2 is a configuration diagram of an embodiment of the present invention;

FIG. 3 is an explanatory diagram of the current transformer ratio automatic switching operation of the present invention,

FIG. 4 is a current characteristic diagram when reverse power is cut off.

[Explanation of symbols]

1... Current transformer (CT), 2, 20... Network relay,
3...Automatic switching means, 4...A/D converter.

Claims (1)

[Claims] Claim 1: A network relay having a reverse power cutoff function that detects the current on the secondary side of the network transformer with a current transformer, detects the current flowing backward from the network side to the network transformer, and cuts off this reverse power. In the relay system, the current transformer is a double ratio with different current transformer ratios, and the network relay is provided with an automatic ratio switching means for switching the ratio of the current transformer. A network relay system for spot network equipment, characterized in that the ratio is automatically switched from large to small when the detected current is above or below a predetermined value.