JPS607454B2 - Differential protection relay method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reed protection relay system for transformer system circuits including devices such as on-load tap switching devices through which bridging current flows by switching operation, and particularly relates to a reed protection relay system for a transformer-based circuit that includes a device such as a tap changer under load, in which a bridging current flows through switching operation. The present invention relates to a novel differential protection relay system that prevents a differential relay from causing unnecessary operation due to this bridging current when current is generated.

Generally, in open circuits including transformers, on-load tap changers, busbars, etc., a differential protection relay system is applied as a system for detecting the occurrence of, for example, a short circuit accident.

As is well known, this protection method connects the secondary side of the current detection transformer provided at each terminal differentially, inserts a differential electrical device such as a ratio differential relay into this rhombic current circuit, and A differential relay turns OFF in case of an external fault, while turning ON only in case of an internal fault to carry out the specified protective operation. When applied to a system, a large total bridge current is generated during the predetermined tap-cutting operation during steady operation, and this bridge current causes unnecessary operation of differential relays that should only operate in response to internal faults. become. When such a bridging current is generated, it is not a pure internal accident, so it is absolutely necessary to avoid the possibility that the covering relay operates unnecessarily and paralyzes the function of the electrical circuit system itself. Conventionally, there are methods for avoiding unnecessary operation of this type of differential relay, such as a method of dulling the sensitivity of the protective relay instead of making it more sensitive, and a method of delaying the operation time of the protective relay instead of increasing its speed. .

In such conventional methods, for example, in the former method, if the bridging transient current is considerably large, the current flowing into the protective general equipment will also be a considerably large value, and in order to avoid unnecessary operation due to this, it is necessary to install a differential relay. However, if such a method is applied, for example, if an accident actually occurs, the specified detection protection will be difficult or impossible, and the relay system will not be able to function properly. I can't. On the other hand, in the latter conventional method, for example, if the bridge switching of the on-load tap switching device is not completed in an extremely short time, unnecessary operations may occur, so the delay time must be made sufficiently long. This affects the protection coordination of the exposed passageway and other exposed passage systems connected thereto, making side adjustment difficult or impossible. Needless to say, in such a case, like the former method, the actual accident detection function cannot be achieved. The present invention was invented in view of this point, and in particular, the present application provides a current detecting transformer in the bridging circuit of the voltage regulating winding, and the bridging circuit at the time of tap switching led to this transformer. By passing current and a current corresponding to the load current flowing in the secondary side of the series transformer through the operating wire of the differential relay, it is possible to compensate for the increase in the primary side current of the voltage regulating transformer caused by these currents. This will be described in detail below based on this example.

First, before explaining this embodiment, we will explain in detail how the conventional differential protection relay system causes unnecessary operations based on the specific circuit configuration diagram shown in Fig. 1. .

Now, in FIG. 1, T indicates a main transformer, and this transformer consists of a primary winding N and adjusting windings N2 and N3 for voltage adjustment. L is a series transformer connected in series to the winding system via adjustment windings N, N2, and N4 and N5 are a primary winding and a secondary winding, respectively. S, , S2 are thyristor switches formed by connecting thyristors in anti-parallel, and prepare the same number of thyristor switches as the number of taps of the adjustment windings N2 and N3, and adjust each thyristor switch as appropriate according to the line voltage. A predetermined voltage adjustment is performed by combining several numbers. CT,,
CL is a current detection transformer provided at each terminal, and although two transformers are shown in the embodiment, there is no problem in operation even if only one transformer is provided. DF is a differential protection relay that performs a specified protective operation, and R
3, M3 are its suppression wire and operating wire. Now, in a transformer circuit system configured as described above, a detection transformer having a differential connection on the secondary side has conventionally been configured with T, , T2 as shown in the figure.
Generally, they are installed on the primary and secondary sides of the
In this case, the transformation ratio of each transformer is determined as follows. That is, conventionally, the influence of the adjustment windings N2 and N3 of the on-load voltage adjustment device is ignored, and the currents j, , i2 taken out from the secondary sides of CT, , CT2 are adjusted so as to match.

This can be expressed as a formula: a. The equation ・N,=a2・N5 is shown, and the relational expression of konuri a・=a20 is written in the column. [Here C
The transformation ratio of T,, CT2 is shown as a,, a2, the number of primary windings of T,, L and the number of secondary windings as N,, N5] Therefore, with this method, the bridge during steady operation is Since the influence of the adjusting windings N2 and N3 due to the bridging current that occurs during switching is ignored, the current flowing into the operating line Ms of the differential relay DF increases due to the bridging current, resulting in poor operation. The force becomes stronger, which causes the DF to perform unnecessary actions. Specifically regarding this bridging current, the tap switching operation performed during steady state is, for example, a voltage detection circuit (not shown).
When it is detected that the load increases and the load voltage drops below a predetermined value, the thyristor switch S on the up tap side is fired,
On the contrary, when it is detected that the load voltage has risen above a predetermined value, the thyristor switch S2 on the lower tap side is fired, so that gate switching is performed randomly.
Moreover, when switching gates (when switching bridges), S, -S2
Since each thyristor switch is in a conductive state, a bridge circuit is formed through these thyristor switches. As is well known, although not shown, a current limiting reactor is generally inserted into this bridging circuit, and has the function of limiting the bridging current itself at the time of bridging switching. To describe the increase in T and primary current when this bridging current is generated, first let the number of turns of the adjustment winding and L primary winding be N2, N3, and N4, respectively, and the bridging current io,
When load current 1 flows, the T2 primary side current corresponding to this 1 is 1L, and when the thyristor switch S or S2 is turned on, the S side shunt current is (1-Q)IL, and the S2 side shunt current is QIL. Then, it is calculated as follows.In other words, as the load current 1 and force 2 flow through the secondary winding, this secondary magnetomotive force becomes N5・1, and the magnetomotive force of the same value as this secondary magnetomotive force is Since it must occur on the primary side of T2, N5・1=
The relational expression N4・IL is obtained, and from this, L corresponding to 1
The primary current 1 is = band.・L......■ It is shown in the formula.

Here, if we assume that only S is energized in the voltage regulator, this S, side shunt (1-Q)/IL, increase in T, primary current △1, is the seed magnetic force on the adjustment winding side. From the relationship between T and the primary magnetomotive force, [(1-Q)・IL]
・N3=△11-N・1 [(1-Q)-device・]・N3=
A.I.・N, → "---△・.=学-[(・-Q)-datsu-・]---■ It is shown by the formula.

Similarly to Z, when only S2 is energized, the increase in T and primary current due to the S2 side shunt IL and Q is △
12 is Q・IL・N2 =△12-NI→Reed-11Q●N2=△12-NI→・
-・△,2 band-band-1-Q------■ In this case, the direction of flow of △12 is opposite to that of △1.

On the other hand, when the bridging current io occurs, T, - the rise in the next-side current is shown by the formula: When bridging current io occurs, T, the total increase in primary current △1 is ■,
From each formula of ■,
Q+Oji&-io→.・．． △1 - rod;・i.

10 [Obi/Takashi (・-Q)-Mother-Kushi-Q]●1-----
■ It is shown by the following formula, and as this formula (■) T and the increase △1 of the primary side current flow into the DF in Figure 1, the operating force of the DF itself increases and the DF causes unnecessary operation. become.

FIG. 2 shows an embodiment according to the present invention, and the present invention is characterized in that a current detection transformer for deriving a new bridging current is provided in the bridging circuit of the on-load voltage regulator. It is something that you have. That is, in the figure, the same parts as in Fig. 1 are given the same reference numerals, and CT3 and CT4 are current detection transformers installed in the bridge circuit, respectively, and the CB inserted on the CT4 side is according to the present invention. This is a new circuit breaker installed to further expand the effectiveness of the circuit breaker.This circuit breaker CB is used to cut off abnormal current caused by continued bridging, for example.

Now, to explain in detail the operation of the present invention configured in this way, for example, the bridging current i during tap cutting operation during steady operation.
When o occurs, as mentioned above, T, the primary current becomes a large value due to bridging current, etc., and this current increase is lo + △1
. CT3, CT
4, so "These are CT3, C
The current component introduced from T4 is as shown below.
In other words, the current directions of the S, side shunt when S is energized and the S2 side shunt when S2 is energized are opposite directions as shown in the figure, so the current transformation ratios of CL and CT4 are respectively a3 ，
The secondary side voltages obtained through a4 and CT3 and CT4 are respectively i
3, i4, the current component i4 introduced from the CL secondary side when S is 0N is 14= [i.

10IL(1-Q)]・1/a4=[i. 10N5/N41
(11Q)]・1/a4. ．． ．． ．．・．． It is shown by the formula: On the other hand, when S2 is set to ○N, the current component i3 introduced from the secondary side of CT3 is - 1 13 = (i.

-QI)・Silkworm=(i.

−Mackerel・−Q)−Poison…−−■ It is shown by the formula.

Therefore, since the connection of CT3 and CL is considered as shown in the figure so that the current components obtained from equations (2) and (2) are added together, the sum of these current components and the sum of the current components introduced from CT In other words, the current components introduced from CT3 and CT4 are combined so that lo + Δ1 and - AI2 are equal, and the current increase detected from CT is compensated in DF. If this is done, the current increase due to the bridging current io will not flow through the DF operation line, and the DF will not perform unnecessary operations. Furthermore, CL, CT
4 causes an extremely small error due to the normal current, but these are extremely small compared to the fault current or bridging current io, so they pose no problem in practice. As described above, according to the present invention, it is possible to reliably eliminate the influence of the bridging current of the load voltage regulator during steady operation, for example, so that the sensitivity of the differential relay can be made sufficiently sensitive, or the operating time can be made extremely fast. Since there is no risk of unnecessary operation even when the system is in use, for example, it becomes possible to provide sensitive and quick accident protection that was previously impossible, and it also becomes extremely easy to coordinate protection with other haze road systems connected to the open road system. .

Furthermore, in the secondary relay relay system, if the switching switch of the on-load tap switching device is defective and a bridge continues between the terminals, it is impossible to identify that the bridge continues. Met. Therefore, due to the continuation of such a bridging condition, the protective relay is activated, forcing the equipment system to be completely shut down. This type of accident is said to be the weakest point in the equipment system compared to other parts, but it is possible for all equipment to stop due to a simple failure such as a bridge accident between terminals. is an extremely bad idea. In this regard, in the present invention, for example, the bridging current is detected by a detection transformer newly installed in the bridging circuit, and this detection signal is introduced into a judgment section consisting of a logic circuit to make a predetermined judgment. Finally, if B is tripped to the circuit breaker inserted in the bridge circuit based on this determination result, it is possible to continue using a part of the on-load voltage regulator, as is clear from the embodiment. In other words, although the switching of the tap of the load voltage regulator is locked in this equipment system, it is possible to continue using it temporarily as a system, and the problems that have been pending with this type of relay electrical system can be solved at once. It is.

[Brief explanation of the drawing]

FIG. 1 shows a circuit example of a secondary differential protection relay system applied to a transformer electrical circuit system, and FIG. 2 shows a specific circuit example of a differential protection relay system according to an embodiment of the present invention. T, is the main transformer, T2 is the series transformer, S,, S2 is the thyristor switch, CT, to CT4 are the current detection transformers,
DF is a differential protection relay, and CB is a circuit breaker. Soup' Zuko 2

Claims (1)

[Claims] 1. A thyristor switch is provided on the secondary side, which has an up tap, a neutral point tap, and a down tap, and a thyristor is connected in inverse parallel to each of the up tap and down tap, and these thyristor switches are connected. A voltage regulating transformer forming a bridge circuit, a series transformer in which one end of the primary winding is connected to the neutral point tap, the other end is connected to the bridge circuit, and the load voltage is extracted from the secondary winding. , a current detection transformer is inserted into the primary winding of the voltage regulating transformer and the secondary winding of the series transformer, and a current differential relay is connected to the differential current circuit of these transformers. In the case where the voltage regulating transformer is provided with specified protection, current detection transformers A and B are installed on the up tap side and the down tap side of the voltage regulating transformer, respectively.
is inserted, and when a bridging current is generated, the primary side current rise of the voltage regulating transformer flowing into the current differential relay is connected in series with the current component of the bridging current led to the transformers A and B. A differential protection relay system characterized by compensation based on the current component of the load current flowing to the secondary side of the transformer.