JP3446268B2 - Transformer protector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for a series transformer inserted in series in a power system for adjusting the voltage phase or the voltage value and the voltage phase of the power system.

[0002]

2. Description of the Related Art Power transformers are generally protected by detecting an internal fault by a difference current between a series winding and an exciting winding. In particular, the magnetizing inrush current that occurs when the transformer iron core is magnetically saturated when the power is turned on is detected as a difference current. It is necessary to judge with. The differential current at the time of magnetic saturation of the iron core is generally a unipolar half-waveform and contains a large amount of the second harmonic component. Therefore, conventionally, the internal accident and the iron core magnetic saturation are distinguished by the second harmonic suppression method.

When an overvoltage is applied to the transformer,
The transformer core may become over-excited and may be magnetically saturated in both positive and negative directions, resulting in a bipolar current difference. Since the second harmonic component contained in the bipolar difference current is small, in such a case, it is difficult to distinguish the internal accident by the conventional second harmonic suppression method.

FIG. 2 shows a phase adjusting transformer composed of a series transformer 3 and an adjusting transformer 4. In FIG. 2, 1
Reference numerals a, 1b, and 1c denote power transmission lines of the phases a, b, and c on the power system 1 side, and reference numerals 2a, 2b, and 2c denote power transmission lines of the phases a, b, and c on the power system 2 side. The series transformer 3 includes series windings 31a, 31b, 31c of the respective phases connected in series with the power system and exciting windings 32a, 32b, 3 of the respective phases for supplying a voltage to the series windings.
2c and. The adjustment transformer 4 includes adjustment windings 41a, 41b, 41c for each phase connected in parallel with the power system and a tap winding 42a having taps for each phase for supplying a predetermined voltage to the excitation winding of the series transformer. 42b, 42c. The voltage to ground of the transmission lines on the side of the power system 1 and the side of the power system 2 in the a phase are VL1 and VL2, respectively, and the voltages of the series winding and the excitation winding of the series transformer are VS1 and V, respectively.
S2, the voltage of the adjusting winding of the adjusting transformer, and the voltage of the tap winding are VE1 and VE2, respectively.

FIG. 3 shows the vector of the voltage at each part in FIG. 2 during steady operation. In FIG. 3, broken lines indicate the directions of the b and c phase voltage vectors in order to clarify the relationship between the three phases. As shown in FIG. 3, the series winding voltage VS1 of the series transformer at the time of steady operation has a substantially quadrature phase with respect to the ground voltage VL1 and VL2 of the power transmission line, and the tap winding tap of the adjustment transformer is provided. VS1 by switching
It is possible to give a predetermined phase difference between VL1 and VL2 by changing the magnitude of the.

FIG. 4 shows a vector of each voltage in FIG. 2 when a one-line ground fault occurs in the a-phase transmission line on the side of the power system 2. The voltage on the side of the power system 1 is directly applied to the series winding of the series transformer. The voltage VL1 on the side of the power system 1 is lower than that during steady operation due to a voltage drop due to system impedance, but as shown in FIG. 4, the series winding voltage VS1 of the series transformer is higher than that during steady operation
And the phase changes by about 90 degrees. On the other hand, since the exciting winding voltage VS2 of the series transformer is generated by the sound two-phase tap winding voltage of the adjusting transformer, it has almost the same value as that in the steady operation. In any case, the series winding voltage V of the series transformer
When S1 becomes large, the iron core of the series transformer becomes overexcited.

[0007]

When the iron core of the series transformer becomes overexcited, the iron core magnetic flux density exceeds the saturation magnetic flux density,
Exciting current increases rapidly. In the overexcited state, the iron core is magnetically saturated on both the positive side and the negative side, so that an exciting current of both polarities is generated and detected as a difference current. In such a case, since the second harmonic component contained in the difference current is small, it is difficult to distinguish the internal accident by the conventional second harmonic suppression method.

On the other hand, in order to prevent magnetic saturation of the iron core due to overvoltage in the event of a system fault, it is sufficient to increase the iron core cross-sectional area, but in this case, there is a drawback that the transformer size becomes large.

An object of the present invention is to provide a transformer protection device which can detect an internal accident without increasing the size of the transformer and without being affected by iron core magnetic saturation.

[0010]

In order to solve the above-mentioned problems, according to the present invention, a first relay element for judging an internal accident by a difference current between a series winding and an exciting winding of a series transformer,
A second transformer that determines the internal fault of the series transformer by the current of at least one pair of return windings connected in anti-parallel and built in the series transformer or the difference current between the return winding and the adjustment winding of the adjustment transformer. Two elements, the relay element and the relay element, are used to detect internal accidents in the series transformer.

[0011]

The pair of return windings contained in the series transformer are wound around the iron core with the same number of turns and are connected in antiparallel. The direction of the current flowing back through the pair of return windings is opposite in each return winding, and the ampere-turn is canceled. Therefore, the exciting current component of the series transformer cannot flow in this return winding, and by utilizing the current in the return winding, the effect of iron core magnetic saturation can be eliminated, and without being affected by iron core magnetic saturation, Internal accidents can be detected. In addition, the first (or second) relay element malfunctions due to some cause by judging by the difference current between the series winding of the series transformer and the exciting winding and the current of the return winding. However, unless the second (or first) relay element also malfunctions, it is not judged as an internal accident. Since the probability of two relay elements malfunctioning or malfunctioning at the same time is extremely small, the protection device of the present invention is a reliable device in which malfunctioning or malfunctioning of one relay element does not cause malfunctioning or malfunctioning of the device. Is.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a phase for one phase out of three phases of a series transformer connected in series to the electric power system and a regulation transformer connected in parallel to the electric power system (a is a phase). Represents).

In FIG. 1, 1a and 2a are transmission lines of a power system to which a series transformer and a regulating transformer are connected, 3 is a series transformer connected in series to the power system, and 4 is connected in parallel to the power system. The regulated transformer 5 designated is a transformer protection device according to the invention. 61a and 62a are circuit breakers,
This is to shut off the circuit when an accident occurs. Also,
Reference numerals 71a, 72a, 73a, 74a, and 75a are current transformers, which are the transmission line 1a, the transmission line 2a, the excitation winding 32a of the series transformer, the return windings 33a and 34a of the series transformer, and the adjustment winding of the adjustment transformer. It is for detecting the current of the line 41a.

The series transformer 3 compensates for a series winding 31a connected in series with the transmission lines 1a, 2a, an exciting winding 32a for supplying a voltage to the series winding, and an ampere-turn of a current supplied to a regulating transformer. And a pair of return windings 33a and 34a connected in anti-parallel to each other.

The adjusting transformer 4 comprises an adjusting winding 41a connected in parallel with the power system and a tap winding 42a for supplying a predetermined voltage to the exciting winding of the series transformer.

The protection device 5 of the present invention is composed of two relay elements, from the current transformers 71a and 72a to the series winding 31a.
The first relay element 51 that derives the current of the exciting winding 32a from the current transformer 73a and synthesizes the difference current so as to be substantially zero during steady operation, and the current transformer 74a to the return winding 33a and The current of 34a is formed with the second relay element 52 which derives the current of the adjustment winding 41a of the adjustment transformer 4 from the current transformer 75a and synthesizes the difference current so that it becomes almost zero during steady operation. There is. Then, the outputs of these two relay elements 51 and 52 are input to the AND circuit. When the AND circuit detects an internal accident, trip output to the circuit breakers 61a and 62a is performed to cut off the power system.

In order to clarify the effect of the present invention, first, an example of winding arrangement of a series transformer and a current distribution of each winding of the series transformer during steady operation will be described.

In FIG. 1, IS1 is a current component of the series winding current of the series transformer that flows from the power transmission line 1a to the series winding 31a and flows to the power transmission line 2a, and IS2 is the excitation winding 32a of the series transformer. Current, IC is the return winding 3 of the series transformer
Reference numeral 3a, 34a represents a current flowing back, IE represents a current of the adjustment winding 41a of the adjustment transformer. Next, FIG. 5 shows an example of winding arrangement of the series transformer. FIG. 5 schematically shows the cross section of the series winding, the excitation winding, the pair of return windings and the current distribution of each winding of the series transformer wound around the iron core 8.

During steady operation, the passing current component IS1 of the series winding 31a is in ampere-turn equilibrium with the exciting winding current IS2 which is wound and arranged so as to face the series winding. The current IE flowing through the adjustment winding of the adjustment transformer is supplied by ½ from each of the power transmission line 1a side and the power transmission line 2a side. A component IE / 2 of the current of the series winding 31a which flows into the adjusting transformer from the upper half portion of the series winding of FIG. 5 is a return winding 33 which is arranged so as to face the series winding portion.
The current IC of a and the ampere-turn are balanced. Of the current of the series winding, the current component IE / 2 that flows into the adjusting transformer from the lower half of the series winding of FIG. 5 is the return winding 34a that is arranged to face the series winding. Current IC and ampere-turn are balanced.

Since the return windings 33a and 34a are connected in anti-parallel, the current IC returns to the return windings 33a and 34a. Further, since the return windings 33a and 34a have the same number of turns, the total of ampere-turns of both is zero. That is, the currents of the return windings 33a and 34a do not include an exciting current component. Similarly, the current components IE / 2 flowing in opposite directions in the upper half and the lower half of the series winding 31a do not include an exciting current component because they cancel each other ampere-turns. That is, the exciting current component of the series transformer is included only in the passing current component IS1 of the current of the series winding 31a or the current IS2 of the exciting winding 32a.

Next, assume a case where a ground fault occurs on the power transmission line 1a or 2a in FIG. As described above, the series transformer becomes overexcited as the voltage of the series winding 31a of the series transformer 3 increases, and the iron core of the series transformer is magnetically saturated. That is, the series winding current IS1 and the excitation winding current I
The ampere-turn equilibrium condition with S2 is different from that during steady operation, and the series winding current IS1 and the excitation winding current IS
The combined differential current with 2 does not become zero, and the first relay element 51 determines that it is an internal accident. However, as described above, since the IC and IE do not include the exciting current component of the series transformer, the current component IE / IE of the return winding current IC and the series winding current that flows into the adjusting winding of the adjusting transformer. The ampere-turn equilibrium condition with 2 is the same as during steady operation. That is,
The differential current combined by the second relay element 52 is almost zero as in the steady operation, and it is not determined that the internal accident.

Therefore, the difference current combined by the first relay element does not become zero, but the difference current combined by the second relay element becomes zero, and the protection device of the present invention causes the ground fault accident due to the AND condition. Do not judge as an internal accident when it occurs.

Next, it is assumed that an internal accident such as partial winding short circuit occurs in the series transformer. When a winding part is short-circuited, it is generally considered that the current distribution is determined so that the ampere-turns are balanced in the entire series winding, excitation winding, and return winding, including the short-circuited portion. That is, the ampere-turn equilibrium conditions of the currents IS1 and IS2 and the currents IC and IE / 2 are different from those in the steady operation and the iron core magnetic saturation, and the first relay element of the present invention is the same as the above-mentioned internal accident. To determine. Further, regarding the second relay element as well, the differential current combined by the second relay element is not zero, and it is determined that the internal accident.

Therefore, the differential current combined in the first relay element does not become zero, and the differential current combined in the second relay element also does not become zero. When a partial short circuit accident occurs, it can be judged as an internal accident.

Another embodiment of the present invention will be described with reference to FIG. The configuration of FIG. 6 differs from that of FIG. 1 in that the voltage of the regulating transformer 4 connected in parallel with the power system is taken directly from the transmission line 1a, not from the intermediate portion of the series winding of the series transformer 3. In the protection device 5 of the present invention, the input current of the first relay element is a current transformer 72a for detecting the current of the series winding 31a, and a current transformer 73a for detecting the current of the exciting winding 32a. And that the input current of the second relay element is derived only from the current transformer 74a installed to detect the current in the return windings 33a and 34a.

By taking the voltage of the regulating transformer 4 directly from the transmission line 1a, the series winding current of the series transformer is
There is only the component IS1 passing from a to 2a, and this current balances the excitation winding current IS2 and the ampere-turn. That is, during steady operation, the currents of the return windings 33a and 34a detected by the current transformer 74a are substantially zero.

When the iron core of the series transformer is magnetically saturated due to a power system accident, the ampere-turn between the currents IS1 and IS2 is different from that during steady operation, and the series winding current IS1 and the exciting winding current IS2 are combined. The generated difference current does not become zero, and the first relay element 51 determines that it is an internal accident. However, since the exciting current does not flow through the return windings 33a and 34a, the current detected by the current transformer 74a is almost zero, and the second relay element does not determine that it is an internal fault.

Therefore, the difference current combined by the first relay element does not become zero, but the difference current combined by the second relay element becomes zero, and the protection device of the present invention causes the power system failure due to the AND condition. Do not judge as an internal accident when it occurs.

In the event of an internal accident in the series transformer, the return winding 33
A return current also flows through a and 34a, and ampere turns are balanced in the entire series winding 31a, excitation winding 32a, and return windings 33a and 34a. That is, the ampere-turn of the current flowing through the series winding and the exciting winding is different from that during the steady operation, and the combined difference current between the series winding current IS1 and the exciting winding current IS2 does not become zero. Relay element 51
Is an internal accident. Further, since the current flows through the return winding, it does not become zero, and the second relay element that receives the current from the current transformer 74a that detects the current through the return winding determines that the internal fault has occurred.

Therefore, since the differential current combined in the first relay element does not become zero and the current input to the second relay element does not become zero, the protection device of the present invention has an AND condition so that an internal accident occurs. It can be judged as an internal accident.

On the other hand, in the winding configuration example of the series transformer shown in FIG. 5, each of the pair of return windings 33a and 34a is placed at a magnetically symmetrical position with respect to the series winding 31a and the exciting winding 32a. Although the windings are arranged, a plurality of pairs of return windings may be arranged. Furthermore, each of the pair of return windings is connected to the series winding 3
1a, it can also be wound and arranged in a magnetically asymmetrical position with respect to the excitation winding 32a.

When the internal fault of the series transformer is, for example, a partial winding short-circuit fault occurs at a symmetrical portion with respect to the return windings 33a and 34a, the return winding current or the return winding is It is also conceivable that the equilibrium condition of the ampere-turn between the current and the adjusting winding current of the adjusting transformer does not change from that during steady operation. By arranging a plurality of pairs of return windings having different magnetic positional relationships, it is possible to reliably detect such an accident. When arranging a plurality of pairs of return windings, the second relay element of the protection device of the present invention derives the current of each return winding pair, and generates a difference current that becomes almost zero during steady operation. Will be configured.

[0033]

According to the present invention, only the internal accident of the transformer can be reliably detected without being affected by the iron core magnetic saturation of the transformer.
And by judging by two relay elements,
Since malfunctions and malfunctions are prevented, it is possible to prevent the iron core of the transformer from being magnetically saturated and prevent the iron core from increasing in size, thus making the transformer compact.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a conventional circuit diagram.

FIG. 3 is a conventional voltage vector diagram.

FIG. 4 is a conventional voltage vector diagram.

FIG. 5 is a cross-sectional view of a winding winding arrangement of a series transformer.

FIG. 6 is an explanatory diagram of another embodiment of the present invention.

[Explanation of symbols]

3 ... Series transformer, 4 ... Adjustment transformer, 5 ... Protective device, 31
a ... Series winding, 32a ... Excitation winding, 33a, 34a ... Return winding, 41a ... Adjustment winding, 42a ... Tap winding, 51
... first relay element, 52 ... second relay element.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshito Ueno 1-1-1 Kokubun-cho, Hitachi-shi, Ibaraki, Ltd. Kokubun Plant, Hitachi, Ltd. (56) Reference JP-A-58-190228 (JP, A) JP-A-58-182425 (JP, A) JP-A-56-147728 (JP, A) JP-A-50-82543 (JP, A) JP-A-47-26652 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02H ^7/ 04-7/055

Claims (4)

(57) [Claims] 1. A voltage phase of the power system, or the voltage value and the voltage phase series windings inserted in series to the power system for adjusting the exciting winding for supplying the voltage to the series winding, It also protects a series transformer with at least a pair of anti-parallel connected return windings excited by said series windings.
A than a front Kijika row winding and the first relay element determines the presence or absence of internal fault of the series transformer due to the difference current between the excitation winding,
A second relay element for determining an internal fault of the series transformer by a current of the return winding, and the first and second relay elements .
The internal condition is judged by the AND condition of the relay elements of
A protective device for a transformer, which is characterized by performing trip output to . 2. A power system in inserted in series windings in series, the <br/> series winding voltage excitation winding for supplying to the, by at least a pair of the series winding connected in antiparallel Adjustment consisting of a series transformer composed of an excitation return winding, an adjustment winding connected in parallel to the power system, and a tap winding having a tap and supplying a predetermined voltage to the excitation winding of the series transformer To protect the phase adjustment transformer with the transformer
There are, as before Kijika row winding and the first relay element determines the presence or absence of internal fault of the series transformer due to the difference current between the excitation winding,
A second relay element for determining an internal fault of the series transformer by a current of the return winding, and the first and second relay elements .
The internal condition is judged by the AND condition of the relay elements of
A protective device for a transformer, which is characterized by performing trip output to . 3. A power system in inserted in series windings in series, the <br/> series winding voltage excitation winding for supplying to the, by at least a pair of the series winding connected in antiparallel Adjustment consisting of a series transformer composed of an excitation return winding, an adjustment winding connected in parallel to the power system, and a tap winding having a tap and supplying a predetermined voltage to the excitation winding of the series transformer To protect the phase adjustment transformer with the transformer
There are, as before Kijika row winding and the first relay element determines the presence or absence of internal fault of the series transformer due to the difference current between the excitation winding,
A second relay element that determines an internal fault of the series transformer by a difference current between the return winding and the adjustment winding of the adjustment transformer, and AND of the first and second relay elements
An internal accident is judged based on the conditions and trip output to the circuit breaker is performed.
Cormorant that transformer protection device according to claim. 4. The transformer protection device according to claim 3, wherein one terminal of the adjustment winding of the adjustment transformer is connected to an intermediate portion of the series winding of the series transformer. .