JPH02237424A - Open-phase detection in three-phase circuit transformer and device therefor - Google Patents

Abstract

PURPOSE:To implement open-phase detection without fail by detecting the temperature difference of windings constituting a delta network and by detecting that one phase is an open-phase. CONSTITUTION:The temperature of each winding of a three-phase circuit transformer 1 is detected by a temperature detector 2 and connected to an arithmetic section 5 of a device main body 4. After each temperature signal was amplified by an amplifier 6, it is inputted into a temperature difference arithmetic circuit 7. When the temperature difference between each phase winding is operated by the temperature difference arithmetic circuit 7 and one of these differences exceeds the set value of a temperature difference setter 9, an output is issued to an alarm circuit 10 by a comparison detection circuit 8.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method and device for detecting phase loss in a three-phase circuit transformer, and in particular to a method for detecting phase loss in a three-phase circuit transformer and a device therefor. The present invention relates to a method and apparatus for detecting an open phase in a three-phase circuit transformer by comparing a temperature difference with a preset temperature difference.

(Prior art) Three-phase circuit transformers that transform three-phase alternating current have various wiring systems depending on the purpose. For relatively low-voltage power distribution, star-shaped one-triangular wiring or triangular-one-triangular wiring are used. In my case, even if one of the three phases is open, it has the advantage of being able to supply three-phase AC to the load as a connection.

However, in the case of the (3) connection, the load is shared between the remaining two phases, so the maximum allowable load is reduced to approximately 87% of that of the triangular connection. Therefore, it is necessary to take measures such as limiting the increase in normal load, but if you continue to supply power without knowing about the loss of power, it will worsen the power factor and lead to power outage accidents due to overload. Therefore, it is desirable to detect and deal with missing n1 accidents at an early stage.

The conventional method for detecting phase loss in triangular connections is to detect phase loss by determining abnormal noise, abnormal vibration, abnormal odor, etc. during daily inspection. There are methods such as installing an overcurrent relay to detect overcurrent due to an open phase.

[Problem to be solved by the invention]

However, the method based on daily inspections lacks reliability because it takes a long time to detect an open phase, and because it relies on human five senses, there is uncertainty.

Furthermore, the method using an overcurrent relay has a problem in that it is impossible to detect an open phase as long as the load is within the allowable load range due to (1) connection.

The present invention solves the problems in the conventional method of detecting one phase of a three-phase circuit transformer and provides a method for reliably detecting a phase loss within the permissible load range of the wiring. It is an object of the present invention to provide an open phase detection device suitable for implementing the method.

[Means for Solving the Problems] To achieve the above object, the method for detecting phase loss in a three-phase circuit transformer according to the present invention detects a change in heat generation in the windings constituting the triangular connection of the three-phase circuit transformer. It is characterized by detecting an open phase in one phase of the triangular connection by comparing the temperature difference between each phase with a preset temperature difference value.

Further, the open phase detection device of the present invention suitable for implementing the above method includes temperature detectors for detecting temperature changes in each phase due to heat generation changes in the windings forming the triangular connection of the three-phase circuit transformer. , a temperature difference calculation circuit that calculates the temperature difference between each phase from the detected value of the detector, and l, ! that sets the temperature difference between each phase.
! The temperature difference setting device is characterized by comprising a temperature difference setting device, and a comparison detection circuit that compares the temperature difference value obtained by the arithmetic circuit with the setting value of the setting device to detect one phase open phase.

[For production]

When one phase of the triangular connection is open, the load current of the missing winding becomes zero, so heat generation due to resistance loss in the winding disappears, and the temperature of the open phase becomes lower than during normal operation. On the other hand, ■
Since the load current of the remaining two-phase windings constituting the wire connection increases, the temperature of the healthy phase tends to rise due to heat generation. The temperature difference between the two increases over time with a delay due to heat capacity after the open phase occurs. Therefore, this temperature difference is compared with a preset temperature difference value, and when the value becomes equal to that value, an open phase can be detected.

The set value of the temperature difference can be determined as appropriate by taking into consideration the temperature imbalance between each phase due to temporary unbalanced load fluctuations, variations in temperature detection accuracy, etc., and this allows for accurate detection of open phase. It can be carried out.

Since the present invention detects temperature imbalance due to changes in heat generation in the windings between a healthy phase and an open phase, it is possible to reliably detect an open phase without being substantially affected by load fluctuations or changes in outside temperature.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an example of an open phase detection device for a three-phase circuit transformer according to the present invention. In the figure, temperature detectors 2 for detecting temperature changes in each phase due to changes in heat generation in the windings of a triangularly connected three-phase circuit transformer 1 are connected to a calculation unit 5 of a main body 4 of the device through wiring 3. There is. The temperature detector 2 converts the temperature of each phase into an electrical value proportional to the temperature, and is, for example, a resistance temperature detector, semiconductor thermistor, etc. made of platinum or copper, etc.
A thermocouple made of platinum-rhodium, alumel-chromel, or the like can be used.

The output (temperature signal) of each temperature detector 2 is amplified by an amplifier 6 provided as necessary, and then inputted to a temperature difference calculation circuit 7. Slight temperature unbalance between each phase or zero point shift between temperature detectors during normal times can be compensated for by adjusting the base level of the amplifier 6.

Three temperature difference calculation circuits 7 are provided, and the outputs of the two amplifiers 6 are inputted differentially to each of them, and between the 1st phase and 2nd phase, the 2nd phase
Temperature differences between phases 3 and 3 and between phases 3 and 1 are calculated. The arithmetic circuit 7 outputs zero when there is no difference between the two input signals, and outputs a positive output signal (
In other words, it is a type of differential amplifier circuit configured to output an absolute value output.

Next, the output of each temperature difference calculation circuit 7 is additively inputted to a comparison detection circuit 8, where it is compared with a set value of a temperature difference setting device 9. The output of this comparison detection circuit 8 is zero when the added output value of each temperature difference calculation circuit 7 is lower than the temperature difference setting value.
Output signal when the temperature rises to a value equal to the set value. In other words, an open phase signal is output.

The arithmetic section 5, which is composed of the amplifier 6, the temperature difference arithmetic circuit 7, and the comparison detection circuit 8 described above, can also be constituted by an IC circuit.

The output of the comparison detection circuit 8 can be directly connected to an external terminal of the device main body 4 and output to a separately provided alarm circuit, but in the example shown in FIG. , lamp display and buzzer alarm can be performed. This alarm circuit 10 may be provided with a terminal 11 for driving an external alarm circuit or the like.

The output of the comparison detection circuit can further be connected to an external control circuit (for example, a load limit interlock circuit, etc.), not shown, via an I/O interface circuit 12 and its terminal 13 provided as necessary.

Next, FIGS. 2 and 3 are diagrams schematically showing examples of how temperature detectors are attached to each phase in the present invention. FIG. 2 shows an example in which temperature detectors are installed close to each winding of a three-phase transformer housed in a single transformer outer box. Temperature detector 2
may be embedded in the winding, attached to its surface, or placed slightly apart from the winding. Furthermore, it can also be installed downstream of the windings within the cooling medium circulating within the outer box.

In either case, the temperature sensor 2 can be attached directly to the transformer inner tube or housed in a heat-conducting protective tube.

When directly attached to the surface of the winding, it is preferable to use, for example, a thin film surface temperature type detection element. When using a protection tube, it is preferable to provide a mounting seat on the outer box of the transformer, attach the protection tube, and insert a temperature sensor into the protection tube from the outside.

Next, FIG. 3 shows an example of attaching a temperature sensor to each phase when the windings of three single-phase transformers housed in separate transformer outer boxes are triangularly connected externally. In this example, a temperature detector 2 is attached to the surface of each transformer outer box. When such an attachment method is adopted, it is preferable to use the above-mentioned surface temperature type detection element as the temperature detector 2. Of course, it is possible to install a temperature converter inside each transformer as in the example shown in FIG.

Next, the operation of the open phase detection device shown in FIG. 1 will be explained.

When each phase of the three-phase circuit transformer 1 is healthy, the output of the temperature detector 2 of each phase is almost the same, and therefore the output of each amplifier 6 that amplifies it is also the same. Therefore, since the output of each temperature difference calculation circuit 7 is zero, the temperature difference signal becomes the temperature difference set value, and the comparison detection circuit 8 does not output an open phase signal.

If one phase of the triangular connection, for example, the second phase, is deficient, the heat generation of the second phase winding stops and the temperature of that phase decreases. On the other hand, the temperatures of the remaining healthy phases, the first phase and the third phase, on the contrary, rise somewhat. These temperature changes are detected by each temperature detector 2 and then amplified by an amplifier 6.
Among the three temperature difference calculation circuits 7, between 1 phase and 2 phases and between 2 phases -
The outputs of the circuits that calculate the differences between the three phases each have values corresponding to the differences, and the outputs of the remaining circuits that calculate the differences between the one phase and the three sums remain substantially zero. Therefore, the increased outputs of the two circuits are added to the next comparison and detection circuit 8 and input manually.

In this way, the temperature imbalance between each phase due to one phase being open is changed into an additively increased output, so
It is possible to obtain open-phase signals with extremely high sensitivity.

Next, these temperature difference signals are compared with the set value from the temperature difference setter 9 in the comparison detection circuit 8, and when the temperature difference signal≧the temperature difference set value is satisfied, an open phase output is output. This open phase output drives the alarm circuit 10 shown in FIG. 1 and is further output to the outside via the I/O interface circuit 12.

〔Effect of the invention〕

Since the open-phase detection method and device for a three-phase circuit transformer of the present invention have the above-described configuration, open-phase can be easily detected even within the permissible load range of the connection. Furthermore, since this method detects temperature imbalance due to temperature changes in the windings between a healthy phase and an open phase, it is virtually unaffected by load fluctuations or changes in outside temperature, so open phase detection can be performed reliably.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of an open phase detection device for a three-phase circuit transformer according to the present invention, and FIGS. 2 and 3 are diagrams schematically showing examples of how temperature detectors are attached to each phase. l...Three-phase circuit transformer 2...Temperature detector 3...
・Wiring 4...Device body 5...Calculation section 6...Amplifier 7...Temperature difference calculation circuit
8... Comparison detection circuit 9... Temperature difference setting device 1
0... Alarm circuit l1... Terminal l2... I/O interface circuit l3... Terminal agent Patent attorney Takumi Kubota

Claims (1)

[Claims] 1) Detecting an open phase in one phase of the triangular connection by comparing the temperature difference between each phase due to heat generation changes in the windings forming the triangular connection with a preset temperature difference value. A method for detecting phase loss in three-phase circuit transformers. 2) Temperature detectors (2) for detecting temperature changes in each phase due to heat generation changes in the windings that make up the triangular connection, and temperatures for calculating the temperature difference between each phase from the detected values of the detectors (2). A difference calculation circuit (7), a temperature difference setter (9) for setting the temperature difference between each phase, and a comparison between the temperature difference value obtained by the calculation circuit (7) and the set value of the setting device (9). An open phase detection device for a three-phase circuit transformer, comprising: a comparison detection circuit (8) for detecting one phase open phase.