JPS5840412B2 - Hentatsukino Kafukakenshiyutsusouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transformer overload detection device that utilizes a potential storage element whose potential changes approximately linearly in accordance with the amount of energization.

During operation, the insulation of a transformer gradually deteriorates due to the effects of temperature, humidity, and oxygen in the atmosphere, and as this progresses, abnormal voltage due to external and internal lightning, or electromagnetic mechanical force during external short circuits may occur. The risk of destruction when subjected to abnormal electrical or mechanical pressure increases.

The lifespan of a transformer is defined as the period from the start of operation to the point at which the above-mentioned danger level becomes extremely high, and this lifespan is most affected when the winding temperature of the transformer is at its highest temperature.

Generally, it is stipulated that a normal life of about 30 years can be expected if the ambient temperature is kept constant at 25°C, continuous operation is performed at the rated load, and the maximum point temperature is 95°C.

However, during actual operation of a transformer, the winding temperature fluctuates due to fluctuations in ambient temperature, load fluctuations, and changes in cooling conditions, and in some cases, even if the life of the transformer is sacrificed slightly, the winding temperature will fluctuate. Sometimes there is an overload.

Therefore, as a conventional transformer overload detection device, Fig. 6a
As shown in the figure, a bridge circuit is formed by four platinum resistors R having the same resistance value, and when the negative side is placed in the oil of a transformer, when the oil temperature rises, the balance of the bridge circuit is broken and the meter A swings.

The winding temperature is estimated by reading the deflection of meter A.

Alternatively, as shown in Figure 6, the load current of transformer TR is transferred to current transformer C.
A method is known in which the temperature of the winding of the transformer is estimated by detecting the temperature at T and reading the load current value using a meter A.

However, with method a, the difference between the oil temperature and the winding temperature is not uniform depending on the size of the transformer, and with method a, the difference between the load current value and the time that the current is flowing is different. The drawback is that the exact winding temperature cannot be determined unless the ambient temperature of the transformer is measured and the ambient temperature of the transformer is taken into consideration.In the end, these methods cannot accurately detect when the transformer is overloaded.

The present invention has been made in view of the above points.

The feature is that it uses a potential storage element whose potential changes approximately linearly according to the amount of current flowing, and stores a voltage in the storage element that corresponds to the winding temperature that changes in a complicated manner within a certain period of time. The purpose of this system is to store the integrated value, display the integrated value (temperature 0 hours) on a display circuit, and use an alarm or the like to notify the time when the integrated value exceeds the allowable value, thereby reducing the life loss of the transformer.

Next, the principle of the device of the present invention will be described.

The winding highest point temperature θH in a steady state when a constant load P is applied to the transformer is given by the following equation.

In some cases, the load fluctuates as shown in Figure 3.
For example, when the load suddenly changes from 1 PN to 2 PN, the oil temperature θ0 changes with a certain time constant, and the change is expressed by the following equation.

It can be seen from these equations (IX2X3) (4) that the winding temperature of the transformer can be calculated by detecting the ambient temperature and load current of the transformer.

An embodiment of the device of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a potential storage element used in the device of the present invention, and this element consists of an anode P mainly made of a silver-tellurium alloy, a cathode N mainly made of silver, and an auxiliary cathode for potential detection. For example, RbA has high ionic conductivity between N'
It is a type of battery that sandwiches a solid electrolyte E made of g, I, or Ag3SI, and silver on the anode P becomes ions in the solid electrolyte E by passing current in the P-)N direction (this is called a charging current). and is deposited on the cathode N, and conversely, when current is applied in the N-)P direction (
The silver deposited on the cathode N is restored and deposited on the anode P by this process (called discharge current).

The electromotive force of this device as a battery shows a value that depends on the activity of silver in the silver-tellurium alloy, and when the atomic composition ratio of silver and tellurium in the silver-tellurium is close to 2, there is a slight charge and discharge. The activity of silver in the anode P changes due to the current, and the relationship between the electromotive force and the charging/discharging capacity l-1 is as shown in Figure 2, where the electromotive force is 0 to 100 mV and the current density is 100 μA/ffl or less. In this case, there is an almost linear relationship both during charging and discharging.

Furthermore, this element has the characteristic that even if the current to the element is cut off at any potential between 0 and 100 mV, the potential immediately before the cutoff is maintained.

In the block diagram of FIG. 4 and the specific electric circuit diagram of FIG. It consists of a DC amplifier AP.

11 is a load current detection circuit, which includes a current transformer CT that detects the load current of the transformer, and a resistor RIO1 that converts this current into a voltage.
It is composed of rectifying diodes D1 to D4 and a smoothing capacitor C1.

11 is an oil temperature conversion circuit, which includes resistors R1□ to R14, a resistor R11 for obtaining a CR time constant, a capacitor C2, and a DC amplifier A.
Consists of P2.

IV is an oil temperature-winding temperature difference conversion circuit and is composed of a resistor R15.

Note that the resistance R1□, R1, is approximately 2/2 of the oil temperature and winding temperature.
Considering that the resistance is three times as large, the resistance R1□ is set to twice the value of the resistance R15.

Reference numeral (2) denotes a time limit setting circuit, which includes resistors R16 to R19 having different resistance values for controlling the charging current value of the potential storage element, a changeover switch SW1, a mechanical or electronic timer TM, and a timer contact TM that opens after the time limit has elapsed.

vl is an integration storage circuit, which includes a potential storage element MD, and a charging/discharging changeover switch SW2 for resetting the elements. Charge/discharge resistance R2□J
R20, DC amplifier AP for amplifying the output potential of the element, 7
11j and resistors R22 to R22.

vll is a display circuit and transistors Tr1 to Tr3
, a light emitting diode D3, an indicator M, a temperature compensating diode Z, resistors R25 to R32, and a variable resistor for setting the allowable temperature of the transformer.

Next, the operation of the device of the present invention will be explained in detail with reference to FIG.

The ambient temperature of the transformer is detected by a heat sensitive element TH and converted into a voltage, and this voltage is amplified by a DC amplifier AP.

Therefore, the voltage that corresponds to the ever-changing ambient temperature is the resistance R.
Appears between both ends of 0.

Also, the load current of the transformer is detected by the current transformer CT and the resistor R1
Due to this, a DC voltage corresponding to the load current (winding temperature) appears at point B via a voltage conversion rectifier circuit.

This voltage is converted into a voltage corresponding to the oil temperature and a voltage corresponding to the difference between the oil temperature and the winding temperature using a conversion circuit in the next stage.

Here, regarding the relationship between the winding temperature and the oil temperature, as mentioned above, the final temperature is 7 times the oil temperature and the winding temperature, so the resistance R1□ is set to be twice the resistance R15. There is.

Furthermore, since the oil temperature changes with a constant time constant, the oil temperature conversion circuit 111 includes a resistor R1 that forms a CR time constant.
1 and a capacitor C2 are provided.

Therefore, the voltage corresponding to the oil temperature is equivalent to the amount of charge in the capacitor C2, and that voltage appears across the resistor R14.

Further, a voltage corresponding to the oil temperature-winding temperature difference appears across the resistor RI5.

As a result, the voltage at point A becomes the sum of the voltage corresponding to the ambient temperature, the voltage corresponding to the oil temperature, and the voltage corresponding to the oil temperature-winding temperature difference.

Now, during measurement, the potential storage element MD is
By setting the charging current value and setting a desired time using the timer TM, the potential storage element is charged with the above-mentioned total voltage within the predetermined time, and the potential changes linearly according to the charging current. .

This potential is amplified by the amplifier AP3, and the pointer of the display meter M swings in accordance with the potential, making it possible to know the winding temperature change in an analog way, and to set the allowable amount in advance by a variable resistor. When the potential rises above the potential, the transistor Trl
is ON, transistor Tr2 is OFF, transistor T
When r3 is turned ON, the light emitting diode D emits light to notify the time of overload of the transformer.

When re-measuring, set the reset switch SW2 to
When connected to the contact point, the potential storage element MD is forced to discharge via the discharge resistor R2□, and the remaining capacity is cleared.

When connected to the a contact point, the display meter M is charged via the charging resistor R20, so that the display meter M can be finely adjusted by operating the changeover switch SW2 at the start of measurement.

As described above, the present invention is a transformer overload detection device that utilizes a potential storage element whose potential changes linearly in accordance with the amount of energized air, and the first detection device detects the ambient temperature of the transformer. a second detection circuit that detects the load current of the transformer and converts it into a voltage corresponding to the winding temperature; and a conversion circuit that converts the second detected voltage into a voltage corresponding to the cooling oil temperature. By providing a circuit and charging the potential storage element with a voltage corresponding to the ambient temperature and oil temperature, and displaying the cumulative amount on the display circuit, the display circuit can very easily indicate when the transformer is overloaded. This can be accurately determined and greatly contributes to extending the life of the transformer.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the potential storage element used in the device of the present invention, FIG. 2 is a voltage-electricity characteristic diagram of the same element, and FIG. 3 is a characteristic diagram of winding temperature rise with respect to load fluctuations. 4 and 5 are block diagrams and specific electric circuit diagrams of the apparatus of the present invention, and FIGS. 6a and 6b are diagrams showing a conventional method. MD: potential storage element, 1: ambient temperature detection circuit, 11: load current detection circuit: 1
1...Oil temperature conversion circuit, 1■...Oil temperature -
Winding temperature difference circuit, ■...Time setting circuit, vl.
... Integration memory circuit, v11°°°°° display circuit, TH... Heat sensitive body, CT... Current transformer,
R□ and C2... Resistor and capacitor that constitute the CR time constant circuit, TM... Timer T? V
1'...Timer contact, M...Display meter,
D... Light emitting diode, APl. Ar1 and Ar1...DC amplifier, Trl~T
r3...Transistor.

Claims (1)

[Claims] 1 a first detection circuit that detects the ambient temperature of the transformer and converts the voltage; a second detection circuit that detects the load current of the transformer and converts it into a voltage corresponding to the winding temperature; A conversion circuit including a voltage dividing resistor and a CR time constant circuit for converting the detected voltage into a voltage corresponding to the cooling oil temperature, and the sum of each detected voltage corresponding to the ambient temperature and oil temperature are used to charge the battery. An overload detection device for a transformer, which includes a potential storage element whose potential changes according to the amount of air, and a display circuit that displays the integrated amount of the element.