KR102219309B1 - Transformer Using Electric Power Distribution Smart OLTC - Google Patents

Abstract

The present invention relates to a transformer for smart OLTC power distribution and, more specifically, to a transformer for smart OLTC power distribution, including a tap changer for 5TAP and 3TAP, a tap change algorithm, a changeover algorithm, a sensor for diagnosing the same, and a diagnostic device. The transformer for smart OLTC power distribution switched by the gear of a motor continuously maintains the load current I during a tap change process of the tap changer for tap change in a transformer having a plurality of taps on one of the primary winding or the secondary winding and allows the cycle current Ic to flow by connecting a switching resistor between two tap joints so that a first tab and a second tab connector among the plurality of tabs are not short-circuited. In the state of being operated by H or L contact, an interlock circuit is coupled to prevent the direct operation from H contact to L contact or from L contact to H contact.

Description

Smart OLTC Distribution Transformer {Transformer Using Electric Power Distribution Smart OLTC}

The present invention relates to a smart OLTC power distribution transformer, and more particularly, a tap switching device for 5TAP and 3TAP that allows a tap to be automatically switched to another tap even when a physical motor gear malfunction due to high temperature and power failure, etc. It relates to a switching algorithm and a smart OLTC distribution transformer including a sensor and a diagnostic device for diagnosing the same.

Recently, as new and renewable power generation facilities (solar power generation, wind power generation, etc.) increase, the need for voltage stabilization is increasing as voltage fluctuations in the distribution system become frequent.

Conventionally, when connecting distributed power sources such as photovoltaic power generation, the upper limit of the standard voltage and tolerance (220V ± 13V) stipulated in Article 18 of the Electricity Business Act and Article 18 of the Enforcement Regulation of the Act is automatically adjusted by automatically adjusting the voltage upper limit margin of the customer. It is stipulated in the law to maintain, and high-reliability tap-changing unit (mechanical/electronic: 200,000 times operation) to allow voltage fluctuations (voltage rise) by distributed power in the distribution line. Smart transformer voltage control method and uninterrupted power supply The technology that applied the information on the power supply (transformer deterioration status and load facility operation monitoring) to the power company and end-users was used in the transformer monitoring system.

In addition, in Articles 20 and 21 of the distributed power grid connection standard, when an overvoltage problem occurs in the connected transformer when the distributed power grid is connected, a voltage switching technology is required at all times. In addition, the main cause of the failure of the pole transformer is a failure due to moisture penetration, so if moisture penetrates the transformer, the risk of inter-layer short circuits in the transformer's internal windings increases. I need this.

Korean Patent Publication No. 2007-0083239 Korean Patent Publication No. 2001-0100086 Korean Patent Publication No. 2009-0048603 Korean Patent Publication No. 2014-0009389 Korean Patent Registration No. 1171246 Korean Patent Publication No. 2012-0133917 Korean Patent Publication No. 2018-0070301 Korean Registered Office No. 0451752 Korean Patent Registration No. 1701442 Korean Patent Publication No. 2004-0081414 Korean Patent Publication No. 2017-0066835 Korean Registered Office No. 0371173 Korean Patent Publication No. 2006-0066014

The present invention has been made to solve the above problems, and the voltage range (3TAP interval 600±50V, 5TAP 300V±) through stability evaluation of 200,000 TAP verification devices (interlock, post-input priority) stability evaluation The purpose is to provide a device that changes tap-changing within 30V).

In addition, the present invention is a sensor and diagnostic device for diagnosing a smart OLTC distribution transformer, a contact check control part in a tap driving device, an error condition in the diagnostic device, and a PD sensor is installed in the tap operation part to provide moisture and turbidity. , Including temperature diagnosis method.

In addition, in the present invention, a switching resistance is connected between the two tap joints so that the load current I is continuously maintained during the tap switching process of the tap-changing device and the first tap and the second tap connector among the plurality of taps are not short-circuited. Make the current Ic flow.

In addition, the present invention is a product developed for an automatic tap-changing smart transformer is a mechanical mechanism that automatically moves so that tap-changing can be safely performed by using spring elasticity even in the case of an intermediate power failure in which tap-changing is performed automatically by detecting the secondary output voltage. I want to implement

In order to solve the above problems, the present invention is a smart OLTC distribution transformer that is switched by a gear of a motor, in a transformer having a plurality of taps in one of the primary winding or the secondary winding. During the tap switching process, the load current I is continuously maintained and a switching resistor is connected between the two tap joints so that the first tap and the second tap connector among the plurality of taps are not short-circuited, so that the cycle current Ic flows.

The switching resistance limits the cycle current Ic generated by the switching circuit, and makes the cycle current Ic and the load current I equal so that the tap connector does not short-circuit until a certain contact reaches a specific gear in the tap switching process. , Make the load current flow.

The tap-changing device moves from a HIGH winding to a LOW winding through a NORMAL winding, or switches from a LOW winding to a HIGH winding through a Normal winding.

When the tap-changer moves from the NORMAL winding to the HIGH winding, current flows through the CLR as the mechanical contact of R coupled in parallel to the CLR is opened in the initial NORMAL winding ON state, and the high winding is closed, resulting in parallel to the CLR resistance. The high-voltage winding is connected in a structure, and automatic switching to the high-voltage winding is completed as the NORMAL winding is opened, and the sequence from the HIGH winding to the NORMAL winding is operated in reverse order.

When the tap-changer moves from the NORMAL winding to the LOW winding, current flows to the CLR as the mechanical contact of R parallel-coupled to the CLR is opened in the initial NORMAL winding ON state, and the LOW contact of the LOW winding is closed to the CLR. A current flows while a voltage is applied in parallel with the flowing current, and the NORMAL winding is automatically switched to the LOW winding as it is opened, and the switching from the LOW winding to the NORMAL winding proceeds in the reverse order.

If the H contact or L contact is operated, an interlock circuit is connected so that direct operation is not performed between the H contact and the L contact or the L contact and the H contact.

When the H contact or L contact is pressed after the initial start at the N contact, the post-input priority circuit is combined to operate immediately.

At least one of a moisture sensor, a temperature sensor, and a turbidity sensor is coupled to the tap changer.

The present invention made as described above allows the tap change to safely and automatically move by using spring elasticity even in the physical stop operation of the motor gear due to high temperature, intermediate power failure, etc. through a multi-step tap switching method so that no arc or switching current is generated. There is an effect that can be done.

In addition, according to the present invention, it is possible to forcibly control the contact point in the tap driving apparatus through a sequence circuit that automatically moves through an interlock circuit having a priority through an interlock circuit.

In addition, the present invention can provide a reliable device because it is possible to diagnose a smart OLTC distribution transformer using a sensor and a diagnostic device.

In addition, the present invention continuously maintains the load current I during the tap-changing process of the tap-changing device, and a switching resistor is connected between the two tap joints so that the cycle current Ic flows. It has the effect of not shorting the 2-tap connector.

1 is a diagram showing a 5 TAP, 3 TAP mechanical model according to the prior invention.
2A is a view showing a motor operating part using spring elasticity during transfer according to the conventional invention.
2B is a view showing a part operated by using spring elasticity during actual transfer.
2C is a view showing a bottom portion to which a 3-tap switching unit is connected, and is a diagram showing a tap output and an electrical configuration.
2D is a view showing a bottom portion to which a 5-tap switching unit is connected, and is a diagram illustrating a configuration of a tap output.
2E is a view showing the front and side surfaces of the tap-changing device, and is a view showing the name of each part.
3 is a view showing a case of moving to a high-voltage winding (N -> H) in a normal state according to an embodiment of the present invention.
4 is a view showing a case of moving to a low-voltage winding (N -> L) in a normal state according to another embodiment of the present invention.
5 is a view showing an example of a transformer tap switching process in which a secondary side output voltage is sensed and automatically switched from a fourth tap to a fifth tap by a gear of a motor according to another embodiment of the present invention.
6 is a view showing a part (mechanical switching process) connected to a mechanical gear operation part and a transformer winding.
7 is a view showing a TAP verification device (200,000 times) for verification of a smart OLTC distribution transformer according to the present invention.
8 (a) (b) is a diagram of an interlock circuit between H and L contacts, and a diagram of a post-input circuit contact during manual operation.
9 is a diagram showing (a) a PLC output portion during automatic operation and (b) a contact sequence portion during automatic operation.
10 is a diagram illustrating the operation of the PLC automatic transfer program.
11 is a diagram showing an operation algorithm of an automatic tap-changing device.
12 is a diagram showing an internal main contact point during TAP switching.
13 is a view showing that a sensor or the like is installed that monitors the state of the main contact point and checks whether the tap is normally switched.
14 is a diagram showing a diagnosis related to monitoring the state of a transformer when switching a transformer TAP using a diagnosis algorithm.

In order to fully understand the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. This embodiment is provided to more completely explain the present invention to those of ordinary skill in the art. Accordingly, the shape of the element in the drawings may be exaggerated to emphasize a clearer description. It should be noted that in each drawing, the same member may be indicated by the same reference numeral. In addition, detailed descriptions of known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention will be omitted.

The switching order of the tap-changing device according to the present invention is a method of switching in the order of (H->N->L) or (L ->N->H), and always moves through the N normal state.

The present invention is a method of checking the internal state by configuring a contact inside the tap to check the state during tap switching.

As shown in Fig. 2A, if there is an open/open state between the high voltage windings of the transformer during tap change, the uninterruptible state cannot be maintained.

Therefore, the contact point of the tap changer must be constructed in a structure in which the contact point of the tap changer is always in contact with the tap terminal.

In Fig. 2b, the mechanical power for automatic tap switching was applied with two boosting/depressing springs and two locking spring structures.

As shown in Fig. 2c, it is composed of a tap output part 70, an arc extinguishing part 40, and a transition resistance connection part connected to the high-voltage winding of a 3-tap transformer.

The tap output part is structured to connect 2-3, 3-4, 4-5 wiring. When No. 2-3 is connected, it is connected to the transformer by a 13,800V high-voltage winding, when No. 3-4 is connected, a 13,200V normal winding, and a 12,600V low-voltage winding connected by No. 4-5.

As shown in Figure 2d, it is composed of a tap output unit 70, an arc extinguishing unit 40, and a transition resistance connection unit connected to the high-voltage winding of a 5-tap transformer.

The tab output unit 70 is 2-3, 3-4, 4-5. It is structured to connect 5-6, 6-7 wiring.

13,800V when 2-3 is connected, 13,500V when high-voltage winding 3-4 is connected, 13,200V normal winding when 4-5 is connected, 12,900V when 5-6 is connected, and 6-7 are connected If so, it is connected to the transformer with a 12,600V low voltage winding.

As shown in Fig. 2e, the tap-changing device includes a motor operation unit 10, a spring elastic control unit 20, a tap position fixing unit 30, an arc extinguishing unit 40, a mechanical tap operation unit 50, and a transition resistance. (60), it consists of a tap output unit (70).

Specifically, the motor operation unit 10 performs a tap switching process of the tap changer for tap switching through a gear, and the spring elastic control unit 20 has an elastic force to enable the automatic tap switching process of the motor operation unit 10 Provides.

The tap position fixing unit 30 fixes the tap position after the tap switching process is completed, and the arc extinguishing unit 40 extinguishes the spark during the tap switching process.

The mechanical tap operation unit 50 mechanically performs a tap switching process, and the transition resistor 60 limits the current Ic during the tap switching process.

Finally, the tap output unit 70 allows the current Ic to flow in the cycle after the tap-switching process, so that an arc or switching current does not occur. Edo spring elasticity can be used to make the tap change safely and automatically move.

As shown in FIG. 3, in the case of moving from the normal state to the high-voltage winding (N -> H), (a) it operates in the normal tap in the initial state.

(b) As the mechanical contact of R attached in parallel to the CLR (transition (limiting current) resistance) is opened, current flows through the CLR, and the size of the CLR is 8-10 ohms, and the time to withstand is 1 to 1.5 seconds. . Also, the current capacity is up to 60A. At this time, the fuse capacity is 20A.

And (c) As the HIGH winding is closed, the high-voltage winding is connected in parallel with the CLR resistance.

Continued (d) As the NORMAL winding is opened, automatic transfer to the high-voltage winding is completed.

The sequence of going from high pressure to low pressure again operates in the reverse order of the above-described process.

As shown in Fig. 4, when moving from the normal state to the low voltage winding (N -> L) first (e) in the initial state, it operates in the NORMAL winding (Normal Tap), and (f) the R that is attached in parallel to the CLR As the mechanical contact is open, a current flows through the CLR (transition (limiting) resistance), and (g) As the contact of the LOW winding is closed, a voltage is applied in parallel with the current flowing through the CLR and the current flows. And (h) As the NORMAL winding is open, it automatically switches to the LOW winding.

Switching from the LOW winding to the NORMAL winding again proceeds in the reverse order of the above-described process.

As shown in FIG. 5, an example of a transformer tap switching process in which the secondary side output voltage is sensed and automatically switched from the 4th tap to the 5th tap by the gear of the motor is shown.

During the tap switching process, a switching resistor is first indirectly connected between the two tap joints so that the load current I is continuously maintained and the 4th and 5th stage tap connectors are not short-circuited.

The changeover resistance is usually used to limit the cycle current Ic generated by the changeover circuit, making the cycle current Ic and the load current I approximately the same so that during the tap switching process, the contact K is shorted between the tap connectors until it reaches gear 5. Does not work, and allows the load current to flow.

When the contact reaches the fifth gear, the switching circuit is disconnected, and the switching process ends in which the original fourth-stage tap voltage is switched to the fifth-stage tap voltage.

6 shows a mechanical gear operation part and a part connected to the transformer winding (mechanical switching process).

At this time, the range of primary TAP voltage (V) is 13,800-13,200-12,600 for 3-TAP, and 600V±60V for TAP interval is 540V ~ 660V.

5-TAP is 13,800-13,500-13,200-12,900-12,600, TAP interval is 300V ± 30V, 270V ~ 330V.

As shown in Figure 7, the TAP to be switched over of the TAP verification device (200,000 times) for verification of the smart OLTC distribution transformer according to the present invention is the primary side, and the secondary side voltage of the transformer is manually and automatically 200V, 220V, The tap is switched by applying a 240V voltage to operate it.

For example, before the switch is turned on, 10 cycles should be performed to check whether the mechanical operation of the switch is smooth and the installation position is reliable, and that the DC resistance for each tap position of the transformer is normal compared to the factory data.

When switching the TAP verification device, the start starts from the N contact point in the middle, and the mechanical and electrical TAP switching test is conducted in a reciprocating operation method of N contact -> L contact -> N contact -> H contact -> N contact.

As shown in Figs. 8 to 10, when the selector switch is set to the manual mode in the manual operation in the control sequence and then the red ON button is pressed, the operation is performed.

8 (a) (b) is a diagram of an interlock circuit between H and L contacts, and a diagram of a post-input circuit contact during manual operation.

If it is operated with H or L contact, it is operated by inserting an interlock circuit so that it does not operate between H contact -> L contact or L contact -> H contact.

In addition, after the initial start at the N contact point, when the H contact or the L contact is pressed, the post input circuit is put to operate.

FIG. 9 is a view showing (a) a PLC output part during automatic operation and (b) a contact sequence part during automatic operation, and FIG. 10 is a diagram illustrating an operation of a PLC automatic transfer program.

As shown in Figs. 9 and 10, when the PB1 automatic input of the selector switch is input, the PLC automatic transfer program is operated starting with the self-maintenance operation of the M1 contact point.

Hereinafter, a diagnostic algorithm for automatically performing tap switching by detecting the secondary output voltage of the automatic tap switching smart transformer will be described.

In addition, as shown in Fig. 11, it is assumed that the reference voltage is 220V in accordance with Article 18 (Quality Standards of Electricity) of the Enforcement Rule of the Electricity Business Act.

The control unit according to the present invention first selects a dead zone area that does not affect the tap switching operation as ±2.

That is, the upper limit of the deadband is 220 × 1.02 = 224.1 [V], and the lower limit of the deadband is 220 × 0.98 = 215.6 [V].

Specifically, as in section A, when the voltage on the secondary side of the transformer is within 224.1 ~ 215.6 [V], the tap-changing operation is not performed as a voltage stabilization section.

In section B, when the voltage exceeds the deadband (±2%) range of the secondary side of the transformer, the controller recognizes it as voltage instability, and the cumulative total of the voltage and duration exceeding the deadband range of the step-up/step-down tap-switching standard is 60 Run %s from the elapsed time.

For example, if the secondary side voltage exceeds 4% of the reference voltage, if the secondary side voltage continuously exceeds the reference voltage for 30 sec, the automatic tap-changer will step down once to the voltage stabilization section of the deadband area. Tap change operation.

As shown in FIG. 12, the contact check control part of the tap driving device among the sensors and diagnosis (OLTC diagnosis) devices is configured with a circuit that automatically moves in case of an intermediate power failure, and the diagnosis device checks an error condition.

In other words, it monitors the state of the internal main contact point when switching the TAP, and checks whether the tap is normally switched.

As shown in FIG. 13, a moisture sensor (S1), a temperature sensor (S2), a turbidity sensor (S3) and a low pressure bushing (S4) are installed.

In addition, PD (Photo Diode) measurement sensors such as ultrasonic sensors, UHF sensors, and infrared sensors are attached to the tap-changing part to monitor and diagnose PD status.

The temperature of the transformer oil for smart OLTC distribution should be -25°C to 100°C, should be free from moisture, and installed in the effective space under the transformer core head and transformer box cover, and the tap-changer switch body (1) is Be in a position that can be locked.

When the transformer TAP is switched by using the state diagnosis algorithm of the PD measurement sensor, a diagnosis mechanism related to monitoring the state of the transformer is used.

For example, condition diagnosis, failure mechanism, field measures, etc. are sequentially performed to perform diagnosis related to transformer condition monitoring when the transformer tap is switched over.

In the case of no voltage, perform COS (Cut Out Switch) operation and disconnection on the vehicle side (terminal lug damage, lead wire disconnection due to lightning, etc.).

In addition, abnormal voltage and current inflow --> COS operation, local disconnection of the primary winding, and failure due to insulation breakdown are identified as field measures: (1) Check COS operation-In case of failure: traces of melting of upper and lower electrodes , Fuse, etc., (2) discharge of gas inside the transformer through repeated operation of the pressure relief valve 2~3 times, and (3) transformer failure determination through transformer inspection (measurement of winding resistance, insulation resistance, etc.).

On the other hand, if it is determined that a problem has occurred in the voltage turn ratio by the PD measurement sensor, it is judged as the occurrence of an abnormal voltage on the secondary side due to local insulation breakdown, and the insulation between the winding layers is destroyed due to an internal failure of the transformer, resulting in an abnormal turn ratio. Diagnose that voltage has occurred. These diagnostics may be displayed through a display device.

On-site measures include (1) COS status (failure, surface UV coating status), (2) civil complaints due to secondary abnormal voltage occurrence, (3) transformer ground connection status and neutral wire crimping status, (4) ) Determination of transformer failure through transformer inspection (winding resistance, insulation resistance measurement, etc.).

If moisture is detected under non-voltage, it is diagnosed as insulation breakdown due to COS operation and moisture inflow, and it is indicated that insulation breakdown occurs due to moisture inflow and dielectric strength decrease. Need to check construction history such as transformer tap change, on-site construction of instantaneous pressure reduction device, (2) .COS operation status check-In case of non-operation: check traces of melting of upper and lower electrodes, fuse, etc. Take measures such as replacing the transformer after pressure relief.

If abnormality of the number of turns and moisture is detected, the condition is diagnosed due to the occurrence of abnormal voltage on the secondary side due to the local insulation breakdown of the transformer due to the inflow of moisture, and then the dielectric strength decreases due to the inflow of moisture. Alarms that an abnormal voltage has occurred, and on-site measures include (1) need to check the construction history such as changing the transformer tap and on-site construction of the instantaneous pressure reduction device, (2) checking the COS status (failure, surface UV coating status), (3 ) Check whether civil complaints occur due to the occurrence of secondary abnormal voltage, (4) Check the transformer ground connection status and neutral wire crimping status, and take on-site measures by replacing the transformer.

If there is no voltage and an abnormality in moisture and illuminance is detected, it is diagnosed as COS operation, insulation breakdown due to moisture inflow, insulation oil contamination and arc detection, and insulation breakdown due to decrease in dielectric strength due to moisture inflow, and insulation oil runs out. It is alarmed as contaminated, and on-site measures include (1) need to check the construction history such as changing the transformer tap and on-site construction of an instantaneous pressure reduction device, (2) checking the COS operation status in case of failure: traces of melting of the upper and lower electrodes, fuse, etc. Use an image sensor for inspection, (3) there is a possibility of residual flue gas in the transformer due to insulation breakdown, (4) Never re-inject COS to prevent safety accidents, (5) Repeat the pressure relief valve 2-3 times Measures are taken by discharging the gas inside the transformer through operation, (6) determining the transformer failure through transformer inspection (measurement of winding resistance, insulation resistance, etc.).

If an abnormality is detected in the turn ratio, moisture, and illuminance, the secondary side abnormal voltage is generated due to local insulation breakdown due to moisture inflow, insulation oil contamination and arc detection are diagnosed, and a local incremental short circuit occurs due to the decrease in dielectric strength due to moisture inflow. It alarms as secondary abnormal voltage is generated due to contamination of insulating oil and abnormal turn ratio, and on-site measures include (1) need to check the construction history such as transformer tap change, on-site construction of instantaneous pressure reduction device, and (2) COS status (failure, surface UV coating status) check, (3) there is a possibility of residual flue gas in the transformer due to insulation breakdown, (4) never re-input COS to prevent safety accidents, (5) transformer inspection (measurement of winding resistance, insulation resistance, etc.) Measures are taken by determining the transformer failure through the method, (6) checking whether civil complaints have occurred due to the occurrence of secondary abnormal voltage, and (7) checking the transformer ground connection status and neutral wire crimp status.

Here, if the temperature is abnormal, the winding temperature rises due to overload operation, and after a long-time overload operation, it is diagnosed as a state of concern for failure due to deterioration of the insulating paper and insulating oil, and alarms that the life of the transformer is shortened due to the increase in the transformer winding temperature and shortening the life of the insulating paper due to overload operation , On-site measures include: 1. Exhaust gas inside the transformer through repetitive operation of the pressure relief valve 2-3 times, 2. Separation of the upper capacity and load in anticipation of an increase in transformer temperature due to overload operation, and check the overload by measuring the load current after replacement Take action.

1: Tap change part switch body
S1: Moisture sensor
S2: temperature sensor
S3: Turbidity sensor
S4: Low pressure bushing

Claims (7)

In the smart OLTC distribution transformer switched by the gear of the motor,
In a transformer having a plurality of taps in one of the primary or secondary windings, the load current I is continuously maintained during the tap-changing process of the tap-changing device for tap-switching, and the first tap and the second tap among the plurality of taps A switching resistor is connected between the two tap joints so that the connector is not short-circuited so that the cycle current Ic flows,
In the state of operating with H or L contact, interlock circuit is combined so that direct operation is not possible between H contact and L contact or L contact and H contact.
The switching resistance limits the cycle current Ic generated by the switching circuit, and makes the cycle current Ic and the load current I equal, so that the tap connector is not shorted until a certain contact reaches a specific gear in the tap switching process. , Smart OLTC distribution transformer, characterized in that the load current flows. delete The method according to claim 1,
The tap changing device,
It moves from the HIGH winding to the LOW winding through the NORMAL winding, or switches from the LOW winding to the HIGH winding through the Normal winding.
When the tap-changer moves from the NORMAL winding to the HIGH winding, current flows through the CLR as the mechanical contact of R connected in parallel to the CLR is opened in the initial NORMAL winding ON state,
As the HIGH winding is closed, the high-voltage winding is connected in parallel with the CLR resistor,
As the NORMAL winding is opened, automatic transfer to the high-voltage winding is completed,
Smart OLTC distribution transformer, characterized in that the order of going from the HIGH winding to the NORMAL winding is reversed. The method of claim 3,
When the tap-changer moves from the NORMAL winding to the LOW winding,
In the initial NORMAL winding ON state, current flows through the CLR as the mechanical contact of R connected in parallel to the CLR opens.
As the LOW contact point of the LOW winding is closed, a voltage is applied in parallel with the current flowing through the CLR, and a current flows,
As the NORMAL winding is OPEN, it is automatically switched to the LOW winding,
Switching from the LOW winding to the NORMAL winding proceeds in the reverse order, characterized in that the smart OLTC distribution transformer. The method according to claim 1,
After initial start at the N contact, if you press the H contact or the L contact, the post input priority circuit is combined and operated so that it operates immediately.
Smart OLTC distribution transformer, characterized in that at least one of a moisture sensor, a temperature sensor, and a turbidity sensor are coupled to the tap changer. delete delete

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