CN103197178B - Transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof - Google Patents

Transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof Download PDF

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Publication number
CN103197178B
CN103197178B CN201310093226.6A CN201310093226A CN103197178B CN 103197178 B CN103197178 B CN 103197178B CN 201310093226 A CN201310093226 A CN 201310093226A CN 103197178 B CN103197178 B CN 103197178B
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transformer
neutral point
circuit
monitoring
point ground
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CN201310093226.6A
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Chinese (zh)
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CN103197178A (en
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高强
李平
耿宝宏
刘齐
钟丹田
原峰
潘丰厚
代继成
王茂军
程大伟
李艳丹
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辽宁省电力有限公司电力科学研究院
辽宁东科电力有限公司
国家电网公司
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Abstract

The invention belongs to transformer online monitoring field, relate to a kind of Intelligent transformer DC magnetic biasing on-Line Monitor Device and monitoring method thereof.The present invention is the outside being arranged on crust of the device by punching Hall current sensor, and filtering circuit, voltage signal conditioning circuit, gear switch circuit and Real Time Clock System, FLASH storage system and controller system are arranged on the core board in crust of the device; Display screen is arranged on crust of the device, and display screen and FLASH storage system are connected to controller system.The present invention may be used for the on-line monitoring of transformer neutral point ground current, wherein monitoring device has transformer neutral point ground current data Real-Time Monitoring and overload alarm function, alarm threshold value can by user's self-defining, when there are abnormal conditions, the display screen of device and the computing machine of remote monitoring all can send alerting signal, enable staff take treatment measures in time, avoid the generation of transformer fault, ensure the stable operation of electric system.

Description

Transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof

Technical field

The invention belongs to transformer online monitoring field, relate to a kind of Intelligent transformer DC magnetic biasing on-Line Monitor Device and monitoring method thereof.

Background technology

Along with expanding economy, high voltage direct current (HVDC) transmission system is just obtaining applying more and more widely in China.Compared with AC transmission system, direct current transportation has that cost is low, loss is little, withstand voltage height, capacity are large and can realize the features such as the asynchronous networking of electric system.In order to realize trans-regional, remote and Large Copacity power transmission, more UHV (ultra-high voltage) and even extra-high voltage direct-current engineering will be had to build up and put into operation.

But the electric network composition of AC and DC mixed running make between AC and DC system influence each other also all the more obvious.When DC transmission system one pole the earth or bipolar off-center operation, DC current will inject the earth by earthing pole, in ground, DC current invades AC system by transformer neutral point ground wire, has an impact to AC system, and wherein impact is exactly cause transformer DC magnetic bias phenomenon the most significantly.In addition, the dynamic change of sun plasma wind and the terrestrial magnetic field earth magnetism " storm " produced that interacts can cause geomagnetic induction current, and geomagnetic induction current also can produce DC magnetic biasing in centre-point earth transformer.

DC current flows through Transformer Winding, produces certain direct current flux in transformer fe interior portion, and make exciting current positive-negative half-cycle obviously asymmetric, magnetic flux offsets, and produces DC magnetic biasing.DC magnetic biasing can cause transformer magnetizing current sharply to increase, and causes magnetic loop that overheated and noise occurs and vibration increases.In DC magnetic biasing situation, there is obvious odd ripple noise in the frequency spectrum of transformer noise, the height caused vibrates the problem brought, and may cause loosening of associate components in transformer, and then threaten the safe operation of transformer.

Therefore need to monitor DC magnetic biasing, eliminate magnetic bias for control in the future and basis is provided.On the neutral point about main-transformer goes between, neutral point direct current monitoring device is installed, monitor the DC current because the factor such as direct current transportation and magnetic storm causes, so that a situation arises and current values to grasp DC magnetic bias current in time, and for taking the measure limiting DC magnetic bias current to create necessary condition.

Summary of the invention

For above-mentioned problems of the prior art, the invention provides a kind of transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof, its objective is situation occurred and the current value of the DC magnetic bias phenomena that monitoring causes because of the factor such as direct current transportation and magnetic storm centering point grounding transformer, being convenient to the rule grasping DC magnetic bias phenomena generation, is take the measure limiting DC magnetic bias current to create necessary condition.

The present invention is achieved through the following technical solutions:

Transformer DC magnetic bias on-Line Monitor Device, be the outside being arranged on crust of the device by punching Hall current sensor, filtering circuit, voltage signal conditioning circuit, gear switch circuit and Real Time Clock System, FLASH storage system and controller system are arranged on the core board in crust of the device; Display screen is arranged on crust of the device, and display screen and FLASH storage system are connected to controller system;

Wherein punching Hall current sensor is connected with crust of the device by cable, be connected with the gear switch circuit of crust of the device inside by crust of the device again, gear switch circuit is connected to filtering circuit and voltage signal conditioning circuit again, is then connected to controller system with Real Time Clock System.

Described punching Hall current sensor is connected with the aviation plug on crust of the device by cable.

Described controller system is also provided with data communication system.

Described punching Hall current sensor is opening installation form.

The switching range of described gear switch circuit has three kinds, is respectively 100mA-1A, 1A-10A and 10A-50A.

Described punching Hall current sensor is fastenedly connected two and half block structured sensors by sensor openings fastening screw.

Transformer DC magnetic bias on-line monitoring method, under being not change the prerequisite of grounding mode of transformer neutral-point, by the electric current that on-line monitoring transformer neutral point ground lead flows through, reflect the electric current flowing through Transformer Winding, and then the DC magnetic biasing degree of reflection transformer, concrete steps are as follows:

(1) under the prerequisite not disconnecting transformer neutral point ground lead, adopt and can the punching Hall current sensor of opening be sleeved on transformer neutral point ground lead, obtain the current signal flowing through transformer neutral point ground lead;

(2) transformer neutral point ground current signal is changed into voltage signal by punching Hall current sensor;

(3), after voltage signal being passed through filtering circuit, modulate circuit and gear switch processing of circuit, the analog to digital conversion circuit sending into controller carries out computing, obtains digitized transformer neutral point ground current;

(4) digital signal in step (3) is shown on the display screen of device, and compare with the transformer neutral point ground current permissible value preset, if be greater than permissible value, the signal of display alarm simultaneously on display screen;

(5) while step (4), current measurement result and time are saved in the FLASH memory of device, are convenient to subsequent analysis transformer DC magnetic bias situation;

(6) real time data by RS485 bus, step (3) calculated or historical data upload to background monitoring computing machine or comprehensive monitoring unit or IED, computing machine or IED carry out various correlation parameter configuration by communication protocol to monitoring device, to meet the on-line monitoring demand of dissimilar transformer.

The method that described measurement flows through transformer neutral point ground lead DC current is as follows:

U 1 = I 1 K R

Wherein, I 1for the DC current on transformer neutral point ground lead;

K is the built-in amplification coefficient of punching Hall current sensor;

R is the built-in sampling resistor of punching Hall current sensor;

U 1for punching Hall current sensor sampling and outputting voltage signal.

K and R can get different values by customizing the punching Hall current sensor meeting dissimilar transformer, meets many-sided needs.

Described obtains digitized transformer neutral point ground current, and concrete methods of realizing is as follows:

U 2 = U 1 R 1 R 2

Wherein, U 2for U 1n magnitude of voltage is doubly amplified after filtering after circuit, modulate circuit, according to U 2size, gear switch circuit selects different ranges automatically, and the numerical value of N changes thereupon;

If the reference voltage of controller AD sample circuit is U ref, switch different ranges by the numerical value adjusting N, guarantee U 2all the time [0, U is dropped on ref] in interval;

Converted by AD, obtain voltage U 2numerical value, by multiple averaging process and oppositely derive, namely what obtain is transformer neutral point ground current numerical value, namely

I 1 = KR 2 R 1 R U 2

Described gear switch circuit can realize 100mA-1A, 1A-10A and 10A-50A.

Advantage of the present invention and beneficial effect are:

The present invention may be used for the on-line monitoring of transformer neutral point ground current, wherein monitoring device has transformer neutral point ground current data Real-Time Monitoring and overload alarm function, alarm threshold value can by user's self-defining, when there are abnormal conditions, the display screen of device and the computing machine of remote monitoring all can send alerting signal, enable staff take treatment measures in time, avoid the generation of transformer fault, ensure the stable operation of electric system.

By the enforcement of technical solution of the present invention, the accurate and stable real-time measurement to transformer neutral point ground current really can be realized.Method for designing of the present invention has following innovative point:

One, the innovation of measuring method:

1, this device high-precisionly the punching Hall current sensor of opening installation form can be sleeved on current signal transformer neutral point ground lead measured on neutral ground line by adopting, the method truly can reflect production and the numerical values recited of DC current on transformer neutral point ground lead, this device and transformer are not electrically connected, neutral ground lead-in wire need not be taken apart, any impact is not produced on the operation of transformer;

2, the electric signal that punching Hall current sensor exports directly accesses measurement mechanism, carries out analytical calculation, and result of calculation carried out storing and showing by Digital Signal Processing to acquisition electric signal.Operations staff can check measurement data and warning message etc. on the spot.

3, when transformer normally works, neutral ground electric current is very little, different transformers is according to differences such as core material, magnetic flux density design value, transformer device structures, allow the ground current flowing through neutral point also different, during normal work be one ampere and arrive a few Amps, but when DC magnetic bias phenomena produces, transformer neutral point ground current will increase, become several amperes to tens amperes, variation range is very large.

This device have also been devised current range gearshift change-over switch, and according to the scope of curent change, device can regulate suitable gear to measure electric current automatically, ensure that the accuracy of measurement and the security of measurement mechanism.This device current measuring range is 50A to the maximum, measuring accuracy 1%, meets the requirement of dissimilar transformer neutral point ground current measurement range and precision completely.

Two, apparatus structure and mounting means: the measurement of this device, display and storage area are contained in the crust of the device of a casting aluminium material, display window has been offered at crust of the device top cover, for installing display screen, be convenient to field observation current data, crust of the device part independent grounding, for shielding extraneous electromagnetic interference (EMI).

This apparatus structure is compact to design, good looking appearance, and on mounting means, adopt and be directly installed on mode near transformer neutral point ground lead by the suspension member of crust of the device, installation method is easy, safety, is convenient to operations staff and installs, operation and maintenance.

1, device carries data display function, temporal information and real-time current data is shown on a display screen, observes when facilitating operations staff to patrol and examine.When Monitoring Data is out-of-limit, display alarm information reminds patrol officer to note by display screen.

2, device has data storage function, and temporal information and real-time current data are kept in the FLASH storage system that device carries, the data power down of storage is not lost, and can preserve the measurement data of more than a year continuously.For the historical data of subsequent analysis calculating transformer neutral ground electric current, the situation of change understanding neutral ground electric current provides foundation.

3, device supports RS-232/485 communication interface, and the multiple spot that can realize based on RS485 bus is monitored.Adopt the MODBUS-RTU communication protocol that industrial circle versatility is good, by communication protocol, the information such as Monitoring Data and monitoring moment are uploaded to computing machine or comprehensive monitoring unit (IED).

4, by computing machine or comprehensive monitoring unit (IED) to device parameter (as unit address, baud rate, odd even effect, sampling time interval, overload alarm value, clock time etc.) carry out flexible configuration, facilitate device to access other on-line monitoring systems, meet the requirement of Different field.

5, device has function when to carry out with computing machine or comprehensive monitoring unit (IED) pair, ensure that accuracy and the consistance of device monitoring time and equipment actual run time.

6, electromagnetic compatibility and protecting circuit designed.Because the electromagnetic environment of substation field is very severe, it is abnormal that high voltage and high-intensity magnetic field very easily make this monitoring equipment work occur, therefore carried out Careful design to the electromagnetic compatibility of this device.By the checking of EMC test, this device meets the standard-required of State Grid Corporation of China to the compatible aspect of installation electromagnetical completely, comprises static discharge, electrical fast transient (eft), surge impact etc., improves the safety and reliability of device work.

7, apparatus of the present invention are aesthetic in appearance, simple to operate, easy for installation, stable, and Hall current sensor can customize according to neutral point lead format, is suitable for Different field and installs and uses.

The present invention has real time on-line monitoring transformer neutral point ground current, data store, display and teletransmission on the spot, off-limit alarm, system pair time and the function such as parameter configuration.Along with the popularization of direct current transportation, application of the present invention is more and more extensive, be applicable to the transformer of number of different types, normal operation for neutral grounded transformer provides foundation and certain guarantee, and provides Data support for the generation rule and numerical values recited analyzing neutral grounded transformer DC magnetic bias phenomena.

Accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments, the present invention will be further described in detail.

Fig. 1 is principle of work schematic diagram of the present invention;

Fig. 2 is functional block diagram of the present invention;

Fig. 3 is networking structure schematic diagram of the present invention;

Fig. 4 is inner structure schematic diagram of the present invention;

Fig. 5 is external structure schematic diagram of the present invention;

Fig. 6 is external perspective structural representation of the present invention;

Fig. 7 is punching Hall current sensor structural representation in the present invention.

In figure: crust of the device 1, aviation plug 2, core board 3, display screen 4, punching Hall current sensor 5, sensor openings fastening screw 6.

Embodiment

The present invention is a kind of transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof, and as shown in Figure 2, Fig. 2 is the functional block diagram of line monitoring device of the present invention; Again as shown in figs. 4-7, Fig. 4, Fig. 5, Fig. 6 and Fig. 7 are respectively the inner structure schematic diagram of on-Line Monitor Device of the present invention, external structure schematic diagram, external perspective structural representation and punching Hall current sensor structural representation.

On-Line Monitor Device of the present invention comprise can the punching Hall current sensor 5 of opening, filtering circuit, gear switch circuit, voltage signal conditioning circuit and Real Time Clock System, FLASH storage system, EEPROM storage system and controller system and display screen and data communication system.

Monitoring device of the present invention is the punching Hall current sensor of opening can be arranged on the outside of crust of the device 1 by installation form, and filtering circuit, voltage signal conditioning circuit, gear switch circuit and Real Time Clock System, FLASH storage system and controller system are arranged on the core board 3 of crust of the device 1 inside; Display screen 4 is arranged on crust of the device 1.Display screen and FLASH storage system are connected to controller system; Wherein punching Hall current sensor 5 is connected with the aviation plug 2 on crust of the device 1 by cable, aviation plug 2 is connected with the gear switch circuit of crust of the device 1 inside, gear switch circuit is connected to filtering circuit and voltage signal conditioning circuit again, is then connected to controller system with Real Time Clock System.Described controller system is also provided with data communication system.The switching range of described gear switch circuit has three kinds, is respectively 100mA-1A, 1A-10A and 10A-50A.

In addition, the service cable of device and telecommunication cable are connected with device by aviation plug 2, ensure that power supply and reliable communications on the one hand, achieve water proof and dust proof protection etc. on the other hand to device inside.Punching Hall current sensor 5 can opening, punching Hall current sensor 5 can be sleeved on transformer neutral point ground lead when not disconnecting transformer neutral point ground lead, easy for installation, in order to ensure the measuring accuracy of punching Hall current sensor, need to use sensor openings fastening screw 6 to carry out fastening process to two and half block structured sensors.

This on-Line Monitor Device is be sleeved on transformer neutral point ground lead by the punching Hall current sensor of opening when specifically implementing, the metering circuit of the secondary singal access device that punching Hall current sensor exports, metering circuit is made up of filtering circuit, gear switch control circuit and voltage signal conditioning circuit.Conditioned simulating signal is sent into controller and is carried out computing by metering circuit, and result of calculation display on a display screen, and is stored in FLASH memory system, for the rule of subsequent analysis transformer DC magnetic bias phenomenon provides Data support.In addition, this on-Line Monitor Device can be connected with on-line monitoring comprehensive monitoring unit (IED) or computing machine, and by MODBUS communication protocol, measurement result is uploaded, computing machine can be configured by the parameter such as communication, measurement, warning, calibration of the serial ports instruments such as COM Debug Assistant to device.

As shown in Figure 3, Fig. 3 is networking structure schematic diagram of the present invention, multiple transformer DC magnetic bias on-Line Monitor Device of bottom realize data communication by RS-485 bus and between on-line monitoring IED and on-line monitoring computing machine, real time data and warning message can be uploaded to on-line monitoring IED and on-line monitoring computing machine by this on-Line Monitor Device, on-line monitoring IED and on-line monitoring computing machine can read the measurement data of infrastructure device simultaneously, and carry out relevant configuration to infrastructure device.

As shown in Figure 1, Fig. 1 is principle of work schematic diagram of the present invention, transformer DC magnetic bias current value is obtained by being sleeved on transformer neutral point ground lead by punching Hall current sensor, device gathers this current signal, computing and store on the spot and show, and is communicated with on-line monitoring IED or monitoring computer by data communication system.

Specific works process of the present invention is as follows: the neutral point current signal collected is given filtering circuit and gear switch circuit by punching Hall current sensor, voltage signal conditioning circuit is passed to again after adjusting to suitable range, then by the analog to digital conversion circuit of controller, this signal is carried out computing, the result of calculation obtained is presented on the display screen of device on the one hand, the collection moment produced with Real Time Clock System is on the other hand deposited into FLASH storage system, together for the situation of change of subsequent analysis neutral ground electric current provides foundation.Device can preset the alarming value of neutral ground electric current, when result of calculation exceedes preset alarm value, warning message is on the one hand in the display of device this locality, and teletransmission is to background monitoring computing machine on the other hand, operations staff is reminded to take measures to process, the generation of prevention transformer fault.Data communication system is except being uploaded to except supervisory control comuter or comprehensive monitoring unit or IED by warning message by RS485 bus, the real time data that also controller can be calculated or the historical data be stored in FLASH are uploaded, and computing machine or IED carry out various parameter configuration by communication protocol to monitoring device, to meet the demand of different size transformer.

Transformer DC magnetic bias on-line monitoring method is, under the prerequisite not changing grounding mode of transformer neutral-point, by the electric current that on-line monitoring transformer neutral point ground lead flows through, reflect the electric current flowing through Transformer Winding, and then the DC magnetic biasing degree of reflection transformer, concrete steps are as follows:

(1) under the prerequisite not disconnecting transformer neutral point ground lead, adopt and can the punching Hall current sensor of opening be sleeved on transformer neutral point ground lead, obtain the current signal flowing through transformer neutral point ground lead;

(2) transformer neutral point ground current signal is changed into voltage signal by punching Hall current sensor;

(3), after voltage signal being passed through filtering circuit, modulate circuit and gear switch processing of circuit, the analog to digital conversion circuit sending into controller carries out computing, obtains digitized transformer neutral point ground current;

(4) digital signal in step (3) is shown on the display screen of device, and compare with the transformer neutral point ground current permissible value preset, if be greater than permissible value, the signal of display alarm simultaneously on display screen;

(5) while step (4), current measurement result and time are saved in the FLASH memory of device, are convenient to subsequent analysis transformer DC magnetic bias situation.

(6) real time data by RS485 bus, step (3) calculated or historical data upload to background monitoring computing machine or comprehensive monitoring unit or IED, computing machine or IED carry out various correlation parameter configuration by communication protocol to monitoring device, to meet the on-line monitoring demand of dissimilar transformer.

The method that wherein said measurement flows through transformer neutral point ground lead DC current is as follows:

U 1 = I 1 K R

Wherein, I 1for the DC current on transformer neutral point ground lead;

K is the built-in amplification coefficient of punching Hall current sensor;

R is the built-in sampling resistor of punching Hall current sensor;

U 1for punching Hall current sensor sampling and outputting voltage signal.

K and R can get different values by customizing the punching Hall current sensor meeting dissimilar transformer, meets many-sided needs.

Wherein said obtains digitized transformer neutral point ground current, and concrete methods of realizing is as follows:

U 2 = U 1 R 1 R 2

Wherein, U 2for U 1n magnitude of voltage is doubly amplified after filtering after circuit, modulate circuit, according to U 2size, gear switch circuit selects different ranges automatically, and the numerical value of N changes thereupon;

If the reference voltage of controller AD sample circuit is U ref, switch different ranges by the numerical value adjusting N, guarantee U 2all the time [0, U is dropped on ref] in interval;

Converted by AD, obtain voltage U 2numerical value, by multiple averaging process and oppositely derive, namely what obtain is transformer neutral point ground current numerical value, namely

I 1 = KR 2 R 1 R U 2

Gear switch circuit described in the present invention can realize 100mA-1A, 1A-10A and 10A-50A.

In laboratory environments, the data obtained are measured as shown in table 1.

Table 1 laboratory measurements

Once apply current source (A) Device display result (A) Device displaying time 0.50 0.50 2012-9-1610:08 1.00 1.01 2012-9-1610:10 2.00 1.99 2012-9-1610:12 5.00 5.03 2012-9-1610:14 8.00 7.95 2012-9-1610:16 10.00 9.97 2012-9-1610:18 15.00 15.12 2012-9-1610:20

Claims (1)

1. transformer DC magnetic bias on-line monitoring method, it is characterized in that: based on a kind of transformer DC magnetic bias on-Line Monitor Device, the punching Hall current sensor (5) of its opening installation form is arranged on the outside of crust of the device (1), and filtering circuit, voltage signal conditioning circuit, gear switch circuit and Real Time Clock System, FLASH storage system and controller system are arranged on the core board (3) in crust of the device (1); Display screen (4) is arranged on crust of the device (1), and display screen and FLASH storage system are connected to controller system; Described controller system is also provided with data communication system; Wherein punching Hall current sensor is connected with crust of the device (1) by cable, be connected by the gear switch circuit that crust of the device (1) is inner with crust of the device (1) again, gear switch circuit is connected to filtering circuit and voltage signal conditioning circuit again, is then connected to controller system with Real Time Clock System; Described punching Hall current sensor (5) is connected with the aviation plug (2) on crust of the device (1) by cable; The switching range of described gear switch circuit has three kinds, is respectively 100mA-1A, 1A-10A and 10A-50A; Described punching Hall current sensor (5) is fastenedly connected two and half block structured sensors by sensor openings fastening screw (6);
Under the prerequisite not changing grounding mode of transformer neutral-point, by the electric current that on-line monitoring transformer neutral point ground lead flows through, reflect the electric current flowing through Transformer Winding, and then the DC magnetic biasing degree of reflection transformer, concrete steps are as follows:
(1) under the prerequisite not disconnecting transformer neutral point ground lead, adopt and can the punching Hall current sensor of opening be sleeved on transformer neutral point ground lead, obtain the current signal flowing through transformer neutral point ground lead;
(2) transformer neutral point ground current signal is changed into voltage signal by punching Hall current sensor;
(3), after voltage signal being passed through filtering circuit, modulate circuit and gear switch processing of circuit, the analog to digital conversion circuit sending into controller carries out computing, obtains digitized transformer neutral point ground current;
(4) digital signal in step (3) is shown on the display screen of device, and compare with the transformer neutral point ground current permissible value preset, if be greater than permissible value, the signal of display alarm simultaneously on display screen;
(5) while step (4), current measurement result and time are saved in the FLASH memory of device, are convenient to subsequent analysis transformer DC magnetic bias situation;
(6) real time data by RS485 bus, step (3) calculated or historical data upload to background monitoring computing machine or comprehensive monitoring unit, computing machine carries out various correlation parameter configuration by communication protocol to monitoring device, to meet the on-line monitoring demand of dissimilar transformer;
The method that described measurement flows through transformer neutral point ground lead DC current is as follows:
U 1 = I 1 K R
Wherein, I 1for the DC current on transformer neutral point ground lead;
K is the built-in amplification coefficient of punching Hall current sensor;
R is the built-in sampling resistor of punching Hall current sensor;
U 1for punching Hall current sensor sampling and outputting voltage signal;
The punching Hall current sensor that K and R meets dissimilar transformer by customization gets different values, meets many-sided needs;
Described obtains digitized transformer neutral point ground current, and concrete methods of realizing is as follows:
U 2 = U 1 R 1 R 2
Wherein, U 2for U 1n magnitude of voltage is doubly amplified after filtering after circuit, modulate circuit, according to U 2size, gear switch circuit selects different ranges automatically, and the numerical value of N changes thereupon;
If the reference voltage of controller AD sample circuit is U ref, switch different ranges by the numerical value adjusting N, guarantee U 2all the time [0, U is dropped on ref] in interval;
Converted by AD, obtain voltage U 2numerical value, by multiple averaging process and oppositely derive, namely what obtain is transformer neutral point ground current numerical value, namely
I 1 = KR 2 R 1 R U 2 ;
Described gear switch circuit realiration 100mA-1A, 1A-10A and 10A-50A.
CN201310093226.6A 2013-03-21 2013-03-21 Transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof CN103197178B (en)

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CN102426287A (en) * 2011-09-30 2012-04-25 云南电力试验研究院(集团)有限公司 On-line monitoring device for magnetic biasing direct current of power transformer
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CN202794326U (en) * 2012-09-18 2013-03-13 周志强 Online monitoring device for grounding current of transformer core
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