MSDTX Transformer Core/Clamp Current Online Monitoring System

Significance of 1. monitoring

Transformer is one of the key equipment in the power system, and its normal operation is an important guarantee for the safe, reliable, stable and economic operation of the power system. When the power transformer is running, there is an alternating magnetic field around the winding. Due to the effect of electromagnetic induction, there is a parasitic capacitance between the high-voltage winding and the low-voltage winding, between the low-voltage winding and the iron core, and between the iron core and the shell. The live winding will generate a floating potential between the iron core and the winding through the coupling effect of the parasitic capacitance. Due to the unequal distance between the iron core and other metal components and the winding, there is a potential difference, when the potential difference between the two points to be able to break down the insulation between them, it will produce intermittent spark discharge, the transformer oil and solid insulation have adverse effects, it is necessary to connect the iron core and the shell, so that it and the shell and other potential. If the iron core or other metal components are grounded at two or more points, the grounding point will form a closed loop, resulting in circulation, which will cause local overheating of the transformer body, resulting in oil decomposition, resulting in a decline in insulation performance. In severe cases, the silicon steel sheet of the iron core will burn out, resulting in a major accident of the main transformer, so the iron core of the main transformer must be grounded. Otherwise, the iron core to the ground will produce floating voltage or iron core multi-point grounding and produce heating fault, a serious threat to the safety of the transformer and the power grid. Through the monitoring of the core grounding current, the core multi-point grounding and other faults can be found in time, and the fault can be nipped in the bud. In the power transformer of large-scale high-voltage electrical equipment, due to the multi-point grounding fault of the iron core and other abnormal conditions, a variety of gases will be generated in the insulating oil. The usual detection methods used by the power department are to detect the fault gas dissolved in the insulating oil and to carry out gas chromatography analysis after sampling the insulating oil of the equipment, and to measure the current of the grounding lower lead of the grounding sleeve outside the transformer core with a clamp ammeter, so as soon as possible. However, in the detection of iron core multi-point grounding phenomenon, it is difficult to distinguish the weak ground fault current and strong electromagnetic environment interference, and it can not be analyzed online, and there are problems in detection accuracy and real-time.

2. product introduction

The transformer core and clamp grounding current monitoring device is used to monitor the grounding fault current of the transformer core and clamp, which can realize continuous on-line monitoring of the grounding current of the core. Through monitoring, the insulation condition of the equipment can be monitored in real time, and faults such as damp or damage of internal insulation, multi-point grounding of the core, foreign matter in the box, oil sludge deposition in the oil tank can be found in time. Early prevention and early treatment of accidents. More importantly, it can provide reliable data basis for the state maintenance of such equipment. Its working principle is:

The system uses high-precision through-core sensor to convert the grounding current signal on the iron core and clamp into a voltage signal. The voltage signal enters the signal conditioning circuit, which automatically switches the range according to the voltage, and finally enters the signal measurement board with DSP as the processing core. The signal measurement board uses a high-performance 32-bit digital processing chip DSP as the core processor. The grounding current of iron core and clamp parts is accompanied by interference signals on site, and these interference signals should be eliminated first during calculation. The traditional method is to use analog filter to remove the interference signal, but the analog filter is easy to be affected by the ambient temperature and humidity, and it is easy to produce zero drift and other phenomena with the change of time, thus introducing new "interference". The powerful digital computing function of DSP can use digital filtering algorithm instead of the original analog filtering algorithm. The digital filtering algorithm is not affected by temperature, humidity and other environmental effects and zero drift, which can perfectly solve various problems caused by analog filters. The signal measurement board calculates the grounding current of the iron core and the clamp and then uploads it to the spacer monitoring IED through the digital bus. Spacer IED uses a unified embedded platform to realize the functions of analysis and judgment, alarm and remote data transmission. By monitoring the size of the iron core grounding current in operation, it is automatically judged that the iron core of the transformer is not grounded or the iron core is grounded at multiple points, so as to prevent the iron core from forming a series of faults caused by floating potential and local overheating, and ensure the safe operation of the power transformer.

3. technical characteristics

• The use of through-core transformer, completely isolated from the secondary circuit, high safety;
• Using distributed measurement structure, that is, local measurement, digital transmission, the protocol conforms to DL/T860 standard;
• Can be charged installation, that is, do not need the main equipment power installation, convenient, fast access system;
• Digital filtering method is used to eliminate the "zero drift problem" caused by analog filters ";
• High-precision active zero-flux sensor is used to intelligently select the conditioning circuit and amplification factor according to the measured current, which effectively improves the measurement accuracy;

4. technical parameters

The technical parameters of the device fully meet or exceed the following national and enterprise standards and regulations:

Inspection Specification for Substation Online Monitoring Devices Part 1: General Inspection Specification Q/GDW 540.1-2010

1. Working environment

• Working voltage: AC 220V ± 10%,50Hz
• Working environment temperature: -40 ℃ ~ 120 ℃
• Power consumption: <5W under rated voltage
• Working environment humidity: ≤ 95%

2. Monitoring parameter indicators

• Measuring current range: 1mA ~ 10A accuracy: ± 1% or ± 1mA, whichever is greater.