TDM-3F – Diagnostic Monitoring System for Main Subsystems of Power Transformers
The most critical elements of the power transformers are:
- High-voltage transformer bushings – OIP and dry bushings;
- Transformer windings insulation;
- Local overheating of windings, cores and magnetic shunts inside the transformer;
- Problems with transformer OLTC condition;
- Problems with windings dynamic resistance to short circuit currents.
At the same time, many functions of transformer parameter monitoring and diagnostics used at present, could be excluded without any loss of monitoring efficiency. These functions monitor parameters which are slowly changing (for example, insulation) or duplicated (for example, relay protection operation monitoring and cooling system control).
The unjustified monitoring functions enhancing of the systems of some producers one day could discredit the idea of on-line monitoring itself.
The «TDM-3F» diagnostic monitoring system is the one of standard configurations of TDM complex diagnostics system. It is based on the principle of minimal sufficiency and provides the efficient monitoring of the most critical power transformers subsystems. It allows to considerably decrease the monitoring system introduction costs without losing the monitoring efficiency.
The following diagnostic functions are realized in the TDM-3F system by hardware and software:
- Monitoring of 3 or 6 high-voltage bushings' condition in accordance with the type of monitored transformer. Customer at his wish could measure the insulation leakage current, the value of capacity C1 and the dissipation factor (relative or absolute) of every high-voltage bushing. DB-2 complex sensors are installed on the test taps, which allows to monitor insulation parameters and measure high-frequency pulses (PD) in the wide frequency range – up to several GHz.
- PD level and distribution in the insulation of bushings, windings and cores. The unique function of the «TDM-3F» system is the synchronic PD measurement by six channels and in two frequency ranges (HV and UHF). It allows almost complete corona pulses rejection. The build-in expert system allows to define the type of defect and to evaluate its danger for the transformer operation. The modern ways of PD measurement and solute gasses data processing gives the most accurate information on the transformer condition.
- The supplement feature of the «TDM-3F» system PD measuring system is the on-line monitoring of transformer windings' deformation. Corona discharge pulses of the HV and LV ends of the winding are used as probe pulses for frequency response analysis (FRA).
- It is necessary to monitor the moisture content in oil of transformer tank for all power transformers with rated voltage of 100 kV and more. This the most important oil diagnostic parameter of transformer operation reliability. Monitoring of solute hydrogen in oil is also necessary for high-power transformers. Many solute combustible gases should be monitored in the power transformers with rated voltage of 220 kV and more.
- The technical condition of transformer OLTC. The use of the «LTC-S» sensors allows to monitor the present location of OLTC, the power of the driving motor in the process of commutation and to analyze the diagram of contactor operation at every commutation.
- The assessment of transformer cooling system efficiency is made on the basis of measuring and analyzes of the transformer tank top and bottom temperature and transformer rated load. Simplified heat model of transformer is used in these calculations.
Primary sensors of TDM-3F system are installed as follows
- The «DB-2» sensors for measuring conduction current and PD pulses are installed on the test taps of high-voltage bushings. If there are no test taps on output isolators of a power transformer LV winding (which is usual for voltages of 6-35 kV), then coupling capacitors should be used.
- The «IFCT-5» load current sensors in phases of transformer primary winding are installed on cables of secondary circuit in measuring current transformers.
- The temperature sensors are installed on the top and bottom part of transformer tank.
- The complex «LTC-S» sensor for OLTC condition monitoring is installed inside of OLTC mounting case. It is connected to the «TDM-3F» monitoring system through interface RS-485.
- The «TDM-Oil» moisture in oil sensor is installed on drain valve in the bottom of transformer tank and is connected to the monitoring system through RS-485 interface.
The connection of the «TDM-3F» system to SCADA system can be done as follows
- By isolated «RS-485» interface.
- By optical connection line.
- By radio channel.
Protocol ModBus RTU or protocol IEC 61850 could be used for information communication to the SCADA system.
Signals of GPS/GLONASS system can be used for synchronization of the diagnostics parameters measurements on several objects with TDM-3F system, which adds to the information validity. GPS/GLONASS system signals receiver is installed in the TDM-3F module.