Dry transformer selection matters needing attention!

2022/04/28

Dry transformer temperature control system

The safe operation and service life of dry transformer largely depends on the safety and reliability of transformer winding insulation. The insulation damage caused by the winding temperature exceeding the insulation tolerance temperature is one of the main reasons that lead to the transformer can not work normally, so it is very important to monitor the transformer operating temperature and alarm control.

(1) Automatic control of fan: temperature signal is measured by Pt100 thermosensitive temperature measuring resistor embedded in the hottest part of low-voltage winding. When the winding temperature reaches 110℃, the system automatically starts the fan cooling. When the winding temperature is low to 90℃, the system automatically stops the fan.

(2) Overtemperature alarm and trip: the winding or core temperature signal is collected through the PTC nonlinear thermosensitive temperature measuring resistance embedded in the low-voltage winding. When the temperature of transformer winding continues to rise, if it reaches 155℃, the system output overtemperature alarm signal; If the temperature continues to rise to 170℃, the transformer can not continue to operate, it is necessary to transport overtemperature trip signal to the secondary protection loop, and the transformer should trip quickly.

(3) Temperature display system: Through embedded in the low voltage winding Pt100 thermistor measured temperature value, direct display of each phase winding temperature (three-phase, according to the inspection and the maximum value and can record the highest temperature), the highest temperature can be in 4 ~ 20 ma analog output, if need to transport to the distance (distance of up to 1200 m) computer, additive with computer interface, one transmitter, Up to 31 transformers can be monitored simultaneously. The overtemperature alarm and trip of the system can also be activated by Pt100 thermistor signal, which further improves the reliability of the temperature control protection system.

Two, dry type transformer protection mode

According to the use of environmental characteristics and protection requirements, dry transformer can choose different enclosures.

IP20 protective shell is usually selected to prevent solid foreign bodies with a diameter greater than 12mm and mice, snakes, cats, birds and other small animals from entering, resulting in short-circuit power failure and other malignant faults, to provide a safety barrier for live parts. If the transformer must be installed outdoors, you can choose IP23 protective shell, in addition to the above IP20 protection function, but also to prevent the vertical line into 60° Angle within the water drop into. But IP23 shell will reduce the cooling capacity of the transformer, the selection should pay attention to the reduction of its operating capacity.

Three, dry type transformer cooling mode

Dry transformer cooling mode is divided into natural air cooling (AN) and forced air cooling (AF). When air cooled naturally, the transformer can run continuously for a long time under rated capacity. When forced air cooling, transformer output capacity can be increased by 50%. Suitable for intermittent overload operation, or emergency overload operation; Because the load loss and impedance voltage increase greatly during overload, it is in non-economic operation state, so it should not be in continuous overload operation for a long time.

Four, the overload capacity of dry transformer

The overload capacity of the dry transformer is related to the ambient temperature, the load before overload (starting load), the insulation heat dissipation of the transformer and the heating time constant. If necessary, you can obtain the dry overload curve from the manufacturer.

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