Dry-type Transformer Selection

Temperature control system
The safe operation and service life of Dry Type Transformer depend largely 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 for the failure of the transformer to work properly. Therefore, it is very important to monitor the operating temperature of the transformer and its alarm control.
⑴ Automatic fan control: The temperature signal is measured by the Pt100 thermistor embedded in the hottest part of the low-voltage winding. When the transformer load increases and the operating temperature rises, when the winding temperature reaches 110℃, the system automatically starts the fan cooling; when the winding temperature drops to 90℃, the system automatically stops the fan.
⑵ Over-temperature alarm and tripping: The winding or core temperature signal is collected through the PTC nonlinear thermistor embedded in the low-voltage winding. When the transformer winding temperature continues to rise, if it reaches 155℃, the system outputs an over-temperature alarm signal; if the temperature continues to rise to 170℃, the transformer can no longer continue to operate, and an over-temperature tripping signal must be sent to the secondary protection circuit, which should cause the transformer to trip quickly.
⑶ Temperature display system: The temperature change value is measured by the Pt100 thermistor embedded in the low-voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and the highest temperature in history can be recorded). The highest temperature can be output as 4-20mA analog quantity. If it needs to be transmitted to a remote computer (up to 1200m away)
Protection method
Usually, IP20 protective shell is selected to prevent solid foreign objects with a diameter greater than 12mm and small animals such as mice, snakes, cats, and birds from entering, causing short circuits and power outages and other malignant faults, and provide a safety barrier for the live parts. If the transformer needs to be installed outdoors, IP23 protective shell can be selected. In addition to the above-mentioned IP20 protection function, it can also prevent water from dripping within an angle of 60° from the vertical line. However, the IP23 shell will reduce the cooling capacity of the transformer. When selecting it, pay attention to the reduction of its operating capacity.
Overload capacity
The overload capacity of dry-type transformers is related to the ambient temperature, the load before overload (initial load), the insulation and heat dissipation of the transformer, and the heating time constant. If necessary, the overload curve of the dry transformer can be obtained from the manufacturer.
How to use its overload capacity? The author proposes two points for reference:
⑴When choosing to calculate the capacity of the transformer, it can be appropriately reduced: fully consider the possibility of short-term impact overload of some equipment such as steel rolling and welding-try to use the strong overload capacity of dry-type transformers to reduce the capacity of transformers; for some places with uneven loads, such as residential areas mainly for night lighting, cultural and entertainment facilities, and shopping malls mainly for air conditioning and daytime lighting, you can make full use of its overload capacity and appropriately reduce the capacity of the transformer so that its main operating time is at full load or short-term overload.
Application status
Dry-type transformers have no oil, so there are no problems such as fire, explosion, and pollution. Therefore, electrical specifications and regulations do not require dry-type transformers to be placed in a separate room. Losses and noise have been reduced to a new level, and conditions have been created for the transformer and low-voltage panel to be placed in the same distribution room.
As an important equipment of the power system of offshore oil platforms, the safe and reliable operation of dry-type transformers is the key to the operation of power systems. In the wet and salty marine environment, dry-type transformers are prone to local discharge and local overheating of insulation. The application of dry-type transformer online monitoring system can effectively realize online monitoring of transformer status and ensure the stable operation of offshore oil platform power systems.
China's annual output of resin-insulated dry-type transformers has reached 10,000MVA, making it one of the countries with the largest production and sales of dry-type transformers in the world. Dry-type transformers are now widely used in almost all electrical systems such as power stations, factories, and hospitals. With the promotion and application of the low-noise (noise of distribution transformers below 2500kVA has been controlled within 50dB) and energy-saving (no-load loss is reduced by 25%) SC (B) 9 series, the performance indicators and manufacturing technology of China's dry-type transformers have reached the world's advanced level.