Temperature Control System
The safe operation and service life of dry-type transformers depend largely on the safety and reliability of the winding insulation. Insulation failure caused by winding temperatures exceeding the insulation's thermal rating is a primary reason for transformer malfunction; therefore, monitoring the operating temperature and implementing alarm and control functions is crucial.
(1) Automatic Fan Control: Temperature signals are acquired via Pt100 thermistors embedded at the hottest point of the low-voltage winding. As the transformer load increases and the operating temperature rises, the system automatically activates the cooling fans when the winding temperature reaches 110°C; the fans automatically stop when the temperature drops to 90°C.
(2) Over-temperature Alarm and Trip: Winding or core temperature signals are collected via PTC non-linear thermistors embedded in the low-voltage winding. If the winding temperature continues to rise and reaches 155°C, the system outputs an over-temperature alarm signal. If the temperature climbs further to 170°C-rendering the transformer unfit for continued operation-an over-temperature trip signal is sent to the secondary protection circuit to trigger an immediate shutdown.
(3) Temperature Display System: Temperature variations are measured using Pt100 thermistors embedded in the low-voltage winding. The system directly displays the temperature of each phase winding (featuring cyclic scanning of the three phases, maximum value display, and historical peak temperature recording). It can output the maximum temperature as a 4–20mA analog signal for transmission to a remote computer (up to 1,200 meters away).
Protection Methods
An IP20 protective enclosure is typically selected; this prevents the entry of solid foreign objects larger than 12mm in diameter as well as small animals (such as rats, snakes, cats, and birds) that could cause severe faults like short circuits or power outages, thereby providing a safety barrier for live parts. If outdoor installation is required, an IP23 enclosure may be chosen; in addition to the IP20 protection features, it prevents the ingress of water droplets falling at angles up to 60° from the vertical. However, an IP23 enclosure reduces the transformer's cooling capacity, so the resulting derating of operating capacity must be taken into account during selection.
Overload Capability
The overload capability of a dry-type transformer depends on factors such as ambient temperature, the load condition prior to the overload (initial load), the transformer's insulation and heat dissipation characteristics, and its thermal time constant. If necessary, the manufacturer can provide the specific overload curve for the transformer.
How can this overload capability be utilized? Here offers two suggestions:
(1) Transformer capacity selection can be optimized by reducing the rated size: By fully accounting for the potential for short-term surge overloads caused by equipment such as rolling mills or welding machines, one can leverage the dry-type transformer's robust overload capability to select a smaller rated capacity.
(2) For applications with uneven load profiles-such as residential areas (where night-time lighting dominates), cultural and entertainment facilities, or shopping malls (where air conditioning and day-time lighting dominate)-the overload capability can be utilized to reduce the rated capacity, allowing the transformer to operate primarily at full load or under short-term overload conditions.
Current Application Status
Since dry-type transformers contain no oil, they eliminate risks associated with fire, explosion, and pollution; consequently, electrical codes and regulations do not require them to be housed in separate rooms. Improvements in reducing losses and noise levels have further enabled the placement of transformers and low-voltage switchgear panels within the same power distribution room.
As critical components of the power systems on offshore oil platforms, the safe and reliable operation of dry-type transformers is essential to the overall system's performance. In the humid, salt-laden marine environment, these transformers are highly susceptible to insulation issues such as partial discharge and localized overheating. The implementation of online monitoring systems allows for real-time assessment of the transformer's condition, thereby ensuring the stable operation of the platform's power system.
China's annual production of resin-insulated dry-type transformers has reached 10,000 MVA, making it one of the world's leading producers and markets for this equipment. Dry-type transformers are now widely used across virtually all electrical applications, including power plants, factories, and hospitals. The widespread adoption of the SC(B)9 series-characterized by low noise (noise levels for distribution transformers under 2,500 kVA are controlled within 50 dB) and energy efficiency (no-load losses reduced by up to 25%)-has brought the performance and manufacturing technology of Chinese dry-type transformers to a world-class level.
