Comprehensive Analysis of Common Accessories of Dry-Type Transformers: From Enclosures to Copper Bars, Master Key Configurations in One Article

Enclosures

Enclosures can be categorized into indoor and outdoor types.

For indoor applications, considering heat dissipation and maintenance needs, it is generally recommended not to install an enclosure if there is sufficient installation space. However, if required by the user, enclosures with multiple observation holes can be provided. Enclosures can also be painted in colors preferred by the user.

The protection level of enclosures is typically IP20 or IP23:

• IP20 prevents the ingress of solid foreign objects larger than 12 mm and protects against accidental impacts.

• In addition to the functions of IP20, IP23 can prevent water droplets from entering within a 60-degree vertical angle, making it suitable for outdoor installation.

Enclosure materials include ordinary steel plates, injection-molded plastics, stainless steel plates, aluminum alloy composite plates, etc.

Temperature Controllers

All transformers are equipped with overheating protection devices. These devices detect and control the transformer temperature via PT thermistors built into the low-voltage windings, and output digital signals through an RS232/485 communication interface. The device provides the following functions:

• During transformer operation, the temperature values of the three-phase windings are displayed on the circuit.

• Displays the temperature value of the hottest-phase winding.

• Over-temperature alarm and over-temperature shutdown.

• Audible and visual alarms, and fan activation.

Air-Cooling Devices

• The cooling methods for dry-type transformers can be divided into natural air cooling (AN) and forced air cooling (AF).

• Under natural air cooling (AN), the transformer can continuously supply 100% of its rated capacity under normal operating conditions.

• Under forced air cooling (AF), a 50% capacity increase can be achieved under normal operating conditions, making it suitable for various emergency overloads or intermittent overload operations. Continuous overload operation using forced air cooling (AF) is generally not recommended, as it leads to greater increases in load losses and impedance resistance.

Copper Bars

• Generally, the cable inlet/outlet methods are classified into top inlet/outlet, bottom inlet/outlet, and side inlet/outlet.

• For transformers with a rated power ≤ 200 kVA, the conventional outlet method is still used; side outlets are connected by the user via cables.

• When the rated power is ≥ 1600 kVA:

• Double-row feeders with a spacing of 10 (for 1600–2000 kVA) or 12 (for 2500 kVA) are used for phases A, B, and C.

• Since the neutral line is located at the top of the transformer, if the neutral line needs to be led out from the bottom of the switchgear, it is recommended that the transformer’s neutral line still enters the switchgear from the top.