10kV High-Overload Oil-Immersed Power Transformers

10kV High-Overload Oil-Immersed Power Transformers Overview

High-overload distribution transformers are designed for distribution networks subject to short-term load peaks. These transformers are ideal for applications where the annual average load remains low, while temporary load demand may rise to 1.5~2 times the rated capacity for several days or weeks, typically for 2~3 hours per day. Typical applications include rural distribution networks with seasonal peak demand during holidays and agricultural periods.

Product Features

Designed for low annual load factors and significant seasonal load fluctuations, high-overload distribution transformers ensure reliable power supply while balancing long-term light-load operation with short-term overload capability.

They feature high energy efficiency, low losses, low no-load current, reduced reactive power consumption, and excellent short-circuit withstand capability.

High Overload Capability

The transformer is designed to withstand the following overload conditions without affecting its normal service life:

• 150% of rated capacity for 6 hours
• 175% of rated capacity for 3 hours
• 200% of rated capacity for 1 hour

Thermal Endurance Capability

High-overload distribution transformers are available with Class B or Class F insulation systems, depending on the insulation materials used. The corresponding temperature limits are listed below.

Example: For a 200kVA Class B insulated high-overload transformer, model S13-M(B)-200/10GZ, operating at an ambient temperature of 40°C, the maximum permissible top-oil temperature is: 80K + 40K = 120°C All materials and components, including insulation materials, accessories, surface coatings and sealing elements, are designed to withstand temperatures above 120°C. With an additional 30K design margin, the maximum design temperature is 150°C.

Selection Criteria

For economical operation, high-overload distribution transformers are recommended for areas where the previous year’s average load factor (β) was below 25%. The load factor is calculated based on annual energy consumption W (kWh) and annual maximum demand Pmax (kW).

Transformer capacity should be selected based on the previous year’s Pmax and the average annual growth rate of maximum demand over the past three years. Where maximum demand data is unavailable, the average annual growth rate of energy consumption may be used instead. Capacity planning should consider a 5~10 year development horizon. Recommended capacities are listed in the following table.

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