Heavy Duty Transformers are used when continuous power is needed for large electrical equipment such as a refrigerator or power tools. Transformers can either step up or step down electrical voltage. Usually if you are using a United States appliance in another country, you will need a step down transformer.
Step down transformers decrease voltage. In North America, 110 - 120 volts electricity is used and appliances are designed for this amount of electricity. In many foreign countries 220 volts of electricity is used. If you plug a United States television into an outlet in Germany (230 volts) without a transformer, you are likely to damage the television permanently.
If you are traveling to Japan you will need a Step Up Transformer, since Japan uses 100 volts electricity, compared to 120 volt electricity in the United States.
Appliances that require a Transformer:
All appliance require different transformer wattage so be sure to check the wattage of the particular appliance.