A transformer that increases the voltage level is called a Step up transformer.

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Voltage transformation in a transformer is governed by the turns ratio. If the secondary winding has more turns than the primary, the output voltage becomes higher than the input, which is why this is called a step-up transformer. In an ideal case, the output voltage equals the input voltage times the ratio of secondary to primary turns, so increasing the turns on the secondary raises voltage while the current drops correspondingly to keep power roughly the same. This is why step-up devices are used to raise voltages for transmission or to match equipment that requires higher voltage. Step down would do the opposite and reduce voltage; an isolation transformer focuses on providing electrical separation rather than changing voltage, and an autotransformer uses a single winding with taps and can be configured to step up or down but behaves differently from the standard two-winding step-up arrangement.