Transformer Upgrades can be used to upgrade a machine's power tier. Transformer Upgrades are placed in one of the four right-most upgrade slots in a machine's interface.
Each Transformer Upgrade increases the machine's power tier by one. One upgrade enables a Low Voltage tier 1 machine to receive Medium Voltage 128 EU/t, two upgrades enables it to receive High Voltage 512 EU/t, and so on. The Transformer Upgrade will also allow the machine to use higher tier storage items such as Energy Crystals.
Important: Make sure to put the transformer upgrade into the machine before applying power. Temporarily removing the wiring while setting up your machines is a good way to do this.