The design of the high-voltage substation must include consideration for the safe operation and maintenance of the equipment. Switching equipment is used to provide isolation, no-load switching, load switching, and interruption of fault currents. High-voltage power systems are generally operated as a three-phase system, and the imbalance that will occur when operating equipment in a single-phase mode must be considered. Air-insulated high-voltage electrical equipment is usually covered by standards based on assumed ambient temperatures and altitude. High-speed arcing horns are the equipment added to disconnect switches to allow them to interrupt small amounts of charging or magnetizing current. A load break switch is a disconnect switch that has been equipped to provide breaking and making of specified currents. Automatic high-speed grounding switches are applied for protection of power transformers when the cost of supplying other protective equipment is deemed unjustifiable and the amount of system disturbance that the high-speed grounding switch creates is judged acceptable.