Experience of the Pacific gas and Electric Co. with the grounded neutral

The paper gives an outline of the distributing system of the Pacific Gas and Electric Company of California which operates at 60 kv., the transformers being Y-connected, with the neutrals solidly grounded. The company considers the grounded neutral system has a number of important advantages with regard to the transformers, the transmission lines, and operation. The fewer turns of larger capacity of the Y-connected transformers and the fixed lower average voltage to ground greatly increases their reliability. The maximum voltage on the line insulators with the grounded neutral is never more than 57.7 per cent of the line voltage, and it is possible to maintain polyphase service at a substation on a branch line with only two wires in case one wire should be cut out. This cannot be done on a delta system unless one phase of the system be grounded, which is very undesirable. With a grounded neutral, a wire down is instantly detected and power must be shut off. In a delta-connected system an arcing ground is often followed by surges which break down the insulation at other points, the cause of this disturbance being the oscillatory character of the arc. In the grounded Y system no such disturbances occur, as the frequency of an arc to ground is the same as that of the system and any damage is confined to the point of failure. It is also believed that operation with the grounded neutral causes less disturbance in telephone and telegraph lines than would be the case in delta-connected lines.