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A grounding transformer. A grounding transformer or earthing transformer is a type of auxiliary transformer used in three-phase electric power systems to provide a ground path to either an ungrounded wye or a delta-connected system. [1] [2] Grounding transformers are part of an earthing system of the network.
Any Δ-Y (delta-wye) connected transformer may be used for the purpose. A nine winding transformer (a "zig zag" transformer) may be used to balance the phase currents of a delta connected source with an unbalanced load. Low-resistance grounding systems use a neutral grounding resistor (NGR) to limit the fault current to 25 A or greater.
The grounding system must also have a minimum of two or more earth pits (electrodes) to better ensure proper grounding. According to rule 42, an installation with a connected load above 5 kW exceeding 250 V shall have a suitable earth leakage protective device to isolate the load in case of earth fault or leakage.
A conventional six-winding, grounding transformer or zigzag bank, [1] with the same winding and core quantity as a conventional three-phase transformer, can also be used in zigzag winding connection. In all cases the first coil on each zigzag winding core is connected contrariwise to the second coil on the next core.
Center-tapped delta transformer Center-tapped delta transformer voltages. High-leg delta service is supplied in one of two ways. One is by a three-phase transformer (or three single-phase transformers), having four wires coming out of the secondary, the three phases, plus a neutral connected as a center-tap on one of the windings.
The neutral conductor is connected to ground at the transformer center tap. Circuits for lighting and small appliance power outlets use 120 V circuits connected between one line and neutral. High-demand applications, such as ovens, are often powered using 240 V AC circuits—these are connected between the two 120 V AC lines.
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The ground shield of S, along with the ground wire ("third wire") P in the components' power cord and the building's utility ground wiring G form a ground loop. One of the best ways to prevent such a ground loop is to insert an isolation transformer in the signal cable S, as shown. The transformer breaks the conductive path between the ground ...