Patent ID: 7239497

Claim:
In an Intelligent Electronic Device (IED) for operation in an electrical power utility substation, a power supply circuit to supply power to internal components of the IED, said power supply circuit comprising: a first power block for converting received power from an external power source to a voltage to be used by the internal components of the IED, said first power block comprising; an external power connector having a positive power line, a negative power line and an earth ground, said external power connector receiving power from the external power source; at least three uni-directional solid state transient voltage suppressors each of which is connected in parallel with a corresponding one of at least three metal oxide varistors and a corresponding one of at least three capacitors, said uni-directional transient voltage suppressors and varistors clamping both differential and common mode high voltage transients to acceptable levels for the internal components by clamping the positive power line to the earth ground, by clamping the negative power line to the earth ground and by clamping the positive power line to the negative power line; wherein the uni-directional transient voltage suppressor will “fail short” when operating parameters arc exceeded which will halt the remainder of the system by causing a fuse to blow thereby isolating the internal components from any other further damaging transients, and wherein the varistors will “fail open” allowing the system to continue functioning, but leaving the remaining circuitry in the path unprotected; a second power block for converting received power from an external power source to a voltage to be used by the internal components of the IED; a first transient suppression circuit associated with the second power block for suppressing electrical transients in power received from the second power block; a second transient suppression circuit associated with the first power block for suppressing electrical transients in power received from the first power block; an electrical OR-ing diode block for outputting power received from the external power source by either the first power block or the second power block to the internal components of the IED; and wherein power received from either the first power block or the second power block is sufficient to drive the IED.