GB836805A - Improved circuit arrangement for detecting faults in three-phase systems - Google Patents

Abstract

836,805. Faults testing. GENERAL ELECTRTC CO. June 27, 1956 [June 27, 1955,] No. 19904/56. Class 37. Three-phase star or delta inductively coupled windings are tested for faults by applying impulse waves of opposed (or similar) polarities simultaneously and respectively to a pair of distinct star (or delta) connected windings, and connecting a voltage indicator responsive to the time variation of an impulse to the star point or the free end of the third winding of a star connected system; or alternatively to the corresponding secondary windings inductively coupled to the impulsed primary windings; so as to respond to the algebraic sum of the impulses developed in the windings supplied therewith. In Fig. 5, a pair of impulse generators producing equal and oppositely poled impulses rising from zero to peak in 1.5 microsec. and falling to peak/2 in 40 microsec. are simultaneously triggered from a synchronizing network to energize primary windings 2, 3 of a 3-phase transformer, whose primary winding 4 is isolated from ground while the star point is grounded over a capacitance 12 shunted by resistance 10 across a cathode-ray oscillograph displaying the profile of the output impulse. In absence of winding faults, the latter as shown at 22 in Fig. 6, lies substantially on the zero axis due to the balance between input impulses and the excited windings, while a single shorted turn in either impulsed winding produces an output pulse as shown at 23. When the star point is inaccessible, the shunted oscillograph is connected between the free end of winding 4 and ground (Fig. 7, not shown), displaying no fault and single shorted turn output impulses as before (Fig. 8, not shown). The shunting impedances enable display sensitivity to be adjusted and may be removed if necessary, and the remaining winding 4 may be tested similarly by impulsing it together with widing 2 or 3. In testing delta connected transformers (Fig. 11), a negative impulse is applied to the common end of windings 31, 33 and the junctions of windings 31, 32 and 32, 33 are grounded over equal impedances 47, while the junction of the delta secondary windings 311, 331 is grounded and the junctions of windings 31<SP>1</SP>, 321 and 321, 331 are connected to the oscillograph, which displays a zero trace 50 of the output impulse for no fault and a trace 51 for a one-turn short circuit in windings 31, 33 (Fig. 12). When the secondary is star connected (Fig. 13), equal impedances 52 are connected across the ends of windings 31<SP>1</SP>, 331, whose star point is grounded, and the oscillograph is connected between the junction of the impedances and ground; zero output impulse voltage 55 appearing across the oscillograph for no fault, and impulse voltage 56 appearing for a one-turn short circuit in windings 31<SP>1</SP>, 33<SP>1</SP> or 31, 33 (Fig. 14). Specification 627,999 is referred to.