Patent GB-682250-A (GB)
Title: Improvements in and relating to electrical protective equipment
Inventor: PEARCE FREDERICK MELVILLE
IPC: H02H1/00
Filed: 1949-11-23
Abstract: 682,250. Protective cut-out arrangements; electromagnetic relays. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Nov. 9, 1950 [Nov. 23, 1949], No. 30061 /49. Class 38 (v) An impedance-measuring protective arrangement has impedance relays ZR<SP>1</SP>... ZR<SP>3</SP> under the control of a transfer relay TR arranged so that under phasefault conditions the current windings of the impedance relays are energised in accordance with the line-toline currents of the protected circuit and the voltage windings are energised in accordance with the lineto-line voltages, whilst under earth-fault conditions the current windings are energised in accordance with the line currents and the voltage windings are energised in accordance with the line-to-earth voltages. Protective circuit. In Fig. 1, the primary windings of two sets of auxiliary current transformers AT<SP>1</SP> ... AT<SP>3</SP> and BT1... BT<SP>3</SP> are connected in series with the star-connected secondary windings of main current transformers CT<SP>1</SP> ... CT<SP>3</SP>. The secondary windings of the "phase fault" auxiliary current transformers AT<SP>1</SP> ... AT<SP>3</SP> are connected in delta and to the lefthand ends (as shown) of the current windings C<SP>1</SP> ... C<SP>3</SP> of the impedance relays whilst the secondary windings of the "earth fault" auxiliary current transformers BT<SP>1</SP> .. BT<SP>3</SP> are connected in star and to the right hand ends of the current windings C<SP>1</SP> ... C<SP>3</SP> of the impedance relays. Contacts TR<SP>1</SP> of the transfer relay are connected as shown so that when the bridging contact is to the right, the current windings C<SP>1</SP> ... C<SP>3</SP> are connected in star across the delta-connected windings of transformers AT<SP>1</SP> ...AT<SP>3</SP> and the secondary windings of the transformers BT<SP>1</SP> ... BT<SP>3</SP> are short-circuited. When the bridging contact is to the left, the current windings are connected in star with the secondary windings of the transformers BT<SP>1</SP> ... BT<SP>3</SP> and the secondary windings of the transformers AT<SP>1</SP>... AT<SP>3</SP> are short-circuited. To introduce a residual component into the energisation of the impedance relay current windings, compensating transformers CCT<SP>1</SP> ... CCT<SP>3</SP> connected between the star points of the main and auxiliary current transformers, have their secondary windings connected across the primary windings of the transformers BT<SP>1</SP>... BT<SP>3</SP>. The voltage windings V<SP>1</SP> ... V<SP>3</SP> of the impedance relays are connected in series with resistors R<SP>1</SP> ... R<SP>3</SP> and these series circuits are connected in delta across the secondary windings of a voltage transformer VT so that the voltage' windings are energised in accordance with the line-toline voltages. When the transfer relay is operated, tappings on the resistors are connected together and to the star point at contacts TR<SP>2</SP> so that voltage windings V<SP>1</SP> ... V<SP>3</SP> are then connected in star for energisation in accordance with the line-to-earth voltages. Relay circuit and operation; Operation of the protective arrangement is initiated by phase-fault "starting" relays and earth-fault "starting" relays supplied by the main current and voltage transformers, the relay coils and connections thereto not being shown. In the event of a phase fault, one or more phase-fault relay closes its contacts PSR<SP>1</SP> to energise an auxiliary relay having a coil OCAR and contacts AR<SP>1</SP> ... AR<SP>3</SP>, the latter opening to remove shortcircuits from the impedance relay current coils C<SP>1</SP> ... C<SP>2</SP>. The phase-fault relay opens contacts PSR<SP>2</SP> to prevent the energisation of the operating coil' OCTR of the transfer relay, the contacts TR<SP>1</SP>, TR<SP>2</SP> of which remain as shown so that the impedance relay connections are those previously referred to for phase faults. If the fault is within the "reach" of the impedance relays ZR<SP>1</SP> ... ZR<SP>3</SP> they close their contacts (not shown) to trip or to initiate the tripping of circuit-breakers (not shown) or to initiate the operation of further protective gear such as a carriercurrent protective system. In the event of an earth fault, one or more earth-fault starting relays closes its or their contacts ESR to effect the energisation of the coil OCTR of the transfer relay through a rectifier BR<SP>1</SP> and the closed contacts PSR<SP>2</SP> of the phase-fault relay. The transfer relay at contacts TR<SP>1</SP> and TR<SP>2</SP> changes the connections of the impedance relay, it also opens contacts TR<SP>3</SP> to render the phase-fault relays ineffective, closes contacts TR4 to energise the auxiliary relay coil OCAR and closes contacts TR<SP>3</SP> to prepare a holding circuit for itself: The auxiliary relay opens its contacts AR<SP>1</SP> ... AR<SP>3</SP> and closes contacts AR<SP>4</SP> to complete the holding circuit for the transfer relay. Should phase and earth faults occur simultaneously, the system will respond to the earth fault first if the transfer relay operates and locks itself in before the phase-fault relay opens its contacts PSR<SP>2</SP>, otherwise the equipment will respond to the phase fault first. In either case, after having cleared one fault, the system can then respond to the other fault if it still remains. Transfer relay construction. To ensure that the connections of the impedance relays are changed in the correct sequence, the transfer relay may have the contact assembly of Fig. 2. The relay armature 20 carries three insulated contacts 22 (one shown) connected to the delta prints 5, 6, 7, Fig. 1. The contacts co-operate with three contacts 23 on spring blades 24 supported by a metal block 25 connected to the star points of the auxiliary transformer windings BT<SP>1</SP>... BT<SP>3</SP> and the voltage transformer windings. The blades 24 also carry contacts 27 which co-operate with contacts 28 on spring blades 29 connected to the tappings of resistors R<SP>1</SP>... R<SP>3</SP>. The block 25 also supports blades 32 carrying contacts 31 co-operating with contacts 33 on spring blades 34 connected to the windings BT<SP>1</SP>... BT<SP>3</SP>. In the de-energised position shown, only the contacts 31. 33 are closed and the windings BT<SP>1</SP> ... BT<SP>3</SP> are short-circuited. When the relay is energised the contacts 22, 23 are closed by the initial movement of the armature to short-circuit the windings AT<SP>1</SP> ... AT<SP>3</SP>. As the movement of the armature continues, the contacts 27 engage contacts 28 to connect the resistance tappings to the star point. Then as the movement continues, insulating abutments 35 on the blades 29, 34 engage and the blades 34 move up to open the contacts 31, 33 to remove the short-circuit from the windings BT<SP>1</SP>... BT<SP>3</SP>. In a modification Fig. 3, (not shown) the need for a special construction of transfer relay is removed by the use of a further auxiliary relay which may also at contacts VAR<SP>3</SP>... VAR<SP>5</SP> short-circuit resistors R<SP>4</SP> ... R<SP>5</SP> provided in series with the voltage windings V<SP>1</SP> ... V<SP>3</SP>, Fig. 1. This enables the use of impedance relays with a short time rating, as full voltage is only applied to them on the occurrence of a fault.