INTERTRIPPING SYSTEM

Abstract: An intertripping station (10) of an intertripping system for use in the protection of power system networks and other applications where isolated intertripping is required. The station has output means (10A) for outputting either a supervision signal or an intertrip signal on the pilot circuit bus. The intertrip signal is of a higher level than the supervision signal and isolation means (TR) is provided between the output means and the bus. The station includes a supervision sensor (K1) for determining the presence of the supervision signal and for providing an alarm (K5) in the absence of that signal. An intertrip signal sender (K4) is also provided for enabling an intertrip signal to be provided by the output means and the station further includes a trip sensor (K2) for detecting the presence of an intertrip signal on the bus and for providing a trip control function at the station.

Description: EM The invention relates to an intertripping system, an intertripping station, a transformer construction and method of controlling and supervising a plurality of intertripping stations. 5 The invention is particularly suitable for . providing interconnected control and supervision between a number of stations. The invention is particularly suitable for use in the protection of power system networks and othe applications where isolated intertripping is required. The ] _ Q invention will be described by way of example with reference to protection of power system networks but it should be appreciated that it may also be employed for other purposes. It is known to provide a master supervisory terminal at a master location in a power distribution ■t r- network and to have a remote or slave supervisory terminal at each of a plurality of remote locations or substations. Various systems have been employed for communication betwee the master and the slave terminal. Direct wiring was employed and a separate communication channel was established between each slave terminal and the master terminal and between each slave of the system. Where a large number of slave terminals were present the number of possible permutations for connections between the slave terminals was large. Such arrangements were only suitable for use in systems having a small number of slave terminals In another known system a multipoint control and . supervisory function was achieved by having a direct SUBSTITUTESHEET terminal and other remote terminals were coupled in series with one another and to the one remote terminal. Such systems were nqt reliable since a fault in one remote 5 terminal of the series would render all subsequent remote terminals of the series ineffective. In yet another system all remote terminals were coupled in parallel with one communication channel from the master terminal. The master terminal transmitted a digital τ_g code representative of a chosen remote terminal which would recognize its unique code and respond by sending a unique code and date which would be decoded at the master terminal. Such systems had protocol problems in determining timing delays for proper transmission and reception of - 5 signals. In addition, these systems were prone to errors due to noise interference problems with the relatively low level of digital signals employed. Systems employing voice frequency signalling are also known in which intertripping was achieved by a frequency shift in the transmitted signal. Such systems were only suitable for point to point communication and thus a master terminal could only effectively communicate with one remote terminal. In such systems signal cancellation and the effects of noise were problems. It is an object of the invention to provide an intertripping system which at least minimises the difficulties referred to above. SUBSTITUTESHEET n er r pp ng s a on including output means for outputting either a supervision signal or an intertrip signal, said intertrip signal being of a level higher than the level of the supervision signal 5 isolation means between the output means and a bus onto which the signal may be supplied, a supervision sensor for determining the presence of the supervision signal and for providing an alarm in the absence of that signal, an intertrip signal sender for enabling the intertrip signal t 10 be provided by the output means and applied to the bus and trip sensor for detecting the presence of an intertrip signal on the bus for providing a trip control function at the station. The system of the invention includes one master j c station and at least one remote station, two way communication being possible between the master station and the remote station(s) , said master station being capable of transmitting a supervision signal onto a bus and able to raise an alarm if the supervision signal is absent or of a π magnitude lower than a predetermined level, the remote station(s) being capable of transmitting their own supervision signal onto the bus of an order of magnitude lower than the master supervision signal and able to raise an alarm if the remote supervision signal is absent or belo a predetermined level whereby the master station or any one of the remote stations may apply an intertrip signal onto the bus to cause the other of the master station and the SUBSTITUTE SHEET rema n m r p s gna . The master station includes output means for outputting either a supervision signal or a trip signal level. These signals may be voltages. The trip Voltage level is substantially higher than the supervision voltage level. It is preferred that the supervision voltage be about 20 VDC and that the trip voltage be an order of magnitude higher. Preferably, the trip voltage level is about 120 VDC or greater. It should be appreciated that both these voltages are arbitrary and all that is necessary is that the trip voltage lev.el be substantially greater than the other voltage level. The master station output means provides a degree of electrical isolation between the bus previously referred to and the remainder of the station. Thus, isolation means is employed between the bus and the output means. The isolation means may be provided by any suitable means capable of providing effective isolation against high voltages in the power system network. Typically isolation. against 15KV is necessary. In one embodiment a pulse transformer is employed interposed between the output means and the bus. Pulse transformers are capable of working in various modes including forward and flyback modes. It is particularly preferred that a flyback pulse transformer be employed. As mentioned above, the output means of the master station may output two distinct voltage levels. In one SUBSTITUTESHEET em o men e u m ompr ses a o converter. The converter may be made adjustable such that the magnitude of the two voltage levels may be adjusted as required, in one embodiment -the converter includes a pulse width 5 modulator which, together with the pulse transformer can provide the two output voltage levels referred to. The master station includes a supervision sensor. The supervision sensor determines whether the supervision signal is being applied to the bus. In the absence of this 10 signal the master station may provide an alarm. The supervision sensor preferably provides a high degree of electrical isolation between the bus and the remainder of • the station. Preferably a reed relay is employed although isolation may be achieved in any other suitable way. 25 Optical isolation or other magnetic field sensors may be used for example. The master station includes a trip sensor. The trip sensor detects when an intertrip signal is impressed o applied to the bus and the station is responsive to provide 2 Q a trip control function for the master station. The trip sensor preferably provides a high degree of isolation between the bus and the remainder of the station. Preferably a reed relay is employed although isolation may be achieved in any other suitable way. _,_ The master station includes an intertrip signal sender. The signal sender may be operative to ensure that the master station outputs, onto the bus, an intertrip SUBSTITUTE SHEET , slave station(s) provide an intertrip output to a protection/intertrip panel whereby the power network may be suitably controlled. 5 The master station may include a sensor to ensure that should the output means not function to output a supervision signal an alarm may be raised. The sensor may compare a signal derived from the output means with a reference level. An alarm may be raised responsive to that 0 comparison. Where the output means includes a transformer the sensor may establish a signal proportional to the current in the primary winding of the transformer and • compare that signal to a reference. The slave or remote stations may be constructed essentially the same as the master station but adapted to output a supervision signal different from the supervision signal put out by the master station. Where the supervision signals are voltages the remote station signal is of a lower level than the master station supervision signal. The Q remaining features of the remote station may be the same as that for the master station. The communication method used between a master station and one or more remote stations or slaves includes outputting a supervision signal onto a bus common to the master station and the or each remote station; the or each remote station outputting a supervision signal; the supervision signals enabling the master and remote stations SUBSTITUTESHEET . further includes applying an intertrip signal onto the bus sensing for the presence of the intertrip signal and causing the master and the remote stations to output a control 5 signal. The method may employ voltage signals whereby the master supervision signal is a higher voltage level than the • remote supervision signal. Preferably the intertrip signal is higher in magnitude than the master supervision signal. 0 The method may include sensing that each station is providing a supervision signal. In case of the absence of such a supervision signal an alarm may be raised. The invention includes a pulse transformer construction having core pieces, a prxmary winding wound on 5 a primary former, a secondary winding wound on a secondary former whereby said windings are arranged coaxial with one another and extending around a common part of the core pieces whereby good magnetic coupling and electrical isolation may be achieved between the windings. Q Preferably one of the formers has tracking grooves and ridges. Preferably it is the secondary former which is provided with the tracking grooves and ridges. The secondary former has a coil receiving part about which the secondary winding may be wound. Preferably, the tracking grooves may be located at each end of the coil receiving part. The former may be substantially cylindrical. The tracking grooves and ridges may form end flanges to the SUBSTITUTE SHEET . The core pieces have a gap between them to ensure that the transformer may function as a flyback pulse transformer. The gap may be of any suitable size -but preferably is about 0.25mm. The core pieces have a core arm about which the windings may locate. Preferably the core pieces each have a plurality of core arms - one either side of a central core arm. The transformer may include one or more station blocks relative to which the ends of the windings may be terminated. Preferably the station blocks are mounted to or ■ associated with the primary former. The primary former has a winding receiving part about which the primary winding may be wound. The primary winding receiving part is preferably receivable within a bore in the secondary former. Preferably this part is cylindrical. It is preferred that the primary former have an end flange which may limit the extent to which the primary winding receiving part may fit within the secondary former. It is preferred that the transformer be encapsulated. A potting compound may be used for this purpose. It is preferred that flashover barriers be present to separate connecting pins or stations of the ends of the windings. Particular preferred embodiments of the invention SUBSTITUTE SHEET accompanying drawings in which: Figure 1 is a. block diagram of an intertripping system according to an embodiment of the invention; 5 Figure 2 is a detailed schematic diagram of a- station according to an embodiment of the invention; ' Figure 3 is a detailed circuit diagram of the station shown in figure 2; Figure 4 is an exploded view of a pulse 10 transformer; Figures 5a and 5b are front and end views, respectively, of a former used in the transformer of figure * 4; Figure 5c is an elevational view of a former for a 5 reed relay; Figure 6a is a sectional view of the transformer taken along line XX of figure 6b; Figure 6b is an elevational view of an assembled transformer; and, _ π Figure 7 is a detailed circuit diagram of an alternative embodiment of a station to that shown in figure 3. As shown in figure 1 an intertrip system includes a master station 10 coupled by a bus to a remote station or „„ slave 11. The bus is made up of a bus or two pilot wires Pl 25 r and P2. As indicated further slaves may be connected in parallel with the bus by further bus 14. The master 10 is SUBSTITUTESHEET 12 does not form part of the invention. Master 10 may be located at a central station or substation and panel 12 is 10 15 • 20 25 control devices at that substation. Similarly slave 11 i s coupled to protection/intertrip panel 13. Panel 13 also does not form part of the invention. 5 The operation of master 10 and slave 11 plus.any additional slaves coupled in parallel to bus or pilots Pl, P2 is such that if a trip signal is generated at any station corresponding trip outputs are produced at all other stations of the system. 10 The master 10 has a pulse transformer TR for providing a DC voltage at the secondary winding S. The construction of the transformer TR is such that it functions as a flyback pulse transformer which is particularly suitable for use with the operation of the remainder of the , _- circuitry. Diode Dl is part of the construction necessary for this type of transformer function. Reed relays l and K2 are coupled in series with zener diode Zl and extend across the secondary winding through diode Dl. In one embodiment the transformer comprises 100 turn primary winding P of 0.25mm wire wound in a single layer and a secondary winding S of 180 turns 0.25i-irα wire in two layers. Relay Kl may have 25000 turns of 0.055mm wire, 20-25 ampere-turns sensitivity with a pick up at 20V and drop off at 18V. Relay K2 may have 3800 turn of 0.112mm wire with 20-25 ampere-turns sensitivity with a pick up at 90V and drop off at 55V. Zener diode Zl is placed in series with relay K2 to reduce the differential between the Kl, K2 are constructed to give good isolation at 15KV between the windings and their respective contacts. As shown in figures 2 and 3 the master 10 has an 5 -intertrip receive relay K3, an intertrip send relay K4 and an intertrip faulty alarm relay K5. A source of DC power is supplied to DC supply j_ terminals. The supply voltages may be either 32VDC nominal (range 26 to 36VDC) or 110VDC nominal (range 88 to 121VDC) . With reference to figure 3, 0 when a nominal voltage of 110VDC is employed suitable resistors Rl, R2, R19 and R2O may be placed in series with relays K3, zener diode Z2, relay K5 and relay K4 respectively. Resistor R2 may be chosen as 820 ohm 5W for 32 VDC and 4K ohm 1W for 110 VDC. Resistors Rl, R19 and R20 5 are not present for the lower nominal voltage and are of a selected value for the higher voltage to ensure continuous operation at this voltage. Each relay K3, K4, K5.has two sets of contacts associated with it. Relay K3 and K4 each have two normally open contacts whilst K5 has two normally Q closed contacts. Each master 10 has a supervising link Ll in series with variable resistor VR1. A slave 11 is constructed in the same fashion as a master except link Ll is not present and resistor VR1 is not necessary. Diode Dl protects the transformer in the case of surges or inadvertant polarity reversal on pilot lines Pl, P2. A detailed circuit diagram of a preferred station SUBSTITUTE SHEET s us ra e e . ower s supp e o s a ons V+ and V-. A surge suppressor SI is connected across these stations. Suppressor SI may comprise a metal oxide varistor or non-linear resistor. Diode D2 provides for reverse polarity protection and has its anode connected to station V+. Relay K3 is connected in series with a normally open contact of relay K2 and that series connection extends between V+ and V-. A flywheel or back emf protection diode D3 is connected across relay K3. As mentioned above 0 resistor Rl is chosen or is optional depending upon the magnitude of the--supply voltage. Similarly resistors R2 and R19 are of a selected value or are absent. Zener diode Z2 ' provides a suitable rail voltage for the circuit. In this case 15VDC is chosen. Capacitor Cl acts as a filter. 5 A pulse width modulator (PWM) is present and its pulse rate is dependant on the position of link Ll, capacitor C2 and resistors R4, R5, R6 and VRl. With the link in the position shown and with the contacts of -relay K4 open the frequency is determined by R4, C2. With the link Q Ll in the other position and with contact of relay K4 open the frequency is determined by C2 and the resultant value of VRl plus R5 in parallel with R4. The resistors have relative values such that when R4, C2 determines the frequency a low output voltage to be applied to the pilots - this would occur when the station is a slave and enables the slave to supervise itself for establishing whether it is functioning correctly. With the contacts of relay K4 closed SUBSTITUTESHEET . t e va ue o pre om na es an a re at ve y g voltage may be applied to the pilots - that is, the intertrip signal. The method by which this voltage is generated follows. With * the link in the broken outline position the 5 resistors are chosen to enable a voltage of an order of magnitude lower than the intertrip signal to be applied to the pilots - that is, the supervision signal. These three voltages may for example be about 2VDC, about 20 VDC and about 120 VDC. These values are arbitrary Q and the high voltage (i.e. 120 VDC) just needs to be appreciably higher than the supervision signal (20 VDC) to ensure that if one slave loses communication with the master . and the impedance seen by the master changes the resultant increase over the supervision signal magnitude is not recognised as an intertrip signal. If it were the remaining • slaves would .respond as if an intertrip signal had been placed on the pilots and this is undesirable. The output at pin 14 of PWM is a pulse train of a particular frequency and is applied to amplifying circuit comprising Ql, Q2. Resistor R8 is a biasing resistor for the amplifier. A pulse at the gate electrode of FET 1 causes it to conduct. This enables a current to flow through the primary of transformer TR and a voltage appears at the secondary of the transformer. This flow of current causes the potential across R10 to increase in a substantially ramp like fashion. When this potential reaches a predetermined level a feedback signal is applied SUBSTITUTE SHEET • through R7 and held by capacitor C3 and applied to pin 11 0 f PWM to turn the PWM off. This in turn ensures that FET 1 i s turned off and PWM times out until the next pulse output at pin 14. The circuit is such that capacitor C3 is -discharged 5 by then. The voltage appearing at the collector of FET 1 is such that when the FET 1 is correctly functioning the voltage is a pulsating one. This pulsating voltage is stored in capacitor C5 via resistor R9, capacitor C4 and is 0 applied to the non-inverting input of comparator A2. Comparator A2 compares this voltage with a reference voltage provided by divider network R13, R14. When the voltage at • the non-inverting input is higher than this reference the comparator A2 provides a high level output to ensure transistor Q4 conducts. Thus, provided relay Kl is energised and its normally open contact is closed, relay K5 is energised and its normally closed contacts are held open. This ensures that an "intertrip faulty" alarm is not generated by not allowing the contacts of K5 to return to Q their normally closed state. If energy is not being transferred to the secondary of the transformer TR the flyback voltage at the primary becomes large and metal oxide varistor S3 conducts and limits the voltage across the FET 1 to protect it from damage. Also transistor Q3 is turned on to apply a low voltage to the inverting input of comparator Al and to the non-inverting input of A2. The output of A2 goes low., The output of Al goes high and the LED does not . illuminate. When the circuit is operating correctly transistor Q4 is turned on and the output of Al is low and LED is illuminated to indicate that the station is functioning 5 correctly. Resistor R15 is a load resistor for the LED and resistor R16 is a biasing resistor for Q4. Diode D5 is a flywheel diode for relay K5. Resistor Rll is a bleed resistor to discharge capacitor C5 and R12 is a bias resistor for Q3. Should the supervision voltage not be on the pilots relay Kl is not energized and its normally open contact will be in its open position and relay K5 will not energize and . the "intertrip faulty" alarm is provided. The operation of a master station is as follows. With power on and energy being transferred to the secondary of transformer TR capacitor C2 and resistors VRl and R5 in parallel with R4 determine the frequency of operation of the PWM and hence the voltage applied to the pilots Pl, P2. When the station is functioning correctly and in the supervisory mode 20VDC is applied to the pilots, relays Kl, K5 are energized and LED is illuminated. If it is desired that the master station produce an intertrip signal to output an appropriate signal to its protection intertrip panel relay K4 is energised. This ensures that R6, C2 control the frequency of the output of the PWM and the 120 VDC intertrip signal is applied to the pilots. The magnitude of this voltage is sufficient to operate reed • re n ser es w re ay K3 is closed to energize K3. This closes the normally open contacts of K3 to provide appropriate control at the protection/intertrip panel of the master. 5 Similarly reed relays K2 of each slave also * operates in the same fashion and K3 of the slave provides an appropriate control signal at the associated protection/intertrip panel of the slave. If, at the master, the energy is not transferred to 0 the secondary of the transformer the LED goes off, relay K5 is de-energised and its contact remain closed to provide an "intertrip faulty" alarm at its associated panel. Also if • the supervision voltage is too low Kl will not hold in and relay K5 will raise the alarm. Thus, at the master an alarm 5 will be provided either if the supervision signal is absent or if it is too low and in addition if the transformer does not transfer energy the alarm will also be raised. In the event of a power failure the contacts of K5 are closed and an alarm will be provided. o A slave is similar in construction and operation to a master except that link Ll is in the position shown in figure 3 and VRl and R5 have no effect. The slave normally outputs 2VDC to the pilot and this enables the slave to check its own operation to ensure that energy is being transferred to the secondary of the transformer. This occurs in an identical fashion to that in the master. A transformer is illustrated in exploded form in SUBSTITUTESHEET • figure 4 and further details are shown in figures 5a, 5b, 6a and 6b. The transformer has two core pieces 30, 31. Piece 30 has two arms 30a, 30b plus a central arm. A core former 34 has station blocks 34a in which the primary and- secondary winding may be terminated relative to pins 35 and 35a - respectively. The former has a spool 34b having a circular end face member and an extending cylindrical part about which the primary P may be wound. Core piece 30 locates between station blocks 34a. The transformer includes a bobbin 36 about which the secondary S is wound. The bobbin 36 has a central bore 40 (see figure 5b) within which the cylindrical part of • former 34b (figure 4) locates.- In this way the windings are closely adjacent one another and in fact coaxial. This enables good coupling between the windings to be achieved. The construction of bobbin 36 is such that it enables this coupling to be effected whilst still affording excellent electrical isolation between the windings. As shown in figure 5a the bobbin has tracking ridges 37, 39 and groove 38 at each of its ends to ensure that a large tracking distance is present between the windings to provide good isolation between them. This assists in the applicability for use of the transformer in high tension applications. Ideally the transformer may be used where 15KV isolation is required. Thus, should a fault occur at the primary and 15KV be impressed on it the secondary will be suitably isolated from this fault. The bobbin 36 is made from a . material which provides good electrical insulation between the windings whilst still allowing them to be closely adjacent for coupling purposes. A suitable material is DELRON ACETAL whilst any equivalant or substitute may be 5 employed. The central arms of the core pieces 30, 31 project into the cylindrical part of former 34b whilst arms 30b, 30a extend adjacent the former 34b. This is shown in figure 6a. Figures 6a and 6b show views of an assembled 0 transformer encapsulated as shown at 62 in a potting compound which may be cast about the transformer in a • suitable mould. Pins 35 project outwardly from the - assembled transformer and flashover barriers 64 are provided between the pins for electrical insulation and isolation 5 between the pins. The core pieces 30, 31 are assembled to provide a gap 60 between them. This gap is necessary to ensure that the transformer operates in the flyback mode. Typically, the gap is about 0.25 mm. Insulating spacers 61 ensure that core piece 31 is suitably spaced for the Q encapsulating step. Fixing nuts 63 are positioned during or before encapsulation and enable the completed transformer to be suitably mounted in use. The primary winding may comprise 100 turns of 0.25mm wire in a single layer. The secondary winding may comprise two layers of 0.25mm wire and 180 turns. Insulating material such as terylene tape may be applied between the layers of the secondary winding. The SUBSTITUTE SHEET encapsulating material may comprise ARALDITE LC177 resin and LC170 hardener. The flyback pulse transformer may"have its secondary short circuited without damage. Figure ^ 5c shows an embodiment of a bobbin 50 for the reed relays Kl, K2. In view of the high isolation characteristics (that is, at least 15KV) the reed relays are specially constructed. The bobbin has a spool portion 52 with a stem 52a about which the coil of the relay may be wound. End cap 53 and head portion 54 are located adjacent opposite ends of spool portion 52. Grooves 56 are present in cap 53 and head portion 54 and assist in the location of a sleeve (not shown) which may be placed over the bobbin 50,. The bobbin has a central bore 51 within which the switching component or reed of the reed relay is inserted. The reed may be an Email miniature reed, catalogue number 2725. Figure 7 is an alternative embodiment to that shown in' figure 3. In figure 7 the following components which are present in figure 3 have been eliminated relay Kl plus its contacts . resistors VRl, R5 and R17 diode Zl. Additional circuitry has been included. Figure 7 employs a linear magnetic field sensor FS which preferably is a low temperature drift type and may be a SIEMENS SAS 231W or equivalent. Sensor FS is closely coupled with relay K2 and is able to sense the magnitude of the pilot supervision SUBSTITUTESHEET • voltage. Sensor FS is associated with comparator A3 which derives its inputs from a reference and from the sensor and A3 provides at output B a low level signal when the signal detected across -the pilots Tl, T2 is less than the 5 reference. This low signal is applied to the base of • transistor Q4 to turn it off. This ensures that relay K5 is de-energised and its normally closed contact are closed and an alarm may be raised to indicate that the supervision signal is not present on pilots Tl, T2. 10 Resistor R24 is in series with relay K2 and it together with capacitor C7 provide additional filtering. This filtering allows fastener intertripping between • stations for the same noise immunity as the circuit of figure 3. 25 The sensor FS also provides a method of regulating the pilot supervision voltage injected onto the pilots by the master station and removes the need to adjust the pilot supervision voltage in the field by adjusting VRl of figure 3. Resistor R22 limits the range of control of the 2 Q supervision pulsing rate within a range of about 6:1. Thus, even if the sensor fails there is no chance of obtaining a false trip output. Resistor VR3 sets the operation threshold of sensor FS and VRS is an offset adjuster. The sensor FS could also be used to sense and regulate the trip _ ς output voltage in much the same way as described above in relation to the supervision voltage. With the intertripping system and the specially SU achieved by the construction of the reed relays and by the flyback DC to DC converter which employs the pulse transformer. A.constant energy pulse is provided -by the converter. The energy transferred, and hence the voltage developed across the pilots is a function of the pulse frequency and is independent of the input supply voltage. The advantages of this are: 1. In one embodiment no feedback is required to maintain a constant output voltage across a constant load represented on the pilots. 2. It is possible to monitor the flyback voltage on the primary of the transformer to determine that energy is being transferred to the secondary and this provides a simple method of self supervision by each station without the need for -isolated sensors on the secondary. 3. The output voltage applied to the pilots is proportional to the square of the pulse frequency of the PWM and thus for a low voltage as is required for supervision the operating frequency is low. This assures a large mean time between failure. With the system of the invention an intertrip signal can be generated by one station to control the production of trip signals at that station and other stations when there is a supply voltage, when pulses are applied to FETl, when energy is transferred to the secondary of the transformer and when the supervision voltage is . s not present an "alarm intertrip faulty" signal is generated to pass an appropriate alarm signal to the or all protection/intertrip panel 13.

Claims: 1. An intertripping station including output means for outputting either a supervision signal or an intertrip signal, said intertrip signal being of a level higher than the level of the supervision signal, isolation means between the output means and a bus onto which the signal may be supplied, a supervision sensor for determining the presence of the supervision signal and for providing an alarm in the absence of that signal,- an intertrip signal sender for enabling the intertrip signal to be provided by the output means and applied to the bus and a trip sensor for detecting the presence of an intertrip signal on the bus for providing a trip control function at the " station. 2. The station of claim 1 wherein the output means comprises a DC to DC converter. 3. The station of claim 2 wherein the converter includes a pulse width modulator. 4. The station of claim 3 wherein said pulse width modulator operates in a constant energy pulse mode. 5. The station of claim 4 wherein said isolation means comprises a pulse transformer having a primary winding and a secondary winding, the primary winding being controlled by the converter to provide the intertrip and supervision signals at the secondary winding, said supervision sensor and said trip sensor are associated with the secondary winding. 6. The station of claim 5 wherein said sensors each SUBSTITUTE SHEET comprise a reed relay each having a relay coil, said coils being connected in series across said secondary winding. 7. The station of claim 5 or 6 wherein said pulse transformer operates in a flyback mode. 8. The station of any one of claims 1 to 7 wherein said intertrip and said supervision signals are voltages having a respective magnitude of about 120 VDC and about 20 VDC. 9. The station of any one of claims 1 to 7 wherein said intertrip and said supervision signals are voltages having a respective magnitude of about 120 VDC and about 2 VDC. 10. The station of any one of claims 1 to 9 wherein said supervision signal sensor includes a sensor for comparing a signal derived from the output means with a reference level and which sensor provides the alarm when the signal derived from the output means is less than the reference level. 11. An intertrip station according to claim -1 wherein said output means comprises a DC to DC converter having a pulse width modulator and wherein said isolation means comprises pulse transformer with a primary and secondary winding, an output from the pulse width modulator being employed to switch current flowing in the primary winding, at least two sets of timing components associated with the modulator, one set of components ensuring that the modulator provides an output enabling the transformer to provide said STITUTE SHEET superv , omponen s e ng associated with the modulator and in response to the intertrip sender to override the one set for ensuring that the modulator provides an output enabling the transformer to provide the intertrip signal, said sensors comprise two reed relays each having a coil both said coils being in series with the secondary winding, the trip relay having a normally open contact and the supervision relay having a normally open contact, an alarm relay in series with the contact of the supervision relay, said alarm relay having at least one normally closed contact whereby when the supervision relay is energised the alarm .contact toggles to raise the alarm, said intertrip signal sender comprising a relay having at least one normally open contact, said intertrip sender ' relay being in series with said second set of components and a control relay in series wih the trip relay contact comprising the control relay to provide the trip control function. 12. An intertrip station substantially as herein described with reference to the drawings. 13. An intertrip system having at least two said stations according to any one of claims 1 to 12 wherein twoway communication is possible between said stations wherein one said station functions as a master station and is able to provide its own said intertrip signal and said supervision signal and the other said station functions as a remote or slave station is able to provide its own said s ave supervision signal being of a level substantialy less than said master supervision signal. 14. An intertrip system substantially as herein described with reference to the drawings. 15. A pulse transformer having core pieces, a primary winding wound on a primary former, a secondary winding wound on a secondary former, said windings and said formers being arranged substantially coaxial with one another and extending around a common part of the core pieces whereby good magnetic coupling and electrical isolation is achieved between the windings. 16. The transformer of claim 15 wherein one of said formers has tracking grooves and ridges. 17. The transformer of claim 16 wherein the secondary former has a cylindrical winding receiving part and an end flange and the tracking grooves and ridges form the end flange. 18. The transformer of any one of claims 15 to 17 wherein the core pieces have a gap between them to enable the transformer to function in a flyback mode. 19. The transformer of any one of claims 15 to 18 wherein the core pieces each have a core arm about which the windings locate, said core pieces each have a pair of further core arms, one arm of each said pair being located either side of the arm about which the windings locate. 20. The transformer of claim 17 wherein the primary prxmary winding is wound, said primary receiving part being received within the secondary former. 21. The transformer of claim 20 wherein the primary former has an end flange which limits the extent to which the primary winding receiving part projects into the secondary former. 22. A transformer substantially as herein described with reference to figures- 4 and 6a and 6b of the drawings. SUBSTITUTE SHEET

Inventors: COOMER RONALD JAMES, HOI AH LOY, ROBINSON JOHN WALTON, COOMER, RONALD, JAMES, HOI, AH, LOY, ROBINSON, JOHN, WALTON
Applicants: SOUTH EAST QUEENSLAND ELECT
Application year: 1986
Main classification: H02H3
IPC codes: H02H3, H02H7, H02J13