AU2002100385B4 - Modified buchholz relay for continuous monitoring of gas generated by transformer internal faults - Google Patents

Description

AUSTRALIA

Patent Act 1990 COMPLETE SPECIFICATIONS INNOVATION PATENT No 2002100385 MODIFIED BUCHHOLZ RELAY FOR CONTINUOUS MONITORING OF GAS GENERATED BY TRANSFORMER INTERNAL FAULTS By John Owen Williams The following statement is a full description of this invention, Including the best method of performing it known to me.

Description [000] This new type of Buchholz relay was developed to continuously monitor the rate that gas is being generated from a substation high voltage power transformer internal fault and automatically disconnect the power supply to the transformer when a gas runaway generating fault is detected, so as to prevent a gas fuelled explosion from rupturing the transformer tank; A function which existing Buchholz relays do not provide.

[001] This new type of Buchholz relay will also detect when air is being drawn into the oil circuit of the transformer through the gland of the oil circulating pump by recording that gas is being detected only when the cooling pump is running, thus preventing erroneous signals, which cannot be detected with existing Buchholz relays.

[002] The new Buchholz relay requires that the low oil level float and surge detecting vane/flap be installed directly in the oil flow through the relay and not be actuated by the flow of gas into the relay, or the overflow of gas out of the relay to the conservator, should the automatic recycling function be inhibited.

[003] The gas section of the relay is enlarged in height so as to accommodate an additional two volumes of gas, making a total of three equal gas volumes, each volume being provided with an equally spaced float switch, allowing the relay to respond to three volumes of gas instead of the usual one volume with existing relays.

[004] The new Buchholz relay is connected by pipe and valves to the top of a gas vessel for storage of gas samples from the relay, excess gas pressure in the storage vessel is automatically relieved by an open ended pipe connection through the top of the transformer conservator and ending up in the conservator oil.

[005] Oil is prevented from discharging from the relay when gas is being purged, by a small float valve mounted on the inlet side of the discharge solenoid valve. The ball in the valve floats on top of the rising oil until it seals the outlet of the valve, thus preventing oil overflowing into the gas vessel.

[006] The low oil level float and oil surge detecting vane/flap in the lower section of the Buchholz relay actuate a mercury or reed switch which immediately disconnects the supply voltage to the transformer. The low oil level float switch and oil surge detecting vane/flap must not be influenced or operated by the presence of gas.

[007] The three gas level float switches are connected to timing and logic circuits in a PLC, where the timing of each switch actuation is compared with each other and thus provide a rate that the gas is being generated. The station PLC is used to monitor and record the rate that the gas is being generated however; the PLC could also be programmed to automatically disconnect the supply voltage to the power transformer when it detects a run away gas fault, thus possibly saving the transformer from a gas fuelled explosion.

[008] The PLC controls the automatic recycling of the relay by discharging the three volumes of gas into the gas storage vessel each time that the relay is full of gas. The rate timing function is inhibited while the relay gas discharge solenoid valve is open and discharging gas, thus ensuring accurate rate measurements as the relay continues to cycle when the solenoid is deenergised.

[009] Gas is discharged out of the Buchholz relay by the pressure head of oil above the relay in the conservator.

[010] A two way valve is mounted directly on to the top discharge connection of the Buchholz relay to allow for commissioning of the relay and as a means of isolation.

[011] Further characteristics and advantages of the present invention will become apparent from the following detailed description and the accompanied drawings, wherein: Figure 1, is a sectional view of the new Buchholz relay with a two way valve/cock, oil float valve and solenoid valve mounted on top.

Figure 2, shows a complete installation of the new Buchholz relay and associated external gas collecting and sampling components.

[012] With reference to the above figures, each part is generally designated with a reference numeral which is retained throughout this description and figures.

[013] With reference to figure 1, the lower half of the Buchholz relay designated 1, contains the components of a conventional Buchholz relay which are; low oil level float 14, oil surge detecting vane/flap 12, transformer supply voltage tripping switch 11, tripping switch operating magnets 10, gas detecting float 15 and associated alarm switch 16, drain plug 22, and tripping switch resetting knob 23. Gas discharge connection at the top of a conventional Buchholz relay is not shown for clarity.

[014] The lower float 14, detects the loss of oil in the Buchholz relay and is not influenced by the presence of gas entering or leaving the relay and as such, must be wholly mounted within the oil flow path through the relay.

[015] The vane/flap 12, which detects an oil surge through the relay from a transformer intemrnal explosion must also be wholly mounted within the oil flow path through the relay and not be influenced by gas entering or leaving the relay. The vaneflap counterweight 13, is adjustable to allow sensitivity calibration for a given installation.

[016] The oil and gas float pivoting bearings 9 are specially constructed to withstand vibrations generated by the transformer.

[017] Reed switches 11, 16,18 and 20 are operated by permanent magnets connected to their respective floats and vane/flap.

[018] The lower gas float 15, must be wholly located within the raised gas section of the relay so as to respond only to the presence of gas.

[019] With reference to figure 1, the top half of the Buchholz relay designated 2, contains the additional items which are necessary for the new design of Buchholz relay to function, in conjunction with the items contained in the lower half of the relay designated 1.

[020] The raised gas volume for floats 17 and 19 are combined with the lower gas volume of gas float 15, and divided into three equal volumes and the three float switches 15, 17 and 19, installed to operate their respective reed switches when the gas level is at the bottom of the respective volume.

[021] The gas level float switches 15, 17 and 19, are designed to automatically reset from the tripped position when the relay is purged of gas.

[022] The combined three gas volumes within the Buchholz relay is provided with a transparent graduated window 24, so as to allow accurate measurement of gas volumes during testing and commissioning.

[023] A two way valve/cock 3, is installed on the Buchholz relay discharge port for use when testing and commissioning or isolation. A plug 21, is fitted to the discharge bypass port when testing has been completed and the valve/ cock switched to discharge through ball valve 5, which is the valves normal operating position.

[024]The float valve 5 is designed to prevent the discharge of oil through the valve when the gas in the Buchholz relay is being purged. A low density solid plastic ball 6, floating on top of the oil as it rises in the valve and blocking the discharge outlet when valve is nearly full of oil.

[025] Solenoid valve 4, allows the Buchholz relay to continually cycle as long as gas is being generated by a transformer internal fault. The solenoid valve 4, is energised when the lower gas float switch 16, is actuated when the three volumes are full of gas, and remains open till the top gas float switch 20, has been reset (thus indicating that the gas is discharging) plus a short time period to allow the relay to completely empty of gas before the solenoid valve 4, de-energises.

[026] When solenoid valve is given an open instruction from the PLC timing and logic circuits, rate of gas generation timing and logic circuits are inhibited until solenoid valve 4, is de-energised. This ensures that the rate timing circuits present an accurate picture of what is actually happening within the transformer.

[027] Although not shown in figure 1 or 2, the Buchholz relay should be provided with a weather shield which should also prevents direct radiation from the sun.

[028] With reference to figure 2, the Buchholz relay 1 and 2, is installed in the connecting pipe between the transformer tank and conservator, the pipe being at an angle of 5 degrees with relation to the transformer tank top after the transformer tank has bee slightly inclined towards the pipe connection to the Buchholz relay, so as to ensure that any gas generated within the transformer will find it's way to the Buchholz relay.

[029]The discharge connection from the bottom of the gas storage vessel is piped to the top of the larger diameter vertical pipe within the conservator where the bottom of the pipe is open.

4 The function of this vertical pipe is to maintain a constant and small positive pressure in the gas storage vessel by the head of oil in the vertical pipe, as any excess pressure would dissipate through the oil.

[030] Valves 35 and 36 are for isolating the Buchholz relay.

[031] Valve 25, is for gas sampling while valve 28, is for drainage of oil vapour condensate.

[032] This invention is susceptible of numerous modifications and variations, all of which are within the scope of this same inventive concept.

[033] Where technical features mentioned in any claim are followed by a reference number, these reference numbers have been included for increasing the intelligibility of the claims and accordingly, such reference numbers do not have any limiting effect on the interpretation of each element identified by way of example by such reference numbers.

Claims (1)

14-DEC-02 SAT 13:34 JOHN 0 WILLIAMS FAX NO. 0741283719 2 CLAIMS DEFININING THE INVENTION ARE AS FOLLOWS 1- Modifications to existing, or to new Buchholz relays where the gas section of the relay is enlarged in height to accommodate additional gas volumes and additional gas level switches, and provided with a solenoid valve and a gas receiver which allows the Buchholz relay to automatically discharge it's gas contents into the gas vessel each time that the relay is full of gas, thus allowing the relay to continuously recycle while monitoring the rate that gas is being generated within the substation H.V Power Transformer. 2. Modifications to existing, or to new Buchholz relays in claim 1, requires that the height of the gas top section of the relay be increased so as to provide an additional two equal volumes of gas on top of the existing gas volume one above the other and additional gas level float switches, one for each gas volume, so as the relay fills up with gas the top float switch is actuated first, then the middle volume float switch is actuated next, then finally the bottom volume float switch is activated last thus indicating that the gas section of the relay is full of gas, and signalling the station PLC to purge the gas out of the relay allowing it to automatically recycle. 3. Modifications to existing or new Buchholz relays in claim 2, requires that each gas level float switch be connected to interconnected timer and logic circuits in the station PLC, where any time difference between timers would indicate a change to the rate that gas is being generated from a transformer internal fault this information may be programmed to disconnect the supply voltage to the transformer when a runaway fault is detected, thus preventing a possible gas fuelled explosion which could rupture the transformer tank. 4. Modifications to existing or new Buchholz Relays in claim 1, requires that the low oil level float switch and oil surge detecting vaneflap be mounted in the oil flow path through the relay, well clear of the raised gas section so as not to be actuated by the accumulation or flow of gas into the relay, or overflow of gas out of the relay should the automatic recycling function be inhibited. Modifications to existing and new Buchholz Relays in claim 2, requires that each gas volume be of the same size and dimensions and that each volume be provided with a gas level float switch mounted so as to operate when the gas reaches the bottom level of each volume, thus ensuring accurate measurements of each gas volume and the rate that the gas is being generated. John Owen Williams 25' November 2002