WO2003098763A1

WO2003098763A1 - Modified buchholz relay for continuous monitoring of gas generated by transformer internal faults

Info

Publication number: WO2003098763A1
Application number: PCT/AU2003/000110
Authority: WO
Inventors: John Owen Williams
Original assignee: John Owen Williams
Priority date: 2002-05-15
Filing date: 2003-02-05
Publication date: 2003-11-27
Also published as: AU2002100385A4; AU2002100385B4

Abstract

The modified Buchholz relay (2) overcomes the problem with existing relays which alarm once when full of gas and cannot provide further information unless the gas is discharged out of the relay manually. The modified Buchholz relay allows the continuous monitoring of the rate of gas being generated in a transformer from an internal fault. The top section of the existing relay (1) is enlarged in height to accommodate additional gas volumes and fitted with additional gas level float switches (15, 17, 19). In order for the relay to continuously monitor a gas fault, the top section of the relay is automatically emptied into a gas receiver vessel (31) each time it is full of gas. This is achieved by automatically energising a solenoid valve (4) mounted on top of the relay thus discharging all the gas out of the relay. Oil is prevented from discharging into the vessel when all the gas has been discharged by a miniature float valve (5) located on the inlet side of the solenoid valve (4).

Description

MODIFIED BUCHHOLZ RELAY FOR CONTINUOUS MONITORING OF GAS GENERATED BY TRANSFORMER INTERNAL FAULTS.

DISCRETION

[000] This new design 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 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 design of Buchholz relay will also detect when air is being drawn into the oil circuit of the transformer through the oil circulating pump shaft gland 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 (could also be one volume) 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 gas outlet of the relay is connected by pipe and valves to a gas vessel for storage of gas samples, excess gas pressure in the storage vessel is automatically relieved by an open ended pipe connection through the top of the conservator and ending up below the conservator oil level.

[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 level 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 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 the station PLC, where the timing of each switch actuation is compared with each other to provide a rate that the gas is being generated.

The PLC is used to monitor and record the rate that the gas is being generated The PLC could also be programmed to automatically disconnect the supply voltage to the 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 de- energised.

[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, is 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 internal 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 vane/flap 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

10, 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 gas 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, 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 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 4 is given an open instruction from the PLC timing and logic circuits, 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 in tropical climates.

[028] With reference to figure 2, Buchholz relay 1 , 2 is installed in the connecting pipe between the transformer tank and conservator, the pipe is inclined at an angle of 5 degrees with relation to the transformer tank top. The transformer tank is also slightly tilted so that the pipe connection to the Buchholz relay is at the highest point, so as to ensure that any gas generated within the transformer will quickly find it's way to the Buchholz relay connecting pipe. [029]The discharge connection from the bottom of the gas storage vessel is piped to the top of the vertical pipe within the conservator where the bottom of the pipe which is below the conservator oil level is open. 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. The small gas pressure assists in the collection of gas samples.

[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

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 fitted with additional gas level switches which are connected to the station PLC, and provided with a solenoid valve mounted on top of the relay 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 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 (could also be one) equal gas volume/s on top of the existing gas volume, one above the other.

3. Modifications to existing or to new Buchholz relays in claim 2, requires that each gas volume be of equal dimensions and height, and that each volume be provided with a float switch which is mounted so as to operate as the oil level (thus the gas volume increasing) falls below the bottom of a given gas volume.

4. Modifications to existing or to new Buchholz relays in claim 3, as the relay fills up with gas, the top float switch operates first, then the middle float switch operates and finally the bottom float switch which signals that the gas section of the relay is now full of gas.

5. Modifications to existing or to new Buchholz relays in claim 4, the station PLC sends a signal to the gas purging solenoid valve to open and the gas discharges into the gas vessel, and as the top volume float switch reactivates indicating that the oil level is increasing thus gas is discharging, it sets a timer which allows all the gas to discharge before issuing a close signal to the solenoid valve, thus allowing the relay to continuously and automatically recycle.

6. Modifications to existing and to new Buchholz relays in claim 5, a ball float valve mounted between the relay and solenoid valve, allows all the gas to discharge out of the relay, but stops any oil from discharging as the floating ball closes off the outlet port on rising oil level, thus ensuring that all the gas has been discharged out of the relay.

7. Modifications to existing and to new Buchholz relays in claim 5, the gas float switches automatically reset on rising oil level.

8. Modifications to existing and to new Buchholz relays in claim 5, gas pressure in the gas vessel is maintained at a low positive pressure determined by the height of oil in the vertical pipe entering the top of the conservator, any excess pressure in the gas vessel bleeds out through the end of the pipe and out through the oil, thus maintaining a positive gas pressure for sample collection

9. Modifications to existing and to new Buchholz relays in claim 1 , requires that the low oil level float element and oil surge element be mounted directly in the oil flow path through the relay and not be influenced in any way by flow or accumulation of gas, and must be manually reset once actuated.

10. Modifications to existing and to new Buchholz relays in claim 1 and 4, the station PLC timer and logic circuits calculates the time difference between the actuation of each gas level float switch and provides a programmed output which could be a time or percentage difference, indicating the progress of a transformer gas producing fault, the PLC could be further programmed to disconnect the supply voltage to the transformer if a runaway gas fault is detected, thus possibly preventing a gas fuelled explosion.

11. Modifications to existing and to new Buchholz relays in claim 1 , a two way valve or cock is installed on the gas outlet at the top of the relay to allow isolation and for commissioning, the bypass outlet is plugged when not in use.