alternatives of buchholz relay and more robust schemes for transformer internal fault protection...

Alternatives of Buchholz relay and more robust schemes for

Transformer internal fault protection

Nishant kumar, Sayan Majumdar, Vikash Prakash Verma, Tanmoy Mulo, Souransu Nandi

Department of Electrical Engg., National institute of Technology, Durgapur, West Bengal, India Email: [email protected],[email protected], [email protected],

[email protected] , [email protected]

Abstract: Transformer is an expensive and one of the most important electrical machines. A Buchholz relay is

used to monitor large transformers for oil loss or insulation breakdown. The relay is located in an inclined pipe

between the transformer and its oil conservation tank (located above the transformer). The Buchholz Relay is

used as a protective device sensitive to the effects of a dielectric failure inside the equipment. However, the

Buchholz relay has a few disadvantages. The relay produces a trip signal during earthquakes and is costly as

well. Thus it is generally used only in the protection of power transformers. This paper suggests three modern

and adaptive methods which are cheaper, efficient and robust. An additional merit is the Control signal (it can

be controlled directly from the control room). The three types of methods are 1. Floating Body Mechanism

based Relay circuit (N1), 2. Piezoelectric based relay circuit (N2), and 3. ULTRASONIC SENSOR based relay

circuit (N3). These three methods are more applicable and reliable than Buchholz relay. The main advantage of

these methods is that the relays are easy to manufacture for different sizes of transformers and controlling in all

these three methods are outside the chamber containing the oil.

1. INTRODUCTION: -

The Buchholz relay was developed in 1921 by Max Buchholz, Oberrat (senior councillor) at Preußische

Elektrizitäts-AG (Prussian electricity supply company) in Kassel[6]. The Buchholz Relay is used as a protective

device sensitive to the effects of dielectric failure inside the equipment. In Buchholz relay there is a chamber

which is placed between the main transformer tank and the conservator. When the transformer is heated or when

any fault occurs, a flammable gas is produced which tries to occupy the upper space of the chamber containing

the oil. The occupation of the flammable gas in the upper space will be possible only when the level of

transformer oil goes down [11]. When a small fault occurs then the level of transformer oil slightly goes down.

When the level of oil goes down, the mercury switch connected to the alarm switch goes down and gets

connected with the conductive hinge which is just beside the mercury switch [6]. Alarm sounds on completion

of the circuit through conductive hinge and arcing is produced. In the same way when a large fault occurs, the

level of transformer oil goes down considerably due to occupancy of a large amount of flammable air in the

upper section of the chamber. Consequently, the mercury switch connected to the trip circuit goes down. Due to

this it touches the hinge which is beside that. This results in the completion and activation of the trip circuit

causing arcing and tripping of the transformer. Hence the above method protects the transformer from Buchholz

relay faults. In Buchholz relay, the upper part of chamber comprises one test cock which is used to test the

quality of air produced by heating of the transformer. This helps to measure the quantity of methane, ethane and

many several components by which we analyse the condition of the transformer. One drain valve is also present

in lower part of chamber to take out the transformer oil in case of fault and emergency.

However, in Buchholz relay the disadvantage is that generally it produces a trip signal in

minor earthquakes [7] and it is costly. Thus Buchholz relay is only used in power transformer protection.

Presently automated systems are being used to control from a single place (Control room). We propose three

methods which are cheaper than Buchholz relay. The construction of Buchholz relay is more complicated than

our methods. These methods are easy to repair, more robust and efficient. The controlling part like alarm circuit

and trip circuit is always outside of the chamber which is easy to handle. Hence manufacturing for different

sizes of transformer becomes simpler

The first method is the Floating body Mechanism based Relay circuit (N1), in which there is a chamber

between the transformer main tank and conservator. The upper part of the chamber consists of a fibre made disk

floating on oil. The disk can slide up and down according to the pressure. It is connected to a vertical control rod

which in turn is connected to a control circuit. According to the displacement of control rod, the situation of

alarm or trip can be decided.

The second method is the Piezoelectric based relay circuit (N2

in the upper part of chamber. In piezoelectric

voltage or potential applied across it [10]

force applied by the flammable gas and in

flammable gas. According to the amount of voltage

The third method is the

chamber consists of an ultrasonic sensor which

measured height is divided into three part

conditions of the transformer. According to operating condition, the

2. FLOATING BODY MECHANISM BASED RELAY CIRCUIT

In this scheme, we introduce a less dense

floating body a metallic control rod is pivoted, which provide

the transformer due to any fault creates pressure inside the relay chamber which pushes the disk.

of the floating body will be utilised

information about the different situation

Fig.1 Floating body Mechanism based Relay circuit (N1)

2.1 Construction and Operation:

In this relay, one floating disk (Fibre

down with the support of an elastic air ti

placed between transformer main tank and the conservator

collecting the gas sample. A drain valve is present at the bottom of the chamber.

vertical control rod which is connected with a control circuit

lengths are dN, dA, and dT , two diode (d1 and d2) and one voltage source(V).

into three zones, namely the Normal zone

no fault occurs, the connecting point of

relay from taking any action; transformer operation smoothly goes

of gas is produced in the transformer [11]. This gas

inside the relay. Consequently, a force

(dA). The circuit gets completed (V - d

condition ,huge amount of gas is produced

Piezoelectric based relay circuit (N2), where a piezoelectric substance is used

piezoelectric substances, the force produced is directly proportional to the

[10]. When a small fault occurs, low voltage is produced due to a small

flammable gas and in large fault high voltage is produced due to a large force applied by

ccording to the amount of voltage, the control circuit will perform the operation.

the ULTRASONIC SENSOR based relay circuit (N3). The

consists of an ultrasonic sensor which measures the level of transformer oil in relay chamber

measured height is divided into three parts which decides the operating condition, i.e. normal, alarm and trip

ing to operating condition, the control circuit performs the operation

FLOATING BODY MECHANISM BASED RELAY CIRCUIT (N1)

introduce a less dense material (Fibre) which can float above oil easily

body a metallic control rod is pivoted, which provides input in control circuit. The gas produced inside

the transformer due to any fault creates pressure inside the relay chamber which pushes the disk.

over here. The different position of the floating body

situations inside.

Floating body Mechanism based Relay circuit (N1)

Construction and Operation:

disk) is used above the oil layer [8]. This disk can move freely up and

air tight seal so that the gas does not leak outside the chamber

placed between transformer main tank and the conservator. One test cock is also connected with

A drain valve is present at the bottom of the chamber. Fibre disk is conne

vertical control rod which is connected with a control circuit. Control circuit consists of three plate

, two diode (d1 and d2) and one voltage source(V). The whole operation is divided

zone (dN), the Alarm zone (dA) and the Tripping zone (dT). Initially when

the connecting point of the control rod contact remains within dN region which prevents the

transformer operation smoothly goes on. In case of a fault condition

[11]. This gas comes into the relay chamber and increases the

acts on the fibre disk and the connecting point reaches the

dA – A – V) via alarm (A) causing a siren. In case of any

produced which develops a higher pressure on the fibre

piezoelectric substance is used

is directly proportional to the

d due to a small

force applied by the

control circuit will perform the operation.

The upper part of

the level of transformer oil in relay chamber. The

, alarm and trip

the operation.

[8]. Above this

gas produced inside

This movement

floating body will give us

can move freely up and

outside the chamber. Chamber is

One test cock is also connected with the disk for

is connected with a

three plates whose

hole operation is divided

). Initially when

which prevents the

fault condition, some amount

and increases the pressure

es the Alarm zone

case of any severe fault

ibre disk causing

connecting point of control rod to move up to the

feed as well as a trip circuit feed. This causes

from oil leakage one leakage protection

any fault occurs due to the leakage of oil,

and touches the leakage protection metallic plate “L”

causing both the trip circuit and the alarm circuit

samples. Another drain valve similar to

2.2 Generalise Mathematical Calculation

Let us assume (since according to transformer and manufacture this value

Mass of floating body with control rod

Range of Pressure for Normal condition

Range of Pressure for Alarm condition

Range of Pressure for Tripping condition

dN ∝∝∝∝ � ��

� ; dA ∝∝∝∝ �

��

Net Applied force on the disk (F) = P*πr

From this calculation, for different

chamber, we can set different length of region (

3. PIEZOELECTRIC BASED RELAY CIRCUIT

Piezoelectricity is the charge that accumulates in certain solid materials in response to applied mechanical stress.

The word piezoelectricity means electricity resulting from pressure

which means to squeeze or press, and electric

charge. The piezoelectric effect is understood as the linear electromechanical interaction between the

mechanical and the electrical state in crystalline materials with no

piezoelectricity is utilised for measuring the voltage which is directly proportional to the force which is

developed in the piezoelectric substance due

upon the amount of flammable gas developed in the upper section of the chamber

fault developed in the transformer.

move up to the dT region. Both the diodes d1 and d2 conduct an a

This causes all the operation related to the transformer to stop.

leakage protection metallic plate “L” is placed above the chamber as shown in figure

of oil, the connecting point of the fibre disk comes down from

protection metallic plate “L”. This means that the floating body hangs

alarm circuit to conduct. Here a test cock is also provided

rain valve similar to the Buchholz Relay is present below the chamber.

Mathematical Calculation

(since according to transformer and manufacture this value will vary)

with control rod =MF, and radius of the disk = r,

Range of Pressure for Normal condition ≡ (0 ↔ PN),

Range of Pressure for Alarm condition ≡ (PN ↔ PA),

Tripping condition≡ (PA ↔ PT),

��

; dT ∝∝∝∝ � ��

��

�

Net Applied force on the disk (F) = P*πr2

- MF*g Where P is the applied pressure.

for different transformer ratings, according to generated pressure and size of relay

different length of region ( dN, dA, dT ).

PIEZOELECTRIC BASED RELAY CIRCUIT (N2)


means electricity resulting from pressure [9]. It is derived from the Greek

electric or electron, which stands for amber, an ancient source of electric

understood as the linear electromechanical interaction between the

mechanical and the electrical state in crystalline materials with no inversion symmetry. The above property of


developed in the piezoelectric substance due to the pressure of flammable gas [10]. The amount of force

developed in the upper section of the chamber [11], which

Fig.2 Piezoelectric based relay circuit (N2)

conduct an alarm signal

stop. For protection

placed above the chamber as shown in figure.1. If

from dN position

s on the L plate

is also provided to collect gas

P is the applied pressure.

pressure and size of relay


Greek word piezo,

ient source of electric

understood as the linear electromechanical interaction between the

he above property of


amount of force depend

depends on the

3.1 Construction

Here, by the above figure 2, it can be seen that there is a chamber present between transformer tank and

conservator just like the Buchholz relay. In the entry section of the chamber from the transformer main tank

there is a flap valve which is used to restrict the fast entry of the flammable gases. In the lower part of the

chamber there is a drain valve through which transformer oil can be ejected and in the upper part, a piezoelectric

plate is present, connected to the amplifier. In the piezoelectric plate there is a test cock to test the gas sample

for the percentage of methane, ethane and other components in the flammable gas. The amplifier is connected to

the coil which is energised according to the voltage produced by the amplifier. When the coil is energised, the

control rod comes down due to the magnetic property of the coil. The amount of voltage determines the distance

by which it comes down. When a high voltage is provided, both the trip circuit and the alarm circuit get

completed due to large downward motion of the control rod. When the voltage is low, due to small downward

motion of the control rod, only the alarm circuit gets completed.

3.2 Working Principle

Piezoelectric sensors have proven to be versatile tools for the measurement of various processes. Here, we use

piezoelectric plate to protect the transformer from faults which are either small or heavy. The whole operation is

divided in three zones: Normal zone (dN), Alarm zone (dA) and Tripping zone (dT). In normal condition, when

no fault occurs, the force acting on the piezoelectric plate is zero. Thus voltage is not generated and the coil is

not energized. The connecting point of the control rod remains within the dN region causing no action to be

taken by the relay; the operation goes on smoothly. When a small fault occurs, low amount of flammable gas

[11] comes in the upper section of the chamber and exerts less pressure on the piezoelectric plate. This pressure

generates a low voltage [9]. Through the amplifier, the voltage is amplified and given across the coil, which

generates a small electromagnetic force causing the control rod to come down in the alarm zone on the dA plate.

The alarm circuit gets completed and produces a siren. Similarly when large faults occur, a higher voltage is

generated. Through the amplifier the voltage is transmitted to the coil which energises it by a larger amount. The

control rod comes down to the trip zone, on the dT plate, completing both the trip circuit and the alarm circuit.

Trip circuit stops the operation and the alarm circuit produce a siren to inform the situation. Thus the

Piezoelectric based relay circuit protects the transformer from internal faults.


Let us assume (since according to transformer and manufacture this value will vary)

Radius of the piezoelectric disk = r,

Range of Voltage for Normal condition ≡ (0 ↔ VN),

Range of Voltage for Alarm condition ≡ (VN ↔ VA),

Range of Voltage for Tripping condition≡ (VA ↔ VT),

dN ∝∝∝∝ � �v��

� ; dA ∝∝∝∝ � �v

��

� ; dT ∝∝∝∝ � �v

��

��

Net Applied force on the disk (F) = P*πr2 Where P is the applied pressure.

From this calculation for different transformer rating, according to generated voltage and size of relay

chamber, we can set different length of region ( dN, dA, dT ).

4. ULTRASONIC SENSOR BASED RELAY CIRCUIT (N3)

In this particular scheme ultrasonic sensor has been used to measure the depth of the oil in the relay chamber.

For this purpose a transmitter and a receiver of Ultrasonic sensor is placed on the upper layer of the relay

chamber. Beside the ultrasonic sensor, a test cock is present to collect the test samples, which is used for the

analysis of faults. The output of the sensor goes through an amplifier to the coil. This voltage energizes the coil.

The output voltage depends on the measured depth of the oil. A metal control rod is present inside the turns. The

scheme also consist a trip circuit and an alarm circuit. This gets excited according to the output signal from the

sensor. There are also two valves: flap valve and drain valve.

Fig.3 Ultrasonic Sensor based relay circuit (N3)

4.1 Operation of the scheme

A short ultrasonic pulse is transmitted at a particular time say zero. This is reflected by the oil. The sensor

receives the signal and converts the signal into an electrical

echo is faded away. The recommended

sent to the signal pin, the Ultrasonic module will output eight 40 kHz ultrasonic signal and d

The measured distance is proportional to the echo pulse width and can be calculated by the formula [2].

(Pulse width, µs)/58=distance (cm)

Fig.4 signals of an ultrasonic sensor

The relationship [3] between the voltage

This means the voltage output goes up linearly

a coil which becomes energized and pull

In normal conditions no gas comes inside the chamber

gas is produced according to the faults [11]

to go down. The sensor senses the height

a coil. The force developed pulls the control rod down

slightly resulting in the lowering of the

Now when the severity of the fault increases, the amount of gas

voltage. This pulls the control rod down

and generates a siren. In the case of oil leakage

This in turn generates a trip signal and protect

based relay circuit (N3) protects the transformer from any internal fault


Let us assume (since according to transformer and manufacture this value will vary)

Range of Height for Normal condition

Ultrasonic Sensor based relay circuit (N3)


receives the signal and converts the signal into an electrical signal. The next pulse can be transmitted when the

cycle period should be no less than 50ms. If a 10µs width trigger pulse is

sent to the signal pin, the Ultrasonic module will output eight 40 kHz ultrasonic signal and detect the echo back.


Fig.4 signals of an ultrasonic sensor

between the voltage (V) and the distance (H) is V=.115H-2.381

linearly as the oil level goes down. The voltage is amplified and fed into

a coil which becomes energized and pulls the metal rod down by an electromagnetic force (F).

inside the chamber keeping the sensor output zero. When any fault

[11]. This gas will take the space inside the chamber causing

height and accordingly produces a voltage which gets amplified

control rod down. If the fault is nominal the control rod is pull

ulting in the lowering of the connecting point to the alarm zone on dA plate and generating

Now when the severity of the fault increases, the amount of gas produced also increases, generating

down to the trip zone on the dT plate. It trips the operation of the transformer

n the case of oil leakages, the oil level will goes down and the measured height increase

trip signal and protects the transformer from danger. In this way, Ultrasonic Sensor

the transformer from any internal faults.

Mathematical Calculation

(since according to transformer and manufacture this value will vary)

Range of Height for Normal condition ≡ (0 ↔ H1),


The next pulse can be transmitted when the

cycle period should be no less than 50ms. If a 10µs width trigger pulse is

etect the echo back.


he voltage is amplified and fed into

F=K*I2

any fault occurs,

causing the oil level

amplified and is fed to

pulled down

generating a siren.

ing a higher

of the transformer

measured height increases.

Ultrasonic Sensor

Range of Height for Alarm condition ≡ (H1 ↔ H2),

Range of Height for Tripping condition≡ (> H2 ),

dN ∝∝∝∝ � �h�1

� ; dA ∝∝∝∝ � �h

�2

�1 ; dT ∝∝∝∝ � �h

�

�2 ;Where H is the height of the chamber

From this calculation for different transformer rating, according to generated height and size of relay

chamber, we can set different length of region ( dN, dA, dT ).

5. ADVANTAGES

� Generally if there is any minor earthquake, the Buchholz relay gives a false alarm and trips the

transformer [7], but by using this scheme this problem can be minimized.

� Here, depending on the situation, different voltages are produced. These voltages can be applied to

modern automation systems for automatic control or control via control room.

� The controlling part of this relay is entirely outside the chamber, so its maintenance and repair is easy.

� Construction is not complex making it easier to construct different sizes of transformers.

� It is more robust, reliable, cheaper and efficient.

6. CONCLUSION

So, it can be concluded that the three proposed schemes are innovative, be it the scheme using FLOATING

BODY MECHANISM BASED RELAY CIRCUIT (N1), PIEZOELECTRIC BASED RELAY CIRCUIT

(N2) or the scheme using ULTRASONIC SENSOR BASED RELAY CIRCUIT (N3). All of them are

having advantages in different regards. For example, the floating body mechanism can be used in

distribution transformers due to its robust construction and low price, where the Buchholz relay is generally

not used due to its high cost. The other two schemes are a good replacement for Buchholz relay in power

transformers. Here, we can control, take required action from the control room or use modern automation

systems as these relays have the ability to send the information in analog signals. Hence, some

disadvantages of using Buchholz relay have been eliminated by using these proposed protection schemes.

7. References [1] Parallax “PING))) Ultrasonic Distance Sensor” [ONLINE] http://www.parallax.com /tabid /768 / ProductID

/92 /Default.aspx

[2] Sunrom Technologies “YOUR SOURCE FOR EMBEDDED SYSTEMS” www.sunrom.com

[3] claymore.engineer “PRE-LAB: - CLAYMORE” [ONLINE] , claymore. engineer. gvsu. edu/

~grimshaj/lab7.doc

[4] IEEE Standard association “C57.104-1991 - IEEE GUIDE FOR THE INTERPRETATION OF GASES

GENERATED IN OIL-IMMERSED TRANSFORMERS” IEEE Standard

[5] Sitemason “TRANSFORMER OIL VOLUME CONVERSION TABLE”, www.sitemason.com/files/.../

transformer%20oil%20volumes.pdf

[6] Elektromotoren und Gerätebau Barleben GmbH “TRANSFORMER PROTECTION RELAYS”EMB

[7] H. C. Hitchcock,” BUCHHOLZ RELAYS, SUPPLY WAS RESTORED IN A MATTER OF MINUTES” THE

1968 INANGAHUA EARTHQUAKE AND ELECTRICTY SERVICES

[8] Ben Coxworth “SUPER-BUOYANT MATERIAL INSPIRED BY WATER STRIDERS” American chemical

society.

[9] Chih-yi Lin “DESIGN AND ANALYSIS OF PIEZOELECTRIC TRANSFORMER CONVERTERS” July

15,1997 Blacksburg, Virginia.

[10] PZT Application Manual “THE PIEZOELECTRIC EFFECT” www.aurelienr.com/

electronique/piezo/piezo.pdf.

[11] E. Takahashi K. Tanaka K. Toda M. Ikeda T. Teranishi M. Inaba T. Yanari, “DEVELOPMENT OF LARGE-

CAPACITY GAS-INSULATED TRANSFORMER” IEEE Transactions on Power Delivery, Vol. 11, No. 2,

April 1996.

[12] M. Duval, J. Aubin, Y. Giguere, G. Pare and Y. Langhame, “OIL ADDITIVES FOR THE EVALUATION OF

HOT SPOT TEMPERATURE IN POWER TRANSFORMER DURING OVERLOADING ” IEEE Transactions

on Electrical Insulation Vol. EI-17 No.5, October 1982

alternatives of buchholz relay and more robust schemes for transformer internal fault protection...

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