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Buchholz Relay in transformer | Buchholz Relay operation and principle
What is Buchholz Relay ?
Construction of Buchholz RelayBuchholz relay in transformer is an oil container housed the connecting pipe from main tank to conservator tank. It has mainly two elements. The upper element consists of a float. The float is attached to a hinge in such a way that it can move up and down depending upon the oil level in the Buchholz relay Container. One mercury switch is fixed on the float. The alignment of mercury switch hence depends upon the position of the float. The lower element consists of a baffle plate and mercury switch. This plate is fitted on a hinge just in front of the inlet (main tank side) of Buchholz relay in transformer in such a way that when oil enters in the relay from that inlet in high pressure the alignment of the baffle plate along with the mercury switch attached to it, will change. In addition to these main elements a Buchholz relay has gas release pockets on top. The electrical leads from both mercury switches are taken out through a molded terminal block.
Buchholz Relay PrincipleThe Buchholz relay working principle of is very simple. Buchholz relay function is based on very simple mechanical phenomenon. It is mechanically actuated. Whenever there will be a minor internal fault in the transformer such as an insulation faults between turns, break down of core of transformer, core heating, the transformer insulating oil will be decomposed in different hydrocarbon gases, CO2 and CO. The gases produced due to decomposition of transformer insulating oil will accumulate in the upper part the Buchholz container which causes fall of oil level in it.
Fall of oil level means lowering the position of float and thereby tilting the mercury switch. The contacts of this mercury switch are closed and an alarm circuit energized. Sometime due to oil leakage on the main tank air bubbles may be accumulated in the upper part the Buchholz container which may also cause fall of oil level in it and alarm circuit will be energized. By collecting the accumulated gases from the gas release pockets on the top of the relay and by analyzing them one can predict the type of fault in the transformer.
More severe types of faults, such as short circuit between phases or to earth and faults in the tap changing equipment, are accompanied by a surge of oil which strikes the baffle plate and causes the mercury switch of the lower element to close. This switch energized the trip circuit of the circuit breakers associated with the transformer and immediately isolate the faulty transformer from the rest of the electrical power system by inter tripping the circuit breakers associated with both LV and HV sides of the transformer. This is how Buchholz relay functions.
Buchholz Relay Operation Certain PrecautionThe Buchholz relay operation may be actuated without any fault in the transformer. For instance, when oil is added to a transformer, air may get in together with oil, accumulated under the relay cover and thus cause a false Buchholz relay operation.
That is why mechanical lock is provided in that relay so that one can lock the movement of mercury switches when oil is topping up in the transformer. This mechanical locking also helps to prevent unnecessary movement of breakable glass bulb of mercury switches during transportation of the Buchholz relays.
The lower float may also falsely operate if the oil velocity in the connection pipe through, not due to internal fault, is sufficient to trip over the float. This can occurs in the event of external short circuit when over currents flowing through the winding cause overheated the copper and the oil and cause the oil to expand.
Closely Related Articles Restricted Earth Fault Protection of Transformer | REF ProtectionWhat is Earthing Transformer or Grounding TransformerDifferential Protection of Transformer | Differential RelaysOver Fluxing in TransformerMore Related Articles What is transformer? Definition and Working Principle of TransformerEMF Equation of Transformer | Turns Voltage Transformation Ratio of TransformerIdeal TransformerTheory of Transformer on Load and No Load OperationResistance and Leakage Reactance or Impedance of TransformerEquivalent Circuit of Transformer referred to Primary and SecondaryHysteresis Eddy Current Iron or Core Losses and Copper Loss in TransformerVoltage Regulation of TransformerSingle Three Phase Transformer vs bank of three Single Phase TransformersParallel operation of TransformersMagnetizing Inrush Current in Power TransformerInstrument TransformersCurrent Transformer CT class Ratio Error Phase Angle Error in Current TransformerVoltage Transformer or Potential Transformer TheoryKnee Point Voltage of Current Transformer PS ClassAccuracy Limit Factor and Instrument Security Factor of Current TransformerIsolation TransformerTransformer Insulating Oil and Types of Transformer OilDGA or Dissolved Gas Analysis of Transformer Oil | Furfural or Furfuraldehyde AnalysisTransformer Accessories | Breather and Conservator Tank | RadiatorSilica Gel Breather of TransformerConservator Tank of TransformerRadiator of Transformer | Function of RadiatorMagnetic Oil Gauge or MOG | Magnetic Oil Level Indicator of TransformerOil Winding and Remote Temperature Indicator of TransformerTransformer Cooling System and MethodsOn Load and No Load Tap Changer of Transformer | OLTC and NLTCTertiary Winding of Transformer | Three Winding TransformerCore of Transformer and Design of Transformer CoreTransformer Testing | Type Test and Routine Test of TransformerTransformer Winding Resistance MeasurementVoltage and Turn Ratio Test of TransformerVector Group Test of Power TransformerOpen and Short Circuit Test on TransformerInsulation Dielectric Test of TransformerTransformer Oil and Winding Temperature Rise TestImpulse Test of TransformerMaintenance of TransformerSweep Frequency Response Analysis Test | SFRA TestInstallation of Power TransformerCommissioning of Power TransformerElectrical Power Transformer | Definition and Types of TransformerStep Up TransformerStep Down TransformerWhat is Auto Transformer ?High Voltage TransformerDistribution Transformer | All Day Efficiency of Distribution TransformerDry Type TransformerAir Core TransformerDesign of Inductor in Switched Mode Power Supply SystemsDesign of High Frequency Pulse TransformerSingle Phase TransformerToroidal TransformerNew Articles Voltage in ParallelVoltage in SeriesVoltage Regulator 7805How to Use a Digital Multimeter?Vector Impedance MeterVoltage Follower