¿Qué es un relé Buchholz en un transformador?

Fecha de publicación:23 de octubre de 2026, 12:14:12

  • A Buchholz relay is a gas- and oil-operated protection device installed in the pipe between the main tank and conservator of suitable oil-immersed transformers.
  • Slowly developing internal faults may generate gas that accumulates in the relay and initiates an alarm.
  • Severe internal faults can create rapid oil movement toward the conservator and operate the trip mechanism.
  • Buchholz protection is normally associated with conservator-type oil-immersed transformers, and alarm and trip stages do not by themselves identify the exact fault source.
  • DGA, protection records and inspection should be used to investigate the cause of any relay operation.

Índice

1. What Is a Buchholz Relay?

A Buchholz relay, also called a gas relay on a transformer, is a gas-operated and oil-surge-operated protection device. It sits in the pipe between the transformer main tank and the conservator. Gas or oil moving from the tank toward the conservator passes through the relay, which can operate contacts for alarm or trip.

Not every oil-immersed transformer uses this device. Sealed and hermetically sealed transformers, and units without a conservator, may use other protection arrangements. A Buchholz relay does not measure oil pressure or dissolved gas concentration.

Característica Relé de Buchholz
Tipo de transformador Oil-immersed transformers with a conservator arrangement
Ubicación típica Pipe between main tank and conservator
Primary Inputs Gas accumulation and oil surge; some designs also respond to low oil level
Función de alarma Contact operated by gas accumulation, depending on relay design
Trip Function Contact operated by oil surge, depending on relay design

2. How Does Buchholz Protection Work?

2.1 Gas Accumulation

Slowly developing internal abnormalities can decompose insulation or oil and generate gas. Because the pipework rises toward the conservator, gas can collect in the relay chamber. Accumulated gas changes the relay's internal mechanism and may operate an alarm contact, depending on relay design.

Gas in the relay does not always mean a severe transformer fault. It requires investigation, since the gas may come from several sources.

2.2 Rapid Oil Surge

Severe internal faults can cause rapid gas generation and sudden oil movement toward the conservator. This oil surge can operate the trip mechanism of the relay. Response depends on fault severity and relay design, and no general operating value applies to every unit.

3. Buchholz Alarm vs Trip

Alarm and trip stages respond to different physical effects. A Buchholz relay alarm is often associated with gas collection, while a trip is often associated with oil surge. Neither stage maps cleanly to minor or major faults, so actual behavior depends on design and configuration.

Condición Typical Relay Response What It May Suggest Recommended Follow-Up
Slow gas accumulation Alarma May indicate a developing internal abnormality Investigate gas, DGA and operating history
Rapid oil surge Viaje May indicate a potentially severe internal event Follow protection and diagnostic procedures

4. What Faults Can Operate a Buchholz Relay?

Several internal conditions can generate gas or move oil:

  • Deterioro del aislamiento
  • Localized overheating
  • Internal arcing
  • Winding or connection faults
  • Core-related overheating
  • Oil decomposition
  • Internal gas formation
  • Rapid oil displacement caused by a severe internal event

Relay operation indicates an abnormal internal condition, while root-cause identification requires additional evidence. That evidence includes DGA, temperature data, protection relay records and inspection.

5. Buchholz Relay vs Pressure Relief Device

Buchholz relays respond primarily to gas accumulation and/or oil surge in suitable conservator-type transformers. A pressure relief device (PRD) responds to excessive internal tank pressure, and a pressure sensor measures pressure. These functions are different and complement each other. Neither the relay nor the PRD replaces the other.

Dispositivo Responde a Ubicación típica Función principal Salida típica
Relé de Buchholz Gas accumulation and/or oil surge Pipe between main tank and conservator Gas / oil movement protection Alarm and trip contacts, depending on design
Pressure Relief Device Excessive internal tank pressure Tanque del transformador, según el diseño Pressure relief Mechanical indication or alarm contact, depending on design
Sensor de presión Measured pressure Tanque de transformador o accesorio del sistema de aceite Pressure measurement and monitoring Signal output, depending on model

6. Buchholz Relay vs DGA

A Buchholz relay is an event-driven protection device. It responds when gas accumulation or oil movement reaches the relay mechanism. DGA is a condition-monitoring and diagnostic method that measures gases dissolved in transformer oil.

Online DGA can trend dissolved gases before or between protection events. Gas patterns and rates of change add context that a relay contact does not provide. DGA does not replace Buchholz protection, and the relay does not replace DGA.

Método Primary Purpose Tipo de datos Continuous Trend Protection Action
Relé de Buchholz Detect gas accumulation or oil surge Contact status (alarm / trip) No, event-driven Yes, through alarm or trip circuits
DGA en línea Track dissolved gases in oil Gas concentrations and trends Sí Monitoring and alarm information, not a replacement for protection relays

INNOFZ describes análisis de gases disueltos monitoring for oil-immersed transformers. Its sistema de monitoreo de DGA en línea page lists seven fault gases measured by gas chromatography, an adjustable sampling cycle with a minimum of 2 hours or less, and MODBUS and IEC 61850 output. It also lists live installation on energized transformers.

Buchholz relay information can be evaluated together with DGA, oil temperature, winding temperature, oil pressure, oil level, protection relay records and alarm history. Protection event plus condition data plus trend history supports better fault assessment. The monitoreo de transformadores sumergidos en aceite application and the wider monitoreo de transformadores solution describe how these parameters can be combined.

7. What to Check After Relay Operation

Resetting a relay does not resolve the root cause. A review after alarm or trip typically includes:

  • Determine whether the alarm or trip element operated
  • Review transformer protection records and other protection operations
  • Inspect visible transformer condition, including leakage where relevant
  • Check oil level and pressure-related indications
  • Review oil temperature and winding temperature
  • Obtain and assess transformer oil and gas information
  • Review DGA results
  • Compare recent loading history

Inspection, testing and return-to-service decisions should follow transformer manufacturer procedures and site safety rules. Relay operation then becomes one input to alarma del transformador assessment and wider transformer diagnostics.

8. Buchholz Relay FAQ

8.1 What is the purpose of a Buchholz relay?

A Buchholz relay protects suitable oil-immersed transformers by responding to internal gas accumulation and oil surge. It can give an alarm for gas collection and a trip signal for rapid oil movement. It indicates an abnormal internal condition but does not identify the exact fault.

8.2 What is the difference between Buchholz alarm and trip?

The alarm element is typically associated with gas accumulation, and the trip element with rapid oil surge. Actual behavior depends on relay design and configuration. Neither stage should be read as a simple minor or major fault label, and both require investigation.

8.3 Which transformers use a Buchholz relay?

Buchholz relays are normally used on conservator-type oil-immersed transformers, where the relay sits between the main tank and conservator. Sealed or hermetically sealed units and transformers without a conservator may use different protection arrangements, so not every oil-immersed transformer has one.

8.4 What should be checked after a Buchholz relay operates?

Check whether alarm or trip operated, then review protection records, oil level, oil and winding temperature, visible leakage, pressure indications, loading history and DGA results. Do not treat relay reset as root-cause resolution. Follow manufacturer procedures and site safety rules before any return-to-service decision.