Buchholz relay
Encyclopedia
In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformer
s and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric
failure inside the equipment.
Depending on the model, the relay
has multiple methods to detect a failing transformer. On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil
accumulates in the top of the relay and forces the oil level down. A float switch
in the relay is used to initiate an alarm signal. Depending on design, a second float may also serve to detect slow oil leaks.
If an arc
forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker
to isolate the apparatus before the fault causes additional damage. Buchholz relays have a test port to allow the accumulated gas to be withdrawn for testing. Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak.
Buchholz relays have been applied to large power transformers at least since the 1940s. The relay was first developed by Max Buchholz (1875–1956) in 1921.
Names like beechwood relay or beech relay are an indication of incorrectly translated German language manuals.
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
failure inside the equipment.
Depending on the model, the relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
has multiple methods to detect a failing transformer. On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil
Transformer oil
Transformer oil or insulating oil is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage...
accumulates in the top of the relay and forces the oil level down. A float switch
Float switch
A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices....
in the relay is used to initiate an alarm signal. Depending on design, a second float may also serve to detect slow oil leaks.
If an arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
to isolate the apparatus before the fault causes additional damage. Buchholz relays have a test port to allow the accumulated gas to be withdrawn for testing. Flammable gas found in the relay indicates some internal fault such as overheating or arcing, whereas air found in the relay may only indicate low oil level or a leak.
Buchholz relays have been applied to large power transformers at least since the 1940s. The relay was first developed by Max Buchholz (1875–1956) in 1921.
Names like beechwood relay or beech relay are an indication of incorrectly translated German language manuals.
External links
- Buchholz relay technical specifications from Electromotoren und Gerätebau Barleben GmbH Contains a detailed description (in English) of the Buchholz detection principles and mechanisms
- Koncar A.k.a Rade Koncar , Buchholz relays , for power and distribution transformers. http://www.koncar-nsp.hr/eng/prikaz.asp?txt_id=1732
- Buchholz relay manufacturer: P&B Weir Electrical (PBSI Group Ltd, UK) http://www.pbsigroup.com/