Buchholz Relays | Reed Switch Type Relays

Reed Switch Type Relays

Reed Switch Type Relays

Buchholz Relays

Transformer Protection Up to 1000 litres 1000 kVA

Pbwel Reed Switch Type Buchholz Relays for use in situations subject to seismic disturbances and mining activities such as blasting.

Shock and vibration acting along the tube of a conventional Mercury switch can cause the Mercury within it to move and momentarily bridge the switch electrodes, even though the switch is tilted in the open position.

This is considered to be a maloperation of the relay, in that it is caused by external influences and not by a fault within the transformer. Consequently where relays are to be used in situations as described above a more suitable alternative to the usual Mercury switch is required.

Magnet operated Reed switch type Buchholz Relays were selected specifically for this purpose and this choice is supported by the following type tests which were successfully withstood.

Reed Switch Type Relays

Reed Switch Type Relays

Ability to Withstand Power Frequency Vibrations

The device having its contact electronically monitored by means of an instrument capable of registering and recording a
contact closure of 1ms duration, shall be subjected to a sinusoidal vibration having a frequency of 100 Hz and an amplitude of
0.25 ± 0.05mm peak to peak (thus a maximum acceleration of 6g) in the plane of movement of the contact making
arrangement for a period of 1000 hours, during which there shall be no maloperation of the contacts.

Ability to withstand power frequency vibrations.

Immediately before and immediately after the vibration test, the stability of the device and its contacts under earth tremor
conditions shall be proved by subjecting the device whilst being vibrated under the conditions of the vibration test above, to further vibrations superimposed on the 100Hz vibration and supplied separately in each of the three perpendicular axes, one of which should be in the same plane as the 100Hz vibration.

These vibrations shall have a constant peak to peak amplitude of 2.5mm and shall be carried by a continuous slow sweep over
the range of 0.1 to 33Hz (at which frequency the maximum acceleration will be 5.5g) in order to search out resonances.

The appearance of these relays is the same as Mercury switch types but they are distinguished from them by the symbol /VO or /Vc/o following their type markings.

The letter V (for vibration) indicates that the relay contains Reed switches, the letter O that the contacts are normally open and the symbol c/o indicates change-over contact reeds.

Thus a type 2DE/VO is a 2” (pipe size) Double Element relay with normally open Reed relay switches. “Normally”, in this context means with the relay full of oil.


In the double element relay, collection of gas causes the oil level with the relay to fall. This is turn causes the upper element to
rotate on its pivots, bringing the magnet it carries into a position where it operates the alarm switch.

An oil surge through the relay will cause the lower element to rotate about its pivots and bring its magnet into a position so as
to operate the tripping switch.

Buchholz Relays By Pbwel

Buchholz Relays By Pbwel

Operating Characteristics of Reed Switch Type Relays

All double element relays are adjusted so that their performance lies within the limits specified in BEBS T2. Alternative values may be available upon request. These switches have Rhodium contacts located midway along the length of their glass tubes. The tubes contain an atmosphere of Nitrogen.

Connected in series with each Reed switch, and mounted within the terminal box is an inductor of approximately 30 microhenries and 0.04ohm. These inductors are intended to protect the Reed switch contacts from the effects of capacitive loads, such as those imposed by long leads or pilot cables, and must not be removed from relays in service.

Protection of Reed switch contacts against the effect of inductive loads, such as are imposed by tripping relays is achieved by
means of a diode wired across each load.

This diode must be rated with forward current at least as high as the steady load current and connected observing polarity
so as to absorb the back e.m.f. A protection unit, designated D2, fitted with suitably rated diodes for this purpose is available.

Buchholz Relays

Technical Information

Buchholz Relays Single Contact Change-over Contact
Reed Switch Type Relays Gunther Type 1526 Gunther Type 1621
Switch Capacity Max. 250 VA/W Max. 60 W/80VA
Switching Current Max. 5A Max. 2A
Switching Voltage (0-60Hz) Max. 250 V Max. 220 V
Initial Contact Resistance Max. 100 milliohms Max. 100 milliohms
Breakdown Voltage Min. 600 v r.m.s 500/400 V d.c
Resonance Frequency 900Hz
Shock Resistance Max. 50g (durations 11ms) Max. 50g (durations 11ms)
Vibration Resistance Max. 35g (50-500Hz) Max. 35g (50-500Hz)
Temperature Resistance -55ºC to +150ºC -40ºC to +50ºC

PBwel is a globally recognised designer, manufacturer and supplier of temporary portable earthing, voltage detectors, Buchholz relays and electrical safety products.

Thorne & Derrick stock and distribute an extensive range of Transformer & Switchgear Equipment for use in LV MV HV Substations including Porcelain Bushings | Bushings MV HV | DIN Bushings | Resin Bushings

Substation Clamps | Overhead Line Clamps | Cable Boxes | Transformer Connectors Joints & Terminations

Data Sheets