Double-float Buchholz gas relay DN25/50/80 for power transformers and reactors
The double-float Buchholz relay is the main EMB gas relay for oil-immersed power transformers with an oil conservator and for arc suppression reactors of any rating. It distinguishes gas accumulation, oil loss and a sudden fault with a pressure surge and issues separate alarm and trip signals. The range covers DN 25, DN 50 and DN 80 connections, weight 3.6–6.2 kg.
- Nominal bore
- DN 25, DN 50, DN 80
- Transformer rating
- DN25 — ≤5000 kVA; DN50 — 5000–10 000 kVA; DN80 — ≥10 000 kVA
- Types
- 04, 21 (thread); 05–09, 23, 24, 26 (round flange); 27, 28, 31 (plain flange); 10 (square); 62, 63 (GB); 41–43 (NF); 51–53 (BS)
- Contacts
- AC/DC 5–250 V, 0.01–6 A; AC 1500 VA / DC 1250 W
Price, availability and lead time on request. We help with analogue selection, customs clearance and delivery.
Description
The relay was invented by Max Buchholz in 1921, it has been produced in Barleben since 1951, and over 70 years EMB has sold more than 1.7 million such devices. The relay is installed in the pipe between the tank and the conservator, and the pipe and relay bores must match. The pipe rises towards the conservator at 0° to 5°, elbows are not allowed, bends have an inner radius of more than 50 mm. In transformers with a flexible diaphragm in the conservator, the same relay serves as a diaphragm rupture detector.
During partial discharges, overheating or insulation decomposition, gas rises into the relay housing and displaces the oil. The upper float drops, closes the reed contact of the alarm circuit, and the staff receive a warning. If oil leaks, the upper float operates first, then the lower one, which issues the trip command. A sudden fault with a pressure surge drives an oil flow towards the conservator, which deflects the flap held by a permanent magnet, and the relay trips the transformer in less than 0.1 s. The flow setting is selected from the range 0.65–3.00 m/s, and the relay operates on gas at 200–300 cm³.
The size depends on the rating. DN 25 is used on transformers up to 5000 kVA, DN 50 on 5000–10 000 kVA, and DN 80 on units above 10 000 kVA. There are threaded types 04 and 21, flanged types with a round flange (05–09, 23, 24, 26), with a plain flange (27, 28, 31) and with a square flange (10). For other pipe standards, versions with connection dimensions to the Chinese standard (62, 63) and to the former French (41–43) and British (51–53) standards are produced.
The housing is cast from aluminium alloy, the inspection windows have a gas volume scale, and the degree of protection is IP56. The cable is routed through M20/M25 or 1/2″ NPT glands, and the RAL colour and contact set (make, break, changeover) are specified when ordering. The contacts are rated for AC/DC 5–250 V and 0.01–6 A, with a dielectric strength of 2500 V. The relay operates at ambient temperatures of −40…+55 °C and oil temperatures of −40…+115 °C, up to +135 °C in the special version, with liquid viscosity of 1–1100 mm²/s. It withstands vibration and shock of class 4M6, pressure of 0.25 MPa, vacuum and magnetic fields of 25 mT. The relays comply with EN 50216-2 and IEC 60076-22-1.
Technical specifications
| Nominal bore | DN 25, DN 50, DN 80 |
|---|---|
| Transformer rating | DN25 — ≤5000 kVA; DN50 — 5000–10 000 kVA; DN80 — ≥10 000 kVA |
| Types | 04, 21 (thread); 05–09, 23, 24, 26 (round flange); 27, 28, 31 (plain flange); 10 (square); 62, 63 (GB); 41–43 (NF); 51–53 (BS) |
| Contacts | AC/DC 5–250 V, 0.01–6 A; AC 1500 VA / DC 1250 W |
| Gas operation | 200–300 cm³ |
| Flow operation | 0.65–3.00 m/s ±15 % |
| Flap operating time | < 0.1 s |
| Liquid temperature | −40…+115 °C |
| Vibration resistance | 2–200 Hz, 2 g; shock 25 g, 6 ms (4M6) |
| Degree of protection | IP56 |
| Weight | 3.6–6.2 kg |
| Standards | EN 50216-2, IEC 60076-22-1 |
Replacement for
transformer protection relays РЗТ-25, РЗТ-50, РЗТ-80 (double-float gas relays DN25/DN50/DN80), РГЧЗ-66, BF-80/Q
selected by purpose and main parameters, please confirm with our manager
Request a price and lead time
Double-float Buchholz gas relay DN25/50/80 for power transformers and reactors. We reply within one business day.
Or email sales@usk.ua or call 044 339-50-20.
Customs codes
| UKTZED (Ukraine) | 8536 49 00 00 |
|---|---|
| HS, 6 digits | 8536 49 |
| CN (EU) | 8536 49 00 |
| HTSUS (USA) | 8536 49 00 85 |
| China customs tariff | 8536 49 00 00 |
Codes are for reference: the final code is determined at declaration for the specific model.
Questions and answers
How is the nominal bore of the relay selected according to the transformer rating?
DN 25 is used for transformers up to 5000 kVA, DN 50 for 5000–10 000 kVA, and DN 80 for ratings above 10 000 kVA.
At what settings does the relay operate?
On gas, the relay operates when 200–300 cm³ has accumulated; the oil flow setting is selected within 0.65–3.00 m/s with a tolerance of ±15 %. The flap operates in less than 0.1 s.
Is this relay suitable as a replacement for РЗТ-80?
For transformers above 10 000 kVA, EMB produces double-float DN 80 relays with alarm and trip functions. The specific type is selected according to the application and flange dimensions, finally together with the manager.
CIS originals replaced by this item
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