The pressure relief valve opens when the pressure inside the transformer’s tank increases over the set operating value and, by venting oil, reduces the pressure in the tank. All models have electrical contacts which can disconnect the transformer, in some cases faster than the Buchholz relay, in the case of major faults. An optical indicator provides visible confirmation of operation.
We supply two PRD designs manufactured by ETI and Messko.
Commonly stocked ETI models are NB 150 mm with pressures 0.4, 0.5 and 0.7 bar and NB 80 mm with pressures 0.3, 0.5 and 0.7 bar, see drawing 10.150.30
Available ETI switches are Telemecanique 1 N/O, 1 N/C (4 pole) and 2 N/O, 2 N/C (8 pole) and the switches latch on operation, see drawing 10.080.30
Directed flow versions are available, type VST080 for the 80 mm and type VQT150 for the 150 mm valves, with drawings 10.T80.41 and 10T15.40 on pages 23 and 24 of the full catalogue.
Messko offers two designs in NB 150 mm, with either a normal cover or an oil directed flow cover.
The switch contacts on either cover, either free flow or oil directed, can be electrically connected through M20 cable glands to a TERMINAL BOX screwed onto the outside of the cover or directly connected through M20 cable glands screwed into the cover to the 8 switch terminals inside the cover.
Downloads:
ETI product data:
Full 24 page ETI catalogue is available here: Series VS
ETI directed flow PRD for NB 80 and NB 150: ETI directed flow NB 80 and NB 150
Messko product data:
Download Short Order Specification Form (doc)
Messko Order Specification Sheet
Messko Technical Data for Pressure Relief Valve
Messko Technical and Ordering Data
Messko MPREC Pressure Relief Device