PAK-exp SERIES – Certified EEX-P Group I Pressurized Substation for Tunelling

Pressurized substation is defined as “internal overpressure housing EEx-pdia I 150°C”, suitable for group I (coal mines with presence of firedamp) and classified area for zones C1ZO – C1Z1 – C1Z2 – C1ZR. PAK-exp series pressurized substations have been developed in two different design:

  • design Eex_p I (group I) for underground applications with presence of firedamp (CH4).
  • design Eex_p II (group II) for petrolchemical applications.

The difference between these two versions is the Eex_d box in which are installed instruments for purging and pressurization control.


Substation, painted both outside and inside is totally enclosed type and
water proof.

The closed-packed structure and the panels are manufactured with 2.5 mm thick steel plate conveniently reinforced.

Bolt, screws and mechanical devices are anti-corrosion treated.


The substation is painted and finished in accordance to the following procedure:

  • sunblasting of the whole surface
  • a coat of rust-preventive paint epoxy type, thickness 40 micron
  • two coats of air-dry epoxy enamel, thickness 60 micron
  • standard RAL 1013 white.

Presurization Equipment

Pressurization equipment includes:

  • EEx-d housing involving electronic system for pressurization and purging control
  • EEx-i safety devices for purging and pressurization control
  • purging pneumatic system including washout valve, pneumatic on-off valve, manually register, air rolling shutter
  • holding pressure system including pressure reducer, pressure gauge and on-off valve

Pressurization System Overview

The pressurization cycle involves firstly a purging phase at machine start up, then a permanent phase for internal overpressure holding and control.

The fluid engaged consists in dry and clean instrument air. Network pressure required is included in the range 7,5 to 3.5 bar. The biggest rate is required for the purging phase while for holding phase the rate falls till 10% or less and is engaged just for compensate eventual losses. Working overpressure is kept around 2 to 5 mbar (200-500 Pa) with alarm set on 0,6 mbar (60 Pa).

At the beginning of the purging phase, a pneumatic valve opening full rate incomes.

An EEx-i safety device for rate control pulls the time count (fixed in 30 minutes). If the rate falls under the set value, the count stops and re-starts when reset usual rate conditions.

Ending the purging phase, the holding rate is started-up by reduced pressure at 5 mbar. In the meantime purging phase stops and machine can be started.

If the internal overpressure falls under 0,6 mbar, pressure lack
alarm incomes.

If the overpressure resets within 30 min. from depressurization, it isn’t
necessary a new purging phase.

The pressurization system and the cooling system are fed by compressed dry-air, pressure 4 ± 7,5 bar. Switches working have been protected by an external door; external doors can be opened without any pressurization loss.

Rated voltageKV24
Insulation level at 50 Hz for 60 secondsKV50
Impulse insulation level (KV BIL)KV125
Rated frequencyHz50-60
Rated secondary voltageVup to 1000
Highest capacity of transformerKVA1250
Fixed P.F.C.U.kVARup to 40
Automatic P.F.C.U.kVARup to 400
Auxiliary voltageVac220
Enclosure (with cabinets closed)IP549 - IPH6
Operating ambient temperature-10 / +40ºC
Humidity (non condensing)Rh 85%
Altitude1000 m a.s.l.