Flameproof transformer unit type ZTO

Flameproof transformer set type ZTO is designed for supplying mining machines and equipment from three-phase or single-phase AC mains with insulated star point of the transformer, located in hazardous areas with a risk of gas and dust explosion.

The transformer set is built based on the enclosure type dSD 05, the main compartment (Ex d) is fitted with a transformer and electrical equipment, while the connection compartment(s) (Ex d or Ex e) accommodates terminals and terminal strips. The flameproof transformer set is equipped with a single manual disconnector, a three-phase transformer and two or four independent 230/133 V AC or 220/127 V AC outgoing feeders and a single 42 V AC auxiliary outgoing feeder. Inside there is a three-phase 3.5 kVA or 5 kVA transformer with H class insulation windings.

The outgoing feeders are controlled and monitored by means of individual control and measuring modules,
that are used to protect electrical systems and three-phase electrical equipment. The relays are equipped with a complete set of protection features (current, leakage, temperature, PE continuity control), control circuits and confirmation. A LED display is used to visualise the operating states and the voltage values for the incoming feeders and the outgoing feeders.

The components used ensure operating reliability of the flameproof transformer set in the underground mining, while meeting safety requirements.


  • independently protected outgoing feeders,
  • clear operating status visualisation,
  • small overall dimensions,
  • easy access to equipment internals.
Zespół transformatorowy ognioszczelny typu ZTO

Explosion protection

(depending on the components used)
I M2 (M1) Ex d [ia,ib] I
I M2 (M1) Ex de [ia,ib] I

OBAC 07 ATEX 109

Rated values

Ingress protection rating

Ambient temperature
-20°C ≤ Ta ≤ +40°C

Rated insulation voltage
1000 (1140) V AC

Rated switching voltage
ZTO-*/1 500/1000 V AC
ZTO-*/2 660/1140 V AC
ZTO-*/3 500/660/1000/1140 V AC

Transformer rated power
ZTO-1/* 3,5 kVA
ZTO-2/* 5,0 kVA

Number of disconnector paths
1 path

Number of main outgoing feeders
2 outgoing feeders

Maximum power output
ZTO-1/* 3,5 kVA
ZTO-2/* 5,0 kVA

Rated current of outgoing feeder
ZTO-1/* 16A at 127 V AC
ZTO-1/* 8.8A at 230 V AC
ZTO-2/* 22.3A at 127 V AC
ZTO-2/* 12.6 at 230 V AC

Auxiliary outgoing feeder
1 outgoing feeder 42 V AC/200 (450) VA

(W x H x D) 845x575x435 mm
(W x H x D) 845x575x435 mm (with grommets)

190 kg


Z T O * / *

Supply voltage:
1 – 500/1000 V AC
2 – 660/1140 V AC
3 – 500/660/1000/1140 V AC

Rated power:
1 – 3,5 kVA
2 – 5 kVA