Search

Premium Membership ♕

Limited Time Offer: Save 15% on PRO Plan with discount code: LRN15 and study specialized LV/MV/HV technical articles and studies.

Home / Technical Articles / TRIHAL – Dry type cast resin HV/LV transformer

Trihal

Trihal is a three-phase dry type transformer cast under vacuum in epoxy resin with an active filler. It is this active filler, essentially composed of trihydrated alumina, which is the origin of the Trihal trademark.

TRIHAL dry type cast resin HV/LV transformer - Schneider Electric
TRIHAL dry type cast resin HV/LV transformer – Schneider Electric

Technology

Magnetic core

Magnetic core in assembling
Magnetic core in assembling

The magnetic core is made from laminations of grain oriented silicone steel insulated with mineral oxide. The choice and grade of steel and the cutting pattern and method of assembly minimises the loss level and the no-load current with the effect of a very low noise level.

Once assembled, it is corrosion protected using a class F, oven-dried alkyd resin.

Low voltage winding

LV polymerization kiln
LV polymerization kiln

The low voltage winding is made of either aluminium or copper foil (according to manufacturer’s preference) in order to achieve zero axial stresses under short circuit conditions; the foil is insulated by a class F inter-layer film, pre-impregnated with heat-activated, epoxy resin.

The ends of the winding are protected and insulated using a class F insulator. The whole winding is polymerised by being placed in an autoclave for 2 hours at 130°C which guarantees :

  • Outstanding resistance to industrial atmosphere aggression,
  • Excellent dielectric withstand,
  • Very good resistance to radial stresses under bolted short circuit conditions.


Each LV winding terminates in a tin plated aluminium or copper connection point, enabling connections to be made without using a contact interface (grease, bi-metal strip). Assembly is carried out according to current practices, including using spring pressure washers under nut and screw heads.


High voltage winding

Winding an HV coil in strip
Winding an HV coil in strip

The high voltage winding is usually wound from insulated aluminium or copper wire, using a method developed and patented by Schneider  Electric : “a linear voltage gradient from the top to the bottom”. For higher currents, the medium voltage winding may be wound using so-called “strip” technology.

These methods are used to obtain very low stress levels between adjacent conductors. This winding is cast and moulded under vacuum in a class F loading and fireproofed resin : the Trihal casting system.

These processes combine to give coils of very high dielectric properties with very low partial discharge level (guaranteed ≤ 10 Pc)* which is a decisive factor in influencing the transformer’s life span and its lightning impulse withstand(1). HV tapping points on the copper connection bars enable connections to be made without using a contact interface (grease, bi-metal strip).

Assembly is carried out according to current practices, including using spring pressure washers under nut and screw heads.

High voltage casting system

The system provides a vacuum cast coating of fire resistant filled resin, a technology developed and patented by Schneider Electric.

The class F casting system comprises :

  • A bisphenol based epoxy resin with a suitable viscosity to ensure excellent impregnation of the windings ;
  • An anhydride hardener modified by a flexiblishing additive. This type of hardener assures very good thermal and mechanical properties. The flexiblishing additive gives the casting system the necessary elasticity to prevent cracking during operation ;
  • An active powdered filler composed of silica and especially of trihydrated alumina througly mixed with the resin and the hardener.

Silica reinforces the casting’s mechanical strengh and improves heat dissipation. The trihydrated alumina guarantees the Trihal transformer’s intrinsic fire performance. The trihydrated alumina produces 3 anti-fire effects which occur in case of calcination of the casting system (when the transformer is exposed to flames).

  • 1st anti-fire effect(1) : refracting shield of alumina.
  • 2nd anti-fire effect(1): barrier of water vapour.
  • 3rd anti-fire effect(1) : temperature held below the fire point.

The result of the combination of the 3 anti-fire effects is immediate self extinguishing of the Trihal transformer.

In addition to its dielectric qualities, the casting system gives the Trihal transformer excellent self extinguishing fire resistance and excellent environmental protection against aggressive industrial atmospheres.

High voltage coil casting process

HV casting process
HV casting process

The process from proportioning the resin up to polymerization, is fully controlled by microprocessor, preventing any inopportune manual operation.

The trihydrated alumina and the silica are vacuum dried and degased to eliminate all traces of humidity and air which could degrade the casting systems dielectric characteristics. Half is mixed with the resin and half with the hardener under hard vacuum and controlled temperature, to give two homogenous premixes.

A new thin film degassing precedes the final mixing. Vacuum casting is then carried out in dried and pre-heated moulds at an optimal impregnation temperature. The polymerization cycle begins with a gelification at 80°C and ends with a long polymerization at 140°C. These temperatures are close to those of a transformer in service, enabling mechanical stresses to be eliminated which could lead to the coating cracking.

HV coil support wedges

The high voltage winding, which is encapsulated in hardened resin, looks like a thick-walled cylinder. This cylinder is centred on the magnetic core and is held in place vertically by an efficient wedging system, during transport, operation and even short-circuits and earthquakes.

Thanks to the original design of these wedges, which we developed ourselves, they can be assembled in a variety of ways to suit different levels of HV insulation. Where conditions of extreme stress exist and were clearly specified on the order form (very heavy HV coils, transport by sea or on very rough roads, installation in a wind turbine head, etc.) a reinforced wedging system (comprising two or even three sets of wedges) is used to palliate the situation and adapt the transformer to requirements.

Forced ventilation

Tangential fans on IP00
Tangential fans on IP00

In the event of temporary overloading, to avoid overheating of the windings, it is possible to install forced ventilation.

For IP00 as for IP31, for powers equal or greater than 1000 kVA, it is possible to install forced ventilation to achieve a temporary increase in power of 40%, without any special modification. In all cases, this temporary increase of 40% can be obtained if detailed on ordering.

However, if an increase in power is requested, account must be taken of the impact of this choice on the following points :

  • Sections of cables and of Prefabricated Busbar Trunking (PBT),
  • The rating of the transformer’s protective circuit breaker,
  • The size of inlet and outlet openings for air in the transformer room,
  • The life span of fans in service, which is considerably shortened compared with that of the transformer (3.5 compared to 30 years).

This option includes the supply of :

  • 2 sets of tangential fans, pre-cabled and connected to 1 single power connector per set,
  • 1 temperature measurement device, either Z or T type.

For Z type, a third set of PTC sensors is added to the standard thermal protection, in place of the R resistor which originally shunts the third Z converter measurement circuit (see diagram shown on the “Z thermal protection” option).

For T type, the digital converter comprises an output (FAN) intended to start the tangential fans (see diagram shown in the T thermal protection option).

This option includes either of the following, dependant on type of transformer :

  • A wiring box, mounted outside of the protective enclosure, to which are connected, sensors and power supplies for the fan sets on a terminal block,
  • A control cabinet, delivered separately (transformer IP00) or mounted on the protective enclosure, including : motor protection fuses, start up contactors and thermal protection device.

This unit is connected to the temperature sensors and fan sets if the transformer is delivered with IP31 enclosure. Otherwise, it is the installer who makes the connections.

Download TRIHAL wiring diagram (PDF) – HERE | Video Courses | Membership | Download Updates

SOURCE: Schneider Electric catalogue – Trihal transformer

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information
author-pic

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

10 Comments


  1. Andrew Zhang
    Feb 28, 2018

    Dear Sirs!
    We kindly asking You to specify cost, delivery cost to Slovakia and delivery time for the following positions:
    TRANSFORMER Schneider Electric type TRINAL dry
    Rated power: 2 000 kVA Electrical insulation strength up to 36 kV Rated frequency 50 or 60 Hz 2pcs
    Manufacturer: Schneider
    Thank you and have a nice day


  2. KRISHNA
    Feb 03, 2018

    1 TRANFORMER THREE PHASE : 2 MVA , 6.6 KV/0.4 KV 50Hz
    VECTOR GROUP OIL IMMERSED ONAN COOLED : DYN11
    IMPEDANCE VOLTAGE : 5.8%
    RATED CURRENT : 175 A PRIMARY & 2887 A SECONDARY
    AMBIENT TEMP. : 50°C
    WINDING MATERIAL : COPPER
    HV CT : 185/1.5 15VA
    CLASS 3 FOR WINDING TEMPERATURE
    TRANSFORMER OIL : UNINHIBITED SHELL DIALA D OR EQUIVALENT
    CONFIRMING TO IEC 60296(2003)
    BS 148 CLASS-1 STANDARDS

    2 TRANSFORMER CAST RESIN DRY TYPE FOR INDOOR APPLICATION :
    2 MVA EXCITATION TRASFORMER
    THREE PHASE 50Hz 11KV & 6.6KV/0.780KV,0.480KV & 0.530KV
    VECTOR GROUP : BOTH YD11 & DYN 5
    PRIMARY : CAST RESIN
    SECONDARY : VPI IMPREGNATED
    MAX RATED SECONDARY CURRENT : 1480A AT UNIT POWER FACTOR
    AMBIENT TEMP. : 50°C
    THERMAL INSULATION CLASS-HV&LV : F
    TYPE OF COOLING : AN
    OVERALL DIMENSIONS : 1700 X 800 1850(L X B X H)MM

    :- REFER DETAIL TECHNICAL&DIMENSIONAL DETAIL OF THE PROPOSED TRANSFORMER


  3. samaneh.Arab
    Nov 25, 2014

    Dear,

    i inform you that, we need transformer from your company, plese connect with us.

    B,r
    Samaneh


  4. samaneh.Arab
    Nov 25, 2014

    Dear,

    i inform you that, our company need transformer but we dont have your related email address, please connect with us.

    B,r
    Samaneh


  5. Kusic
    Sep 18, 2014

    Please send estimates of no load excitation current and no load power for 2 or 3 winding transformers 138kV/4kV/4kV


  6. Nolly
    Feb 28, 2012

    What is the phasing code or mark for trihal dry type transformer?


  7. Abdul Rauf A.G
    Nov 21, 2011

    Good day.
    Please send instalation details of DRY TYPE TRANSFORMER, Common for ABB and Group Schneider.


  8. Verma
    Oct 14, 2011

    Nice Article and good technically proven.


    • Edvard
      Oct 14, 2011

      Thank you Verma!


      • mohamed abd elhameed
        Sep 13, 2020

        what is the different between cast cast and cast impregnated in schneider

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

eighty three  +    =  eighty eight

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge