Dry Type Transformers: Types and Applications
Dry Type Transformer
Types of Dry Type Transformers
- Cast Resin Dry Type Transformer (CRT)
- Vacuum pressure Impregnated Transformer (VPI)
Cast Resin Dry Type Transformer (CRT)
- High short time over load capacity.
- Lower load losses and higher efficiency
- No use of oil – Zero risk to fire hazard make it suitable for indoor installation.
- Can be fitted outdoor in IP 45 enclosure.
- Does not absorb moisture- non hygroscopic.
- Eco-friendle and safe
Vacuum Pressure Impregnated Transformer (VPI)
- High mechanical strength.
- Void free insulation.
- No temperature fluctuation.
- Easy maintenance.
- Less prone to fire hazard.
Advantages of Dry Type Transformer
- Safety for people and property.
- Maintenance and pollution-free solution.
- Easy installation.
- Side clearance is less.
- Environmentally friendly.
- Excellent capacity to support overloads.
- Reduced cost on civil installation works and fire protection systems.
- Excellent performance in case of seismic events.
- No fire hazard.
- Excellent resistance to short circuit currents.
- Long lasting due to low thermal and dielectric heating.
- Suited for damp and contaminated areas.
Disadvantages of Dry Type Transformer
- Dry type transformer is long lasting and with less chance of winding failure. But once it fails whole set up is to changed, i.e. complete change of high voltage and low voltage winding with limb.
- For same power and voltage rating, dry type transformer is costlier than oil cooled transformer.
Application of Dry Type Transformer
- Chemical, oil and gas industry
- Environmentally sensitive areas (e.g. water protection areas)
- Fire-risk areas (e.g. forests)
- Inner-city substations
- Indoor and underground substations
- Renewable generation (e.g. off-shore wind turbines )
Important Factors to Design a Dry Type Transformers
3. Selection of Core Material with Low Hysteresis Loss
The core of the transformer must have high permeability and less hysteresis loss in order to have better efficiency. The CRGO stell is used for the core material . The CRGO steel offers higher permeability and the minimum hysteresis loss.
The leakage reactance of the transformer must be as minimum as possible to get better voltage regulation of the transformer.The regulation of the transformer shows drop in the secondary voltage with increase of loading on transformer. The leakage reactance is generally kept within 2 % during transformer design.
5. Life Expectancy
The life of the transformer depends upon the useful life of the insulation. The life of the insulation is dependent on the temperature. The rise in temperature cause deterioration in the insulation value which may further cause breakdown of the insulation. Insulation class B, F and H is preferred for dry type transformer to withstand higher temperature. The temperature rise must be calculated during desin stage of the transformer to get higher life expectancy of the transformer.
The no load losses of the transformer depends on the eddy current and hysteresis loss. The no load losses can be minimized by use of the CRGO core and by keeping the leakage reactance as minimum as possible. The load losses depends on the resitance of the conductor. Thus, by keeping the winding resistance within moderate value losses, voltage regulation and the efficiency of the transformer can be improved.
If the load on the transformer increases above its rated kVA, the transformer is said to be overloaded. The overloading cause rise in temperature of the transformer which reduce the useful life of the transformer. The cooling system should be designed to cater the temporary overloading of transformer.
If the dry type transformer is to be used for supplying the current to non-linear loads the temperature rise takes place due to harmonics in the current waveform. The transformer for such application must be assigned K-factor.
9. Insulation Level
In transformer design, insulation level adjustment is an important factor. Generally insulation level is chosen as per basic impulse level and system over voltage. Strong insulation level increases the life of a transformer.