Buying a Dry-type Transformer.

Dry type transformers require minimum maintenance to provide many years of reliable trouble free service. A dry-type transformer has no moving parts and is a completely static solid state device, under normal operating conditions, are usually insure a long and trouble-free life. Dry type transformers provide a safe and reliable power source which does not require fire proof vaults, catch basins or the venting of toxic gasses. These important safety factors allow the installation of dry type transformers inside buildings close to the load, which improves overall system regulation and reduces costly secondary line losses.

Things you need to have ready before buying a Transformer.

• 1. Primary voltage.
• 2. Secondary voltage.
• 3. Frequency of cycle.
• 4. Power Rate or Capacity (kVA). To do this you must determine the largest load you can expect at any given time.
  
  Your can use our "Transformer Calculator" to determine required capacity. For single phase: this is done by multiplying the load current (amperes) by the load voltage.
  For example, if the load is 80 amperes, such as a motor, and the secondary voltage is 240 volts, then 240 x 80 equals 19200 VA. 20 kVA transformer is required.
  For three phase 240 x 80 *1.73 (square root of 3) then divide by 1000 equils 33.26 kVA Always select the transformer larger than the actual load. This is done for safety purposes an allows for expansion.
  Determine what those loads are-based on operational requirements, then determine the kVA each will draw. Once you done the individual calculations and added them up to arrive at the maximum load, you should add in factors for reasonable unplanned load growth (20% is common) and for planned addition load.

But don't stop there. The following includes some additional factors you'll have to consider when choosing a transformer.

• Indoor or outdoor mounted, pad mounted
• Primary voltage: delta or wye (usually dictated by the utility)
• Secondary voltage (480V for small facilities) or delta-wye 3,4,or 5 wire configuration (4 is the most common)
• Power factor and efficiency
• Impedance
• Temperature rise
• Case style (consider footprint, height, access, cooling)
• Location, space requirement
• Seismic requirement
• Accessories (including taps) and instrumentation
• Basic impulse level, which is the withstand rating in kV
• Based on these criteria, you can work with a manufacturer to select the correct transformer for your service entrance.

Some definitions to know about transformers:

• Rated voltage. The rated voltage is the maximum voltage (phase-phase), expressed in kV rms, of the system for which the equipment is intended. It is also known as maximum system voltage.
• Rated insulation level. The combination of voltage values which characterize the insulation of an instrument transformer with regard to its capability to withstand dielectric stresses.
• Rated frequency. The rated (power) frequency is the nominal frequency of the system expressed in Hz, which the instrument transformer is designed to operate in.
• Ambient temperature. Average 24 hours ambient temperature above the standardized +35 °C influences the thermal design of the transformers and must therefore be specified.
• Primary windings The primary winding is designed as a multi-layer coil of double enamelled wire with layer insulation of special paper. Both ends of the windings are connected to metal shields.
• Core. The transformer has a core of carefully selected material, to give a flat magnetization curve. The core is over-dimensioned with a very low flux at operating voltage.
• Impregnation.Heating in a vacuum dries the windings. After assembly, all free space in the transformer (approximately 60%) is filled with clean and dry quartz grains. The assembled transformer is vacuum-treated and impregnated with degassed mineral oil. The transformer is always delivered oil-filled and hermetically sealed.

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