On Load Distribution Transformer

By fulfilling the BIS-1180 (Jan 2014) criteria, the on-load distribution transformer, under ISI approval, ranges from 200 KVA to 2500 KVA. While under IS-2026, the ranges of 2500 KVA to 5000 KVA, use standard voltage classes to achieve the highest efficiency levels. Below some critical points are discussed-

  • Types of transformers - Pad-mounted – both for in and outdoor applications
  • Paper insulated copper conductor with multiple layers
  • Standards maintained- BIS-1180, IS-2026, and IEC 60076 
  • Designed for less maintenance and silent operations, including a minimum guarantee of 15 years

Features of On-Load Transformer

  • Step-lap design is used for the magnetic circuit to record lower losses and high-quality CRGO material with grades like ZDKH, ZDMH, AMORPHOUS, MOH, and others is used to record low magnetizing current within the core
  • Sourced by regular and reputed vendor HINDALCO & STERLITE, the electrolytic grade with 99.99% pure high-quality Copper, is used for the electric circuit, including Foil winding in the L.V coil of the transformer
  • Tolerance of lightning impulse and voltage surges due to High Dielectric Insulation property
  • Effective cooling, by ONAN-based natural convection, through axial and radial ducts  

Technical Specifications

Consistent voltage fluctuations from the H.V. side require the installation of On-Load Transformers. Hence, AVR is used by the On-Load Transformers for tap changes to supply constant output voltage without any power cut. Thereby, optimization of total industrial power consumption results in power savings.

Type Indoor/ Outdoor
Voltage Class 3.3, 6.6, 11, 22, 33 KV.
Vector Group Dyn11 or other specified by customer
No. of phase 3 phases
Frequency 50/60 Hz
Tap Range ±10 %, +5% to -15% in 1.25% steps in 17 positions
Winding Material Copper with multiple paper covering
Applicable Standards IS-1180:2014 (Part-1), IS-2026, IEC 60076
Painting Epoxy or specified by customer


  • Use of On-Load Transformer helps in limiting the voltage at the L.V. side to balance the voltage fluctuations from the H.V. side
  • Shut-down of the factory is not desirable during the tap changing and only the On-Load Transformer can eliminate this obstacle
  • During automatic tap changes, the desirable range of L.V. side voltage can be maintained by using an RTCC panel with AVR (Automatic Voltage Regulator)
  • The On-Load Transformer can enhance transformer efficiency and reduce the losses of the transformer and other equipment, resulting in power saving and an overall rise in the life-cycle of the transformer and other electrical equipment     


Frequently Asked Questions

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