OEM/ODM Auto Transformer Factories & Suppliers

An autotransformer utilizes a single continuous magnetic winding per phase that serves as both primary and secondary, transferring power through a combination of electromagnetic induction and direct electrical conduction. In contrast, an isolation transformer has electrically isolated primary and secondary windings. When the voltage transformation ratio is relatively small (e.g., co-ratio K = (V_HV - V_LV) / V_HV < 0.5), autotransformers deliver significantly lower physical size, lower core losses, superior efficiency, and lower procurement costs.

The co-ratio (K) is calculated as K = (V_HV - V_LV) / V_HV. The physical frame size (Equivalent KVA) required for an autotransformer is determined by multiplying the pass-through KVA rating by the co-ratio: Equivalent KVA = Pass-Through KVA × K. For example, stepping down 380V to 220V results in K = (380-220)/380 = 0.421. Therefore, a 100kVA pass-through autotransformer only requires the physical core and copper frame of a 42.1kVA conventional transformer, yielding massive raw material savings and reduced losses.

Dry-type (VPI or Cast Resin) autotransformers are strongly recommended for indoor installations, high-rise buildings, commercial centers, CNC workshops, and environments with strict fire safety regulations (F1 rating). Oil-immersed autotransformers are best suited for outdoor substations, high-voltage utility networks (11kV to 33kV+), heavy industrial plants, and applications requiring maximum thermal dissipation under continuous overload conditions.

Continuous copper or aluminium foil winding replaces conventional round wire turns with flat strip sheets across the full axial height of the coil. This distributes electromagnetic forces evenly during short-circuit faults, eliminating axial displacement stresses. Furthermore, foil winding eliminates internal transposition joints, minimizes eddy current losses, and ensures uniform thermal distribution to prevent hot-spot degradation.

In accordance with IEC 60076 and IS 2026, standard factory routine testing includes: (1) DC Winding Resistance measurement, (2) Voltage Ratio & Vector Phase Group verification, (3) Separate-Source AC Insulation Withstand Test, (4) Induced Overvoltage Withstand Test, (5) No-Load Loss & No-Load Current measurement, and (6) Short-Circuit Impedance & Load Loss measurement. Full routine test certificates are provided with every shipment dossier.

Yes. We regularly host client-appointed third-party inspection agencies at our Rajkot manufacturing facility. The FAT schedule is coordinated upon approval of General Arrangement (GA) drawings, allowing inspectors to witness routine tests, inspect dimensional compliance, verify paint thickness/coating, and audit raw material test reports before factory sealing.

Because primary and secondary circuits share a common neutral point, earth fault currents can travel between voltage levels. It is standard engineering practice to solidly ground the autotransformer neutral point and install neutral current transformers (RCT/NCT), restricted earth fault (REF) protection, overcurrent/earth fault relays, and surge arresters on both HV and LV bushings to prevent transient overvoltages.

Standard distribution-class dry-type or oil-filled autotransformers typically ship within 3 to 5 weeks after drawing approval. Custom-engineered power units, high-voltage traction autotransformers, or compact substations requiring specialized tap changers (OLTC) generally take 6 to 10 weeks, inclusive of drawing sign-off, fabrication, testing, and seaworthy export crating.