Frequently Asked Questions

  • What is an isolation transformer?

    An isolation transformer is referred to a transformer that has its primary and secondary windings separated. It is also commonly referred as double-wound transformer, dual-winding transformer and separate-winding transformer.
    See difference between isolation transformers and autotransformers for more informaton.

  • What is an autotransformer?

    As opposed to an isolation transformer, an autotransformer has a common winding for primary and secondary. It is also known as single-winding transformer.
    See difference between isolation transformers and autotransformers for more informaton.

  • What is a control transformer?

    A transformer intended for power supply of control circuit is a control transformer. It is designed to provide high stability (regulation) during a short period of overload condition typically referred to as inrush.

  • What is inrush current?

    The inrush current is a current several times of the electrical device's full load current drawn when the device is first turned on. During this period, the transient current can flow for several cycles before reaching its steady state current. Inrush current is rated at number of times in transformer. Transformers usually have an inrush rating of 8 to 15 times. For very small transformers, the inrush can go up to 25 to 40 times.

  • What is exciting current?

    After the transformer is energized, a small current flows through its winding. This current is known as exciting current.

  • Can a transformer be connected reversely?

    Yes, a transformer can be connected reversely. However, the output voltage will be less than the rated voltage due to the compensation factor of the windings.

  • Is it possible to connect a single phase transformer to a 3 phase supply?

    Yes, connect the two primary leads of the single phase transformer to any two wires of the 3 phase supply. This will cause unbalance load on the 3 phase supply. It is also commonly known as 2 phase to single phase in Singapore.

  • Can a transformer rated at 60Hz operate on a 50Hz service?

    A transformer designed for 60Hz cannot operate on a 50Hz service as more losses will occur and lead to higher temperature rise and shorter life span. On the contrary, a transformer rated 50Hz can operate on a 60Hz service.

  • Are GS Transformers designed for 50 or 60Hz?

    Our transformers are designed for 50/60Hz operations. Transformers designed for 50/60Hz can operate up to 400Hz. At 400Hz, however, compensation factor would need to be taken into consideration.

  • What is voltage regulation?

    Voltage regulation is the ability to provide constant secondary voltage given a constant primary voltage over a wide range of load conditions.

    Voltage regulation is defined as:

    Transformer regulation equation

    Where
    VNL: No-load voltage
    VFL: Full-load voltage

  • What is intermittent rating?

    A transformer can be operated in continuous or intermittent mode. When a transformer is operating in an intermittent duty cycle, the maximum power can be increase significantly during that short period of time.

    Intermittent power can be calculated using the following formula:

    Transformer duty cycle equation

  • What is the effect of using a transformer in high altitude?

    Dry type transformers used above 1000 metres require derating due to the reduced cooling capacity of the less dense air. The capacity of the transformer should be derated 0.3% for every 100 metres above 1000 metres.

  • Why are transformers rated in kVA not kW?

    Generally, there are 2 kind of losses in a transformer; Iron losses and copper losses. Since iron losses depend on voltage and copper losses on current, the total losses depend on voltage and current, and no power factor is involved. Transformers are rated in kVA as kW would include power factor.

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