“Marmelosa”, 11/203, Mambakkam Road, Medavakkam, Chennai- 600100, India

044-22771709, 22771516


ASTA-certified CTs


Control Transformers

Technical Section

A control transformer is a transformer that supplies power to control, and/or auxiliary equipment not intended for direct connection to the main circuit. Control transformers are specifically used to provide control supply voltage for the control circuit of AC motor starters i.e. starter coils, timers, indicating lamps, etc.


Control Transformers for contactor application must:

  1. Energise the coil
  2. Maintain a contact for a definite period of time.

The initial energizing of the coil takes 5 to 40 milli-seconds and requires 3 to 10 times the nominal current. Following this Ampere Inrush an amount of current is required to hold the contact in circuit. This is referred to as Sealed Amperes. The values multiplied by the voltage yield the Inrush VA and the Sealed VA respectively.

In comparison a standard design transformer such as a General Purpose transformer whose VA rating is based on the steady state load condition will not be able to handle the inrush current and still deliver sufficient voltage to reliably operate the electro-magnetic control components.

KAPPA Industrial Control Transformers are low reactance type, designed to ensure good regulation at short time loads. To ensure superior voltage regulation, appropriate attention is devoted to reducing the percentage reactance and resistance drops. Reduction of these values to a minimum greatly improves secondary voltage regulation.


Our Transformers are tested in accordance with our own stringent quality control standards and a number of Electrical tests including Turns ratio, Exciting current, Core loss and applied potential tests are conducted to assure conformance to design specifications. All tests are conducted in conformance with standards. Both LV and MV control transformers are offered.

Transformers can be supplied either in open execution or with enclosure.

Specifications: In order to completely specify the control transformer, the following information is required.