Control Transformers
 
  Special Requirements:
 

Industrial control equipments demand a momentary overload capacity of three to eight times’ normal capacity. This is most prevalent in solenoid or magnetic contactor applications where inrush currents can be three to eight times as high as normal or holding currents but still maintain normal voltage at these momentary overloaded conditions.

General control transformers are designed for good regulation up to 100 percent loading, but their output voltage drop rapidly on momentary overloads of this type making them unsuitable for high inrush application. The current standards require electromagnetic devices to operate reliably at a minimum of 85% of their rated voltage. However contact life may be affected with continuous start-up at that voltage level. Therefore the minimum 90% voltage at momentary loaded condition is preferred for good contact life of electromagnetic devices.

 
  Design Features:
 

GR Industrial control transformers are designed especially for maintaining a high degree of regulation even at eight time’s normal load. This results in a larger and generally a little expensive transformer.

GR industrial control transformers are also designed with a metallic shield between the primary and secondary windings to attenuate transient noise. This is especially important in critical applications such as process controllers and many other microprocessor controlled devices.

 
  Control Transformer Capacity Selection:
 

All electromagnetic control devices have currents requirements: the first to energize the coil the second to maintain the contact for definite period of time. The initial energizing of the coil, which takes 5 to 20 milliseconds, requires many times more current than normal. This is referred to as Volt-ampere inrush. Which immediately followed by the sealed volt amperes – the amount of current required to hold the contact in the circuit.

 
  Easy, four steps:
 
  • Determine what your primary (supply) and secondary (output) voltage requirements are, as well as your required frequently (i.e. 50Hz)
  • Determine the total inrush VA of the control circuits from the manufactures data the contactor data table. Do not neglect the current requirements of indicating lights and timing devices that do not have inrush VA but are energized at the same time as the other components in the circuit. Their total VA should be added to the total inrush VA.
  • Refer to the inrush VA data chart. If the nominal supply voltage does not fluctuate more then 5% then reference the 95% secondary voltage column. If the nominal supply voltage does not fluctuate more than 10% the 90% secondary voltage column should be used to size the transformer. Current standards require electromagnetic devices to operate reliably at a minimum of 85% of their rated voltage.
  • However contact life may be affected with continuous start-up at that voltage level. Therefore, the minimum 85% secondary voltage column should only be used as reference. Go down the column you have selected until you arrive at the inrush VA does not to, but not less than, the inrush VA of your control circuit.
  • Read to the far left side of the chart below and you have selected the continuous normal VA rating of the transformer needed. The total sealed VA of the control circuit must not exceed the normal VA rating of the transformer selected from the manufacturer’s data or the contactors data table.
 
  Features:
 

Voltage regulation of GR control transformer exceeds standard requirements. Secondary voltage drops between no-load and momentary overload remains exceptionally low. This excellent secondary circuit voltage regulation assures reliable operation of electromagnetic components and may permit the usage of a smaller and less expensive industrial control transformer.

  • Constructed with high quality silicon steel lamination to minimize core loses and increase efficiency.
  • Design incorporate precision wound coils for improved regulation.
  • 130 degree insulation class, 70 degree temperature rise.
 
 
 
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