What is the inrush current for a transformer?
Inrush Current is a form of over current that occurs during energisation of a transformer and is a large transient current which is caused by part cycle saturation of the magnetic core of the transformer. For power transformers, the magnitude of inrush current is initially 6 – 10 times the rated load current.
How is transformer inrush current calculated?
Inrush current calculations: Approximately inrush current I(peak) is equal to the ratio between the root 2 times of maximum applied voltage to DC winding resistance. This calculation gives you the approximate value of the inrush current to understand.
Do transformers have high inrush current?
The inrush current may be up to 10 times higher than normal rated current of transformer. Although the magnitude of inrush current is so high but it generally does not create any permanent fault in transformer as it exists for very small time.
How do I stop inrush current?
Inrush current can be reduced by increasing the voltage rise time on the load capacitance and slowing down the rate at which the capacitors charge. Three different solutions to reduce inrush current are shown below: voltage regulators, discrete components, and integrated load switches.
What causes high inrush currents in a transformer?
Transformer Controlled Switching When a transformer is de-energised, the magnetic core will contain a certain amount of residual magnetic flux. This residual flux is dependent on the voltage across the transformer at the time of de-energisation and can intensify saturation leading to high transient inrush current on re-energisation.
What happens when a varistor is too high?
A varistor fails if the rate of rising of voltage and the peak is too high, in that case, the inrush of current will exceed its limits and it will rapture. It may also fail due to degradation and show continuity even at low voltages. 4).
Where did the name of the varistor come from?
A varistor is a device that meets our requirement and controls voltage spikes very effectively thus protecting our circuit. The name of this can be derived from a Variable resistor. Power electronic devices that handle large currents are also protected by varistors.
How to select the right varistors For overvoltage circuit?
1 Circuit conditions such as the peak voltage and current during the surge event 2 The MOV continuous operating voltage (should be at 20% above maximum system voltage under normal conditions) 3 The number of surges the MOV must survive 4 Acceptable let-through voltage for the protected circuit
