Example: A 100kVA, 440V transformer has a DC winding resistance of 0.45 ohms, Calculate the inrush current of the transformer. Hence inrush current is equal to the 6 times of the full load current.
How can we reduce the inrush current of a transformer?
- Hysteresis flux of the transformer can be reduced.
- Switching on the transformer at the voltage peak.
- Increasing the frequency at the switching time.
- Reducing the voltage at the switching time.
Why does inrush current appear in transformer?
When a transformer is first energized or reenergized after a short interruption, the transformer may draw inrush current from the system due to the core magnetization being out of sync with the voltage. The transient drives the core into saturation and draws a large amount of current into the transformer.Dec 9, 2015
How much inrush can a transformer handle?
Most texts books advise that transformer inrush current can be as high as 10 times the transformer's rated current (In) and furthermore will have a high harmonic content during this period. This advice is correct for when switching a transformer onto a mains supply where the source impedance of the supply is low.
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.
How high can inrush current be?
These currents can be as high as 20 times the steady state currents. Even though it only lasts for about 10ms it takes between 30 and 40 cycles for the current to stabilize to the normal operating value.
Does transformer have inrush current?
Transformer Inrush Current Protection A transformer draws inrush current that can exceed saturation current at power up. The Inrush Current affects the magnetic property of the core. This happens even if the transformer has no load with its secondary open.
What affects inrush current?
At ambient temperature the NTC device exhibits a high resistance, when the power is turned-on, the high resistance limits the amount of inrush current flowing into the circuit. As the current flows, the thermistor temperature increases thereby reducing the resistance significantly.
How can I reduce my 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.
How does transformer handle inrush current?
A transformer draws inrush current that can exceed saturation current at power up. The Inrush Current affects the magnetic property of the core. If turn-on occurs when the AC voltage wave is at its peak value, there will be no inrush current drawn by the transformer.
Why inrush current of transformer is high?
After the steady state maximum value of flux, the core becomes saturated and the current required to produce the rest of flux is very high. So the transformer primary will draw a very high peak current from the source. This is known as the transformer inrush current or magnetizing inrush current of the transformer.