Inrush current, also referred to as “locked rotor current,” is the excessive current flow experienced within a motor and its conductors during the first few moments following the energizing (switching on) of the motor.
What is current inrush and why it happens?
Inrush current is the instantaneous high input current drawn by a power supply or electrical equipment at turn-on. This arises due to the high initial currents required to charge the capacitors and inductors or transformers. … These currents can be as high as 20 times the steady state currents.
What is the difference between inrush current and starting current?
Inrush current or input surge current is the maximum amount of current drawn by the electrical device when it is turned ON for the first time. Electrical devices consuming alternating current,draws current several time greater than their full load current value at the instant of starting.
How is motor inrush current measured?
To measure the inrush current, technicians can use either a hard-jawed clamp meter or a flexible current probe. Only meters that offer an inrush button can measure inrush current.
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.
What causes inrush?
High inrush current is the result of the maximum instantaneous input current drawn by an electrical device during the initial power up. As technology continues to advance, most systems today run efficiently and maintain a low impedance which in turn contributes to high inrush current.
What is the effect of inrush current?
In few cases the amount of current supplied to the circuit gets beyond the acceptable maximum voltage of the load circuit, causing permanent damage to the load. In high voltage AC motors, the high inrush current causes the power switch to trip or sometimes burned out.
Do DC motors have inrush current?
DC motor inrush is the maximum, instantaneous input current drawn by the DC motor when first turned on and it is important to know how to limit the inrush current to prevent possible damage to the motor.
How much is inrush current?
As previously mentioned, inrush current is the maximum peak current, experienced in the system and it can be twice or ten times of the normal rated current. This unwanted current spike can damage the device like in transformer, inrush current can cause tripping of the circuit breaker, every time it turns ON.
Is Locked rotor the starting current?
A motor at rest acts as if its rotor is locked. The locked rotor current and the starting current of a motor are one and the same. It is the starting current drawn by a motor when full nominal voltage is applied to its terminals.
How is inrush current calculated in DC?
The peak value of the inrush current is determined by the equation, i=C*dv/dt. The capacitance is the total capacitance of the EMI filter and the input capacitance of the DC-DC converter. The dv/dt is the slope of the applied voltage waveform.