Limiting Inrush Currents
When switching on an emergency power installation, there are many different factors that can cause a dip in power. One of these factors is the inrush current, also known as the switch-on current. In this article, we explain exactly what it is, how we can limit it, and why it is important to do so.
What is an inrush current?
An inrush current is the power needed to start up a device or bring it up to the correct operating speed. It is a very brief surge of current that occurs when a non-linear load is switched on.
There are different types of inrush currents:
Resistive inrush current
This type of current occurs when the resistance is low at startup and increases during operation. Examples include heating elements.
Inductive inrush current
This current is caused when a coil is switched on, such as in a transformer. The energy is used to create a magnetic field.
Capacitive inrush current
This type of inrush current occurs when devices with a switched-mode power supply are powered on.
How to limit inrush currents
Inrush currents can be limited in several ways, for example with the following solutions:
Adjusting the startup device
Using a frequency converter
Using solid-state relays
Adding a delay
Adding a resistor with bypass relay in series
Star-delta starter
Using a soft starter
The consequences of inrush currents
When large inrush currents occur on a project, they can cause a voltage drop or dip in the network. Such a drop can lead to complete electrical installations and devices shutting down. Even if no devices or installations shut down, it can still cause parts of equipment to wear out much faster. This leads to both direct and indirect financial damage.
