The i²t (current squared through time) algorithm protects the motor from overheating due to excessive currents during operation.

What is i²t?

As motors do their work, the internal temperatures rise, heating up the motor coils. If temperatures get too high, overload conditions can affect performance, and overheating may cause motor failure.

To prevent this from happening, users must monitor overcurrents carefully, but this is challenging. Temperatures can be very different at different spots within the motor, making it difficult to map out hot spots with precision.

Instead, monitoring power flow rather than direct internal temperature can provide a better view of where potential hotspots will occur. These formulas, known as i²t methods, measure RMS current as it moves through motor windings.

i²t is an expression of thermal energy that results from current flow. In fuses, this expression happens in:

Melting i²t – The current required to melt a circuit
Arcing i²t – Thermal energy passed by a fuse during arcing.
Total clearing i²t – The time from overcurrent inception until complete interruption.

Fuses also need protection from electrical pulses. The pulse cycle withstand capability is also part of the rating of a fuse. It uncovers the number of pulses a fuse can withstand before undergoing thermal stress.

i²t is an IEC standard for safe operations. It helps regulate power supply. It can also identify the different melting integral of fuses when the rated voltage, current, and breaking capacity are all the same.

What is the purpose of i²t algorithms?

The formulas work to protect the motor by ensuring that the power dissipated doesn’t go over the designed threshold. A motor must maintain equilibrium while also operating at its fullest capacity. This is the foundation for overcurrent protection.

Nominal current is continuous current a motor can stand and still operate within its overheating threshold. In standard motors, currents above this continuous current will cause overheating and loss of performance.

With i²t protection, the motor senses this threshold when reached and implements the protective mechanism to prevent disaster. The algorithm monitors the threshold and implements limits to prevent overheating. When the tracking variable falls below that threshold, the algorithm removes limits.

How does i²t protection work?

The calculation considers the continuous current and the maximum current limit, both of which are based on the characteristics of the motor itself — think size, configuration, and cooling methods. Multiply those figures by the max duration time for the peak current, and you have the basic threshold a motor can withstand before causing a short circuit or triggering the melting point.

The current values are designed to measure the current flowing through a motor rather than monitoring based on the ambient temperature measurements. The max current can be monitored against the normal operating current.

The microcontroller receives the inputs from the current sensor. The user programs the metrics into the formula so that the algorithm can monitor the current. The algorithm monitors each phase independently, but overage detected at any point triggers the protection device.

The protection device includes fuse characteristics. As ambient temperatures rise, the fuse responds faster to protect the motor components. Under low voltage situations, the motor can operate as normal, only triggering the protection device when thermal energy increases beyond the threshold.

Why use i²t?

It’s vital to protect torque motors through a variety of heat monitors. i²t provides a time plus current calculation with ampere rating and rated currents. It can also tell users the breaking capacity of fuses, allowing developers to assess the current rating for different fuse elements.

Circuit protection is another valued asset for i²t algorithms. Overloaded circuit voltage can also ruin machinery, so using i²t principles to identify current characteristics is an excellent use case. For motor algorithms, it’s a fail-safe, allowing for the smooth, safe operation of high torque motors.

Copley Controls is dedicated to providing optimal performance in all aspects of our products. Whether it’s innovations for servo motors or the highest quality stepper options, customers can rely on the best and safest operations.

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