One of the critical issues that arise when a motor starts is the transient conditions that can cause complications. These complications include inrush current, low power factor, and voltage drop. Inrush current refers to the maximum instantaneous current drawn by a motor at the time of starting. The motor's model can be seen as a transformer, where the stator represents the primary and the rotor represents the shorted secondary. Like transformers, mutual induction occurs in motors, depending on the slip of the rotor.

sld presentation
sld presentation

The slip is the difference between the speeds of the rotor and stator. During motor startup, the slip is at its maximum value, resulting in a high inrush current. This high current can potentially overheat equipment and damage insulation, leading to further complications. The starting of a motor also affects the power factor. To develop the necessary magnetic field, the motor draws high magnetization current, which decreases the power factor. A low power factor indicates that power transmission is not being efficiently utilized and can result in power loss and equipment damage.

Voltage drop is another issue encountered during motor starting. The high inrush current leads to a voltage drop on feeder branches and other components before reaching the motor. This decreased voltage can disrupt the operation of the motor and other loads in the system. Given the problems associated with motor starting, it is crucial to conduct motor starting studies to identify potential complications and implement mitigation techniques. Motor starting studies help in designing a protection scheme for the system and predicting uncertainties that may arise during motor startup. By understanding the effects of motor starting, such as voltage dips, high currents, voltage drop, and fluctuations, preventive measures can be taken to safeguard the system.

Motor starting studies involve a systematic procedure to collect data, develop a comprehensive system model using software like ETAP or SKM, perform calculations for voltage drop and power flow, and analyze the results against industry standards such as NFPA 70E and IEEE guidelines. Based on the analysis, recommendations are provided to resolve identified issues. Various techniques can be used to mitigate the problems associated with motor starting. These include the use of auto transformers, soft starters, star-delta starters, and direct-on-line starters. Each technique has its advantages and suitability depending on the motor's size and requirements.

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By performing motor starting studies, the following outcomes can be achieved:
Identification and mitigation of voltage dip points
Prevention of nuisance tripping
Understanding the impact of motor load changes on the system
Increase in system reliability
Reduction of inrush current through protection schemes
Minimization of motor stalling

If you require motor starting studies, you can rely on VB® Engineering, a reputable expert in the field. Our team of certified professionals follows proper procedures and industry standards to deliver reliable motor starting studies and design effective protection schemes for your systems.