{"id":17515,"date":"2020-01-22T11:00:04","date_gmt":"2020-01-22T19:00:04","guid":{"rendered":"http:\/\/www.palada.net\/index.php\/2020\/01\/22\/news-11250\/"},"modified":"2020-01-22T11:00:04","modified_gmt":"2020-01-22T19:00:04","slug":"news-11250","status":"publish","type":"post","link":"http:\/\/www.palada.net\/index.php\/2020\/01\/22\/news-11250\/","title":{"rendered":"Avoid electrical network stress during large motor starting using simplified calculations at design stage"},"content":{"rendered":"

Credit to Author: Jerome Guillet| Date: Mon, 20 Jan 2020 14:16:07 +0000<\/strong><\/p>\n

This post is part of a series of motor management<\/a> blogs that discuss different aspects of large motor integration in the electrical network and industrial process.<\/p>\n

Voltage drop during load energization is a major concern in heavy industries. Furnaces, transformers, and large motors are examples of loads with high inrush currents, generating voltage drop. \u00a0In the same time motors exposed to voltage drop will have their torque reduced, experiencing deceleration and even stalling. Sensitive electronic devices can fail when voltage drop occurs. To cope with these issues, voltage drop protection is used to disconnect loads at a defined threshold. If voltage drops are not addressed in the design phase, they may later be responsible for process downtime and production losses.<\/p>\n

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Figure 1 Motor starting current and generated voltage drop<\/em><\/p>\n<\/div>\n

For large motors, it is best to address the issue as early as possible in the early design stage of a project. However, at this stage fewer inputs are available, so this can be challenging.<\/p>\n

That is why, quick simplified calculations can be relevant, compared to time-consuming simulations based on multiple assumptions.<\/p>\n

A simple method of calculation is to focus only on predominant reactances, neglecting resistances, and consider the electrical network as an impedant circuit. This method is valid if cables can be omitted.<\/p>\n

Consider the following electrical network with one starting motor:<\/p>\n

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Figure 2 Equivalent circuit of a starting motor with initial loads in parallel<\/em><\/p>\n<\/div>\n

Where,<\/p>\n

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Based on the figure above, the starting voltage and voltage drop can be expressed as:<\/p>\n

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Several parameters can help to maintain a high starting voltage and reduce the voltage drop during starting.<\/p>\n

These parameters are shown in the next table:<\/p>\n

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Effectively, limiting the voltage drop, Vdrop, is possible through:<\/p>\n

Increasing equivalent starting reactance \"\"with:<\/p>\n