Category Archive for: «Variable Speed Drives»

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Few Good Tips For Estimating and Optimizing Pumping Energy Costs

Duration diagram // To help estimate pumping energy costs To compare different system and pumping equipment proposals and make an intelligent choice, three facts will need to be established: Will the process require varying flow rate, and, if so, must it be continuously variable or can flow rate be varied in steps? Can on-off batch pumping […]

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Comparison of Soft Starting and Frequency Converter Motor Starting

Soft starting A soft starter is, as you would expect, a device which ensures a soft starting of a motor. A softstarter has different characteristics to the other starting methods. It has thyristors in the main circuit, and the motor voltage is regulated with a printed circuit board. The softstarter makes use of the fact […]

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What To Check When Commissioning Variable Speed Drives

The purpose of commissioning VSDs The main purpose of commissioning VSDs is to ensure that: The AC converter and motor have been correctly installed and meet the wiring and safety standards such as IEC 60364 or Australian standard AS 3000. The power and motor cables are correctly sized, installed and terminated. All power cable shields […]

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Comparison of Motor Speed Control Methods

Why motor speed control? It is often desirable to control the motor speed, usually for reasons process control for such variables as flow or pressure. Such applications as fans and pumps often have varying output requirements, and control of the motor speed is more efficient than mechanically limiting the process output with such devices as […]

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Line Harmonic Currents – Adjustable Frequency Control Created

Nonlinear loads Nonlinear loads like adjustable frequency controls create line harmonics when connected to the AC power distribution system. These harmonic currents are a result of non-sinusoidal current, which is a characteristic of all adjustable frequency controls using diodes or silicon controlled rectifiers (SCRs) on the input. The control’s input current is composed of the fundamental sinusoidal current […]

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10 Things to Consider When Selecting a High Quality Medium Voltage Drive

10 Considerations to Identify Medium voltage drives have been available for over 35 years, but have only recently achieved very high reliability and simplicity within the past few years. Below are 10 considerations on how I would go about specifying and selecting a very high quality medium voltage drive based on my 35 years of […]

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Effects of Speed Variation on Rotodynamic Pumps

Varying the rotational speed A rotodynamic pump is a dynamic device with the head generated by a rotating impeller. Thus, there is a relationship between impeller peripheral velocity and generated head. Peripheral velocity is directly related to shaft rotational speed, for a fixed impeller diameter. Varying the rotational speed therefore has a direct effect on […]

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Case study – Effect of utility-induced surges in a steel mill with variable speed drives

Problem A steel mill with variable speed drives (VSDs) had problems of frequent tripping of the VSDs with the indication ‘overvoltage in AC line’. Each tripping caused severe production disruption and resulted in considerable monetary loss due to lost production. Steady-state measurements by true RMS voltmeter showed that voltage was normal and within the specified […]

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Keeping Motor At Correct Temperature When Connected To a Frequency Converter

Two types of influence When a motor is connected to a frequency converter it must be kept at the correct temperature, and this is subject to two types of influence: If the speed decreases, the cooling air volume goes down. If a non-sinusoidal motor current is present, more heat is generated in the motor. At […]

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Benefits and Potential Drawbacks of VSDs

Introduction VSDs (Variable Speed Drives) offer several benefits, some of which are relatively easy to quantify, and others of which are less tangible, but there are some potential drawbacks, which must be avoided. Benefits we get from VSDs 1. Energy Savings With rotodynamic pump installations, savings of between 30% and 70% have been achieved in […]

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