Category Archive for: «Variable Speed Drives»

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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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PLC Application For Speed Control of AC Motors With Variable Speed (VS) Drive

AC Motor Drive Interface A common PLC application is the speed control of AC motors with variable speed (VS) drives. The diagram in Figure 1 shows an operator station used to manually control a VS drive. The programmable controller implementation of this station will provide automatic motor speed control through an analog interface by varying […]

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Basic Mechanical Terms used in Drives Applications

Index Terms below are the basic mechanical terms associated with the mechanics of DC drive operation. Many of these terms are familiar to us in some other context. Force Net Force Torque Speed Linear Speed Angular (Rotational) Speed Acceleration Law of Inertia Friction Work Power Horsepower Force In simple terms, a force is a push […]

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VLT Drives in Wastewater Treatment Plant Applications

The most common use of frequency converters is to drive sludge pumps, elevators, conveyers, aeration, chemical dosing, clarifiers, digesters, presses and centrifugal dewatering. Treatment steps Preliminary treatment In the beginning water is being pumped into the plant from the collection basin. The frequency converter is using water level as input to control the speed (flow) […]

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Few Words About Frequency Converters

Introduction Since the late 1960’s, frequency converters have undergone extremely rapid changes, largely as a result of the development of microprocessor and semi-conductor technologies and their reduction in prices. However, the basic principles of frequency converters remains the same. Frequency converters can be divided into four main components: 1. Rectifier The rectifier, which is connected to a single/three-phase AC […]

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