Excitation Speed Governor Sample

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2018-01-22 10:38

Electromagnetic Coupling Excitation Speed Governor

1.Basic Principle:

The speed-regulating device is composed of two internally and externally concentric rotating bodies: the inner rotating body is provided with magnetic poles and excitation windings made of magnetic materials, and after the direct current is applied to the excitation windings, N and S alternatively distributed magnetic poles are generated along the circumference of the rotating body. which are referred to as magnetic rotor; the external rotating body is equipped with a copper conductor compounded on the magnetic material, and is referred to as copper rotor. The magnetic rotor generates magnetic lines of force across the space gap and the copper conductors on the copper rotor and forms a magnetic circuit in the magnetically permeable material. In order to reduce the eddy current loss in the magnetic material of the copper rotor, it’s better to use silicon steel sheet as the magnetic material of the copper rotor. In order to reduce the excitation power, the smaller the gap between the two rotating bodies is, the better it is, as long as relative rotation can be formed. The rotating shaft of a rotating body is connected with a rotating shaft (usually a three-phase asynchronous motor) that generates an active torque, and it is called an active shaft for short; the rotating shaft of the other rotating body is connected with the rotating shaft of the dragged machine, and it is simply referred to as a driven shaft. When the excitation windings are energized, when the two rotating bodies produce relative motion, an induced current will be generated in the copper rotor, and this current will prevent the relative motion from being generated under the influence of the magnetic field force. The torque on the drive shaft is also transmitted to the driven shaft by the action of the electromagnetic force. According to the law of electromagnetic induction and Ampere’s law, the magnitude of the transmission torque M has the following relationship:

M=k(n1-n2)B2L2r2

Where: B is the air gap flux density, L is the length of the copper rotor, r is the radius of the copper rotor,

N1 is the revolving speed of the drive shaft, n2 is revolving speed the driven shaft, and k is the proportionality constant.

We know that the magnetic flux density B changes with the magnitude of the excitation current, and changing the magnitude of the excitation current is very simple and easy. Therefore, the magnetic flux density B can be easily changed from zero to a maximum value. If the output torque is constant, changing the magnetic flux density B can change the revolving speed n2 of the driven shaft from 0 to n1. To maintain the revolving speed n2 of the dragged machine constant, changing the magnetic flux density B can change the transmission torque M with the change of drag torque of the dragged machine, that is, when the output power continuously changes, changing B can have the dragged machine operate at a constant speed.

2. Main Features

The greatest advantage of this device is its high transmission efficiency. At full speed operation, the efficiency of this device is similar to that of variable frequency speed control and permanent magnet speed control. However, at the half-speed operation, the transmission torque M is 1/2, the square of the magnetic flux density B is 1/4, the excitation loss is the square of the excitation current, and the excitation loss is only 1/16 that during the full-speed operation, and the efficiency is higher than the above two speed control technologies. So it has great energy-saving significance.

Compared with the frequency control device, this device has the following advantages:

1. Design life is much longer than that of frequency control devices;

2. The operational reliability is high and the equipment is rarely repaired;

3. There is no harmonic pollution to the power grid, and frequency control devices will cause significant harmonic pollution. Harmonic components will cause additional heating and loss of the motor in the power grid. After the harmonic waves exceed a certain standard, additional harmonic elimination devices should be installed according to regulations of the power grid management department.

4. There is no rigid connection between the motor of the device and the dragged machine, so the mechanical vibration is relatively small;

5. The production cost is lower than that of the frequency control device.

Compared with the electromagnetic speed control motor, the device mainly improves the efficiency greatly. Efficiency of the electromagnetic speed control motor is only 80%. The reason for the low efficiency is that the eddy current loss in the iron cylinder (external rotating body) is too large, and the manufacturing capacity is only below 100 kW. At present, production has basically stopped. The manufacturing capacity of this device will no longer be limited, and that of air cooling ones can be 3000kW, or even greater.

Compared with the permanent magnet speed control motor, the device is mainly easy to adjust. The permanent magnetic speed governor changes the magnetic flux density B by adjusting the air gap between the permanent magnet and the copper conductor when on load. As the load changes, the air gap adjustment mechanism also moves inconstantly, causing mechanical wear and energy loss. Second, as time goes on, the performance of the permanent magnet changes, which affects the output power. In addition, in the case of a strong magnetic field, the assembly of the mechanism requires high environmental conditions.

In modern production and life, all electric power-driven machinery is inseparable from the AC asynchronous motor and this kind of motor has the advantages of economy, reliability and high efficiency. However, it is not speed-adjustable, or it is difficult to adjust the speed, the speed adjusting scope is small, and the efficiency is low. For a long time, the situation of energy waste has been very serious. Due to design and margin, output of all existing motors is more than 10% higher than the actual need (margin of flow or air flow), and some even reach 30%, in order to meet the actual operating conditions, valves or dampers have always been used at the motor load terminal (fans, pumps) to regulate the flow or pressure, and this regulation mode has caused the following undesirable consequences:

1. High energy consumption: the use of a valve or a damper to regulate flow or pressure results in serious tube damage, low system efficiency, and energy waste;

2. Poor safety and stability of the system. When the flow rate is reduced and the opening of the valve is reduced, the fan or the pump runs at a position of poor efficiency and high wear. The long-term partial valve opening will accelerate the wear of the valve body itself, resulting in poor control characteristics of the valve, shortened equipment life and more maintenance.

3.Application Areas

The device is specially used for machines dragged by squirrel-cage motors. In occasions where the dragged machine requires a great change in speed, the device is installed between the motor and the dragged machine.

4.Model Description

CWTS - 6400H(F)

CW---Magnetic Coupling, TS---Speed Control, 6400---Maximum Transmission Torque, H---Integral with the Motor, F---Independent Installation

5.Product Specification

The basic function of this device is to transmit the torque on the drive shaft to the driven shaft through the action of the electromagnetic force. Therefore, the product specifications are divided based on the maximum transmission torque, and combined with the squirrel cage motor frame number, the product specifications are as follows: