Electric motors are highly integrated machines that can develop faults in many areas and, if left unattended, a damaged motor can result in dangerous working conditions. AC motor dynamometers and DC motor dynamometers are key to the development and testing of electric motors. Therefore, the efficiency of a dc machine can also be expressed in the following forms: Efficiency = (Input – Losses) / Input ———————–②, Efficiency = Output / (Output + Losses) ——————–③, The most obvious method of determining the efficiency of a dc machine is to directly load it and measure the input power and output power. This figure shows a DC power supply connected to two of the three terminals of a-connected 3-phase IM. The smaller the. 2. Both motor and generator would have run without any external power supply, if there are no losses in the machine. Accuracy in determining the mechanical power output of the motor is limited. The efficiency of a dc machine depends upon its losses. The biggest advantage of Swinburne’s test is that the shunt machine is to be run as motor under no load condition requiring little power to be drawn from the supply based on the no load reading, efficiency can be predicted for any load current. Insulation Resistance Test The test is one of important test in the induction motor routine testing and is done to measure the winding insulation resistance of the armature, field poles, probes, space heater and bearings (if … Performed … When an electric motor is broken, one suspect is the armature with commutator of the motor. The smaller the losses, the greater is the efficiency of the machine and vice-versa. Plugging. Your email address will not be published. This method suffers from three main drawbacks. IEEE Standard Test Procedure for Polyphase Induction Motors and Generators 3 Park Avenue, New York, NY 10016-5997, USA ... motor or generator of any size. The main objective of motor testing is to assess the integrity of a motor and ultimately prevent the occurrence of unnecessary failure. Electrically these two machines are mechanically connected in parallel and controlled in such a way that one machine acts as a generator and the other as motor. Thirdly, even if it is possible to provide such loads, large power will be dissipated, making it an expensive method. Required fields are marked *, Testing of DC Machines (DC Motor and DC Generator), There are several tests that are conducted for testing a dc machine (. First, this method requires the application of load on the machine. This method enables the determination of losses without actually loading the machine. First, losses determine the efficiency of the machine and appreciably influence its operating cost. The output of motor is used to drive the generator and the electrical output of generator is used as an input to the motor. DC Machines can be tested by three different methods namely Direct Method, Indirect Method and Regenerative Method. The most common method of measuring the efficiency of a dc machine is to, (instead of measuring the input and output on load). Your email address will not be published. VEX Robotics DC Motor Testing DC motors are an integral part of hobbyist and competition robotics, and proper motor selection is essential to successful robot design. DC Motor Armature Testing For a DC Motor Armature, There is a simple method of determining the condition of the Armature. The generator can be hand-cranked or line-operated to develop a high dC voltage which causes a small current through and over surfaces of the insulation being tested (Fig. To test your DC motor, touch the leads of the ohmmeter to the leads of the motor. We fix the brake band with the help of wooden blocks gripping on the pulley. Then we tie one end of the brake band with the ground through a spring balance (S). Required fields are marked *. If the motor itself has developed a fault, the fault may be a burnt wir… In the case of a DC motor that has two brushes, none of the brushes needs to be raised, in the case of a DC motor that has four or more sets of brushes, all but two sets to determine the efficiency of the machine. The consideration of losses in a dc machine is important for two principal reasons. These specifications define the method of preparing a sample, the equipment to be used and the test method. To pinpoint specific motor issues, a range of diagnostic tools are available, such as clamp-on ammeters, temperature sensors, megohmmeters (or simply meggers, used for Megger tests), winding analyzers, and oscilloscopes. The most important performance tests to be conducted on the dc machine are: The magnetization or open-circuit test. The most common test performed on oil is the dielectric test. This method has the obvious advantage of convenience and economy. When testing an assembled DC motor armature, the best method is to perform whats commonly known as a bar-to-bar test using the motor brushes. In this method full load is applied to the machine and output is directly measured. If brake is to be applied to a series motor, the brake must be tight before the motor is started, otherwise the armature may get damaged and break into pieces. By Indirect method of testing of dc machines, the efficiency of shunt and compound dc machines can be determined. This article mainly deals with the determination of the efficiency curve. Then we can use Eq. For instance, the motor might be overheating or emitting strange sounds and smells; use these obvious is… The open circuit test gives the mmf and hence the excitation current or field current needed to generate the … This method also enables the determination of losses without actually loading the machine. The above tests will be discussed in detail in the coming articles. This method suffers from three main drawbacks. Flux Control Method. In this test, power drawn from the supply only corresponds to no load losses of the machines. We apply here a brake to a water-cooled pulley mounted on the motor shaft. This test is a key test in the induction motor testing. Another possibility is that the driven load is jammed, binding or mismatched. In areas where driving ground rods may be impractical, the two-point method can be used.With this method, the resistance of two electrodes in a series is measured by connecting the P1 and C1 terminals to the ground electrode under test; P2 and C2 connect to a separate all-metallic grounding point (like a water pipe or building steel).The dead earth method is the simplest way to obtain a ground resistance re… The efficiency of a dc machine depends upon its losses. (adsbygoogle = window.adsbygoogle || []).push({}); Though this method is simple, bt involves complication in the measurement of mechanical power input in the case of generator and output in case of a motor. The other machine operates as a generator and feedback power into the supply. Swinburne’s Test of DC Machine (Generator and Motor), How to Select an Electronic Contract Manufacturing Partner, 7 FE Electrical and Computer Practice Problems with Solutions, 2 Important Distribution Transformer Testing Methods. Connect Positive end of the DC power supply at one end and the Negative end at the opposite end. Drop Test Method: Give a DC Voltage across the commutator Segments for one pole pitch area from a Power supply or Battery. This is a direct method of testing the motor. Direct method of testing. By this method, the efficiency and losses of only small machines can be determined. Brake Test of DC Machine. The open circuit test is needed to determine the open circuit characteristic or magnetizing characteristic of a dc machine. If there is any reading on any of these then the motor is bad, do not use it. Dynamic Braking is an inefficient method of braking as all the generated energy is dissipated as heat in resistances. Although the efficiency can be calculated with fair accuracy from the results obtained with this method, the disadvantage of this method is that the machine is run light during the test which gives no indication as to the temperature rise on load or to the commutating qualities of the machines. Swinburne's test3. There are three different methods of determining the efficiency of a dc machine, namely. The test voltages, governed by IEEE, are reflected in Table II. The most important performance tests to be conducted on the dc machine are: This article mainly deals with the determination of the efficiency curve. The determination of the efficiency of DC machine is important for the testing of DC machines. The power is required to supply the losses only, so there is no difficulty in applying this method even to very large machines. Thus the total power drawn from the supply is only for supplying the internal losses of the two machines. When an electric motor fails to start, runs intermittently, runs hot, or continually trips its overcurrent device, there my be a variety of causes. In direct method of testing the generator or motor is put on full … Check for burnt, damage to body or cooling fan or shaft. The simplest of the indirect test is Swinburne’s test. It is also known as reverse current braking. This method consists of measuring the losses and then calculating the efficiency. The Hipot Test for Dielectric Strength: Determining Efficacy of Cable Insulation. to determine the efficiency of the machine. BRAKE TEST ON DC SHUNT MOTOR • Another method of testing the d.c. motor is brake test method. Each revision of the st andard since its 1964 introduction as an IEEE standard ... test is defined and each efficiency test method is now covered in more detail and step-by-step instructions HOPKINSON’S METHOD OF TESTING A DC MOTOR  Two identical dc machines are coupled, both mechanically & electrically  One of these two machines is operated as a generator to supply the electrical power to the motor and the other is operated as a motor to drive the generator  Due to the drop in the generator output voltage we need an extra voltage … There are several tests that are conducted for testing a dc machine (generator or motor) to judge its performance. In the case of a generator, the input mechanical power is measured by connecting some form of dynamo-meter to the prime mover and water resistance load is applied. Where to buy cheap cable for my welding plant. It is not practically possible to arrange loads for machines of large capacity. 2. This method is wasteful since all the input is to be wasted and can only be used in case of small machines due to the difficulty of having enough power and suitable brake arrangements in case of larger machines. There are several tests that are conducted for testing a dc machine (generator or motor) to judge its performance. It is difficult to provide full load for the large capacity motor. 1. Direct test 2. The power that a dc machine receives is called the input and the power it gives out is called the output. Knowing some basic methods and techniques along with having a few test instruments handy helps detect and diagnose problems with ease. The iron and friction losses are determined by measuring the input to the machine on no-load, the machine being run as a motor at normal voltage and speed. Secondly, for machines of large rating, loads of the required sizes may not be available. Your email address will not be published. We can then use Eq ②  or Eq ③ to determine the efficiency of the machine. Test the shunt field continuity by measuring and … What is welding cable? The method may be applied to level compound generators and to shunt motors. Direct method is suitable for small DC machines. The most obvious method of determining the efficiency of a dc machine is to directly load it and measure the input power and output power. Thus very large machines may be tested as the power required is small. The armature terminals or supply polarity of a separately excited DC motor or shunt DC motor when running are reversed. 2). The input and output are measured and efficiency is determined by η=output/input. Therefore, the efficiency of a d.c. machine, like that of any energy-transferring device, is given by; Output = Input – Losses and Input = Output + Losses. The DC voltage is applied to all three phases of the winding and raised slowly to a preprogrammed voltage step level and held for a predetermined time period. 1. In this method (simplest indirect method) the losses are measured separately and efficiency at any desired load is pre-determined. But due to losses, generator output is not sufficient to drive the motor and vice-versa. Mechanical motor testing includes things like looking into the cracks of a motor's rotor and lamination sheet makeup. Do you manufacture electric motors? With the motor at normal operating temperature, the vibration velocity shall not exceed 2.8 mm/s RMS, or 4 mm/s PEAK, in any direction.. For bearings fitted with proximity probes, the unfiltered peak-to-peak value of vibration (including shaft ‘run-out‘) at … The regenerative method requires two identical machines, one of them operates as a motor and drives the other, which is mechanically coupled to it. 2. One method used in electric motor dynamometer testing services involves applying water flow proportional to the load. In this I describe about different testing methods of DC machine like 1. 2). Though this method is very simple in looking but involves complication in the measurement of mechanical power input in the case of a generator, and output in the case of a motor. This current (usually at an applied voltage of 500 volts or more) is measured by the ohmmeter, which has an indicating scale. Consequently, M1 operates as a motor, and M2 as a generator. Direct Method of testing of DC Machine is also known as Brake Test. Power required for this test is small. Iron loss in some cases is as high as 50%. Do you want some ideas on how to test them? The determination of the efficiency curve. Electric motors have had a reputation for being a mix of science and magic. It is set for torque control (Fig. The copper losses are calculated from measured values of the various resistances.

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