The consideration of losses in a dc machine is important for two principal reasons. The dyno allows for variable and full load testing necessary to ensure optimal function. The open circuit test is needed to determine the open circuit characteristic or magnetizing characteristic of a dc machine. 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. It is set for torque control (Fig. 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. The simplest of the indirect test is Swinburne’s test. Brake adjusting the tension of belt, the load is adjusted to give the various values of currents. In this method full load is applied to the machine and output is directly measured. 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. This method has the obvious advantage of convenience and economy. Direct Method of testing of DC Machine is also known as Brake Test. Your email address will not be published. To test your DC motor, touch the leads of the ohmmeter to the leads of the motor. 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. In this method (simplest indirect method) the losses are measured separately and efficiency at any desired load is pre-determined. In this test, power drawn from the supply only corresponds to no load losses of the machines. Basic operational voltage equation of a DC motor is given as E = E b + I a R a and hence, I a = (E - E b) / R a Now, when the motor is at rest, obviously, the back emf E b = 0. Your email address will not be published. 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 … (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. Then we can use Eq. Performed … Do you want some ideas on how to test them? A DC motor must have 100% field strength to produce its maximum torque and to keep the armature amperage within proper limits. During factory tests it is useful to take oil samples before testing and again after testing in order to perform a dissolved gas in oil analysis. 2. The disadvantage of this method is that machine is run light during this test which gives no indication to the temperature rise on load or to the commutating qualities of the machine. One method used in electric motor dynamometer testing services involves applying water flow proportional to the load. Knowing some basic methods and techniques along with having a few test instruments handy helps detect and diagnose problems with ease. DIRECT METHOD OF TESTING: In this method, the DC machine is loaded directly by means of a brake applied to a water cooled pulley coupled to the shaft of the machine. 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. Then we tie one end of the brake band with the ground through a spring balance (S). 1. Plugging. The most important performance tests to be conducted on the dc machine are: The magnetization or open-circuit test. Your email address will not be published. Power required for this test is small. But due to losses, generator output is not sufficient to drive the motor and vice-versa. There are several tests that are conducted for testing a dc machine (generator or motor) to judge its performance. Do you manufacture electric motors? For instance, the motor might be overheating or emitting strange sounds and smells; use these obvious is… to determine the efficiency of the machine. The above tests will be discussed in detail in the coming articles. Where to buy cheap cable for my welding plant. By this method, the efficiency and losses of only small machines can be determined. If the motor itself has developed a fault, the fault may be a burnt wir… Through this test full-load testing of two d.c. shunt machines can be carries out, mainly identical ones. If there is any reading on any of these then the motor is bad, do not use it. 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. The basic circuit for the DC test is shown in the figure. Reduced field strength will cause high armature currents. The open circuit test gives the mmf and hence the excitation current or field current needed to generate the … Brake test is a direct method. The smaller the. We can then use Eq ② or Eq ③ to determine the efficiency of the machine. Electric motors have had a reputation for being a mix of science and magic. So when a motor fails to operate it may not be obvious what the problem is. This method has the obvious advantage of convenience and economy. We apply here a brake to a water-cooled pulley mounted on the motor shaft. This article mainly deals with the determination of the efficiency curve. Then we can use Eq ① to determine the efficiency of the machine. In direct method of testing the generator or motor is put on full … It is difficult to provide full load for the large capacity motor. This test is a key test in the induction motor testing. This current (usually at an applied voltage of 500 volts or more) is measured by the ohmmeter, which has an indicating scale. The input and output are measured and efficiency is determined by η=output/input. The most common method of measuring the efficiency of a dc machine is to determine its losses (instead of measuring the input and output on load). This method enables the determination of losses without actually loading the machine. There are three different methods of determining the efficiency of a dc machine, namely. Sometimes the trouble lies within the power supply, including branch circuit conductors or motor controller. Thus very large machines may be tested as the power required is small. Thus the total power drawn from the supply is only for supplying the internal losses of the two machines. 1. 2). Check for burnt, damage to body or cooling fan or shaft. The important Tests of DC machines are classified as under. You may find that when it runs ungrounded that the casing becomes live at up to supply voltage. The determination of the efficiency curve. When an electric motor is broken, one suspect is the armature with commutator of the motor. 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. The copper losses are calculated from measured values of the various resistances. The power is required to supply the losses only, so there is no difficulty in applying this method even to very large machines. Jammed, binding or mismatched it runs ungrounded that the driven load is to... 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