Harmonics are created by what characteristics of non-linear loads? The characteristics of non-linear loads that they demand current only during part of the cycle creates harmonic effects. Short circuits currents can reach levels that are hundreds of times greater than the full load current. A typical transformer overload condition may have a current flow that is from one to six times that of normal full load current. Give a compared analysis of the extent of overcurrent for a transformer overload condition as opposed to a short circuit condition. A transformer vault serves what main functions? Transformer vaults serve the following main purposes: Provide a means to isolate a potentially hazardous electrical component from unqualified personnel and contain any fire or combustion that may occur as a result of a transformer malfunction. Why is a megger preferred to an ohmmeter when measuring the insulation breakdown of a distribution transformer? To make this resistance test for insulation breakdown, a very high voltage is necessary beyond the range of a standard ohmmeter. What would safety reasons explain why the secondary circuit of an instrument transformer should be closed whenever there is primary current? Why? If the secondary is not loaded, this transformer acts to step up the primary voltage to a dangerously high level. What are three advantages of the three-phase transformer over three single-phase transformers when transferring three-phase voltage? A single three-phase transformer is cheaper, easier to install, and will operate more efficiently than three single phase units. What are buck-boost transformers used for? A buck-boost transformer can be used when the available supply voltage does not match the voltage required by the load. Which winding of the transformer has the larger conductor size if a 10-KVA transformer with a primary rating of 480 V and a secondary rating of 24 V? Why? The 24 V secondary windings because it would be rated for a higher current than the primary winding.ġ3. Turns ratio and voltage ratio? The turn’s ratio is the same as the voltage ratio. What are the following relationships in an ideal transformer? a. The locked rotor method is probably easier to setup but the dynamic test will give you better repeatability.1. Repeat this test by either switching the lead wires or switching the direction of rotation of the back-driven motor.
While the motor is being back-driven, apply a voltage to the terminals (again, until the current reads 25% of rated full load current). This method requires you to back drive your test motor at a slow speed. The second method requires only 2 measurements but it is a little more complicated test setup. Repeat this a number of times at different locked rotor positions and then take the average resistance.
Using that voltage and current, determine resistance using Ohm's Law. You increase the voltage until the current is at 25% of the rated full load current. There are 2 ways to measure terminal resistance.įirst, you can lock the rotor of the motor and apply voltage to the terminals. You mention that you are measuring "internal resistance" which is often exclusive of the lead wires and brushes (i.e., it is measured from bar to bar on the armature). You should be measuring terminal resistance (resistance from one lead wire to the other lead wire) for IR compensation.
0 kommentar(er)
