跳至主要内容

The general tests of electric motors：2

2. Determination of dc resistance of winding:
1) Significance of dc resistance measurement:
The dc resistance of the windings in cold state is one of the main parameters of three-phase asynchronous motors. By comparing the measured value of the resistance of the windings with the design value, it is possible to check whether the windings have broken wires and short-circuit between turns, whether the welding parts have virtual welding or open welding, whether the contact points have bad contact and other phenomena.
2) Dc resistance measurement method:
Measuring the dc resistance of the motor should be done when the winding is cold.First, place the motor indoors for a period of time, and measure the temperature of the motor winding end or core with a thermometer.At this time, the measured temperature is the actual temperature of the winding in the cold state.If the temperature of the winding end or core cannot be measured, the temperature of the housing may be substituted.For large and medium motors, the thermometer should be placed for at least 15min.
The direct current resistance of the winding is measured by a double - arm or single - arm bridge.Resistance at or below 1 ohm must be measured using a double arm bridge.When using automatic detection device or digital micrometer to measure the resistance of the winding, the test current through the measured winding should not exceed 10% of its normal operating current, the power on time should not exceed 1min.
Open the cover of the junction box for measurement. For the three outgoing windings in the junction box, the dc resistance of l1-l2, l2-l3 and l1-l3 windings shall be measured respectively.For the motor winding with six outgoing terminals, the dc resistance of U1 -- U2, V1 -- V2 and W1 -- W2 phases should be measured.
                     
3)Judgement of dc resistance:
At present, most of us use direct resistance tester to measure the winding dc resistance, making the measurement of dc resistance more convenient and fast.The measured dc resistance value is recorded. The dc resistance of each phase or each branch winding should not be more than 2% of its minimum value after correcting the errors caused by different lead lengths.The relative change should not be more than 2% when compared with the value measured at the same temperature;For stator windings already connected internally, the measured dc resistance imbalance should not exceed 1%.

评论

发表评论

此博客中的热门博文

Advantages and disadvantages of rare earth permanent magnet synchronous motor compared with squirrel-cage asynchronous motor

A ：high efficiency and energy saving 1) no slip error, no fundamental wave loss of iron and copper on the rotor; 2) the rotor permanent magnet is used for excitation, and the power factor can reach 1, saving the reactive power. On the other hand, the stator current decreases, the stator copper loss decreases, and the efficiency increases. 3) the polar arc coefficient is generally greater than the polar arc coefficient of the asynchronous motor. When the power supply voltage and the stator structure are fixed, the average magnetic density is smaller than the asynchronous motor and the iron loss is smaller. 4) stray loss of rare earth permanent magnet synchronous motor: it is generally believed that the non-sinusoidal magnetic field of the permanent magnet increases the stray loss, but on the other hand, the large air gap of the rare earth permanent magnet synchronous motor reduces the stray loss. B ：small size, light weight, high power density 1) analysis from the persp...
发表评论
阅读全文

A detailed explanation of the causes of excessive three-phase motor current

When the motor current is high, it is often reflected in the serious heating of the motor. The following seven points basically summarize the reasons for the excessive current of the motor. Let's learn about them. Ⅰ. power supply problem In terms of power supply, the motor may overheat for the following reasons: 1, the power supply voltage is too high When the power supply voltage is too high, the electromotive force, flux and flux density of the motor increase accordingly. Since the size of iron loss is proportional to the square of magnetic flux density, the iron loss increases, leading to overheating of the core. The increase of magnetic flux leads to the sharp increase of excitation current component, resulting in the increase of copper loss of stator windings and overheating of windings. Therefore, when the power supply voltage exceeds the motor's rated voltage, the motor will overheat. 2. Too low power supply voltage When the power supply voltage is...
发表评论
阅读全文

The general tests of electric motors：1

The comprehensive inspection and maintenance of the motor not only includes the routine motor cleaning, the measurement of tolerance , the replacement of bearings, the inspection of leads, but also includes some test items. Below I make a simple summary of the general test items of the motor. The inspection test items of three-phase asynchronous motor include: insulation resistance measurement, winding dc resistance measurement, voltage withstand test and no-load test, etc. 1. Measurement of insulation resistance: Measuring the insulation resistance between each phase winding and each phase winding on the housing is the most convenient and non-destructive inspection of insulation.Though these inspection, it detect whether the winding insulation is seriously affected by moisture or has serious defects. The following defects can also be found effectively: the overall insulation quality is poor; Insulation become damp; There are penetrating conductive channels between the...
发表评论
阅读全文