0 in the introduction of modern power system, the widespread adoption of capacitor
compensated negative sequence, filter, pressure of pumping unit.
In order to increase the pressure and volume, capacitor often take series parallel method, once the capacitor series (
Connection, foreign will present a general capacity value, ordinary capacitance measuring instrument will not be able to measure the one online capacitance value.
To measure the capacity of a capacitor, the capacitance in parallel systems dismantle down, the actual operation is very complex, and, when recovery insurance fracture and the phenomenon of poor contact, appear easily cause capacitor system input, the differential protection action tripping.
Based on this, this paper introduces a practical capacitor tester.
1 principle of capacitance tester in order to realize do not stitch, simulation of running status of online measurement, can be in on the bus (
I), as shown in figure 1, AI AI
Ac electric pressure to bear on shunt capacitance, then using current clip-on table points don't measure the electrical flow of each measured capacitance, through formula X = U/I calculate the capacitance of capacitive reactance;
Can also according to the formula of R c/t a n (x = x
9 0 °-
To calculate the capacity loss (
R is the resistance of the capacitor, q is the phase Angle between the applied voltage and capacitor current)
Discriminant capacitor oil shortage, thus, carbide and be affected with damp be affected with damp, and so on and so forth.
1 voltage according to the calculation, for the traction power supply system using 4 now.
51 f capacitance, the price of 1 a current, the applied power frequency voltage above 700 v, in order to ensure the safety of operator safety testing equipment, must try to reduce the applied voltage.
The way adopted in the design of frequency conversion, such as using 100 hz voltage, for the same capacitor, voltage can reduce 2 times;
Using 200 hz voltage, can reduce 4 times.
After the test, in order to keep the capacitor is not stored charge, applied voltage and is unfavorable and exorbitant, choose the 12 v.
Capacitance of 1 F, in 5 ohz capacitive reactance is 3.
18 k12, using 12 v voltage, current measured by the clip-on table for 4 ma.
This 4 ma when the current is measured with clip-on table, the accuracy of the output precision is capacitance measurement.
Ordinary ammeter to ensure milliamperes current measurement accuracy is very easy to do, but for clip-on ammeter, it is very difficult, subject to the size of the jaw, closure gap and the position of the wires in pliers mouth, and many other factors.
Is more serious is that under the interference of traction power supply system harmonic, a milliamperes clip-on table of no-load measured values above 2 a, cannot be in field application.
To improve the clip-on table on the accuracy of measurement to ensure that the capacitance measurement accuracy, almost impossible to achieve.
From the point of the test results of the scene, clip-on table to measure the main interference value is 2, 3, harmonic, to eliminate the influence of interference, improve the measurement accuracy must also avoid the influence of the harmonic.
Based on the above two considerations, the use of variable frequency sine inverter circuit, 30 ~ 2000 hz frequency adjustable, maximum current 3 a, the highest voltage 12 v ac RMS.
2 current through the measured capacitance current measurement using ac clip-on measure table, first ask the inner diameter of the clip-on table is slightly greater than the measured capacitance diameter of lead terminal;
Secondly, when using the 200 hz voltage source, the 1 f capacitance, measured by the current which is only 15 ma, as a result, the accuracy requirement of the measurement of clip-on table is also higher.
At the same time, in order to cooperate with single-chip microcomputer, clip-on table of current ratio according to primary 1 ma/secondary parallel 100 ko, resistance, 1 v voltage selection.
3 phase measuring phase Angle between current and voltage being measured for 9 o.
, which indicates that the measured capacitance no loss.
If not 9 o ° Angle, is thought to be caused by loss.
Design with 10 MHZ (
Pulse measurement of phase difference, in 50 hz current to be measured can be 0.
Can be easily calculated on the basis of capacitor dielectric loss and power consumption.
Conclusion portable capacitance tester can simulate condenser system online running state, in the case of not stitch or insurance, easily measure capacitor charged runtime performance capacity and dielectric loss, especially can be easily applied to multiple capacitors in parallel systems, and can be used to check the status of electrical connection capacitor system and insurance and capacitor be affected with damp be affected with damp, the actual situation of oil shortage, etc.
Using frequency sine signals, low voltage, electric current is small, measurement, after the completion of capacitor energy storage, do not need to discharge, no security threat to the operator, very suitable for field use
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