Correct use and maintenance of the transformer calibrator - News - Global IC Trade Starts Here.

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The measurement accuracy of the transformer calibrator is relatively high, but because of its complicated working circuit, especially its series of technical characteristics, it must be used correctly during verification or measurement.
First, the influence of external magnetic field In the laboratory of the transformer calibrator, the relevant measuring equipment and power supply equipment, and even the current carrying wire of high current should be reasonably laid out, otherwise, the transformer calibrator will be larger. error. In general, at least the transformer calibrator must leave the current riser at a distance of not less than (3 to 15) meters from the high current conductor.
Second, the wiring method When connecting the standard transformer and the tested transformer to the transformer calibrator, you must first ensure that the polarity of the wiring is correct. Otherwise, the signal obtained from the difference circuit may not be the difference between the two currents (or voltages), but the sum of the two currents (or voltages), which may easily burn out the transformer calibrator.
Second, the high and low potential terminals of the transformer must also be considered. For the current transformer, only when the L1 terminal in the primary circuit and the K1 terminal in the secondary circuit are close to ground potential, measuring the current injected from the L1 terminal and the current output from the K1 terminal represent the mutual inductance. The true error of the device. For the voltage transformer, its X terminal and x terminal are at a low potential, and the A terminal and the Q terminal are at a high potential. According to the JJG314-1994 procedure, the a terminal of the standard transformer and the detected transformer a are detected at the timing. The terminals are shorted together and the difference between their secondary voltages is taken between the X terminals of the two. If the polarity of the potential terminal is reversed, it may cause a leakage error. For current transformers and voltage transformers, the influence of this factor is more obvious when the accuracy is higher (for example, above 0.05). When testing on a transformer below 0.1, the effect is relatively weak.
Third, the grounding problem Grounding is a way to reduce the impact of leakage current. When using a transformer calibrator for the measurement of the transformer or the measurement of the impedance admittance, consider whether the circuit of the transformer calibrator is always at a low potential for both the current transformer and the voltage transformer. Leakage current to ground.
However, for the current transformer, the differential comparison method is used for the detection, and the K1 terminal is not allowed to be directly grounded. Therefore, a reasonable grounding point should be selected according to the actual situation of the specific circuit. In order to make this grounding measure effective, when grounding or measuring with the transformer calibrator, be sure to ground the grounding terminal provided on the panel reliably.
In order to reduce the leakage current generated by the primary circuit of the current transformer to the transformer calibrator, grounding measures should also be taken for the primary circuit. In general, when the primary current rating is greater than 1A, it can be grounded on either side of the primary circuit. However, when the primary rated current is greater than or equal to 1A, according to the provisions of JJG313-1994, the imaginary branch shall be used to achieve the virtual ground. Of course, some weak current transformers have an auxiliary ground point in their own circuit and allow direct grounding, which reduces operational troubles.
Fourth, the reasonable choice of the range of the transformer calibrator has more functions, the function switch must be selected when using, the range should be selected. Otherwise it is easy to cause unnecessary human failure. For example, when verifying a current transformer with a rated secondary current of 1A, if the range of the transformer calibrator is inadvertently placed at 5A, it is easy to make the current transformer and the standard current transformer generate 5 times. Overloading, this is very dangerous. Similar problems exist for the verification of voltage transformers.
5. The error characteristics of the load matching current transformer and voltage transformer are very sensitive to the load impedance (or admittance). If the load selection does not match, it is likely to cause misjudgment or make the tested transformer in the standard transmission process. Inaccurate. To this end, the impedance transformer (or admittance) of the standard transformer connected to the transformer calibrator should be matched, that is, the actual load assumed in the verification circuit should be equal to the technical condition of the transformer. The rated load specified in . Since the relevant circuit of the transformer calibrator has already applied a part of the load to the transformer, the internal load (impedance or admittance) of the transformer calibrator circuit (including the conductor) must be tested first. Then, in combination with the actual parameters of the current load box or the voltage load box, an accurate matching can be performed with the appropriate connecting wires before it can work.
6. Polarity test Before the formal verification error, it is necessary to check the polarity of the polarity. If the connection mode is correct, the polarity indicator is still found to be active, indicating that there is a problem with the internal polarity of the tested transformer. Otherwise, Test again. If the measurement line is normal at this time, it indicates that the polarity of the tested transformer is reversed. This step must not be omitted, otherwise it is prone to human accidents.
Seven current transformer secondary open circuit For general current transformers, the number of turns of the secondary winding is very high. Under the condition of working with rated current, once the secondary open circuit occurs, it will produce high on the secondary winding. The open circuit voltage jeopardizes equipment and personal safety. Therefore, when conducting current transformer test, it is forbidden to open circuit at rated current.
8. The core of the demagnetization current transformer generally has two materials, namely iron-nickel alloy (ie, permalloy) or silicon steel sheet. For a current transformer using iron-nickel alloy as the iron core, if the no-load (ie, secondary open circuit) demagnetization is used, the excitation current does not rise, so it is better to use the closed-circuit demagnetization method. The current transformer with silicon steel sheet as the iron core can be used in two ways.
IX. Sensitivity check When using the transformer calibrator for verification or measurement, it should ensure that the measurement line achieves sufficient sensitivity. To do this, check that the line sensitivity is sufficient during the test. The resonant galvanometer should be tuned at any time to maximize sensitivity. However, the sensitivity level should be gradually increased during the test until the line sensitivity reaches the required level.
X. Selection principle of measurement range Since the transformer calibrator performs verification or measurement at different working points of each range, the measurement error generated by itself is not equal. Generally speaking, the closer the working point is to the measurement full scale, Then the measurement error is smaller. Therefore, in order to minimize the measurement error caused by the transformer calibrator, it should be operated as much as possible above half the full scale of each range. Of course, it is better to carry out quantitative error estimation based on the requirements of the test allowable error and the actual error characteristics of the transformer calibrator, which is more reliable. After doing it a few times, there is a quantitative concept.