I. Measurement principle The on-site electric energy error measurement uses the fixed low-frequency pulse method in the standard table method, that is, the number of pulses of a certain low frequency (such as the color code on the indicator turntable or the photoelectric pulse of the electronic watch) is stopped by the checklist. The method of the table compares the electrical energy. The relative error γ (%) of the checked table is calculated according to the formula (1).
Where: γ0——the fixed system error (%) of the standard table, when no correction is needed, γ0=0; W——the measured electric energy value, that is, the electric energy value accumulated in the standard table (J); W0——calculated electric energy value That is, when the meter is in error-free operation, when the N low-frequency pulses are output, the energy value (J) that should be accumulated in the standard meter is calculated according to equation (2).
Where: C0 - the pulse constant of the standard table (PL / kW · h or PH / kW · h); n0 - the number of calculated pulses, calculated according to equation (3).
Where: CL - the low frequency pulse constant of the meter being checked (P/kW·h).
Since J=Ws=kW·h/3.6×106, substituting equation (3) into equation (2), the calculated energy value can be written as:
Considering that the accumulated electrical energy is proportional to the high frequency pulse of the standard meter, it can be converted into the calculated number of pulses:
If the table constant is 1600 pulses/kW·h, the standard table, that is, the calibrator has a pulse constant of 3.6 × 107 pulses/kW·h. When N=1, that is, when the number of sampling pulses (number of revolutions) is 1, the number of pulses calculated by the calibrator is 22,500. If the cumulative number of pulses of the calibrator is 22584 and the system error is +0.05%, the relative error of the checked meter is -0.32%. Data processing should be corrected according to the determined system error to improve the accuracy of the measurement.
Second, the wiring method is divided into two types: the first is to connect the meter and the calibrator current loop in series, the voltage terminal is connected in parallel; the second is to use the calibrator clamp-type transformer to sample the current signal, the voltage terminal in parallel. The accuracy of the current loop series measurement is higher, which can reach 0.02 level. When the clamp type transformer is used, it is easy to cause inaccurate measurement and poor repeatability due to unstable sampling, etc. The accuracy is generally set to 0.2.
Third, the choice of wiring method for the measurement accuracy requirements, such as the on-site measurement of the energy meter connected through a dedicated junction box, the current series of current loops is commonly used. In the high-voltage metering, the electric energy meter measures the electric energy by measuring the voltage and current output from the secondary side of the voltage and current transformer. The secondary side of the current transformer in operation is strictly prohibited to open. In the event of an open circuit accident, high voltage discharges will occur between the open ends, jeopardizing the safety of equipment and operators. Therefore, the wiring must be carefully and carefully ensured to be foolproof. For the measurement accuracy is not high, such as the current direct-on energy meter, or the current loop series can not be used, the clamp-type transformer access mode should be used, and the measurement result is corrected according to the determined system error.
Fourth, how to correctly wire the correct wiring is the premise to ensure the safety and accuracy of the calibrator work. For an electric energy meter equipped with a dedicated junction box, the terminal of the current circuit of the external detection device in series is generally reserved, and the current circuit of the calibrator and the meter to be inspected can be connected or restored in series by disconnecting or connecting the current connection piece. The original current path. The specific method is: after confirming that the wiring is correct, gently pull the current connection piece, the connection piece should have no contact discharge phenomenon; at the same time, the calibrator should display the current value of each phase to determine the correct wiring. If there is a discharge phenomenon during the process of loosening the connecting piece, it means that the current circuit of the calibrator and the checked meter is not connected, and the connecting piece should be quickly returned to the original position, and the wiring should be re-examined. After the measurement is completed, the current connection piece should be returned to the original position, and the wiring of the calibrator should be removed after confirming the error. When using a clamp-type transformer, the current should be clamped to the center of the jaws one by one in the correct current direction and phase sequence. The voltage terminal is connected in the correct phase sequence, and the voltage terminal of the meter is connected in parallel with the voltage terminal of the calibrator.
V. Eliminating the measurement error of the clamp-type transformer When measuring with a clamp-type transformer, there is a problem of low measurement accuracy and poor measurement repeatability. Through trial and error, the author found that this is related to whether the surface of the jaw is clean and the contact between the surfaces is tight. If the surface of the jaw is not clean, the surface contact is not good, which will weaken the conduction force of the magnetic line. The pressure generated by the weight of the clamp transformer and the current line caught in the jaw loosen the jaw and increase the distance of the contact surface. It will also weaken the conduction force of the magnetic lines of force. Both of these conditions can make the measurement error negative. Cleaning the jaw contact surface (wiping the jaw contact surface with a flannel) or increasing the pressure of the contact surface (tightening the jaws with a rubber band) can make the contact closer, thereby increasing the conduction force of the magnetic field lines and making measurement errors. Correction.
A model calibrator performs the basic error test data before, after, and after the surface of the jaws is cleaned, as shown in Table 1. The test data confirms that the above analysis is correct, especially the method of increasing the contact surface pressure, so that the effect of correcting the measurement results is more obvious. Therefore, the jaw contact surface must be cleaned before measurement with a clamp-type transformer. In order to completely solve the problem of loose jaws, it is recommended to increase the jaw locking device to ensure the close contact of the jaw contact surface, and improve the accuracy and repeatability of the calibrator when measuring with a clamp-type transformer.
6. Judging the correctness of the measurement results After the calibrator is correctly wired, enter the power error measurement mode, can you measure the relative error of the energy meter under real-time conditions? the answer is negative. If the wiring of the energy meter is wrong, as long as the calibrator is correctly wired to the meter, it can still detect a plausible power error. We can simulate the wrong wiring of the electric energy meter on the electric energy meter verification device, and measure the error of the active power and the electric energy meter with the calibrator, and compare with the standard value output by the electric energy meter verification device and the error of the electric energy meter. The following three measurements of the three-phase four-wire electronic energy meter and three kinds of three-phase three-wire electronic energy meter are measured. Among them, the three-phase four-wire electric energy meter works in three-phase equilibrium state, the phase voltage is 220V, the phase current is 5A, and the power factor is equal to 1; and the three-phase three-wire electric energy meter works in three-phase equilibrium state, the line voltage is 100V, phase current It is 5A and the power factor is 0.94. The wiring conditions and measured data are shown in Table 2.
Among them, Note 1 and Note 3 are the active power value and the power error value measured by the electric energy meter field calibrator; Note 2 is the active power value output by the electric energy meter verification device; Note 4 is the electric energy meter measured by the electric energy meter verification device Actual error.
The above test shows that it is not enough to judge whether an online electric energy meter is correctly metered by using the measured electric energy error when using the calibrator. It should also be combined with the actual electric load, with the calibrator vector analysis function or draw a hexagonal diagram. The method makes it possible to make an error measurement after determining that the electric energy meter itself is wired correctly.
A Main Distribution Frame (MDF) is a signal distribution frame or cable rack used in telephony to interconnect and manage telecommunication wiring between itself and any number of intermediate distribution frames and cabling from the telephony network it supports.
What's more,we can also offer you the MDF Termination Block with good quality and low price.
MDF Patch Panel, Patch Panel Rack, Network Patch Panel
NINGBO YULIANG TELECOM MUNICATIONS EQUIPMENT CO.,LTD. , https://www.yltelecom.com