Transformer load box

The measurement accuracy of the transformer load box is easily affected by the secondary side load. If the load is not matched, it can lead to problems such as differential ratio and angle deviation exceeding the standard, which in turn affects the reliability of the power measurement and protection system.

Core Definition and Working Principle

The measurement accuracy of the transformer load box is easily affected by the secondary side load. If the load is not matched, it can lead to problems such as differential ratio and angle deviation exceeding the standard, which in turn affects the reliability of the power measurement and protection system. The core function of the transformer load box is to simulate the true load state of the transformer secondary circuit and establish a standard testing environment for transformer calibration. Its working principle is to construct an impedance circuit that meets the testing standards by combining precise resistors, capacitors, inductors, and other components, and connect it between the secondary end of the tested transformer and the calibrator, so that the transformer is under load conditions close to actual operation. For example, the current transformer load box needs to be connected in series between the K2 end of the transformer and the Tx end of the calibrator, while the voltage transformer load box is connected in parallel to enable the calibrator to accurately detect the actual error of the transformer. Compared to simple loads such as ordinary resistors, it can accurately control power factor and load capacity, avoiding calibration result deviation caused by load parameter distortion.

Main classifications and characteristics

Transformer load boxes can be classified into different types according to their adaptation objects and adjustment methods, and each type of product is suitable for different scene requirements. According to the adaptation object, it can be divided into current transformer load box and voltage transformer load box. The former supports secondary current testing of 1A or 5A, with a rated capacity typically ranging from 2.5-80VA, which can meet the testing needs of most current transformers. Its load is measured in VA, and the resistance value of the secondary load of the current transformer can be converted to capacity through a formula; The latter is suitable for 100V secondary voltage, with a rated capacity range of 1.25-158.75VA, and is commonly used for insulation performance and error stability testing of voltage transformers. According to the adjustment method, it can be divided into fixed and adjustable types. Fixed load boxes are suitable for laboratory standard testing, with stable performance and small errors; Adjustable load capacity can be flexibly adjusted according to the parameters of different transformers, such as the intelligent model of 0-100VA, suitable for complex on-site testing conditions. In addition, there are compatible products such as TK98-H that can simultaneously meet the detection requirements of current and voltage transformers.

Key technical parameters

The technical parameters determine the adaptation range and calibration accuracy of the load box. In terms of environment, mainstream products are suitable for working environments with temperatures ranging from 15-25 ℃ and humidity below 70% (25 ℃). Some outdoor models can withstand a wide temperature range of 5-40 ℃, and the power frequency is adapted to the 50Hz standard of the power system. In terms of capacity and measurement range, the voltage load box covers 20% -120% of the rated value, while the current load box mostly covers 1% -120%, and can cope with testing conditions such as transformer overload. Accuracy is the core indicator, with most products achieving an accuracy of ± 3%. Some high-precision models also come with fixed error compensation, such as the ± 3% ± 0.0025VA accuracy standard for current load boxes. In addition, the test voltage is generally 2kV, which can meet the safety requirements of insulation testing on the secondary side of the transformer. The power factor is fixed at two common operating conditions: 0.8 (inductive) and 1.0 (resistive).

Core application scenarios

This device is widely used in key areas such as power measurement and testing, production quality inspection, and system operation and maintenance. In the quality inspection of transformer production, a load box is required to apply rated voltage or even 120% of the rated voltage to transformers of different specifications such as 10kV before leaving the factory, comprehensively test the error stability and insulation performance, and screen for unqualified products. In the field of power measurement and testing, when verifying the energy meter on site at a substation, it can simulate the actual load to test the transformer error, ensuring the accuracy of the billing system and avoiding economic disputes caused by measurement deviations. In the operation and maintenance of new energy scenarios such as wind farms and photovoltaic power stations, it is possible to regularly detect the stability of transformer output signals in response to load changes caused by wind speed and light fluctuations, and to proactively troubleshoot equipment failures caused by load matching issues.

Key points for use and maintenance

Proper use and maintenance are key to ensuring its performance. When wiring, the current load box should pay attention to controlling the total resistance of the connecting wires within 0.06 Ω. If a series calibrator is connected, the load of the calibrator should be included in the calculation; The voltage load box needs to ensure reliable wiring to prevent false connections from heating up and damaging the equipment. In terms of environmental control, avoid working in high temperature or humid environments above 65 ℃, and take ventilation and cooling measures when using outdoors. In terms of maintenance, it is necessary to regularly calibrate the equipment parameters. It is recommended to do so at least once a year, and check whether the wiring is loose and whether the internal resistance and capacitance are normal. If any abnormalities are found, they should be repaired and replaced in a timely manner to avoid errors accumulating and affecting the calibration accuracy. In addition, reliable grounding is required during equipment use, which is not only a necessary measure to ensure the safety of operators, but also an important means to prevent electromagnetic interference from affecting test data.