Connect the secondary load.
JIG1021-2007 stipulates that the lower limit load of the voltage transformer is 2.5VA, which is independent of the rated load. If the user has requirements, take 1/4 of the rated load as the lower limit load.
Power voltage transformers often have multiple secondary windings.
The regulations stipulate that when setting the rated load, all windings with load defined secondary loads must be connected; when setting the lower limit load, only the measured winding is set to the lower limit load, and other windings should be unloaded.
The secondary load of the voltage transformer is generally provided by a voltage load box.
The voltage load box usually only has 08 and 1.
The capacity of the load box is generally up to 150VA.
When the load box cannot provide the required power factor and power capacity, or when the voltage transformer with multiple secondary windings does not have a voltage load box of the appropriate range or there are not enough load boxes connected to each secondary winding, the error of the voltage transformer cannot be directly measured.
In another case, if a three-phase voltage transformer with a grounded neutral point is used to measure electric energy according to the three-wire two-element method, when measuring the error of the three-phase voltage transformer under the actual secondary load, it is necessary to set a secondary load with a non-standard power factor.
Configuring such a load box will increase the cost of equipment and the workload of operators, which is very uneconomical.
Electromagnetic voltage transformer The error of the transformer is mainly composed of no-load error and load error.
When the primary voltage of the voltage transformer remains unchanged, the no-load excitation current is basically unchanged.
After the load is added to the secondary side of the voltage transformer, a secondary load current is generated and a primary load current is induced on the primary side.
The load currents on both sides generate resistance voltage drop and leakage magnetic voltage drop on the primary and secondary windings respectively, causing load error.
Since the load error is only related to the load current and the internal impedance of the winding, and the internal impedance of the winding is basically linear, it can be considered that it does not change with the load current.
In this way, the load error is proportional to the load current, and their relationship can be expressed by a primary curve, so the load error curve of the voltage transformer can be calculated by formula or chart.
