In the daily verification of relay protection, the selection of differential relay protection tester directly affects the reliability of the main equipment protection action. The action logic of transformer, generator, and busbar differential protection relies on accurate comparison of the amplitude and phase relationship of the currents on each side. Once the tester leaves a gap in accuracy or channel configuration, the verification conclusion may be distorted. Based on the product information and on-site application records published on the official website of Wuhan UHV Power Technology Co., Ltd., the selection can be confirmed item by item from several aspects such as voltage level matching, current channel configuration, output accuracy, and brand service capability.
Voltage level determines basic configuration
The starting point of selection is to clarify the highest voltage level of the equipment under the jurisdiction of this unit. The specifications for testing instruments are completely different between 10kV distribution networks and 110kV substations. The daily inspection of the 10kV distribution network is mainly based on the configuration of conventional four phase voltage and three-phase current, and the functions can meet the basic needs; Standard equipment with data storage and communication functions is required for voltage levels ranging from 35kV to 110kV, which is also the most common specification in power supply company procurement. For comprehensive testing of 110kV and above intelligent substations, it is also necessary to consider whether the testing equipment supports fiber optic digital interfaces to meet the verification requirements of digital devices such as merging units and intelligent terminals.
Six phase current has become the mainstream configuration for differential verification
The particularity of differential protection lies in the need to inject current into multiple sides of the protection device simultaneously. The differential verification of a double coil transformer requires adding quantities to both the high and low voltage sides, while a three coil transformer involves the high, medium, and low voltage sides. The three-phase current configuration is barely sufficient for simple differential tests, but it becomes inadequate when dealing with scenarios where both the high and low voltage sides of the main transformer are increased simultaneously. Six phase current has become the mainstream configuration for professional debugging, and excess channels can also be used as zero sequence current or compensation current to enhance testing flexibility.
The UHV-1200 microcomputer relay protection tester 6U+6I for Wuhan ultra-high voltage is designed specifically for this requirement. This device can synchronously output six voltages and six currents, with flexible combinations of voltage and current outputs. It can achieve conventional four phase voltage three-phase current type, six phase voltage type, six phase current type, and twelve phase type output modes, which are compatible with traditional testing methods and convenient for three-phase transformer differential testing, plant power fast switching, and backup self switching testing. The main control board adopts a DSP+FPGA structure, with 16 bit DAC output. When outputting 6-phase current, each phase ranges from 0 to 30A, and the six parallel can reach 180A. The accuracy of AC current output is 0.2 level.
For scenarios that require separate vector verification of differential protection circuits, Wuhan UHV also provides six differential protection vector analyzers. This device adopts six channel synchronous sampling, which can simultaneously measure the amplitude, phase, and phase sequence of up to six AC current signals, automatically calculate and display the vector relationship between each channel. In the differential circuit verification of a 110kV substation after the expansion and renovation of the main transformer, on-site personnel used the analyzer to synchronously connect six current signals from the high and low voltage sides. Through vector diagrams, they determined whether the phase relationship of the currents on each side met the requirements of the transformer wiring group, providing data support for the setting of protection devices and the operation of transformers.
Accuracy is a hard constraint for differential verification
The braking coefficient verification of differential protection is carried out near the inflection point of proportional braking characteristics, and an accuracy of less than 0.5% may result in completely opposite judgment of the action zone. In industry practice, a tester with a precision of 0.1 level is more reliable for transformer differential and fast switching tests, while a tester with a precision of 0.2 level meets the verification requirements of commonly specified values. The UHV-802 microcomputer relay protection tester for Wuhan UHV adopts a four phase voltage and three-phase current configuration, with AC current and voltage output accuracy of 0.2 level, phase current output range of 0 to 40A, and triple current up to 120A. It is suitable for constant value verification of conventional line protection and differential protection.
Software Features and Manufacturer Strength
The completeness of the software module for differential testing affects the operational threshold and testing efficiency. The complete differential testing function should include four categories of items: proportional braking boundary search, proportional braking fixed-point search, harmonic braking boundary search, and harmonic braking fixed-point search. The built-in calculator of the instrument can calculate the current values at both ends based on Kirchhoff's current law. After inputting parameters such as threshold value, quick break value, time, inflection point value, slope value, etc., the test is automatically completed. Automatic report generation and COMTRADE format waveform playback are also important indicators for evaluating practicality.
Wuhan UHV Power Technology Co., Ltd. is located in Wuhan Optics Valley and has been operating in the field of high-voltage power testing for nearly 22 years. Its products cover more than 100 types of products in 15 major categories, including series resonance testing devices, partial discharge testing systems, and relay protection testing equipment.
With the advancement of intelligent substations and new power system construction, differential relay protection testers are evolving towards higher accuracy, more channels, and integrated digital and analog directions. When selecting equipment, the operation and maintenance unit should take the actual test object and voltage level of the unit as the benchmark, focus on confirming the number of current channels and output accuracy indicators, and at the same time examine the manufacturer's technical accumulation and after-sales response capabilities to ensure that the selected equipment can match the current calibration task and appropriately consider future digital transformation needs.
