Three-Phase Relay Protection Tester Product Introduction

The three-phase relay protection tester is a specialized instrument used in power plants, substations, and laboratories to verify the performance of relay protection devices. For complex protection schemes such as transformer differential protection, the instrument accurately simulates the amplitude and phase relationships of currents on both sides, testing key performance parameters including the starting current, proportional braking characteristics, and harmonic suppression characteristics. Featuring a portable integrated design, it incorporates a high-performance DSP control module, a high-precision D/A conversion module, and a high-power amplifier module. Operated via microcomputer control with a visual interface, the instrument simultaneously outputs multiple independent current signals to simulate the current differences between the high-and low-voltage sides of a transformer. Utilizing closed-loop control and digital filtering technologies, it ensures stable and accurate output signals, making it ideal for periodic verification and handover testing of differential protection systems.

• The transformer differential protection functions like a coordinated safety valve for dual-side pipeline networks, simultaneously monitoring water flow conditions on both the high-voltage and low-voltage sides. During normal operation, the water flows balance equally on both sides, keeping the safety valve closed.
• The differential test signal simulates the water flow conditions on both sides: under normal operating conditions, the water flow rates on both sides are equal but in opposite directions, resulting in a zero flow difference; during internal faults, the flow difference between the two sides suddenly increases, triggering the activation of the safety valve.
• A qualified differential protection system = a precisely coordinated safety valve: It acts accurately and promptly when the internal fault differential current reaches the set value; during external faults, it reliably locks out even under high braking currents to prevent false activation.
• Non-compliant differential protection = failed interlocked safety valve: either the internal fault progresses severely yet the valve fails to respond, or an external fault triggers false tripping, making it impossible to accurately distinguish faults within or outside the protection zone.

This "differential protection operating characteristic" constitutes the core of our verification. A greater deviation in the braking coefficient and a larger error in the operating current indicate poorer performance of the safety valve and a higher risk to the transformer. Failure to promptly isolate the transformer during internal faults may result in transformer burnout or even widespread power outages.

The differential operating condition simulation testing method employs a precision testing machine specifically designed for conducting "interlocking tests" on dual-side safety valves. This machine can simulate various braking currents and differential current operating conditions, sequentially testing the safety valves' operating thresholds to determine their compliance. The three-phase relay protection tester utilizes this methodology, employing high-precision, independently adjustable multi-channel current sources to perform comprehensive verification of differential protection performance.

• Power Grid Company: Regular calibration of main transformer differential protection, completion acceptance of newly constructed transformer projects
• Power Engineering Company: Transformer Installation and Commissioning, Handover Testing of Differential Protection Devices
• Industrial Enterprises: Daily Maintenance of Differential Protection Systems for Self-Propried Power Station Transformers
• Equipment Manufacturer: Factory quality inspection and characteristic debugging of differential protection devices
• Third-party testing institution: Quality inspection of differential protection devices, judicial appraisal of faults

1. Proportional braking and starting current testing: The most fundamental and core test item conducted on-site. The wiring must strictly adhere to the schematic diagram of the protected device, the actual CT wiring configuration, and the setting notification document. Typically, predetermined currents are applied to both the high-voltage and low-voltage current input terminals of the protection device to simulate the differential current during internal faults and the crossing braking current during external faults, thereby verifying the protection's starting parameters and proportional braking characteristic curve.
2. Current Phase and Hexagram Test: Used to verify the correct phase sequence, polarity, and wiring of the secondary circuit of a current transformer (CT). The tester simultaneously outputs three-phase voltage and three-phase current, generating a current hexagram that assists field personnel in identifying potential misoperation or failure of differential protection caused by incorrect CT wiring.
3. Harmonic braking characteristic testing: This test simulates the excitation inrush current condition during no-load transformer closing. The tester superimposes specific harmonic components (e.g., second and fifth harmonics) on the fundamental current to verify whether the differential protection can reliably trip based on harmonic content, thereby preventing false tripping caused by inrush currents. The physical wiring remains consistent with conventional proportional braking testing, with the distinction lying in the signal waveform configuration within the software.

Next, using the proportional braking characteristic test of transformer differential protection as an example, we will illustrate the experimental procedures and the operational protocols that must be followed.

1. The primary equipment of the transformer must be completely de-energized, and comprehensive safety isolation measures such as power shutdown, voltage testing, and grounding wire installation must be implemented.
2. All trip outlet hard pressure plates and functional soft pressure plates of the tested differential protection device must be removed (including those for high-voltage side, low-voltage side, bus tie, and potential reclosing pressure plates), leaving only the device's DC power supply and AC sampling circuit energized to prevent actual trip incidents during testing.
3. During testing, the instrument housing and protective device housing must be reliably grounded.
4. Record in detail the setting values of the differential protection, including the starting current, braking coefficient, harmonic braking coefficient, as well as the current tap position and CT ratio information.

1. Perform all wiring when the instrument and protection device are completely powered off. According to the design drawings of the protected device and the actual wiring configuration of the on-site CT, connect the instrument's current output terminals to the high-voltage and low-voltage current input terminals of the protection device. If the protection requires voltage for logical judgment (e.g., voltage recovery lockout), connect the instrument's three-phase voltage outputs to the corresponding three-phase voltage input terminals of the protection device.
2. Connect the protected trip output contact (typically a non-electrical protection or signal contact, confirmed to not actually trip) to the instrument's input terminal for detecting the protection action signal.
3. The instrument's grounding terminal must be reliably connected to both the protective device housing and the grounding electrode, ensuring secure and tight wiring without any looseness.

1. 10.4" Touch Screen Display
2. Keyboard Area
   1. [Stop] key: Used to stop a test midway.
   2. [ESC] key: cancel selections.
   3. [Back] key: Used for deleting the previous digit or character when entering numbers or text.
   4. [Start] key: Used to start the test after entering the test module. [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] keys: Used for numeric input.
   5. [●] key: Decimal point key.
   6. [+] key: Plus sign key.
   7. [−] key: Minus sign key.
   8. [TAB] key: Used to switch states via "key trigger" in the "State Sequence" module.
   9. [/] key: Used to enter the "/" symbol.
   10. [Enter] key: Confirm.
   11. [←] key: Move selection to the left or modify data.
   12. [↑↓] keys: Up and down keys, used to move selection or modify data. [→] key: Move the selection to the right or modify data.
3. Connect to the USB communication port of a PC. A USB flash drive, USB mouse, or USB keyboard can be plugged in.
4. Connect to the PC communication port; the device can be operated from a PC via an Ethernet cable.
5. IA, IB, IC, and IN are current output terminals. The small signal lamps above each current terminal (IA, IB, IC) indicate whether the corresponding current output has an open load.
6. UA, UB, UC, UN are voltage output terminals.
7. 8 pairs of dry contact outputs for digital signals. Dry contact rating: DC 220V / 0.2A; AC 220V / 0.5A.
8. Digital input terminals, compatible with both dry contacts and 0–250V potential inputs, 10 channels in total, with the positive terminal as the common terminal.
9. DDC 110V/220V fixed output terminal. DC power supply selector switch with three positions: 220V / 0 / 110V, which can be used as a field test power supply.
10. Note: Before powering on, check that the three-position toggle switch is set to the "0" position. The DC power supply must be switched to the "0" position when not in use or before powering on.
11. Indicator area: Buzzer alarm light, power light, overheat light (indicates protection when the power amplifier in the instrument has been operating for too long and temperature rises), and running light.

1. Reconfirm that all wiring is correct and reliable, with no exposed test wires and all protective tripping plates properly engaged.
2. Turn on the power supply of the instrument host, and wait for the industrial computer to start up normally and enter the software main interface.
3. In the software, select the corresponding test module (e.g., "Differential Protection Proportional Braking"), enter the device setpoint values as prompted, and configure test parameters such as the braking current measurement point, sample delivery time, and contact jitter delay.
4. After confirming that the settings are correct, turn on the amplifier power switch and click the "Start Test" button. The instrument will automatically output the corresponding braking current and differential current according to the preset test parameters.
5. Wait for the test to complete; the software will automatically generate the proportional braking characteristic curve and test report, recording the operating current at each test point and the calculated braking coefficient.
6. After completing all test items, first cease output operations in the software, then shut off the power supply of the amplifier, and finally disconnect the main unit power supply. Only after the equipment is completely powered off may the test cables be removed. Follow the principle of "removing cables before restoration" to re-establish the original wiring of the protective device and the disconnected trip contact plates.

1. Testing is strictly prohibited when the primary equipment is not de-energized and safety measures have not been implemented.
2. It is strictly prohibited to reverse the current wiring between the high and low voltage sides, or to connect an external power source to the instrument's output terminals; doing so may damage the instrument and lead to incorrect protection judgments.
3. The wiring must be determined according to the design drawings before powering on; the device must be turned off before disconnecting the wires. It is strictly prohibited to insert or remove any test cables while the power amplifier is powered on.
4. It is strictly prohibited to directly shut down the instrument while current output is active. First, terminate software output, then sequentially disconnect the power supply and the main unit's power supply to prevent reverse electromotive force or erroneous signals that may cause false protection activation.
5. When testing braking characteristics, test points should reasonably cover the boundary between the action zone and the braking zone. Test points should be densely distributed in areas adjacent to the complete braking characteristic curve to ensure comprehensive verification of the protection's action threshold.

1. The test wiring and parameter settings must strictly simulate the actual field operating conditions to obtain test results comparable to the device's set values.
2. Test results should not be evaluated solely based on an isolated "braking coefficient" value; instead, the action boundary curves plotted at each search test point should be compared with the device's theoretical characteristics and regulatory requirements to determine whether they fall within the permitted action zone or non-action zone.
3. If the braking curve exhibits abnormal deviation or irregular dispersion, first verify that the external CT wiring phase sequence, polarity, and transformation ratio settings are correct. After eliminating potential wiring errors, conduct a thorough diagnostic analysis of the protection device itself.
4. Upon completion of all testing and troubleshooting procedures, the protective device must be restored to its original wiring configuration, set parameters, and all switch positions. Only after verification by a second person confirms accuracy may the device be commissioned to ensure the safe operation of the transformer.