1. Hardware System of Microcomputer Protection Devices
1.1 Data Acquisition Unit
This is the analog input system, including current and voltage formation and analog-to-digital conversion modules, which accurately converts analog input quantities into digital quantities.
1.2 Data Processing Unit
This is the main microcomputer system, including the microprocessor, read-only memory, random access memory, timers, and parallel interfaces. The microprocessor executes various protection programs stored in the program memory, analyzes and processes the data input from the data acquisition system into the random access memory to perform various relay protection functions.
1.3 Digital Input/Output Interface
This is the switching value input/output system, composed of several parallel interfaces, optocouplers, and intermediate relays, to complete functions such as trip output, signal alarm, external contact input, and human-machine interaction.
1.4 Communication Interface
Includes communication interface circuits and interfaces to achieve multi-machine communication or networking.
1.5 Power Supply
The power supply required for the normal operation of the microcomputer protection device.
2. Testing Process of Microcomputer Protection Devices
2.1 Selection of Test Instruments
There are three main test instruments for microcomputer protection devices: the microcomputer relay protection tester, the three-phase current generator, and the multimeter.
1) For testing high-voltage microcomputer protection devices, it is advisable to use a microcomputer relay protection tester that can simultaneously output three-phase voltage and three-phase current and has input timing capability.
2) For testing low-voltage microcomputer protection devices, if the current sampling values are output to the microcomputer protection device through a current transformer, a microcomputer relay protection tester can be used; if the current sampling values are directly output to the microcomputer protection device through a dedicated transformer, only a three-phase current generator can be used to apply test current on the primary side.
2.2 Test Precautions
1) The test instrument and the panel cabinet should be reliably grounded to ensure that the microcomputer protection device and the test instrument share a common ground.
2) During power-up or testing of the microcomputer protection device, it is strictly forbidden to plug or unplug device modules or touch module circuits. If plugging or unplugging is necessary, the power must be turned off first, the external test power must be disconnected, and static electricity on hands should be discharged or an anti-static wrist strap should be worn before operation.
3) When changing test leads during testing, it is strictly forbidden to mistakenly apply high voltage to low-voltage or communication terminals.
4) The selection of test points must be accurate. The voltage and current wires of the tester should not be directly connected to the terminals of the microcomputer protection device, but should be connected at the root of the transformer to detect the attenuation of the signal during acquisition and ensure the completeness of the test.
2.3 Preparation Before Testing
1) Before testing, carefully read the manual or commissioning outline of the microcomputer protection device, and verify that the manual, the nameplate of the microcomputer protection device, the actual drawings, and the transformation ratios of the system voltage and current are consistent.
2) Carefully read the manual of the microcomputer relay protection tester and master the operating procedures before testing. Avoid incorrect operations that may apply unbearable voltage and current to the microcomputer protection device, causing equipment damage.
3) Tighten the screws or quick-connect modules of the microcomputer protection device to ensure secure connections.
4) Enter the protection menu to set the protection settings. When inputting settings, be sure to understand the content of the setting sheet, organize it, and label it for future reference.
2.4 AC Circuit Verification
1) Apply test current on the secondary side of the current transformer in the panel cabinet according to the drawings. When removing bolts, pay attention to labeling and preservation. The test point for voltage analog quantities can be on the terminal block, but ensure that the voltage cannot be transmitted to the small busbar.
2) Change the amplitude and phase of voltage and current on the tester, apply test values, and record the sampling values displayed on the LCD screen of the microcomputer protection device and the actual values of the tester. The error between the two values should be less than ±5%. Test recording points can be recorded at three positions, with one upward (0%, 50%, 100%) and one downward (100%, 50%, 0%) during the test, and the two displayed values should show no significant change. The test table is as follows.
2.5 Switching Value Check
The switching value check should be carried out together with the functional test.
1) Input Switching Value Check
(1) The input switching values of the microcomputer protection device include two parts: one is the hard contact input, which belongs to the broad sense of input switching value check, that is, an external switch contact directly connected to the microcomputer protection device. When the external contact closes, the LCD display will show the defined switching value; the other is the soft contact input, which belongs to the narrow sense of input switching value check, that is, a reaction of an internal logic relationship in the microcomputer protection, such as when an overcurrent fault occurs, the internal logic starts a signal to display "Overcurrent Trip" on the panel.
(2) The input switching value check should be carried out one by one on the drawings, and the corresponding electrical equipment should be opened and closed according to the actual situation to change the state contacts. The switching value state displayed on the LCD screen or the panel indicator light should change accordingly. To ensure reliable operation of the switching value contacts, each switching value should be checked no less than 3 times.
(3) It is strictly forbidden to simulate the conduction of each contact on the backplane terminals of the microcomputer protection device. Only when the state of the actual electrical equipment is not reflected or is incorrectly reflected on the microcomputer protection system, can the switching value be simulated on the backplane terminals to determine whether the problem lies with the microcomputer protection or the line or electrical equipment.
2) Output Switching Value Check
The output contacts are also divided into hard output contacts and soft output contacts. The state of hard output contacts can be measured with a multimeter. The state change of soft output contacts can only be judged based on logical relationships.
3) Switching Value Check
(1) Alarm Signal Contact Check
The alarm signal contact check should simulate the corresponding fault according to the logical relationship. If a fault occurs but there is no corresponding alarm indication or the indication is incorrect, it is judged as an error. For example, when simulating a PT disconnection fault, the LCD display of the microcomputer protection device should show "PT Disconnection Alarm", simultaneously light up the "Alarm" lamp, and activate the "Signal Relay". The alarm signal contact is a momentary contact.
(2) Trip Signal Contact Check
The trip signal contact belongs to the soft contact in the microcomputer protection device. After the protection action that trips, the LCD display shows "xx Protection Trip", and the central processing unit lights up the "Trip" lamp and activates the corresponding "Trip Signal Relay". The trip lamp and central signal contact are latching contacts.
(3) Trip Output Contact Check
The trip output contact belongs to the hard contact in the microcomputer protection device. After the protection action that trips, it sends a signal and activates the corresponding trip output relay, and the trip output contact closes. The trip output contact is a latching contact.
2.6 Protection Function Test
The protection function test is the core content of the microcomputer protection device test, focusing on verifying whether the input settings are correct, and whether the protection action time and output meet the requirements.
1) Definite Time Protection Test
(1) Setting Value Approximation Test Method
Turn off other protection items to prevent misoperation. Set the setting time to 0s, use the tester to approach the setting action value with a step of 0.1A until the microcomputer protection device issues a trip command, and record the actual action value. The error range between this value and the setting value should be within ±5%. Then adjust the setting time to the value required by the setting sheet, and directly apply the actual action value tested above with the tester. At this time, the trip time is the actual trip time, and the error range between this value and the setting time should be within ±5%.
(2) Fixed Setting Value Test Method
Turn off other protection items, and apply 0.95 times, 1.05 times, and 1.2 times the setting action value with the tester. The protection should reliably not operate at 0.95 times, reliably operate at 1.05 times, and test the protection action time at 1.2 times. The error range between this value and the setting time should be within ±5%.
2) Inverse Time Protection Test
Turn off other protection items, apply the setting value corresponding to a certain point in the inverse time formula with the tester, test the action time of the microcomputer protection, and compare the test value with the theoretical time calculated from the inverse time formula. The error should be within ±5%, and it is advisable to select 5 points for this test.
3. Recheck After Testing
3.1 Verify the Setting Sheet
Since protections are often turned off and on during testing, confusion can easily occur. After the entire group test is completed, two people should jointly review the settings.
3.2 Restore Removed Wires
Restore the removed wires one by one according to the drawings or labels, and ensure correct restoration. When restoring current wires, be careful not to connect the polarity of the transformer incorrectly or connect the protection current wires to the measurement position.
3.3 Check the Current Terminal Block Connectors
Restore the opened connectors on the terminal block, and have a dedicated person check them. Even if they are connected together, they must be tightened with a screwdriver to prevent poor contact.
3.4 Tighten All Core Wire Terminals
To prevent loosening of terminals during testing, all core wire terminals must be tightened after testing to avoid poor crimping of the core wires.
