The high current generator adopts an energy-saving high-permeability current booster, and is equipped with a digital electric stopwatch to meet time measurement. It has the characteristics of large output power, strong overload capacity, clear reading, and flexible movement. It is suitable for power system technicians to test current transformers, protection devices, and secondary circuit current tests.
The temperature rise test of the high current generator is carried out using the high current generator. The test principle adopts the direct load method, that is, the electrical equipment is operated with actual load, and various electrical quantities and temperature rises of each part are measured. Through the temperature rise test, the aging and damage of insulating materials and structural parts are checked.
1. Basic requirements for temperature rise test of high current generator
1. In order to ensure accurate data measured in the temperature rise test, the accuracy of the meters used to measure stator electrical quantities shall not be lower than 0.5 class, and those used to measure rotor shall not be lower than 0.2 class.
2. The temperature rise test of the generator is a long-term thermal stability test. For each load test, the rotor current is required to remain stable, and the variation range should not exceed 1% of the test current; the stator voltage, current, and power should also be kept as stable and three-phase balanced as possible, with a variation range not exceeding 3% of the test value. For this reason, the automatic voltage regulator should be removed during the test, and the power factor should be maintained at the rated value.
3. During the test of the high current generator, the temperature θ0 of the cooling medium should be at or close to the rated value. Under each test load, the temperature variation of the cooling medium should not exceed 1K.
During the test, under each load, after stabilizing for 1 hour, measure each measured electrical quantity and temperature every 15 or 20 minutes until stable. The so-called thermal stability means that the temperature of each part of the motor does not change by more than 2K within 1 hour. The time required to reach thermal stability depends on the type and capacity of the motor, generally about 3-4 hours.
2. Preparations before the temperature rise test of the high current generator
1. Familiarize with technical data
Before the test of the high current generator, the test personnel should be familiar with the instructions and relevant technical data provided by the electrical equipment manufacturer, especially the insulation structure, insulation class, allowable temperature (temperature rise) values of each part, operating conditions, and the embedding positions of temperature measuring elements.
2. Formulate test plan
Based on the information mastered, the high current generator test plan is formulated in consultation with relevant technical personnel of the power plant.
3. Measure the DC resistance of stator and rotor windings
When conducting the generator temperature rise test, the cold-state DC resistance of the generator stator and rotor windings is very important basic data in the temperature rise test. This is because when measuring the average temperature of the stator and rotor windings under power, the cold-state resistance is used as the reference value to convert the average temperature of the winding, so its measured value directly affects the accuracy of the temperature rise test. Therefore, the DC resistance value should be measured accurately before the test.
Precautions for temperature rise test of high current generator:
1. The test work shall be carried out by at least two people, one operating and one supervising to ensure safety;
2. The shell must be grounded. Do not ignore the prevention of personal safety accidents because of low voltage;
3. The wire from the secondary side of the current booster to the tested object should not be too long, the cross-section should be sufficient, and the contact surface should be cleaned. Otherwise, the joint will heat up, and even the current cannot rise to the rated value;
4. Before work, check that the power supply has sufficient capacity, otherwise the power cord heating and voltage drop will affect normal operation;
5. There should be no flammable materials at the work site. For temperature rise tests, sufficient fire extinguishing equipment should be prepared;
6. For continuous (temperature rise) tests, someone should be on duty at the site. Regularly check the heating condition of the current source equipment, wires, and joints, and make records. Due to grid voltage fluctuations, pay attention to adjusting TD to maintain the rated test current;
7. The test work should comply with the relevant provisions of the electric power safety work regulations and formulate practical safety measures.
