According to the requirements of the "pre-regulation", the
Stator Core test of the generator is after reassembling or replacing, repairing the silicon steel sheet or when necessary (including doubts about the temperature of the stator core measuring point; after the first overhaul, after the rotor is withdrawn; This is done after replacing the stator bar or wedge. According to whether the loss and the temperature rise of each part exceed the specified value, it is comprehensively judged whether the insulation between the iron chips is good, and the iron core is prevented from being overheated and an accident occurs.
First, test wiring and method
1. Test wiring diagram
Figure 4-11 shows the three test wirings, the instrument used is not less than 0.5. Prepare more than 20 alcohol thermometers, disperse 10 or more in the circumferential and axial directions of the teeth, place 2 in the crotch, and measure the initial temperature of the core and room temperature. When conditions permit, temperature and recording can be measured with an infrared camera.
2. Calculation of excitation coil and measuring coil
The number of excitation coil turns is calculated according to formula (4-5)
In the formula B - core core magnetic density, generally take 1T or 1.4T (for indirect cooling, turbo generators below 100MW and small capacity hydro-generators can take 1T; for direct cooling of turbo generators and large Hydrogenerator takes 1.4T)
U1——excitation coil voltage, V;
S——the cross-sectional area of the stator core, cm;
L——the axial length of the stator core, cm;
K——core filling factor, taking 0.93;
L1——the total length of the stator core, cm;
L2——the width of the stator core ventilation groove, cm;
n - the number of ventilation slots;
H——the stator core back height, cm;
D1——the effective outer diameter of the stator core, cm;
D2——the effective inner diameter of the stator core, cm;
H1——the height of the stator core, cm.
Excitation current is calculated according to formula (4-6)
Second, the test steps and precautions
(1) Short-circuit the stator windings to three phases with a 50 mm2 cross-sectional area. If the stator winding has a grounding point, it only needs to be short-circuited and cannot be grounded.
(2) Wiring according to the wiring diagram (see Figure 4 - n), so that the excitation coil and the measuring coil are perpendicular to each other.
(3) Turn on the power, quickly turn off the power after reading the indicator value, and calculate the actual magnetic density B' according to formula (4-9).
B'=U2/4.44fSW2=45U2/SW2
U2 in the formula - measuring the voltage value induced by the coil,
W2 - measure the number of turns of the coil, 匝.
The actual magnetic density B' should be consistent with the selected value. If the difference is large, the number of turns should be adjusted appropriately.
(4) Turn on the power again, and after 10 minutes, check the heat condition with an infrared camera. If it is found to be significantly too high, smoking or redness, the test should be stopped and recorded. The meter value or the infrared temperature measurement value is read every 10 minutes, and the power is turned off after 90 minutes (when the magnetic density is IT) or 45 minutes (when the magnetic density is 1, 4T), and the test is terminated.
(5) Note:
1) The excitation and measuring coil wires should be well insulated and do not touch the iron core (metal sheath wires or armored cables cannot be used).
2) Measures should be taken to prevent metal objects from falling into the generator.
3) Measures should be taken to prevent ventilation from affecting temperature.
4) If the local hot spot is found, the temperature difference is not obvious, the magnetic density can be increased to 1.2-1.4T, or the test voltage can be appropriately increased.
(6) Measurement data calculation formula:
September 05, 2022
