The stator winding is subjected to electromagnetic force during operation. When a sudden short circuit occurs at the outlet end, the electromagnetic force will increase by several tens of times. In addition, if the coil of the high-voltage motor is in poor contact with the groove wall, a capacitor discharge will occur, causing electrical corrosion, and the vertical motor must also prevent the wire rod from sinking. Therefore, the stator windings must also take reliable fastening measures.

Electromagnetic force and fastening of the bar in the slot

The electromagnetic force of the inner bar of the core slot is proportional to the product of the current of the upper and lower bars and the length of the bar in the slot; and inversely proportional to the slot width of the stator. The direction of action of the force is that when the current direction in the same slot bar is the same, the electromagnetic force presses the two layers of bars to the bottom of the groove; when the currents in the two layers of the bars are opposite, the electromagnetic force will be the upper bar Pressing against the wedge, the lower bar is pressed against the bottom of the groove. If the same line bar is in the same phase, the current direction is always the same; when the phase current reaches the amplitude, the electromagnetic force acting on the bar reaches the maximum value; if the same line bar is out of phase, the current direction Sometimes the same, and sometimes the opposite, the electromagnetic force acting on the bar is always less than the maximum value described above. According to the calculation results, when a 100,000 kW generator is in normal operation, the electromagnetic force acting on the length of the lower bar is about 20 N, and the electromagnetic force acting on the length of the upper bar is about 15 N. . If the single phase is suddenly short-circuited, the magnetic force is about 120 times of normal operation, and about 70 times if the saturation effect is taken into account.

In large steam turbine generators, the following three structural modes are often used for fastening the stator bars in the slots：
(1) The notch is wedged by a pair of wedges, and the pad is made of an elastic corrugated pad, the groove bottom and the interlayer pad are made of a semiconductor compliant material. After the wire rod is embedded in the groove, it needs to be pressed and cured.
(2) Fix with filler, put a thin liner before the lower thread, and coat the semiconductor filler. After the lower layer rod is embedded, it will fill the gap and embed the layer rod. After the rod in the tank is pressed, it is cured.
(3) The notch is wedged to the head wedge, and the side is wedged by the “expanded slotted die” method. That is, when the core is press-fitted, each stack of a certain length (300~500 mm) is stacked with a core having an enlarged groove shape. After the coil is embedded in the groove, a semiconductor wedge is inserted into the side surface, and the structure does not need to be solidified. 

Stator winding end fastening

For high-voltage, high-speed large-sized motors, the ends are generally extended for a long time, and thus are subjected to large mechanical forces. In particular, the electromagnetic force generated by a sudden short circuit can reach more than 100 times of the steady state, which causes the winding end to withstand the bending moment, and the maximum bending moment is generated at the winding slot. Not only the sudden short circuit, but also the load variation during operation, will also produce impact stress on the winding end. If the winding ends are not securely fastened, the windings at the slots are insulated. Due to the constant small impact, frequent vibrations will occur, causing the insulation to be injured, dropped, or even broken, resulting in a high voltage breakdown accident. Therefore, the winding ends must be securely fastened in the axial, radial and tangential directions.

The stator winding bar can be fixed by a comb tooth plate or a counter wedge insulating block at the slot.

For medium and small capacity turbo generators, the ends of the windings can be entangled on the end hoops with impregnated non-woven glass ropes, polyester glass ropes or polyester tapes. The coils are padded with spacers and then fastened with polyester tape. In order to prevent eddy current heating, the winding end supports are mostly made of a non-magnetic material.

For a large-capacity generator or a generator with a high line load (water-cooled motor), the end of the stator winding is fixed to the insulating bracket by an insulating platen.

In order to allow the stator winding bars to have relative displacement to the core, some large-capacity generators employ end-fixing structures that can follow in the axial direction.

For large hydro-generators, in order to prevent the bar from sinking, epoxy polyester felt is used between the end pad, the spacer block, the end hoop, the pressure plate and the like, and the upper and lower bars. Conformal material, or fixed with a polyester felt bundle impregnated with epoxy adhesive.

Reprinted from the network