ST SERIES Single-Phase AC Synchronous Generator
ST SERIES Single-Phase AC Synchronous Generator
ST SERIES Single-Phase AC Synchronous Generator
Construction
ST Series generators are rotating field types. In this type of generator, the output power comes from windings are held fixed in position on the motor frame (the stator) while an electrically-generated magnetic field is rotated past the stator windings by turning the rotating assembly (the rotor). The rotor windings carry DC current obtained by rectifying a portion of the generators AC output. This exciting current is self generated, and is used in a manner which causes the output voltage to be self-regulating to a large extent. ST Series generator construction is intended to be drip-proof that is, a few drops of liquid onto the generator should not immediately cause damage. However, like all electrical equipment, the generator should be protected from damp conditions, immersion in water, or water dripping onto the generator. The frame and end covers are cast iron. The stator is built from high quality 0.5mm thick silicon steel laminations, wound with Class E temperature rated insulated wire. The rotor is wound with Class B temperature rated insulated wire. Overall, the generator carries a protective class rating of IP 21. Schematic and details of wiring are shown below.
The output frequency of the generator is completely dependent on the rotational speed of the generator shaft. If accurate output frequency is needed, then some means must be provided to accurately govern the speed of the prime mover which drives the generator. However, the output voltage is also dependent on the rotational speed of the prime mover (as well as the amount of current in the field windings). If very accurate frequency of the
output power is not necessary, as might be the case for incandescent lighting applications, it is possible to use the output voltage as an indicator of the proper rotational speed. All that is necessary is to regulate the speed of the prime mover so that the voltmeter indicates the rated voltage. Since the output voltage depends partially on the prime movers rotational speed, the output voltage provides a fairly accurate estimate of the rotational speed. The resulting frequency may not match commercial power line standards exactly, but the voltage will be correct and for applications such as incandescent lighting, correct voltage and close frequency is sufficient for use.
If an exact adjustment of voltage is needed, you must set both the rotational speed and the current through the field windings. Remove the short connection strip between terminals F2R and R1 in the terminal box, and connect a rheostat (variable power resistor) between these two points. Set the prime mover speed to the exact required speed by means of a tachometer on the prime mover or a frequency meter on the output power. (Either method works equally well as the output frequency is controlled only by the prime mover rotational speed.) The output frequency will now be exactly 50Hz or 60Hz. Adjust the rheostat resistance to set the desired output voltage. Once the rheostat is adjusted in this manner with no load, it is generally unnecessary to readjust it for correct voltage under load. Rheostats should be rated for 10 ohms, 150W for ST1 through ST7.5 generators, and 5 ohm, 200W for ST10 through ST20 generators. Suitable rheostats are available on separate special order at additional cost.
Connect output wiring to the output terminals U1 and U2 inside the terminal box of the generator. Pay particular attention to making sure that the wires connected to the generator output are of a heavy enough wire gauge to carry the output current rated output current. Open the outer covering plate of the rear cover and inspect the brushes to ensure that the brushes are making good contact with the slip rings. If this is the first operation of the generator, the slip rings should be cleaned with fine emery cloth abrasive sheet. Ensure that the wiring to the load is correctly installed, secure, and that switches and fuses or circuit breakers rated for carrying and interrupting the rated power output are in place. Switches and/or circuit breakers capable of isolating all electrical loads should be correctly installed, and should be opened before starting the generator. Once the generator is up to speed and indicating the correct output voltage, the switches may be closed.
a. Remove the load(s) from the output by opening the output switch(es). b. Stop the prime mover. Cautions: a. Be very careful not to allow short circuits at the output of the generator. This can damage the rectifier diodes in the voltage regulating circuit. b. Before stopping the generator, remove all output electrical loading first before turning off the prime mover. If you turn off the prime mover while the generator is under load, the resulting spin-down and gradually reducing electric fields will erase the residual magnetism in the rotor that allows the generator to start selfexcitation. c. If the residual magnetism in the rotor is too weak to start self-excitation, the rotor will need to be re-magnetized.
Necessary Precautions
When inspecting and overhauling the generator, follow these precautions:
a. Keep the disassembled parts in a suitable container to prevent loss or contamination. b. Mark terminal leads before disconnecting them so they can be easily identified and replaced in the correct positions on reassembly. c. Whenever the bearing covers are removed, take care to prevent contamination of the bearing with dirt and dust. Clean the surrounding area before opening the cover, and protect the bearing cover and bearing with clean paper. d. When mounting a brush, make certain that its position is correct and that it makes good contact with the slip rings. e. After the generator is properly installed, turn the rotor by hand to make sure that it moves freely.
KW A ST1-2 ST2-2 ST3-2 ST5-2 ST2 ST3 ST5 ST7.5 ST10 ST12 ST15 ST20 ST24 1 2 3 4 2 3 5 7.5 10 12 15 20 24 190 190 216 216 216 216 254 254 279 279 318 318 318 B 159 159 178 178 178 178 254 254 203 203 228 228 228 C
Installation Dimensions External Size Wt. (kg) D E F G H K a b h1 h L1 L2 g 70 28 60 8 24 112 12 30 220 15 335 410 235 30.5 35 70 28 60 8 24 112 12 30 220 15 335 410 235 30.5 40 89 89 89 89 108 108 121 121 133 133 133 32 32 32 32 38 38 42 42 48 48 48 80 80 80 80 80 80 110 110 110 110 110 10 10 10 10 10 10 12 12 14 14 14 27 27 27 27 33 33 37 37 42.5 42.5 42.5 132 132 132 132 160 160 180 180 200 200 200 12 12 12 12 15 15 15 15 19 19 19 34 34 34 34 50 50 60 60 60 60 60 250 250 250 250 310 310 339 339 378 378 378 18 18 18 18 25 25 25 25 30 30 30 385 385 385 385 440 440 480 480 540 540 540 480 480 480 480 580 580 610 610 660 660 660 270 270 270 270 325 325 365 365 400 400 400 34.8 34.8 34.8 34.8 40.8 40.8 44.8 44.8 51.2 51.2 51.2 60 65 65 70 120 130 140 155 192 202