Replacement of Faulty Diodes (See Fig. 11).

SECTION A THE WINDINGS AND THE MAIN RECTIFIER ASSEMBLY

DISMANTLING THE MACHINE - TM-55-1930-209-14P-9-4_792

TM-55-1930-209-14P-9-4 Water Purification Barges (NSN 1930-01-234-2165) Electric Power System Manual
Page Navigation
748

Voltage Balance between Phases The voltages between the three phases, and each phase to neutral, should be balanced, and if an unbalance is shown on any phase of more than 1%, this indicates that a fault exists in the main stator windings. This test should be carried out with all of the customer's external connections removed to eliminate the possibility of external shorts between the machine and the main isolator. Further tests can be made on the resistance values of the stator windings (see Winding Resistance Chart, at the end of this section). Voltage Balanced but Reading Low when Separately Excited This indicates that a fault exists in either the main rotating rectifier assembly, or one of the excitation windings i.e. the main rotor and/or the exciter stator and rotor. First check that the d.c. separate excitation supply is not lower than 12 volts, and that the speed is correct Rectifier Diodes The diodes on the main rectifier assembly can be checked with a multimeter. The flexible leads connected to each diode should be disconnected at the terminal end, and the forward and reverse resistance checked. A healthy diode will indicate a very high resistance (infinity) in the reverse direction, and a low resistance in the forward direction. A faulty diode will give a full deflection reading in both directions with the test meter on the 10,000 ohms scale, or an infinity reading in both directions. Replacement of Faulty Diodes (See Fig. 11). The rectifier assembly is split into two plates, the positive and negative, and the main rotor is connected across these plates. Each plate carries 3 diodes, the negative plate carrying negative based diodes, and the positive plate carries positive based diodes. Care must be taken to ensure that the correct polarity diodes are fitted to each respective plate. When fitting the diodes to the plates they must be tight enough to ensure a good mechanical and electrical contact, but should not be overtightened. The recommended torque tightening is 2.03 - 4.74 Nm. Surge Suppressor This is a protection device which prevents high transient voltages from damaging the main rectifier diodes. All machines are fitted with a single surge suppressor connected across the +ve & -ve rectifier plates. The resistance of this device varies considerably, depending upon the meter used to check it. As a general guide, the forward resistance should be in excess of 500 ohms. The reverse resistance should be considerably higher i.e. above 10 k ohms. A faulty surge suppressor will be either open circuit or short circuit in both directions. Main Excitation Windings If after establishing and correcting any fault on the rectifier assembly the output is still low when separately excited, then the main rotor, exciter stator and exciter rotor winding resistances should be checked (see Resistance Charts), as the fault must be in one of these windings. The exciter stator resistance is measured across leads X and XX . The exciter rotor and main rotor resistances, can be obtained from the connections to the main rectifier assembly The exciter rotor is connected to six studs which also carry the diode lead terminals. The main rotor winding is connected across the two rectifier plates. The respective leads must be disconnected before taking the readings. A.V.R. Supply Leads from Main Stator The final test which can be made in the separately excited condition is to ensure that the supply from the main stator to the A.V.R. is correct. The voltages at the A.V.R. leads are derived from the main stator winding and the levels can be determined by checking the connections and referring to the wiring diagram. SECTION B THE ELECTRONIC CONTROL SYSTEM A.V.R. Should the previous tests prove successful, any faults can now be assumed to be within the voltage control system and its respective wiring. This system can be affected by bad connections, therefore, the wiring between the auxiliary terminals and the A.V.R. push-on terminals should be carefully examined for broken, loose or corroded connections. The sensing circuit leads have been covered in a previous section. Accessories Forming an integral part of the electronic circuitry there may be fitted one or more electrical accessory. These items must also be checked for loose, broken or corroded connections, and their resistance values checked. See Section 6 - Accessories. 10

Privacy Statement
Press Release
Contact