2010-03-08 - The CM-MPN family of 3-phase voltage monitors offer a new cost effective, feature rich, solution for protection of rotation sensitive three phase equipment. Container shipping, rail shipping and 3 phase moveable equipment may be reverse phase connected at any time. The CM-MPN senses this dangerous phase reversal fault and signals a reversing contactor to correct the phase sequence before the equipment starts. The CM-MPN provides safer and more reliable mobile equipment operation for 380 to 690 V systems. See the complete application description . . . read more
The CM-MPN monitors the 3 phase voltages for proper voltage level on all three phases during a short start up delay. Relay R2 energizes first if the phase sequence is correct. When all voltages are acceptable internal relay R1 energizes allowing the motor or equipment to start. These contacts are connected to a reversing contactor to automatically correct the phase sequence (if needed) before permitting the equipment to energize. (see application images).Application Description: To use this application the phase sequence monitoring function must be selected, the operating mode must be 2x1 c/o (SPDT) and the control circuitry must be wired as shown.
At the end of the 200 ms "ts2" startup delay, if the phase voltages are present and the phase sequence is acceptable, R2 (in circuit diagram K1) energizes transferring contacts 25-26, 25-28. This establishes the correct state of the reversing contactor before power is applied. (50 ms later) At the at the end of the 250 ms "ts1" startup delay, R1 (in circuit diagram K1) energizes transferring contacts 15-16, 15-18. If the phase sequence is correct, closing the R1 15-18 contacts applies power to the K2 coil of the reversing contactor. The motor is energized and rotates in the forward direction. If the phases are reversed, R2 does not energize after the Ts2 time delay. When R1 energizes the K3 coil of the reversing contactor is energized effectively reversing (correcting) the phase sequence problem. The motor starts and runs in the forward direction. If an over, under or unbalance fault occurs the R1 15-18 contacts open, however the R2 contacts do not transfer as they only respond to phase sequence, in this application.
inhibiting means for inhibiting the operation of said write-in means, when a predetermined time delay interval has elapsed after the system has been rendered operable, in order to lock the stored phase sequence information in said memory device;
and switching means, responsive to said read-out means, for interconnecting the three terminals of the three-phase AC power supply to the three terminals of the load in accordance with the interconnection pattern required to provide the load with the desired phase sequence.
This invention relates to a system for sensing the phase sequence of a three-phase AC power supply and for connecting a phase-sensitive, three-phase load to that power supply in a manner dictated by the phase sequence sensed in order that the AC power, as applied to the load, will have a desired sequence.
The invention may be employed in any three-phase electrical system where a phase-sensitive load is employed, such as a motor-driven compressor for a refrigeration system. Unless the phase voltages are applied to the motor in the correct sequence, the motor will rotate in the wrong direction and the compressor will not function properly. The invention is particularly attractive in an environment where the AC power source must be energized and requires a warm-up or stabilizing period during which the line voltages slowly build up to normal magnitude and, moreover, where the AC supply provides phase voltages having either one of the two possible phase sequences. For example, this may be the case when an engine generator (such as a diesel generator) is employed as the three-phase AC power source. Hence, the invention is ideally applicable to a refrigeration system in a truck.
The present invention provides a novel phase sequence correcting system for insuring that the phase voltages applied to a three-phase load are correctly sequenced. This is achieved by means of a unique digital logic arrangement which is of relatively inexpensive construction; requires very little power; is highly efficient, accurate and reliable; and can be contained within a small space. SUMMARY OF THE INVENTION
The phase sequence correcting system of the invention controls the coupling of a three-terminal, three-phase AC power supply to a three-terminal, phase-sensitive load to apply three-phase power to the load in a desired phase rotation sequence. The system comprises a phase sequence sensing means for detecting the phase rotation sequence of the three-phase AC power supply. There is a memory device and write-in means, which responds to the sensing means, for actuating the memory device to store information therein representing the phase sequence of the AC power supply. Inhibiting means inhibits the operation of the write-in means, when a predetermined time delay interval has elapsed after the system has been rendered operable, in order to lock the stored phase sequence information in the memory device. Read-out means is provided for reading out the stored phase sequence information from the memory device. Finally, the system comprises switching means, responsive to the read-out means, for interconnecting the three terminals of the three-phase AC power supply to the three terminals of the load in accordance with the interconnection pattern required to provide the load with the desired phase sequence. DESCRIPTION OF THE DRAWING
The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further advantages and features thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawing which schematically illustrates a phase sequence correcting system, constructed in accordance with one embodiment of the invention, and the manner in which the system controls the coupling of a three-phase AC power supply to a phase-sensitive, three-phase load. DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
The phase sequence of the three phase voltages produced by AC power supply 10 may be either ABC or BAC. To explain, when the sequence is ABC the phase on line conductor A will lead that on conductor B by 120° and the phase found on line conductor C will lag phase B by 120°. When the only other possible phase sequence (namely BAC) is present at the output of power supply 10, phase B leads phase A by 120° and phase C lags phase A by 120°. In the particular embodiment illustrated it will be assumed that phase-sensitive load 12 is a compressor motor and requires the phase sequence ABC or L1-L2-L3 in order to rotate in the right direction. In other words, the phase on line conductor L1 must lead that on line conductor L2 by 120°, which in turn must lead the phase on line conductor L3 by 120°. As will be explained, AC power source 10 will be appropriately connected to load 12 so that the load receives the three phase power in accordance with the phase sequence L1-L2-L3.
The network comprising resistors 14, 15, 16 and 17 and capacitor 18 provides a relatively simple sensing arrangement for detecting the phase sequence existing at power supply 10. The resistance of resistor 14 is made equal to the reactance of capacitor 18 at the commutating frequency. When supply 10 provides 440 volts, resistors 15, 16 and 17 preferably have the resistances 36K, 3.3K and 56K ohms respectively. The manner in which the detector operates is described in detail in "Electrical Engineering Science," by Preston R. Clement and Walter C. Johnson, McGraw-Hill Book Company Inc., New York, 1960, pages 558 and 559. By means of vector diagrams, it can be demonstrated that when the phase sequence is ABC at power supply 10 the alternating voltage between circuit junctions 19 and 21 will have a relatively high magnitude, whereas that alternating voltage will be of relatively low magnitude when the phase sequence at power supply 10 is BAC. This voltage is appropriately divided by resistors 15 and 16 to provide, across resistor 16, a trigger voltage for silicon unilateral switch or SUS 23 having a value within the switching range of the switch. When the phase sequence is BAC the alternating voltage across resistor 16 will be less than the threshold level of SUS 23 and thus will be insufficient to turn that device on. On the other hand, in the presence of phase sequence ABC, the voltage across resistor 16 will be sufficient to trigger SUS 23 into conduction early in each positive half cycle, thereby causing current flow through the light emitting diode or LED 24 of optically coupled isolator 25. Resistor 26 prevents false triggering by leakage currents in LED 24 and SUS 23. Diode 28 is included to maintain the same impedance in both current directions between junctions 19 and 21.
Attention will now be directed to timer 52 and its function. When the entire system is intially rendered operative or turned on, transients could occur or power supply 10 may require a few seconds to build up the line voltages to their normal magnitude. During that stabilizing time, the signals applied to coupler 25 may be erratic before the switching transients die out and the line voltages reach their normal magnitude. For that reason, it is important that no connections be made between power supply 10 and load 12 until a stable phase sequence signal is determined at the end of the stabilizing period. Timer 52 insures that no connections are made to the load until that period has passed. It may take any of a variety of different constructions in order to initially produce a logic "0" output at the instant the system is turned on and to maintain that logic "0" signal until a predetermined time delay interval (namely the stabilizing period) has elapsed. For example, this time delay may be made around 5 seconds. At the conclusion of the time delay, the output of timer 52 should produce a logic "1" signal which remains so long as the system remains energized. Timer 52 may, for example, take the form illustrated and described in "Electric Design," Jan. 4, 1974, page 158. 2b1af7f3a8