外文翻译中英文翻译电力绞车的控制.doc

外文翻译、中英文翻译——电力绞车的控制 英文原文 Electrical Winch Controls by Tom Young The form of motor control we all know best is the simple manual station with up and down pushbuttons. While these stations may still be the perfect choice for certain applications， a dizzying array of more sophisticated controls is also available. This article addresses the basic electrical requirements of the motors and user interface issues you will need to address before spcifying， building or buying winch controls. begin with， the manual control stations should be of the hold-to-run type， so that if you take your finger off of the button the winch stops. Additionally， every control station needs an emergency stop E-stop that kills all power to the winch， not just the control circuit. Think about it―if the winch isn’t stopping when it should， you really need a failsafe way to kill the line power. It’s also a great idea to have a key operated switch on control stations， especially where access to the stations is not controlled. Safe operation by authorized personnel must be considered when designing even the simplest manual controls. Controlling Fixed Speed Motors The actual controlling device for a fixed speed winch is a three phase reversing starter. The motor is reversed by simply switching the phase sequence from ABC to CBA. This is accomplished by two three-pole contactors， interlocked， so they can’t both be closed at the same time. The NEC requires both overload and short circuit protection. To protect the motor from overheating due to mechanical overloads a thermal overload relay is built into the starter. This has bi-metallic strips that match the heating pattern of the motor and trips contacts when they overheat. Alternatively， a thermistor can be mounted in the motor winding to monitor the motor temperature. Short circuit protection is generally provided by fuses rated for use with motors. A separate line contactor should be provided ahead of the reversing contactor