EATON Crane Control System Complete Guide

3.5 Protection and Monitoring Relays

C304 series DC overload relay: used to monitor the load of DC motors, providing both inverse time and instantaneous tripping characteristics. The inverse time version uses an oil damper (the transport protection plug needs to be removed before installation), usually set between 125% -175% of the full load current; The instantaneous version uses a dry damper, set between 200% -300%. There are two methods available: manual and automatic reset.

Low voltage monitoring relay (LVMR): specifically designed to solve the problem of voltage loss during the descent (regenerative power generation) of cranes. It continuously monitors the DC bus voltage, and when the voltage is below the threshold (defined by NEMA standards) that can reliably maintain the contactor and relay in contact, it will automatically disconnect the undervoltage relay and trigger the brake to prevent equipment from losing control due to low voltage.

901/902 type magnetic field control relay: used to respond to changes in magnetic field current, providing normally open or normally closed contacts, and applied for magnetic field demagnetization protection or acceleration/deceleration control.

KPR type reverse relay: By monitoring the polarity of the armature voltage, it detects whether the DC motor is reversed and triggers the corresponding control circuit.

4. Timing and auxiliary equipment

4.1 C84 Static Online Timer

C84 is an all solid state timer that can be directly connected in series with DC contactor coils up to Size 8, without the need for intermediate relays. Its timing range is 0.05 to 180 seconds, providing two versions of normally open and normally closed contacts. Solid state design means no moving parts, eliminating the possibility of arcing and mechanical failures.

4.2 7313 VTH/CTH Time Relay

These are traditional oil damping time relays, providing multiple contact combinations and delay ranges, widely used to replace the timing function in old-fashioned control systems. The comparison table of old and new models provides convenience for system upgrades.

5. Product selection and system integration

For engineers, the correct selection is the key to the success of the system. Eaton's product catalog provides a clear selection process:

Determine application requirements: specify whether it is a lifting or walking mechanism, the required braking torque, motor power, and voltage level.

Select brake: Calculate the full load torque according to the formula and determine the required brake size based on AISE standards. Select the coil (series or parallel) based on the power supply type and whether a rectifier panel is required.

Select the master switch: Determine the required number of circuits, speed gear, and whether a joystick or stepless control is needed based on the complexity of the control.

Select contactor: Determine the contactor capacity based on the motor current and working mode (continuous or intermittent), and choose the corresponding installation method, coil voltage, and auxiliary contacts.

Select protective components: Select overload relays based on the rated current of the motor, and configure low-voltage monitoring or magnetic field protection relays according to system safety requirements.

Complete configuration: Combine the complete order number based on the selection table in the catalog, or provide detailed technical descriptions for non-standard requirements.