TSUBAKI SHOCK RELAY THEORY OF OPERATION – HOW DOES IT WORK?
Shock time: The Shock Relay does not respond to excess current if it does not exceed the preset shock time.
Shock time: When excess current goes beyond the preset time the Shock Relay responds.
Start time: Within a set time, the Shock Relay does not respond to motor starting current.
Shock Relay operation (trip)
Motor rotation speed
Rotation speed /current
Set current value
Motor load current
Short period of current surge
Overload
Set start time value
Set shock time value Set shock time value
Time
Start-up
Steady area
Overload area Stoppage
Figure 1: Shock Relay operation example
Figure 1 above reflects a typical set-up for a Tsubaki Shock Relay. As depicted in the above example, the Shock Relay is set up to accept a higher motor amperage draw at start-up for a limited amount of time. This “Start Time” period allows the motor to spool to its steady state operation mode where maximum continuous RPM is achieved, and current draw drops to a normal value that is below the maximum “Current Value” set in the Shock Relay. As depicted, the amperage draw of the motor then momentarily increases (resulting in a drop in RPM due to induced load) above the maximum “Current Value” setting, but quickly falls back to a steady state value. Since the “Shock Time” value was not exceeded, the Shock Relay does not trip, and allows continued operation. However, as time passes by, the Shock Relay senses an increase in motor amperage draw and a drop in RPM that exceeds set current value and “Shock Time.” The overload condition sensed by the Shock Relay causes the unit to trip, resulting in the Shock Relay breaking the motor starter contact – thus, shutting the system down to prevent mechanical damage from occurring.
Important Key Concepts: * Shock Relays generally work with any voltage AC motor, single or three-phase. * Besides the power to the motor, the Shock Relay needs its own power supply. Power supply requirements generally fall into 115 or 230V single phase. * It is best practice to have one Shock Relay monitor one motor. Grouping multiple motors to a single Shock Relay generally does not give satisfactory results.
www. ustsubaki .com
4
Made with FlippingBook Digital Proposal Creator