Rockwell Automation Publication 825-UM004D-EN-P - November 2012 81
Configuring Protection & Logic Functions Chapter 6
Start Inhibit
When the protected motor is rated for a specific maximum number of starts per
hour or minimum time between starts, set the Starts/Hr. and Min. Off Time
settings accordingly. If the maximum number of starts per hour is achieved and
the motor stops or is tripped, the relay asserts the Trip output contact to prevent
an additional start until 60 minutes after the oldest start. If the motor stops or is
tripped within the minimum time between starts period, the relay asserts the Trip
output contact to prevent a new start until the minutes after the most recent start
equals the Min. Off Time setting.
In certain pump applications, fluid flowing backward through the pump could
spin the pump motor for a short time in the reverse direction after the motor is
stopped. An attempt to start the motor during this time can be damaging. To
prevent motor starts during the backspin period, enter a time in minutes in the
RESTART BLK TIME setting. If the relay trips or the motor is stopped, the relay
generates a trip signal and maintain it for at least this amount of time. The relay
does not issue a start during the Restart Block period.
The relay maintains the trip signal until enough time passes for the motor to be
safely restarted. During the lockout period, the relay displays a countdown time in
minutes to the next allowed start.
The Emergency Restart function overrides all three limits, clearing % TCU to
zero and allowing the motor to be put back in service for an emergency.
Phase Reversal Protection
The 825-P uses phase currents or phase voltages (if available) to determine
that the phase rotation of signals applied to the relay matches the phase rotation
setting. When you set Ph. Rev. Enable equal to Y, the relay trips 0.5 seconds after
incorrect phase rotation signals are applied to the relay.
For relays equipped with current inputs only, the trip occurs approximately
0.5 seconds after the motor start is initiated. When the relay is equipped with
voltage inputs, the trip occurs approximately 0.5 seconds after AC voltages are
applied to the relay.
Table 23 - Start Inhibit Settings
Setting Prompt Setting Range Factory Default
STARTS/HR. Off, 1…15 Off
MIN. OFF TIME Off, 1…150 min Off
RESTART BLK TIME Off, 1…60 min Off
Table 24 - Phase Reversal Setting
Setting Prompt Setting Range Factory Default
PH REV. ENABLE Y, N N
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