4.2
SEL-749M Relay Instruction Manual Date Code 20080918
Protection and Logic Functions
Application Data
Report Settings. Lists settings for the event reports and sequential event
reports.
Logic Functions. Explains the settings and operation of the logic functions
of the SEL-749M.
When you calculate the protection element settings to protect your motor,
proceed through the subsections listed earlier. Skip the RTD- and voltage-
based protection subsections if they do not apply to your specific relay model
or installation. See Section 6: Settings for the list of all settings (SEL-749M
Settings Sheets) and various methods of accessing them.
NOTE: The DeviceNet port
parameters can only be set at the rear
of the relay on the DeviceNet card
(see Figure E.1 and Figure E.2).
You can enter the settings by using the front-panel SET RELAY function (see
Section 8: Front-Panel Operations), the serial port (see Section 7:
Communications), the EIA-485 port (see Appendix D: Modbus RTU
Communications Protocol), or the DeviceNet™ port (see Appendix E:
DeviceNet).
Application Data
It is faster and easier for you to calculate settings for the SEL-749M if you
collect the following information before you begin (collect the information for
each speed for a two-speed motor application):
➤ Specifications of the protected motor, including the following
details:
➢ Rated full load current
➢ Service factor
➢ Locked rotor current
➢ Maximum locked rotor time with the motor at ambient
and/or operating temperature
➢ Maximum motor starts per hour, if known
➢ Minimum time between motor starts, if known
➤ Additional data regarding the motor application, including the
following information:
➢ Minimum no load current or power, if known
➢ Motor accelerating time—this is the normal time
required for the motor to reach full speed
➢ Maximum time to reach motor full load—this time may
be significantly longer than the motor accelerating time,
particularly in pump motor applications where the
motor may run at full speed for some time before the
pump reaches full head and full load
➤ Current transformer primary and secondary ratings and
connections
➤ System phase rotation and nominal frequency
➤ Voltage transformer ratios and connections, if used
➤ Type and location of resistance temperature devices (RTDs), if
used
➤ Expected fault current magnitudes for motor or cable ground
and three-phase faults
Courtesy of NationalSwitchgear.com
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