8 S&C Instruction Sheet 681-530
Product Overview
The overcurrent control is programmed using a personal computer connected to the
control via a USB cable. The control features a variety of time-current characteristic
(TCC) curves and denite time settings listed in the "Overcurrent Control Settings" section
starting on page 56. Each overcurrent control can control up to two fault interrupters.
Current transformers inside the tank provide primary current sensing for the switch-
gear. The overcurrent control is capable of sensing and responding to phase overcurrents,
ground overcurrents, negative sequence, and sensitive earth faults.
Power derived from the current transformers is used to operate the control and to
charge the trip capacitors that discharge into magnetic latching solenoids to trip the fault
interrupters during a fault. No external power is required for operation of the control
in the field.
Without power from the current transformers, the overcurrent control will draw its
power from the connected personal computer via the USB connection.
The overcurrent control features time-current characteristic (TCC) curves consisting
of phase-overcurrent curves and ground-overcurrent curves. The families of curves are
as follows:
• IEEE (ANSI. U.S.) curves per IEEE Standard C37.112-1996 and IEC curves per IEC
60255-3: U1, U2, U3, U4, U5, C1, C2, C3, C4, and C5
• S&C standard speed curves (for use in place of conventional “E”-rated power fuses)
• S&C “K”-speed curves (for use in place of conventional “K”-rated power fuses)
• S&C “T”-speed curves (for use in place of conventional “T”-rated power fuses)
• Tap fault interrupter curves
• Main fault interrupter curves
The TCC curves can be customized into hundreds of different curves using a variety of
definite-time delay settings. For even more specialized shapes, there are two definite-time
settings that can be programmed. The definite-time settings can be programmed with
a minimum time value of 0 seconds, which is used to create an instantaneous overcur-
rent response. Ground Protection, Negative Sequence, and Sensitive Earth Fault
protection elements are also available. The factory default settings for the overcurrent
control are shown in the “Factory Default Protective Settings” section on page 44.
On switchgear configured for Single-Phase Trip/Single-Phase Lockout trip mode,
Ground Protection, Negative Sequence, and Sensitive Earth Fault settings are
disabled and are not selectable.
A choice of 50- or 60-Hertz operation is also offered.
Time-Current
Characteristics and
Settings
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