CHAPTER 4: KEYPAD SETPOINTS
S2 SYSTEM SETUP USING THE KEYPAD
369 MOTOR MANAGEMENT RELAY – QUICKSTART GUIDE
4–33
resistance grounded systems where fault current can be quite high, a 1 A or 5 A CT
should be used for either zero-sequence (core balance) or residual ground sensing. If a
residual connection is used with the phase CTs, the phase CT primary must also be
entered for the ground CT primary. As with the phase CTs the type of ground CT should
be chosen to handle all potential fault levels without saturating.
•
VT CONNECTION TYPE, VT RATIO, and MOTOR RATED VOLTAGE
: These voltage
related setpoints are visible only if the 369 has metering installed.
The manner in which the voltage transformers are connected must be entered here or
none if VTs are not used. The VT turns ratio must be chosen such that the secondary
voltage of the VTs is between 1 and 240 V when the primary is at motor nameplate
voltage. All voltage protection features are programmed as a percent of motor
nameplate or rated voltage which represents the rated motor design voltage line to
line.
For example: If the motor nameplate voltage is 4160 V and the VTs are 4160/120
open-delta, program
VT CONNECTION TYPE
to “Open Delta”,
VT RATIO
to “34.67:1”,
and
MOTOR RATED VOLTAGE
to “4160 V”.
•
NOMINAL FREQUENCY
: Enter the nominal system frequency here.
The 369 has variable frequency functionality when the
NOMINAL FREQUENCY
is set to
“Variable”. All of the elements function in the same manner with the exception of the
voltage and power elements, which work properly if the voltage waveform is
approximately sinusoidal. When using a pulse width modulate drive, and an unfiltered
voltage waveform is present, the unit will not be able to accurately measure voltage,
but an approximately sinusoidal current waveform can be measured accurately. If the
NOMINAL FREQUENCY
is set to “Variable”, the filtering algorithm could increase the
trip and alarm times for the undervoltage and underfrequency elements by up to 270
ms. If the level exceeds the threshold by a significant amount, trip and alarm times will
decrease until they match the programmed delay. The exceptions to this increased
time are the short circuit and ground fault elements, which will trip as per
specification.
Note that when the
NOMINAL FREQUENCY
setting is “Variable”, the element pickup
levels and timing are based on the measured values of the 369.
Frequency is normally determined from the Va voltage input. If however this voltage
drops below the minimum voltage threshold the Ia current input will be used.
Note
The minimum currrent at which the frequency may be measured is 3A.
•
SYSTEM PHASE SEQUENCE
: If the phase sequence for a given system is ACB rather
than the standard ABC the phase sequence may be changed. This setpoint allows the
369 to properly calculate phase reversal and power quantities and is only visible if the
369 has metering installed.
For full details of System Setup using the 369 keypad, please refer to the
369 Motor
Management Relay Instruction Manual
.
