Ct Inputs; Motor Data - GE 239 Instruction Manual

CHAPTER 4: PROGRAMMING
4.3.1

CT Inputs

Note
4.3.2

Motor Data

239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
At PHASE CT PRIMARY > 50 A
a factor of 10 to remove the extra decimal place (see FIGURE 4–3: Setpoints Page 2 –
System Setup above). If changing the
50 A value, the
MOTOR FULL LOAD CURRENT
restore the correct value. In previous firmware versions, crossing the 50 A value by
changing the PHASE CT PRIMARY
setting by a factor of 10 automatically, often without the operator's knowledge.
• PHASE CT PRIMARY: Enter the primary current rating of the phase current
transformers. All three phase CTs must be of the same rating. For example if 500:5 CTs
are used, the phase CT primary value entered should be 500. When the relay is
shipped with factory defaults loaded, the phase CT ratio is set off. When off is the CT
value, the 239 is forced to a trip state as a safety precaution until a valid CT value is
entered. Ensure that the CT is connected to the correct 1 A or 5 A terminals to match
the CT secondary.
• GROUND SENSING: Ground sensing on solid or low resistance grounded systems is
possible with residually connected phase CTs as shown in FIGURE 2–3: Typical Wiring
Diagram on page 2–18. If this connection is used enter residual. The ground CT
primary will automatically be the same as the phase CTs. For more sensitive ground
current detection a separate core balance (zero sequence) CT which encircles all three
phase conductors can be used. In this case select core balance 50:0.025. A GE Multilin
50:0.025 CT is available. If a conventional 5 A secondary CT is used to encircle the 3
phase conductors, enter core balance x:5. It is then necessary to specify the CT
primary using the next message
• GROUND CT PRIMARY: This message will only be visible if the ground sensing in the
previous message is selected as core balance x:5. Enter the CT primary current. For
example, if a 50:5 CT is installed for ground sensing enter 50. One amp CTs can also be
used for ground sensing. In this case enter the CT primary value multiplied by 5. For
example, if a 100:1 ground CT is installed and the ground sensing is selected as core
balance x:5 enter 500 for the primary value.
• NOMINAL FREQUENCY: Enter the nominal system frequency as either 50 or 60 Hz. The
239 uses this information in the detection of Phase Short Circuit and Ground Fault
Trips.
• MOTOR FULL LOAD CURRENT (FLC): Enter the full load amps from the motor
nameplate. This is the maximum rated current at which the motor can operate
without overheating. It is the 1.0× pickup point on the timed overcurrent
characteristic. When the current exceeds this value, the timed overcurrent feature
begins to time, eventually leading to a trip. Immediate overload warning and
undercurrent setpoints are multiples of this value. Timed overcurrent is not active
during motor starting.
• OVERLOAD PICKUP INHIBIT: Enter the overload pickup (service factor) specified on
the motor nameplate if shown. Otherwise enter an overload pickup of 1.00. The pickup
inhibit will operate during start and/or run depending upon the value programmed in
, the 239 shifts the MOTOR FULL LOAD CURRENT
PHASE CT PRIMARY
is reset to 0 A, forcing the operator to
setting changed the MOTOR FULL LOAD CURRENT
GROUND CT PRIMARY
settings by
setting causes it to cross the
.
4–21