GE 745 TRANSFORMER MANAGEMENT RELAY, Instruction Manual

Page: 96 / 408

5-46 745 Transformer Management Relay GE Power Management
5.6 S4 ELEMENTS 5 SETPOINTS
5
5.6.3 SETPOINT GROUP
Each protection and monitoring element setpoint (programmed in S4 ELEMENTS ) has four copies, and these set-
tings are organized in four setpoint groups. Only one group of settings are active in the protection scheme at a
time. The active group can be selected using the
ACTIVE SETPOINT GROUP setpoint or using a logic input. The
setpoints in any group can be viewed or edited using the EDIT SETPOINT GROUP setpoint.
5.6.4 DIFFERENTIAL
This section contains the settings to configure the percent differential element, including all associated har-
monic inhibit features. The 745 provides three independent harmonic inhibit features:
HARMONIC INHIBIT
, which
implements an inhibit scheme based on 2
nd
or 2
nd
+ 5
th
harmonic which is ‘in-circuit’ at all times;
ENERGIZATION
INHIBIT
, which allows changing the characteristics of the inhibit scheme during energization to improve reliability;
and
5TH HARMONIC INHIBIT
, which implements an inhibit scheme based on 5
th
harmonic only, allowing inhibiting
the percent differential during intentional overexcitation of the system.
a) PERCENT DIFFERENTIAL
This section contains the settings to configure the percent differential element. The main purpose of the per-
cent-slope characteristic of the differential element is to prevent maloperation because of unbalances between
CTs during external faults. These unbalances arise as a result of the following factors:
• CT ratio mismatch (not a factor, since the 745 automatically corrects for this mismatch)
• Onload tap changers which result in dynamically changing CT mismatch
• CT accuracy errors
• CT saturation
y
SETPOINT GROUP
y
[ENTER] for more
This message indicates the start of the SETPOINT GROUP section. To continue
with these setpoints press , or press to go to the next
section.
ACTIVE SETPOINT
GROUP: Group 1
Range: Group 1 / Group 2 / Group 3 / Group 4
Select the number of the
SETPOINT GROUP
whose settings are to be active in
the protection scheme. This selection will be overridden if a higher number
setpoint group is activated using logic inputs.
EDIT SETPOINT
GROUP: Active Group
Range: Group 1 / Group 2 / Group 3 / Group 4 / Active Group
Select the number of the SETPOINT GROUP whose settings are to be viewed
and/or edited via the front panel keypad or any of the communication ports.
Selecting
Active Group
selects the currently active setpoint group for editing.
GROUP 2 ACTIVATE
SIGNAL: Disabled
Range: Disabled / Logc Inpt 1 (2-16)
Select any logic input which, when asserted, will (remotely) select
SETPOINT
GROUP 2 (3-4)
to be the active group. This selection will be overridden if a
higher number setpoint group is activated using the
ACTIVE SETPOINT GROUP
setpoint or another logic input.
y
DIFFERENTIAL
y
[ENTER] for more
This message indicates the start of the
DIFFERENTIAL
section. To continue
these setpoints, press , or press to go to the next section.
E N T E R
M E SSA G E
EN TE R
M E SS A G E