GE L90 Instruction Manual page 94

5.1 OVERVIEW
The main characteristics of an element are shown on the element logic diagram. This includes the input(s), settings, fixed
logic, and the output operands generated (abbreviations used on scheme logic diagrams are defined in Appendix F).
Some settings for current and voltage elements are specified in per-unit (pu) calculated quantities:
pu quantity = (actual quantity) / (base quantity)
• For current elements, the 'base quantity' is the nominal secondary or primary current of the CT. Where the current
source is the sum of two CTs with different ratios, the 'base quantity' will be the common secondary or primary current
to which the sum is scaled (i.e. normalized to the larger of the 2 rated CT inputs). For example, if CT1 = 300 / 5 A and
CT2 = 100 / 5 A, then in order to sum these, CT2 is scaled to the CT1 ratio. In this case, the 'base quantity' will be 5 A
secondary or 300 A primary.
• For voltage elements the 'base quantity' is the nominal primary voltage of the protected system which corresponds
(based on VT ratio and connection) to secondary VT voltage applied to the relay. For example, on a system with a
13.8 kV nominal primary voltage and with 14400:120 V Delta-connected VTs, the secondary nominal voltage (1 pu)
would be:
For Wye-connected VTs, the secondary nominal voltage (1 pu) would be:
Many settings are common to most elements and are discussed below:
• FUNCTION setting: This setting programs the element to be operational when selected as "Enabled". The factory
default is "Disabled". Once programmed to "Enabled", any element associated with the Function becomes active and
5
all options become available.
• NAME setting: This setting is used to uniquely identify the element.
• SOURCE setting: This setting is used to select the parameter or set of parameters to be monitored.
• PICKUP setting: For simple elements, this setting is used to program the level of the measured parameter above or
below which the pickup state is established. In more complex elements, a set of settings may be provided to define the
range of the measured parameters which will cause the element to pickup.
• PICKUP DELAY setting: This setting sets a time-delay-on-pickup, or on-delay, for the duration between the Pickup
and Operate output states.
• RESET DELAY setting: This setting is used to set a time-delay-on-dropout, or off-delay, for the duration between the
Operate output state and the return to logic 0 after the input transits outside the defined pickup range.
• BLOCK setting: The default output operand state of all comparators is a logic 0 or "flag not set". The comparator
remains in this default state until a logic 1 is asserted at the RUN input, allowing the test to be performed. If the RUN
input changes to logic 0 at any time, the comparator returns to the default state. The RUN input is used to supervise
the comparator. The BLOCK input is used as one of the inputs to RUN control.
• TARGET setting: This setting is used to define the operation of an element target message. When set to Disabled, no
target message or illumination of a faceplate LED indicator is issued upon operation of the element. When set to Self-
Reset, the target message and LED indication follow the Operate state of the element, and self-resets once the oper-
ate element condition clears. When set to Latched, the target message and LED indication will remain visible after the
element output returns to logic 0 - until a RESET command is received by the relay.
• EVENTS setting: This setting is used to control whether the Pickup, Dropout or Operate states are recorded by the
event recorder. When set to Disabled, element pickup, dropout or operate are not recorded as events. When set to
Enabled, events are created for:
(Element) PKP (pickup)
(Element) DPO (dropout)
(Element) OP (operate)
The DPO event is created when the measure and decide comparator output transits from the pickup state (logic 1) to
the dropout state (logic 0). This could happen when the element is in the operate state if the reset delay time is not '0'.
5-4
13800
×
--------------- - 120 115 V
=
14400
13800 120
×
--------------- - --------- -
66.4 V
=
14400
3
L90 Line Differential Relay
5 SETTINGS
(EQ 5.1)
(EQ 5.2)
GE Multilin