GE L90, Инструкция по эксплуатации

Страница: 480 / 900

5-256 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
GROUPED ELEMENTS CHAPTER 5: SETTINGS
5
5.7.8.2 Inverse TOC curve characteristics
The inverse time overcurrent curves used by the time overcurrent elements are the IEEE, IEC, GE Type IAC, and I
2
t standard
curve shapes. This allows for simplified coordination with downstream devices.
If none of these curve shapes is adequate, FlexCurves can be used to customize the inverse time curve characteristics. The
definite time curve is also an option that can be appropriate if only simple protection is required.
Table 5-28: Overcurrent curve types
A time dial multiplier setting allows selection of a multiple of the base curve shape (where the time dial multiplier = 1) with
the curve shape (
CURVE
) setting. Unlike the electromechanical time dial equivalent, operate times are directly proportional
to the time multiplier (
TD MULTIPLIER
) setting value. For example, all times for a multiplier of 10 are 10 times the multiplier 1
or base curve values. Setting the multiplier to zero results in an instantaneous response to all current levels above pickup.
Time overcurrent time calculations are made with an internal
energy capacity memory variable. When this variable
indicates that the energy capacity has reached 100%, a time overcurrent element operates. If less than 100% energy
capacity is accumulated in this variable and the current falls below the dropout threshold of 97 to 98% of the pickup value,
the variable must be reduced. Two methods of this resetting operation are available: “Instantaneous” and “Timed.” The
“Instantaneous” selection is intended for applications with other relays, such as most static relays, which set the energy
capacity directly to zero when the current falls below the reset threshold. The “Timed” selection can be used where the
relay must coordinate with electromechanical relays.
IEEE curves
The IEEE time overcurrent curve shapes conform to industry standards and the IEEE C37.112-1996 curve classifications for
extremely, very, and moderately inverse curves. The IEEE curves are derived from the operate and reset time equations.
Eq. 5-15
where
T = operate time (in seconds)
TDM = Multiplier setting
I = input current
I
pickup
= Pickup Current setting


PHASE TOC6


 PHASE IOC1

See page 5-263



PHASE IOC12


 PHASE

DIRECTIONAL 1
See page 5-264

 PHASE

DIRECTIONAL 2
IEEE IEC GE type IAC Other
IEEE Extremely Inverse IEC Curve A (BS142) IAC Extremely Inverse I
2
t
IEEE Very Inverse IEC Curve B (BS142) IAC Very Inverse FlexCurves A, B, C, and D
IEEE Moderately Inverse IEC Curve C (BS142) IAC Inverse Recloser Curves
IEC Short Inverse IAC Short Inverse Definite Time