GE UR F35 Series Instruction Manual page 271

Multiple feeder protection system

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Time overcurrent time calculations are made with an internal energy capacity memory variable. When this variable indi-

cates that the energy capacity has reached 100%, a time overcurrent element will operate. If less than 100% energy capac-

ity 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 "Instan-

taneous" 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. The IEEE curves are derived from the formulae:

where: T = operate time (in seconds), TDM = Multiplier setting, I = input current, I

A, B, p = constants, T

= characteristic constant

Table 5–20: IEEE INVERSE TIME CURVE CONSTANTS

IEEE CURVE SHAPE

IEEE Extremely Inverse

IEEE Very Inverse

IEEE Moderately Inverse

Table 5–21: IEEE CURVE TRIP TIMES (IN SECONDS)

IEEE EXTREMELY INVERSE

IEEE VERY INVERSE

IEEE MODERATELY INVERSE

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= reset time in seconds (assuming energy capacity is 100% and

CURRENT ( I / I

F35 Multiple Feeder Protection System

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= Pickup Current setting

5.6 GROUPED ELEMENTS

is "Timed"),