5.4.4. Current unbalance I2> (46)
Current unbalance function (CUB) is used for instant- and time delayed unbalanced network protection
and detection of broken conductor for various applications including feeder, lter and machine
applications of utilities and industry. The number of available instances of the function depends of the
IED model. Function measures constantly negative- and positive sequence current magnitudes which
on the operating decisions are based. In broken conductor mode (I2/I1) phase current magnitudes are
monitored also for minimum allowed loading current.
Two possible operating modes are available, I2 mode which monitors negative sequence current and
I2/I1 mode, which monitors the ratio of negative sequence current ratio to positive sequence current.
The used symmetrical component magnitudes are calculated in the relay from the phase current inputs
IL1, IL2 and IL3. Zero sequence current is also recorded into the registers as well as the angles of the
positive, negative and zero sequence currents for better veri cation of the fault cases. Blocking signal
and setting group selection controls the operating characteristics of the function during normal
operation.
Outputs of the function are Start Trip and Blocked signals. Setting parameters are static inputs for the
function which are changed only by user input in the setup phase of the function. Non-directional
unbalance function utilizes total of eight separate setting groups which can be selected from one
common source.
The function can be operating on instant or time delayed mode. In time delayed mode the operation
can be switched to de nite time or IDMT mode. For IDMT operation IEC and ANSI standard time
delays are supported as well as custom parameters.
The operational logic consists of input magnitude processing, input magnitude selection, threshold
comparator, block signal check, time delay characteristics and output processing.
Inputs for the function are the operating mode selections, setting parameters and measured and pre-
processed current magnitudes and binary input signals. Function outputs START, TRIP and BLOCKED
signals which can be used for direct IO controlling and also for user logic programming. The function
registers its operation into 12 last time-stamped registers and also generates general time stamped
ON/OFF events to the common event buffer from each of the three output signals. In instant operating
mode the function outputs START and TRIP events simultaneously with equivalent time stamp. Time
stamp resolution is 1ms. Function provides also cumulative counters for START, TRIP and BLOCKED
events.
In the following gure is presented the simpli ed function block diagram of the CUB function.
Figure. 5.4.4. - 71. Simpli ed function block diagram of the CUB function.
AQ-T216
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
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