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TRICONEX 4351B processor card

The balanced voltage function is intended mainly for preventing incorrect voltage measurement by other devices. It compares the voltages (amplitudes) of two generally identical voltage sources connected to the same busbar phase by phase. The function picks up when the difference between voltages of the same phase exceeds a set pick-up value (V-Unbalance). A tripping signal is emitted for the source with the lower voltage (Trip-Line1 or Trip-Line2) and a general tripping signal (Trip) generated after a set time delay (Delay) and providing the tripping condition remains fulfilled throughout the delay time. These signals are available for blocking protection and instrumentation connected to the faulty source and thus prevent false tripping or measurements. The tripping signals are maintained for the setting of the reset time (t-Reset) after the tripping condition is no longer fulfilled. The function is thus suitable for detecting v.t. circuit faults (fuse failure) and faults on the protection and metering circuits connected to them. Notes:
Only voltages of similar sources, which have coincident amplitudes and phase-angles and are connected to the same busbar, should be compared. Wherever possible the voltages should also be processed by neighbouring sampling groups and by the same input unit. The purpose of this is to limit signal conditioning er rors should the power system frequency deviate from the rated frequency fN and during transients. To prevent false tripping during extreme variations of frequency, either the pick-up setting can be increased or the balanced voltage function can be blocked by a frequency function.

Application example

Differing primary rated voltages of the v.t's can be compensated by appropriately setting the reference values of the corresponding A/D channels. The adjusted reference values then apply for all the protection functions connected to the same channels.The protection monitors the voltages of the two v.t's 1 and 2: In the event of a fault (in this example an open-circuit lead in the circuit of v.t. 1), the protection function detects an unbalance and after the set delay time generates the tripping signals 'Trip' and 'Trip-Line1'.These then initiate blocking of the metering and protection devices (such as underimpedance, voltage controlled overcurrent and distance protections etc.) connected to v.t. 1. Typical settings: Max. voltage difference (V-Unbalance) 0.20 UN

Underimpedance (Underimped) A. Application Back-up phase fault protection for the generator feeder. B. Features
circular operating characteristic (see Fig. 3.5.13.1)
adjustable time delay
insensitive to DC component in voltage and current
insensitive to harmonics in voltage and current
single or three-phase measurement
detection of the lowest impedance in the three-phase mode
underimpedance measurement enabled by undercurrent unit (0.1 IN). C. Inputs and outputs I. C.t./v.t. inputs:
current
voltage II. Binary inputs:
Blocking III. Binary outputs:
pick-up
tripping IV. Measurements:
impedance (value)