Functions
6-1117SJ62 Manual
C53000-G1140-C121-1
6.11 Voltage Protection (27, 59)
6.11.1 Description of Voltage Protection
6.11.1.1 Measurement Principle
VT Connection The voltages supplied to the device may correspond to the three phase-to-ground volt-
ages, or two phase-to-phase voltages and the displacement voltage, depending on
how the voltage transformers are connected.
Current
Supervision
The primary voltage transformers are arranged, depending on the system, either on
the supply side or the load side of the associated circuit breaker. These different ar-
rangements lead to different behavior of the voltage protection function when a fault
occurs. When a circuit breaker is opened, full voltage remains on the supply side while
the load side voltage becomes zero. Opening the circuit breaker when voltage trans-
formers are located on the load side of the circuit breaker causes the undervoltage
protection to remain picked up. Therefore, the flow of current through the circuit break-
er can be used as an additional criteria for pickup of undervoltage protection. When
current supervision is active, for undervoltage pickup to occur, the current through the
circuit breaker must exceed a minimum current level which corresponds to the current
flow monitoring setting at address %NU&ORVHG,0,1. The circuit breaker is
tripped, when the current decreases below the current flow monitoring setting , and
undervoltage protection will drop out.
Preparation of Mea-
sured Data
Using a Fourier Analysis, the fundamental harmonic component of the three phase-to-
phase voltages are filtered out and passed along for further processing. For undervolt-
age protection, the positive sequence components of the phase-to-phase voltages are
evaluated, while for overvoltage protection, the largest of the three phase-to-phase
voltages is evaluated.
6.11.1.2 Overvoltage Protection (59)
Application The overvoltage protection has the task of preventing insulation failure by protecting
against abnormally high voltage levels.
Abnormally high voltages often occur in low loaded, long distance transmission lines,
in islanded systems when generator voltage regulation fails, or after full load shutdown
of a generator from the system.
Function The fundamental harmonic of the largest phase-to-phase voltages is provided to the
overvoltage protection element (59 element). When an adjustable setting is exceeded,
the 59 element pickups, and after an adjustable time delay elapses, initiates a trip sig-
Note:
If current supervision is turned off, the undervoltage function will pick up without 3
phase voltage applied. The device cannot be programmed if in pickup. Apply 3 phase
voltage to continue with programming!
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