Current circuit supervision CCSRDIF compares the residual current from a three-
phase set of current transformer cores with the neutral point current on a separate input
taken from another set of cores on the same current transformer.
The minimum operate current, IMinOp, must be set as a minimum to twice the residual
current in the supervised CT circuits under normal service conditions and rated
primary current.
The parameter Ip>Block is normally set at 150% to block the function during transient
conditions.
The FAIL output is connected in the PCM configuration to the blocking input of the
protection function to be blocked at faulty CT secondary circuits.
9.2 Fuse failure supervision SDDRFUF
9.2.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Fuse failure supervision SDDRFUF - -
9.2.2 Application
Different protection functions within the protection IED, operates on the basis of the
measured voltage in the relay point. Examples are:
• impedance protection functions
• undervoltage function
• energizing check function and voltage check for the weak infeed logic
These functions can operate unintentionally if a fault occurs in the secondary circuits
between the voltage instrument transformers and the IED.
It is possible to use different measures to prevent such unwanted operations. Miniature
circuit breakers in the voltage measuring circuits, located as close as possible to the
voltage instrument transformers, are one of them. Separate fuse-failure monitoring
IEDs or elements within the protection and monitoring devices are another
possibilities. These solutions are combined to get the best possible effect in the fuse
failure supervision function (SDDRFUF).
SDDRFUF function built into the IED products can operate on the basis of external
binary signals from the miniature circuit breaker or from the line disconnector. The
first case influences the operation of all voltage-dependent functions while the second
one does not affect the impedance measuring functions.
Section 9 1MRK 505 291-UEN A
Secondary system supervision
174
Application manual
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