ABB REG670 - Setting Guidelines

current, due to difference between the three phase current transformers, can be in the
same range as the secondary earth fault current. Thus if physically possible, cable CT
is recommended for such applications in order to measure 3I
0
correct.
As indicated above, there will be very small neutral voltage or residual current if the
stator earth fault is situated close to the generator neutral. The probability for this fault
is quite small but not zero. For small generators the risk of not detecting the stator earth
fault, close to the neutral, can be accepted. For medium and large generator it is
however often a requirement that also theses faults have to be detected. Therefore, a
special neutral end earth fault protection STEFPHIZ is required. STEFPHIZ can be
realized in different ways. The two main principles are:
•
3
rd
harmonic voltage detection
• Neutral point voltage injection
The 3
rd
harmonic voltage detection is based on the fact that the generator generates
some degree of 3
rd
harmonic voltages. These voltages have the same phase angle in
the three phases. This means that there will be a harmonic voltage in the generator
neutral during normal operation. This component is used for detection of earth faults
in the generator, close to the neutral.
If the 3
rd
harmonic voltage generated in the generator is less than 0.8 V RMS
secondary, the 3
rd
harmonic based protection cannot be used.
In this protection function, a 3
rd
harmonic voltage differential principle is used.
10.6.3 Setting guidelines
The 100% Stator earth fault protection, 3rd harmonic based (STEFPHIZ)protection is
using the 3
rd
harmonic voltage generated by the generator itself. To assure reliable
function of the protection it is necessary that the 3
rd
harmonic voltage generation is at
least 1% of the generator rated voltage.
Adaptive frequency tracking must be properly configured and set for
the Signal Matrix for analog inputs (SMAI) preprocessing blocks in
order to ensure proper operation of the generator differential
protection function during varying frequency conditions.
Operation: The parameter Operation is used to set the function On/Off.
Common base IED values for primary current (setting IBase), primary voltage
(setting UBase) and primary power (setting SBase) are set in a Global base values for
settings function GBASVAL. Setting GlobalBaseSel is used to select a GBASVAL
function for reference of base values. The setting UBase is set to the rated phase to
phase voltage in kV of the generator.
1MRK 502 071-UEN - Section 10
Voltage protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 433
Application manual