Siemens SIPROTEC 4 Manual page 191

Phi, address 3151 and angle 50Ns-2 DeltaPhi, address 3152. The trip delay time is set under address
3114 50Ns-2 DELAY. The actual settings are based on the respective application.
The minimum voltage 50Ns-1 Vmin of the high-current element 50Ns-1 is set under address 3153, the
pickup current 50Ns-1 PICKUP under 3117. The respective phase angle 50Ns-1 Phi is set under address
3154, the angle 50Ns-1 DeltaPhi is entered under address 3155. The angle should be set to 180° so that
the element functions non-directionally. The trip delay time is set under address 3118 50Ns-1 DELAY.
Positive angle settings (address 3151 and 3154) turn the tripping area in the „capacitive" direction, i.e. ground
current capacitive compared to ground voltage.
Negative angle settings turn the tripping area in the "inductiv" direction, i.e. ground current inductive
compared to ground voltage.
Angular Error Compensation (Ι Transformer)
The high reactive component in a resonant grounded system and the inevitable air gap of the toroidal current
transformer often require the angle error of the toroidal current transformer to be compensated. In addresses
3102 to 3105 the maximum angle error CT Err. F1 and the associated secondary current CT Err. I1 as
well as another operating point CT Err. F2/CT Err. I2 are set for the actually connected burden. The
device thus approximates the transformation characteristic of the transformer with considerable accuracy. In
ungrounded or grounded systems angle compensation is not required.
Ungrounded System
In an ungrounded system with a ground fault on a cable, capacitive ground currents of the galvanically
connected system flow via the measuring point, except for the ground current generated in the grounded
cable, since the current last-mentioned will flow directly to the fault location (i.e. not via the measuring point).
A setting equal to about half the ground current is to be selected. The measurement method should be SIN
φ, since capacitive ground current is most relevant here.
Resonant-Grounded System
In resonant-grounded systems, directional determination on the occurrence of a ground fault is more difficult
since the low residual wattmetric current for measurement is usually dwarfed by a reactive current (be it
capacitive or inductive) which is much higher. Therefore, depending on the system configuration and the posi-
tion of the arc-compensating coil, the total ground current supplied to the device may vary considerably in its
values with regard to magnitude and phase angle. The relay, however, must evaluate only the active compo-
nent of the ground fault current, that is, Ι
regard to phase angle measurement of all instrument transformers. Furthermore, the device must not be set
to operate too sensitive. When applying this function in resonant-grounded systems, a reliable direction deter-
mination can only be achieved when toroidal current transformers are connected. Here the following rule of
thumb applies: Set pickup values to about half of the expected measured current, thereby considering only the
residual wattmetric current. Residual wattmetric current predominantly derives from losses of the Petersen
coil. Here, the COS φ measurement method is used since the resistive residual wattmetric current is most rele-
vant.
Grounded System
In grounded systems, a value is set below the minimum anticipated ground fault current. It is important to
note that 3I0 DIR (current value RELEASE DIRECT.) only detects the current components that are perpendic-
ular to the directional limit lines defined at addresses 3124 and 3125. COS φ is the method of measurement
used, and the correction angle is set to –45°, since the ground fault current is typically resistive-inductive
(right section of Figure 2-81 "Directional curve for cos-ϕ-measurement" in the functional description of the
sensitive ground fault detection).
Electrical Machines
One may set the value COS φ for the measurement method and use a correction angle of +45° for electrical
motors supplied from a busbar in an ungrounded system, since the ground current is often composed of an
overlap of the capacitive ground current from the system and the resistive current of the load resistance (left
SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
2.12 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
cos ϕ. This demands extremely high accuracy, particularly with
Ns
Functions
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