Functions
2.40 DC Voltage/Current Protection (ANSI 59NDC/51NDC)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
274
If we assume that the earthing transformer has an ohmic winding resistance of R ≈ 150 Ω, a DC current of I
0
=
945 V/150 Ω = 6.3 A will flow through its starpoint.
Note: The ohmic winding resistances of earthing and neutral transformers can differ widely depending on the
type. For a concrete application, they should be obtained from the manufacturer, or determined by measure-
ments.
If not tripped, the earth fault current would cause a temperature overload that would destroy the wye-connected
voltage transformers and the earthing transformer. To ensure that the protection will pick up reliably, it is set to
a value of less than half the fault current, in this example to 2 A. With the shunt and shunt converter used in the
example, this current causes a secondary current of 4 mA (see above ) (fault current ≈ 6 A, selected pickup
value = 2 A, setting value = 4 mA).
Delay
The tripping delay can be set at address 7206 T DC. The set time is an additional time delay not including the
operating time of the protective function.
For the startup earth fault current protection T DC is determined by the permissible temperature load of the
earthing and/or neutral transformer. A value of 2 s or less is quite common.
Note: It should be noted that in operating condition 0, the operating times for pickup and dropout are 4 times
longer due to the more complex filter procedure needed to eliminate disturbances.
2.40.3 Settings
2.40.4 Information List
Addr. Parameter Setting Options Default Setting Comments
7201 DC PROTECTION OFF
ON
Block relay
OFF DC Voltage/Current Protection
7202 MEAS.METHOD mean value
RMS
mean value Measurement Method
(MEAN/RMS Values)
7203 DC >/< DC >
DC <
DC > Method of Operation (DC >/<)
7204 U DC >< 0.1 .. 8.5 V 2.0 V DC Voltage Pickup
7205 I DC >< 0.2 .. 17.0 mA 4.0 mA DC Current Pickup
7206 T DC 0.00 .. 60.00 sec; ∞ 2.00 sec Time Delay for Trip of DC Protec-
tion
No. Information Type of In-
formation
Comments
5293 >BLOCK DC Prot. SP >BLOCK DC protection
5301 DC Prot. OFF OUT DC protection is switched OFF
5302 DC Prot.BLOCKED OUT DC protection is BLOCKED
5303 DC Prot. ACTIVE OUT DC protection is ACTIVE
5306 DC Prot.pick.up OUT DC protection picked up
5307 DC Prot. TRIP OUT DC protection TRIP
5308 Failure DC Prot OUT Failure DC protection
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