ABB RELION REX640 Technical Manual page 523

1MRS759142 C
REX640
Technical Manual
The equation defines the "operate" and "restrain" regions of the protection. The third
harmonic differential protection operates according to the following equation.
U U Beta U
H T + H N ≥ ⋅
3 _ 3 _
GUID-A98DED72-BA44-41BE-861C-07B4531038A6 V1 EN
Ū Neutral side third harmonic voltage phasor
3H_N
Ū Terminal side third harmonic voltage phasor
3H_T
Beta
Setting to achieve a required degree of security under healthy conditions
|Ū +Ū | Magnitude of the third harmonic differential voltage
3H_T 3H_N
Beta ·|Ū
| Magnitude of the third harmonic bias (restrain) voltage
3H_N
Factor Beta, which is a setting, can be determined from the condition.
Beta U
⋅ H N
3 _
K
=
U U
H T + H N
3 _ 3 _
GUID-F09C7662-73B6-42B7-B795-CD5B1FE0A118 V1 EN
K is the security factor, for example K = 1.5.
normal, healthy condition of the protected generator, with a high enough value for K,
so that no unwanted operation of the protection should be expected, regardless the
load on the generator.
To assure a reliable functioning of the protection, it is necessary that
the generator produces third harmonic voltage which is at least 1% of
the generator rated voltage.
As phase-to-phase voltages do not contain a third harmonic component, in situations
where the VTs on the terminal side are connected between phase-to-phase, the
differential protection in
setting is set to "No voltage" and H3EFPSEF operates as a simple neutral side third
harmonic undervoltage protection.
When H3EFPSEF is reduced to function as only a third harmonic
neutral point undervoltage protection, it is necessary to block the
function during startup and shutdown of generator and also when
there is no sufficient voltage.
Calculating Beta value
The setting Beta gives the proportion of the third harmonic voltage in the neutral point
of the generator to be used as bias quantity. Beta must be set so that there is no risk of
trip during the normal, non-faulted operation of the generator. If Beta is set high, this
limits the portion of the stator winding covered by the protection. In most cases, the
default setting "3.00" gives an acceptable sensitivity for an earth fault near the neutral
H N
3 _
Equation 73
Equation 73 cannot work. In such case, the Voltage selection
Section 4
Protection functions
(Equation 72)
(Equation 73)
must be satisfied in the
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