Siemens Reyrolle 7SR5, Руководство пользователя

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Parameter:
Gn 87T-BD > HB2 Setting
•
Default setting:
0.15 x I
(0.15 ⋅ I)
This defines the minimum level of even harmonic content in the relay operating current that will inhibit
operation of the 87T-BD function element. The lowest setting provides the most stability under magnet-
izing inrush conditions.
The setting value can be decreased to a smaller proportion of 2nd harmonic. Settings below 0.1 ⋅ I are
not recommended as for internal fault and current-transformer saturation, a proportion of 2nd harmonic
also arises – over sensitive settings may cause the protection function to be blocked.
Parameter:
Gn 87T-BD > 8HB5 Element
•
Default setting:
Disabled
An increase in transformer voltage or decrease in system frequency may result in the transformer
becoming overexcited. This function element can be used to prevent differential protection operation
during allowable overexcitation conditions.
Stationary over-fluxing is characterized by odd-numbered harmonics so the detection of high levels of the
3rd or 5th harmonic can be used to block the differential protection. The 3rd harmonic is eliminated in
the delta winding of transformers so the 5th harmonic is used.
If the setting value is exceeded blocking can be initiated. Phase segregated or 3 phase blocking can be
implemented, see 87T HB5 Bias.
Parameter:
Gn 87T-BD > HB5 Setting
•
Default setting: 0.3 x In (0.3 ⋅ I
rated
)
The default setting can be used unless a false operation for differential protection caused by over-fluxing
unbalance, in which case a lower setting should be adopted after checking the waveform record for the
level of unbalance current.
Parameter:
Gn 87T-BD > Setting
•
Default setting: 0.2 x In (0.2 ⋅ I
rated
)
This sets the minimum differential current pickup threshold. This setting is selected to ensure stability in
the presence of CT and relay errors when low levels of bias current are present i.e. low load levels. The
default setting is a practical value between sensitivity and possible disturbing influence. Typically this
setting is chosen to be equal to the fist bias slope setting (S1), see below.
If the line CTs are similar e.g. typical in the case of reactor or motor applications a more sensitive setting
is possible.
Parameter:
Gn 87T-BD > S1
•
Default setting:
0.2x
(0.2 ⋅)
The slope of the first bias slope is selected to be greater than the maximum unbalance, it is selected to
ensure stability when through fault or heavy load current flows in the transformer.
Steady state unbalance current due to the transformer tap position, relay tolerance and to CT measure-
ment errors produces differential (operate) current. The differential current will increase with increasing
load or through fault current in the transformer and so to ensure stability. The differential current
required for operation increases with increasing bias current. The recommended setting is equal to the
tap change range. As the protection is optimized around the center tap position then using the total tap
change range provides a 100 % safety margin. For example if the tap change range is +10 to -20 %, the
overall range is 30 % so a 0.3x setting is chosen.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
316 Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019