ABB REC670 Applications Manual page 277

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
Where:
• t is the operating time of the relay
op
• T is fixed time delay (setting)
01
• K is a constant (setting)
• I is measured subsynchronous current in primary amperes
S
The existing relay was applied on a large 50Hz turbo generator which had shaft
mechanical resonance frequency at 18.5Hz. The relay settings were T
seconds, K= 35566 Amperes and minimal subsynchronous current trip level was
set at I =300 Amperes primary.
S0
Solution:
First the IED configuration shall be arranged as shown in
settings for SMAI HPAC filter and multipurpose function shall be derived from
existing relay settings in the following way:
The subsynchronous current frequency is calculated as follows:
= - =
50 Hz 18.5 Hz
f
s
EQUATION13000030 V1 EN-US
In order to properly extract the weak subsynchronous signal in presence of the
dominating 50Hz signal the SMAI HPAC filter shall be set as given in the
following table:
Table 30: Proposed settings for SMAIHPAC
I_HPAC_31_5Hz: SMAIHPAC:1
ConnectionType
SetFrequency
FreqBandWidth
FilterLength
OverLap
Operation
Now the settings for the multi-purpose overcurrent stage one shall be derived in
order to emulate the existing relay operating characteristic. To achieve exactly the
same inverse time characteristic the programmable IDMT characteristic is used
which for multi-purpose overcurrent stage one, which has the following equation
(for more information see Section "Inverse time characteristics" in the TRM).
System protection and control
31.5 Hz
Ph — N
31.5
0.0
1.0 s
75
On
Section 12
01
= 0.64
Figure 102. Then the
(Equation 105)
271