ABB REG670 - Page 473

• t
op
is the operating time of the relay
• T
01
is fixed time delay (setting)
• K is a constant (setting)
• I
S
is measured subsynchronous current in primary amperes
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
01
= 0.64
seconds, K= 35566 Amperes and minimal subsynchronous current trip level was set
at I
S0
=300 Amperes primary.
Solution:
First the IED configuration shall be arranged as shown in
Figure 221. Then the 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 18.5 31.5
s
f Hz Hz Hz= - =
EQUATION13000030 V1 EN (Equation 258)
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 50: Proposed settings for SMAIHPAC
I_HPAC_31_5Hz: SMAIHPAC:1
ConnectionType Ph — N
SetFrequency 31.5
FreqBandWidth 0.0
FilterLength 1.0 s
OverLap 75
Operation On
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).
[ ]
p
t
A
s B k
i
C
in
æ ö
ç ÷
ç ÷
= + ×
ç ÷
æ ö
-
ç ÷
ç ÷
>
è ø
è ø
EQUATION13000031 V1 EN
(Equation 259)
1MRK 502 071-UEN - Section 13
System protection and control
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 467
Application manual