13.1.3 Setting guidelines
13.1.3.1 Setting example
A relay type used for generator subsynchronous resonance overcurrent protection shall be
replaced. The relay had inverse time operating characteristic as given with the following
formula:
EQUATION13000029 V1 EN (Equation 523)
Where:
• 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 296. 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 524)
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 45: Proposed settings for SMAIHPAC
I_HPAC_31_5Hz: SMAIHPAC:1
ConnectionType Ph — N
SetFrequency 31.5
FreqBandWidth 0.0
Table continues on next page
1MRK 506 369-UUS - Section 13
System protection and control
Line distance protection REL670 2.2 ANSI 619
Application manual
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