13.1.3 Setting guidelines
13.1.3.1 Setting example
GUID-5A3F67BD-7D48-4734-948C-01DAF9470EF8 v2
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-US (Equation 250)
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 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-US (Equation 251)
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
Table continues on next page
1MRK 502 071-UUS A Section 13
System protection and control
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 505
Application manual
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