ABB RET670 - Page 539

CurveType: Selection of the curve type for the inverse delay. The IEEE curves or tailor
made curve can be selected depending of which one matches the capability curve best.
TDforIEEECurve: The time constant for the inverse characteristic. Select the one
giving the best match to the transformer capability.
t_CooolingK: The cooling time constant giving the reset time when voltages drops
below the set value. Shall be set above the cooling time constant of the transformer.
The default value is recommended to be used if the constant is not known.
t_MinTripDelay: The operating times at voltages higher than the set Pickup2. The
setting shall match capabilities on these high voltages. Typical setting can be 1-10 second.
t_MaxTripDelay: For overvoltages close to the set value times can be extremely long if
a high K time constant is used. A maximum time can then be set to cut the longest
times. Typical settings are 1800-3600 seconds (30-60 minutes)
AlarmPickup: Setting of the alarm level in percentage of the set trip level. The alarm
level is normally set at around 98% of the trip level.
tAlarm: Setting of the time to alarm is given from when the alarm level has been
reached. Typical setting is 5 seconds.
Service value report
A number of internal parameters are available as service values for use at
commissioning and during service. Remaining time to trip (in seconds) TMTOTRIP,
flux density VPERHZ, internal thermal content in percentage of trip value
THERMSTA. The values are available at local HMI, Substation SAsystem and PCM600.
Setting example
Sufficient information about the overexcitation capability of the protected object(s)
must be available when making the settings. The most complete information is given in
an overexcitation capability diagram as shown in figure
218.
The settings Pickup2 and Pickup1 are made in per unit of the rated voltage of the
transformer winding at rated frequency.
Set the transformer adapted curve for a transformer with overexcitation characteristics
in according to figure
218.
Pickup1 for the protection is set equal to the permissible continuous overexcitation
according to figure
218 = 105%. When the overexcitation is equal to Pickup1, tripping
is obtained after a time equal to the setting of t1.
This is the case when
VBase is equal to the transformer rated voltages.
For other values, the percentage settings need to be adjusted accordingly.
1MRK504116-UUS C Section 3
IED application
533
Application manual