Hitachi Relion 670 Series Applications Manual page 173

1MRK506375-UEN Rev. N
temperatures are reached. If the temperature continues to increase to the trip value TripTemp, the
protection initiates trip of the protected object.
The following applications are possible by using thermal overload protection function with one time
constant LPTTR:
• Thermal overload protection of overhead lines where the outside air temperature is given as the
ambient temperature to the function. Alternatively, an average outside air temperature can be
given as a setting value. Note that for such application, the primary conductor heating time
constant shall be used. The reference temperature TRef shall be set as primary conductor
temperature raise above the ambient temperature for the set reference current. The trip
temperature TripTemp shall be set as maximum permissible primary conductor temperature in
degrees Centigrade.
• Thermal overload protection of power cables. Note that for such application, the ambient
temperature shall actually represent the soil temperature. Note that for such application, the
overall cable heating time constant shall be used. The reference temperature TRef shall be set
as primary conductor temperature raise above the soil temperature for the set reference current.
The trip temperature TripTemp shall be set as maximum permissible cable temperature in
degrees Centigrade.
• Thermal overload protection of power transformer where the outside air temperature is given as
the ambient temperature to the function. Alternatively, an average outside air temperature can
be given as a setting value. Note that for such application, the power transformer oil heating
time constant, which is typically available from transformer heat run test (i.e. transformer
temperature rise test) shall be used. The reference temperature TRef shall be set as top oil
temperature raise above the ambient for the set reference current of 100% (i.e. 60°C in
accordance with IEC 60076-2). The trip temperature TripTemp shall be set as maximum
permissible top oil temperature in degrees Centigrade. For power transformer manufactured by
ABB, a trip value of 105°C is recommended. The same value is also recommended in IEC
60076-7 published in 2005.
• Thermal overload protection of power transformers where the top oil temperature is measured
using a sensor and provided to the function as ambient temperature. Note that for such
application, the power transformer winding to oil heating time constant (i.e. typically much
shorter than the power transformer oil heating time constant) shall be used. Some typical values
of this time constant is around five minutes. The reference temperature TRef shall be set as hot-
spot winding temperature rise above the top oil temperature for the set reference current of
100% (e.g. 18°C in accordance with IEC 60076-2 published in 2011). If required, additional
safety factor (e.g. 1.3) can be used to increase the TRef value. The trip temperature TripTemp
shall be set as maximum permissible winding hot-spot temperature in degrees Centigrade. The
conservative trip value, in accordance with IEC 60076-7 published in 2005, is 98°C or 110°C
depending on type of paper insulation used. Note that higher value can be used if higher relative
ageing rates for the power transformer are allowed. For power transformer manufactured by
ABB, the trip value for hot-spot temperature of 130°C is recommended.
• Any of the above four application where additional configuration logic is used based on LCPPTR
function output TEMP (i.e. estimated protected object temperature in degrees Celsius) and
associated comparator (i.e. REALCOMP) and timer (i.e. TIMERSET) function blocks. By using
such additional logic, for example, an automatic control of power transformer cooling fans can
be engineered within the IED.
8.6.3 Setting guideline
The parameters for the Thermal overload protection, one time constant, Celsius LPTTR are set via
the local HMI or PCM600.
tPulse: Trip signal pulse length.
SensAvailable: Indication for external temperature sensor availability.
DefaultAmbTemp: Default ambient temperature used when external ambient temperature sensor is
set to off or invalid.
Railway application RER670
Application manual
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Section 8
Current protection
IP14994-1 v1
M15094-3 v8
167