Hitachi Relion 670 Series Applications Manual page 172

Section 8
Current protection
tPCrv, tACrv, tBCrv, tCCrv: Parameters for customer creation of inverse time characteristic curve
(Curve type = 17). The time characteristic equation is:
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EQUATION1958 V1 EN-US
tINNonDir is the definite time delay for the non directional earth fault current protection, given in s.
OpUN> is set On to activate the trip function of the residual over voltage protection.
tUN is the definite time delay for the trip function of the residual voltage protection, given in s.
8.6 Thermal overload protection, one time constant,
Celsius LPTTR
8.6.1 Identification
Function description
Thermal overload protection, one time
constant, Celsius
8.6.2 Application
Equipment in the power system is designed for a certain maximum load current level. If the current
exceeds this level the losses will be higher than expected. As a consequence the temperature of the
conductors will increase. If temperature of the equipment reaches too high values, the equipment
might be damaged:
• The sag of overhead lines can reach unacceptable value.
• If the temperature of conductors, for example aluminium conductors, gets too high the material
will be destroyed.
• In cables the insulation can be damaged as a consequence of the overtemperature. As a
consequence of this phase to phase or phase to earth faults can occur.
• The paper insulation used inside a power transformer will deteriorate quicker and expected life
of the transformer will be shortened. Even an internal flash-over may occur.
In stressed situations in the power system it can be required to overload lines and transformers for a
limited time. This should be done while managing the risks safely.
The thermal overload protection provides information that makes a temporary overloading possible.
The thermal overload protection estimates the conductor temperature continuously in Celsius. This
estimation is made by using a thermal model based on the current measurement.
If the temperature of the protected object reaches a set alarm level AlarmTemp, a signal ALARM can
be given to the operator. This enables actions in the power system to be taken before dangerous
166
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IEC 61850 IEC 60617
identification identification
LPTTR
θ>
1MRK506375-UEN Rev. N
(Equation 57)
GUID-446B7894-9CAC-47C6-BABC-8D3F4C7CA5F4 v1
M17106-1 v7
ANSI/IEEE C37.2
device number
26
M15283-3 v9
Railway application RER670
Application manual