3.4.215
knee point voltage
r.m.s. value of the sinusoidal voltage at rated frequency applied to the secondary terminals of the transformer, all other terminals being open-circuited, which, when increased by 10 %, causes the r.m.s. value of the exciting current to increase by 50 %
[SOURCE: IEC 60050-321:1986, 321-02-34]
3.4.216
knee point e.m.f.
e.m.f. of a current transformer at rated frequency, which, when increased by 10 %, causes the r.m.s. value of the exciting current to increase by 50 %
Note 1 to entry: While the knee point voltage can be applied to the secondary terminals of a current transformer, the knee point e.m.f. is not directly accessible. The values of the knee point voltage and of the knee point e.m.f. are deemed as equal, due to the minor influence of the voltage drop across the secondary winding resistance.
3.4.217
rated knee point e.m.f.
lower limit of the knee point e.m.f.
Note 1 to entry: The rated knee point e.m.f. appears in the specifications of class PX and PXR protective current transformers.
3.4.218
rated turns ratio
specified ratio of the number of primary turns to the number of secondary turns
EXAMPLE 1 1/600 (meaning 1 primary turn to 600 secondary turns)
EXAMPLE 2 2/1200 (meaning 2 primary turns to 1200 secondary turns)
Note 1 to entry: The rated turns ratio appears in the specifications of class PX and PXR protective current transformers.
Note 2 to entry: Rated turns ratio and rated transformation ratio are both defined as primary to secondary entities.
If they shall be compared, the value of the rated turns ratio has to be inverted.
3.4.219
turns ratio error
difference between the actual turns ratio and the rated turns ratio, expressed as a percentage of the rated turns ratio
3.4.220
dimensioning factor
factor to indicate the multiple of rated secondary current (Isr) occurring under power system fault conditions, inclusive of safety margins, up to which the transformer is required to meet performance requirements
Note 1 to entry: See formula under 3.4.217.
3.4.221
instantaneous error current
difference between the instantaneous values of the secondary current multiplied by the rated transformation ratio and the primary current
Note 1 to entry: When both alternating current components and direct current components are present, the constituent components are separately identified as follows
3.4.222
peak instantaneous error
peak value of instantaneous error current (see 3.4.221) for the specified duty cycle, expressed as a percentage of the peak value of the rated primary short-circuit current
3.4.223
peak alternating error component
peak value of the alternating component of the instantaneous error current, expressed as a percentage of the peak value of the rated primary short-circuit current
3.4.224
specified duty cycle (C-O and / or C-O-C-O)
duty cycle in which, during each specified energization, the primary short circuit current is assumed to have the worst-case inception angle (see Figure 201)
3.4.225
Specified primary time constant
that specified value of the time constant of the d.c. component of the primary short-circuit current on which the transient performance of the current transformer is based (see Figure 202)
3.4.226
duration of the first fault
duration of the fault in a C-O duty cycle, or of the first fault in a C-O-C-O duty cycle
Note 1 to entry: See Figure 201.
3.4.227
duration of the second fault
duration of the second fault in a C-O-C-O duty cycle
Note 1 to entry: See Figure 201.
3.4.228
specified time to accuracy limit in the first fault
time in a C-O duty cycle, or in the first energization of a C-O-C-O duty cycle, during which the specified accuracy has to be maintained
Note 1 to entry: See Figure 201. This time interval is usually defined by the critical measuring time of the associated protection scheme.
3.4.229
specified time to accuracy limit in the second fault
time in the second energization of a C-O-C-O duty cycle during which the specified accuracy has to be maintained
Note 1 to entry: See Figure 201. This time interval is usually defined by the critical measuring time of the associated protection scheme.
